Analysis on the position estimation error in position-sensorless operation using pulsating square wave signal injection

This paper presents the theoretical analysis on the errors in voltage synthesis and position estimation due to the voltage distortion in position-sensorless operation. Especially, the pulsating square wave signal injection method into the estimated d-axis would be focused on, revealing the nature that the position estimation performance depends on the frequency of the injected signal. From the analysis, it would be shown that, in no load condition, the voltage distortion of one phase mainly has a 2
^nd
order harmonic component in negative sequence by the signal of the frequency to the same switching frequency of the inverter and it leads to position estimation error with 3
^rd
order harmonic component. In the case of a half frequency of the switching frequency or in case of heavy load conditions, the effect of inverter nonlinearity does not affect the position estimation error. Therefore, only the effect of cross-coupling inductances is reflected in these cases, and the position estimation error appears in the form of 6
^th
order harmonics. Simulation and experimental results verify the validity of the analysis.