The Analysis And Suppression Of Bearing Current In Varied Frequency Supply AC Motor

With the development of power electronics technology, Variable Frequency Drive (VFD)are used in the new energy generation, high-speed trains and many AC and DC traction drive transmission systems. The inverter generates high frequency common-mode voltage, and coupled by stray capacitances inside motors, shaft voltage and bearing current are induced, resulting electrical corrosion of bearing. The bearing life is greatly shortened. Also it is a serious threaten to the safe operation of the system. Therefore, it is important to study the bearing current problem of variable frequency power supply system. Effective suppression methods for bearing current should be developed to improve the reliability of the system.Firstly, the formation mechanism of the bearing current is introduced and the research progress of bearing currents are concluded. Secondly, analyze the parameters that may effect the common mode voltage. VFD system set up in Matlab is used for analyzing the influence of IGBT dead time, IGBT and diode voltage drop, IGBT fall time on common mode voltage. It shows that dead time has no effect common mode voltage amplitude. But with the rise of dead time, the magnitude in carrier frequency of common mode voltage increases. IGBT and diode voltage drop, IGBT fall time barely change common mode voltage. Then, the experiment shows the same conclusion with the simulation.Thirdly, a new passive filter is set up. The dissertation describes the working principle of the common mode filter. The parameter values of filter elements are determined. The common mode voltage, bearing voltage and bearing currents under inverter with filter are compared with no filters. The experiment shows that the filter does help to reduce bearing current.Finally, the experiment platform is built up, the hardware and software of the inverter is described. The measurement method of common mode voltage, bearing voltage and bearing current is given.