Weight-Transducerless Rollback Mitigation Adopting Enhanced MPC with Extended State Observer for Direct-Drive Elevators

The permanent magnet traction machine has become the tendency of modern gearless elevators, because of small volume, high efficiency, and good dynamics. However, the direct-drive elevator car will slide during the electromagnetic brake releasing at elevator startup, if the speed controller cannot generate a suitable electromagnetic torque to trace the change of the uncertain disturbance on traction sheave. To attenuate the car sliding of the gearless elevator installed with an ordinary resolution encoder, a weight-transducerless rollback mitigation strategy adopting an enhanced model predictive control with extended state observer (ESO) for speed loop is proposed. The ESO is used to overcome the mismatch of predictive model caused by the braking torque and the unknown car load. Both the stability and the parameter selection of the observer are analyzed. Additionally, a nonlinear tracking differentiator is used to process the raw speed signal generated by the conventional speed differential sampling instead of the low-pass filter, which can overcome the vibration of the elevator car when the brake releases. Finally, experimental results verify that the proposed control strategy can achieve shorter sliding distance and smaller sliding speed for the direct-drive elevator installed with an ordinary-resolution encoder.