Modular multilevel converter (MMC) is a relatively new and promising topology for HVDC systems. HVDC systems should remain connected during grid faults and isolate the fault. This paper studies the dynamic performance of transformer-less MMC integrated HVDC systems during unbalanced conditions and asymmetrical grid faults. It proposes a new control technique to improve unbalanced system’s performance. The objective of the proposed controller is eliminating negative and zero sequence currents and to improve the overall performance. The controller calculates zero and negative sequence reference voltages and eliminates zero and negative sequence currents without using any current regulator. Therefore the controller is very fast and robust. The effectiveness of the proposed control technique has been validated by EMTDC /PSCAD simulations.
Low voltage ride through control of modular multilevel converter based hvdc s...Ghazal Falahi
Low Voltage Ride Through (LVRT) is an important grid requirement for Voltage Source Converter (VSC) based HVDC links. This paper studies the performance of the modular multilevel converter (MMC) VSC based HVDC systems during faults or voltage dips and proposes a new control strategy to improve the LVRT performance. The proposed algorithm controls the system to generate the required active and reactive powers that are calculated mathematically based on the ratings of the MMC-HVDC system and LVRT requirements. The injected active and reactive power values obey the LVRT guidelines and are adaptable to different grid codes. The mathematical calculations are presented and EMTDC/PSCAD simulation evaluates the performance of the proposed method.
Thd minimization of modular multilevel converter with unequal dc valuesGhazal Falahi
Different modulation techniques used to control multilevel converters can be classified based on the selected converter topology and optimization goals. Among all proposed modulation methods low switching frequency modulation techniques are very popular for multilevel converters yet non-real time low switching frequency methods cannot be applied to multilevel converters with unequal or varying DC values because these modulation techniques rely on look up tables and the size of look up tables will be huge in this case. This paper proposes a new modular multilevel converter (MMC) structure with unequal DC values. Some well-known low switching frequency modulation techniques and the commonly used PWM based methods are compared and using the new low switching frequency modulation technique called minimal total harmonic distortion (THD) modulation for MMC with unequal DC values is proposed. The PSCAD simulation results show that the new converter topology with unequal DC values has much lower THD compared to the typical MMC. Modulation algorithm is implemented in digital signal processor (DSP) and controller hardware in the loop (CHIL) implementation in RTDS verifies the real-time performance of the algorithm.
Design consideration of an mmc hvdc system based on 4500 v:4000a emitter turn...Ghazal Falahi
Excessive power loss is a major concern in high voltage and high power applications and is considered one of the main drawbacks of VSC-HVDC system when compared with traditional HVDC system based on thyristor technology. This is primarily caused by high switching loss associated with switching devices used in the VSC-HVDC. This issue can be largely addressed by using the emerging MMC-HVDC topology, which requires much lower switching frequency than traditional VSC-HVDC. Emitter turn-off thyristor (ETO) is one of the best high power switching devices packed with many advanced features. ETO thyristor based MMC-HVDC system is therefore an extremely attractive choice for ultra-high voltage and high power HVDCs. This paper discusses the operation principle of ETO based MMC-HVDC as well as its design and loss comparison with other solutions.
Performance improvement of parallel active power filters using droop control ...Ghazal Falahi
In this paper, a new method based on droop control scheme is proposed for controlling parallel operation of active filters. The harmonic components of the load current are extracted by an enhanced phase-locked loop (EPLL). In the parallel group, each filter operates as a conductance and the harmonic workload is shared among them. A droop relationship between the conductance and non-fundamental apparent power controls the operation of each unit. The non-fundamental apparent power has been calculated based on IEEE Std 1459. Principles of operation are explained in this paper and simulation results which are presented approve the effectiveness of this method. The results indicate a significant reduction in Total Harmonic Distortion (THD) in a rectifier application.
Design, Modeling and control of modular multilevel converters (MMC) based hvd...Ghazal Falahi
Modular multilevel converter (MMC) is a relatively new and promising topology, which has gained a lot of interest in industry in the recent years due to its modular design and easy adaption for applications that require different power and voltage level, such as power transmission through HVDC. This presentation investigates the operation of MMC based HVDC systems and proposes new solutions to improve the performance of the system by using new devices and improving the control strategies.
The power electronics device which converts DC power to AC power at required output voltage and frequency level is known as inverter. Multilevel inverter is to synthesize a near sinusoidal voltage from several levels of dc voltages. In order to maintain the different voltage levels at appropriate intervals, the conduction time intervals of MOSFETS have been maintained by controlling the pulse width of gating pulses. In this paper single phase to three phase power conversion using PWM technique. The simulation is carried out in MATLAB/Simulink environment which demonstrate the feasibility of proposed scheme.
Low voltage ride through control of modular multilevel converter based hvdc s...Ghazal Falahi
Low Voltage Ride Through (LVRT) is an important grid requirement for Voltage Source Converter (VSC) based HVDC links. This paper studies the performance of the modular multilevel converter (MMC) VSC based HVDC systems during faults or voltage dips and proposes a new control strategy to improve the LVRT performance. The proposed algorithm controls the system to generate the required active and reactive powers that are calculated mathematically based on the ratings of the MMC-HVDC system and LVRT requirements. The injected active and reactive power values obey the LVRT guidelines and are adaptable to different grid codes. The mathematical calculations are presented and EMTDC/PSCAD simulation evaluates the performance of the proposed method.
