Four phase switch-mode inverter

Abstract

In this project a four phase switch-mode DC/AC inverter was designed, built and evaluated. From Etteplantech and Chalmers University of Technology a common need for a well behaving and versatile inverter in the medium power range was found. The final product was targeted to be able to deliver up to 7 kW of power, with an input DC voltage of 600 V. The finished product managed to operate a 4 kW induction machine to its limits, with a maximum tested switching frequency of 18 kHz. This must be seen as a success. A larger strain on the inverter was not done due to lack of a larger machine, but individually the 600 V supply voltage and the 10 A per phase output current was tested successfully. The resulting inverter is very versatile; with the right control system it’s capable of operating any electrical machine. The input control logic can handle both 3.3 and 5 V signals, while the input DC voltage can be in the 25 to 600 V range. Basic simulations done during the project shows that an RC-snubber would be able to lower the EMI by lowering the dv/dt during switching, while introducing extra losses in the snubber circuit without lowering the losses in the IGBTs, only moving them from turn-off to turn-on. In the finished hardware, the snubber circuit was therefore only prepared for, not implemented.