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

1/2

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.