Influence Analysis And Countermeasures Of Output Voltage Of Inverter Driven By Long Cable

When the inverter and motor are far apart,a long cable connection is required,which will bring some negative effects to the variable frequency speed control system.When the output PWM voltage of the converter is transmitted through long cable,overvoltage is often present on the motor side,including differential mode overvoltage and common mode overvoltage.Differential mode overvoltage will destroy the insulation performance of motor winding,common mode overvoltage will threaten the insulation of motor bearing,and the resulting common mode current will cause electromagnetic interference.The fundamental voltage of the motor terminal is smaller than the output voltage of the inverter due to the fundamental voltage drop caused by the long cable,and the accuracy of the stator voltage acquisition will directly affect the performance of the speed sensorless control system.In this paper,the transmission process of PWM voltage wave is analyzed by the long-line transmission theory,the relationship between the maximum overvoltage and the square wave bandwidth is analyzed from the frequency domain,and the relationship between the overvoltage maximum and the rising time and transmission time of the pulse is analyzed from the point of view of time domain.Based on this,hardware measures are taken to suppress the differential mode overvoltage,and the parameter design methods of the RLC filter on the inverter side and the RC filter on the motor side is analyzed.The filter parameters are optimized by analyzing the filter energy consumption and satisfying the limit condition of overvoltage while reducing the energy consumption.After blocking pulse,the filter capacitance may cause self-excitation of motor.This paper analyzes the reason of self-excitation,compares several self-excitation suppression measures,and further optimizes the parameter selection of the filter.For common-mode overvoltage,two kinds of hardware suppression measures are introduced in this paper,which are increasing common-mode circuit reactance and paralleling low common-mode impedance branch.The common mode voltage suppression algorithm is mainly studied.As for two-level and three-level inverter circuits,the generation mechanism of common-mode voltage is analyzed,and the amplitude of common-mode voltage generated by SVPWM algorithm is reduced by selecting suitable voltage space vector.Based on this,the influence of dead zone on two-level and three-level common mode suppression algorithm is analyzed.Four flux linkage observation models are introduced for asynchronous motor vector control,and their characteristics are summarized.For speed sensorless control,the characteristics of three model reference adaptive algorithms,which are based on flux linkage,reverse electromotive force and reactive power,are compared.Considering the influence of long cable and stator resistance,the advantages of MRAS based on reactive power in the speed sensorless system of long-line drive induction motor are analyzed.