900-V SiC Based, Two-Phase Interleaved, Single Inductor, RSCC DC/DC Converter for Use in 1500VDC PV Application

Abstract

Two-phase interleaved resonant switched capacitor (RSCC) topology with the single resonant inductor in the series with input connection, for use in 1500VDC two-stage PV systems connected to the grid, is presented in this paper. Two switching legs with its resonant capacitors operate in counter phase with 50% of duty cycle. In this way, total capacitance seen by the resonant inductor is doubled, compared to the single-phase case. This behaviour provides the possibility of the reduction of DC bus capacitors volume. Additionally, ripple in the DC bus capacitors is significantly reduced due to the fact that the energy of the resonant inductor is transfered to the output in both halfs of the resonant cycle, compared to the single-phase case. Full ZVS transitions in all 900V SiC devices is obtained, under all loads and input voltage conditions. Model of the resonant current shape that is forced for obtaining ZVS transitions in the switching devices is explained and presented. On the contrary to the previous, simple sinusoidal approximation of the resonant current that can describe the behaviour of the topology only under nominal load, this model can describe the behaviour of the resonant current under all loads and input voltage conditions. This model can be implemented in any kind of the optimization algorythm that is based on the euro efficiency as a performance indice. Additionally, a back-to-back losses measurement technique for voltage-fed converters that operate in open loop is presented. Previously described theoretical analysis of the presented topology is justified by building a 7kW prototype of 99.75% of euro efficiency and 12.1kW/kg of the specific power.