Influence of control strategy on the performance of permanent magnet synchronous drive motor
The two typical control strategies for permanent magnet synchronous drive motors are vector control and direct torque control. Both have their own advantages and disadvantages. The vector control is based on the mathematical model of the controlled permanent magnet synchronous drive motor, and the motor torque is realized by controlling the armature winding current.
The permanent magnet synchronous drive motor has relatively low speed torque under vector control, and the speed range is wide. Under the control of the rotor field orientation vector, no reactive excitation current is needed, so the unit current can generate the maximum electromagnetic torque. Relative to vector control. Direct torque control eliminates complex spatial coordinate transformations. The stator flux linkage orientation control can realize direct observation and control of the motor flux linkage and torque in the stator coordinate system, and has the advantages of simple control mode, fast torque response and easy realization of full digitization.
At present, advanced control algorithms have achieved good results in two control strategies, such as direct torque control of permanent magnet synchronous drive motor based on sliding mode variable structure, which solves the problem of traditional permanent magnet synchronous drive motor direct torque control. Problems with large current, flux linkage and torque ripple.
A new direct torque control method for permanent magnet synchronous drive motor based on duty cycle control uses a precise mathematical model to calculate the duty cycle of the active time of the currently selected effective voltage vector over the entire sampling period using the torque error. Adjust the effective time of the effective voltage vector in real time. The torque ripple is effectively reduced. The cerebellar model joint controller CMAC based on the proportional-integral-derivative neural network is introduced into the permanent-magnet synchronous motor AC speed control system, replacing the speed outer loop PI controller in the traditional double-loop control system.
In addition, based on the research of vector control and direct torque control strategy, high-performance control technology has also developed rapidly, greatly improving the performance of permanent magnet synchronous drive motors.
1) Weak magnetic speed expansion technology. Electric vehicles, especially direct-drive electric vehicles, require a permanent magnet synchronous drive motor with a wide range of speed regulation. The speed range of the motor is limited by the mechanical strength of the motor itself and the range of the constant power zone above the base speed. Weak magnetic control is required for this situation. The built-in rotor structure makes the motor have a salient pole effect. And make full use of the reluctance torque to widen the range of the weak magnetic region.
2) Torque ripple suppression technology. There are two main reasons for the torque ripple of permanent magnet synchronous drive motor: the non-idealized magnetic circuit and control method caused by its own structure to amplify the error of the introduced parameters. therefore. By optimizing the structure of the permanent magnet synchronous drive motor and improving the rotor magnetic field distribution, it is also possible to optimize the control strategy from the motor control level, reduce the stator cogging torque, and finally achieve torque ripple suppression.
Based on the above analysis, the built-in permanent magnet synchronous drive motor uses direct torque control weak magnetic speed expansion technology. It has a significant effect on the improvement of its own performance.
Conclusion
This paper analyzes the influence of magnetic properties, rotor structure, armature winding and control strategy of permanent magnet materials on the performance of permanent magnet synchronous drive motor. The permanent magnet steel adopts NdFeB rare earth permanent magnet material, the rotor adopts built-in structure and the armature winding is selected. The fractional slot winding is combined with the direct torque weak magnetic speed expansion technology. It can effectively improve the main performance indicators of permanent magnet synchronous drive motor.
