Sensorless direct torque control method for permanent magnet synchronous motor

The invention discloses a sensorless direct torque control method for a permanent magnet synchronous motor. The method comprises the following steps: firstly, stator currents ialpha and ibeta and stator voltages ualpha and ubeta under alpha and beta coordinates are input into an improved Runberg observer module to estimate back electromotive force, then the estimated back electromotive force is substituted into a phase-locked loop to calculate a rotor position angle and an estimated rotating speed, and the rotor position angle and the estimated rotating speed are respectively applied to a dq/alpha and beta coordinate transformation module; and an abc/dq coordinate transformation module and a motor rotating speed feedback module. An observer subtracts the estimated current from the actuallymeasured current to serve as an error value to carry out closed-loop correction on the estimated value of the state observer, so that the observer can enter a stable and convergent state again underthe condition that the sys