This document discusses controlling parallel DC-DC converters in a DC microgrid using a virtual output impedance method. It begins with introductions to power converters and DC converters. It then discusses types of DC converters, their performance parameters, output impedance, and how output impedance mismatch can cause circulating currents. It proposes using a virtual output impedance control loop to compensate for differences in converter output voltages and reduce circulating currents. Simulation results show this method can decrease circulating currents to near zero while maintaining voltage regulation within allowed deviations.
A dual active bridge dc-dc converter for application in a smart user networkAlessandro Burgio
Abstract—The paper presents a dual active bridge converter, i.e. an isolated bidirectional DC/DC converter composed of two full-bridge DC/AC converters and an isolation high frequency (HF) transformer, useful for application in a DC-powered microgrid. The dual active bridge converter connects a battery energy storage system to a DC bus so to provide a high level of reliability and resilience to grid disturbances. In particular, the proposed converter ensures a stable DC bus voltage when the microgrid is operated in islanded mode. Numerical results demonstrate the good dynamic response of the converter under transient condition of
Power factor improvement is the essence of any power sector for realible operations. This report provides literature study of a fixed capacitor thyristor controlled reactor type of power factor compensator by matlab simulation and implementation in programmed microcontroller. To retaining power factor closed to unity under various load condition the arduino ATmega8 microcontroller is used which is programmed by keil software. The simulation is done using proteus software which display power factor according to the variation in load whenever a capacitive load is connected to the transmission line, a shunt reactor is connected which injects lagging reactive VARs to the power system. This report also includes the matlab simulation for three phase power factor improvement by using fixed capacitor thyristor controlled reactor. As a
result the power factor is improved. The results given in this report provides
suitable matlab simulation and proteus simulation based reactor power compensation and power factor improvement and techniques using a FCTCR.
A dual active bridge dc-dc converter for application in a smart user networkAlessandro Burgio
Abstract—The paper presents a dual active bridge converter, i.e. an isolated bidirectional DC/DC converter composed of two full-bridge DC/AC converters and an isolation high frequency (HF) transformer, useful for application in a DC-powered microgrid. The dual active bridge converter connects a battery energy storage system to a DC bus so to provide a high level of reliability and resilience to grid disturbances. In particular, the proposed converter ensures a stable DC bus voltage when the microgrid is operated in islanded mode. Numerical results demonstrate the good dynamic response of the converter under transient condition of
Power factor improvement is the essence of any power sector for realible operations. This report provides literature study of a fixed capacitor thyristor controlled reactor type of power factor compensator by matlab simulation and implementation in programmed microcontroller. To retaining power factor closed to unity under various load condition the arduino ATmega8 microcontroller is used which is programmed by keil software. The simulation is done using proteus software which display power factor according to the variation in load whenever a capacitive load is connected to the transmission line, a shunt reactor is connected which injects lagging reactive VARs to the power system. This report also includes the matlab simulation for three phase power factor improvement by using fixed capacitor thyristor controlled reactor. As a
result the power factor is improved. The results given in this report provides
suitable matlab simulation and proteus simulation based reactor power compensation and power factor improvement and techniques using a FCTCR.
In the modern power system the reactive power compensation is one of the main issues, the transmission of active power requires a difference in angular phase between voltages at the sending and receiving points (which is feasible within wide limits), whereas the transmission of reactive power requires a difference in magnitude of these same voltages (which is feasible only within very narrow limits). The reactive power is consumed not only by most of the network elements, but also by most of the consumer loads, so it must be supplied somewhere. If we can't transmit it very easily, then it ought to be generated where it is needed." (Reference Edited by T. J. E. Miller, Forward Page ix).Thus we need to work on the efficient methods by which VAR compensation can be applied easily and we can optimize the modern power system. VAR control technique can provides appropriate placement of compensation devices by which a desirable voltage profile can be achieved and at the same time minimizing the power losses in the system. This report discusses the transmission line requirements for reactive power compensation. In this report thyristor switched capacitor is explained which is a static VAR compensator used for reactive power management in electrical systems.
Seminar Topic For Electrical and Electronics Engineering (EEE)
Generation of High Frequency AC High VoltagePratheep M
This ppt explained the generation of high frequency ac high voltage using tesla coil. Also it explains more about the tesla coil and derivation of generation of high frequency ac voltage using tesla coil.
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.
