应用于分布式单相光伏并网发电系统的组合双极性直流变换器

Composite Bipolar DC-DC Converters for Distributed Single-phase Photovoltaic Grid-connected Generation System

为了解决单相光伏并网发电系统中性点偏移和半桥逆变器并网损耗较大的问题,从Cuk、Zeta、Sepic中提取出了电感电容二极管(inductor capacitor diode,LCD)单元,并将其应用于传统变换器以提高变换器的电压增益。根据Cuk和Buck/Boost变换器输入电压与输出电压极性相反,Sepic和Zeta变换器输出电压与输入电压极性相同的特点,提出4种具有双极性输出的直流变换器。选择其中的Cuk-Zeta组合变换器进行了工作原理分析,并对组合变换器中的电感进行磁集成,给出了变换器主要工作波形和各模态等效电路图,推导得到了变换器电压增益和开关管、二极管的电压应力。研究结果表明,组合变换器的电压增益与LCD单元的个数有关,为Cuk或Zeta变换器电压增益的2N倍;在输入与输出电感比值λ>1,且耦合系数k趋近于1/√λ时,变换器输出电感电流接近零纹波。实验验证了理论分析的正确性,新型组合变换器有效解决了中性点偏移问题,通过磁集成实现了零纹波输出,降低了变换器损耗。

In order to solve the problem of neutral point offset and large grid-connected loss of half-bridge inverters in single-phase photovoltaic grid-connected power generation system, inductor capacitor diode(LCD) units are extracted from Cuk, Zeta and Sepic, and applied to traditional converters to improve the voltage gain of converters. According to the characteristics that the polarity of input voltage and output voltage of Cuk and Buck/Boost converters is opposite and the polarity of output voltage of Sepic and Zeta converters is the same as that of input voltage, four DC converters with bipolar output are proposed. The working principle of Cuk-Zeta combined converter is analyzed, and the inductance of the combined converter is integrated magnetically. The main working waveforms and equivalent circuit diagrams of each mode of the converter are given. The voltage gain of the converter and the voltage stresses of the switches and diodes are deduced. The results show that the voltage gain of the combined converter is related to the number of LCD units, which is 2N times the voltage gain of Cuk or Zeta converter. When the ratio of input inductance to output inductance λ>1 and the coupling coefficient k approaches 1/√λ, the output inductance current of the converter approaches zero ripple. Experiments verify the correctness of the theoretical analysis and effectively solve the problem of neutral point offset. The zero ripple output can be realized by high voltage gain and magnetic integration of the combined converter, which reduces the loss of the converter.