Analytical investigation of voltage source inverter fed induction motor drive under fault conditions

Improved reliability and fault tolerant operations of converter system are extremely important for industrial AC drives. In this paper an induction motor drive with fault tolerance capability is investigated through an analytical model. After the faulted leg in six-step voltage source inverter operation has been detected, the motor is driven by the converter reconfiguration known as the four-switch inverter, but with reduced performances. Two possible modes of operation utilizing in different ways (four or six times) only four possible voltage vectors can be used. Based on space-vector decomposition technique of the voltage vectors we can find separate symmetrical voltage vector components. For both modes of operation an analytical closed-form solution of the motor currents and electromagnetic torque is derived. Analytically closed calculated waveforms are verified by experiments. Experimental results are in good agreement with the theoretical predictions to verify the theory.