Magnetic field tracking controller in speed sensorless induction motor drive

In rotor flux oriented speed sensorless vector control system, the steady state equations based synchronous angular speed deduction method is both simple and cost saving to obtain the magnetic field position. For the disadvantage of inaccuracy in transient state, a method of angle error acquisition between practical and estimated magnetic field is proposed by means of current injection in this paper. Inserting sine current of some frequency and amplitude in the direction of the estimated magnetic field, when the estimated angle deviates from the actual one, the electromotive force of motor will contain a component related with the angle error according to the mechanical characteristics and electromagnetic relation of motor. The angle error can be effectively compensated by extracting the component and designing a magnetic field tracking controller so that estimated magnetic field position can fast track the practical one. Applied in speed sensorless low speed drive system simulation, the method makes satisfactory results and has some application prospects.