Optimal Commutation Error Compensation Strategy for High-Speed Sensorless Brushless DC Motors

In the control system of high-speed sensorless brushless dc motors (BLDCMs), the phase current lag caused by impedance characteristics cannot be ignored. To achieve optimal commutation, aligning the fundamental components of the phase-back electromotive force (EMF) with the phase current is necessary. However, this article reveals that short-duration clamping voltage pulses caused by diode freewheeling result in the extracted phase-back EMF fundamental signal leading the ideal sinusoidal back EMF, ultimately resulting in advanced commutation. Consequently, this article quantitatively calculates the advance angle induced by short-duration clamping voltage pulses and proposes an optimal commutation error compensation strategy. This strategy combines phase-back EMF reshaping, fundamental signal extraction based on an improved synchronous frequency filter (SFF), and a segmented successive compensation algorithm to converge the phase difference between the fundamental signals of phase current and reshaped phase-back EMF to zero, thereby eliminating the influence of short-duration clamping voltage pulses and achieving optimal commutation. Finally, experimental results validate the effectiveness of the proposed strategy.