TECHNICAL REQUIREMENTS AND SPECIFICATIONS OF STATE-OF-THE-ART HVDC SWITCHING ...Power System Operation
TECHNICAL REQUIREMENTS AND SPECIFICATIONS OF STATE-OF-THE-ART HVDC SWITCHING EQUIPMENT TECHNICAL REQUIREMENTS AND SPECIFICATIONS OF STATE-OF-THE-ART HVDC SWITCHING EQUIPMENTTECHNICAL REQUIREMENTS AND SPECIFICATIONS OF STATE-OF-THE-ART HVDC SWITCHING EQUIPMENTTECHNICAL REQUIREMENTS AND SPECIFICATIONS OF STATE-OF-THE-ART HVDC SWITCHING EQUIPMENTTECHNICAL REQUIREMENTS AND SPECIFICATIONS OF STATE-OF-THE-ART HVDC SWITCHING EQUIPMENTTECHNICAL REQUIREMENTS AND SPECIFICATIONS OF STATE-OF-THE-ART HVDC SWITCHING EQUIPMENTTECHNICAL REQUIREMENTS AND SPECIFICATIONS OF STATE-OF-THE-ART HVDC SWITCHING EQUIPMENTTECHNICAL REQUIREMENTS AND SPECIFICATIONS OF STATE-OF-THE-ART HVDC SWITCHING EQUIPMENTTECHNICAL REQUIREMENTS AND SPECIFICATIONS OF STATE-OF-THE-ART HVDC SWITCHING EQUIPMENTTECHNICAL REQUIREMENTS AND SPECIFICATIONS OF STATE-OF-THE-ART HVDC SWITCHING EQUIPMENTTECHNICAL REQUIREMENTS AND SPECIFICATIONS OF STATE-OF-THE-ART HVDC SWITCHING EQUIPMENT
International Journal of Engineering Research and Applications (IJERA) aims to cover the latest outstanding developments in the field of all Engineering Technologies & science.
International Journal of Engineering Research and Applications (IJERA) is a team of researchers not publication services or private publications running the journals for monetary benefits, we are association of scientists and academia who focus only on supporting authors who want to publish their work. The articles published in our journal can be accessed online, all the articles will be archived for real time access.
Our journal system primarily aims to bring out the research talent and the works done by sciaentists, academia, engineers, practitioners, scholars, post graduate students of engineering and science. This journal aims to cover the scientific research in a broader sense and not publishing a niche area of research facilitating researchers from various verticals to publish their papers. It is also aimed to provide a platform for the researchers to publish in a shorter of time, enabling them to continue further All articles published are freely available to scientific researchers in the Government agencies,educators and the general public. We are taking serious efforts to promote our journal across the globe in various ways, we are sure that our journal will act as a scientific platform for all researchers to publish their works online.
In the modern power system the reactive power compensation is one of the main issues, the transmission of active power requires a difference in angular phase between voltages at the sending and receiving points (which is feasible within wide limits), whereas the transmission of reactive power requires a difference in magnitude of these same voltages (which is feasible only within very narrow limits). The reactive power is consumed not only by most of the network elements, but also by most of the consumer loads, so it must be supplied somewhere. If we can't transmit it very easily, then it ought to be generated where it is needed." (Reference Edited by T. J. E. Miller, Forward Page ix).Thus we need to work on the efficient methods by which VAR compensation can be applied easily and we can optimize the modern power system. VAR control technique can provides appropriate placement of compensation devices by which a desirable voltage profile can be achieved and at the same time minimizing the power losses in the system. This report discusses the transmission line requirements for reactive power compensation. In this report thyristor switched capacitor is explained which is a static VAR compensator used for reactive power management in electrical systems.
Seminar Topic For Electrical and Electronics Engineering (EEE)
Generation of High Frequency AC High VoltagePratheep M
This ppt explained the generation of high frequency ac high voltage using tesla coil. Also it explains more about the tesla coil and derivation of generation of high frequency ac voltage using tesla coil.
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.
