scholarly journals Unbalanced Current Sharing Control in Islanded Low Voltage Microgrids

Energies ◽  
2018 ◽  
Vol 11 (10) ◽  
pp. 2776 ◽  
Author(s):  
Foad Najafi ◽  
Mohsen Hamzeh ◽  
Matthias Fripp
Keyword(s):  
Output Power ◽  
Control Structure ◽  
Nonlinear Loads ◽  
Negative Sequence ◽  
Current Sharing ◽  
Current Controller ◽  
Voltage Controller ◽  
Zero Sequence ◽  
Resonant Controller ◽  
Virtual Impedance

This paper reports a new control strategy to improve sharing of unbalanced currents in islanded LV microgrids. This technique provides fast and effective sharing of positive-, negative- and zero-sequence currents, and is the first example of zero-sequence current sharing in the literature. The controllers are designed in the stationary frame. The control structure consists of four loops: (1) the current controller; (2) the voltage controller; (3) the droop controller and the (4) negative and zero sequence current controllers. The output current is considered unknown for the controller and is added to the control system as a disturbance. The proposed controller features a high gain in fundamental and harmonic frequencies, hence a good voltage quality is obtained in the presence of unbalanced and nonlinear loads. To this aim, a proportional-resonant (PR) controller is adopted as the current controller. By using a multi-resonant controller as current controller, a unified control structure is obtained which is suitable for both grid-connected and islanded modes. The voltage controller is designed using a resonant controller so that the voltage can have low VUF and THD in the presence of unbalanced and nonlinear loads. Furthermore, in this paper, the droop method is applied to the control structure to share real and reactive powers. Simulation studies show that the conventional droop method cannot share the oscillatory part of the output power that is due to the presence of unbalanced loads in the microgrid. This paper relies on using zero and negative sequence virtual impedance controller to share the oscillatory part of output power. By using zero-sequence virtual impedance controller (ZSVIC) and negative-sequence virtual impedance controller (NSVIC), the zero and negative sequence currents in the microgrid are controlled and shared effectively. By compensating zero- and negative-sequence currents locally, the flow of these currents in the microgrid is minimized, and the overall power quality of the islanded LV microgrid is improved.

scholarly journals Unbalanced Current Sharing Control in Islanded Low Voltage Microgrids

2018 ◽  
Author(s):  
foad najafi ◽  
Matthias Fripp
Keyword(s):  
Output Power ◽  
Control Structure ◽  
Nonlinear Loads ◽  
Negative Sequence ◽  
Current Sharing ◽  
Current Controller ◽  
Voltage Controller ◽  
Zero Sequence ◽  
Resonant Controller ◽  
Virtual Impedance

This paper reports a new control strategy to improve sharing of unbalanced currents in islanded LV microgrids. This technique provides fast and effective sharing of positive-, negative- and zero-sequence currents, and is the first example of zero-sequence current sharing in the literature. The controllers are designed in the stationary frame. The control structure consists of four loops; 1)~the current controller; 2)~the voltage controller; 3)~the droop controller and the 4)~negative and zero sequence current controllers. The output current is considered unknown for the controller and is added to the control system as a disturbance. The proposed controller features a high gain in fundamental and harmonic frequencies, hence a good voltage quality is obtained in the presence of unbalanced and nonlinear loads. To this aim, a proportional-resonant (PR) controller is adopted as the current controller. By using a multi-resonant controller as current controller, a unified control structure is obtained which is suitable for both grid-connected and islanded modes. The voltage controller is designed using a resonant controller so that the voltage can have low VUF and THD in the presence of unbalanced and nonlinear loads. Furthermore, in this paper droop method is applied to the control structure to share real and reactive powers. Simulation studies show that the conventional droop method cannot share the oscillatory part of the output power that is due to the presence of unbalanced loads in the microgrid. This paper relies on using zero and negative sequence virtual impedance controller to share the oscillatory part of output power. By using zero-sequence virtual impedance controller (ZSVIC) and negative-sequence virtual impedance controller (NSVIC), the zero and negative sequence currents in the microgrid are controlled and shared effectively. By compensating zero- and negative-sequence currents locally, the flow of these currents in the microgrid is minimized, and the overall power quality of the islanded LV microgrid is improved.

scholarly journals Unbalanced Current Sharing Control in Islanded Low Voltage Microgrids

2018 ◽  
Author(s):  
Foad Najafi ◽  
Matthias Fripp
Keyword(s):  
Output Power ◽  
Control Structure ◽  
Low Voltage ◽  
Nonlinear Loads ◽  
Negative Sequence ◽  
Current Controller ◽  
Voltage Controller ◽  
Zero Sequence ◽  
Resonant Controller ◽  
Virtual Impedance

