A Novel Stator Flux Estimator Based on Modified Integrator

In voltage-model-based flux estimation of direct torque control system,a low-pass filter is normally used instead of a pure integrator to avoid the errors caused by the DC drift and initial value.But the estimated stator flux becomes inaccurate since it introduces magnitude and phase errors.A new stator flux observer based on modified integrator with variable cutoff frequency is proposed in this paper.Utilizing a fuzzy controller,the cutoff frequency of low-pass filter can be adjusted in real time according to the online motor operating states.Consequently,it can eliminate the magnitude and phase errors caused by low-pass filter and improve the precision of stator flux estimation efficiently.The simulation scheme of direct torque control based on a new stator flux observer with variable cutoff frequency is built in the Matlab6.5/Simulink,Its feasibility is verified by the simulation results.