Analysis Of Bearing Current Problem Of Induction Motor Fed By PWM-inverter Based On Calculation Of Electromagnetic Field

With broaden application of modern convert technique in industrial control, More and more PWM-invertor with high-frequency switch have been used in field of improving characteristic of speed control of AC motor,however, it also bring us some adverse effects. The non-zero of zero sequence voltage component of stator windings due to asymmetric of output PWM voltage by invertor at a same time will build a high-frequency common mode voltage on motor terminal, which will produce bearing current through capacitive coupling path inside motor.The large dv/dt caused by high-frequency switch’s action will charge for the film capacitor formatted inside bearing, then it will build up the shaft voltage on the motor shaft. Once the shaft voltage reach to the threshold of breakdown voltage of lubricant film, the film inside bearing will be destroyed and EDM(Electromagnetic Discharge Machining)current will occur in bearing simultaneously which may do heavy damage to bearing life。Given the great adverse impact on reliable operation of motor caused by shaft voltage and bearing current, the research of its generation mechanism and suppressing program has important realistic meaning.The thesis firstly made analysis to generation mechanism of bearing current in induction motor, then we carried out model building using infinite element analysis software based on the actual2.2kW asynchronous squirrel-cage motor system fed by PWM invertor, we get high-frequency coupling parameters of motor through numerical calculation of infinite element analysis software。The effect on coupling capacitor from geometric dimensioning and material property of motor also has been studied.Combining capacitive parameter above, bearing current model based on vary-frequency speed control system of motor was established and simulated,the values of voltage and current of corresponding part in motor were obtained and the effect on values above from invertor parameters also had been analyzed.The selective analysis to EDM current and its affecting factor has been carried out.At last, by use of bearing current data get from Simulink model simulation,calculation of electrical magnetic field about bearing current model was carried out in the infinite element software,Relevant field parameters and their distribution in space of motor was obtained which will provide theoretic reference for optimization in motor’s production design of suppressing bearing current.