Nonlinear speed sensorless control of a surface-mounted PMSM based on a Thau observer

This paper presents an alternative to solve the speed sensorless control of a surface-mounted synchronous motor based on localization of compact invariant sets (LCIS) and the Thau observer. Through the LCIS, the domain of attraction of the system dynamics is analyzed, allowing to obtain global knowledge about its operational bounds and its associated Lipschitz constant. Necessary and sufficient conditions for existence of a stable observer are fulfilled by two inequalities, providing two different sets of stability conditions and, as a consequence, two observers are proposed. The observer design is based on the availability of stator currents for measurement and stator voltages for feedback in a rotating reference frame. The designed observers are able to work in a wide speed range and also estimate rotor position accurately, even at low speed and zero-crossing speed. Simulations demonstrate that the observers can estimate both rotor speed and position. Additionally, the observers are experimentally validated with the Technosoft MCK28335 platform. Results show that the observers can solve sensorless problem in a real-world scenario.