Research On Position Sensorless Control Of High Power Permanent Magnet Synchronous Motor

Permanent Magnet Synchronous Motor is widely used because the advantages of simple structure,small size,small mass,large starting torque,fast dynamic response,high power density,high operating efficiency,etc.Due to the defects of high cost,large volume,complicated wiring and poor anti-interference ability of mechanical position sensors,the position sensorless control algorithm is widely used in the field of motor control.However,there is no single algorithm that can meet the operating requirements of the full speed range of the motor.Therefore,it is very important to study the sensorless control technology of permanent magnet synchronous motor in the full speed range.In order to meet the applications of higher voltage level and higher power,it is of great significance for improving system performance and economic benefits to study the pulse width modulation algorithm of high-power NPC three-level converter at low switching frequency.Firstly,aiming at the problems of low switching frequency of high-power converters,wide fundamental frequency domain,and low carrier ratio when the motor is running at high speed,in order to improve the quality of output waveform and reduce harmonic content,the muti-mode subsection synchronous modulation algorithm is put forward.The methods and principles for selecting the carrier ratio value,dividing the frequency band interval,and determining the carrier ratio switching scheme are analyzed.Aiming at the problem of output voltage phase mutation,current impulse and torque ripple existing in the process of carrier ratio switching,method for switching at low point of carrier signal is adopted.This method has higher precision and shorter delay than traditional switching methods.Simulation results show that the output waveform of this modulation algorithm has high sineness and low total harmonic distortion,and excellent control of the high-power motor converter at low switching frequency is achieved.Secondly,the saturation salient polarity of the permanent magnet synchronous motor is analyzed.Based on the equal width basic voltage vector and the characteristics of the NPC three-level converter,a method of generating twelve groups of equal width basic voltage vectors by large and medium vectors is proposed to calculate the initial position of the rotor.The problem of low detection accuracy of the initial position of the rotor or complex algorithm is solved.The high detection accuracy of the method is verified by simulation,which can meet the requirements of the smooth start of the motor.Thirdly,in the medium and high speed stage,based on the fundamental wave model of the permanent magnet synchronous motor,a low-pass filter compensation integrator is used to integrate the back electromotive force to detect the rotor position.It is verified by simulation that the method is simple and reliable,with high detection accuracy and good dynamic and steady-state performance.Finally,the starting process of motor of permanent magnet synchronous motor based on I/f control and the basic principle of sensorless vector control are analyzed.Two synchronous rotating coordinate systems are established based on these two control strategies,and the relationship between the two coordinate systems is analyzed in detail.The switch between these two control strategies is equivalent to the switch between two synchronous rotating coordinate systems.The effectiveness of the switch algorithm is verified by simulation,and the position sensorless control of the permanent magnet synchronous motor in the full speed range is realized.