Research On The Direct Torque Control Of Induction Motor

As a recently-developed high-performance speed-control technology for ACIM (Alternate Current Induction Motor), DTC (Direct torque control) can provide good dynamic performance by controlling the torque output directly. DTC utilizes the working operation of the voltage-type inverter to control the rotation and halt of the stator flux, thus to regulate the angle between the stator flux and the rotator flux. In this paper, a Motorola DSP 56F8346-based DTC closed-loop system for ACIM is constructed and studied.The state-of-art and further development trends of AC drive are firstly discussed. The principle of DTC is illustrated, and some common circular flux track control techniques are analyzed, and followed the detailed description of the design and implementation of the major modules of DTC system. By analyzing the dynamic mathematical model of the ACIM and the equations for torque and flux estimation, a brand-new algorithm is put forward for DTC of ACIM. With the algorithm, a linearization method is used to estimate the spatial voltage vetor, which is further used to control the radius and direction of the increment of stator flux, so as to drive the difference between the referenced torque and the actual torque, the difference between the referenced flux and the actual flux to dimilish. Due to no complex calculation such triangle function and coordinate transformation involved, the algorithm can fit the embedded applications best. As proved by the simulation experiment, the algorithm features good torque control results, and presents the advantages of little torque ripple and rapid torque response.A hardware experimental system for DTC is constructed with an existing Motorola DSP EVM (Evaluation Module) and a self-made power stage board. The detailed description of the hardware design and trial-and-error of the power stage board is included, such as the circuitry schematic, selection of components, and the calcution of some major circuitry parameters. The embedded software is also coded for the implementation of the algorithm. Some associated experiments are conducted and experimental results analyzed. Lastly, the paper is ended with the further research guide.