In order to improve the precision of sensorless control of permanent magnet synchronous motor in full speed domain

a composite control method combining high-frequency square wave signal injection and improved sliding mode observer based on rotor flux is designed. Firstly

the high-frequency square wave signal of pulse vibration is injected in zero and low speed sections

and the high-frequency current signal and fundamental current signal are separated by simple algebraic operation

which avoids the use of filter in the process of extracting the rotor position information

and improves the accuracy of rotor position observation. Secondly

the improved sliding mode observer method is used in medium and high speed sections with the introduction of adaptive feedback gain based on rotor speed

and then the rotor flux is used to extract the rotor position information

which further improves the running stability and control accuracy of the motor. Finally

the weighted function is used to switch the control strategies of zero

low speed and medium

high speed

so as to construct the full speed domain control algorithm. This algorithm is simulated and verified under the loaded startup

full speed domain running and restart at coasting condition respectively. The simulation results show that the designed full speed domain control algorithm can achieve the stable and efficient full speed domain running of motor under different working conditions

which has good dynamic performance and stability.