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

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 ω_mech,est is subtracted from the reference (desired) speed , and the error between the two acts on a PI-controller to generate the torque reference signal . The estimated speed generates the reference signal for the stator flux linkage (thus allowing flux weakening for extended range of speed operation), which is compared with the estimated stator flux linkage . The errors in the electromagnetic torque and the stator flux, combined with ...