Research On Pulsating Torque For Brushless Motor Drive System For Electric Power Assisted Mountain Bike

Nowadays, 'Green Gym' has got a lot of people's attention.In this context, the Electric Power Assisted Mountain Bike is becoming more and more popular.In this paper, two problems of the permanent magnet motor driven system are studied by using a field-circuit combined analysis method,(1) Permanent magnet motor compound driven based on Hall position sensors;(2) Fault tolerant control of full speed range.Firstly, in this paper, a finite element analysis method is used to measure the key parameters and characteristics of the permanent magnet motor for mountain bike.In order to study the magnetic saturation effect, magnetic weak properties, the core loss and other nonlinear characteristics more in depth,A motor modeling scheme based on reduced order finite element model is proposed.This method makes use of the Simplorer platform to simulate the motor finite element model and the Simulink control algorithm.Secondly, a compound driven of permanent magnet brushless motor with sine and square wave based on three Hall sensors was presented in this paper.Square wave driven is performed in a low speed region which requires a larger torque output capability, while the vector control is adopted in the high speed area because of the vibration and noise.On the basis of the discussion on rotor position estimation and position calibration for permanent magnet brushless motor, principle and optimization of the switching process between two different driving modes are analyzed. In order to improve the robustness of the switching process control, an adaptive fuzzy controller is used to keep the output torque unchanged pre and post switching process by taking the command current iq a gain compensation, the speed fluctuation can be controlled within acceptable limits during the switching process.Once again, in order to ensure the safety of the mountain bike when Hall signal failure occurs.A fault tolerance control strategy of whole speed range of the permanent magnet motor in the mountain bike is studied.When the partial Hall signal is faulty, the rotor position is estimated according to the non fault signals.If the Hall signals are completely lost,the permanent magnet motor will be driven without using position sensors.According to different speed range, in the low speed region, the high frequency voltage injection method is adopted, and the extended back EMF method is used in the high speed region.In the transition region, the two methods are normalized and weighted to obtain the rotational speed and rotor position information.The characteristics of high frequency parameters of permanent magnet motor and the influence of different injection conditions on the position identification and magnetic polarity identification are discussed.Finally, in order to verify the correctness of the proposed motor control algorithm, a prototype of the motor is made.The hardware of the controller is designed and made according to the required function.Then, the core driver software is compiled and debugged according to the fault tolerance control algorithm and the compound driven strategy.All of this build a test platform of the permanent magnet motor driven system.On this platform, we have carried out a comprehensive and in-depth system experiment, analysis and comparative study.The Experimental results show that,(1) The permanent magnet motor is driven by square wave in the low speed region, and the torque output capability is stronger.But in the high speed area, the permanent magnet motor is driven by sine wave, and the noise of the motor is lower.The whole process of transition from the low speed area to the high speed area is very smooth;(2) The proposed position estimation algorithm can be used to observe the rotor position of the motor, and the simulation results are in good agreement with the actual situation.