Sensorless high‐speed BLDC machine using hardware‐RFO

Abstract

Purpose

The purpose is to present a sensorless control method by which high‐resolution rotor position information is estimated and used for phase‐advancing operation of a high‐speed permanent magnet (PM) brushless DC (BLDC) motor.

Design/methodology/approach

The proposed sensorless control approach uses hardware to observe the flux vector which is excited by rotor magnets. It can provide the rotor position which is the same as the phase angle of the observed flux vector.

Findings

High‐resolution rotor position signal of the BLDC motor for dynamic phase‐advancing control cannot be directly obtained from the conventional Hall‐effect sensors, or via the traditional back‐EMF‐based sensorless control strategies in which the back‐EMF may be even undetectable at high‐speed. The proposed rotor‐flux‐observer (RFO)‐based sensorless control method overcomes these problems, and meanwhile provides high‐resolution rotor position information for the phase‐advancing purpose.

Originality/value

The RFO‐based sensorless control is traditionally applied to PM brushless ac (BLAC) operations, where the motor voltage vector can be calculated from the inverter switching status. However, this is not readily applicable to a BLDC motor since the voltage of the floating phase cannot be calculated. Moreover, during high‐speed operation, the microprocessor may not be sufficiently fast to calculate the high‐resolution rotor position. Therefore, in this paper, it is proposed to use hardware to observe the rotor‐flux‐vector. The microprocessor only samples the vector's α‐ and β‐components and calculates the phase angle, hence, its burden is low. The proposed method is validated with a 1.8 kW 85,000 rpm BLDC motor system.

Citation

Shen, J., Hao, H., Jin, M. and Fei, W. (2012), "Sensorless high‐speed BLDC machine using hardware‐RFO", COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, Vol. 31 No. 1, pp. 182-190. https://doi.org/10.1108/03321641211184904