900V SiC Based, Hybrid, Multilevel DC/DC Topology for 1500VDC PV Application

Very compact, highly efficient, hybrid DC/DC topology, consisted of a standard interleaved boost converter followed by a multilevel Resonant Switched Capacitor Converter (RSCC), that employs 900V Silicon-Carbide (SiC) devices, for use in emerging, two-stage, grid connected 1500V Photo-Voltaic (PV) systems is presented in this paper. Operation principle of this topology is described: controllability of its output voltage and power processing distribution among its stages in function of input voltage. Depending on operating region, certain amount of input power is not processed, but it is transferred directly to the output. This behaviour increases significantly efficiency of the analyzed topology, compared to the solutions presented in literature. The presented topology obtains full ZVS transitions in all operating conditions, even without load. ZVS transitions and employed SiC MOSFETs are the key elements for the high converter efficiency. Triangular Conduction Mode (TCM) in boost stage and resonant switching technique in RSCC part are used to obtain ZVS transitions in all the switches under wide range of loads and PV voltages. Results of multivariable optimization (pareto front) for the presented topology are provided. Previously described theoretical analysis is fully experimentally confirmed by building and measuring a 10kW prototype of 8.26kW/kg of specific power and 404.6cm³ of volume occupied only by power stage components. Euro efficiency of 99.48% in nominal input/output voltage conditions is achieved.