Improved High Frequency Signal Injection Method Based on Fundamental Current Extraction for Permanent Magnetic Synchronous Motors

High-frequency-injection (HFI) method has good performance in position estimation during start-up and low speed operations. However, HFI has suffered from phase lag and torque ripples according to existing literature. Additionally, the injected voltage is distorted by the inverter nonlinearity effects, which will deteriorate the estimated position. In digital control system, time-delay of control period affects the accuracy of estimated position, thus the position error increases. This paper proposes an improved filterless HFI method based on fundamental current extraction (FCE) strategy. FCE method obtains fundamental frequency current as feedback current by subtracting high-frequency signals from sampling current, thus the torque ripples caused by high-frequency current component decreases. Besides, the influence of inverter nonlinearity and digital time-delay has been analyzed and a compensation method is proposed to eliminate the estimated position error. The simulation results verify the effectiveness of the proposed method.