Voltage sag independent operation of induction motor based on Z-source inverter

This paper describes an adjustable speed drive system for driving an induction motor beyond its nominal speed, even in the presence of input voltage sags. The system is based on the Z-source inverter, which offers several advantages over traditional current or voltage source inverters as it can operate in both buck or boost mode. The boost operation is achieved with controlled short-circuiting of the inverter phase legs that is otherwise forbidden in traditional inverters. These shoot through states are accomplished with the modification of the space vector modulation which is thoroughly explained. In order to assure the required output voltage and ride-through ability during voltage sags, the method for selecting the proper inverter voltage is introduced. The control of the induction motor is carried out with the field oriented control coupled with the field weakening regime of the induction motor. The experimental setup is based on a prototype with a DSP control system to verify the operation of the proposed system.