Hybrid Resonant ZVZCS PWM Full-Bridge Converter for Large Photovoltaic Parks Connecting to MVDC Grids

A novel hybrid resonant zero-voltage zero-current switching pulsewidth modulation full-bridge converter with capacitive output filter is proposed in this paper, which is suitable for large photovoltaic parks connecting to medium-voltage dc (MVDC) grids. The hybrid resonant converter, with two full-bridge cells sharing a bridge leg and connecting the secondary windings of two transformers in series, operates in discontinuous current mode and can achieve zero-current switching for main power switches and rectifier diodes over the whole load range. Meanwhile, the auxiliary switches with small current rating can realize zero-voltage switching naturally. Hence, the switching loss is reduced, which is vital in MVDC applications. By the trajectory formulas of the resonant current and voltage, the trajectory paths can be achieved, which is helpful to compare the peak and turn-off currents of switches. The design rules of main parameters can be deduced with the trajectory formulas and paths. The influence of the turns ratio of auxiliary transformer and the resonant capacitance on the peak and turn-off currents is discussed in detail. A simulation model is established in the software PLECS and the operation principles of the converter are verified. A 150 V-1500 V/2 kW prototype was built to validate the operation principles and parameters optimization.