单相级联H桥光伏并网逆变器具有模块化易拓展、输出电流谐波低等优势。但H桥模块的直流侧光伏电池板由于环境因素导致其输出功率不平衡，甚至一路或多路H桥的功率降为0，使得该模块成为虚设单元，影响了系统的稳定运行和冗余能力。因此提出一种改进的“方波+脉冲宽度调制+排序算法”的混合调制策略，利用低频方波调制从根本上扩大系统的稳定工作范围并配合高频脉冲宽度调制减小输出波形的谐波分量。同时对直流侧电压误差进行排序控制实现最大功率点跟踪，并在此基础上从有功功率角度分析了系统的稳定工作条件。所提出的混合调制控制策略结构简单、容错性强，能够实现对虚设单元的稳定控制以及正常模块的独立最大功率点跟踪性能。最后通过仿真和实验验证了所提混合控制方案的正确性。%The single-phase cascaded H-bridge (CHB) inverters for grid-connection photovoltaic (PV) systems have been explored with the features of modular, low harmonics and so on. The power harvested from PV modules are different exceedly because of serious environment, or even one or more modules' power are equal zero that becoming dummy units which affect system's stability and redundancy. This paper proposes an improved hybrid modulation which is a mix of "staircase + pulse width modulation (PWM)+sorting algorithm". This method adopts low frequency staircase modulation to expand stable operating region fundamentally, and uses high frequency PWM modulation to shape the current and decrease its total harmonic distortion (THD). Moreover, sorting the errors of dc voltages to get maximum power point tracking (MPPT) control, then analyze this method's stable operating condition from active power point. The proposed hybrid modulation have simple control structure, and can control the dummy unit effectively with individual MPPT. Finally, the simulation and experiment results validate the effectiveness and feasibility of the developed ideal.
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