In order to improve the reliability of the permanent magnet traction system of electric locomo-tives and reduce costs

a sensorless control system for permanent magnet motor based on hybrid mode was designed. In the low-speed region

a square wave high-frequency voltage with a frequency equal to the switching frequency was injected into the system. After extracting the high-frequency current

a robust observer was designed to estimate the rotor position of the motor by taking advantage of the characteristic that the motor is equivalent to an inductive load when the high-frequency voltage is injected

realizing low-speed full torque performance. In the medium and high-speed range

an extended back electromotive force model of the permanent magnet motor was established in the d and q axes. A high-precision Luen-berger observer was designed to observe the back electromotive force

and after adjustment by a robust observer

the rotor position of the motor was estimated. In order to ensure a smooth transition during the algorithm switching process

the same position robust observer was used to design the switching strategy

achieve low load ratio sensorless control. Using a direct drive permanent magnet synchronous motor as the control object

experiments were conducted on the traction platform of the permanent magnet direct drive traction system. The experimental results show that the designed control algorithm can achieve full speed range sensorless control high-performance operation of the direct drive motor

and the position estimation error in the high-speed zone is within 4 degrees.