Reduction of injection voltage in signal injection sensorless drives using capacitor-integrated inverter

In signal injection sensorless drives, the injection voltage can´t be reduced under a certain value. The lower limit of the injection voltage mainly comes from the inverter nonlinearity that distorts the injection voltage and degrades the position estimation performance. After analyzing the inverter nonlinearity during the voltage injection, it is revealed that the parasitic capacitances of IGBT switches have a positive effect on sensorless control. Based on this analysis, this paper proposes a method to reduce the injection voltage by connecting additional capacitors to the inverter output. Simulation and experimental results are provided to verify the effectiveness of the proposed idea. In the experiment, using the capacitor-integrated inverter, the injection voltage can be reduced to less than a half without degrading sensorless control performance.