An improved dynamic model for induction motors including core losses

Abstract

The simulation of induction motors is based on static and dynamic models that allow the study of their mechanical performances, as well as their power consumption and losses. The purpose of this paper is to present an improved dynamic model for squirrel-cage induction motors (IM) which includes the core losses in addition to the copper and mechanical losses that are already taken into consideration in the commonly used models. The goal of this model is to compute accurate efficiency values in order to build a control system of the IM, aiming to improve the energy efficiency. Therefore, core losses are computed using the Bertotti model, which is a function of the magnetic field and the frequency. These losses are then included in the induction motor dynamic equations through a variable resistor that depends mainly on the magnetic field and frequency. The proposed model is simulated using Matlab/Simulink and the obtained results are experimentally validated. Then, energy efficiency equations are obtained using an improved model, taking into consideration the main losses in the machine. Energy efficiency contours are drawn, in order to track the best efficiency zone according to flux, speed and load torque.

An energy-efficient scalar control taking core losses into account

“…However, as the results are similar for all points with some differences in the efficiency improvement, the presented results correspond to an operation at 50 per cent of rated speed and 25 per cent of rated torque. This choice corresponds to a low torque operating point, where the optimization is most effective (Khoury et al , 2016), as stated in Section 2.3.…”

“…The computed equivalent resistor can be included, as detailed in Khoury et al (2016) and based on the works of Levi (1994). The dynamic model of the IM in the stationary reference frame becomes as shown in Figure 1(b), based on the classic IM steady-state model which takes core losses into consideration.…”

“…The improved dynamic model is simulated and experimentally validated in Khoury et al (2016), and proven to give an accurate representation of the IM performance and core losses variations according to the operating point.…”

“…The best efficiency zone is obtained for values of 40 to 70 per cent of rated stator flux, depending on the operating speed. The computed values of energy efficiency are experimentally validated in Khoury et al (2016) for various loads.…”

Energy-Efficient Field-Oriented Control for Induction Motors Taking into Account Core Losses

“…However, an accurate optimization study must consider the effect of the main losses. Thus, an improved IM model taking into account core losses through an equivalent resistor was developed and detailed in [15]. In the following, a brief summary describes the methodology used as well as the model obtained.…”