Switching Frequency Voltage Injection Method for Sensorless Control Using Current Derivatives in IPMSM Drives

In saliency-based sensorless control with switching frequency voltage injection, the accuracy of rotor position estimation is deteriorated by the injected voltage errors arising from pulsewidth modulation (PWM). To resolve this issue, current derivatives within an active voltage vector are employed for precise position estimation. Accurate measurement of current derivatives requires a sufficient active vector time, necessitating additional voltage injection in low-speed regions. Considering the increased losses from additional injection, this article proposes two types of voltage injection methods that ensure only the minimum active vector time without modifying the PWM scheme. In the proposed methods, the magnitude and direction of injected voltages are analytically determined by considering the angle between the injected and fundamental voltages. Consequently, the proposed injection methods reliably ensure the minimum active vector time regardless of the load conditions, thereby improving the position estimation accuracy. Experimental results under various operating conditions verify the effectiveness of the proposed methods.