- The document proposes a new control strategy called Current Matching Control (CMC) for multi-terminal HVDC transmission systems used to integrate offshore wind farms.
- CMC matches the current references of the grid-side converters to the wind farm side converters through real-time telecommunications. This allows stable sharing of DC currents between converters.
- The performance of CMC is validated through simulations of a four-terminal MTDC network connecting two offshore wind farms to two mainland grids. Results show CMC can effectively control the system under steady state and transient scenarios.
Dynamic performance comparison of DFIG and FCWECS during grid faultsTELKOMNIKA JOURNAL
Among several types, variable speed-based wind turbine generator (WTG) is the most popular type installed worldwide. This type of WTG is able to extract 5% more energy from wind speed compared to the fixed speed WTG. There are two kinds of variable speed based WTG; Doubly Fed Induction Generator (DFIG) and Full Converter Wind Energy Conversion System (FCWECS). DFIG and FCWECS are placed at the first and second topWTG installation worldwide since 2004. However, both of them are very sensitive to the grid dip fault and may violate the allowable margins identified by various international Fault Ride Through (FRT) codes. This paper aims to investigate the responses of DFIG and FCWECS during certain level of grid dips and compare their performanceunder such event. Results show some differences of the performance of DFIG and FCWECS during voltage sag event, however the voltage profile at the point of common coupling is much better in case of DFIG. Results also recommend that DFIG can be effective when connected to weak grids whilst FCWECS is preferably to be connected to strong grids.
This paper deals with the design of filters and THD analysis of a low - frequency ac (20Hz) transmission system. The LFAC system is interfaced with the 50Hz main power grid with a cycloconverter. The wind power is collected in dc form,and is connected to the L FAC transmission line with a twelve pulse inverter. The waveforms at the sending end and receiving end of the transmission line are plotted.THD analysis of LFAC system is carried out. The circuit model of LFAC system is simulated in MATLAB/SIMULINK.
PaperLoad following in a deregulated power system with Thyristor Controlled S...rajeshja
Load following is considered to be an ancillary service in a deregulated power system. This paper investigates
the effect of a Thyristor Controlled Series Compensator (TCSC) for load following in a deregulated
two area interconnected thermal system with two GENCOs and two DISCOs in either areas. Optimal
gain settings of the integral controllers in the control areas are obtained using Genetic Algorithm by
minimizing a quadratic performance index. Simulation studies carried out in MATLAB validates that a
Thyristor Controlled Series Compensator in series with tie-line can effectively improve the load following
performance of the power system in a deregulated environment.
Sliding Mode Control of Three Levels Back-To-Back VSC- HVDC System Using Spac...IJPEDS-IAES
In this study, a sliding mode strategy proposed to control a three levels Back- to-Back High Voltage Direct Current (HVDC) system based on the three- level voltage source converter (VSC). The voltage-balancing control of two split DC capacitors of the VSC-HVDC system is achieved using three-level space vector modulation with balancing strategy based on the effective use of the redundant switching states of the inverter voltage vectors. Finally, a complete simulation of the VSC-HVDC system validates the efficiency of the proposed strategy law. Compared to the conventional control, Sliding Mode Control scheme for the VSC-HVDC system shows the attractive advantages such as offering high tracking accuracy, fast dynamic response and good robustness.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
The Operation of the GCCIA HVDC Project and Its Potential Impacts on the Elec...Power System Operation
The Gulf Cooperation Council Interconnection Authority (GCCIA) has constructed and commissioned a 400kV interconnection grid between Kuwait, Saudi Arabia, Bahrain, Qatar and United Arab of Emirates (UAE), that includes 900 km of overhead lines, seven 400kV substations, a 1800MW three-pole back-to-back HVDC converter station and a submarine cable to Bahrain. This paper summarizes the design features of the GCCIA Back-to-Back HVDC station, illustrates both the technical considerations and physical characteristics of the project, and highlights the operational experience since its operation in 2009. Also, the paper provides some environmental aspects and personal recommendations, and sum up with illustrative conclusion over the covered topics.
Index Terms—high-voltage direct-current transmission, interconnection, GCCIA, back-to-back HVDC, power system operation, grid connectivity, power system converters
Dynamic performance comparison of DFIG and FCWECS during grid faultsTELKOMNIKA JOURNAL
Among several types, variable speed-based wind turbine generator (WTG) is the most popular type installed worldwide. This type of WTG is able to extract 5% more energy from wind speed compared to the fixed speed WTG. There are two kinds of variable speed based WTG; Doubly Fed Induction Generator (DFIG) and Full Converter Wind Energy Conversion System (FCWECS). DFIG and FCWECS are placed at the first and second topWTG installation worldwide since 2004. However, both of them are very sensitive to the grid dip fault and may violate the allowable margins identified by various international Fault Ride Through (FRT) codes. This paper aims to investigate the responses of DFIG and FCWECS during certain level of grid dips and compare their performanceunder such event. Results show some differences of the performance of DFIG and FCWECS during voltage sag event, however the voltage profile at the point of common coupling is much better in case of DFIG. Results also recommend that DFIG can be effective when connected to weak grids whilst FCWECS is preferably to be connected to strong grids.
This paper deals with the design of filters and THD analysis of a low - frequency ac (20Hz) transmission system. The LFAC system is interfaced with the 50Hz main power grid with a cycloconverter. The wind power is collected in dc form,and is connected to the L FAC transmission line with a twelve pulse inverter. The waveforms at the sending end and receiving end of the transmission line are plotted.THD analysis of LFAC system is carried out. The circuit model of LFAC system is simulated in MATLAB/SIMULINK.
PaperLoad following in a deregulated power system with Thyristor Controlled S...rajeshja
Load following is considered to be an ancillary service in a deregulated power system. This paper investigates
the effect of a Thyristor Controlled Series Compensator (TCSC) for load following in a deregulated
two area interconnected thermal system with two GENCOs and two DISCOs in either areas. Optimal
gain settings of the integral controllers in the control areas are obtained using Genetic Algorithm by
minimizing a quadratic performance index. Simulation studies carried out in MATLAB validates that a
Thyristor Controlled Series Compensator in series with tie-line can effectively improve the load following
performance of the power system in a deregulated environment.
Sliding Mode Control of Three Levels Back-To-Back VSC- HVDC System Using Spac...IJPEDS-IAES
In this study, a sliding mode strategy proposed to control a three levels Back- to-Back High Voltage Direct Current (HVDC) system based on the three- level voltage source converter (VSC). The voltage-balancing control of two split DC capacitors of the VSC-HVDC system is achieved using three-level space vector modulation with balancing strategy based on the effective use of the redundant switching states of the inverter voltage vectors. Finally, a complete simulation of the VSC-HVDC system validates the efficiency of the proposed strategy law. Compared to the conventional control, Sliding Mode Control scheme for the VSC-HVDC system shows the attractive advantages such as offering high tracking accuracy, fast dynamic response and good robustness.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
The Operation of the GCCIA HVDC Project and Its Potential Impacts on the Elec...Power System Operation
The Gulf Cooperation Council Interconnection Authority (GCCIA) has constructed and commissioned a 400kV interconnection grid between Kuwait, Saudi Arabia, Bahrain, Qatar and United Arab of Emirates (UAE), that includes 900 km of overhead lines, seven 400kV substations, a 1800MW three-pole back-to-back HVDC converter station and a submarine cable to Bahrain. This paper summarizes the design features of the GCCIA Back-to-Back HVDC station, illustrates both the technical considerations and physical characteristics of the project, and highlights the operational experience since its operation in 2009. Also, the paper provides some environmental aspects and personal recommendations, and sum up with illustrative conclusion over the covered topics.
Index Terms—high-voltage direct-current transmission, interconnection, GCCIA, back-to-back HVDC, power system operation, grid connectivity, power system converters
PERFORMANCE OF LFAC TRANSMISSSION SYSTEM FOR TRANSIENT STATEijiert bestjournal
This paper deals with the transient performance of a low - frequency ac (20Hz) transmission system for a wind ramp event . The LFAC system is interconnected with the 50Hz grid with a Cycloconverter . The wind power from the offshore is in the form of dc,and is interconnected to the LFAC transmission line with a twelve - pulse thyristor inverter. The graphs of transient response of proposed system parameters are plotted. The circuit model of LFAC system is simulated in MATLAB/SIMULINK.
The Operation of the GCCIA HVDC Project and Its Potential Impacts on the Elec...Power System Operation
The Gulf Cooperation Council Interconnection Authority (GCCIA) has constructed and commissioned a 400kV interconnection grid between Kuwait, Saudi Arabia, Bahrain, Qatar and United Arab of Emirates (UAE), that includes 900 km of overhead lines, seven 400kV substations, a 1800MW three-pole back-to-back HVDC converter station and a submarine cable to Bahrain. This paper summarizes the design features of the GCCIA Back-to-Back HVDC station, illustrates both the technical considerations and physical characteristics of the project, and highlights the operational experience since its operation in 2009. Also, the paper provides some environmental aspects and personal recommendations, and sum up with illustrative conclusion over the covered topics.