Thd minimization of modular multilevel converter with unequal dc valuesGhazal Falahi
Different modulation techniques used to control multilevel converters can be classified based on the selected converter topology and optimization goals. Among all proposed modulation methods low switching frequency modulation techniques are very popular for multilevel converters yet non-real time low switching frequency methods cannot be applied to multilevel converters with unequal or varying DC values because these modulation techniques rely on look up tables and the size of look up tables will be huge in this case. This paper proposes a new modular multilevel converter (MMC) structure with unequal DC values. Some well-known low switching frequency modulation techniques and the commonly used PWM based methods are compared and using the new low switching frequency modulation technique called minimal total harmonic distortion (THD) modulation for MMC with unequal DC values is proposed. The PSCAD simulation results show that the new converter topology with unequal DC values has much lower THD compared to the typical MMC. Modulation algorithm is implemented in digital signal processor (DSP) and controller hardware in the loop (CHIL) implementation in RTDS verifies the real-time performance of the algorithm.
Design consideration of an mmc hvdc system based on 4500 v:4000a emitter turn...Ghazal Falahi
Excessive power loss is a major concern in high voltage and high power applications and is considered one of the main drawbacks of VSC-HVDC system when compared with traditional HVDC system based on thyristor technology. This is primarily caused by high switching loss associated with switching devices used in the VSC-HVDC. This issue can be largely addressed by using the emerging MMC-HVDC topology, which requires much lower switching frequency than traditional VSC-HVDC. Emitter turn-off thyristor (ETO) is one of the best high power switching devices packed with many advanced features. ETO thyristor based MMC-HVDC system is therefore an extremely attractive choice for ultra-high voltage and high power HVDCs. This paper discusses the operation principle of ETO based MMC-HVDC as well as its design and loss comparison with other solutions.
Performance improvement of parallel active power filters using droop control ...Ghazal Falahi
In this paper, a new method based on droop control scheme is proposed for controlling parallel operation of active filters. The harmonic components of the load current are extracted by an enhanced phase-locked loop (EPLL). In the parallel group, each filter operates as a conductance and the harmonic workload is shared among them. A droop relationship between the conductance and non-fundamental apparent power controls the operation of each unit. The non-fundamental apparent power has been calculated based on IEEE Std 1459. Principles of operation are explained in this paper and simulation results which are presented approve the effectiveness of this method. The results indicate a significant reduction in Total Harmonic Distortion (THD) in a rectifier application.
Design, Modeling and control of modular multilevel converters (MMC) based hvd...Ghazal Falahi
Modular multilevel converter (MMC) is a relatively new and promising topology, which has gained a lot of interest in industry in the recent years due to its modular design and easy adaption for applications that require different power and voltage level, such as power transmission through HVDC. This presentation investigates the operation of MMC based HVDC systems and proposes new solutions to improve the performance of the system by using new devices and improving the control strategies.
The power electronics device which converts DC power to AC power at required output voltage and frequency level is known as inverter. Multilevel inverter is to synthesize a near sinusoidal voltage from several levels of dc voltages. In order to maintain the different voltage levels at appropriate intervals, the conduction time intervals of MOSFETS have been maintained by controlling the pulse width of gating pulses. In this paper single phase to three phase power conversion using PWM technique. The simulation is carried out in MATLAB/Simulink environment which demonstrate the feasibility of proposed scheme.
Torque Ripple Minimization of a BLDC Motor Drive by Using Electronic Commutat...AI Publications
Brushless DC motors are having a major problem with harmonics in torque. The variations in speed and production of noise should be minimized by using proper topologies. BLDC motors have been gaining attention from different Industrial and domestic appliance manufacturers, because of their high efficiency, high power density and easy maintenance and low cost. This paper presents a three phase BLDC motor with low cost drive to be driven without DC link capacitor. The proposed technique uses an electronic commutation and operates the machine exclusive of the intermediate DC link capacitor. The designing of Brushless DC motor drive system along with control system for torque ripple minimization, speed controller and current controllers are presented using MATLAB / SIMULINK and results are evaluated.
Modular Multilevel Converters Part-I: A Review on Topologies, Modulation, Mod...IJPEDS-IAES
This article is devoted to the Multi-level inverters review and in particular to the form and function of modular multilevel inverters (MMI), with their different topologies, modulation, modeling and control schemes Detailed analysis with their functions of MMI has been made in comprehensive manner with existing literature available till date. All existing methods are compared in detail with proposal for the best methods available. The article has made strategic conclusions on MMI to make the system more robust in operation with less complexity in design and control.
This paper presents combinations of level shifted pulse-width modulation algorithm with conventional discontinuous pulse-width modulation methods for cascaded multilevel inverters. In the proposed DPWM a zero sequence signal is injected in sinusoidal reference signal to generate various modulators with easier implementation. The analysis four various control strategies namely Common Carrier (CC), Inverted Carrier (IC), Phase Shifted (PS) and Inverted Phase Shift (IPS) for cascaded multilevel inverter fed induction motor drive has been illustrated. To validate the proposed work experimental tests has been carried out using dSPACE controller. Experimental study proves that using proposed algorithms reduction in common-mode voltage with fewer harmonics along with reduced switching loss for a cascaded multilevel inverter fed motor drive has been achieved.
This paper addresses a novel approach for designing and modeling of the isolated
flyback converter. Modeling is done without parasitic as well as with parasitic components.
A detailed analysis, simulation and different control strategy are conferred for flyback
converter in continuous conduction mode (CCM). To verify the design and modeling at
primary stage, study of the converter is practiced in CCM operation for input AC voltage
230V at 50Hz and output DC voltage of 5V and 50W output power rating using PSIM 6.0
software. Simulation result shows a little ripple in output of the converter in open loop. Finally
in order to evaluate the system as well as response of the controller, flyback converter is
simulated using MATLAB. This work, highlighting the modeling when the system have
transformer and facilitate designers to go for it when they need one or more than one output
for a given application upto 150W
Digital Current Mode Controller for Buck ConverterIJMREMJournal
Power electronics applications are widely used in different fields of engineering like computer,
Telecommunication, electrical power and Mechanical), one of the most useful power electronics converters is
DC-DC buck converter. Owing to its numerous applications, its performance needs to be improved through a
suitable controller. In this Paper, A digital current mode controller is proposed and implemented for Buck
converter. Proposed current mode control technique is simulated in MATLAB/SIMULINK and results are
validated through hardware implementation. Both simulation and experimental analysis show effectiveness of
the proposed controller.
