Zero speed sensorless scheme for PMSM under decoupled sliding mode control

Position estimation at low/zero speed for permanent magnet synchronous machines is commonly achieved with the injection of high frequency signals. This paper presents a new sensorless scheme that accurately observe the rotor angle at low speeds, including standstill condition, without injecting high frequency signals. The algorithm is built upon a previous sliding mode current controller and uses the switching functions slopes inaccuracies produced by the saliency effect to determine the rotor position and speed. Thanks to the equivalent control concept and together with a sliding mode based PLL observer defined by a complex switching function, the algorithm provides both rotor position and speed in a compact form. The paper includes the main working principle and defines the operational range of the proposed scheme. Finally, the feasibility of the method is corroborated through experimental results in sensorless configuration.