Term Index- High-Voltage Direct-Current Transmission, interconnection, GCCIA, back-to-back HVDC, power system operation, grid Connectivity, power system converters.
Control Method for Unified Power Quality Conditioner Using Fuzzy Based Nine-S...IJERA Editor
A nine-switch power converter having two sets of out-put terminals was recently proposed in place of the
traditional back-to-back power converter that uses 12 switches in total. The nine-switch converter has already
been proven to have certain advantages, in addition to its component saving topological feature. Despite these
advantages, the nine-switch converter has so far found limited applications due to its many perceived
performance tradeoffs like requiring an oversized dc-link capacitor, limited amplitude sharing, and constrained
phase shift between its two sets of output terminals. Instead of accepting these tradeoffs as limitations, a nineswitch
power conditioner is proposed here that virtually “converts” most of these topological short comings into
interesting performance advantages. Aiming further to reduce its switching losses, an appropriate discontinuous
modulation scheme is proposed and studied here in detail to doubly ensure that maxi-mal reduction of
commutations is achieved. With an appropriately designed control scheme then incorporated, the nine-switch
converter is shown to favorably raise the overall power quality in experiment, hence justifying its role as a
power conditioner at a reduced semiconductor cost.
DESIGN & ANALYSIS OF A CHARGE RE-CYCLE BASED NOVEL LPHS ADIABATIC LOGIC CIRCU...VLSICS Design
This paper focuses on principles of adiabatic logic, its classification and comparison of various adiabatic logic designs. An attempt has been made in this paper to modify 2PASCL (Two Phase Adiabatic Static CMOS Logic) adiabatic logic circuit to minimize delay of the different 2PASCL circuit designs. This modifications in the circuits leads to improvement of Power Delay Product (PDP) which is one of the figure of merit to optimize the circuit with factors like power dissipation and delay of the circuit. This paper investigates the design approaches of low power adiabatic gates in terms of energy dissipation and uses of Simple PN diode instead of MOS diode which reduces the effect of Capacitances at high transition and power clock frequency. A computer simulation using SPECTRE from Cadence is carried out on different adiabatic circuits, such as Inverter, NAND, NOR, XOR and 2:1 MUX.
HVAC power transmission using submarine power cable s has limitation of charging current at nominal frequency. Therefore,HVDC power transmission technology has been established. However,a new intermediate techn ology of Low Frequency AC Transmission is established for transmission of pow er. This paper deals with the performance of a low-frequency ac (20Hz) transmissi on system for steady state. The LFAC system is interconnected with the 50Hz grid wi th a cycloconverter. The wind power from the offshore is in the form of dc,and i s interconnected to the LFAC transmission line with a twelve-pulse thyristor inv erter. The waveforms at the sending end and receiving end of the transmission line are plotted. The circuit model of LFAC system is simulated in MATLAB/SIMULINK.
Performance Evaluation of Centralized Reconfigurable Transmitting Power Schem...TELKOMNIKA JOURNAL
Network-on-chip (NoC) is an on-chip communication network that allows parallel communication among all cores to improve inter-core performance. Wireless NoC (WiNoC) introduces long-range and high bandwidth radio frequency (RF) interconnects that can possibly reduce the multi-hop communication of the planar metal interconnects in conventional NoC platforms. In WiNoC, RF transceivers account for a significant power consumption, particularly its transmitter, out of its total communication energy. This paper evaluates the energy and latency performance of a closed loop power management mechanism which enables transmitting power reconfiguration in WiNoC based on number of erroneous received packets. The scheme achieves significant energy savings with limited performance degradation and insignificant impact on throughput.
Modelling and Operation of HVDC Based Power Transmission Systemijtsrd
Submodule overcurrent caused by DC pole-to-pole fault in modular multilevel converter HVDC MMC-HVDC system is one of the important research objects about its electrical characteristics. In this paper, the fault mechanism before and after the converter blocked was analyzed respectively and the circuit model for the analysis of submodule overcurrent was explored. The analytic equation for overcurrent calculation was deduced and a detailed analysis was also performed. The changes of submodule overcurrent stress with different circuit parameters were obtained and the key issues were also summed up. The results indicate that the submodule overcurrent is the AC system three-phase short-circuit current superposed the discharging current before the converter blocked, and the submodule overcurrent is the AC system three-phase short-circuit current superposed the valve reactor freewheeling current after the converter blocked. From the computation and simulation results, it is concluded that the analytical method is feasible and its calculation results are comparatively precise. Mohd Liaqat "Modelling and Operation of HVDC Based Power Transmission System" Published in International Journal of Trend in Scientific Research and Development (ijtsrd), ISSN: 2456-6470, Volume-3 | Issue-2 , February 2019, URL: https://www.ijtsrd.com/papers/ijtsrd20319.pdf
Paper URL: https://www.ijtsrd.com/engineering/electrical-engineering/20319/modelling-and-operation-of-hvdc-based-power-transmission-system/mohd-liaqat
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
• Introduction: VSC-HVDC connections
• VSC-HVDC structure and controller
• VSC-HVDC connected OWF frequency control
- Control strategy
- Simulation results
• VSC-HVDC interconnector frequency control
- Control strategy
- Simulation results
• Conclusion and future works
IJERA (International journal of Engineering Research and Applications) is International online, ... peer reviewed journal. For more detail or submit your article, please visit www.ijera.com
VSC BASED HVDC SYTEM DESIGN AND PROTECTION AGAINST OVER VOLTAGESIJERD Editor
High Voltage Direct Current system based on voltage source converter (VSC-HVDC) is becoming
more effective solution for offshore wind plants and supplying power to remote regions. In this paper, the
control of a VSC-based HVDC system (VSC-HVDC) is described. Based on this control strategy, appropriate
controllers utilizing PI controllers are designed to control the active and reactive power at each end station.The
operation performance of a voltage source converter (VSC) based HVDC (VSC-HVDC system) system is
explained under some characteristic faulted conditions with and without protection measures. A protection
strategy is proposed to enhance the continuous operation performance of the VSC-HVDC system. The strategy
utilizes a voltage chopper to suppress over-voltages on the DC side of the VSC. Digital simulation is done to
verify the validity of the proposed control strategy and protection strategy
Abstract:-This paper deals with open loop study of fixed capacitor thyristor controlled reactor (FC-TCR) system simulation using Matlab/Simulink for various loading. The modelling of the FC-TCR is verified using the Matlab/Simulink. First power flow results are obtained and power profile have been studied for an uncompensated then results are compared with the results obtained after compensating using the FC-TCR.Its observed that current drawn by FC-TCR is varied by changing firing angle. In compensation without FC-TCR, load increases and power factor become less and in compensation with FC-TCR, load increases and power factor become near to the unity.Hence by providing compensation Voltage, power profile of system will be improved and system losses are reduced.
Implementation of DC voltage controllers on enhancing the stability of multi-...IJECEIAES
Because of the increasing penetration of intermittent green energy resources like offshore wind farms, solar photovoltaic, the multi-terminal DC grid using VSC technology is considered a promising solution for interconnecting these future energies. To improve the stability of the multi-terminal direct current (MTDC) network, DC voltage control strategies based on voltage margin and voltage droop technique have been developed and investigated in this article. These two control strategies are implemented in the proposed model, a ±400 kV meshed multi-terminal MTDC network based on VSC technology with four terminals during the outage converter. The simulation results include the comparison and analysis of both techniques under the outage converter equipped with constant DC voltage control, then the outage converter equipped with constant active power control. The simulation results confirm that the DC voltage droop technique has a better dynamic performance of power sharing and DC voltage regulation.
Impact of LCC–HVDC multiterminal on generator rotor angle stability IJECEIAES
Multiterminal High Voltage Direct Current (HVDC) transmission utilizing Line Commutated Converter (LCC-HVDC) technology is on the increase in interconnecting a remote generating station to any urban centre via long distance DC lines. This Multiterminal-HVDC (MTDC) system offers a reduced right of way benefits, reduction in transmission losses, as well as robust power controllability with enhanced stability margin. However, utilizing the MTDC system in an AC network bring about a new area of associated fault analysis as well as the effect on the entire AC system during a transient fault condition. This paper analyses the fault current contribution of an MTDC system during transient fault to the rotor angle of a synchronous generator. The results show a high rotor angle swing during a transient fault and the effectiveness of fast power system stabilizer connected to the generator automatic voltage regulator in damping the system oscillations. The MTDC link improved the system performance by providing an alternative path of power transfer and quick system recovery during transient fault thus increasing the rate at which the system oscillations were damped out. This shows great improvement compared to when power was being transmitted via AC lines.
