The cascaded H-bridge (CHB) converter has become a promising candidate topology for utility-scale photovoltaic systems thanks to merits like modular structure, distributed maximum power point tracking (MPPT), and direct distribution grid access without medium-voltage transformers. However, module mismatches arising from nonideal elements like partial shading and parameter variations pose a technical challenge for such systems. If not dealt with properly, module mismatches can lead to adverse effects like unbalanced dc-link voltages of the modules, distortion of grid current, and reduced power generation. Conventional methods, such as reactive power compensation and level-shifted pulsewidth modulation (LS-PWM) based compensation, can alleviate this issue, but their performances are still limited by the allowable modulation range of power converters. In this paper, a compensation strategy combining reactive power compensation with a novel modulation method is proposed to extend the operating range in terms of module mismatch. Experimental results on a 2.4 kW/208 V single-phase setup are presented and have demonstrated that the proposed method can not only ride through a larger range of module mismatches but also improve solar power utilization and system efficiency owing to reduced switching events, noncompromised MPPT, and less required reactive power.

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级联H桥（CHB）转换器凭借模块化结构、分布式最大功率点跟踪（MPPT）和无需中压变压器直接接入配电网等优点，已成为公用事业规模光伏系统的有前途的候选拓扑。然而，由部分阴影和参数变化等非理想元素引起的模块失配给此类系统带来了技术挑战。如果处理不当，组件不匹配可能会导致组件直流母线电压不平衡、电网电流畸变、发电量下降等不利影响。传统方法，例如无功功率补偿和基于电平移位脉宽调制（LS-PWM）的补偿，可以缓解这个问题，但它们的性能仍然受到功率转换器允许的调制范围的限制。本文提出了一种将无功功率补偿与新型调制方法相结合的补偿策略，以扩大模块失配的工作范围。给出了 2.4 kW/208 V 单相设置的实验结果，并证明所提出的方法不仅可以克服更大范围的模块失配，而且由于减少了开关事件、不受影响的 MPPT，还可以提高太阳能利用率和系统效率，并且所需的无功功率更少。