Online Detection of High-Resistance Connections With Negative-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 negative-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 negative-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 negative-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 an experimental study on a 4-kW induction motor drive.