Development Of PV-boosted Full-bridge Soft-switch DC-DC Converter

With the global energy crisis intensifying, renewable energy development and utilization become more and more important. Solar energy is accepted commonly because of its advantages such as economy and cleanness. Pressure and insulation of solar panels will limit the number of photovoltaic modules series-connected, so photovoltaic power generation system in general uses DC-DC boosted links. PV-boosted DC-DC converter's performance will have a direct impact on the conversion efficiency of photovoltaic power generation system, it's significant to research on high-efficiency PV-boosted soft-switch DC-DC converter. This paper presented analysis and study on topology and control of PV-boosted soft-switch DC-DC converter of three-phase photovoltaic power generation system, which can operate independently and grid-connectedly. Finally, the experimental prototype was completed.Firstly, several typical full-bridge ZVZCS DC-DC converter topologies were compared. According to PV-boosted DC-DC converter's characteristics, a full-bridge ZVZCS DC-DC converter topology was given, using series-wounded structure and double-CDD snubber circuit in the secondary. This paper analyzed the converter's principle and soft switching conditions, described the design process of high-frequency transformer and output filter inductance, the selection of devices and the calculation of parameters, as well as simulated by MATLAB.According to the mathematical model of photovoltaic cell, a simulation platform of photovoltaic cell was established by MATLAB. With compare of several maximum power point tracking (MPPT) methods, a maximum power point tracking process of CVT start, single variable INC was simulated by MATLAB. The simulation result showed that the algorithm started quickly, tracked accurately.The digital control system of PV-boosted full-bridge ZVZCS DC-DC converter was designed, based on TMS320F2812. A novel digital phase-shift method based on DSP was adopted, using only one event manager, without additional hardware. Based on the magnetic bias of full-bridge circuit and the application of photovoltaic converter, detection and protection circuits to the fault of DC magnetic bias, over-current, under-voltage and over-temperature were designed, which improved function of photovoltaic converter. In this paper, the control strategy was described, which used PI and MPPT control method. The design of the software and the main flow chart were given, too.Finally, the 15kVA PV-boosted full-bridge ZVZCS DC-DC converter experimental prototype was completed and the results of experiment showed that main circuit's parameters was right, zero-voltage zero-current switching was achieved correctly and converter's work was stable.