TECHNICAL REQUIREMENTS AND SPECIFICATIONS OF STATE-OF-THE-ART HVDC SWITCHING ...Power System Operation
TECHNICAL REQUIREMENTS AND SPECIFICATIONS OF STATE-OF-THE-ART HVDC SWITCHING EQUIPMENT TECHNICAL REQUIREMENTS AND SPECIFICATIONS OF STATE-OF-THE-ART HVDC SWITCHING EQUIPMENTTECHNICAL REQUIREMENTS AND SPECIFICATIONS OF STATE-OF-THE-ART HVDC SWITCHING EQUIPMENTTECHNICAL REQUIREMENTS AND SPECIFICATIONS OF STATE-OF-THE-ART HVDC SWITCHING EQUIPMENTTECHNICAL REQUIREMENTS AND SPECIFICATIONS OF STATE-OF-THE-ART HVDC SWITCHING EQUIPMENTTECHNICAL REQUIREMENTS AND SPECIFICATIONS OF STATE-OF-THE-ART HVDC SWITCHING EQUIPMENTTECHNICAL REQUIREMENTS AND SPECIFICATIONS OF STATE-OF-THE-ART HVDC SWITCHING EQUIPMENTTECHNICAL REQUIREMENTS AND SPECIFICATIONS OF STATE-OF-THE-ART HVDC SWITCHING EQUIPMENTTECHNICAL REQUIREMENTS AND SPECIFICATIONS OF STATE-OF-THE-ART HVDC SWITCHING EQUIPMENTTECHNICAL REQUIREMENTS AND SPECIFICATIONS OF STATE-OF-THE-ART HVDC SWITCHING EQUIPMENTTECHNICAL REQUIREMENTS AND SPECIFICATIONS OF STATE-OF-THE-ART HVDC SWITCHING EQUIPMENT
International Journal of Engineering Research and Applications (IJERA) aims to cover the latest outstanding developments in the field of all Engineering Technologies & science.
International Journal of Engineering Research and Applications (IJERA) is a team of researchers not publication services or private publications running the journals for monetary benefits, we are association of scientists and academia who focus only on supporting authors who want to publish their work. The articles published in our journal can be accessed online, all the articles will be archived for real time access.
Our journal system primarily aims to bring out the research talent and the works done by sciaentists, academia, engineers, practitioners, scholars, post graduate students of engineering and science. This journal aims to cover the scientific research in a broader sense and not publishing a niche area of research facilitating researchers from various verticals to publish their papers. It is also aimed to provide a platform for the researchers to publish in a shorter of time, enabling them to continue further All articles published are freely available to scientific researchers in the Government agencies,educators and the general public. We are taking serious efforts to promote our journal across the globe in various ways, we are sure that our journal will act as a scientific platform for all researchers to publish their works online.
A Modern Technique of Deduction in Leakage Current in Resonant Bi-directional...IJMTST Journal
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to a converter to produce grid voltage of adequate requirement and then to convert DC to AC voltage for grid
cnnection. Usually, the first stage is a DC-DC boost type converter which is responsible for extracting maximum
power from panel and boosting PV voltage to a value higher than peak of grid voltage. A converter is proposed,
which is derived from an active network based converter, is chosen as the first stage and a five level inverter is
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switching stress. The Inverter used is having the advantage of low filter requirement, reduced stress, EMI and
reduced THD level. A closed loop control of the converter is done to maintain constant output voltage under
varying input voltage. MATLAB R2014a version software is used to simulate the model. The prototype of the
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Fuzzy based control of Transformer less Coupled inductor based DC-DC converterIJERA Editor
Most of the industrial applications use any one of the basic DC-DC converter configurations namely buck,
boost, buck–boost, and Cuk converters. These converters are non-isolating converters. Buck-boost converters
use inductors for storing energy from the source and release the same to load or output. This results in high
stress across magnetic components. This drawback restricts usage of buck-boost converters to low power
applications. Flyback converters popularly have known as buck-boost converters uses transformers for
achieving wide range of step down and step up voltages. Coupled inductor based converters or tapped inductor
based converters are used for achieving wide input – wide output conversion ratios. Coherent transition between
step-down and step-up modes is achieved by a proper control scheme. This paper proposes fuzzy logic based
closed loop control scheme for control of converter switches. Theoretical derivations of control parameters with
their membership values, mamdani based rules for development of fuzzy rules and simulation results of a
coupled inductor based DC-DC converter using MATLAB / SIMULINK are concluded.
