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Advanced Electric Drives: Analysis, Control, and Modeling Using MATLAB/Simulink by Ned Mohan

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9Direct Torque Control (DTC) and Encoderless Operation of Induction Motor Drives

9-1    Introduction

Unlike vector-control techniques described in previous chapters, in the direct-control (DTC) scheme, no dq-axis transformation is needed, and the electromagnetic torque and the stator flux are estimated and directly controlled by applying the appropriate stator voltage vector [1–3]. It is possible to estimate the rotor speed, thus eliminating the need for rotor speed encoder.

9-2    System Overview

Figure 9-1 shows the block diagram of the overall system, which includes the speed and the torque feedback loops, without a speed encoder. The estimated speed ωmech,est is subtracted from the reference (desired) speed c9-math-5001, and the error between the two acts on a PI-controller to generate the torque reference signal c9-math-5002. The estimated speed generates the reference signal for the stator flux linkage c9-math-5003 (thus allowing flux weakening for extended range of speed operation), which is compared with the estimated stator flux linkage c9-math-5004. The errors in the electromagnetic torque and the stator flux, combined with ...

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