Research On Direct Torque Control Methods And Experiment Of PMSM

Permanent Magnet Synchronous Motors (PMSM) have many advantages of small size, high power density and high efficiency. These advantages are responsible for its wide utilization with the rapid development of the power electronics technology and modern control theory. Direct torque control (DTC) of PMSM theory does not need rotating coordinate transformation, and has good dynamic performance. Thus, it has become a hot spot of academic research. Based on the traditional PMSM DTC theory, speed-loop control strategy, stator flux estimation and speed estimation methods are deeply researched in this paper. The corresponding simulation and experimental study is done.The main contents and innovations of this paper are as following.1. Speed regulator based on ADRC of PMSM DTC is designed. ADRC adopts nonlinear control method, and is composed of track-differentiator (TD), extended state observer (ESO), nonlinear state error feedback (NLSEF) and the disturbance compensation. Disturbance can be estimated and compensated real time. In order to suppress external disturbances such as changes in loads and friction torque, and internal disturbances such as motor parameters changes in the PMSM servo system, the changes of above parameters are seen as a PMSM servo system disturbance. The appropriate given speed transition signal is extracted by TD. The system states and systems disturbance are real-time estimated by ESO according to the actual speed signal. The initial electromagnet torque value is got by NLSEF. The estimated value of disturbance is compensated feedforward in real time. Then, the final electromagnet torque value is got. The control ability of the electromagnetic torque is improved in this method. Simulation and experimental results show that, from low to high speed operating range, the impact of disturbance can be effectively weaken, and the anti-interference ability has been greatly improved.2. Stator flux linkage and speed estimation based on extended kalman filter (EKF) is designed. Voltage integration stator linkage computation method in the traditional DTC has the disaventages of error accumulation and saturation, which results to inaccurate stator flux estimation. There are big ripples on flux linkage and torque in traditional DTC system; meanwhile, increased motor volume and inconvenience maintenance is casused by mechanical speed sensor. The flux linkage and speed observer is based on two-phase stationary coordinate. The EKF observer is designed with the input signals of PMSM voltage and current and the state variables of stator flux linkage and speed. Stator flux linkage and speed are estimated at the same time. The principle of the smallest mean square of estimation error is adopted in the algorithm. The shortcomings of traditional method are avoided. Simulation and experimental results show that, the ripples on flux linkage and torque are effectively reduced, the performance of PMSM DTC system steady-state operation is improved, the speed is accurately estimated and speed sensorless operation is achieved, and the excellent dynamic performance of DTC is maintained.3. PMSM DTC based on EKF and SVM is researched. Hysteresis comparators and switching voltage vector selection table in traditional DTC result to big ripples on flux linkage and inconstant switching frequency. The two implementation methods of voltage Space vector modulation (SVM) are analyzed in Chapter five. The difference between the two implementation methods is pointed out. The smaller inverter switching loss based on the second SVM implementation method is concluded. Stator flux linkage and speed estimation based on EKF and SVM DTC is combined effctively. Hysteresis comparators and switching voltage vector selection table are replaced. Switching frequency is ensured constant and flux linkage and torque ripples are reduced further. Simulation and experimental results have verified this method.