Direct Torque Control Of Permanent Magnet Synchronous Motor Based On The New Stator Flux Observer

Direct torque control (DTC) is widely used in the field of AC speed regulationwith the advantages of simple structure, fast dynamic response and parameterdependentless. The stator flux observation is one of the important parts in the DTCdrive system of permanent magnet synchronous motor (PMSM). The accuracy of thestator flux observer directly affects the performance of the control system. The statorflux is calculated directly by the integration of the back-EMF in the stationarycoordinate of the traditional voltage-flux-observer model. Stator resistance which is atime-varied parameter is used in the calculation of stator flux. So, when the statorresistance is changed, the accuracy of the stator flux observation will be influenced.Meanwhile, stator current and stator voltage measurement error and integral initialvalue settings will lead to DC drift problems of the pure integrator. As a result, theaccuracy of the stator flux observer will be influenced. To solve these problems, anovel method combined adaptive stator flux observer with forward voltagecompensation is proposed in this paper.The problems of the traditional stator flux observer are analyzed in detail basedon the math model of PMSM and the principle of DTC. The influence of the statorresistance change and integral drift on the stator flux observer is studied. Andamplitude attenuation and phase deviation of the low-pass filter is also analyzed,which provides a theoretical basis for the design of the new adaptive flux observer.To improve the accuracy of the stator flux observation in the DTC systems, anadaptive stator flux observer is designed in the stationary coordinate based on thetraditional stator flux observer. The adaptive law of the stator resistance is designedaccording to Popov stability theory, which can ensure the stability of the stator fluxobserver. To inhibit the integration drift, low-pass filter is used to replace the pureintegrator. And combined voltage feed-forward compensation algorithm, the adaptiveflux observer can compensate the amplitude attenuation and phase shift of thelow-pass filter. A permanent magnet synchronous motor direct torque control systemsimulation platform is build and a simulation model of the new adaptive flux observeris designed. The simulation is studied in the case of stator resistance step change andstator voltage DC component. The simulation results show that the new adaptive fluxobserver can quickly and accurately track the stator resistance variation and inhibit the integral drift, which ensure the accuracy of the stator flux observer. And the observercan be run in the very low speed ranges, which effectively improve the low-speedperformance of the direct torque control system.