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Due to the asymmetry of the actual back electromotive force (back EMF), the performance of the conventional commutation deviation correction method degrades in sensorless control of the brushless direct current (BLDC) motor. This article proposes a high-precision sensorless optimal commutation deviation correction strategy, which considers the asymmetry problems of the back EMF. First, this article discusses the optimal commutation issues and the internal power factor angle based commutation deviation correction method. Then, given the issue of the nonsinusoidal phase current integration and the asymmetric back EMF, a dual improved second-order generalized integrator with a positive sequence component extractor (DISOGI-PSCE) is proposed. The DISOGI-PSCE can effectively deal with the dc component and harmonics in flux-linkage and current integration, as well as the asymmetry of the back EMF. Finally, experimental tests are performed on a magnetically suspended control moment gyroscope BLDC motor, which verified the effectiveness of the proposed high-precision sensorless optimal commutation deviation correction method. [ABSTRACT FROM AUTHOR]

In view of the sensorless commutation deviation of brushless dc motor with asymmetric three-phase back electromotive force (EMF), this article presents a correction method of commutation deviation based on the principle of current consistency before and after commutation to achieve optimal commutation. First, this article analyzes the different factors resulting in the commutation deviation of the motor with asymmetric three-phase back-EMF, and then points out the deviation disadvantage. Based on the analysis, a commutation deviation correction method based on current consistency in ideal optimal commutation is proposed. At the same time, in order to eliminate the influence of waveform distortion caused by winding inductance in the commutation process, dc-link current reconstructor is proposed. Based on the reconstructed current value after commutation, an optimal commutation phase estimator based on commutation current consistency is designed to estimate the position of each commutation point. Finally, experimental results confirm that the proposed method can achieve high-precision deviation correction and optimal commutation at each commutation point in the case of asymmetric three-phase back-EMF. [ABSTRACT FROM AUTHOR]

Phase-to-neutral voltage or neutral-to-virtual neutral voltage zero-crossing points (ZCPs) detection method is usually used for sensorless brushless dc motor commutation control. Unfortunately, neither of them can be realized in lower speed range. In this paper, a simple commutation point detection method is proposed based on detecting inactive phase terminal to dc-link midpoint voltage. It eliminates the requirement of neutral wire or virtual neutral voltage and provides an amplified version of back electromotive force at the ZCPs which makes the lower speed range detection possible. As the speed increases, commutation point error is enlarged due to the low-pass filter. Utilizing the symmetry of the terminal to midpoint voltage, the phase error can be corrected. However, due to the nonlinear relationship between the detected voltage difference and phase error, it is difficult to regulate the error fast and robustly. Therefore, a novel phase regulator based on fuzzy neural network is proposed in this paper with simple structure and learning ability. The validity of the proposed ZCPs detection method and commutation instant shift correction method are verified through experimental results. [ABSTRACT FROM AUTHOR]

Back-EMF zero crossing-based sensorless motor driving method suffers from a starting problem since there is no back-EMF at standstill, while the ${\rm{V}/ }f$ or ${\rm{I}/ }f$ based method is parameter sensitive. Without position sensors, smoothly driving a nonsalient BLDC motor from standstill is difficult. To solve this problem, the relationship between preposition current, energizing time, and transient speed in startup process is analyzed. Based on this relationship, starting from standstill and directly switching to self-synchronization stage can be realized without external-synchronization process. In addition, to lower the back-EMF zero-crossing points (ZCPs) detection speed, the line voltages difference ZCPs detection circuit is designed, and a novel phase error correction method based on a neuro-fuzzy controller is presented to provide accurate commutation point in the high-speed range. The experimental results show that reliable startup and accurate commutation can be guaranteed by the proposed strategy. [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]

Existing methods of compensation of commutation instants are generally developed based on the assumption that the back electromotive force (EMF) is trapezoidal wave and the three-phase windings are symmetrical. But this is not the fact. The actual back EMF waveform and commutation ripple would make the conventional methods disabled. According to the actual back EMF waveforms, the relationship between commutation point shift and the difference of dc-link current, which is sampled at the points before and after commutation, is analyzed. Based on this relationship, a novel self-compensation method of commutation error is proposed, which can be used both in sensorless motor and in hall sensor-based motor. As the shift phase is obtained through analytical method, fast convergence speed can be achieved. Furthermore, the influences caused by the freewheeling of turn-off phase inductance and the unbalanced three-phase windings are analyzed and removed. At last, the validity of the proposed self-compensation method is verified through experimental results. [ABSTRACT FROM PUBLISHER]

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]