Interleaved Dual Three-Phase Machine Interturn Short-Circuit Fault Mitigation Topology Using Current Source Inverter Drive

Many types of short circuit faults may occur in electric machines, due to winding insulation failure. The interturn fault is one of the most insidious types, especially in surface permanent magnet synchronous machines (SPMSM). This article evaluates a method to reduce the fault current caused by a short between two adjacent turns. We interleave turns from dual three-phase windings, which do not share a common neutral point. This causes a short circuit between any two adjacent turns to become a phase-to-phase short circuit, and the fault current must pass through the motor terminals. Dual three-phase current source inverters, each having the dc link inductance split between the positive and negative sides, have been used to greatly reduce this fault current so that the machine can continue running with a minimal penalty in performance. By using the dc link inductors of the dual three-phase current source inverters, this fault current mitigation is achieved passively and without the need for additional components. This approach was evaluated in simulation and experimentally. For the motor evaluated, the measured fault current was limited to 15.2% of the rated current.