Parameter estimation for induction motors to study the effects of voltage, frequency and slip Anna-Kaisa Repo 1 , Marko Hinkkanen 2 , and Antero Arkkio 1 HELSINKI UNIVERSITY OF TECHNOLOGY 1 Laboratory of Electromechanics, 2 Power Electronics Laboratory P.O. Box 3000, FI-02015 TKK, Finland Email: Anna-Kaisa.Repo@tkk.fi; Marko.Hinkkanen@tkk.fi; Antero.Arkkio@tkk.fi Keywords «Induction motor», «Estimation technique», «Automotive application» Abstract Parameter estimation for cage-induction machines is studied by means of 2D finite-element (FE) computations. The estimation methods are based on the time-harmonic and time-stepping FE analyses. The parameters are estimated in a wide operation range. The main purpose of the paper is to study how the steady-state and small-signal parameters vary in the case of a cage-induction machine designed for a frequency converter supply. The estimation is performed at 13 different supply frequencies. At every frequency, several flux levels are studied. Slips that provide the best efficiency are looked for and the parameters are estimated at these points. For comparison, the parameters of a typical grid-supplied cage-induction machine are also estimated at several slips and flux levels. Introduction The finite-element analysis (FEA) is an accurate method for the study of electrical machines. A steady-state operation of a machine can be depicted well with the time-harmonic FEA. The information provided by the field solution can be compressed to a physically interpretable form - parameters of circuit models [1]-[3]. The steady-state circuit model for a machine is required in many applications such as drives. In order to model transient phenomena, the time-stepping FEA has to be applied. In addition, the time-stepping FEA can be used to model small-signal dynamics around a steady-state operation [4], [5]. From the data provided by the time-stepping FEA, the parameters of analytical small-signal models can be estimated. In the paper, the parameter estimation for two different types of four-pole cage-induction machines is presented. Induction machine A has a copper rotor cage and, in order to operate efficiently, it has to be supplied by a frequency converter. Hence, it is suitable for applications requiring a wide speed range. Such application is, for example, a motor of an electrical vehicle. The rated power of machine A is 80 kW. The circuit parameters are estimated at different flux levels and supply frequencies at such slips which give the best efficiency at the respective supply. Both the rated flux and field weakening region are examined. Induction machine B with deep aluminium rotor bars is designed to be supplied from a grid and the speed is varied by load. The starting properties are important and during the start-up the slip or rotor frequency varies in a wide range. The effects of saturation are also included in this study. Thus, the circuit parameters are estimated at 50 Hz line frequency and the slip and flux level are varied. The rated power of machine B is 37 kW. The parameters are estimated using two different FE analyses. Since the steady-state parameters are estimated using the time-harmonic FE analysis, numerous operation points can be easily studied. On the other hand, the time-stepping FEA requires a lot of computation and therefore some interesting operation points are chosen. Basically, these operation points are those in which the machine can operate for longer periods of time.