Abstract: An analysis of the reasons for speed vibration in the low-speed range of a single-cylinder compressor system in a variable-frequency air conditioning system, caused by the non-constant load during the compressor’s operating cycle, is conducted. Based on the estimation of the motor rotor position, an effective method for automatically estimating the current load condition is proposed. According to the estimated load, automatic torque current feedforward compensation is performed. A simple load torque observer is designed using an output feedback method. This observer is a simplified design of the traditional second-order Luenberger observer, featuring fast convergence and small phase delay, making it easy to implement on embedded platforms. Since the observer itself belongs to the category of adaptive control, the use of the load torque observer can avoid the frequent parameter tuning caused by open-loop compensation. Simulation and experimental verification show that this method can significantly reduce speed fluctuations at low speeds of the compressor, validating its effectiveness.

Key words: Adaptive control, Torque observer, PMSM sensor less, Compressor low-speed