Position error in sensorless control of brushless DC motor based on average line to line voltages

In position sensorless control permanent magnet brushless DC motor drives the estimation of position is prone to errors, the accurate prediction of this error helps us to correct the position error or to choose the application where the error can be acceptable. In this paper the accurate prediction of position error in sensorless method based on average line to line voltages and the effect of different parameters on the position error are presented. The main sources of error are signal processing circuits and machine parameters. The filters are inevitable in low cost sensorless techniques and winding impedance is inherent property of motor. At low speed and full load the voltage drop in winding resistance is comparable with induced back EMF, which causes a severe phase delay in generation of virtual hall signals. The Analytical prediction of phase delay caused by the winding resistance drop is presented. Understanding the principle of the sensorless operation based on average terminal voltages and parameters affecting the error will help in selection of motors for low cost applications like blowers, cooling fans and similar home appliances. Analysis for the same is carried out and the results concurs the analysis.