Speed control and maximum efficiency operation of three-phase squirrel cage induction motors supplied by modified Γ - Z impedance source inverter

A three-phase squirrel cage induction motor (IM) drive system supplied by a new modified structure of Gamma - Z impedance source inverter (Gamma - Z ISI) is proposed. The two main goals are speed (torque) control, and efficiency improvement. The modified Gamma - Z ISI has the ability to boost the input voltage. This improves the operation range of the system particularly for limited DC-link voltage conditions. A first order integral-terminal sliding mode (ITSM) controller is designed incorporating the motor and inverter dynamic model equations. The maximum efficiency strategy based on Lagrange's theorem is achieved by optimizing the motor input power (input energy) as the objective function under the constant load torque. The maximum efficiency strategy using energy saving is suitable for electric drive system applications. Also, the control method is resilient to any change in motor parameters and unmodulated system dynamics. Furthermore, its output control error can be eliminated in a limited interval. Finally, a prototype of the system using a 1.5 kW three-phase squirrel cage IM is provided and several tests are conducted. The experimental results show the efficacy of the proposed method.