A method to reduce common mode & differential mode dv/dt at the motor terminals in PWM rectifier PWM inverter type adjustable speed drive systems
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abstract
In this paper, it is shown via analysis and experiments that common mode dv/dt transitions at motor terminals is twice as severe in a regenerative (PWM rectifier/PWM inverter) type ASD compared to a non-regenerative (diode rectifier/PWM inverter) type ASD system. It should be noted that higher common mode dv/dt at the motor terminals results in: (i) higher induced shaft voltage at each dv/dt transition, which can result in bearing currents and cause pitting/fluting of the bearings (ii) higher leakage currents to ground which can interfere with plant zero sequence protection system. The paper proposes a method to reduce these effects. An input/output filter topology with interconnection to dc-link midpoint is proposed. This method reduces both common mode and differential mode dv/dt at motor terminals, permits the use of long motor leads, and the filter components can be installed within the rectifier/inverter enclosure. Finally experimental results are presented on a 20 kW PWM ASD test stand.
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Applied Power Electronics Conference and Exposition, 1998. APEC '98. Conference Proceedings 1998., Thirteenth Annual
