Finite-set MPC enabled hybrid power converters comprised of Si/SiC power modules

Abstract

This thesis presents a hybrid grid-tied converter, composed of a slow-switching frequency, fully rated Silicon (Si)-Insulated-gate bipolar transistor (IGBT) based inverter complimented with a part-rated high-switching frequency auxiliary inverter based on Silicon Carbide (SiC)-Metal-Oxide Semiconductor Field-Effect Transistor (MOSFET)s. The SiC-MOSFET converter behaves as an active filter compensating the current harmonics levels caused by the Si-IGBT converter. The synergy between both devices at the converter level along with the control strategy aims to: provide a higher power quality, improve the system efficiency, shrink passive filters and enhance the controller bandwidth. Effective operation of the hybrid converter requires that the IGBT switching frequency is minimised whilst limiting the current in the SiC-MOSFET inverter. Achieving this balance while maintaining control over the total output current was enabled by the development of a Finite Control Set Model Predictive Control (FCS-MPC) controller. Two potential variants on of the hybrid converter were studied, each with its respective control strategy. The topologies are: parallel hybrid converter and shunt hybrid converter. These were evaluated by using simulations and the results benchmarked using a laboratory demonstrator. Experimental results required the design and construction of a 90 kW test bench, which combined 1.2kV Si-IGBT and SiC-MOFET inverter modules in a hybrid configuration. The test bench consists of rectifier and the hybrid converter placed in independent cabinets and is designed to recirculate power with the three phase AC supply. The hybrid converter cabinet contains the 400A IGBT and of 300A SiC-MOSFET inverters together with their auxiliary electronics, measurement devices and passive components. Control of both converters is implemented using the FPGA of a dSPACE platform. Safety implementations were since early stage considered. Results obtained from the experimental hardware showed good agreement with simulation results and demonstrated the capability of the hybrid converter to control output current whilst minimising switching loss in the IGBT converter. These results validated the concept of the FCS-MPC for hybrid converters and provide confidence that the concept could be extended to MW applications