Study Of SRM Sensorless Control System Based On An Improved Current Gradient Method

Switched reluctance motor(for short SRM) is a new type of speed regulating motorthat has the advantages of both AC regulating system and DC regulating system. It is anew generation of stepless speed system after variable frequency speed control system andBLDCM speed control system. SRM has some advantages, such as simple and firmstructure, wide range of speed regulation, excellent speed control performance, highefficiency and high reliability. So SRM is considered to be a milestone in the process ofelectric drive system development. For SRM speed regulating system usually operates inself-synchronous state, the rotor position angle is needed when operating in speed orposition loop control. The rotor position angle usually is detected by position encoder,which not only increases equipment cost and complexity of system structure but alsoreduce the reliability of system, at the same time reduce speed control performance forlimited resolution ratio of position encoder. And sometimes position encoder cannot beinstalled in some special work environment. These problems make SRM sensorlesscontrol a research hotspot.In this paper, firstly research and analyse typical position estimation method by phasecurrent gradient and external signal injection, and summarize problems in the two methods,then put forward a new position estimation method by phase current gradient, in whichabsolute reference position can be calculated by detecting specific current curve on theboth side of lowest inductance sector. The paper introduces the SRM structurecharacteristics and working principle, demonstrates the principle and control method ofproposed method, establishes nonlinear inductance model of SRM, at the same timeestablishes the simulation model of typical double loop system and proposed sensorlesscontrol system by MATLAB software.Simulation result coincides with theoretical analysis, and the proposed new positionestimation method by phase current gradient can estimate position and speed exactly. Atlast, experiment of basic control method and typical current-speed double loop system arecompleted, and the primary experiment of sensorless control system is carried out with control chip of DSP TMS320F28335.