High-frequency signal injection (HFSI) is typically used for sensorless control of electrical machines at low speeds or standstill. In electrically excited synchronous machines (EESMs), the rotor circuit functions as a buck converter with high-frequency switching signals. These signals can be used, eliminating the need for additional injections. This article proposes a sensorless control method based on the rotor switching signal. The unipolar nature of the rotor modulation voltage is analyzed, and the gradient of the high-frequency current is calculated directly, without filters. The method considers fundamental current, magnetic cross-coupling, and saturation, enhancing accuracy and extending operation range. Experimental results on EESM test benches confirm the method's effectiveness.

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