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This paper presents a new direct torque controlled space vector modulated method to improve the sensorless performance of matrix converter drives using a parameter estimation scheme. The flux and torque error are geometrically combined in a new flux leakage vector to make a stator command voltage vector in a deadbeat manner. A new sensorless method of estimating the rotor speed, flux, stator resistance, and rotor resistance is derived and verified with experimental results. Common terms in the error dynamics are utilized to find a simpler error model involving some auxiliary variables. Using this error model, the state estimation problem is converted into a parameter estimation problem assuming the rotor speed is constant. The proposed adaptive schemes are determined so that the whole system is stable in the sense of Lyapunov. The effectiveness of the proposed algorithm is verified by experiments. Index Terms--AC-AC power conversion, AC motor drives, observers.

In this paper, an improved direct torque control (DTC) method for sensorless matrix converter drives is proposed, which is characterized by minimal torque ripple, unity input power factor, and good sensorless speed-control performance in the low-speed operation, while maintaining constant switching frequency and fast torque dynamics. It is possible to combine the advantages of matrix converters with the advantages of the DTC strategy using space-vector modulation and two PI controllers. To overcome the degrading of dynamic torque response compared with the basic DTC method and the phase-current distortion due to the nonlinearity of the matrix converter, an overmodulation strategy and a simple nonlinearity-compensation method using PQR transformation are also presented. Experimental results are shown to illustrate the feasibility of the proposed strategy. Index Terms--AC motor drives, ac--ac power conversion, adaptive observers, induction motor drives.

This paper presents a new sensorless vector control system for high-performance induction motor drives fed by a matrix converter with nonlinearity compensation. The nonlinear voltage distortion that is caused by commutation delay and ON-state voltage drop in the switching devices is corrected by a new matrix converter model. A reduced-order extended Luenberger observer is employed to bring better response in the whole speed operation range, and a method to select the observer gain is presented. Experimental results are shown to illustrate the performance of the proposed system. Index Terms--AC-AC power converter, ac motor drives, observers.

A direct torque control algorithm for three-level inverter-fed induction motors is presented. Basic voltage selection methods similar to two-level inverter provoke some problems such as stator-flux drooping phenomenon and undesirable torque control deterioration appeared, especially at low-speed operation. To overcome these problems, an algorithm with the basic switching sectors subdivided and intermediate voltage vectors applied is proposed in this paper. This algorithm basically considers applications in which direct torque-controlled induction motors are fed by three-level inverters with maximum switching frequency lowered around 1 kHz. An adaptive observer is also employed to bring better responses at the low-speed operation, by estimating some state variables and motor parameters which take a deep effect on the performance of the low-speed operation. Simulation and experiment results verify effectiveness of the proposed algorithm. Index Terms--Direct torque control, induction motor, low-speed operation, three-level inverters.