Method And Experimental Research On Common Mode Voltage Suppression In Inverter Drive Motor System

With the development of power electronics technology and devices,PWM inverter has been widely used in various fields of national production because of its superior performance.The inverter drive motor system is a typical application in the field of frequency control,the inverter control technology and its influence on the speed regulation system are the focus of research in this field.The traditional method of PWM modulation will lead to high common mode voltage inverter driving system,between the motor and the casing internal bearing under the action of coupling capacitance in the generated axial current,leading to motor oil film bearing insulation breakdown caused by damage to the motor shaft,even around the electromagnetic radiation to the week.Therefore,understanding of the common mode voltage from the nature of the influence factors and mechanism,find the effective method to restrain the common mode voltage,improve the overall performance and operating reliability of the inverter drive system is of vital importance to the development of frequency control system.Firstly,the development status of inverter drive motor system and the problems existing in frequency conversion speed regulation system are introduced.The mathematical model of three-phase PWM inverter and the cause of common mode voltage are deeply analyzed.The most common inverter drive systems are the two level and the three level inverter.The paper starts with the mathematical model and studies the operating principle of the two inverters respectively.Analysis of the common mode voltage generation path shows that it is due to the selection of zero vectors in the modulation method.After the Fourier analysis of the inverter output waveform,it is found that the harmonic amplitude of the common mode voltage is the largest at the carrier frequency,which provides theoretical support for the filter design to suppress the common mode voltage.The method of suppressing common mode voltage is divided into hardware and software.The hardware method is mainly to increase the filter or change the topology of inverter.The software method is mainly to improve the modulation algorithm and zero zero vector control.The method of feedforward active filter and passive filter and a three-phase four leg inverter hardware class suppression of common mode voltage;the hardware method in suppressing common mode voltage although has certain effect,and the engineering application is more,but the hardware methods require additional equipment and control system complexity.Then the study of stochastic variable delay PWM and asymmetric NZPWM software method,software method for reducing the common mode voltage although do not need to add other equipment,but the large amount of computation and the computation ability of higher controller.Based on the traditional model predictive control,a model predictive control(SCMV-MPC)method for suppressing common mode voltage is proposed in this paper,in which no zero vector control is combined.SCMV-MPC considers only nonzero vectors to achieve VSI control while suppressing common mode voltages.The traditional method of PWM modulation in a period with a vector control method,and reduce SCMP-MPC in a cycle with two voltage vector to compensate voltage state number;vector and selected respectively,can effectively reduce the error of load current and reference current.The SCMV-MPC method achieves a satisfactory load current waveform at the same time that the common mode voltage of the inverter drive motor system is limited to ±Vdc/6.Finally,the design process of the system simulation and experiment platform is introduced.The effectiveness of the theory and simulation is verified by theoretical research and physical experiments.