A hybrid resonant three-level converter comprised of dual transformers is proposed in this paper, which is suitable for the application of distributed photovoltaic power accessing the medium voltage dc distribution network. The proposed converter can be obtained by adding a control circuit into the traditional neutral point clamped (NPC) three-level (TL) circuit, achieving the basic TL circuit operating with a fixed duty cycle. Pulse width modulation (PWM) is adopted for the control circuit to realize zero current switchings for the basic TL circuit, which delivers most of the power, under full load range. As a result, the switching loss of the converter can be significantly reduced. The influences of the turn ratio of the second transformer and resonant capacitance on the switch current, the peak value of resonant voltage, and the value of the resonant inductance value are discussed in detail, and the parameters design principles are put forward. Finally, a prototype is built to verify the performance of the proposed converter.

中文翻译：

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基于双变压器的混合谐振三电平ZCS变换器

本文提出了一种由双变压器组成的混合谐振三电平变流器，适合分布式光伏发电接入中压直流配电网的应用。所提出的转换器可以通过在传统的中性点钳位（NPC）三电平（TL）电路中添加控制电路来获得，从而实现以固定占空比工作的基本TL电路。控制电路采用脉宽调制(PWM)，实现基本TL电路的零电流开关，在满负载范围内提供大部分功率。结果，可以显着降低转换器的开关损耗。详细讨论了第二变压器匝数比和谐振电容对开关电流、谐振电压峰值和谐振电感值的影响，并提出了参数设计原则。最后，构建原型来验证所提出的转换器的性能。