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.
discusses about the reduction of commutation torque ripple in BLDC motor and various convention methods and the proposed method for 2 level inverter and 3 level inverter
Simulation of D-STATCOM to study Voltage Stability in Distribution systemijsrd.com
This paper presents the simulation of D-statcom to understand the improvement of voltage stability [1] of distribution system. The power circuits of the D-STATCOM and distribution networks are made up of simpower system blocks, while the control circuits made with the simulink blocks The STATCOM is applied to regulate transmission voltage to allow greater power flow in a voltage limited transmission network, in the same manner as a static var compensator (SVC), the STATCOM has further potential by giving an inherently faster response and greater output to a system with depressed voltage and offers improved quality of supply. The main applications of the STATCOM are; Distribution STATCOM (D-STATCOM) exhibits high speed control of reactive power to provide voltage stabilization and other type of system control. The DSTATCOM protects the utility transmission or distribution system from voltage sag and /or flicker caused by rapidly varying reactive current demand. During the transient conditions the D-STATCOM provides leading or lagging reactive power to active system stability, power factor correction and load balancing.
PID Controller Response to Set-Point Change in DC-DC Converter ControlIAES-IJPEDS
Power converter operations and efficiency is affected by variation in supply
voltage, loads current, circuit elements, ageing and temperature. To meet the
objective of tight voltage regulation, power converters circuit module and the
control unit must be robust to reject disturbances arising from supply, load
variation and changes in circuit elements. PID controller has been the most
widely used in power converter control. This paper presents studies of
robustness of PID controller tuning methods to step changes in the set point
and disturbance rejection in power converter control. A DC-DC boost
converter was modelled using averaged state-space mothod and PID
controllers were designed with five different tuning methods. The study
reveals the transient response and disturbance rejection capability of each
tuning methods for their suitability in power supply design applications.
LOW VOLTAGE RIDE - THROUGH CAPABILITY OF WIND FARMSEditor IJMTER
Nowadays wind turbines are generally required to offer ancillary services similar to those
provided by conventional generators. One of the most important services wind turbines must offer is
to stay connected to the grid in fault situations delivering the reactive current specified in the recent
grid codes. In this paper, FACTS solutions for fixed speed wind farms such as DVR (Dynamic
Voltage Restorer) are presented as well as classic control and crowbar solutions for variable speed
wind turbines.
A Sub-Region Based Space Vector Modulation Scheme for Dual 2-Level Inverter S...IJECEIAES
This paper deals the implementation of 3-level output voltage using dual 2level inverter with control of sub-region based Space Vector Modulation (SR-SVM). Switching loss and voltage stress are the most important issues in multilevel inverters, for keep away from these problems dual inverter system executed. Using this proposed system, the conventional 3-level inverter voltage vectors and switching vectors can be located. In neutral point clamped multilevel inverter, it carries more load current fluctuations due to the DC link capacitors and it requires large capacitors. Based on the subregion SVM used to control IGBT switches placed in the dual inverter system. The proposed system improves the output voltage with reduced harmonic content with improved dc voltage utilisation. The simulation and hardware results are verified using matlab/simulink and dsPIC microcontroller.
The speed of a DC motor can be controlled by varying the voltage applied to the terminal. It can be done by controlling a PWM-VSC (PWM-Voltage Source Converter). This paper analyzes an control strategy of PWM-VSC using fuzzy logic to obtain varying DC voltage and according to the DC motor speed as desired. The control strategy of PWM-VSC directly using the switch variable in dq rotating reference frame as input variables. The fuzzy logic controller proposes to get a DC voltage variation stable by adjusting amplitudo of the network current. The simulation Fuzzy Logic Controller results show that the design fuzzy logic produce a good dynamic of DC voltage and DC motor speed without overshoot. On the network, Total Harmonic Distortion less than 5 % and unity power factor.
Average Phase-Leg Technique on Coupling Impedance Impact Modular Inverter Par...IJMTST Journal
The modular multilevel converter (MMC) is an emerging and highly attractive multilevel converter topology
for high-voltage and high-power applications. This paper proposes the control method of parallel-connected
modular multilevel converters (parallel-MMCs), which assumes that the multiple MMCs are directly connected
at both ac and dc sides to effectively enhance the power rating as expected. Two key problems were first
solved for the parallel-MMCs under the normal operation conditions: voltage balancing of sub modules and
mitigation of circulating currents, where the novel transformed third-order harmonic resonant controller in the
synchronous reference frame was employed to mitigate the dominant second-order and fourth-order
circulating currents and a sixth-order harmonic resonant controller is used to attenuate the zero-sequence
sixth-order circulating current existed in all phase currents per MMC. Considering the high risk of switches
fault in the parallel-MMCs, the fault-tolerant operation schemes were then proposed in this paper to address
the major concerns of open-circuit and short-circuit switch fault in a sub module, respectively. Carefully
controlling the healthy sub modules and the corresponding phase arms, the parallel-MMCs can successfully
maintain their balanced capacitor voltages and mitigate the circulating currents with the qualified output
waveform obtained. In addition, the parallel configuration of MMCs provides the unique solution for the
short-circuit switch fault operation which was seldom discussed in the published literature works with
respect to the MMC fault-tolerant operation schemes. MATLAB simulations and the constructed experimental
prototype have verified the performance of the proposed control strategy.
