Brushless DC motor drives (BLDC) are finding expanded use in high performance applications where torque smoothness is essential. The nature of the square-wave current excitation waveforms in BLDC motor drives permits some important system simplifications compared to sinusoidal permanent magnet AC (PMAC) machines. However, it is the simplicity of the BLDC motor drive that is responsible for causing an additional source of ripple torque commonly known as commutation torque to develop. In this paper, a compensation technique for reducing the commutation torque ripple is proposed. With the experimental results, the proposed method demonstrates the effectiveness for a control system using the BLDC motors that requires high speed and accuracy.
- Brushless DC motor drives
- Torque ripple
- Trapezoidal back EMF
Fig. 1. The block diagram of the speed controller.
EXPECTED SIMULATION RESULTS:
Fig. 2. Experimental result in low-speed range (without compensation).
Fig. 3. Experimental result in low-speed range (with compensation).
Fig. 4. Experimental result in the high-speed range (without compensation).
Fig. 5. Experimental result in the high-speed range (with compensation).
Fig. 6. Experimental result in the high-speed range (with compensation).
Fig. 7. Sine wave response for the proposed speed controller.
This paper has proposed a compensation technique for reducing the commutation torque ripple in high-performance BLDC motor drives. The idea is to equalize the mismatched times of two commutated phase currents during the commutation intervals. In low-speed operation, a method to slow down the rising time of the on-going phase current can be a desirable technique. In high-speed operation, a method to slow down the falling time of the off-going phase current becomes a desirable strategy. However, it is not easy to implement the proposed strategies by using cost-effective one-chip microprocessors because it is needed to calculate the commutation time intervals within the sampling period in low and high speed operation. Instead of calculating the commutation time intervals, two dimensional lookup tables that describe the relation of the commutation time interval and the motor parameters such as the back EMF and the initial motor current, are used. For the experiments, a 16-bit microprocessor was used for the controller. Additionally a CPLD (1600 gates) was used to generate gate signals of the inverter and the commutation time signals. To verify the feasibility of the propose method, it is applied to the spindle motor drive control for the industrial sewing machines. The effects of torque ripple are particularly undesirable in the industrial sewing machines. They lead to speed oscillations which cause deterioration in the performance. In addition, the torque ripple may excite resonances in the mechanical portion of the drive system, produce acoustic noise. With the experimental results, the proposed method demonstrates the effectiveness for a high-performance control system using the BLDC motors that requires high speed and accuracy.
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