A 12-Step Sensorless Drive for Brushless DC Motors Based on Back-EMF Differences

Abstract

This paper presents a new 12-step sensorless drive for brushless dc motor based on back-electromotive force (back-EMF) differences, which are estimated from the disturbance observer (DOB) structure. Availability of rotor position information with a resolution of 30°and commutation without phase shift are the advantages of using the back-EMF differences. Unlike the conventional methods that obtain part of the back-EMF signal from the manipulation of three phase voltages, the proposed DOB structure can access the entire back-EMF profile. By designing a proper low-pass filter in the DOB structure, the back-EMF difference can be well detected with lower sensor noise. Compensation of delay commutation introduced by the filter is also discussed. Experiment results showed that the proposed sensorless drive is capable of running the motor in lower speed, and performs better under different speed and load torque as compared with the conventional method.Index Terms-Back electromotive force (back-EMF) detection, back electromotive force differences, brushless dc motor (BLDC), delay compensation, disturbance observer (DOB), sensorless control, torque ripple.

Commutation Error Compensation Strategy for Sensorless Brushless DC Motors

“…(e a + e b − 2e c )dt (15) By decomposing (15) into a combination of two items, it is reformulated as The phase current satisfies i a + i b + i c = 0 in the freewheeling period t fw . Substituting the phase current relationship, (13) into the second item of (17), it is simplified as (18) where I c is the final value of the outgoing phase current before commutation.…”

“…(u dc − e a − e b +2e c )dt = 3RI c t fw /2 + 3LI c (19) From (13), the phase current i c in the freewheeling period t fw is solved as…”

“…Many estimation and observer methods of commutation error compensation have been proposed to achieve high-precision commutation [12][13][14][15][16][17][18]. In reference [12], the torque constant is employed as the reference signal of the rotor position to obtain accurate commutation signals.…”

“…In reference [12], the torque constant is employed as the reference signal of the rotor position to obtain accurate commutation signals. In reference [13], the rotor position is acquired from the back-EMF difference, which is estimated from the disturbance observer structure. Discrete-time sliding mode observer [14] and iterative sliding mode observer [15] have been introduced to obtain precise commutation signals for sensorless permanent magnet synchronous motor control.…”

A Lag Angle Compensation Strategy of Phase Current for High-Speed BLDC Motors

“…Jang and Kim [7] determine the commutation position of BLDCM in such a way as to generate the symmetric terminal voltages of the non-energized phase at the beginning and at the end of the commutation period. Wang and Lee [8] employ the first-order and second-order Butterworth filters depending on different speed zone to minimize the influence from sensor noise and to reduce delay. Zhou et al [9] proposes a novel selfcompensation method of commutation error based on the relationship between the commutation point shift and the difference of DC-link current.…”