Efficiency-optimized flux trajectories for closed cycle operation of field oriented induction machine drives

Abstract

A structured design procedure for system integration is presented. A dynamic programming scheme is developed which optimizes efficiency of an induction-machine drive which is operated in closed-cycle and which has both control and state constraints. Application of rotor-flux feed-forward field-orientation control for an induction machine reduces the system equations to contain only three state variables: rotor flux, velocity, and position. Maximum stator current and rotor velocity are set as constraints. Saturation effects are modelled to provide a state-dependent constraint on the rotor-flux magnitude. Load is treated as a function of the rotor position, which is appropriate for many mechanical system applications. To optimize efficiency for closed-cycle operation of the motor, both machine losses as well as the cycle time must be minimized using an appropriate objective function. State trajectories of the system that simultaneously optimize machine efficiency and cycle time are found by dynamic programming. Flux trajectories for the optimal solution are found to vary significantly over the machine cycle. The validity of the energy optimization is investigated experimentally on a feedforward, field-oriented induction machine. >