Research On Flux-weakening Control Method For Direct-drive Permanent Magnet Synchronous Motor

As gradually increased environmental awareness of Chinese citizens, the concept of low-carbon economy has become popular. Electric bus is booming in China by the influence of energy shortages, and the technology has gradually become matured. The advantages of electric bus are zero emissions and low operating cost, which makes it popular year by year in the public transport market. Benefit from government subsidies, its large-scale industrialize production can be easier to become realized.The control of high torque PMSM(permanent magnet synchronous motor) is one of the key technologies of direct-drive system using in electric bus. Its research on elevators, lifting and other areas has become the focus. This thesis studies the PMSM control system of the direct-drive electric bus, especially for wide speed range required by the car driver. In addition flux weakening control algorithm is discussed and the whole drive control scheme is designed.First, the rotor structure of direct-drive PMSM is introduced in this thesis, including the hidden type and salient type. Mathematical models are analyzed in different coordinate system. Based on the above, analyzing the vector control in dq and MT coordinate system. By comparison with different control strategies, the final choice of the system is the simple control method(id=0) which is easy to realize.Second, one of the features of the direct-drive motor is low speed. In order to meet the bus driver’s requirements of the wide speed range, this thesis focus on the relevant theory of flux-weakening. For follow questions: with the changes of PMSM load in flux weakening area, the current oscillation appears and the steady-state error fluctuation of speed becomes bigger. An improved weakening control algorithm based on the current error close-loop is proposed. Based on analyzing the principle of SVPWM, in order to improve the utilization of the DC-link voltage of the inverter, over modulation method is proposed for weakening control strategy.Third, through modeling and simulation using MATLAB/Simulink, improved leading angle weakening algorithm is verified to be correctness. This thesis introduces the design of direct-drive PMSM control system, including the hardware design, software design and experiment platform construction. Through the system power experiments, the system design is verified to be correctness. By further testing, the control system is withstood the test of long-running, all aspects of the control indicators are proved to meet the design requirements.