**ABSTRACT:**

This paper describes the reduction in torque ripple due to phase commutation of brushless dc motors. With two-phase 120^{0} electrical conduction for the inverter connected to the conventional three-phase BLDC machine, the commutation torque ripple occurs at every 60 electrical degrees when a change over from one phase to another occurs. This effect increases the commutation time at higher speeds which increases the torque ripple. The torque ripple is reduced by changing the switching mode from 120^{0} to a dual switching mode with 120^{0} switching at lower speeds and 180^{0} electrical for the inverter at higher speeds.

**KEYWORDS:**

- Brushless dc motor
- Current commutation
- Torque ripple
- Electric vehicle

** SOFTWARE: **MATLAB/SIMULINK

**CIRCUIT DIAGRAM:**

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Fig. 1. PWM inverter and equivalent circuit of BLDC motor

**EXPECTED SIMULATION RESULTS:**

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Fig.2. (a) Relative torque ripple amplitude and (b) The duration of commutation time

**CONCLUSION:**

This paper has presented an analytical study of torque ripple comparison due to commutation of phase currents in a brushless dc motor for both 1200 and 1800 conduction modes. The results have been validated by simulation and experimental verification. In three-phase switching mode at high speeds the torque ripple and losses are minimized and therefore the efficiency of the machine is increased. But the same cannot be achieved at low speed in this mode. On the other hand, the 1200 situation is exactly opposite. Thus a composite switching scheme is proposed for satisfactory operation of the machine at all speeds. The effectiveness of the method is validated by suitable experiments.

**REFERENCES:**

[1] T. Li, and G. Slemon, “Reduction of cogging torque in permanent magnet motors,” *IEEE Trans. on Magnetics*, vol.24, no.6, pp.2901-2903, Nov. 1988.

[2] R. Carlson, M. Lajoie-Mazenc, and J.C.D.S. Fagundes, “Analysis of torque ripple due to phase commutation in brushless DC machines,” *IEEE Trans. Ind. Appl.*, vol.28, no.3, pp. 632-638, May/Jun. 1992.

[3] H. Tan, “Controllability analysis of torque ripple due to phase commutation in brushless DC motors,” in *Proc. 5th int. conf. Elect. Mach. And Syst.*, Aug. 18-20, 2001, vol.2, pp. 1317-1322.

[4] Y. Murai, Y. Kawase, K. Ohashi, K. Nagatake and K. Okuyama, “Torque ripple improvement for brushless DC miniature motors,” *IEEE Trans. Ind. Appl.*, vol.25, no.3, pp. 441-450, May/Jun. 1989.

[5] C.S. Berendsen, G. Champenois, and A. Bolopion, “Commutation strategies for brushless DC motors: Influence on instant torque,” *IEEE Trans. Power Electron.*, vol.8, no.2, pp. 231-236, Apr.1993.