Converter Topology for Megawatt Scale Applications with Reduced Filtering Requirements, formed of IGBT Bridge operating in the 1000 Hz Region with Parallel Part-Rated High-Frequency SiC MOSFET Bridge

This article investigates the design and control of the parallel-hybrid converter (PHC), which consists of parallel connection of a silicon insulated gate bipolar transistor (IGBT) bridge and a partially rated silicon carbide (SiC) mosfets bridge with a shared dc bus. The IGBT bridge processes the bulk of the power, while switching at a low frequency to maximize efficiency, while the SiC mosfets bridge's lower relative switching loss is exploited to filter low-order harmonics from the IGBT bridge. A finite-set model predictive controller is detailed that allows IGBT switching frequencies down to 1 kHz to be achieved while also tightly controlling the magnitude of current in the SiC bridge. A genetic algorithm is utilized to automatically tune the control and investigate the design of the output filter as well as the influence of the controller time-step and horizon length on the performance. Power loss estimates of a 1.5 MW application case are made showing potential for significant power-loss reductions. Experimental tests validate an field-programmable gate array (FPGA) implementation of the controller and topologies performance, with IGBT bridge frequencies below 1.2 kHz and grid-current total harmonic distortion below 3% achieved. The ability of converter to switch operation between a high-current and a low-current mode and dynamic performance is also verified.