Voltage Source Var Compensator Based on Rotary Phase Shifting Transformer and Its Control Strategy
Yan Xiangwu1, Guo Yan1, Peng Weifeng1, Jia Jiaoxin1, Shao Chen1, Zhao Wei2, Huo Jingming3
1. Hebei Provincial Key Laboratory of Distributed Energy Storage and Microgrid North China Electric Power University Baoding 071003 China; 2. Baoding Power Supply Subsidiary Company of State Grid Hebei Electric Power Supply Co. Ltd Baoding 071000 China; 3. Zhuozhou Power Supply Subsidiary Company of State Grid Hebei Electric Power Supply Co. Ltd Baoding 072750 China
Abstract:The proportion of renewable energy represented by photovoltaic and wind power connected to the grid is increasing annually. Due to their intermittent and stochastic characteristics, it often leads to complicate power distribution, increase network losses, and degrade frequency and voltage quality. However, the existing reactive power compensation equipment cannot satisfy both accurate compensation and low cost. In recent years, scholars have also proposed some hybrid compensation devices, but most of the topologies still suffer from the dynamic response problems caused by capacitor switching. To solve the above problems, this paper proposes a topology of voltage source var compensator (VSVC) based on rotating phase shift transformer (RPST) with reference to the voltage source converter (VSC) structure of static synchronous compensator (STATCOM), which can realize continuous and bidirectional reactive power compensation by adjusting the phase shift angle of RPST. First, two primary windings of the RPSTs are connected in parallel to the grid through the connecting inductor, while the secondary windings are wired in a star pattern on both sides of the compensation capacitor. By adjusting the phase shift angle of the two RPSTs, a variable voltage phase can be synthesized on both sides of the compensation capacitor, regulating the compensated reactive power of the VSVC. When the phase shift angle is small, the amplitude of the synthesized capacitor voltage is large. The VSVC operates in a capacitive condition, emitting reactive power to the grid. When the phase shift angle is large, the capacitor voltage amplitude is small and the VSVC works in an inductive condition, absorbing reactive power from the grid. A dual closed-loop control strategy including power external loop control and current internal loop control is constructed based on VSVC to obtain the phase shift angle of the two RPSTs and then realize the closed-loop control of reactive power. Simulation results for VSVC indicate that when an inductive load of (1+j1)MV•A is set at the end of the line, VSVC is not put in at the initial moment. The power factor on the power side is 0.605, with the current phase on the power side lagging behind the voltage. The VSVC is put in at 0.05 s, which operates under capacitive condition and raises the power factor to 1 at about 0.03 s. When a capacitive load of (1-j1)MV•A is set at the end of the line, the power factor of the power side is 0.793 before VSVC is put in, and the phase of the current ahead of the voltage phase. The VSVC is put into working in inductive condition and raises the power factor to 1 around 0.03 s. The response time is less than 0.02 s under both operating conditions, the regulation time is no more than 0.03 s, the overshoot is lower than 20%, and the steady-state error is 0. The inductive and capacitive reactive load changes are set at the end of the line respectively. The initial reactive load is 0.3 MVar when the active load is 1 MW, increasing to 0.6 Mvar at 0.5 s, and then increasing to 1 Mvar at 1 s, with response time around 0.030 s and regulation time around 0.035 s, without overshoot and error. It proves that VSVC can achieve full range of reactive power compensation in both capacitive and inductive operating conditions. The experimental results show that VSVC can achieve the closed-loop compensation required by real power systems, and the adjustment speed is related to the servo motor speed, RPST pole pair number and rotor shaft gear ratio. The following conclusions can be drawn from the simulation and experimental analysis: (1) VSVC utilizes the phase shifting function of RPST to synthesize a voltage phase with fixed phase and continuously variable amplitude on both sides of the capacitor, which has continuous and bidirectional reactive power compensation capability. (2) Applying the instantaneous reactive power theory, a double closed-loop control strategy applicable to VSVC is proposed, which has the characteristics of strong robustness and excellent control accuracy. (3) Simulations and experiments verify the effectiveness of the proposed topology and control strategy.
颜湘武, 郭燕, 彭维锋, 贾焦心, 邵晨, 赵炜, 霍京明. 基于旋转移相变压器的电压源型无功补偿器及其控制策略[J]. 电工技术学报, 2023, 38(16): 4448-4464.
Yan Xiangwu, Guo Yan, Peng Weifeng, Jia Jiaoxin, Shao Chen, Zhao Wei, Huo Jingming. Voltage Source Var Compensator Based on Rotary Phase Shifting Transformer and Its Control Strategy. Transactions of China Electrotechnical Society, 2023, 38(16): 4448-4464.
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