In this article, we present a novel three-phase multilevel inverter (MLI) design for photovoltaic applications which does not require large dc-link capacitors to buffer the 120-Hz power ripple and allows individual inverter module to process trapezoidal power instead of sinusoidal power. This new design features two inverters connected in parallel to each dc source and N inverters connected in series to each grid phase to support the grid voltage. The trapezoidal operation improves the overall system’s efficiency by allowing the inverter module to output peak or zero power for most of the ac cycle. We present the controller design and simulate the proposed MLI system in power electronics simulation software (PLECS). We demonstrate an experimental 110-V dc input, 208 $V_{\text{rms}}$ three-phase ac output, and 1-kW five-level prototype with $>$ 95% efficiency. With the same inverter module, we compare the efficiency of the proposed design to the conventional MLI design, where all modules share phase power evenly. We demonstrate that the proposed design consistently outperforms the conventional design in efficiency, with $>$ 20% loss reduction at light load conditions.

中文翻译：

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一种新型高效三相多电平光伏逆变器，降低直流母线电容

在本文中，我们提出了一种适用于光伏应用的新型三相多级逆变器 (MLI) 设计，它不需要大型直流链路电容器来缓冲 120 Hz 电源纹波，并允许单个逆变器模块处理梯形功率而不是正弦功率. 这种新设计具有两个并联连接到每个直流电源的逆变器和N个逆变器串联连接到每个电网相位以支持电网电压。梯形操作允许逆变器模块在交流周期的大部分时间输出峰值或零功率，从而提高了整个系统的效率。我们介绍了控制器设计，并在电力电子仿真软件 (PLECS) 中仿真了所提出的 MLI 系统。我们展示了一个实验性的 110-V 直流输入，208$V_{\text{rms}}$三相交流输出和 1 kW 五级原型$>$95% 的效率。使用相同的逆变器模块，我们将所提出的设计的效率与传统的 MLI 设计进行比较，在传统的 MLI 设计中，所有模块平均共享相功率。我们证明，所提出的设计在效率方面始终优于传统设计，其中$>$轻载条件下损耗降低 20%。