Characterization of Dead Time Effects for Common-Mode-Reducing Modulation Methods

Common-mode voltage (CMV) in inverter-fed electrical machines causes bearing currents and electromagnetic interference affecting the reliability of drive systems. Special modulation methods have been developed to reduce CMV. This paper characterizes unwanted CMV caused by dead time effects during simultaneous switching events in two phases. Theoretical analysis is followed by simulation and validated with measurements. The results show the CMV disturbance as a function of the phase shift φ between phase voltage and -current. CMV is not affected by dead time for IφI <; 30° and reaches the highest level of disturbance at IφI = 90°. These findings allow to apply dead time-compensating methods depending on operating points to reduce CMV efficiently.