Enhancement of output voltage using current shaping in sensorless AC machine drive

In a motor drive system using the voltage source inverter, a dead time is normally inserted to prevent a short circuit. The dead time causes an error between an output voltage and reference voltage. Because of the error, a back-emf based sensorless method cannot be applied to a low speed area. The conventional dead-time compensation method adjusts the timing of the gating signal according to the polarity of currents and the sequence of signals. But there still exists the voltage error in the low current at low speed. This paper analyses the conventional dead-time compensation method and the voltage error in the operation area. Then this paper proposes a method which can reduce the error. In order to rapidly pass the area with the high voltage error, the current reference is adjusted and the pass-over time is reduced. Therefore, the voltage error can be also reduced with the proposed method. The adjusted current references have no effect on the torque reference. So there is no additional torque ripple instead of the distorted phase current by the proposed method. Experimental results proved that the proposed method reduces the voltage error and improves the performance of the back-emf based sensorless method.