Performance comparison of different control strategies for the regulation of ...IJECEIAES
In last years, DC-DC converters solve the most issues in the industrial application in the area of power electronics, especially renewable energy, military applications and affiliated engineering developments. They are used to convert the DC input that unregulated to regulated output perhaps larger or smaller than input according to the type of converters. This paper presents three primary control method used for negative output Super lift Luo DC-DC converter. These methods include a voltage mode control (VMC), current mode control (CMC), and Sliding mode control (SMC). The goal of this article is to study and selected an appropriate and superior control scheme for negative DC-DC converters. The simulation results show the effectiveness of Sliding mode control for enhancing the performance of the negative DC-DC converter. Also, this method can keep the output voltage constant under load conditions. Simulation results obtained by the MATLAB/Simulink environment.
Torque Ripple Minimization of a BLDC Motor Drive by Using Electronic Commutat...AI Publications
Brushless DC motors are having a major problem with harmonics in torque. The variations in speed and production of noise should be minimized by using proper topologies. BLDC motors have been gaining attention from different Industrial and domestic appliance manufacturers, because of their high efficiency, high power density and easy maintenance and low cost. This paper presents a three phase BLDC motor with low cost drive to be driven without DC link capacitor. The proposed technique uses an electronic commutation and operates the machine exclusive of the intermediate DC link capacitor. The designing of Brushless DC motor drive system along with control system for torque ripple minimization, speed controller and current controllers are presented using MATLAB / SIMULINK and results are evaluated.
Modular Multilevel Converters Part-I: A Review on Topologies, Modulation, Mod...IJPEDS-IAES
This article is devoted to the Multi-level inverters review and in particular to the form and function of modular multilevel inverters (MMI), with their different topologies, modulation, modeling and control schemes Detailed analysis with their functions of MMI has been made in comprehensive manner with existing literature available till date. All existing methods are compared in detail with proposal for the best methods available. The article has made strategic conclusions on MMI to make the system more robust in operation with less complexity in design and control.
This paper presents combinations of level shifted pulse-width modulation algorithm with conventional discontinuous pulse-width modulation methods for cascaded multilevel inverters. In the proposed DPWM a zero sequence signal is injected in sinusoidal reference signal to generate various modulators with easier implementation. The analysis four various control strategies namely Common Carrier (CC), Inverted Carrier (IC), Phase Shifted (PS) and Inverted Phase Shift (IPS) for cascaded multilevel inverter fed induction motor drive has been illustrated. To validate the proposed work experimental tests has been carried out using dSPACE controller. Experimental study proves that using proposed algorithms reduction in common-mode voltage with fewer harmonics along with reduced switching loss for a cascaded multilevel inverter fed motor drive has been achieved.
This paper addresses a novel approach for designing and modeling of the isolated
flyback converter. Modeling is done without parasitic as well as with parasitic components.
A detailed analysis, simulation and different control strategy are conferred for flyback
converter in continuous conduction mode (CCM). To verify the design and modeling at
primary stage, study of the converter is practiced in CCM operation for input AC voltage
230V at 50Hz and output DC voltage of 5V and 50W output power rating using PSIM 6.0
software. Simulation result shows a little ripple in output of the converter in open loop. Finally
in order to evaluate the system as well as response of the controller, flyback converter is
simulated using MATLAB. This work, highlighting the modeling when the system have
transformer and facilitate designers to go for it when they need one or more than one output
for a given application upto 150W
Digital Current Mode Controller for Buck ConverterIJMREMJournal
Power electronics applications are widely used in different fields of engineering like computer,
Telecommunication, electrical power and Mechanical), one of the most useful power electronics converters is
DC-DC buck converter. Owing to its numerous applications, its performance needs to be improved through a
suitable controller. In this Paper, A digital current mode controller is proposed and implemented for Buck
converter. Proposed current mode control technique is simulated in MATLAB/SIMULINK and results are
validated through hardware implementation. Both simulation and experimental analysis show effectiveness of
the proposed controller.
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.
discusses about the reduction of commutation torque ripple in BLDC motor and various convention methods and the proposed method for 2 level inverter and 3 level inverter
Simulation of D-STATCOM to study Voltage Stability in Distribution systemijsrd.com
This paper presents the simulation of D-statcom to understand the improvement of voltage stability [1] of distribution system. The power circuits of the D-STATCOM and distribution networks are made up of simpower system blocks, while the control circuits made with the simulink blocks The STATCOM is applied to regulate transmission voltage to allow greater power flow in a voltage limited transmission network, in the same manner as a static var compensator (SVC), the STATCOM has further potential by giving an inherently faster response and greater output to a system with depressed voltage and offers improved quality of supply. The main applications of the STATCOM are; Distribution STATCOM (D-STATCOM) exhibits high speed control of reactive power to provide voltage stabilization and other type of system control. The DSTATCOM protects the utility transmission or distribution system from voltage sag and /or flicker caused by rapidly varying reactive current demand. During the transient conditions the D-STATCOM provides leading or lagging reactive power to active system stability, power factor correction and load balancing.
PID Controller Response to Set-Point Change in DC-DC Converter ControlIAES-IJPEDS
Power converter operations and efficiency is affected by variation in supply
voltage, loads current, circuit elements, ageing and temperature. To meet the
objective of tight voltage regulation, power converters circuit module and the
control unit must be robust to reject disturbances arising from supply, load
variation and changes in circuit elements. PID controller has been the most
widely used in power converter control. This paper presents studies of
robustness of PID controller tuning methods to step changes in the set point
and disturbance rejection in power converter control. A DC-DC boost
converter was modelled using averaged state-space mothod and PID
controllers were designed with five different tuning methods. The study
reveals the transient response and disturbance rejection capability of each
tuning methods for their suitability in power supply design applications.