This paper presents application and control of the gate-controlled series capacitor (GCSC) for series compensation and subsynchronous resonance (SSR) damping in doubly-fed induction generator (DFIG)-based wind farms. The GCSC is a new series FACTS device composed of a fixed capacitor in parallel with a pair of antiparallel gate-commuted switches. The study considers a DFIG-based wind farm, which is connected to a series-compensated transmission line whose parameters are derived from the IEEE first benchmark model for computer simulation of the SSR. The small-signal stability analysis of the system is presented, and the eigenvalues of the system are obtained. Using both modal analysis and time-domain simulation, it is shown that the system is potentially unstable due to the SSR mode. Therefore, the wind farm is equipped with a GCSC to solve the instability of the wind farm resulting from the SSR mode, and an SSR damping controller (SSRDC) is designed for this device using residue-based analysis and root locus diagrams. Using residue-based analysis, the optimal input control signal to the SSRDC is identified, which can damp the SSR mode without destabilizing other modes, and using root-locus analysis, the required gain for the SSRDC is determined. MATLAB/Simulink is used as a tool for modeling, design, and time-domain simulations.
PERFORMANCE OF LFAC TRANSMISSSION SYSTEM FOR TRANSIENT STATEijiert bestjournal
This paper deals with the transient performance of a low - frequency ac (20Hz) transmission system for a wind ramp event . The LFAC system is interconnected with the 50Hz grid with a Cycloconverter . The wind power from the offshore is in the form of dc,and is interconnected to the LFAC transmission line with a twelve - pulse thyristor inverter. The graphs of transient response of proposed system parameters are plotted. The circuit model of LFAC system is simulated in MATLAB/SIMULINK.
The Operation of the GCCIA HVDC Project and Its Potential Impacts on the Elec...Power System Operation
The Gulf Cooperation Council Interconnection Authority (GCCIA) has constructed and commissioned a 400kV interconnection grid between Kuwait, Saudi Arabia, Bahrain, Qatar and United Arab of Emirates (UAE), that includes 900 km of overhead lines, seven 400kV substations, a 1800MW three-pole back-to-back HVDC converter station and a submarine cable to Bahrain. This paper summarizes the design features of the GCCIA Back-to-Back HVDC station, illustrates both the technical considerations and physical characteristics of the project, and highlights the operational experience since its operation in 2009. Also, the paper provides some environmental aspects and personal recommendations, and sum up with illustrative conclusion over the covered topics.
Term Index- High-Voltage Direct-Current Transmission, interconnection, GCCIA, back-to-back HVDC, power system operation, grid Connectivity, power system converters.
Control Method for Unified Power Quality Conditioner Using Fuzzy Based Nine-S...IJERA Editor
A nine-switch power converter having two sets of out-put terminals was recently proposed in place of the
traditional back-to-back power converter that uses 12 switches in total. The nine-switch converter has already
been proven to have certain advantages, in addition to its component saving topological feature. Despite these
advantages, the nine-switch converter has so far found limited applications due to its many perceived
performance tradeoffs like requiring an oversized dc-link capacitor, limited amplitude sharing, and constrained
phase shift between its two sets of output terminals. Instead of accepting these tradeoffs as limitations, a nineswitch
power conditioner is proposed here that virtually “converts” most of these topological short comings into
interesting performance advantages. Aiming further to reduce its switching losses, an appropriate discontinuous
modulation scheme is proposed and studied here in detail to doubly ensure that maxi-mal reduction of
commutations is achieved. With an appropriately designed control scheme then incorporated, the nine-switch
converter is shown to favorably raise the overall power quality in experiment, hence justifying its role as a
power conditioner at a reduced semiconductor cost.
DESIGN & ANALYSIS OF A CHARGE RE-CYCLE BASED NOVEL LPHS ADIABATIC LOGIC CIRCU...VLSICS Design
This paper focuses on principles of adiabatic logic, its classification and comparison of various adiabatic logic designs. An attempt has been made in this paper to modify 2PASCL (Two Phase Adiabatic Static CMOS Logic) adiabatic logic circuit to minimize delay of the different 2PASCL circuit designs. This modifications in the circuits leads to improvement of Power Delay Product (PDP) which is one of the figure of merit to optimize the circuit with factors like power dissipation and delay of the circuit. This paper investigates the design approaches of low power adiabatic gates in terms of energy dissipation and uses of Simple PN diode instead of MOS diode which reduces the effect of Capacitances at high transition and power clock frequency. A computer simulation using SPECTRE from Cadence is carried out on different adiabatic circuits, such as Inverter, NAND, NOR, XOR and 2:1 MUX.
HVAC power transmission using submarine power cable s has limitation of charging current at nominal frequency. Therefore,HVDC power transmission technology has been established. However,a new intermediate techn ology of Low Frequency AC Transmission is established for transmission of pow er. This paper deals with the performance of a low-frequency ac (20Hz) transmissi on system for steady state. The LFAC system is interconnected with the 50Hz grid wi th a cycloconverter. The wind power from the offshore is in the form of dc,and i s interconnected to the LFAC transmission line with a twelve-pulse thyristor inv erter. The waveforms at the sending end and receiving end of the transmission line are plotted. The circuit model of LFAC system is simulated in MATLAB/SIMULINK.
Performance Evaluation of Centralized Reconfigurable Transmitting Power Schem...TELKOMNIKA JOURNAL
Network-on-chip (NoC) is an on-chip communication network that allows parallel communication among all cores to improve inter-core performance. Wireless NoC (WiNoC) introduces long-range and high bandwidth radio frequency (RF) interconnects that can possibly reduce the multi-hop communication of the planar metal interconnects in conventional NoC platforms. In WiNoC, RF transceivers account for a significant power consumption, particularly its transmitter, out of its total communication energy. This paper evaluates the energy and latency performance of a closed loop power management mechanism which enables transmitting power reconfiguration in WiNoC based on number of erroneous received packets. The scheme achieves significant energy savings with limited performance degradation and insignificant impact on throughput.
Modelling and Operation of HVDC Based Power Transmission Systemijtsrd
Submodule overcurrent caused by DC pole-to-pole fault in modular multilevel converter HVDC MMC-HVDC system is one of the important research objects about its electrical characteristics. In this paper, the fault mechanism before and after the converter blocked was analyzed respectively and the circuit model for the analysis of submodule overcurrent was explored. The analytic equation for overcurrent calculation was deduced and a detailed analysis was also performed. The changes of submodule overcurrent stress with different circuit parameters were obtained and the key issues were also summed up. The results indicate that the submodule overcurrent is the AC system three-phase short-circuit current superposed the discharging current before the converter blocked, and the submodule overcurrent is the AC system three-phase short-circuit current superposed the valve reactor freewheeling current after the converter blocked. From the computation and simulation results, it is concluded that the analytical method is feasible and its calculation results are comparatively precise. Mohd Liaqat "Modelling and Operation of HVDC Based Power Transmission System" Published in International Journal of Trend in Scientific Research and Development (ijtsrd), ISSN: 2456-6470, Volume-3 | Issue-2 , February 2019, URL: https://www.ijtsrd.com/papers/ijtsrd20319.pdf
Paper URL: https://www.ijtsrd.com/engineering/electrical-engineering/20319/modelling-and-operation-of-hvdc-based-power-transmission-system/mohd-liaqat
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
• Introduction: VSC-HVDC connections
• VSC-HVDC structure and controller
• VSC-HVDC connected OWF frequency control
- Control strategy
- Simulation results
• VSC-HVDC interconnector frequency control
- Control strategy
- Simulation results
• Conclusion and future works
IJERA (International journal of Engineering Research and Applications) is International online, ... peer reviewed journal. For more detail or submit your article, please visit www.ijera.com
VSC BASED HVDC SYTEM DESIGN AND PROTECTION AGAINST OVER VOLTAGESIJERD Editor
High Voltage Direct Current system based on voltage source converter (VSC-HVDC) is becoming
more effective solution for offshore wind plants and supplying power to remote regions. In this paper, the
control of a VSC-based HVDC system (VSC-HVDC) is described. Based on this control strategy, appropriate
controllers utilizing PI controllers are designed to control the active and reactive power at each end station.The
operation performance of a voltage source converter (VSC) based HVDC (VSC-HVDC system) system is
explained under some characteristic faulted conditions with and without protection measures. A protection
strategy is proposed to enhance the continuous operation performance of the VSC-HVDC system. The strategy
utilizes a voltage chopper to suppress over-voltages on the DC side of the VSC. Digital simulation is done to
verify the validity of the proposed control strategy and protection strategy
Abstract:-This paper deals with open loop study of fixed capacitor thyristor controlled reactor (FC-TCR) system simulation using Matlab/Simulink for various loading. The modelling of the FC-TCR is verified using the Matlab/Simulink. First power flow results are obtained and power profile have been studied for an uncompensated then results are compared with the results obtained after compensating using the FC-TCR.Its observed that current drawn by FC-TCR is varied by changing firing angle. In compensation without FC-TCR, load increases and power factor become less and in compensation with FC-TCR, load increases and power factor become near to the unity.Hence by providing compensation Voltage, power profile of system will be improved and system losses are reduced.
