scholarly journals A Novel VSG-Based Accurate Voltage Control and Reactive Power Sharing Method for Islanded Microgrids

2019 ◽  
Vol 11 (23) ◽  
pp. 6666 ◽  
Author(s):  
Bowen Zhou ◽  
Lei Meng ◽  
Dongsheng Yang ◽  
Zhanchao Ma ◽  
Guoyi Xu
Keyword(s):  
Reactive Power ◽  
Control Method ◽  
Low Voltage ◽  
Voltage Drop ◽  
Reference Value ◽  
Voltage Control ◽  
Synchronous Generator ◽  
Stability Control ◽  
Control Area ◽  
Power Sharing

Islanded microgrids (IMGs) are more likely to be perturbed by renewable generation and load demand fluctuation, thus leading to system instability. The virtual synchronous generator (VSG) control has become a promising method in the microgrids stability control area for its inertia-support capability. However, the improper power sharing and inaccurate voltage control problems of the distributed generations (DGs) in microgrids still has not been solved with a unified method. This paper proposes a novel VSG equivalent control method named Imitation Excitation Control (IEC). In this method, a multi-objective control strategy for voltage and reactive power in a low voltage grid that considers a non-negligible resistance to reactance ratio (R/X) is proposed. With the IEC method, the voltage drop across feeders is compensated, thus the terminal voltage of each inverter will be regulated, which will effectively stabilize the PCC (point of common coupling) voltage and inhibit the circular current. Meanwhile, this method can realize accurate reactive power tracking the reference value, making it accessible for reactive power scheduling. What is more, the reasonability of the IEC model, namely the equivalent mechanical characteristic and transient process inertia support between VSGs and conventional synchronous generators (SG), is illustrated in this paper. Moreover, steady-state stability is proved by the small-signal modeling method, and the energy required by inertia support is given. Finally, the simulation result validates the effectiveness of the proposed method, and it is also demonstrated that the proposed method outperforms the conventional droop control method.

scholarly journals Control Method of Parallel Inverters with Self-Synchronizing Characteristics in Distributed Microgrid

Energies ◽  
2019 ◽  
Vol 12 (20) ◽  
pp. 3871 ◽  
Author(s):  
Yan ◽  
Cui ◽  
Cui
Keyword(s):  
Reactive Power ◽  
Control Method ◽  
Dynamic Performance ◽  
Synchronous Generator ◽  
Power Sharing ◽  
Control Mode ◽  
Stable Operation ◽  
Centralized Control ◽  
Local Data ◽  
Precise Control

The centralized control mode is no longer applicable for microgrid operation due to the high penetration rate of distributed energy, which is responsible for the widespread interest in the use of the distributed microgrid. Focusing on the issues of power coupling and uncontrollable droop coefficient at the terminal of the connecting line between the micro-source and AC bus, which is rarely considered, this paper proposes an improved virtual synchronous generator (VSG) control strategy based on local data considering precise control of the droop coefficient and realizing the power decoupling and the expected droop characteristics. Then, combined with the virtual rotor characteristic matching method, the reasonable active and reactive power sharing of the parallel microgrid inverters are realized in terms of static and dynamic performance without additional improvement of reactive power control. Finally, the effectiveness and feasibility of the proposed method are verified based on the MATLAB/Simulink simulation platform. The combination of the proved strategy and matching principle endows inverters with self-synchronization characteristics, forming the self-synchronizing voltage sources, which gives the distributed microgrid a higher self-stability, autonomy and robustness to ensure the stable operation of the microgrid.

scholarly journals Low-Voltage Ride-Through Operation of Grid-Connected Microgrid Using Consensus-Based Distributed Control

Energies ◽  
2018 ◽  
Vol 11 (11) ◽  
pp. 2867 ◽  
Author(s):  
Woon-Gyu Lee ◽  
Thai-Thanh Nguyen ◽  
Hyeong-Jun Yoo ◽  
Hak-Man Kim
Keyword(s):  
Distributed Control ◽  
Reactive Power ◽  
Control Method ◽  
Low Voltage ◽  
Power Sharing ◽  
Consensus Algorithm ◽  
Stable Operation ◽  
Low Voltage Ride Through ◽  
Primary Layer ◽  
Secondary Layer

