On-line detection of high resistance connections with inverse-sequence regulators in three phase induction motor drives

High-resistance connections in electric drives can cause localized overheating and motor supply voltage unbalance, which degrade the performance, efficiency, and reliability of the system. An enhanced field oriented control scheme for induction machines that is capable of detecting resistive unbalance due to high resistance connections, and regulating the inverse sequence current is proposed as the main contribution of this paper. Resistive unbalance is detected and located while maintaining the symmetric drive behavior both under transient and steady-state operating conditions. The inverse-sequence regulator adopted in addition to the traditional current regulator for rotor field oriented control is used to compensate for the voltage unbalance caused by the inherent asymmetries in the cable and stator winding and by the poor contacts. A model that shows the relationship between the resistive unbalance and inverse-sequence current components is derived from the analysis of the proposed scheme. The theoretical analysis and the validity of the detection technique are confirmed with a preliminary experimental study on a 4 kW induction motor drive.