Speed Sensorless Vector Control Using Rotor-Flux-Induced Voltage with Integrator for Improved Stability

In sensorless vector control of induction motors, the E2d method estimates stator angular velocity based on the rotor-flux-induced voltage. Although this method features a simple structure, it poses a challenge when integrated with a speed controller: the optimal filter time constant for the rotor-flux-induced voltage varies between low-speed and medium-to-high-speed ranges to maintain stable operation. This study proposes a compensation approach that incorporates the integral of the q-axis current deviation into the conventional stator speed estimation formula. Nyquist analysis using a linearized model, along with experiments on a 2.2-kW induction motor, confirms that the proposed method enhances stability in the medium-speed range without sacrificing stability at the low speed.