Design of Flux-Axis Angular Speed Estimation using Induced Voltage in Speed Sensor-less Field Oriented Control for Induction Motor

This paper proposes a design method of the flux-axis angular speed estimation using induced voltage in a speed sensor-less field oriented control for induction motor (IM) drive systems. In this method, the d-axis induced voltage is regulated to zero by a feedback control to estimate the flux-axis angular speed. A low pass filter (LPF) is necessary in this estimation to avoid the recursive calculation. In this paper, the design method of compensation gain k
pem
and the cut-off angular frequency of LPF ωlpf are considered. As a result, the relation between k
pem
, ωlpf, convergence time of the d-axis induced voltage have a match to the equation and designed model in this paper. Furthermore, the maximum error between the simulation and estimated results of the time constant of the flux-axis angular speed introduced due to LPF is 3.7% when ωlpf is 200 rad/s. As the experimental results, when a torque step of 100% is applied to the induction motor, the convergence time of the motor speed is 1.6 s as the worst case with k
pem
set as 2.0 p.u. and the cut-off angular frequency set as 1000 rad/s. However, if k
pem
is set as 2.0 p.u. andω lpf is set as 400 rad/s, the convergence time of the motor speed is 0.43 s as the best case, which is reduced by 73.1 % compared to the worst case. As the result, k
pem
should decide by the target steady-state error, ωlpf should bigger than the cut-off angular frequency of the PI controller ωASR. Where, if the ωlpf is high, the convergence time of the motor speed is high.