User-Side Voltage Regulation Method Based on Rotary Power Flow Controller
Yan Xiangwu1, Peng Weifeng1, Shao Chen1, Jia Jiaoxin
1. Hebei Provincial Key Laboratory of Distributed Energy Storage and Microgrid North China Electric Power University Baoding 071003 China; 2. State Grid Hebei Electric Power Research Institute Shijiazhuang 050021 China
Abstract：In view of the problem of user-side voltage exceeding the limit and voltage fluctuation caused by a high proportion of photovoltaic grid connection, a rotary power flow controller (RPFC) consisting of a rotary phase shifting transformer (RPST) can be used for voltage regulation and control. This paper compared the voltage regulation of RPST and RPFC. The voltage regulation strategy of RPST mainly consists of two parts: power factor limitation and output voltage phase control. RPST connects a series output voltage with fixed amplitude and adjustable phase in the line by changing the phase θRPST .During the voltage regulation of RPST, there is a certain phase offset δ between the voltages ${{\dot{U}}_{\text{1}}}$ and ${{\dot{U}}_{\text{2}}}$, this offset will cause a phase shift between the $\dot{I}$ and ${{\dot{U}}_{\text{1}}}$, resulting in a change in the line power factor. To ensure that the line power factor meets the minimum specified requirements, the regulation range of RPST should be limited. The RPFC control strategy consists of three parts: output voltage amplitude calculation, rotation angle control and speed coordination control. RPFC regulates the output voltage amplitude ΔURPFC by adjusting the rotation angles α1 and α2, keeping the phase constant. To ensure that the stator voltages ${{\dot{U}}_{\text{st}1}}$ and ${{\dot{U}}_{\text{st}2}}$ are symmetrical about the ${{\dot{U}}_{1}}$, the speed of the servo motor is adjusted to keep the rotation angle always satisfying α1+α2=0 to achieve the coordinated regulation of speed. This paper developed an RPFC experimental prototype and built a voltage regulation scenario at 220V voltage level to compare and analyze the voltage regulation capability of RPST and RPFC in terms of steady and transient control characteristics, respectively. In terms of steady-state control characteristics, the rotation angle of the voltage regulator is adjusted and the load power remains unchanged. In the process of RPST regulation, the voltage phase shift between ${{\dot{U}}_{\text{1}}}$ and ${{\dot{U}}_{\text{2}}}$ tend to increase and then decrease. In the process of RPFC regulation, the voltage phase shift is not generated. In terms of transient control characteristics, the load power is changed and the ${{\dot{U}}_{\text{2}}}$ is set to 220 V. Both RPFC and RPST can control the ${{\dot{U}}_{\text{2}}}$ within the set range. In the process of RPST regulation, the line power factor does not meet the specified requirements. In the process of RPFC regulation, the line power factor is consistent with the power factor without regulator. The following conclusions can be drawn from the experiments analysis: (1) The control structure of RPST is relatively simple. However, RPST changes the user-side voltage phase in the regulation process, resulting in phase shift between line voltages, its regulation range will be limited by the power factor. (2) RPFC indirectly controls the output voltage amplitude by adjusting the magnitude of the rotation angle to achieve closed-loop control of the user-side voltage, and quantifies the duty cycle of the servo motor according to the deviation of the rotation angle from its set value to achieve coordinated control of the rotation angle speed and ensure that RPFC does not produce voltage phase shift during voltage regulation. (3) The experimental results show that both RPST and RPFC can realize voltage regulation, but RPST will change the line power factor during the regulation process, while RPFC always keeps the power factor constant during the regulation process, which has better application prospects.
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2023, Vol. 38 
