Common mode current elimination in multi-drive industrial systems

The paper deals with the common mode current issue in a multi-drive system. Common mode currents are caused by step variations of the common mode voltage, strictly related to the sequence of the inverter states during the voltage pulsewidth modulation. An inexpensive technique that allows to compensate the common mode voltage variation in multi-drive systems composed of two or more inverters is proposed, in order to eliminate the common mode currents. The common mode current paths and generation mechanisms are reviewed and the influence of the inverter state sequence on the common mode voltage and currents is pointed out. Based on such considerations, a new digital PWM modulation strategy is introduced to compensate the common mode voltage variations generated in a two PWM inverter system