Since the penetration of distributed energy resources (DERs) and energy storage systems (ESSs) into the microgrid (MG) system has increased significantly, the sudden disconnection of DERs and ESSs might affect the stability and reliability of the whole MG system. The low-voltage ride-through (LVRT) capability to maintain stable operation of the MG system should be considered. The main contribution of this study is to propose a distributed control, based on a dynamic consensus algorithm for LVRT operation of the MG system. The proposed control method is based on a hierarchical control that consists of primary and secondary layers. The primary layer is in charge of power regulation, while the secondary layer is responsible for the LVRT operation of the MG system. The droop controller is used in the primary layer to maintain power sharing among parallel-distributed generators in the MG system. The dynamic consensus algorithm is used in the secondary layer to control the accurate reactive power sharing and voltage restoration for LVRT operation. A comparison study on the proposed control method and centralized control method is presented in this study to show the effectiveness of the proposed controller. Different scenarios of communication failures are carried out to show the reliability of the proposed control method. The tested MG system and proposed controller are modeled in a MATLAB/Simulink environment to show the feasibility of the proposed control method.

scholarly journals A Reactive Power-Voltage Control Strategy of an AC Microgrid Based on Adaptive Virtual Impedance

Energies ◽  
2019 ◽  
Vol 12 (16) ◽  
pp. 3057
Author(s):  
Yao Liu ◽  
Lin Guan ◽  
Fang Guo ◽  
Jianping Zheng ◽  
Jianfu Chen ◽  
...  
Keyword(s):  
Distributed Generation ◽  
Control Strategy ◽  
Reactive Power ◽  
Reference Value ◽  
Voltage Control ◽  
Power Sharing ◽  
Voltage Reference ◽  
Voltage Control Strategy ◽  
Voltage Recovery ◽  
Virtual Impedance

As an effective carrier of distributed generation, a microgrid is an effective way to ensure that distributed power can be reasonably utilized. However, due to the property of line impedance and other factors in a microgrid, reactive power supplied by distributed generation units cannot be shared rationally. To efficiently improve reactive power sharing, this paper proposes a reactive power-voltage control strategy based on adaptive virtual impedance. This method changes the voltage reference value by adding an adaptive term based on the traditional virtual impedance. Meanwhile, a voltage recovery mechanism was used to compensate the decline of distributed generation (DG) output voltage in the process. MATLAB/Simulink simulations and experimental results show that the proposed controller can effectively improve the steady state performance of the active and reactive power sharing. Finally, the feasibility and effectiveness of the proposed control strategy were verified.

scholarly journals A Centralized Shifted Voltage Control Method for Accurate Power Sharing in DC Islanded Microgrids

2021 ◽  
Vol 19 ◽  
pp. 155-159
Author(s):  
Minh-Duc Pham ◽  
◽  
Hong-Hee Lee
Keyword(s):  
Output Voltage ◽  
Control Method ◽  
Voltage Drop ◽  
Renewable Energy Sources ◽  
Control Variable ◽  
Voltage Control ◽  
Power Sharing ◽  
System Stability ◽  
Small Scale ◽  
Dc Microgrid

Due to line impedance mismatch among renewable energy sources (RESs), it is hard to realize accurate power sharing in the DC microgrid system. To solve this issue, a distributed power sharing strategy for adjusting the RES output voltage is developed by adding shifted output voltage into each local controller. Thanks to the shifted voltage, the influence of voltage drop caused by the droop controller is effectively mitigated, so that the DC bus voltage is constantly balanced regardless of the load changes. The proposed method is realized with a centralized approach, and all the required control variable to determine the reference voltage is transmitted through low-bandwidth communication. The controller design and system stability are analyzed in detail with a simplified microgrid model. Small-scale DC microgrid is simulated to verify the effectiveness of the centralized shifted voltage control method.

A Power Sharing Method for Parallel Inverters with Virtual Synchronous Generator Control Strategy

2016 ◽  
Vol 4 (2) ◽  
pp. 317
Author(s):  
Sara Yahia Altahir Mohamed ◽  
Xiangwu Yan
Keyword(s):  
Control Strategy ◽  
Reactive Power ◽  
Voltage Drop ◽  
Synchronous Generator ◽  
Power Sharing ◽  
System Stability ◽  
Droop Control ◽  
Active And Reactive Power ◽  
Virtual Inertia ◽  
Virtual Synchronous Generator

<p>A new power sharing method of a virtual sychronous generator control based inverters is introduced in this paper. Since virtual synchronous generator has virtual inertia and damping properties, it significantly enhances the grid stability. However, its output power considerably affects by the line impedance. Thus, in this paper, the relation between the droop control and the line impedance is analyzed at first. Then, by appling an improved droop control strategy to an inverter based on the virtual sychronous generator control, achieving proportional active and reactive power sharing unaffected by the line impedance is realized. The result shows that a smooth response is achieved. As well as, the voltage drop caused by the line impedance is totally compensated. As a result, the system stability is furtherly improved. At last, the effectiveness of the proposed method is verified through MATLAB/Simulink.</p>

The reactive power voltage control strategy of PV systems in low-voltage string lines

