In this paper, a novel motor control method is proposed to improve the performance of sensorless drive of BLDC motors. In the terminal voltage sensing method, which is a great portion of sensorless control, a precise rotor position cannot be obtained when excessive input is applied to the drive during synchronous operation mode. Especially in the transient state, the response characteristic decreases. To cope with this problem, the unknown input (back-EMF) is modelled as the additional state of system in this paper. Taking into account the disturbance adopted by the back-EMF, the observer can be obtained by an equation of the augmented system. An algorithm to detect the back-EMF of a BLDC motor using the state observer is constructed. As a result, a novel sensorless drive of BLDC motors that can strictly estimate rotor position and speed is proposed.
Fig. 1. Block diagram of BLDC motor drive.
EXPECTED SIMULATION RESULTS:
Fig. 2. Speed response for the start and transient state. (a) In the proposed sensorless scheme. (b) In the conventional scheme use sensor.
Fig. 3. Simulation results of the proposed sensorless scheme at 2000 (rpm). (a) Rotor speed. (b) Rotor position. (c) Phase current. (d) Line-to-line back-EMF. (e) Commutation function. (f) Commutation signal.
Fig. 4. Simulation results of the proposed sensorless scheme at 100 (rpm). (a) Rotor speed. (b) Rotor position. (c) Phase current. (d) Line-to-line back-EMF. (e) Commutation function. (f) Commutation signal.
In this paper, the unknown input (back-EMF) is modeled as the additional state of system. Considering disturbance that is adopted by back-EMF, the observer can be obtained effectively using the equation of augmented system and estimating back-EMF. As a result, an effective algorithm to estimate rotor position and speed of motor using the state observer is proposed. Use of sensorless control method can remove problem on manufacture that is happened in circuit to detect rotor position and speed. Moreover the production of inexpensive motor controller may be possible because the additional circuit such as encoder is not necessity. In cases using the proposed sensorless control method, the start-up performance has an almost analogous transient state characteristic after forced alignment, compared with the conventional method. This method also provides useful motor control because it is possible to analyze about transient state as well as steady state unlike various sensorless control methods that have been recently proposed. In addition, it can be easily applied in industry applications requiring the low-cost style drive of BLDC motor because actual realization is very simple.
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