Nonlinear Loss-Minimizing Control of Induction Motors for EV Applications

In this paper, a novel nonlinear controller for induction motors used in EV applications is proposed to achieve field-oriented operation with minimum losses at the steady state, while inherently guaranteeing the required operating constraints. By taking the expression of the total (iron and copper) losses of the motor, an optimization problem is formulated to minimize the motor losses under the required equality and inequality constraints (torque, voltage and current constraints). Opposed to conventional loss-minimizing control that requires the solution of the entire optimization problem and continuous update of the reference motor currents in order to guarantee all necessary constraints, in this paper, a novel bounded controller is introduced with a specific nonlinear dynamic structure that inherently accomplishes all voltage and current constraints, while achieving field-oriented operation. Hence, a simplified optimization problem is required to be solved once offline to obtain the desired property that the motor currents should satisfy in order to minimize the entire motor losses, thus simplifying the controller implementation. In order to verify the theoretical contribution, the proposed controller is directly compared to the well-known field-oriented control and the conventional loss-minimizing control for the same induction motor control scenario.