2017 ◽  
Author(s):  
Feng Zhang ◽  
Xiaolong Guo ◽  
Xiqiang Chang ◽  
Guowei Fan ◽  
Lianger Chen ◽  
...  
Keyword(s):  
Control Strategy ◽  
Reactive Power ◽  
Low Voltage ◽  
Voltage Control ◽  
Voltage Control Strategy ◽  
Pv Systems

scholarly journals Distributed Finite-Time Secondary Frequency and Voltage Restoration Control Scheme of an Islanded AC Microgrid

Energies ◽  
2021 ◽  
Vol 14 (19) ◽  
pp. 6266
Author(s):  
Junjie Ma ◽  
Xudong Wang ◽  
Siyan Zhang ◽  
Hanying Gao
Keyword(s):  
Power Distribution ◽  
Finite Time ◽  
Voltage Drop ◽  
Impedance Control ◽  
Reference Value ◽  
Voltage Regulation ◽  
Active Power ◽  
Power Sharing ◽  
Control Scheme ◽  
Voltage Deviation

To solve the problems of frequency and voltage deviation caused by the droop control while meeting the requirements of rapid response, a distributed finite-time secondary control scheme is presented. Unlike the traditional cooperative controllers, this scheme is fully distributed; each unit only needs to communicate with its immediate neighbors. A control protocol for frequency restoration and active power sharing is proposed to synchronize the frequency of each unit to the reference value, and achieve accurate active power distribution in a finite-time manner as well. The mismatch of the line impedance is considered, and a consensus-based adaptive virtual impedance control is proposed. The associated voltage drop is considered to be the compensator for the voltage regulation. Then, a distributed finite-time protocol for voltage restoration is designed. The finite-time convergence property and the upper bound of convergence times are guaranteed with rigorous Lyapunov proofs. Case studies in MATLAB are carried out, and the results demonstrate the effectiveness, the robustness to load changes, plug-and play capacity, and better convergence performance of the proposed control scheme.

scholarly journals Secondary Control for Storage Power Converters in Isolated Nanogrids to Allow Peer-to-Peer Power Sharing

Electronics ◽  
2020 ◽  
Vol 9 (1) ◽  
pp. 140 ◽  
Author(s):  
Eva González-Romera ◽  
Enrique Romero-Cadaval ◽  
Carlos Roncero-Clemente ◽  
Mercedes Ruiz-Cortés ◽  
Fermín Barrero-González ◽  
...  
Keyword(s):  
Power Flow ◽  
Control Method ◽  
Low Voltage ◽  
Hierarchical Control ◽  
Power Converter ◽  
Power Sharing ◽  
Primary Control ◽  
Secondary Control ◽  
Control Loops ◽  
Energy Interchange

It is usual in literature that power sharing among grid-forming sources of an isolated microgrid obeys their energy rating, instead of economic agreements between stakeholders, and circulating energy among them is usually avoided. However, these energy interchanges make strong sense and classical power sharing methods must be reformulated in the context of prosumer-based microgrids. This paper proposes a secondary control method for a prosumer-based low-voltage nanogrid that allows for energy interchange between prosumers, where storage systems, together with PV generators, are the controllable grid-forming sources. A power flow technique adapted to islanded microgrids is used for secondary control algorithm and the whole hierarchical control strategy for the prosumer converter is simulated and validated. This hierarchical control consists of three stages: tertiary control plans the energy interchange among prosumers, secondary obtains different voltage and power setpoints for each of the grid-forming sources, and, finally, primary control guarantees stable voltage and frequency values within the nanogrid with droop rules. Inner control loops for the power converter are also defined to track setpoints and assure stable performance. Simulation tests are carried out, which prove the stability of the proposed methods and the accuracy of the setpoint tracking.

scholarly journals Multiple-Point Voltage Control to Minimize Interaction Effects in Power Systems

Energies ◽  
2019 ◽  
Vol 12 (2) ◽  
pp. 274 ◽  
Author(s):  
Yun-Hyuk Choi ◽  
Yoon-Sung Cho
Keyword(s):  
Power Systems ◽  
Power System ◽  
Control Method ◽  
Voltage Control ◽  
Control Area ◽  
Multiple Point ◽  
Control Scheme ◽  
Control Schemes ◽  
Power System Performance ◽  
Neighboring Area

This paper proposes an advanced continuous voltage control method that implements multiple-point control to ensure peak power system performance. Most control schemes utilize generators to regulate the pilot point voltage of a control area. However, exact control of a single pilot point is difficult because of the influence of adjacent areas in a meshed power system. To address this challenge, the proposed method accesses multiple pilot points to mitigate the effects of the neighboring area. In simulations of the Korean power system, the proposed control scheme offered a considerable improvement in performance when compared with the conventional, currently implemented voltage control system.

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