【正文】 r covers the design of variablefrequency speedregulating Measurement System, which is a new topic in 1980s’. It discusses the affection of variable frequency power supply on Asynchronous motor, which is one of the key ponents of the Asynchronous Motor system. Also, according to the design characters of this kind of motor which are introduced. And Designed by Computer Aided As basis, Finally Design a new motor ，Based on the validity and correctness of the principles, the design of test data was been proved. Keywords： Variablefrequency； speedregulation ； Dynamometer CAD1 INTRODUCTIONVoltage source pulse width modulation (PWM) inverters have been widely used in the adjustable speed systems due to their favorable performance. The recent advancements in power electronic switching devices have enabled high frequency switching operation ,reduced the switching time and improved the performance of the PWM inverters for driving induction motors. The switching frequency of up to 20 kHz is mon with the insulated gate bipolar transistors (IGBT) for inverters. PWM inverter volume was reduced as well as the output harmonics and noises. Nevertheless, the high switching speed results in high rate of voltage rise (dv/dt) of up to 6000V per microsecond. This has adverse effects on the induction motors leading to premature aging of the insulation materials. Insulation failure was found in some motors when they had been used for 12 years. The winding insulation of some motors was destroyed even in the test （1）. Especially, in many industrial applications the PWM inverter and the motor must be at separate locations, and long cables are required. Because characteristic impedance of the motor is much more than that of the cable, the PWM voltage is reflected at motor terminal, which results in a high frequency oscillating voltage at motor terminal. It is approximately two times of dclink voltage, which further determinates the motor insulation. This can be well explained by transmission lines theory. It had been proved by our experiments （2）. Meanwhile, some experiments and research reports have indicated that insulation deterioration frequently takes place on the first turn of lineend coil. Then, the research on the voltage distribution in the coil is very important and significant to probing into the mechanism of motor insulation deterioration, to the development of variable frequency technology and to the design, manufacturing and application of induction motors. In this paper, we will focus on the motors used largely in industry and powered by acdcac voltage source PWMIGBT inverters. We will analyze PWM voltage distribution in motor windings and investigate the premature aging mechanism of winding insulation.2 HIGH FREQUENCY MODEL OF THE MOTORAs is known well, an induction motor at power frequency can be represented by an equivalent circuit depicted in , which affords an easy way was to analyze the motor performance. In the equivalent circuit of Fig. 1,Rs and Ls are stator winding resistance and leakage inductance。 Rr and Lr are rotor winding resistance and leakage inductance。 Lm is mutual inductance between stator and rotor. The corresponding impedance Z(ω) can be readily derived from the equivalent circuit. Even though the equivalent circuit describes the steadystate electric characteristics of a balanced induction motor at low frequencies well, it fails to express the steadystate electric and dielectric properties of the motor at high frequencies.Fig. 1. Equivalent circuit of motor at power frequencyThe voltage stressed on stator winding insulation of a PWM inverterfed induction motor will be much higher pared to that of motor fed by sinusoidal excitation. In order to disclose the reason for motor winding premature deterioration, we analyzed the parameter changes of the motor equivalent circuit at high frequencies to establish a high frequency model of the motor. Principles of avoiding the premature aging of insulation would be presented, which is based on the theoretical and simulation research of the voltage stressed on windings and the voltage distributed in coils. Because of highfrequency transient effect of PWM voltage pulse, the magnetic material acts like flux barrier and hence most of the flux produced be the stator winding will be leakage fluxes. The high frequency eddy currents induced in the rotor confine the flux to the air gap and hence there will be no flux penetration through the airgap. Therefore, the motor high frequency parameters change largely pared to that of motor driven by power frequency voltage. Numerous investigations on high frequency modeling of ac induction motors were recently reported. Those high frequency models may be divided into two broad categories depending on the purposes of the analysis .First, the models based on Finite Element， Analysis were proposed to examine the motor at a per turn level. These kinds of models are plex and are primarily used for motor design. The second categories are used to examine application specific problems with founding particular simulation model. These motor models are relatively simple and easily interfaced with the simulation software. The paper establishes a model of the stator winding at high carrier frequencies, simulating the motor terminal voltage and distribution of turntoturn voltage using the equivalent model established in Matlab. Motivation for the simulation arises from a need to probe into the reasonof stator winding premature deterioration . Equivalent circuit of singlephase stator winding at power frequencyA single phase stator winding at power frequency can be modeled as an equivalent circuit as shown in . In this circuit, there is no capacitance which dominants the impedance at high frequency and reflects dielectric properties and also no core loss resistance representing eddy current inside the magnetic core .These parameters are usually neglected at