Motor overvoltages limitation by means of a new EMI-reducing PWM strategy for three-level inverters

Pulse-width-modulated (PWM) voltage-source inverters are known to provoke high-frequency disturbances in motor-drive applications, especially when long cables are used. Indeed, the parasitic elements of the cable along with steep voltage transitions due to semiconductor switchings are responsible for conducted electromagnetic emissions as well as high over- voltages on the motor terminals. Therefore, several specific PWM schemes have been proposed in order to reduce these phenomena without requiring large passive filters. However, strategies which reduce common-mode currents (main conducted electromagnetic emission) tend to increase the overvoltages generated on the motor. This paper focuses on a new PWM strategy which reduces the common-mode currents generated by three-level inverters. It provides a control algorithm which makes sure that the motor overvoltages never exceed those of conventional strategies, while improving the electromagnetic-compatibility performance of the drive.