This article investigates the virtual third harmonic back electromotive force (EMF)-based sensorless drive method for high-speed brushless dc (BLDC) motors. Conventional zero-crossing point (ZCP) detection methods of virtual third harmonic back EMF require hardware low-pass filters and voltage comparators, causing serious phase lag. To avoid the undesired phase lag of hardware, the proposed method employs algorithmic oversampling technique to reconstruct the envelope of virtual third harmonic back EMF. Besides, the number of sampling points is dynamically adjusted according to the pulsewidth modulation duty ratio to guarantee the accuracy of ZCP detection. In addition, the influence of asymmetric motor parameters, i.e., phase resistance and inductance, on sensorless commutation is analyzed in depth. With asymmetric impedances, ZCPs of virtual third harmonic will deviate from their ideal positions. Consequently, the commutation events, which are searched based on ZCPs, will also be triggered at inaccurate positions and then the control performance will be deteriorated. In order to suppress the negative influence, a novel phase compensation method is proposed. All the theoretical analyses are validated by experiments at a 60 000 r/min BLDC drive platform.

中文翻译：

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考虑机器参数不对称性的基于虚拟三次谐波反电动势的高速 BLDC 电机无传感器驱动

本文研究了用于高速无刷直流 (BLDC) 电机的基于虚拟三次谐波反电动势 (EMF) 的无传感器驱动方法。传统的虚拟三次谐波反电动势的零交叉点（ZCP）检测方法需要硬件低通滤波器和电压比较器，造成严重的相位滞后。为避免硬件出现不希望的相位滞后，所提出的方法采用算法过采样技术来重建虚拟三次谐波反电动势的包络。此外，采样点数根据脉宽调制占空比动态调整，保证ZCP检测的准确性。此外，还深入分析了不对称电机参数，即相电阻和电感对无传感器换向的影响。具有不对称阻抗，虚拟三次谐波的 ZCP 将偏离其理想位置。因此，基于 ZCP 搜索的换向事件也会在不准确的位置触发，从而降低控制性能。为了抑制负面影响，提出了一种新的相位补偿方法。所有理论分析均通过在 60 000 r/min BLDC 驱动平台上进行的实验验证。