In this paper, a new control strategy for power management improvement of islanded LV microgrids is proposed. The controllers are designed in the stationary frame. The control structure consists of four loops; 1)~the current controller; 2)~the voltage controller; 3)~the droop controller and the 4)~negative and zero sequence current controllers. The output current is considered unknown for the controller and is added to the control system as a disturbance. The proposed controller features a high gain in fundamental and harmonic frequencies, hence a good voltage quality is obtained in the presence of unbalanced and nonlinear loads. To this aim, a proportional-resonant (PR) controller is adopted as the current controller. By using a multi-resonant controller as current controller, a unified control structure is obtained which is suitable for both grid-connected and islanded modes. The voltage controller is designed using a resonant controller so that the voltage can have low VUF and THD in the presence of unbalanced and nonlinear loads. Furthermore, in this paper droop method is applied to the control structure to share real and reactive powers. Simulation studies show that the conventional droop method cannot share the oscillatory part of the output power that is due to the presence of unbalanced loads in the microgrid. This paper relies on using zero and negative sequence virtual impedance controller to share the oscillatory part of output power. By using zero-sequence virtual impedance controller (ZSVIC) and negative-sequence virtual impedance controller (NSVIC), the zero and negative sequence currents in the microgrid are controlled and shared effectively. By compensating zero- and negative-sequence currents locally, the flow of these currents in the microgrid is minimized, and the overall power quality of the islanded LV microgrid is improved.

scholarly journals Enhanced Circular Chain Control for Parallel Operation of Inverters in UPS Systems

2020 ◽  
Vol 12 (19) ◽  
pp. 8062 ◽  
Author(s):  
Mahdi Shahparasti ◽  
Mehdi Savaghebi ◽  
Majid Hosseinpour ◽  
Navid Rasekh
Keyword(s):  
Control Structure ◽  
Parallel Operation ◽  
Nonlinear Loads ◽  
Uninterruptible Power Supply ◽  
Loop Control ◽  
Current Sharing ◽  
Circular Structure ◽  
Uninterruptible Power ◽  
Equal Power ◽  
A Current

In this paper, a current sharing method based on the circular chain control (3C) method is proposed for controlling parallel inverters of unequal ratings in uninterruptible power supply (UPS) applications. Due to its circular structure, 3C is one of the most convenient methods which can be used in UPS as well as microgrid systems. However, the conventional 3C control strategy is only applicable to inverters of equal power ratings. The proposed method not only retains the circular structure of the 3C method, but also provides adaptability for the parallel operation of inverters with different power ratings. Moreover, this method adds hot-swap capability to the parallel inverter. A two-loop control structure is used to control the inverters. For proper current sharing, currents of inverters are conveyed in a circular structure with appropriate gains through control links. Simulation and experimental results for linear and nonlinear loads verify the effectiveness of the proposed strategy.

Research on Output Power Control Strategy of Parallel Microgrid Based on Improved Virtual Impedance

2021 ◽  
Author(s):  
Li Shiguang ◽  
Liu Guangjie ◽  
Gao Zhengzhong ◽  
Sun Yuchen ◽  
Xu Yujuan
Keyword(s):  
Power Control ◽  
Output Power ◽  
Control Strategy ◽  
Virtual Impedance

CURRENT HARMONICS MITIGATION FROM GRID CONNECTED VARIABLE SPEED WIND TURBINE DUE TO NONLINEAR LOADS USING SHUNT ACTIVE POWER FILTER

2017 ◽  
Vol 79 (4) ◽  
Author(s):  
Sajid Hussain Qazi ◽  
Mohd Wazir Mustafa ◽  
U. Sultana ◽  
Nayyar Hussain Mirjat
Keyword(s):  
Wind Turbine ◽  
Active Power Filter ◽  
Active Power ◽  
Variable Speed ◽  
Nonlinear Loads ◽  
Shunt Active Power Filter ◽  
Current Harmonics ◽  
Power Filter ◽  
Current Controller ◽  
Synchronous Reference Frame

The quality of power nowadays is of great concern due to increasing demand of supply and energy resources are limited, another cause is increasing penetration of nonlinear loads in the power system. In order to overcome energy supply challenges, the focus of technologists is shifting to the renewable energy side such as the wind and solar energy and so on. As such, mitigating effect of nonlinear loads have become ever important as well. In this context, various techniques have been used by researchers in past decades. Shunt active power filter (APF) have long been used to mitigate current harmonics from fixed wind turbine generator (WTG). In this study shunt APF has been applied with variable speed WTG using synchronous reference frame (SRF) for the extraction of compensation signal for APF. Gate driver signals are generated from Bang-Bang Controller (Hysteresis Band Current Controller HBCC). A MATLAB/SIMULINK based Model have been developed. The Simulation results show decreased THD levels of the system and clearly suggest the effectiveness of Shunt APF in meeting the IEEE-519 standard recommendation for harmonic levels in WTG.

scholarly journals Enabling Grid-Feeding Converters With a Dissonant-Resonant Controller for Negative-Sequence Voltage Elimination

2020 ◽  
Vol 35 (4) ◽  
pp. 4342-4352 ◽  
Author(s):  
Manel Velasco ◽  
Pau Marti ◽  
Antonio Camacho ◽  
Juan M. Rey ◽  
Jaume Miret ◽  
...  
Keyword(s):  
Negative Sequence ◽  
Resonant Controller
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