Comparison of efficiency performance of two converters for high-speed AC drives

This paper presents an efficiency comparison of two converters designed for driving high-speed AC machines. In such applications, an inverter based on Si- IGBTs is not a viable solution since the switching losses became too high and physical limits of such devices do not match the required elevated switching frequencies. The use of SiC devices allows higher switching frequencies and reduced losses but issues mainly related to quickened motor insulation aging arise because of high dv/dt values. In this work a topology, made up of a Si IGBT inverter fed by a SiC MOSFET DC-DC converter, is benchmarked over an inverter based on SiC MOSFETs in terms of efficiency. The advantage of the first solution is to reduce the switching frequency and the dv/dt values without reducing the control frequency. Therefore, the major result is to lower the stress on the motor winding insulation. To assess and compare the efficiency performances of the two schemes, simulation and experimental tests have been carried out. Results show the feasibility of the proposed solution.