The Study Of Long-cable And Over-voltage Suppression For Frequency Converter System

A multitude of modern industrial processes use adjustable speed control system with frequency converter for motors to achieve the purpose of saving energy.In some special industry occasions,which need to use the long cable to connect converter with motor,and when the length of long cable is more than 100 meter that will makes motor terminal producing over-voltage,the over-voltage may damage motor and seriously affect the energy-saving of the whole system.Therefore,how to reduce the over-voltage of motor has become one of the hot spots which are studied by scholars at home and abroad.With the transformation of urban power grids,long-cables are not only used in variable frequency drive system,but also widely presented in power transmission and distribution of long-distance and high-voltage,electric signal transmission in network and communications and so on.This paper bases on the theory of even transmission line,studied the electromagnetic transmission characteristics of long-cable.Further analysis points out that under the high frequency AC,the electromagnetic proximity effect of coupling transmission lines will not only make each other generate mutual inductance,capacitance and conductance, but mutual resistance also exists;then according to telegraph equation,using the experimental methods to calculate characteristic parameters of three phase-ground coupling transmission lines.These are important basis for establishing the long-cable model of converter system.Based on the above analysis,this paper establishes the circuit model of frequency converter system,then uses simulation software MATLAB and PSpice to simulate different long cable models,respectively.By using the cable model with PSpice will not only have the accurate result,but also can easily observe the voltage waveform at any points of the cable.Depending on the simulation with PSpice,we understand the voltage through the long cable much more deeply,and design the parameters of RLC filter of the converter output.The simulation and experiment are all verified that the filter has a good effect for over-voltage suppression and protects motors,finally reduces the electromagnetic interference of the whole system.