电压不平衡时基于改进无差拍控制的VSC-HVDC系统

VSC-HVDC在电网电压不平衡情况下,输出功率及直流母线电压会产生二倍频波动,进而影响系统的稳定运行。文中研究了柔性直流输电系统在电压不平衡情况下的改进无差拍控制策略,该策略以瞬时有功功率波动分量为零为约束条件,推导了正负序参考电流表达式。针对传统无差拍控制算法存在的控制延时及对交流侧电感参数变化鲁棒性差的问题,提出了一种改进无差拍控制策略。该控制策略利用拉格朗日插值法预测出下一个采样时刻的参考电流;对电网电压进行了线性预测;对网侧电流进行了非线性预测。最后借助MATLAB/Simulink平台搭建相应的仿真模型,仿真结果证明了该控制策略的正确性和有效性。

VSC-HVDC System with Improved Deadbeat Control when Voltage is Unbalanced

In the case of unbalanced grid voltage, the output power and DC bus voltage of the VSC-HVDC will induce double frequency fluctuation, which affects the stable operation of the system. Aiming to solve the problem, the improved deadbeat control strategy for flexible DC transmission systems under voltage imbalance was studied. The positive and negative sequence reference current expressions were derived by taking the instantaneous active power fluctuation component as zero. Aiming at the control delay of the traditional deadbeat control algorithm and the poor robustness of the change of the inductance parameters on the AC side, an improved deadbeat control strategy was proposed. The control strategy used Lagrangian interpolation to predict the reference current at the next sampling time, then linearly predicted the grid voltage and nonlinearly predicts the grid side current. Finally, the corresponding simulation model was built by MATLAB/Simulink platform. The simulation results proved the correctness and effectiveness of the control strategy.