Improved sensorless operation of permanent magnet brushless AC motors based on online optimal efficiency control

In general, accurate position estimation is one of the primary goals in sensorless control of permanent magnet brushless AC motors. However, it is often necessary to compensate the nonlinear effects of motors and drives which may significantly deteriorate the position estimation. In some applications, such as cooling fan and water pump, energy conservation is also a critical concern. In this paper, optimal efficiency of the machine and drive system is selected to be the objective for sensorless operation, and thus accurate rotor position and nonlinearity compensation are not required. By on-line calculating the active input power, this paper combines the optimal efficiency searching concept with sensorless technique to improve the sensorless operation performance of permanent magnet brushless AC motors at steady-state. Experimental results confirm that the energy efficiency with sensorless operation can be significantly improved with the proposed method, even though the estimated position information may be not accurate.