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Inaccurate commutation in brushless dc motor (BLDCM) will induce current harmonic and increase motor loss, which reduce motor efficiency. Meanwhile, for the sensorless BLDCM, the motor commutation is seriously affected by detection errors and calculation errors, which are caused by the nonideal conditions and the parameters variation. In this paper, a novel commutation error correction method is proposed to determine optimal commutation instant for the sensorless high-speed BLDCM. First, the relationship between commutation error and motor phase current is analyzed. According to this relationship, an initial commutation error can be calculated and compensated in one conduction interval. Then, online commutation corrections are performed to compensate for the residual error in following conduction intervals. The correction accuracy of commutation instant is determined by the phase current integral difference. This method is insensitive to motor parameters and back electromotive force waveform. Therefore, the commutation error is effectively eliminated in the whole speed range. Finally, the feasibility and effectiveness of the proposed method are evaluated by experimental results. [ABSTRACT FROM AUTHOR]

Due to the phase delay caused by low-pass filter, device retarding, and software retarding, the extracted sensorless motor commutation signal deviation occurs. Unfortunately, the relationship between the phase shift and inactive phase freewheeling has been scarcely referred to through the published papers, and most of the commutation instant shift compensation methods present slow convergence rate. Therefore, a fast commutation instant shift correction method based on analyzing the back-electromotive force (EMF) harmonic information is proposed in this paper. The method is effective both in the steady-speed control and in variable-speed control. Considering that commutation instant shift may induce inactive phase freewheeling and negative torque in motor windings, the freewheeling condition and motor electric operation condition are analyzed as well. Furthermore, to exactly delay the zero-crossing points (ZCPs) of EMF by 30° and compensate the commutation instant shift, the speed detection accuracy and feedback frequency are enhanced by measuring and summing up the 2 × P consecutive half-period of the ZCPs signal. Finally, the validity of the proposed commutation instant shift correction method is verified through experimental results. [ABSTRACT FROM AUTHOR]

In this paper, a newly designed braking torque control scheme with improved toque estimation and control characteristics in a small inductance brushless DC motor is presented. The motor torque is estimated according to the back electromotive force (EMF) shape function that is fitted by neural network and corrected by temperature. Upon this, a hybrid braking torque control structure that combines dynamic braking and plug braking is proposed for the smooth and continuous braking torque. These two braking modes operate, respectively, in the relatively high- and low-speed ranges. During dynamic braking, a predictive torque control method is proposed to suppress the torque fluctuation that is induced by the supplying voltage namely back EMF descent. During plug braking, an effective torque ripple reduction method is designed to weaken the large torque ripple which is caused by high winding voltage, low winding impedance, and three-phase inverter modulation. In addition, different pulse width modulation patterns and the most suitable operating conditions for each braking mode have been studied. Finally, experimental results are presented to demonstrate the validity and effectiveness of the proposed braking torque control scheme. [ABSTRACT FROM AUTHOR]

In this paper, precise accelerated torque control for a small inductance brushless dc motor (BLDCM) is achieved by electromagnetic torque control and disturbance torque suppression. First, the electromagnetic torque ripple is reduced in commutation and conduction regions. In the former region, the ripple is suppressed by overlapping commutation control and optimizing the duty ratio of the active controller. In the latter region, the unbalance ripple caused by the unbalanced three phase windings is reduced by the proposed asymmetry compensation function, and the disturbance ripple created by the back electromotive force (EMF) is compensated by feedforward control. Second, the disturbance torque has been observed and compensated through the improved disturbance torque controller whose compensation coefficient is obtained by line-to-line back EMF coefficient estimation. And, both the disturbance observation and speed measurement are all synchronized with the encoder pulse alteration. Experimental results are presented to demonstrate the validity and effectiveness of the proposed accelerated torque control scheme. [ABSTRACT FROM AUTHOR]

Due to the small inductance, modulation of three-phase inverter induces serious torque ripple. In addition, the increase in modulation frequency is limited by the processor speed. Therefore, the traditional torque control approaches are not suitable. In order to solve the aforementioned problems, a new instantaneous torque control method for small inductance brushless dc motor is proposed by improving the torque estimation and control. First, instantaneous torque is estimated through improved position information and back electromotive force (EMF) coefficient estimation. The former is achieved by the proposed hall sensors position calibration and compensation method, and the latter is obtained by neural network fitting. Second, the torque ripple reduction is realized in the conduction and commutation region. The ripple caused by three-phase inverter modulation is suppressed by the dc-link buck converter pulsewidth modulation control method. Upon this, an asymmetry compensation function is designed to solve the problem of unbalance among three phase windings. After that, back EMF disturbance, which is applied to current dynamics, is compensated through feedforward control. Subsequently, the commutation ripple is reduced by the outgoing phase control. Finally, the validity of the proposed torque control method is verified through experimental results. [ABSTRACT FROM PUBLISHER]