Consideration of DC/DC converter for photovoltaics with soft switching with modified pushpull current source inverter circuit

Abstract

The object of research is the power part of the two-stage converter. The paper evaluates the parameters of the power part of the two-stage converter with transformer isolation, designed for the transfer of solar battery energy to the 400 V constant voltage network with the possibility of maintaining the maximum power point tracker (MPPT). The primary stage of the converter is made as a push-pull current source inverter topology with an additional switch, which is installed between the common point of the transformer’s primary half-windings and the common point of the primary stage switches. The primary stage switches are made as a series connection of MOSFET transistors and Schottky diodes. The secondary stage has the traditional topology of a half-bridge voltage source inverter on MOSFET. A special switching algorithm of separated commutation is described, which provides non-dissipative snubber turn-on for of the current source inverter switches and their natural zero current turn-off switching (ZCS). The role of a snubber is performed by the leakage inductance of the transformer. For voltage source inverter switches, natural zero voltage switching (Zero Voltage Switching, ZVS) is provided. The role of non-dissipative capacitive switching snubbers may be performed by the MOSFET own output capacitance. The essence of this algorithm is to create a delay between the moment of forced switching on of the main key of the primary link and the moment of forced switching off of the transistor of the secondary link. There is also a small interval of energy return to the input source. Adjustment of the converter for the implementation of MPRT can be carried out by adjusting the ratio of the durations of the conduction state of the main and additional switches of the primary stage relative to the duration of the half-period of the frequency conversion. The types of switches were selected, static losses were estimated, simulation modeling was carried out in the MATLAB/Simulink environment, which confirmed the theoretical conclusions and the presence of soft switching modes.