Implementation of DC voltage controllers on enhancing the stability of multi-...IJECEIAES
Because of the increasing penetration of intermittent green energy resources like offshore wind farms, solar photovoltaic, the multi-terminal DC grid using VSC technology is considered a promising solution for interconnecting these future energies. To improve the stability of the multi-terminal direct current (MTDC) network, DC voltage control strategies based on voltage margin and voltage droop technique have been developed and investigated in this article. These two control strategies are implemented in the proposed model, a ±400 kV meshed multi-terminal MTDC network based on VSC technology with four terminals during the outage converter. The simulation results include the comparison and analysis of both techniques under the outage converter equipped with constant DC voltage control, then the outage converter equipped with constant active power control. The simulation results confirm that the DC voltage droop technique has a better dynamic performance of power sharing and DC voltage regulation.
Impact of LCC–HVDC multiterminal on generator rotor angle stability IJECEIAES
Multiterminal High Voltage Direct Current (HVDC) transmission utilizing Line Commutated Converter (LCC-HVDC) technology is on the increase in interconnecting a remote generating station to any urban centre via long distance DC lines. This Multiterminal-HVDC (MTDC) system offers a reduced right of way benefits, reduction in transmission losses, as well as robust power controllability with enhanced stability margin. However, utilizing the MTDC system in an AC network bring about a new area of associated fault analysis as well as the effect on the entire AC system during a transient fault condition. This paper analyses the fault current contribution of an MTDC system during transient fault to the rotor angle of a synchronous generator. The results show a high rotor angle swing during a transient fault and the effectiveness of fast power system stabilizer connected to the generator automatic voltage regulator in damping the system oscillations. The MTDC link improved the system performance by providing an alternative path of power transfer and quick system recovery during transient fault thus increasing the rate at which the system oscillations were damped out. This shows great improvement compared to when power was being transmitted via AC lines.
This paper presents application and control of the gate-controlled series capacitor (GCSC) for series compensation and subsynchronous resonance (SSR) damping in doubly-fed induction generator (DFIG)-based wind farms. The GCSC is a new series FACTS device composed of a fixed capacitor in parallel with a pair of antiparallel gate-commuted switches. The study considers a DFIG-based wind farm, which is connected to a series-compensated transmission line whose parameters are derived from the IEEE first benchmark model for computer simulation of the SSR. The small-signal stability analysis of the system is presented, and the eigenvalues of the system are obtained. Using both modal analysis and time-domain simulation, it is shown that the system is potentially unstable due to the SSR mode. Therefore, the wind farm is equipped with a GCSC to solve the instability of the wind farm resulting from the SSR mode, and an SSR damping controller (SSRDC) is designed for this device using residue-based analysis and root locus diagrams. Using residue-based analysis, the optimal input control signal to the SSRDC is identified, which can damp the SSR mode without destabilizing other modes, and using root-locus analysis, the required gain for the SSRDC is determined. MATLAB/Simulink is used as a tool for modeling, design, and time-domain simulations.
High-efficiency 2.45 and 5.8 GHz dual-band rectifier design with modulated in...IJECEIAES
This paper presents a new rectifier design for radio frequency (RF) energy harvesting by adopting a particular circuit topology to achieve two objectives at the same time. First, work with modulated input signal sources instead of only continuous waveform (CW) signals. Second, operate with a wide input power range using the Wilkinson power divider (WPD) and two different rectifier diodes (HSMS2852 and SMS7630) instead of using active components. According to the comparison with dual-band rectifiers presented in the literature, the designed rectifier is a high-efficiency rectifier for wide RF power input ranges. A peak of 67.041% and 49.089% was reached for 2.45 and 5.8 GHz, respectively, for CW as the input signal. An efficiency of 72.325% and 45.935% is obtained with a 16 QAM modulated input signal for the operating frequencies, respectively, 69.979% and 54.579% for 8PSK. The results obtained demonstrate that energy recovery systems can use modulated signals. Therefore, the use of a modulated signal over a CW signal may have additional benefits.
HVDC System a Need for Future Power Transmissionijtsrd
The continuously increasing demand for electric power and the economic access to remote renewable energy sources such as off-shore wind power or solar thermal generation in deserts have revived the interest in high-voltage direct current HVDC multiterminal systems networks . A lot of work was done in this area, especially in the 1980s, but only two three-terminal systems were realized. Since then, HVDC technology has advanced considerably and, despite numerous technical challenges, the realization of large-scale HVDC networks is now seriously discussed and considered. For the acceptance and reliability of these networks, the availability of HVDC circuit breakers CBs will be critical, making them one of the key enabling technologies. Numerous ideas for HVDC breaker schemes have been published and patented, but no acceptable solution has been found to interrupt HVDC short-circuit currents. This paper aims to summarize the literature, especially that of the last two decades, on technology areas that are relevant to HVDC breakers. By comparing the mainly 20 years old, state-of-the art HVDC CBs to the new HVDC technology, existing discrepancies become evident. Areas where additional research and development are needed are identified and proposed. for the couple of well-known applications are discussed. Mohd Liaqat "HVDC System: a Need for Future Power Transmission" Published in International Journal of Trend in Scientific Research and Development (ijtsrd), ISSN: 2456-6470, Volume-3 | Issue-2 , February 2019, URL: https://www.ijtsrd.com/papers/ijtsrd20318.pdf
Paper URL: https://www.ijtsrd.com/engineering/electrical-engineering/20318/hvdc-system-a-need-for-future-power-transmission/mohd-liaqat
TCSC AND SVC OPTIMAL LOCATION TO IMPROVE THE PERFORMANCE OF POWER SYSTEM WITH...eeiej_journal
Wind generation connection to power system affects steady state and transient stability. Furthermore, this
effect increases with the increase of wind penetration in generation capacity. In this paper optimal location
of FACTS devices is carried out to solve the steady state problems of wind penetration. Two case studies
are carried out on modified IEEE39 bus system one with wind reduction to 20% and the second with wind
penetration increase by 50% in the two cases system suffer from outage of one generator with load at bus
39 decreases from 1104 MW to 900 MW.
Analysis of Six Active Power Control Strategies of Interconnected Grids with ...Power System Operation
In this paper, the generator angle stability of several active power control schemes of a
voltage-source converter (VSC)-based high-voltage DC (HVDC) is evaluated for two interconnected
AC systems. Excluding frequency control, there has been no detailed analysis of interconnected grids
depending upon the converter power control, so six different types of active power control of the
VSC-HVDC are defined and analyzed in this paper. For each TSO (transmission system operator),
the applicable schemes of two kinds of step control and four kinds of ramp-rate control with a droop
characteristic are included in this research. Furthermore, in order to effectively evaluate the angle
stability, the Generators-VSC Interaction Factor (GVIF) index is newly implemented to distinguish
the participating generators (PGs) group which reacts to the converter power change. As a result,
the transient stabilities of the two power systems are evaluated and the suitable active power control
strategies are determined for two TSOs. Simulation studies are performed using the PSS®E program
to analyze the power system transient stability and various active power control schemes of the
VSC-HVDC. The results provide useful information indicating that the ramp-rate control shows a
more stable characteristic than the step-control for interconnected grids; thus, a converter having a
certain ramp-rate slope similar to that of the other generator shows more stable results in several cases.
Power Comparison of CMOS and Adiabatic Full Adder Circuits VLSICS Design
Full adders are important components in applications such as digital signal processors (DSP) architectures and microprocessors. Apart from the basic addition adders also used in performing useful operations such as subtraction, multiplication, division, address calculation, etc. In most of these systems the adder lies in the critical path that determines the overall performance of the system. In this paper conventional complementary metal oxide semiconductor (CMOS) and adiabatic adder circuits are analyzed in terms of power and transistor count using 0.18UM technology.
The strategy is based on an autonomous distributed control
scheme in which the DC bus voltage level is used as an indicator of the power balance in the
microgrid. The autonomous control strategy does not rely on communication links or a
central controller, resulting in reduced costs and enhanced reliability. As part of the control
strategy, an adaptive droop control technique is proposed for PV sources in order to
maximize the utilization of power available from these sources while ensuring acceptable
levels of system voltage regulation
POWER COMPARISON OF CMOS AND ADIABATIC FULL ADDER CIRCUITSVLSICS Design
Full adders are important components in applications such as digital signal processors (DSP) architectures and microprocessors. Apart from the basic addition adders also used in performing useful operations such as subtraction, multiplication, division, address calculation, etc. In most of these systemsthe adder lies in the critical path that determines the overall performance of the system. In this paper conventional complementary metal oxide emiconductor (CMOS) and adiabatic adder circuits are analyzed in terms of power and transistor count using 0.18UM technology.
