New online loss- minimization-based control of scalar and vector-controlled induction motor drives

Abstract

The extended use of induction motors (IMs) has brought on the interest to improve the drive efficiency and power factor for energy saving. Vector control provides an ability to rapidly and accurately control the electromagnetic torque of the IM. But the conventional vector controlled drive system operates at rated flux even at low values of torque. This fact decreases the efficiency of the IM when it operates at light load conditions. The motor efficiency can be improved by operating the motor at optimum flux by controlling the d-axis current in d-q reference frame in vector controlled drives. This paper presents a new and accurate loss model based controller (LMC) to improve the efficiency and the power factor of field oriented controlled induction motor, by calculating the optimal air gap flux. So in this paper, an expression for the optimal flux is calculated from the new LMC, where all the motor losses are represented as function of the air gap flux. The new LMC will provide optimum efficiency even if the motor drive operates far from the rated point. A loss-minimization scheme based on LMC for a scalar controlled induction motor drive system, based on calculating the optimal flux for loss minimization, is also developed and its performance is compared with that of vector control drive in terms of efficiency optimization, power factor correction and dynamic performance. The performance of both scalar and vector controlled drives are demonstrated through simulation in MATLAB/SIMULINK environment.