This paper presents a review of recently used direct torque and flux control (DTC) techniques for voltage inverter-fed induction and permanent-magnet synchronous motors. A variety of techniques, different in concept, are described as follows: switching-table-based hysteresis DTC, direct self control, constant-switching-frequency DTC with space-vector modulation (DTC-SVM). Also, trends in the DTC-SVM techniques based on neuro-fuzzy logic controllers are presented. Some oscillograms that illustrate properties of the presented techniques are shown.

Direct torque control of PWM inverter-fed AC motors - a survey

A method for estimating the rotor flux and speed of an induction motor based on adaptive control theory is presented. The method is applied to a direct field-oriented induction motor control without speed sensors. The influence of the parameter variation on the speed estimation can be removed by the proposed parameter adaptive scheme. The validity of the adaptive flux observer is verified experimentally. >

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DSP-based speed adaptive flux observer of induction motor

This paper presents a new direct power control (DPC) strategy for a doubly fed induction generator (DFIG)-based wind energy generation system. The strategy is based on the direct control of stator active and reactive power by selecting appropriate voltage vectors on the rotor side. It is found that the initial rotor flux has no impact on the changes of the stator active and reactive power. The proposed method only utilizes the estimated stator flux so as to remove the difficulties associated with rotor flux estimation. The principles of this method are described in detail in this paper. The only machine parameter required by the proposed DPC method is the stator resistance whose impact on the system performance is found to be negligible. Simulation results on a 2 MW DFIG system are provided to demonstrate the effectiveness and robustness of the proposed control strategy during variations of active and reactive power, rotor speed, machine parameters, and converter dc link voltage

/pdf/direct-active-and-reactive-power-control-of-dfig-for-wind-3hgltet7w2.pdf

Direct active and reactive power control of DFIG for wind energy generation

This paper describes a new approach to estimating induction motor speed from measured terminal voltages and currents for speed-sensorless vector control. The proposed approach is based on observing the instantaneous reactive power of the motor. The estimated speed is used as feedback in an indirect vector control system. The described technique is very simple and robust to variations of motor parameters. The new approach is not dependent upon the knowledge of the value of the stator resistance, nor is it affected by stator resistance thermal variations. Furthermore, pure integration of sensed variables, in principle, is not required at all. Therefore, this new method can achieve much wider bandwidth speed control than previous tacholess drives. The effectiveness is verified by simulation and experiment. >

Robust speed identification for speed sensorless vector control of induction motors

A speed estimation method for an induction machine and its application to a flux observer-based field orientation (FOFO) control system proposed previously is presented. The motor speed is estimated on the basis of the difference between two flux estimators. The convergence of the method is analyzed, and a novel pole assignment method is proposed. The speed estimator is applied to the FOFO controller. The system has been implemented using a DSP, and some laboratory experiments showing that the speed-sensorless FOFO operates with enough stability and has a strong robustness to rotor resistance variation are reported. >

Speed sensorless field orientation control of the induction machine

Mechanical speed measurement used to be an undesired necessity for inverter-fed induction machines. A possible way of calculating the exact speed without mechanical devices is presented. In addition, a simplified algorithm that is applicable for drives that do not demand high dynamic speed control performance (e.g., fans and pumps) is described. The control scheme is based on the analog basic version of direct self control (DSC) of inverter-fed induction machines and needs only a few additional operational amplifiers for signal processing. The performance, including start-up of an already rotating drive, is documented. >

G. Gierse

Papers

Direct self control (DSC) of inverter-fed induction machine: a basis for speed control without speed measurement