Loss Minimization of Induction Motors in a Transient Regime

Abstract

This paper presents a novel design of an energy optimization approach for Induction Motor (IM) drives. Differently from former optimal control studies, the proposed control strategy is based on a designed cost function given as a weighting sum of power and energy models. The problem to be considered is to achieve the loss minimization of IM drives for any possible constraints imposed by the machine power quantity, such as ramp inputs in accelerate and decelerate modes and during different torque levels. The suggested energy optimization strategy, using the concept of Rotor Field Oriented Control (RFOC), allows a low-order current-fed IM model by means of a high-gain current control loop, which considers the stator currents as new inputs to the model and the rotor flux as a main state variable. An optimal rotor flux trajectory is determined by an off-line algorithm based on an optimal closed-loop control problem resulting in the Hamilton Jacobi Bellman equation. The resolution leads to an analytical solution which is implemented to RFOC and performs loss energy minimization during transient speed. Aiming to check the validity of the proposed strategy, a comparison study is conducted between RFOC operating with the optimal rotor flux and RFOC using a rated flux norm. The simulation and experimental results obtained for a 1.5 KW laboratory IM demonstrate the effectiveness of the proposed strategy.