Sensorless Control Of PMSM Based On Third Harmonic Back-EMF

Permanent magnet synchronous motor has been widely applied to automatic control system,electric vehicle and aerospace field because of its advantages such as high power density,simple structure and wide speed regulation.In order to realize high performance of PMSM control,sensors are always considered necessary,which will increase instability of the system though.In order to get rid of such problem,many scholars turn to seek for sensorless control.Compared with other sensorless strategies,sensorless control based on third harmonic back-EMF has many superiorities such as free of pulse width modulation(PWM)noise and less influenced by variation of machine parameters.Sensorless control according to harmonic-shaped motor is studied in this thesis.Firstly,this thesis introduces the development history and research status of PMSM in general and compares with different kinds of sensorless control strategies about their principle,advantages and application in detail.Secondly,this thesis establishes the mathematic model of PMSM and expounds the basic principle of vector control,of which i_d=0 is chosen as the vector control strategy in this thesis.Thirdly,this thesis engages in sensorless control based on third harmonic back-EMF in theory.Detection circuit is conducted to separate third harmonic back-EMF from fundamental one.In order to achieve instantaneous rotor position and speed,a phase-locked loop(PLL)is always proposed,in which third harmonic back-EMF and its integration taken as the input signal.However,direct integration may result in integral drift and saturation.To avoid such circumstance and achieve high-resolution position,an improved PLL structure is introduced in this paper,whose stability is analyzed in frequency domain.Lastly,vector control experiments with and without position sensor are conducted based on MicroLabBox in order to verify the feasibility of theory study,of which results show that the method introduced in this thesis has a good performance on estimation accuracy under steady state and has the capacity of adjusting itself to the sudden change of speed.