A NOVEL CONTROL STRATEGY FOR POWER QUALITY IMPROVEMENT USING ANN TECHNIQUE FO...IJERD Editor
The proposed system presents power-control strategies of a Micro grid-connected hybrid generation
system with versatile power transfer. This hybrid system allows maximum utilization of freely available
renewable energy sources like wind and photovoltaic energies. For this, an adaptive MPPT algorithm along with
standard perturbs and observes method will be used for the system.
The inverter converts the DC output from non-conventional energy into useful AC power for the
connected load. This hybrid system operates under normal conditions which include normal room temperature
in the case of solar energy and normal wind speed at plain area in the case of wind energy. However, designing
an optimal micro grid is not an easy task, due to the fact that primary energy carriers are changeable and
uncontrollable, as is the demand. Traditional design and optimization tools, developed for controlled power
sources, cannot be employed here. Simulation methods seem to be the best solution.
The dynamic model of the proposed system is first elaborated in the stationary reference frame and
then transformed into the synchronous orthogonal reference frame. The transformed variables are used in
control of the voltage source converter as the heart of the interfacing system between DG resources and utility
grid. By setting an appropriate compensation current references from the sensed load currents in control circuit
loop of DG, the active, reactive, and harmonic load current components will be compensated with fast dynamic
response, thereby achieving sinusoidal grid currents in phase with load voltages, while required power of the
load is more than the maximum injected power of the DG to the grid. In addition, the proposed control method
of this paper does not need a phase-locked loop in control circuit and has fast dynamic response in providing
active and reactive power components of the grid-connected loads.
Anlysis of a pmsg based offshore wind farm fed to a onshore grid through hybr...eSAT Publishing House
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology
International Journal of Computational Engineering Research(IJCER) ijceronline
nternational Journal of Computational Engineering Research (IJCER) is dedicated to protecting personal information and will make every reasonable effort to handle collected information appropriately. All information collected, as well as related requests, will be handled as carefully and efficiently as possible in accordance with IJCER standards for integrity and objectivity.
The primary focus of the journal is on Information Technology and Computer Engineering. This suggests that the journal covers a wide range of topics within these disciplines.
The Art of the Pitch: WordPress Relationships and SalesLaura Byrne
Clients don’t know what they don’t know. What web solutions are right for them? How does WordPress come into the picture? How do you make sure you understand scope and timeline? What do you do if sometime changes?
All these questions and more will be explored as we talk about matching clients’ needs with what your agency offers without pulling teeth or pulling your hair out. Practical tips, and strategies for successful relationship building that leads to closing the deal.
Smart TV Buyer Insights Survey 2024 by 91mobiles.pdf91mobiles
91mobiles recently conducted a Smart TV Buyer Insights Survey in which we asked over 3,000 respondents about the TV they own, aspects they look at on a new TV, and their TV buying preferences.
GDG Cloud Southlake #33: Boule & Rebala: Effective AppSec in SDLC using Deplo...James Anderson
Effective Application Security in Software Delivery lifecycle using Deployment Firewall and DBOM
The modern software delivery process (or the CI/CD process) includes many tools, distributed teams, open-source code, and cloud platforms. Constant focus on speed to release software to market, along with the traditional slow and manual security checks has caused gaps in continuous security as an important piece in the software supply chain. Today organizations feel more susceptible to external and internal cyber threats due to the vast attack surface in their applications supply chain and the lack of end-to-end governance and risk management.
The software team must secure its software delivery process to avoid vulnerability and security breaches. This needs to be achieved with existing tool chains and without extensive rework of the delivery processes. This talk will present strategies and techniques for providing visibility into the true risk of the existing vulnerabilities, preventing the introduction of security issues in the software, resolving vulnerabilities in production environments quickly, and capturing the deployment bill of materials (DBOM).
Speakers:
Bob Boule
Robert Boule is a technology enthusiast with PASSION for technology and making things work along with a knack for helping others understand how things work. He comes with around 20 years of solution engineering experience in application security, software continuous delivery, and SaaS platforms. He is known for his dynamic presentations in CI/CD and application security integrated in software delivery lifecycle.
Gopinath Rebala
Gopinath Rebala is the CTO of OpsMx, where he has overall responsibility for the machine learning and data processing architectures for Secure Software Delivery. Gopi also has a strong connection with our customers, leading design and architecture for strategic implementations. Gopi is a frequent speaker and well-known leader in continuous delivery and integrating security into software delivery.
Neuro-symbolic is not enough, we need neuro-*semantic*Frank van Harmelen
Neuro-symbolic (NeSy) AI is on the rise. However, simply machine learning on just any symbolic structure is not sufficient to really harvest the gains of NeSy. These will only be gained when the symbolic structures have an actual semantics. I give an operational definition of semantics as “predictable inference”.
All of this illustrated with link prediction over knowledge graphs, but the argument is general.
Connector Corner: Automate dynamic content and events by pushing a buttonDianaGray10
Here is something new! In our next Connector Corner webinar, we will demonstrate how you can use a single workflow to:
Create a campaign using Mailchimp with merge tags/fields
Send an interactive Slack channel message (using buttons)
Have the message received by managers and peers along with a test email for review
But there’s more:
In a second workflow supporting the same use case, you’ll see:
Your campaign sent to target colleagues for approval
If the “Approve” button is clicked, a Jira/Zendesk ticket is created for the marketing design team
But—if the “Reject” button is pushed, colleagues will be alerted via Slack message
Join us to learn more about this new, human-in-the-loop capability, brought to you by Integration Service connectors.
And...
Speakers:
Akshay Agnihotri, Product Manager
Charlie Greenberg, Host
Elevating Tactical DDD Patterns Through Object CalisthenicsDorra BARTAGUIZ
After immersing yourself in the blue book and its red counterpart, attending DDD-focused conferences, and applying tactical patterns, you're left with a crucial question: How do I ensure my design is effective? Tactical patterns within Domain-Driven Design (DDD) serve as guiding principles for creating clear and manageable domain models. However, achieving success with these patterns requires additional guidance. Interestingly, we've observed that a set of constraints initially designed for training purposes remarkably aligns with effective pattern implementation, offering a more ‘mechanical’ approach. Let's explore together how Object Calisthenics can elevate the design of your tactical DDD patterns, offering concrete help for those venturing into DDD for the first time!
Essentials of Automations: Optimizing FME Workflows with ParametersSafe Software
Are you looking to streamline your workflows and boost your projects’ efficiency? Do you find yourself searching for ways to add flexibility and control over your FME workflows? If so, you’re in the right place.
Join us for an insightful dive into the world of FME parameters, a critical element in optimizing workflow efficiency. This webinar marks the beginning of our three-part “Essentials of Automation” series. This first webinar is designed to equip you with the knowledge and skills to utilize parameters effectively: enhancing the flexibility, maintainability, and user control of your FME projects.
Here’s what you’ll gain:
- Essentials of FME Parameters: Understand the pivotal role of parameters, including Reader/Writer, Transformer, User, and FME Flow categories. Discover how they are the key to unlocking automation and optimization within your workflows.
- Practical Applications in FME Form: Delve into key user parameter types including choice, connections, and file URLs. Allow users to control how a workflow runs, making your workflows more reusable. Learn to import values and deliver the best user experience for your workflows while enhancing accuracy.
- Optimization Strategies in FME Flow: Explore the creation and strategic deployment of parameters in FME Flow, including the use of deployment and geometry parameters, to maximize workflow efficiency.
- Pro Tips for Success: Gain insights on parameterizing connections and leveraging new features like Conditional Visibility for clarity and simplicity.
We’ll wrap up with a glimpse into future webinars, followed by a Q&A session to address your specific questions surrounding this topic.
Don’t miss this opportunity to elevate your FME expertise and drive your projects to new heights of efficiency.
Epistemic Interaction - tuning interfaces to provide information for AI supportAlan Dix
Paper presented at SYNERGY workshop at AVI 2024, Genoa, Italy. 3rd June 2024
https://alandix.com/academic/papers/synergy2024-epistemic/
As machine learning integrates deeper into human-computer interactions, the concept of epistemic interaction emerges, aiming to refine these interactions to enhance system adaptability. This approach encourages minor, intentional adjustments in user behaviour to enrich the data available for system learning. This paper introduces epistemic interaction within the context of human-system communication, illustrating how deliberate interaction design can improve system understanding and adaptation. Through concrete examples, we demonstrate the potential of epistemic interaction to significantly advance human-computer interaction by leveraging intuitive human communication strategies to inform system design and functionality, offering a novel pathway for enriching user-system engagements.
