This article proposes a new approach for dc-link second-order harmonic power cancellation in an online uninterruptible power supply based on a single-phase switched-capacitor dc/ac converter. The proposed topology has only one-stage power conversion from ac to dc to ac. The inverter output voltage contains five levels and the magnitude comes with a boost functionality. It has an advantage over the conventional structure in terms of number of power devices, small LC filter size, and less total harmonic distortion with better output waveforms. Because of the high-temperature operability and the faster switching speed of GaN semiconductor based power devices, cooling system size will further decrease, and with less reverse recovery, no snubber circuits are required. A small size dc-link capacitor can be achieved through coordination control of rectifier and inverter to cancel the second-order oscillation power. Maximum available phase difference between rectifier's and inverter's modulation references is investigated and high modulation indices are proved to be feasible for second-order power cancellation in the dc link. Theoretical analysis, simulation, and experimental results are provided to validate the effectiveness of the topology and control of the proposed converter.

中文翻译：

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基于开关电容的UPS系统中双线频电流纹波的缓解

本文提出了一种基于单相开关电容器 DC/AC 转换器的在线不间断电源中直流链路二次谐波功率消除的新方法。建议的拓扑结构只有从交流到直流再到交流的一级电源转换。逆变器输出电压包含五个电平，幅度具有升压功能。它在功率器件数量、LC滤波器尺寸小、总谐波失真小、输出波形更好等方面优于传统结构。由于基于 GaN 半导体的功率器件的高温可操作性和更快的开关速度，冷却系统尺寸将进一步减小，反向恢复更少，不需要缓冲电路。通过整流器和逆变器的协调控制来消除二阶振荡功率，可以实现小尺寸的直流母线电容器。研究了整流器和逆变器调制参考之间的最大可用相位差，并证明高调制指数对于直流链路中的二阶功率消除是可行的。提供了理论分析、仿真和实验结果来验证所提出的转换器的拓扑和控制的有效性。