LOW VOLTAGE RIDE - THROUGH CAPABILITY OF WIND FARMSEditor IJMTER
Nowadays wind turbines are generally required to offer ancillary services similar to those
provided by conventional generators. One of the most important services wind turbines must offer is
to stay connected to the grid in fault situations delivering the reactive current specified in the recent
grid codes. In this paper, FACTS solutions for fixed speed wind farms such as DVR (Dynamic
Voltage Restorer) are presented as well as classic control and crowbar solutions for variable speed
wind turbines.
A Sub-Region Based Space Vector Modulation Scheme for Dual 2-Level Inverter S...IJECEIAES
This paper deals the implementation of 3-level output voltage using dual 2level inverter with control of sub-region based Space Vector Modulation (SR-SVM). Switching loss and voltage stress are the most important issues in multilevel inverters, for keep away from these problems dual inverter system executed. Using this proposed system, the conventional 3-level inverter voltage vectors and switching vectors can be located. In neutral point clamped multilevel inverter, it carries more load current fluctuations due to the DC link capacitors and it requires large capacitors. Based on the subregion SVM used to control IGBT switches placed in the dual inverter system. The proposed system improves the output voltage with reduced harmonic content with improved dc voltage utilisation. The simulation and hardware results are verified using matlab/simulink and dsPIC microcontroller.
The speed of a DC motor can be controlled by varying the voltage applied to the terminal. It can be done by controlling a PWM-VSC (PWM-Voltage Source Converter). This paper analyzes an control strategy of PWM-VSC using fuzzy logic to obtain varying DC voltage and according to the DC motor speed as desired. The control strategy of PWM-VSC directly using the switch variable in dq rotating reference frame as input variables. The fuzzy logic controller proposes to get a DC voltage variation stable by adjusting amplitudo of the network current. The simulation Fuzzy Logic Controller results show that the design fuzzy logic produce a good dynamic of DC voltage and DC motor speed without overshoot. On the network, Total Harmonic Distortion less than 5 % and unity power factor.
Average Phase-Leg Technique on Coupling Impedance Impact Modular Inverter Par...IJMTST Journal
The modular multilevel converter (MMC) is an emerging and highly attractive multilevel converter topology
for high-voltage and high-power applications. This paper proposes the control method of parallel-connected
modular multilevel converters (parallel-MMCs), which assumes that the multiple MMCs are directly connected
at both ac and dc sides to effectively enhance the power rating as expected. Two key problems were first
solved for the parallel-MMCs under the normal operation conditions: voltage balancing of sub modules and
mitigation of circulating currents, where the novel transformed third-order harmonic resonant controller in the
synchronous reference frame was employed to mitigate the dominant second-order and fourth-order
circulating currents and a sixth-order harmonic resonant controller is used to attenuate the zero-sequence
sixth-order circulating current existed in all phase currents per MMC. Considering the high risk of switches
fault in the parallel-MMCs, the fault-tolerant operation schemes were then proposed in this paper to address
the major concerns of open-circuit and short-circuit switch fault in a sub module, respectively. Carefully
controlling the healthy sub modules and the corresponding phase arms, the parallel-MMCs can successfully
maintain their balanced capacitor voltages and mitigate the circulating currents with the qualified output
waveform obtained. In addition, the parallel configuration of MMCs provides the unique solution for the
short-circuit switch fault operation which was seldom discussed in the published literature works with
respect to the MMC fault-tolerant operation schemes. MATLAB simulations and the constructed experimental
prototype have verified the performance of the proposed control strategy.
Performance comparison of different control strategies for the regulation of ...IJECEIAES
In last years, DC-DC converters solve the most issues in the industrial application in the area of power electronics, especially renewable energy, military applications and affiliated engineering developments. They are used to convert the DC input that unregulated to regulated output perhaps larger or smaller than input according to the type of converters. This paper presents three primary control method used for negative output Super lift Luo DC-DC converter. These methods include a voltage mode control (VMC), current mode control (CMC), and Sliding mode control (SMC). The goal of this article is to study and selected an appropriate and superior control scheme for negative DC-DC converters. The simulation results show the effectiveness of Sliding mode control for enhancing the performance of the negative DC-DC converter. Also, this method can keep the output voltage constant under load conditions. Simulation results obtained by the MATLAB/Simulink environment.
International Journal of Computational Engineering Research(IJCER) is an intentional online Journal in English monthly publishing journal. This Journal publish original research work that contributes significantly to further the scientific knowledge in engineering and Technology.
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
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.
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.
This paper investigates the performance of line commutated converter (LCC) based monopolar
HVDC transmission system feeding a weak AC network with hybrid reactive power compensators (RPC’s) at the
inverter AC side. The hybrid compensator is an equal mix of any two of the following compensators:
synchronous compensator (SC); static var compensator (SVC); static synchronous compensator (STATCOM).