Securing your Kubernetes cluster_ a step-by-step guide to success !KatiaHIMEUR1
Today, after several years of existence, an extremely active community and an ultra-dynamic ecosystem, Kubernetes has established itself as the de facto standard in container orchestration. Thanks to a wide range of managed services, it has never been so easy to set up a ready-to-use Kubernetes cluster.
However, this ease of use means that the subject of security in Kubernetes is often left for later, or even neglected. This exposes companies to significant risks.
In this talk, I'll show you step-by-step how to secure your Kubernetes cluster for greater peace of mind and reliability.
GraphRAG is All You need? LLM & Knowledge GraphGuy Korland
Guy Korland, CEO and Co-founder of FalkorDB, will review two articles on the integration of language models with knowledge graphs.
1. Unifying Large Language Models and Knowledge Graphs: A Roadmap.
https://arxiv.org/abs/2306.08302
2. Microsoft Research's GraphRAG paper and a review paper on various uses of knowledge graphs:
https://www.microsoft.com/en-us/research/blog/graphrag-unlocking-llm-discovery-on-narrative-private-data/
Current matching control system for multi-terminal dc transmission to integrate offshore wind farms
1. Current Matching Control System for Multi-Terminal DC
Transmission to Integrate Offshore Wind Farms
J. Zhu, C. Booth, G.P. Adam
Department of Electrical and Electronic Engineering,
University of Strathclyde, Glasgow G1 1XW, UK.
Email: zhu.jiebei@eee.strath.ac.uk
Keywords: HVDC, voltage source converter, multi-terminal used for many HVDC installations [3], but is not well suited
DC, control. to MTDC, in comparison to VSC. A summary of the
advantages of VSC over LCC is listed below:
Abstract VSC has a smaller footprint which facilitates offshore
installations of reduced platform size [3];
The inherent features of Voltage Source Converters (VSCs) LCC requires large filtering components;
are attractive for practical implementation of Multi-Terminal VSC provides additional reactive power support and AC
HVDC transmission systems (MTDC). MTDC can be used voltage regulation for wind farms connected to weak AC
for large-scale integration of offshore wind power with systems, and possesses black-start capability;
onshore grids. However, many of the control strategies for VSC improves wind farm AC fault ride-through
MTDC that have been proposed previously for offshore wind capability and facilitates Grid Code compliance at
farm integration depend on local control of the wind turbine reduced costs [4];
generators. Power reversal can be achieved in VSC without changing
the DC voltage polarity, facilitating the realisation of a
This paper proposes a new control strategy, termed Current flexible MTDC transmission system.
Matching Control (CMC), which can be used with any MTDC transmission systems have attracted much attention
number of converter terminals, and is independent of the for wind farm integration [5][6][7]. Firstly, MTDC reduces
types of wind turbines used within each wind farm. The converter numbers when compared to numerous point-to-
proposed CMC matches the current reference of the grid side point HVDC solutions. Secondly, it is conceivable that, due to
converter to that of the wind farm side converters. In order to limited correlations of weather systems in geographically
achieve such current matching, a telecommunication system dispersed wind farm locations, the overall variability of wind
will be required to facilitate calculations of the grid side power may be reduced by interconnecting many
current references to be carried out in real time. To validate geographically-dispersed wind farm systems via a large-area
the performance of the proposed control strategy, a generic MTDC system, thus increasing the overall availability of
four-terminal MTDC network, which integrates two offshore energy. In future, energy storage devices may be integrated
wind farms with two mainland grids, is simulated and results with MTDC system [1], which further supports energy
relating to several steady state and transient scenarios are availability and quality of supply. MTDC is also being
presented. proposed as the means of interconnecting independent large-
scale AC power systems, (e.g. European super-grid proposal
1 Introduction [5] to promote the interconnection of Norwegian hydro,
French nuclear, Sahara solar and North sea wind power into a
There has been a tremendous pace of development of large- common MTDC) to resolve local power shortages or
scale offshore wind farms in recent years. It is anticipated that congestion, to enable international power sharing, and to
there will be an approximate increase of 26.6 GW in provide an excellent level of overall power system reliability.
aggregate generation capacity over the period from 2009/10 As discussed in [5], there are many challenging obstacles to
to 2016/17 in the UK, 11.7 GW of which will be contributed the introduction of MTDC. The control system for an MTDC
by wind power [1]. More broadly, the European Wind Energy must be robust, coordinated and reliable, as problems with
Association has, in its “high wind” scenario, a target of 180 one terminal have the potential to affect the entire MTDC
GW from wind energy sources in by 2020, of which 35 GW network. A number of control strategies are proposed [6]
will be sourced from offshore wind installations. This [8][9] which will be introduced later. These strategies remain
capacity target for offshore wind increases to 120 GW by at the modelling and testing stages of development. Critical
2030 [2]. concerns about these strategies are the controllability and
These targets, if they are achieved, will have great impact on reliability of MTDC systems, as most of the proposed
power transmission design, planning, construction and strategies manage an MTDC system without use of
operation. Many offshore wind farms will require long- communications between terminals. The proposed current
distance power transmission systems. AC may not be suitable matching control strategy employs minimal (in terms of
due to high power losses over longer distances. Classical line- required traffic and bandwidth) telecommunications between
current-commutated (LCC) HVDC transmission has been terminals in an MTDC network. While there may be concerns
2. Fig.1 The test MTDC system configuration
over use of communications, modern telecommunication paper focuses on the dynamics of AC and DC interaction,
technologies are increasingly highly developed, reliable and which is dictated by the converter control. As the control
redundant [10]. Furthermore, risk can be mitigated by system for VSC employs vector control in the synchronous
employing redundancy, through continuous monitoring of rotating reference frame dq, the current references id_ref and
telecommunications channels, and ensuring operation can iq_ref which are derived by the commanded active power Pcomm
continue, albeit in a less efficient fashion, if and reactive power Qcomm, are given in equation (1). In the
telecommunications is lost. Operation of the scheme is based rotating reference frame, the d-axis voltage Vd, aligned with
on measurement (discretely, with a step of 1-2ms in this one of three phases, is equal to the magnitude of AC voltage,
example) of the total DC current provided by wind farm side and the q-axis voltage Vq is zero.
rectifiers (i.e. WFR1 and WFR2 in Fig.1) and allocation
(matching) of this current across the inverters, according to a Pcomm Q
pre-determined sharing factor. This is described in more idref , iqref comm (1)
Vd Vd
detail in Section 4. The scheme also provides further
protection for the entire MTDC system by monitoring the DC
voltage. Finally, the system can operate if the Once the current references id_ref and iq_ref are generated, the
telecommunication system fails, but accurate sharing of the inner current control loops adjust the actual id and iq values to
inverter currents may not be possible. be in accordance with the computed reference values. This
process takes a short period to complete and is determined by
the natural frequency of the converter control dynamic in
2 MTDC system configuration Laplace equation (2), which contains the proportional gain
MTDC topology design may vary depending on specific (kp) and the integral gain (ki) of the proportional-and-integral
situations (e.g. the locations of grid connection points and (PI) controller, reactor inductance (L) and resistance (R):
offshore wind farms, available undersea cable routes). Fig.1
presents a four terminal MTDC system for wind farm idq
kp
Li
k
integration, which utilises bi-polar cables R5 with nominal DC L
Rk p
(2)
s2 s
idqref ki
voltage of 200 kV (± 100 kV). On the offshore side, two wind L L
farms are connected via two voltage source neutral-point
clamped rectifiers (WFR1, WFR2). On the onshore side, two From the DC side perspective of the VSC in Fig.2, the DC
grid-connected inverters (GCI3, GCI4) feed power to two voltage udc across the converter or the output capacitors, the
independent 2000 MVA equivalent AC power systems. All DC current idc injected by the converter, and the current ic
VSCs are rated at 200 MVA. Targets of converter control conducted by the DC cables, are related as shown in equation
differ for WFR1 and WFR2, implementing frequency and AC (3). The capacitors are charged (or discharged) to possess a
voltage control at the point of common connection (PCC) certain DC voltage. The current idc injected to the MTDC
with wind farms, while GCI3 and GCI4 are equipped with a network by the converter is calculated from AC side PCC
current controller and DC voltage regulator respectively, in currents id and iq, pulse-width-modulation index M and
addition to AC voltage/or reactive power control. converter terminal voltage angle with respect to the PCC
voltage, using equation (4):
2.1 AC/DC interaction for a VSC dudc
C idc ic (3)
Instead of presenting an in-depth study of the VSC control dt
system formulae, such as those presented [9] and [7], this idc Mid cos Miq sin (4)
3. Fig.3 MTDC control strategies: (a) voltage margin (b) voltage droop
namely voltage margin control [9] and voltage droop control
[8] [6].
3.1 Voltage margin control (VMC)
Fig.2 DC equivalent circuit for the MTDC
In VMC control, one node’s DC voltage is controlled by a DC
voltage controller (DCVC). This effectively acts as a DC
2.2 Equivalent MTDC circuit
voltage slack bus, with other VSCs operating in current
As demonstrated in Section 2.1, the DC property of individual control mode as illustrated in equations (1) and (2).
