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.