The HVDC transmission system model is implemented in the Matlab with the firefly algorithm based optimal
proportional integral (PI) controller for rectifier and inverter control. The transient performances of hybrid
RPC’s (SC+SVC, SVC+STATCOM and SC+STATCOM) are judged under various fault conditions and the
outcomes are compared with the performance of the SC, SVC and STATCOM to highlight the supremacy of the
hybrid compensators. The simulation results validate that the equal mix of SC and STATCOM has a steady and
fastest response. The results also demonstrate the superiority of the firefly algorithm based optimal PI
controller over the conventional PI controller. The harmonic analysis is also carried out under steady state
operation to assure the quality of power supply on the inverter AC side
This paper investigates the performance of line commutated converter (LCC) based monopolar HVDC transmission system feeding a weak AC network with hybrid reactive power compensators (RPC’s) at the inverter AC side. The hybrid compensator is an equal mix of any two of the following compensators: synchronous compensator (SC); static var compensator (SVC); static synchronous compensator (STATCOM). The HVDC transmission system model is implemented in the Matlab with the firefly algorithm based optimal proportional integral (PI) controller for rectifier and inverter control. The transient performances of hybrid RPC’s (SC+SVC, SVC+STATCOM and SC+STATCOM) are judged under various fault conditions and the outcomes are compared with the performance of the SC, SVC and STATCOM to highlight the supremacy of the hybrid compensators. The simulation results validate that the equal mix of SC and STATCOM has a steady and fastest response. The results also demonstrate the superiority of the firefly algorithm based optimal PI controller over the conventional PI controller. The harmonic analysis is also carried out under steady state operation to assure the quality of power supply on the inverter AC side.
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Saudi Arabia stands as a titan in the global energy landscape, renowned for its abundant oil and gas resources. It's the largest exporter of petroleum and holds some of the world's most significant reserves. Let's delve into the top 10 oil and gas projects shaping Saudi Arabia's energy future in 2024.
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Control of modular multilevel converter based hvdc systems during asymmetrical grid faults
1. Control of Modular Multilevel Converter based
HVDC Systems During Asymmetrical Grid Faults
Ghazal Falahi
FREEDM Systems Center
Electrical and Computer Engineering Department
North Carolina State University
Raleigh US
Alex Huang
FREEDM Systems Center
Electrical and Computer Engineering Department
North Carolina State University
Raleigh US
Abstract— Modular multilevel converter (MMC) is a relatively
new and promising topology for HVDC systems. HVDC systems
should remain connected during grid faults and isolate the fault.
This paper studies the dynamic performance of transformer-less
MMC integrated HVDC systems during unbalanced conditions
and asymmetrical grid faults. It proposes a new control
technique to improve unbalanced system’s performance. The
objective of the proposed controller is eliminating negative and
zero sequence currents and to improve the overall performance.
The controller calculates zero and negative sequence reference
voltages and eliminates zero and negative sequence currents
without using any current regulator. Therefore the controller is
very fast and robust. The effectiveness of the proposed control
technique has been validated by EMTDC /PSCAD simulations.
Keywords-MMC, HVDC, unbalanced operation, zero-
sequence,negative-sequence.
I. INTRODUCTION
Voltage source converter (VSC) based HVDC is a relatively
new type of transmission system incorporating controllable
switching converters. VSC-HVDC systems can produce active
and reactive power independently, which allows them to
operate with small or no AC support. HVDC systems have
high voltage ratings on both AC and DC sides and multilevel
converters are good candidates to provide high voltage on both
sides of an HVDC system. Among multilevel converters,
modular multilevel converter (MMC) is a fairly new structure
introduced by Marquardt Lesnicar and is a suitable candidate
for VSC based HVDC [1].
HVDC transmission systems should continuously deliver
power. The HVDC interconnection grid codes state that the
converter station must support the grid voltage during faults
by injecting reactive current. Moreover, the faulty side should
be isolated from the healthy side and the system should be
restored to normal operating condition as quickly as possible
[1-4]. Zero and negative sequence components increase
system’s current, which may cause protection devices to
activate. A well-designed control system should keep systems
normal operation and prevent the protection devices from
tripping frequently.
This paper studies the dynamics performance of transformer-
less MMC-HVDC system during unbalanced conditions and
proposes an alternative solution to improve the performance of
the system during faults. This study incorporates modulation
waveform and mathematical calculation of zero and negative
voltage components and modifies the control structure to
eliminate undesired current terms generated due to the fault.
The proposed controller is fast and robust. Furthermore it
eliminates zero and negative current components without
using current regulator or any additional controller.
This paper is organized as follows. Section II covers the MMC
mathematical model and operation principal. Section III
demonstrates MMC-HVDC control, operation, and dynamic
performance. Section IV presents the proposed solution to
eliminate zero sequence and negative sequence during
network transients and faults and compares the results for both
cases with and without the additional controller and section V
concludes the paper.
II. MMC MATHEMATICAL MODEL AND OPERATION
PRINCIPAL
The three-phase MMC converter configuration used in HVDC
applications is shown in Fig. 1. The converter is composed of
three-phase legs each consisting of two arms made by series
connection of some identical half-bridge modules called cells
or sub-modules (SM). The SMs are inserted or bypassed based
on the switching state of the two switching device in each half
bridge. The two switches are complementary and table 1
shows the sub-module output voltage in different switching
states. The currents in phase-k (k=a, b, c) consist of ik-up and ik-
low which are the upper and lower arm current in each phase.
Applying KVL to the arms of the converter yields to the
following:
(1)
(2)
2. (3)
(4)
Where uk is the phase k voltage, u0 is the potential to ground
DC side neutral point and the inductance of each arm equals
2L. The MMC grid connection dynamic is described as
(5)
Control system for the each MMC converter shown in fig. 1
includes four parts [5]:
1. An individual capacitor voltage controller, which keeps the
sub module capacitor voltages on their reference values.
2. The averaging controller that controls the total capacitor
voltages in each leg to follow the reference value which is
2Vdc.
3. The system controller, which controls active and reactive
power. The reference of active power is determined by
network demanded active power or the DC-link voltage
controller. The reference for reactive power is either
determined by ac voltage regulator or by the reactive power
demand.
4. The PWM voltage command generation, which adds up the
output of three mentioned controllers to build the modulation
waveform. The overall control structure is shown in fig. 4. The
ac voltage command or modulation index for each phase is
calculated by adding the output of three mentioned controllers
as shown in the following equations.
