Real-time dynamic efficiency optimization for induction machines

This paper discusses efficiency optimization for induction motors in dynamic operation, such as in traction or servo drives. Steady-state schemes are inefficient in dynamic operation, and existing dynamic optimization schemes can not be implemented in real-time. As remedy, a heuristic solution to the dynamic optimization problem is proposed that can be calculated online at every sampling step. A numerical analysis of the dynamic optimization problem reveals that the optimal flux can be approximated as an exponential function whose time constant depends on the motor parameters, the setpoint and the direction of flux control. The flux is controlled such that a desired asymptotic torque response is obtained while the ohmic and iron losses are minimized. The experimental results on an industrial 2.2 kW servo drive point out the energy saving potential of the dynamic efficiency optimization.