星形链式STATCOM直流侧输入阻抗及交直流功率耦合关系分析

星形链式静止同步补偿器(STATCOM)在交流系统发生故障时容易产生直流侧电压失稳现象,为其应用带来难题.首先引入相位补偿因子及电流交叉解耦环节推导交流侧输入导纳,通过对功率模组数学模型进行拓展分析推导直流侧输入阻抗.根据所得交流侧输入导纳及直流侧输入阻抗,建立交、直流侧电压扰动之间的关系,分析交、直流功率耦合关系.分析结果表明,交流侧电压扰动经交流侧输入导纳产生扰动电流,直流电压控制环对直流侧电压扰动的闭环控制也会产生扰动电流,2个扰动电流共同经直流侧输入阻抗形成直流侧电压扰动.采用经低通滤波的系统电压全前馈控制以及系统电压部分前馈控制策略进行实验验证,实验结果表明所提方法可以准确地分析交流系统故障下直流侧电压扰动水平.

Analysis on DC-side input impedance and AC/DC power coupling relationships of star cascaded STATCOM

The phenomenon of DC-side voltage instability of star cascaded STATCOM(STATic synchronous COMpensator) occurs frequently when AC system fault happens, which brings difficulties to its application. Firstly, the phase compensation factor and current cross decoupling technology are introduced to deduce the AC-side input admittance, and the DC-side input impedance is deduced by mathematical model extended analysis of the power module. According to the obtained AC-side input admittance and DC-side input impedance, the relationship between AC-side voltage disturbance and DC-side voltage disturbance is established, and the AC/DC power coupling relationship is analyzed. Analysis result shows that the AC-side disturbance voltage causes AC disturbance current through AC-side input admittance, and DC-side voltage disturbance also causes AC disturbance current through DC voltage control loop. The final DC-side voltage disturbance is formed by two AC disturbance current through DC-side input impedance. The full feedforward control of system voltage based on low-pass filter and partial feedforward control of system voltage are adopted to verify the experimental results. The experimental results show that the proposed method can accurately analyze the DC-side voltage disturbance level under AC system fault.