The commutation torque ripple in the six-step square-wave driving mode of the brushless DC motor affects the motor performance and generates mechanical vibrations and noise when used for industrial applications. The cause of commutation torque ripple is analysed in this study and a non-linear transient model of the phase current during the commutation interval is developed. According to the transient-current model, the commutation voltage and the time required to produce a constant torque can be calculated without current sampling; this makes the control system easier to realise in industrial applications, and reduces the need for a high performance controller. Based on the pulsewith modulated chopping method and quasi-Z-source net, the proposed control system can adjust the motor speed using a constant-voltage power supply and reduce the commutation torque ripple over the entire speed-adjustable range. A torque transducer is used to measure the dynamic torque ripple in the experiment. The results show that the proposed commutation torque-ripple reduction strategy can reduce the dynamic torque ripple by about 70% in both simulation and experiment compared with the traditional driving methods. Torque ripple in BLDCM driving systemThe torque ripple of the BLDCM is formed by three components: cogging torque, reluctance torque and mutual torque [23]. Cogging torque is a common shortcoming in PM motors, and can be minimised during motor design. PM motors with surface mounted

In this study, a no-dead-time modulation method based on the H6 topology is proposed. The main objective is to reduce the total harmonic distortion (THD) of the inverter output voltage and improve the output-voltage waveform quality. On the basis of the working state of the main circuit, the proposed method selects an appropriate switch modulation, thereby realising the objective of not inserting a dead time, most of the time. Simulations and experiments demonstrate that the modulation method suppresses the THD better than the conventional modulation algorithm, at all power factors and power levels. Furthermore, with the increase in power, the output current increases, but the current commutation interval decreases and the output-voltage suppression effect THD is better. It can also be concluded that simultaneously there is a higher DC-link voltage utilisation efficiency in the no-dead-time modulation method than in the conventional modulation method.

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