VSCs in the MTDC can be represented as a “controlled”
current source, shown in the equivalent circuit in Fig.(2). The VMC equips all converters with DCVCs, but the DCVC of
extremely small inductance and capacitance of the DC only one converter station must be activated. Considering the
network with respect to direct current are neglected. V-I characteristic of Fig.3(a), GCI4 has its DC node voltage
controlled at udc4 ref by the activated DCVC, represented as the
As the focus of this section is on the analysis of DC network solid line. This acts to balance the current flows from
behaviour, it is essential to analyse the effect of the variation rectifiers WFR1 and WFR2 to inverter GCI3, by automatically
in DC current idc from one converter station, on either its DC “sliding” its current output along the constant DC voltage
voltage and/or the DC voltage at other stations. Taking WFR1 udc4_ref. Inverter GCI4 has an inherent current limit. If this
as an example, a control action to increase WFR1 current idc1 limit is exceeded (e.g. strong wind pushing more current
will quickly charge its DC capacitors and boost its DC though rectifiers into the MTDC), GCI4 will not be able to
voltage udc1 to a higher value, based on equation (3). The maintain the DC voltage, and will operate at its maximum
higher udc1 with respect to other DC node voltages acts to current output. According to the analysis in Section 2.2, the
supply the conducted current ic1 into the MTDC network. The DC network voltage will continuously rise in line with current
increased current ic1 charges capacitors at other nodes, until “surplus” in the MTDC network. The voltage will ultimately
the voltage levels at all the nodes reach a new higher rise to a new level (udc3_ref) that activates the back-up DCVR
equilibrium value. The rectifier DC voltage is slightly higher in the other inverter GCI3. In this case, GCI3 begins
than the inverter voltage so that current flows from rectifier maintaining the MTDC voltage at udc3_ref, the dashed line in
node(s) to inverter node(s). The magnitude of individual Fig.3(a). The term “voltage margin” refers to the difference
converter DC voltage depends on two elements: (a) the between udc4 _ref and udc3_ref in Fig.3(a).
conducted current though the node; (b) the resistances
between the nodes. 3.2 Voltage droop control (VDC)
VDC basically has multiple activated DCVCs (in both of the
Thus, it can be concluded that a temporary current mismatch
inverters in this example). The two DCVCs are controlled at
between rectifier and inverter in the MTDC results in an
different levels for inverter current dispatch, as shown in
overall DC voltage variation. As the converter control
Fig.3(b). The V-I droop characteristic is obeyed by GCI3 to
systems use DC voltage information to function, it is
share the total current with GCI4. To demonstrate the droop
desirable to quickly address any DC current surplus (by
operation, for example, in order to increase the current of
increasing exported current) or DC current shortage (by
GCI3 and decrease GCI4 based on the droop characteristic, the
reducing exported current), so that a stable DC voltage
DCVC in GCI3 converter control must lower the voltage
operating point for the MTDC system will be realised.
reference udc3_ref and then its current output “slides” along the
Communications between rectifier and inverter nodes in the
droop to the right hand side, to output more current.
system is therefore critical to the operation of this scheme.
3 Previously reported MTDC control 4 Proposed current matching control strategy
strategies As discussed in Section 2.2, a stable DC network operating
point can be achieved by quickly acting to reduce any
Historically, there have been two distinct control strategies mismatch between rectifier and inverter DC currents. As both
used to facilitate power dispatch from DC to AC systems, WFR1 and WFR2 inject all the power generated by wind farms
into MTDC network, they will operate in current control
4. mode. GCI3 and GCI4 will operate using the proposed CMC
in order to address the shortcomings of the VMC and VDC
control, regarding DC current mismatch that may arise during
changes in wind power generation. The detailed operation of
the scheme is now presented.
4.1 Converter operating states
To facilitate the development of the proposed control
strategy, it is important to understand VSC operating states
with their control references in the MTDC system. The Fig.4 The Central CMC with communicated variables
following equations (5) and (6) are given, referring to Fig.2:
uS udc1 R1ic1 udc 2 R2ic 2 (5)
uS udc3 R3ic3 udc 4 R4ic 4 (6)
uS is the sending end voltage and uR is the voltage at the
receiving end of the DC link. ic1 to ic4 are the rectifier and
inverter currents as shown in Fig.2. R5 is given by:
uS uR R5ic5 (7)
ic5 is the current through the DC link as shown in Fig.2.
Kirchhoff’s current law dictates that: Fig.5 CMC and the additional protection loop
idc1 idc 2 idc3 idc 4 0 (8)
idc3 (1 KS )(idc1 idc 2 ) (11)
As demonstrated in VMC and VDC, GCI4 has its DCVC
activated to control DC voltage at udc4; the other converters DC current reference for idc3 is transmitted from the CMC to
WFR1, WFR2 and GCI3 control their currents at idc1 idc2 and the GCI3 converter control system, to produce a commanded
idc3 respectively. Therefore, by combining equation (5), (6), active power reference, given in equation (12):
(7) and (8), the following converter operating state matrix, Pcomm3 idc3udc3 (12)
which incorporates DC network resistance, can be derived: In this way, GCI4 with activated DCVC maintains the current
udc1 R1 R4 R5 R4 R5 R4 1 idc1 balance in the MTDC network, but GCI3 also acts to
u
dc 2 R4 R5 R4 R5 R4 1 idc 2
effectively preserve the current matching by adjusting its
udc3
(9)
R4 R4 ( R3 R4 ) 1 idc3 output active power, using the data relating to the total
ic 4
1 1 1 0 udc 4
rectified current. By setting a proper sharing factor KS,
accurate current allocation between GCI3 and GCI4 is
4.2 Current matching control principle achieved. For example, a setting of KS=0.4 will allocate 40%
of the total current to GCI4, with the remaining 60% allocated
Fig.4 shows the communicated variables of the proposed to GCI3.
CMC for an MTDC. The green blocks in Fig.1 and Fig.4 are
telecommunication feedback signals “idc1”and “idc2” from the Additionally in Fig.5, there is an over-voltage and under-
rectifiers WFR1 and WFR2, based on equation (4). Feedback voltage protection function placed within the main control
signal “udc4” from GCI4 is used for over- or under-voltage loop in Fig.5. It will detect MTDC over-voltage or under-
protection. The current reference for GCI3 converter is voltage by monitoring the feedback signal DC voltage “udc4”
continuously updated by the proposed CMC and transmitted at GCI4, and will trigger the back-up DCVR in GCI3 if udc4
to the GCI3 vector control, via the communicated control exceeds an upper or lower constraint value (set to 180 kV and
signal “idc3_ref”. 220 kV in this simulation).
Modern wireless communication system has been proposed in In the event of telecommunication failure, which could be
HVDC application to secure power reliability [12] and it is detected by the loss of data, or by use of a standard
here used here to favour the CMC strategy for the MTDC communications health monitoring signal, GCI3 also adopts a
system. Fig.5 illustrates the CMC inner control logic, where triggering voltage which is higher (230 kV) than the higher
the total rectifier current from WFR1 and WFR2 is the sum of DC voltage protection constraint of GCI4 (220 kV). If this
feedback signals “idc1”and “idc2”. Rectified current is divided voltage is exceeded, the converter control system in GCI3 will
between the inverters GCI3 and GCI4 by applying a sharing trigger its back-up DCVR in any case. With the CMC strategy,
factor KS. KS represents the portion of the expected power to the converter operating states can be ascertained with
be exported from the MTDC network through GCI4, given by reference to equation (13):
equation (10). Accordingly, the reference current idc3 for GCI3 udc1 R1 R4 R5 R4 R5 R4 1 idc1
u
is given by equation (11): dc 2 R4 R5 R4 R5 R4 1
idc 2
udc3 (1 K S )(idc1 idc 2 )
(13)
idc 4 KS (idc1 idc 2 ) (10)
R4 R4 ( R3 R4 ) 1
ic 4
1 1 1 0
udc 4
5. 5 Performance Evaluation Table.1: Simulation event description and timescales
Time (s) Events
For the performance evaluation of the proposed CMC
1 Sharing factor KS changes from 0.6 to 0.4
strategy, a generic four-terminal MTDC network with each
converter station rated at 200MVA is simulated in Matlab PWFR1 changes from 0.3 to 0.5 pu
3
PWFR2 changes from 0.4 to 0.7 pu
SimPowerSystems [14], as shown in Fig.1. The central CMC
5 3-ph-earth fault at GCI4 (100 ms)
unit is placed in an independent block from the converter
7 Permanent trip of GCI4
current control systems of each of the four converters. DC
cable resistances are obtained from typical HVDC cable
parameters [15] and copper resistivity at 0 in [16]. This
results in modelled resistance values of 1.61 for R2 and R4,
0.32 for R1 and R3, and 1.94 for R5. The performance of
the MTDC using the proposed CMC is examined, under
steady state and fault conditions. Several events have been
simulated, and details are listed in Table 1.
