H桥级联STATCOM直流侧电容电压平衡控制的研究

Research on DC Capacitor Voltage Balance Control for Cascaded H-bridge STATCOM

针对H桥级联静止同步补偿器(STATCOM)直流侧单电容电压波动引起相内及总体电压不平衡的问题,提出采用3种控制器协调控制的策略。直流侧单电容电压控制器为电压内环,单电容电压与参考电压作比较经过PI调节实现H桥单元电容电压平衡控制。直流侧总电压和无功电流控制器为电压、电流双环控制,总电容电压平方和与参考电压作比较经过PI调节实现总电容电压的平衡控制。同时提出一种获取无功参考电流的方法,该方法计算简单可有效提高系统运行的可靠性。H桥级联七电平STATCOM的仿真与实验表明,所提控制策略在系统稳态和负载突变时直流侧电容电压在允许范围内波动,具有良好的动态性,网侧电压与电流基本同相位,最终实现了直流侧电容电压的平衡控制,验证了所提控制策略的有效性。

Aiming at the problem that the voltage fluctuation of single capacitor on DC side of the cascaded H-bridge static synchronous compensator（STATCOM） causes unbalance of the phase and the total voltage, a coordinated control strategy of three controllers was proposed. In this strategy, the DC-side single-capacitor voltage controller is of voltage loop, and the single-capacitor voltage is compared with the reference voltage for PI adjustment to achieve voltage balance control of the H-bridge unit capacitor. The controller for DC-side voltage and reactive current is of voltage and current double-loop control, and the square sum of the total capacitance voltage is compared with the reference voltage for PI adjustment to achieve balance control of the total capacitance voltage. Moreover, a simple method for obtaining the reactive reference current was proposed to effectively improve the reliability of the system. Simulation and experiment on the cascaded H-bridge seven-level STATCOM showed that the proposed control strategy could keep the DC- side capacitor voltage within the allowable range with good dynamic performance and robustness when the system is in steady state and the load changes suddenly, and could make the phases of the grid- side voltage and current approximately same. Ultimately, balance control of the DC- side capacitor voltage was achieved, which verifies the effectiveness of the proposed control strategy.