**A Novel Method of Reducing Commutation Torque Ripple for Brushless DC Motor Based on Cuk Converter**

**Abstract**

Based on Cuk converter, a novel commutation torque ripple reduction strategy is proposed for brushless DC motor (BLDCM) in this paper. Output modes (buck-boost mode and boost mode) of the Cuk converter during commutation period and normal conduction period are altered by designing a mode selection circuit, which can reduce commutation torque ripple over the entire speed range. During the commutation period, Cuk converter operates in the boost mode to step up the input voltage of three-phase bridge inverter and then meet the voltage demand of commutation period, such that the commutation torque ripple can be reduced by keeping the non-commutated current steady. In order to improve the utilization rate of the converter, during the normal conduction period, Cuk converter operates in the buck-boost mode and the input voltage of three-phase bridge inverter is regulated by adopting PAM (Pulse Amplitude Modulation) method without the inverter PWM chopping, which can reduce the voltage spike damage to the motor windings caused by turn-on/off of MOSFET in the inverter and simplify the program of modulation method further. The experimental results verify the correctness of the theory and the effectiveness of the proposed approach.

**PROPOSED SYSTEM: **

In this paper, a mode selection circuit is designed to alter the output mode of the Cuk converter. During commutation period, Cuk converter operates in the boost mode and its output voltage can meet the voltage demand of commutation period, such that the commutation torque ripple can be reduced effectively by keeping the non-commutated phase current steady over the entire speed range. During normal conduction period, Cuk converter operates in the buck-boost mode and the input voltage of the three-phase bridge inverter is regulated by the PAM method without the inverter PWM chopping, which can reduce voltage spike damage to the motor windings caused by turn-on/off of MOSFET in the inverter, simplify the program of modulation method and improve the utilization rate of the Cuk converter. In order to reduce the commutation torque ripple in high speed range, DC-DC converter is introduced to increase the input voltage of the three-phase bridge inverter in. Z-source inverter is added and the required input voltage of the inverter is obtained by adjusting the duty cycle of shoot-through vectors to keep non-commutated phase current steady. However, the input voltage of the inverter is larger than the power supply voltage during both the normal conduction period and commutation period. In, during normal conduction period, the BLDCM is supplied by power voltage and the desired voltage for commutation period is adjusted by SEPIC converter. During commutation period, the SEPIC converter is applied by a switch selection circuit to suppress the commutation torque ripple. However, the converter is employed only in commutation period and the effect of commutation torque ripple suppression depends on dynamic response of SEPIC converter. In the field of commutation torque ripple reduction there are still several challenges for the existing methods. In order to avoid switching modulation methods, the commutation torque ripple reduction strategy should be applied over the entire speed range. In addition, the same modulation method should be adopted during both normal conduction period and commutation period. In order to effectively reduce the commutation torque ripple in the high speed range, DC-DC converter is required to step up the input voltage of the three-phase bridge inverter and meet the voltage demand of commutation period, meanwhile, the utilization of the DC-DC converter should be enhanced as far as possible.

**CONCLUSION **

This paper proposes a novel commutation torque ripple reduction strategy of Cuk converter fed BLDCM. In the proposed method, during the commutation period, the output modes of the Cuk converter are altered by the designed mode selection circuit to step up the input voltage of three-phase bridge inverter, such that the commutation torque ripple can be reduced by keeping the non-commutated current steady over the entire speed range. In conclusion, the proposed approach has the following advantages: 1) In this paper, Cuk converter operates in two different output modes by a designed mode selection circuit and different input voltages of three-phase bridge inverter is obtained, which provides the possibility to step up the input voltage of the inverter and then meet the voltage demand of the commutation period. 2) The proposed method can effectively reduce the commutation torque ripple over the entire speed range, which avoids the switch of modulation methods between high speed and low speed that may reduce the system stability, and simplifies the program of modulation method. 3) Since the inverter PWM chopping is not required during the normal conduction period, the voltage spike damage to the motor windings caused by turn-on/off of MOSFET in the inverter is reduced, and the utilization of the Cuk converter is enhanced.

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