Additional Average Torque Enhanced High Efficiency Sensorless Method by Using Variable-Axis High Frequency Current Injection

In this article, the phenomenon of the additional average torque produced from high frequency (HF) current injection is first revealed and a novel high efficiency and robust variable-axis HF injection based sensorless method for interior permanent magnet synchronous motor (IPMSM) utilizing the discovered phenomenon is proposed. First, the production mechanism and characteristics for the additional average torque are introduced and analyzed. Besides, the stability margin and the rate of convergence for variable-axis HF injection based sensorless method are analyzed, and a robust position tracking performance is achieved with the proposed sensorless method by synthesizing signals from both <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i>- and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i>-axis. In addition, to maintain the signal-to-noise ratio (SNR) for position observer under variable-axis injection condition, a compensation-based HF SNR controller is proposed. The validity of the HF SNR controller and the performance of the proposed variable-axis HF injection based sensorless method are verified with experiments. The experimental results also prove the ability of efficiency improvement in a wide range of operation conditions with the proposed method.