| Permanent magnet synchronous motors have many advantages such as wide speed range,high efficiency,high power factor,and large starting torque.They are widely used in electric vehicles,industrial servos,wind power generation and locomotive traction.The development of modern electric drive systems is The wide application of permanent magnet motors provides a strong guarantee.However,compared with the permanent magnet synchronous motor directly powered by the power grid,the vibration and noise of the variable frequency drive permanent magnet synchronous motor greatly affect the performance of the motor,which is the key problem to be solved in the development stage of the inverter and motor.The stator current of the permanent magnet synchronous motor powered by the inverter contains rich harmonic components.The current harmonics are closely related to the electromagnetic force waves,especially the high-frequency electromagnetic force waves generated by the high-frequency current harmonics near the switching frequency of the inverter.High,easy to approach the natural frequency of the motor and cause resonance.The vibration and noise of the motor are mainly generated by the electromagnetic force wave acting on the inner surface of the stator.Studying the harmonic current and electromagnetic force wave of the permanent magnet synchronous motor powered by the inverter can provide suitable selection of control strategies and suppression of motor vibration and noise reference.In this paper,vector control and direct torque control are used as the control strategy of the inverter.The stator current harmonics of the motor are studied in depth.The time and space distribution of the electromagnetic wave of the motor powered by the inverter under different control strategies are analyzed.The control angle considers weakening high-frequency electromagnetic force waves.The specific work content of this article is as follows:1.The change law of frequency spectrum distribution,content and amplitude of stator current harmonics of permanent magnet synchronous motor under vector control is studied and verified by experiments.Firstly,according to the basic principle of space vector modulation,the expression of the voltage harmonics of the output line of the inverter is analyzed,and the frequency distribution law of PWM harmonic current is summarized,which provides a theoretical reference for the simulation analysis of harmonic current.The joint simulation finite element model of vector control permanent magnet synchronous motor is established to study the influence of motor load periodic changes,variable speed adjustment and other factors on the stator current harmonic content.At the same time,the speed characteristics and load characteristics of the PWM harmonic current are studied in depth,and the relationship between the amplitude of the harmonic component and the speed and torque is summarized.A 7.5kW permanent magnet motor was selected for the experiment,and the changes of the current harmonic content and PWM harmonic amplitude at different speeds and torques were measured and analyzed.The simulation results were verified through experiments.2.The variation law of frequency spectrum distribution,content and amplitude of permanent magnet motor stator current harmonics under direct torque control strategy is studied.According to the different modulation techniques,direct torque control is divided into traditional direct torque control and direct torque control based on SVPWM technology.Law of change.The finite element co-simulation model of the inverter-motor system under these two direct torque control strategies was built to compare and analyze the motor stator current harmonic spectrum under the two direct torque control strategies.Given the different speed and load of the motor,study the change law of the current harmonic content under different speed and torque conditions,and the relationship between the PWM harmonic amplitude and the speed and torque.3.The time and space distribution of the radial and tangential electromagnetic excitation force waves and harmonic amplitude of the permanent magnet synchronous motor under no-load,sinusoidal power supply and inverter power supply are studied.The expression of the radial electromagnetic force wave of the motor under no-load,sinusoidal power supply and inverter power supply is analytically derived using the magnetomotive force-permeability method,and the order and frequency of the electromagnetic force wave are obtained,which is provided for the simulation of the electromagnetic force wave Theoretical reference.The analytical method can quickly and accurately obtain the order and frequency of electromagnetic force waves,which can only be qualitatively analyzed,and the finite element method can accurately obtain the amplitude of each electromagnetic force harmonic.The frequency converter-motor system model under vector control and direct torque control is used to simulate the corresponding electromagnetic force waves,and the Matlab program is used to perform two-dimensional Fourier decomposition of the electromagnetic force waves to obtain the time and space distribution maps.The order,frequency and amplitude of the electromagnetic force harmonics obtained by the motor under no-load and sinusoidal current supply are used as a reference,and compared with the electromagnetic force harmonic components under the rich current harmonics when the motor is powered by the inverter.Analysis of the electromagnetic force waves under different power supply conditions can provide a reference for further research on the vibration and noise of the motor.4.Choose a suitable inverter control strategy to suppress high-frequency electromagnetic force waves.The frequency converter introduces high-frequency time harmonic current under the action of fixed switching frequency.The high-frequency electromagnetic force generated by the frequency converter has a higher harmonic frequency,which is easy to resonate with the natural frequency of the motor and cause high frequency noise of the motor.Establish a simulation model of random PWM control strategy,calculate the current and high-frequency electromagnetic force wave of the motor in the rated state,perform Fourier decomposition to obtain the frequency spectrum of current harmonics and electromagnetic force harmonics,and the current obtained at a fixed switching frequency of the inverter The harmonic spectrum and the electromagnetic force harmonic spectrum are compared and analyzed to demonstrate the effectiveness of the random PWM modulation technique in weakening high-frequency electromagnetic force waves. |
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