Stable sensorless transition algorithm for PM synchronous motors under load

The back EMF-based sensorless control of PMSMs is widely applied to the blowers and hermetic compressors of heating, ventilation and air-conditioning (HVAC) systems. For the sensorless control of PMSMs, a smooth transition from the I–f startup to the closed loop speed control with a rotor speed estimator is required. This paper proposes a smooth transition algorithm that can minimize torque and speed fluctuations under all load conditions. At the starting of a transition, the dq current based on the reference rotor position for I–f control is switched to the dq current with the estimated rotor position. The operating point of the dq current moves from I–f control to MTPA (maximum torque per ampere) operation, while the dq current follows a constant torque curve. Experimental results show that the torque and speed fluctuations under the proposed transition algorithm were significantly reduced under all load conditions.