Multilevel Inverter with Variable Voltage Levels for Optimized Current Ripple Emulation of Three-Phase Machines

Power-hardware-in-the-loop emulators aim to emulate the behavior of a real electric machine during the operation with a device-under-test inverter. To reproduce the waveform of the machine's phase currents, including the current ripple within one switching period of the device-under-test inverter, the emulator has to provide a suitable countervoltage per phase. This paper shows that the required countervoltage per phase changes between seven steady oscillating voltage traces and proposes the design and control of a multilevel inverter with variable voltage levels that is able to apply the required voltage shape exactly. It further discusses how the number of required voltage traces and therefore the required power electronics system of the emulator can be significantly reduced by an optimized voltage control. The regarded system is designed to emulate the behavior of a 20 kW permanent magnet assisted synchronous reluctance machine.