A 12-Step Asynchronous PWM Scheme for High-Speed Brushless DC Drives With Commutation Compensation

The 150 (degrees) mode 12-step control (150-TSC) is suitable for high-speed drives since it can generate a quasi-sinusoidal current waveform compared with the conventional 120 (degrees) mode six-step control. However, for high-speed brushless direct current drives, the relatively large commutation angle of 150-TSC will cause a noticeable phase delay error. Additionally, the low switch-to-fundamental ratio will cause significant pulsewidth modulation (PWM) delay, which leads to large current oscillation and ripple. In this article, an asynchronous PWM scheme is proposed for 150-TSC to eliminate PWM delays. A phase delay error compensation method based on stator current is further proposed. The optimal phase advance angle is generated for minimum stator current magnitude with the help of the gradient descent optimization algorithm. A quasi-sinusoidal phase current can be achieved and the current harmonics can be reduced. The effectiveness of the proposed strategy is verified by experimental results.