Backstepping control with unknown load torque observer of permanent magnet synchronous motors

We propose a load torque estimator based on the backstepping control of permanent magnet synchronous motors (PMSMs) for robot joints. The load torque estimator is designed to estimate an unknown load torque that include a constant load torque. An auxiliary state variable is proposed to avoid amplifying of the measurement noise in the load torque estimator. The backstepping control method uses a Lyapunov function to compensate for the unknown load torque while tracking the desired rotor angle. The closed-loop stability of the proposed method is studied using the Lyapunov theorem. As a result, the proposed method improves the rotor angle tracking performance in the presence of an unknown load torque. Its performance is validated via simulations. © ICROS 2018.