Design and analysis of analog filtering method for signal injection based sensorless control

In this paper, the angle estimation error in the signal injection based sensorless control using analog band pass filter (BPF) is analyzed. The analog BPF has been used to minimize a level of the injection voltage. However, the current which pass through the analog BPF is distorted and the sampled q-axis current is not zero even though the additional voltage signal is injected on the real rotor position. Because of that reason, the angle estimation error which has fluctuation components at three times or six times per rotation or the dc constant component can be incurred. Each cause of the components is studied from Fourier analysis of the modulated voltages by PWM inverter and the current responses. The shape of the angle error depends on the quality factor and the level of the injection voltage. The experimental results verify this analyses and the filter design guide to minimize the angle error is mentioned.