Fig.6 shows the direct current injected into the DC network
from the wind farm rectifiers WFR1 and WFR2, while Fig.7
illustrates the direct current flow from the DC network into
the grid connected inverters GCI3 and GCI4 (the red dashed Fig.6 Direct current idc1 and idc2 from WFR1 and WFR2
line represents the reference current idc3ref for GCI3, calculated
by the CMC). Initially, GCI3 and GCI4 share the current flow
based on the specified sharing factor KS=0.6, that is 60% for
GCI4, and 40% for GCI3. At t=1s, when KS is changed from
0.6 to 0.4, a new current reference is assigned to GCI3 to
increase its DC current, and the current quickly tracks the
reference change. GCI4 is observed to decrease its current
from 60% to 40%.
At t=3s, due to the simulated increase in wind power
production (a gust simulated by a step change in wind speed),
the active power references for WFR1 and WFR2 change and,
as shown in Fig.7, their DC current input to the MTDC rises Fig.7 Direct current idc3 and idc4 from GCI3 and GCI4
to 0.7 and 0.5 pu respectively. This increased input current is
exported and shared correctly by GCI3 and GCI4, based on KS.
Fig.8 presents the DC voltage of WFR1, WFR2, GCI3 and
GCI4. At t=5s, there is a severe AC voltage dip due to a
100ms duration three-phase-to-earth fault at PCC4. In this
case, GCI4 contributes limited current to the fault to support
the grid voltage at PCC4 until the fault is cleared. It can be
noticed that a transient DC over-current occurs not only at
GCI4 but also at WFR1, WFR2 and GCI3. This is due to the
temporary reduction in the power transfer capability of GCI4
as the voltage magnitude at PCC4 collapses. That is because
of DC voltage interactions across all converters. The DC Fig.8 DC voltage udc of WFR1,WFR2,GCI3 and GCI4
over-current is effectively limited by the converter current t=7.3s. Immediately, the CMC triggers the back-up DCVC in
control system to no greater than 1.8 pu; this current is GCI3’s converter controller via communicating the control
exported by the CMC and returns to normal values as soon as signal “Trigger_DCVC_3” (highlighted in orange in Fig.1
the fault is cleared. and Fig.5), and GCI3 begins controlling the DC voltage to a
higher target level using its DCVC (220 kV in this case). This
At t=7s, inverter GCI4 is tripped, and the total rectifier current is to allow the DC capacitors to absorb the additional power
mismatches the inverter GCI3 current output (sharing only that cannot be temporarily transferred to the AC side through
60% of total current based on KS=0.6) during a short period, GCI3. The CMC therefore can continue to operate the MTDC
leading to significant over-voltage in the MTDC network as after tripping of inverter GCI4.
shown in Fig.8. The protection control loop, depicted in the
lower part of Fig.5, detects the over-voltage when feedback
It should be noted that inverter GCI3 is directly controlled by
signal udc4 reaches the upper constraint level (220 kV) at
the CMC, so plays an important role in continuously adjusting
6. being conducted to analyse the performance of this system
under other scenarios, with different control targets (e.g. to
provide voltage support to connected grid AC systems) and to
more extensively compare performance with other existing
and emerging MTDC control strategies.
Acknowledgement
The authors gratefully acknowledge the kind support of the
Engineering and Physical Sciences Research Council and
Rolls-Royce plc.
Fig.9 AC current output at PCCs of WFR1,WFR2,GCI3 and GCI4 References
its DC current export to ensure the DC network current [1] GB National Grid, Seven Year Statement. Available:
balance, as shown by the red dashed line in Fig7. Inverter http://www.nationalgrid.com/NR/rdonlyres/A2095E9F-A0B8-4FCB-
GCI4, with its DCVC activated, acts as the DC side “slack 8E66-6F698D429DC5/41470/NETSSYS2010allChapters.pdf.
[2] European Wind Energy Association (EWEA), Wind Enery Scenarios
bus” to maintain voltage stability in the MTDC system, and it up to 2030. Available:
also contributes to power dispatch in conjunction with http://www.ewea.org/fileadmin/ewea_documents/documents/publicatio
inverter GCI3. There is minimal DC voltage variation ns/reports/purepower.pdf.
throughout the entire simulation process, with amplitudes of ± [3] W. Long, S. Nilsson. "HVDC transmission: yesterday and today," IEEE
Power and Energy Magazine, vol.5, no.2, pp.22-31.
10 kV, until the activation of the DCVC at GCI3 at t=7.3s due
[4] Y. Jiang-Hä fner, R. Ottersten. "HVDC with Voltage Source Converters
to the loss of GCI4. From this point forward, the DC current – A Desirable Solution for Connecting Renewable Energies," Large-
through GCI3 is not controlled by the CMC, and it scale integration of wind power into power systems, Germany.
automatically acts to balance the MTDC network current, as [5] D. Van Hertem, M. Ghandhari. “Multi-terminal VSC HVDC for the
shown by the GCI3 DC current reference (red dashed line) European supergrid: obstacles,” Renewable & Sustainable Energy
Reviews (Elsevier).
and actual DC current in Fig.7. [6] L. Xu, L. Yao. "DC voltage control and power dispatch of a multi-
terminal HVDC system for integrating large offshore wind farms," IET
From the AC side, the converters are controlled by their Renewable Power Generation , vol.5, no.3, pp.223-233.
individual vector control systems, as introduced in Section [7] J. Zhu, C. Booth. "Future multi-terminal HVDC transmission systems
2.1. Fig.9 shows that the AC-side currents associated with the using Voltage source converters," 2010 45th International Universities
Power Engineering Conference (UPEC).
converter PCCs under the proposed CMC control are stables [8] G.P. Adam, O. Anaya-Lara, G. Burt. "Multi-terminal DC transmission
and coordinated. The output AC current/power of inverter system based on modular multilevel converter," Proceedings of the 44th
GCI3, which is primarily dictated by the DC current reference International Universities Power Engineering Conference (UPEC).
from the CMC in equation (12), is observed to be [9] T. Nakajima, S. Irokawa. "A control system for HVDC transmission by
voltage sourced converters," Power Engineering Society Summer
continuously varied to achieve the DC current matching Meeting, 1999. IEEE , vol.2, pp.1113-1119.
function. [10] M. Chen, M. Huang, Y. Ting, H. Chen, T. Li. "High-Frequency
Wireless Communications System: 2.45-GHz Front-End Circuit and
System Integration," IEEE Transactions on Education, vol.53, no.4,
6 Conclusions pp.631-637.
[11] A. Abu-Siada, S. Islam. "Application of SMES Unit in Improving the
This paper has presented the theory and examples of Performance of an AC/DC Power System,", IEEE Transactions on
operation of a novel current matching control (CMC) scheme Sustainable Energy, vol.2, no.2, pp.109-121.
for MTDC networks, where the total rectified (input) current [12] Jiuping Pan; Nuqui, R.; Srivastava, K.; Jonsson, T.; Holmberg, P.;
to the MTDC network is used as basis for actively controlling Hafner, Y.-J.; , "AC Grid with Embedded VSC-HVDC for Secure and
Efficient Power Delivery," Energy 2030 Conf., 2008. ENERGY 2008.
the inverted (output) current from the network to supplied AC IEEE , vol., no., pp.1-6, 17-18 Nov. 2008.
grid systems. Power sharing and ability to protect against [13] S. Cole, J. Beerten, R. Belmans. "Generalized Dynamic VSC MTDC
voltage violations are also features of the scheme. The Model for Power System Stability Studies," IEEE Transactions on
scheme requires communications, but can still operate in the Power Systems, vol.25, no.3, pp.1655-1662.
event of loss of communications facilities. The CMC scheme [14] MathWorks. "VSC-Based HVDC Link," Available:
http://www.mathworks.com/help/toolbox/physmod/powersys/ug/f8-
can be used with any number of converter terminals, and 9059.html.
independent of the types of the wind turbines used within [15] ABB, HVDC Light Cables- Submarine and land power cables,
each wind farm. Available:
http://www05.abb.com/global/scot/scot245.nsf/veritydisplay/1591f1390
98f62e5c1257154002f9801/$file/hvdc%20light%20power%20cables.p
The theoretical study and simulation results prove that, with df.
coordination between the CMC and local converter control [16] D. R. Lide. CRC Handbook of Chemistry and Physics 75th ed. Boca
systems, the passiveness of previous control strategies – Raton, CRC Press.
voltage margin and voltage droop – is avoided. This enables a
stable and secure DC network operating environment, allows
flexibility of power allocation across inverters, and provides
an effective restriction of DC over-voltages. Future work is