This thesis proposes a sensorless direct torque control (DTC) of interior permanent-magnet synchronous motor (IPMSM) using square-wave-type stator flux injection at low speed region. Two representative methods are used to estimate the stator flux in DTC system: voltage model and current model. In general, the current model is used at low speed region and the stator flux and electromagnetic torque is estimated using d-q axis current and the rotor position. In current model, the position sensor such resolver or encoder is necessary to calculate the d-q axis current, and the position sensor increases the volume and cost of system while decreasing reliability due to its noise. To overcome the weakness which the position sensor is essential, a novel method to estimate the rotor position in DTC system using sinusoidal stator flux injection is proposed. In this method, however, not only the process of estimating the rotor position is complex, but also there is time delay because of using digital filters such band pass filter and low pass filter. In this thesis, as an advanced method, sensorless DTC of IPMSM using square-wave-type stator flux injection is proposed. Compared to injecting sinusoidal stator flux method, the process of estimating the rotor position is simplified and time delay is decreased because low pass filter is eliminated in the proposed method. The validity of the proposed sensorless DTC of IPMSM using square-wave-type stator flux injection is demonstrated by the simulation and experimental results.