(j:1-n) (6)
(j: n+1 - 2n) (7)
The voltage command is normalized by each dc-capacitor
voltage Vcju and compared with a triangular waveform having a
maximum value of unity and minimum value of zero with a
carrier frequency of fc. Carrier shifted PWM modulation
technique is used for switching and carrier waveform of each
cell is phase shifted by 360/n [5].
TABLE I. SWITCHING STATE OF SUB-MODULES
State S1 S2 Vsm
1 ON OFF Vc
2 OFF ON 0
3 OFF OFF 0
Fig. 1: Modular multilevel converter
I. HVDC MMC OPERATION
The single line diagram of an MMC-HVDC system is shown
in fig. 2, which consists of two MMCs connected to the utility
grid on one side and the DC transmission line on the other
side. The DC link voltage in this system is maintained by the
sum of sub-module voltages inserted in the converter leg and
there is no bulky DC link capacitor as in other VSC-HVDC
systems. HVDC transmission systems regulate active and
reactive power by changing the amplitude and phase of the
converter line currents with respect to PCC and there are
usually two control loops to maintain the power control.
The outer controller regulates the power transfer between the
AC and DC systems and the inner or faster controller is
responsible for tracking the references generated by the power
control, DC or AC voltage control loop. MMC 2 is usually the
grid side converter and MMC 1 is the generator side converter.
The main objective of the control system is to keep the DC-
link voltage constant while keeping sinusoidal grid currents.
As soon as a fault occurs due to short circuit or any other issue
in the AC system or in case of unbalance condition in the
network there will be positive, zero and negative sequence
voltages and currents in the system. In HVDC configuration
with transformer, the Y/ transformer eliminates the zero
sequence components. In transformer-less MMC-HVDC
configuration zero sequence component is present in the
voltages, which results in high zero sequence currents. In
addition to zero sequence negative sequence also exists in the
system voltages resulting in negative sequence current flowing
in the system, which deteriorate the performance.
The MMC-HVDC system is simulated in PSCAD/EMTDC for
the parameters presented in table 2. Figs 5 and 6 show the
normal operation of the system under study. The dynamic
performances of the modeled system during power command
reversal is shown in Fig. 5. The active power reversal
command is sent at t=0.4 secs and reactive power is reversed
at t=0.7secs and P1, P2, Q1 and Q2 are plotted. Fig. 6 shows the
step change in DC link reference voltage.
Cell 2
Cell n
Cell (n+1)
Cell (n+2)
Cell 1
Cell (2n)
DC
link
va
vb
vc
DC
link
u0
ia-up
ia-low
Udc/2
Udc/2
ia
ib
ic
2L
2L
2L 2L
2L 2L
La
Lb
Lc
ib-up ic-up
ib-low ic-low
ua
ub
uc
S1
S2
VS
M
V
c
3. Fig.2 HVDC MMC single line diagram
Fig. 3 MMC individual and total capacitor voltage controller
V*ac
PI
i*odref
Vod
iod
PI
i*qref
0Leq
0Leq
ioq
Voq
3dq/abc
System controller
P*ref
PI
V*dc
Vdc
Q*ref
PI
Vac
Fig. 4 power controllers
II. MMC-HVDC SYSYEM OPERATION UNDER FAULTS
Any fault in the MMC-HVDC system leads into to the
changes of series of parameter values therefore faults can be
detected through observing the variables that carry the fault
signatures [7]. To study the performance of the simulated
system and understand the impact of fault on the dynamic
performance, a SLG fault is applied to MMC-HVDC system
on converter 2 side at 0.3 secs. In order to investigate the fault
propagation in the system no additional control is
implemented at this point. PCC voltage and currents become
imbalanced as soon as fault is applied and zero and negative
sequence appear in the system voltages and currents.
During unbalance grid condition the negative-sequence
components will cause the DC link to oscillate at double
fundamental frequency however DC-link voltage oscillations
in MMC-HVDC system is not very significant because the
MMC sub-module capacitors maintain the DC-link voltage.
There is also ripple due to zero-sequence component if the
midpoint DC link is not grounded. Fig. 7 shows the dynamic
response of MMC-HVDC system to changes in rms AC
voltages when the outer loop in side 2 controls the AC rms
voltage and gives the reactive power command to the inner
control loop. The AC voltages are changed from 0.95pu to
1.05 pu at t=0.3 sec and they return to 0.95pu at t=0.4 sec.
Fig 8 shows the performance of the MMC-HVDC system
when SLG fault is applied at converter 2 side. The top plot in
Fig. 8 shows the PCC voltage for three phases. When SLG
fault is applied at t=0.3 sec the PCC voltages and currents
become unbalanced. Fourth and fifth plot from the top show
the zero sequence voltage and current appear in the system
starting 0.3 sec. Negative sequence in the voltages are shown
in the fourth plot.
Fig. 5 Power reversal test
Fig. 6 Step change in DC link voltage
Fig. 7 Dynamic response of MMC-HVDC system to changes in rms AC
voltage
The presence of negative and zero sequence components in the
system weakens the performance and could damage
semiconductors or cause the protection devices to trip
therefore the control system should be modified to eliminate
these components as fast as possible.
