Carrier signal injection method in three shunt sensing inverter for sensorless AC machine drive

In this paper, the voltage signal injection at the half of the carrier frequency is proposed for sensorless control in a Three Shunt Sensing Inverter (TSSI). As the injection frequency in sensorless control, high frequency is preferred for a rapid angle estimation and small audible noise. However, the maximum sampling frequency for the current reconstruction is limited to the carrier frequency in TSSI. Using 120° OFF Discontinuous Pulse Width Modulation (DPWM) with the high carrier frequency, the average switching frequency is set as two-third of the carrier frequency and the injection frequency is the half of it. Since the switching loss of the d-axis injection is up to 32% larger than the one of the q-axis injection, the q-axis injection method is proposed. The switching loss, conduction loss, copper loss, and iron loss are analyzed and the power losses are compared according to the injection axis from the simulations and experimental results.