Research On Common Mode Current Suppression Of Inverter Driven Motor

With the continuous development of power electronics technology,power systems based on inverter-driven motors are widely used in many occasions.As the core component of the frequency converter,the high-frequency switch device was mainly focused on the control of the fundamental wave in the past.Its two-state characteristics of on and off make the threephase voltage output by the frequency converter unbalanced instantly.This kind of commonmode voltage applied to the motor side will not only threaten the insulation of the motor,but also generate high-frequency common-mode currents,which will cause electrical corrosion to the bearing and affect the operation of the system.In this article,based on the purpose of improving the reliability of the inverter-driven motor system,common-mode current suppression methods are discussed and explored from the perspective of common-mode loops,drive topology,and modulation schemes.First,in order to study the nature of common-mode current,the common-mode loop that conducts common-mode current in a general inverter drive system is studied.The main methods include lumped parameter modeling,finite element simulation and spectrum analysis.As the core equipment affected by the common mode current,the motor is found to have abundant circulating currents inside its materials,and part of the circulating currents use the entire topology as a loop to circulate common mode currents.Affected by operating conditions and common mode voltage,if the insulation of the bearing fails,the current density of the path in the bearing increases sharply.Therefore,in order to ultimately suppress the influence of the common-mode current,limiting the common-mode voltage will be the most fundamental idea.Through the comparison of frequency components,it is analyzed that reducing the commonmode voltage with PWM modulation can effectively suppress the generation of common-mode current.For the drive system of voltage source inverter,this paper proposes a topology that drives multi-module motors with parallel inverters.Considering the design of the motor body,the modularized power output of the system is realized.In terms of modulation,the common-mode output of the even-numbered bridge arms is complementary.The common-mode voltage of this method is theoretically zero,which reduces the common-mode voltage excitation from the source,so the common-mode current on the motor side is more effectively suppressed.Not only that,the carrier phase-shifting technology can also be applied to this topology at the same time to further reduce torque ripple and vibration on the basis of suppressing common-mode current,and improve system performance.For the current source drive system,this paper proposes a common-mode modulation suppression strategy based on a non-isolated back-to-back current source inverter drive system.The scheme is based on the five-stage symmetrical current space vector modulation to optimize the selection of the zero current vector,and at the same time make the vector sequencing on both sides of the rectifier and inverter coordinated.This method changes the amplitude and frequency characteristics of the common-mode voltage,suppresses the interference of the common-mode current on the control,and improves the system reliability and power density.Based on the above research work,some reasonable motor drive common-mode suppression methods can be designed for the application topology.