Research On Direct Torque Control Algorithm For Switched Reluctance Motor

Switched reluctance drive system (SRD) is a new speed control system which has been developed rapidly in recent decades. It has simple structure, flexible control, high reliability, wide speed range, etc. However, it has large torque ripple because of its double-salient pole structure and magnetic saturation. Moreover, the torque ripple suppression effect of traditional control strategies is not obvious. In order to improve system performance, this dissertation, from the perspective of control strategy, carries out the study of SRD and presents the design of the related hardware and software for experimental platform, which aims to apply the ideas of direct torque control (DTC) to SRD.This dissertation introduces the characteristics and working principles of SRD at first. Some basic equations for theoretical analysis are given. We discuss the mathematical models of switched reluctance motor (SRM) by using these basic equations. It shows that the SRM is a highly nonlinear electromechanical energy conversion device. With the quasi linear model, the working characteristics of SRM are obtained, and four kinds of SRM control strategies are analyzed. There are significant differences between DTC and traditional control methods. The stator flux linkage vector is approximated for round, so DTC has lower torque ripple. After compared the advantages and disadvantages of four kinds of control strategies, the SRD control algorithm will adopt the DTC.Reference to the thought of direct torque control technology for traditional AC motor, this dissertation describes the principle of DTC for SRM in detail, especially the space voltage vector selection, coordinate transformation and the establishment of the switch table. A nonlinear model is given for flux and torque calculation, which is set up with curve fitting method. Based on the above theory research, an experimental platform is established, which uses DSP as the core. All the modules of hardware and software are briefly introduced. Finally, in the MATLAB simulation environment, the simulation system of DTC for SRM is built. The simulation results show that the direct torque control can effectively reduce the torque ripple.