Study On Sensorless Direct Torque Control For Direct-driven Permanent Magnet Synchronous Wind Power Generator

As the world’s fastest development of new energy sources, wind energy has drawn worldwide attention. Compared with the DFIG, direct-driven permanent magnet wind power generation system is considered to be important research direction of wind power generation technology due to its high conversion efficiency and flexible power control ability. Direct torque control (DTC) is a kind of advanced control strategy of AC motor, which has advantages of fast torque response and simple control structure. The DTC method for directly -driven wind power generation system has important practical significance. But conventional DTC has disadvantages of large ripples of torque and flux. Traditionally, optical encoders or rotary transformer are used to obtain rotor position information of permanent magnet synchronous generator. However,the additional sensors not only increase the cost but also make the system affected by environmental factors easily. Therefore, the sensorless control technology has become the hot spot of directly-driven wind power generation system.This paper first introduces the mathematical model of permanent magnet synchronous generator, and analyzes the wind turbine model and operating characteristics. Directly-driven wind power generation model is builded according to the theoretical analysis and the DTC is used as control strategy.Secondly, this paper introduces conventional integral flux observer,then analyzes several improved methods in common use, and puts forward a new method. The method solves problem that caused by inaccurate measurement in practical application. Theoretical analysis and simulation results show the effectiveness and feasibility of this kind of method.Thirdly, this paper study the model of permanent magnet synchronous generator, and then derived permanent magnet synchronous generator rotor position detection method based on stator flux according to the relationship between the power angle and the position of the rotor.Fourthly, this paper uses the method of fuzzy DTC to replace traditional DTC. The fuzzy control theory is applied in DTC. Fuzzy DTC make appropriate decisions according to distinguish the range of flux error and torque error,which optimizing the switch state selection. The simulation results show that the method has obvious inhibiting effect to torque and flux ripple and greatly improved the performance of DTC.Finally, the digital signal processor TMS320F2812 is used as core chip to design the control system. This paper designs voltage and current detection circuit, PWM drive circuit and protection circuit. The C language program is written based on the hardware circuit and further debugging have been done. Experiments are performed on the drag experiment platform of 1kw permanent magnet synchronous generator. The main circuit, control circuit and related circuit had set up. The experimental results show that the proposed sensorless technique can accurately detect position and it has high accuracy and good dynamic performance which can be considered as actual production application.