Implementation Method of Integrated Transformer for Transmission Line Measurement and Inductive Power Taking Based on Voltage Source PWM Rectifier
Wang Yifan1, Ren Chunguang1, Zhang Baifu1, Yang Yu2, Han Xiaoqing1
1. Shanxi Provincial Key Laboratory of Power System Operation and Control Taiyuan University of Technology Taiyuan 030024 China; 2. State Grid Shanxi Electric Power Company Maintenance Branch Taiyuan 030024 China
Abstract：The online monitoring technology of transmission lines is an important guarantee for realizing the safe and stable operation of energy interconnection and transmission and distribution systems. When the traditional current transformer (CT) supplies power to the online monitoring equipment, the large fluctuation of the current will lead to the problem of insufficient energy harvest of the CT at low current and saturation of the CT magnetic core at high current. In measurement, traditional CT has measurement error due to the excitation current and is susceptible to the influence of winding abnormal current. To address these issues, this paper proposes an implementation method of the integrated transformer based on voltage source PWM rectifier (VSR) for measurement and induction energy. This method controls the VSR to work in different modes according to the magnitude of the CT primary side current, thus achieving accurate measurement of the excitation current and primary side current. Firstly, a scheme of core selection and turn number design is presented, which can effectively reduce the volume and weight of CT. Secondly, control modes of VSR is described, which can be divided into four parts: full compensation, partial compensation, no compensation and demagnetization control. Thirdly, the discriminant criteria for VSR in each mode of operation and the applicable current range for each mode are introduced. Fourthly, the control strategy of each mode and its effect after control are introduced, which can output a continuously stable voltage and maintain the excitation impedance within a constant range for a long time. Finally, the measurement method of excitation current and the corresponding calculation method of primary side current in each mode are introduced, which can avoid the error caused by the nonlinear characteristics of the iron core and the change of the excitation current to accurately obtain the primary side current. In this integrated strategy, the VSR is dynamically adjusted according to the primary side current to output and stabilize the voltage. When the primary side current is low, the excitation compensation mode is adopted to improve the output power and voltage; When the primary side current is too high, the demagnetization mode is used to reduce the voltage and output the desired power. Meanwhile, the corresponding primary side current calculation method is adopted for each mode, so as to realize the real-time monitoring of the primary side current. Simulation results of different primary side current figures show that, when the primary current of traditional current transformer is low, the output voltage is low. When the primary side current is high, the iron core is saturated, the voltage waveform is distorted. In contrast, the measuring and power taking device with VSR can maintain a relatively stable voltage when the current fluctuates. Comparison of experimental output waveform show that, when the primary side current is 60A, the circuit containing VSR increases the output voltage from 73.53V to 85.85V. When the primary side current is 150A, 300A and 500A, the secondary side voltage has been seriously distorted into a spike wave. After the demagnetization control of VSR, the saturation of iron core is effectively suppressed, the problem of output voltage waveform distortion in high current is solved, and the output voltage is stabilized at about 83V. The simulation and experiments results show: ①When the primary side current varies in the range of 60-500A, the CT can maintain a stable voltage of 80V and a power output of 30W. ②The excitation branch can be effectively regulated to monitor the transmission line current in real time with 1% accuracy.
王祎凡, 任春光, 张佰富, 杨宇, 韩肖清. 基于电压源型PWM整流电路的输电线路测量与感应取电一体化互感器实现方法[J]. 电工技术学报, 2023, 38(1): 15-25.
Wang Yifan, Ren Chunguang, Zhang Baifu, Yang Yu, Han Xiaoqing. Implementation Method of Integrated Transformer for Transmission Line Measurement and Inductive Power Taking Based on Voltage Source PWM Rectifier. Transactions of China Electrotechnical Society, 2023, 38(1): 15-25.
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