When the permanent magnet synchronous precision drive inverter is running at low speed, torque fluctuation is a key issue affecting the stability and accuracy of the system. This fluctuation is usually caused by motor design, control algorithm or external interference, and needs to be suppressed by multi-dimensional technical means. The following analysis is carried out from the perspectives of fluctuation causes, control strategy optimization, hardware compensation, etc., to explore systematic solutions.
When the permanent magnet synchronous motor is running at low speed, the torque fluctuation mainly comes from two aspects. One is the design defects of the motor body, such as uneven distribution of permanent magnet poles and air gap magnetic field distortion, which lead to periodic deviations in electromagnetic force distribution; the other is the limitations of the control algorithm, such as current sampling delay, PWM modulation harmonic injection, etc., which make the actual output torque deviate from the command value. In addition, external factors such as the cogging effect and load disturbance of the mechanical transmission system will also aggravate the fluctuation. Understanding these causes is the premise for formulating targeted suppression strategies.
As the core link of permanent magnet synchronous precision drive inverter control, the current loop has a direct impact on the torque output due to its response speed and accuracy. Under low-speed conditions, the current loop performance can be improved by the following measures: First, feedforward compensation technology is used to introduce the dynamic changes of the motor back electromotive force into the control loop in advance to offset its impact on the current loop; second, the PI parameters are optimized to balance the dynamic response and steady-state accuracy by adaptively adjusting the proportional and integral coefficients; third, a resonant controller is introduced to suppress torque fluctuations at specific frequencies. These measures can significantly reduce the current harmonic content, thereby reducing torque pulsation.
The inverter dead time is an important cause of current distortion. When running at low speed, the voltage error caused by the dead time effect will be amplified, which will cause torque fluctuations. Through dynamic dead time compensation technology, real-time monitoring of current polarity and adjustment of the switch conduction time can effectively eliminate the dead time effect. In addition, the use of space vector modulation (SVPWM) instead of traditional SPWM can improve voltage utilization and reduce harmonic content. Furthermore, by optimizing the carrier frequency and modulation ratio, the torque pulsation caused by high-frequency harmonics can be suppressed while ensuring efficiency.
The torque of a permanent magnet synchronous motor is closely related to the flux linkage. When running at low speed, the flux observation error will directly lead to torque fluctuation. To this end, a sliding mode observer or an extended Kalman filter can be introduced to improve the accuracy of flux control by estimating the flux state in real time and compensating for the observation error. At the same time, for the spatial harmonics of the permanent magnet flux, the harmonic injection method can be used to actively superimpose the reverse harmonic current to offset the flux distortion. This method needs to be combined with the motor parameter identification technology to ensure the accuracy of the compensation amount.
The cogging effect and load inertia of the mechanical transmission system are external causes of torque fluctuation. The permanent magnet synchronous precision drive inverter can isolate some mechanical vibrations by optimizing the connection between the motor and the load, such as using an elastic coupling or a magnetic coupler. In addition, adding a damping device on the load side or optimizing the load distribution can reduce the impact of inertia mutation on torque. For high-precision application scenarios, active vibration control technology can also be combined to monitor mechanical vibration in real time through sensors and reversely compensate for it to achieve mechatronic coordinated suppression.
Traditional control strategies may fail under complex working conditions, while adaptive control and intelligent algorithms can provide stronger robustness. For example, model reference adaptive control (MRAC) can adapt to motor parameter changes and load disturbances by adjusting controller parameters online; fuzzy control or neural network algorithms can optimize control instructions to reduce torque fluctuations by learning historical data. Such methods do not require precise modeling, but they need to be combined with real-time feedback systems to achieve closed-loop control, and they have certain requirements for hardware computing power.
Torque fluctuation suppression needs to be verified through system-level debugging. First, use an oscilloscope or power analyzer to monitor the current and voltage waveforms to locate the fluctuation frequency and amplitude; second, identify the main harmonic components through spectrum analysis, and adjust the control parameters in a targeted manner; finally, perform closed-loop tests combined with load characteristics to evaluate torque smoothness and dynamic response. In addition, long-term operation monitoring can identify potential problems, such as increased fluctuations caused by permanent magnet demagnetization or mechanical wear, which require timely maintenance or replacement of components.
The suppression of low-speed torque fluctuations of permanent magnet synchronous precision drive inverter needs to be promoted in a coordinated manner from multiple dimensions such as control algorithms, hardware design, and mechanical optimization. With the development of power electronics technology and intelligent control algorithms, more efficient solutions will emerge in the future, driving high-precision drive systems to develop in a wider speed range and higher reliability.
