A Closed-Loop Voltage Model Observer for Sensorless Induction Motor Drives Based on the Orthogonality and Sliding-Mode Technique

The sliding-mode observer (SMO)-based voltage model (VM) design is an effective way to improve the robustness of speed estimation in sensorless induction motor (IM) drives. However, this article reveals that the existing SMO-based VM is unable to remove the dc offset present in the rotor flux derivative, resulting in the integral drift problem of rotor flux estimation. To address this problem, this article proposes a SMO-based closed-loop VM observer based on the orthogonality between the rotor flux and its derivative. First, by introducing the orthogonality into the design of observer structure, the rotor flux estimation can be incorporated into the stator current observer. Second, by ensuring the stability of current observer, the SMO law can compensate the deviation between the estimated rotor flux and the ideal orthogonality. Finally, the SMO law will act as the feedback term to remove the dc offset in the rotor flux derivative and stabilize the pure integral for rotor flux estimation. The contrast and verification experimental results from a 2.2-kW IM test bench confirm the accuracy and robustness improvement of rotor flux and speed estimation.