PHASE 2 R2 hybrid based landsman converter.pptxGunal16
We have implemented the Landsman converter for an AC/DC grid using a hybrid energy source, and present our hardware implementation in this paper The Landsman converter is a proposed solution to reduce the number of reverse conversions required in individual AC or DC grids, and to simplify the connection of various renewable AC and DC sources and loads to the power system. The input sources for the system are solar panels and wind energy conversion systems (WECS), each equipped with a Landsman converter. The WECS and solar panels are connected to the input DC line. To store energy, a bidirectional DC/DC converter and battery are connected to the DC bus. The dsPIC microcontroller is its ability to generate Pulse Width Modulation (PWM) signals, which are used to provide the gate pulse to the Landsman converter and single-phase voltage source inverter. The single-phase voltage source inverter converts the DC supply to AC and supplies it to the load. grid synchronization, with variable DC and AC loads connected to their respective DC and AC buses to simulate different loads
The measurement of various ouput of this hardware is taken in digital oscilloscope.
The hardware's output measurements are taken using a
digital oscilloscope. the input voltage of 12v is given to the landsman converter from the energy source is shown in figure 11 using DSOWe have implemented the Landsman converter for an AC/DC grid using a hybrid energy source, and present our hardware implementation in this paper The Landsman converter is a proposed solution to reduce the number of reverse conversions required in individual AC or DC grids, and to simplify the connection of various renewable AC and DC sources and loads to the power system. The input sources for the system are solar panels and wind energy conversion systems (WECS), each equipped with a Landsman converter. The WECS and solar panels are connected to the input DC line. To store energy, a bidirectional DC/DC converter and battery are connected to the DC bus. The dsPIC microcontroller is its ability to generate Pulse Width Modulation (PWM) signals, which are used to provide the gate pulse to the Landsman converter and single-phase voltage source inverter. The single-phase voltage source inverter converts the DC supply to AC and supplies it to the load. grid synchronization, with variable DC and AC loads connected to their respective DC and AC buses to simulate different loads
The measurement of various ouput of this hardware is taken in digital oscilloscope.
The hardware's output measurements are taken using a
digital oscilloscope. the input voltage of 12v is given to the landsman converter from the energy source is shown in figure 11 using DSOWe have implemented the Landsman converter for an AC/DC grid using a hybrid energy source, and present our hardware implementation in this paper The Landsman converter is a proposed solution to reduce the number of reverse conversions required in individual AC or dc grid
High Efficiency Dc-Dc Converter for Renewable Energy Applications and High Vo...IOSRJEEE
Renewable sources like solar PV cell is prefer to be operated at low voltages. This paper proposes a novel high voltage gain, high efficiency dc-dc converter based on coupled inductor, intermediate capacitor. The input energy acquired from the source is first stored in the coupled inductor and intermediate capacitor in a lossless manner. Improve the voltage gain and efficiency of the system. Exorbitant duty cycle values are not required for high voltage gain, when prevent the problems such as diode reverse recovery. Presence of a passive clamp network causes reduced voltage stress on the switch. Overall performance of the renewable energy with a step-up DC/DC converter using closed loop control action is used in the proposed system, improving the overall efficiency of the system.
International Journal of Engineering Research and Applications (IJERA) is a team of researchers not publication services or private publications running the journals for monetary benefits, we are association of scientists and academia who focus only on supporting authors who want to publish their work. The articles published in our journal can be accessed online, all the articles will be archived for real time access.
Our journal system primarily aims to bring out the research talent and the works done by sciaentists, academia, engineers, practitioners, scholars, post graduate students of engineering and science. This journal aims to cover the scientific research in a broader sense and not publishing a niche area of research facilitating researchers from various verticals to publish their papers. It is also aimed to provide a platform for the researchers to publish in a shorter of time, enabling them to continue further All articles published are freely available to scientific researchers in the Government agencies,educators and the general public. We are taking serious efforts to promote our journal across the globe in various ways, we are sure that our journal will act as a scientific platform for all researchers to publish their works online.
Electrical, Electronics and Computer Engineering,
Information Engineering and Technology,
Mechanical, Industrial and Manufacturing Engineering,
Automation and Mechatronics Engineering,
Material and Chemical Engineering,
Civil and Architecture Engineering,
Biotechnology and Bio Engineering,
Environmental Engineering,
Petroleum and Mining Engineering,
Marine and Agriculture engineering,
Aerospace Engineering.
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Control of parallel dc dc converters in a dc microgrid
1. 1/12
Power Electronic Systems & Chips Lab., NCTU, Taiwan
Control of Parallel DC-DC Converters in a DC Microgrid
Using Virtual Output Impedance method
電力電子系統與晶片實驗室
Power Electronic Systems & Chips Lab.
