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Sensorless Control of Permanent Magnet Synchronous Motor with Double Frequency Square Wave Voltage Injection

In the process of rotor position detection based on single frequency sinusoidal voltage injection in static reference frame, when filter method and direct calculation method are used to eliminate the dc component, the removal effect is not ideal and the result is easily affected by the change of inductance. A double frequency square wave voltage injection method was proposed to detect the rotor position at low speed. This method combines the advantages of high injected frequency of square-wave voltage injection method and simple signal processing of sinusoidal voltage injection method. The high frequency square wave signals with different frequencies are injected into the α and β axes respectively, and the corresponding high frequency response current is decomposed into the sum of sinusoidal signals of different frequencies by Fourier decomposition. After the high frequency signal is extracted, the position signal is demodulated by multiplying it with the fixed frequency cosine modulation wave. After passing through a filter, the four response currents containing the rotor position information are obtained, and the dc component is eliminated by the difference of the response current. Finally, the rotor position is estimated by using the two- phase type locked loop. The experimental results show that the proposed method is insensitive to the variation of inductance, and can accurately estimate the rotor position at low speed, with good stability and dynamic performance.