How to calculate the reference voltage vector is an important issue in space vector modulation direct torque control (SVM-DTC) of permanent magnet synchronous motor (PMSM). The effect of zero vector on electromagnetic torque during all speed range is analyzed on the basis of the relation between voltage vector and torque current component. And the analysis shows that in conventional DTC system of PMSM available voltage vector is only six which is the mainly cause of high ripple of torque. A robust SVM- DTC method of PMSM is designed in which the reference voltage vector is calculated with the flux position, error of torque and flux. The method is simple to implement and insensitive to motor parameters error. First order filter cascaded with high pass filter (HPF) is adopted to estimate stator flux accurately. The experimental results are carried out and show that the improved SVM-DTC has the advantage of simplicity, robustness and improved performance.
- Direct torque control
- Space vector modulation
- Torque ripple
Fig.1 Block diagram of improved SVM-DTC system
EXPECTED SIMULATION RESULTS:
a) Experimental waveforms of conventional DTC
b) Experimental waveforms of proposed SVM-DTC
Available voltage vector has only six which mainly causes high ripple of torque in conventional DTC. To maintain robustness and simplicity of conventional DTC system, a simple method of calculating amplitude and angle of the voltage vector is adopted in SVM-DTC. It requires only the torque and flux errors. The simulation and experimental results show that the proposed SVM-DTC scheme has excellent steady-state performance while retaining the merits of the quick dynamic responses, simplicity and robustness as in conventional DTC.
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