交通大學 • 電機控制工程研究所
台灣新竹‧交通大學‧電機控制工程研究所‧電力電子實驗室~鄒應嶼 教授
Sushil Kumar
2. 2/12
Outline
1. Introduction
2. Types of DC Converter
3. Performance parameter of DC converter
4. What is output impedance ?
5. Circulating Current and output Impedance
6. Microgrid
7. Control of DC-Dc converters by using virtual impedance
8. Droop control Startagy
9. How Virtual impedance work?
10. Simulation Study
11. Advantages and disadvantages of this scheme
12. Conclusion
13. Question Arises
3. 3/12
Introduction
Power Converter:-
For the control of electric power, power conditioning the
conversion of one form to another from is necessary that is
done by static power converters
DC Converter
A DC converter is an electrical circuit which accepts a DC input
and generates a DC output of a different voltage.
Usually achieved by high frequency switching action employing
inductive and capacitive filter elements
DC converter is used for unregulated DC to regulated DC.
:
4. 4/12
Types of DC Converter
1. Buck Converter :- Voltage step down and current step up
2. Boost Converter:- Inverse of Buck, Voltage up ,current down
3. Buck Boost converter:- Output Voltage may be less then or
higher than input voltage, as per user requirement, hybrid of
Buck and boost both hence buck-boost.
5. 5/12
Performance parameters of DC-DC converters
There are many performance parameter whose take attention
while we design the converter. These are:-
1. Operating Frequency
2. Inductor Selection
3. Capacitor Selection
4. Switch component
6. 6/12
What is Output Impedance ?
• The output impedance is defined as the output voltage
response of a converter for the excitation of current (load
current, VL) at constant input voltage (Vin) and a specific
value of duty ratio D.
• Output impedance is mismatch due to unequal output voltage
or variation in current.
• It is very necessary that output impedance of output
converters should be same.
7. 7/12
Circulating Current and Output impedance
• The mismatch in the output voltages will increase the current
sharing difference and flow of circulating current.
• We can also say that output impedance mismatching is
responsible for circulating current or vice versa.
• The circulating current phenomena we can understand by this
table 1.
Where, Vdc1, Vdc2 are the output currents R1, R2 are cable resistances, I1 and I2 are
o/p currents and Ic12 and Ic21 are the Circulating currents of two converters
respectively.
8. 8/12
Microgrid
Microgrid :-
An active power distribution network
Capability of autonomous distribution
Renewable energy sources connected with common bus
Can say Local power station
Work as a autonomous as well as tie with Grid
Types:-
AC Microgrid
DC Microgrid
9. 9/12
Control of DC-DC Converters by using Virtual Impedance
Method
Importance of Virtual Impedance :-
Virtual impedances can be used to match the grid-side
impedance in AC microgrids
The Virtual Impedance can be programmed at the certain
frequency to form the expected harmonic impedance, which
enables the function of harmonic sharing and damping.
Virtual Impedances can be employed to realize the resonance
damping in the LCL filters. By using the additional current
sensors and multiple control loops, the resonance peaks
imposed by LCL filters can be attenuated.
10. 10/12
Continue…
The virtual impedance loop can either be embedded as an
additional degree of freedom for active stabilization and
disturbance rejection, or be employed as a command reference
generator for the converters to provide ancillary services.
connect a virtual impedance in parallel or series with the input
impedance of the load converter , the magnitude or phase of the
load converter’s input impedance is modified in a small range of
frequency, to solve the instability problem of a cascaded system
11. 11/12
Droop control strategy using virtual impedance
Three control levels:-
Primary control:- Voltage and Freq. stabilization after islanding
Secondary Control:- check for any deviations caused by primary
Tertiary control:- Govern the power flow between Microgrid & main
Grid
Droop Control Method:-
It is method to share load between parallel connected sources
In order to obtain proper load sharing we use decentralized droop
control method i.e. No communication between the sources hence
name decentralized.
12. 12/12
Droop control in DC Microgrid
• In the parallel DC-DC Converter, the output voltage of the
converter given a droop with increase in load power.
Fig.1. DC Microgrid Architecture
Fig.2. P-V Droop Characteristics
As P1max < P2max, the sloop or droop of voltage converter 1 is
greater than that of 2. At any particular voltage V*, the power shared
by Converter 1 is P1* and that of converter 2 is P2*. The total load is
sum of P1* and P2*
13. 13/12
Effect of droop control
• Voltage regulation is adverse effected by droop control so the
slope of droop characteristics is designed keeping in mind the
max. value of voltage deviation.