PI
Vc*
Vcju
(j=1-2n)
±
-1 :-Ik-up , Ik-low 0
+1 :-Ik-up , Ik-low 0
VBju*
Individual DC voltage controller
PI PI
1/2
Vc*
Vcu
Ik-low
Ik-up
Icir*
Icir
VAu*
Total DC voltage controller 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
-2.5
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
2.5
Activeandreactivepowerside1&2(pu)
P2
Q1
P1
Q2
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
-1
0
1
2
3
4
5
Time (secs)
Vdc(pu)
Vdc ref
Vdc
0 0.1 0.2 0.3 0.4 0.5 0.6
-1.5
-1
-0.5
0
0.5
1
1.5
Time(sec)
Vabcside2(pu)
Va
Vb
Vc
0.1 0.2 0.3 0.4 0.5 0.6
-2
-1
0
1
2
time (sec)
Q1&Q2(pu)
Q1
Q2
0 0.1 0.2 0.3 0.4 0.5 0.6
-4
-3
-2
-1
0
1
2
3
time(sec)
P1&P2(pu)
P1
P2
4. There are different methods to eliminate zero and negative
sequence components and most of the presented methods
focus on eliminating zero and negative sequence current
components using an additional controller. This paper
proposes an alternative control structure, which is based on
modifying the modulation waveform via adding additional
terms according to measured zero and negative sequence
voltages.
III. PROPOSED CONTROL STRUCTURE
The transformer-less MMC-HVDC simulation results confirm
that during faults or unbalance condition, there are zero and
negative sequence voltages in the system, which cause zero
and negative sequence current to flow in the system. The basic
idea of the proposed control structure is to command the
converter to generate required zero and negative sequence that
matches the zero and negative sequence voltage present in the
system. Adding virtual zero and negative sequence sources to
the system will help reducing zero and negative sequence
currents seen by the VSC during fault or unbalanced
conditions. Figs. 10 and 11 simply illustrate the structure of
the proposed controller. The zero and negative sequence
elimination terms are added to the modulation.
The process of calculating the negative sequence voltage
includes direct measurement and scaling of PCC zero and
negative sequence voltages and forcing the converter
controller to generate the same voltages at its output terminals.
Virtual voltages generated by the converter cancel out the
measured zero and negative voltages in PCC and force the
converter’ negative sequence currents to zero. The calculations
are all done instantly without using current regulator therefore
the controller is very fast.
Time (secs)
Fig. 8 MMC-HVDC system dynamic when SLG fault is applied at PCC2
TABLE II. MMC-HVDC SYSTEM SPECIFICATIONS
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5
-3
-2
-1
0
1
2
3
PCCvoltages(pu)
Ea
Eb
Ec
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5
-2
-1
0
1
2
3Phasecurrents(pu)
ia
ib
ic
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
Vdc(pu)
Vdc
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
Zerosequencevoltages(pu)
E0a
E0b
E0c
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5
-0.25
-0.2
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
0.2
0.25
Zerosequencecurrent(pu)
izero
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
Negativesequencevoltages(pu)
Ea
Eb
Ec
System parameters Values
AC system 138 kV-LL rms
Power 50 MW
Fundamental frequency 60Hz
MMC switching frequency 180Hz
Source inductance Ls 2mH
Arm inductance 7mH
Submodule capacitor 2500uF
DC link voltage 340 KV
5. Fig. 9 Dynamic performance of MMC-HVDC system with proposed control
structure SLG fault applied at 0.3 sec
Fig. 10 Zero and negative sequence calculation
Fig.11 Proposed control structure
Equations (8)-(10) summarize zero and negative sequence
calculations [8-9].
(8)
(9)
= = (10)
Fig. 9 demonstrates the performance of the proposed control
structure in MMC-HVDC system when SLG fault is applied at
0.3 sec. The top plot shows three-phase currents in converter
2 side, which remain balanced after SLG fault is applied. The
id and iq components of the negative sequence current are
displayed in the second plot. Third plot shows the DC link
voltage waveform and fourth plot shows zero sequence current
when the new control structure is applied.
The updated modulation waveform calculation is shown in
Fig. 11 and includes the output of all controllers. The
additional zero and negative sequence elimination terms are
circled in red.
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
3Phasecurrentsside2(pu)
ia
ib
ic
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5
-0.12
-0.1
-0.08
-0.06
-0.04
-0.02
0
0.02
0.04
0.06
0.08
Id&Iqnegativesequence(pu)
Idneg ref
Idneg
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5
0
1
2
3
4
5
6
Vdc(pu)
Vdc
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5
-0.1
-0.05
0
0.05
0.1
Zero-sequencecurrent(pu)
izero
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
Ea0,Eb0,Ec0(pu)
E0a
E0b
E0c
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5
-1
-0.5
0
0.5
1
daneg,dbneg,dcneg(pu)
Eaneg
Ebneg
Ecneg
dazero
Zero sequence
calculation dbzero
dczero
n
n
n
Ea
Eb
Ec
Ea0
Eb0
Ec0
daneg
Vcju
Eliminating
zero
sequence
Eliminating
positive
sequence
Vcjv
Vcjw
dbneg
dcneg
n
n
n
VAu*
VBju* Vi/n E/(2n)
Vju* (j=1-n)
dAneg dAzero
VAu*
VBju* Vi/n E/(2n)
Vju* (j=n+1-2n)
dAneg dAzero
6. After updating the control structure, zero and negative
sequence currents are almost zero. The calculated zero and
negative voltages terms that added to the modulation are
shown in Fig 9.
III. CONCLUSION
This paper analyzed the dynamic performance of an MMC-
HVDC system during normal operation and SLG AC fault. In
addition, an alternative control structure was proposed to
eliminate zero and negative sequence currents during faults
and unbalanced conditions. The presented method uses
instantaneous calculated values of negative and zero sequence
and does not use any additional controller thus it is very fast
compared to other solutions that incorporate some type of
controller to eliminate negative and zero sequence. The
control diagram of the recommended algorithm was presented
and PSCAD simulations prove the fast response of the
proposed control structure.
ACKNOWLEDGMENT
This work used ERC shared facilities supported by the
National Science Foundation. The author would also like to
thank Saman Babaei.
REFERENCES
[1] Lesnicar, A.; Marquardt, R., "An innovative modular multilevel
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