Abstract: In traditional direct torque control (DTC), a PI controller is used in the speed loop. However, the inherent integral saturation of the PI controller affects flux linkage observation. Furthermore, the limited six sectors and voltage vector are also contributing factors to large torque and flux linkage ripple. To address the shortcomings of large flux linkage and torque ripple in traditional DTC for permanent magnet synchronous motors, a closed-loop torque and flux linkage control combining speed loop optimization control and twelve-sector subdivision is proposed. The control system was simulated in Matlab/Simulink. Compared with traditional DTC, simulation results show a significant reduction in flux linkage and torque ripple.
Keywords: DTC; sliding mode variable structure; twelve sectors; PMSM
Based on the speed loop optimization and 12 sector breakdown of the PMSM DTC
Abstract : To traditional direct torque control, speed loop with PI regulator which is inherent in the integral saturation phenomenon will affect the observations of the flux; In addition, limited six-sector and the voltage vector is one of the reasons for the torque and flux ripple. For the shortcomings of the conventional direct torque control of permanent magnet synchronous motor flux and torque ripple, speed loop optimal control and the 12-sector breakdown of the combination of torque, flux closed-loop control is proposed. The control system was simulated in Matlab / Simulink environment, compared with the conventional DTC, the simulation results show that the flux and torque ripple is significantly reduced.
KeyWords : DTC; Sliding Mode Variable Structure; 12-sector; PMSM
1. Introduction
Since the theory of Direct Torque Control (DTC) was proposed by German scholar M. Depenbrock and Japanese scholar I. Takahashi in the 1980s, it has received widespread attention and in-depth research from scholars around the world [1-6]. DTC abandons the idea of decoupling and directly controls torque and flux linkage, which has the advantages of fast torque response and insensitivity to changes in rotor parameters [7]. However, it has its own shortcomings, such as the PI link as a speed regulator and the limited sector.
The inherent defects of the integrator are one of the important reasons for the low-speed bottleneck of DTC. The use of traditional PI regulators will lead to the disadvantages of weak parameter robustness and limited load disturbance capability of the system. Traditional DTC uses hexagonal flux control or six-interval circular flux control [8-10]. The structure of circular flux control is relatively simple and the control effect is good when the parameters are accurate, but it has strict requirements for the interval judgment of stator flux. When the measurement error caused by various reasons, especially the nonlinear time-varying stator resistance, causes the wrong interval, the control performance of the motor will be affected [11].
This paper addresses the traditional Direct Current Control (DTC) method for Permanent Magnet Synchronous Motors (PMSMs). Instead of the traditional PI regulator, a novel circular flux linkage DTC method with twelve sectors is proposed, effectively improving upon the large voltage vector ripple in flux linkage and torque control inherent in the traditional six-sector division. The two are effectively combined, and modeling and simulation using MATLAB/Simulink demonstrate that the system exhibits excellent control performance. This also provides new insights for the hardware and software design of PMSM DTCs.
5. Conclusion
Comparative analysis of the simulation results above clearly shows that optimizing the speed loop can significantly reduce torque ripple; compared with six sectors, twelve sectors can effectively reduce flux ripple; compared with the traditional PMSMDTC, the twelve-sector microstepping control with optimized speed loop significantly improves both torque and flux ripple, and its settling time is significantly shortened.
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