单相Buck型D-CAP无功补偿电流波形校正技术研究

Reactive Power Compensation With Improvement of Current Waveform Quality for Single-phase Buck-type D-CAP

动态电容器(D-CAP)在进行无功补偿时,由于电网谐波电压与开关管压降的影响,其补偿电流将发生畸变。在此以单相Buck型D-CAP为研究对象,介绍了一种具有电流波形质量改善功能的无功补偿控制策略。首先通过建立Buck型D-CAP的状态空间平均模型,分析了其无功补偿的原理,并给出了基本的控制方式。然后结合电路的工作过程,分析了引起补偿电流畸变的原因。根据偶次谐波调制(EHM)原理,为抑制补偿电流第k+1次谐波,可在占空比中加入第k次谐波成分。由此提出了一种基于多同步旋转坐标变换的无静差电流跟踪控制策略,用于实现动态无功补偿,同时选择性地抑制补偿电流的低次谐波。最后仿真和实验结果验证了相关理论分析与所提控制方法的正确性。

Dynamic capacitor(D-CAP)is often designed to implement dynamic reactive power compensation,whose compensation current might distort due to background harmonic voltage from the grid and voltage drop of switches.A reactive power compensation control strategy is presented with waveform quality amelioration of output capacitive current for single-phase Buck-type D-CAP.Through establishing state-space average model,reactive power compensation principle and basic control mothed of Buck-type D-CAP are analyzed.Meanwhile,the reasons that result in the distortion of D-CAP compensation current are discussed based on circuit analysis.In order to suppress k+1 harmonic of compensation current,k harmonic component can be introduced to duty ratio of Buck-type D-CAP by means of even harmonic modulation(EHM).Then a selective current tracking control strategy with nearly zero steady-state error in multiple synchronous reference frames is adopted to realize dynamic reactive power compensation and alleviate low-order harmonic distortion of compensation current simultaneously.Finally,a series of simulation and experimental results are provided to verify the correctness of theoretical analysis and proposed control method.