准Z源级联多电平光伏并网逆变器3次谐波补偿策略

光伏组件遮挡、老化等问题会使单相准Z源级联多电平逆变器单元间功率不平衡，严重时功率较大的单元会过调制，导致并网电流畸变甚至影响系统稳定。针对此问题，对单相准Z源级联多电平逆变器进行模型分析，阐述了过调制机理和最优3次谐波注入原理。在此基础上，提出一种优化的3次谐波补偿控制策略。该方法不仅能保证系统最大功率输出和单元间直流母线电压平衡，而且能根据拟合曲线选择出最优的3次谐波补偿系数，扩大逆变器运行范围，确保严重功率不平衡时所有单元都不过调制，抑制并网电流畸变效果明显。仿真和实验结果均验证了所提控制策略的有效性。

Third harmonic compensation strategy for a quasi-Z-source cascaded multilevel photovoltaic grid-connected inverter

Problems such as occlusion and aging of photovoltaic modules can cause power imbalance between single-phase quasi-Z-source cascaded multilevel inverters. In severe cases, units with larger power will be over-modulated, resulting in grid-connected current distortion and even affecting system stability. To address this problem, a model of a single-phase quasi-Z-source cascaded multilevel inverter is analyzed, and the over-modulation mechanism and optimal third harmonic injection principle are expounded. An optimized third harmonic compensation control strategy is proposed. This method can not only ensure the maximum power output of the system and the balance of DC bus voltage between units, but also select the optimal third harmonic compensation coefficient according to the fitting curve, expand the operating range of the inverter, ensure that all units are not modulated when the power imbalance is serious. The effect of suppressing the grid-connected current distortion is evident. Simulation and experimental results verify the effectiveness of the proposed control strategy.