High-Frequency Signal Injection Method Based on Duty Cycle Shifting Without Maximum Fundamental Voltage Magnitude Loss

High-frequency signal injection (HFSI) method is widely used in machine sensorless control in low speed operation range. The conventional HFSI methods are to superimpose high-frequency voltage signals onto the commanded stator voltage vector. Thus, the magnitude of the voltage used for machine torque production is sacrificed and these methods are not applicable for high-speed operation range. In this paper, a new HFSI method, in which high-frequency signal is generated by shifting the duty cycles between two neighboring switching periods, is proposed. This method allows injecting a high-frequency signal at half of the switching frequency without the necessity to sacrifice the machine fundamental voltage amplitude. This may be utilized to develop a new position estimation algorithm without involving the machine inductance in the medium- to high-speed range. As an application example, a new position estimation algorithm using the proposed HFSI method is developed and applied to a synchronous reluctance machine drive system. The proposed algorithm focuses on the medium- to high-speed range with the advantage of no filter needed for position information extraction and a machine-inductance-independent sensorless control implementation scheme is achieved. Experimental results are given to support the proposed new approaches.

I. Introduction

Electrical machine sensorless control has been studied extensively in the past decades in order to reduce the system cost and complexity. Many high-performance methods have been reported. Position sensing via high-frequency signal injection (HFSI) is widely used from standstill to low-speed operation range [1]–[21]. The conventional HFSI method, for example, superimposes a rotating high-frequency carrier voltage vector onto the commanded voltage vector [1]–[8]. The position information can then be extracted by evaluating the resultant current at the carrier frequency. Besides injecting a rotating voltage vector, alternating voltage carrier signal injected to a specific spatial direction may also be used for rotor position estimation [9]–[16].