• Cable resistance that is connected
to source and point and common
coupling is also mentioned
because the higher value of
resistance has poor voltage
regulation and due to this we
can not give more sloop to the
droop characteristics.
Load sharing will be better if
cable resistance is less.
Fig.3. Effect of cable resistance on P-V
droop Characteristics
14. 14/12
Effect of droop control
• When droop gain used is higher, current sharing error of the
converters reduces
• Voltage regulation is increased
• High value of droop gains provide stabilizing effect on DC
Microgrid but also increase losses.
A trade off is required is selecting the droop gain as a small value and a
higher value can adversely affect the system
15. 15/12
Droop Control using Virtual impedance
Two DC-DC converters connected
in parallel
The equivalent ckt. DC power supplies
connected to a common load through
resistive output impedance.
Nominal output voltage should be same.
In case of minor difference of output voltage , a circulating
current flows between the sources
Virtual Impedance is programmed to reduce the
circulating current
16. 16/12
How virtual impedance work ?
The Control Input to the voltage loop expressed
as:-
Vo* = Vref – RdIo ……………….(1)
Where
Io is the measured output current
RD is the virtual impedance
Vref is the no load output reference voltage
If Ev is the maximum output deviation, RD and
Vref is
Vref = Vn – Ev/2 …………(2)
RD = Ev/ Imax ………….(3)
Where Vn is the nominal output voltage
Imax is the max output current
The virtual impedance control loop
compensate the difference in voltage
reference Vo* = V*o1-V*o2
The current sharing between the two converters are
Δ Io = Io1-Io2= Δ Vo* /RD
17. 17/12
Simulation Study
• Simulation study done by connecting two buck converter back to
back. The parameter used are given in table 1.
• The design parameter given in
Table 2.
The design equation of the buck
converter
L= 1.25 (1-D)RL / 2f
C= (1-D) / 8Lf2 (ΔVo/Vo)
Where,
D is the duty ratio
ΔVo is the peak to peak ripple output
Voltage, Vo is the reference voltage
18. 18/12
Design Parameter
Nominal output voltage = 380 V
Nominal Output voltage = 120 V
Virtual Output impedance = 8 Ω
Proposed control strategy output time = 0.5 s
Sudden increase in load at 0.8 s
Load resistance change from 100 Ω to 80 Ω
Maximum Voltage deviation= 5 %
Current before applied virtual impedance
different and after 0.5 second the difference
goes almost zero even after 0.8 second sudden
increase in load but voltage drop due to this
action
19. 19/12
Advantages and disadvantages
Advantages:-
1. Circulating current decrease aprrox. to zero by using this method.
Disadvantages:-
1.Voltage deviations caused due to load variation is the major disadvantages of
this method.
2. Secondary control and territory control also required for further control the
grid system network
20. 20/12
Conclusion
• Output impedance matching is one of the most important concept
in converter
• If impedance don’t match the circulating current will be flow in
between the converter that are connected parallel
• If the output resistance
difference between the two
converter is more, then the
current sharing error and
voltage regulation is
deteriorated. (Fig.7)
21. 21/12
Conclusion
1.With higher value of virtual output impedance the load sharing
has improved
2. Current sharing error between the converter will be reduced
3.Voltage deviation or droop will be more
4. For a smaller value of virtual impedance voltage deviation is
less but current sharing error is higher.
5. Additional control i.e. secondary control for synchronization
and territory control is also required to control the bidirectional
power flow.
22. 22/12
Questions Arises
1. if there are more then two converter connected in parallel than
this technique will be effective or not?
i.) The value of virtual impedance changed every time or
predefined.
ii) If the value is predefine or fixed then how can we give
the proportional feedback as we required to compensate
the current sharing error.
2. What about the Cable resistance, It will be same or variable
because all converter not at same distance. It could effect
stability.
3. What about the output impedance- I think output impedance also
a control variable in this case.
23. 23/12
4. Line impedance is hard to calculate because its may very with
different load and in this approach conductor resistance also
mentioned , so this is the point for confusion.
5. If circulating current is more and so after applied virtual
impedance, voltage should not be more or less than maximum
voltage deviation for example if output is 100 V and voltage
deviation is +/- 5% so maximum voltage deviation will be 5 V so
product of Virtual impedance and circulating current is less than
5 V, if more current not be removed.