Research On Sensorless Direct Torque Control Of Permanent Magnet Synchronous Motor Fed By Three-level Inverter

It has become a research hotspot in power drive field of high-voltage large-capacity AC drive technology based on multilevel inverter in recent years. At the same time, permanent magnet synchronous motor(PMSM) is widely used in draught fan, railway and aerospace in the field of speed regulation for its advantages such as small volume, low inertia, and high efficiency. Compared with field-oriented control(FOC), direct torque control(DTC) is received great attention for its simple structure, fast response, and robustness against motor parameter variation, but there are some drawbacks like high torque ripple, high stator voltage and current harmonic contents and variational switching frequency resulted in conventional direct torque control system.The PMSM drive system is discussed in this paper as the research object, which is supplied by a diode-clamped three-level inverter. First of all, the structure and working principle of the three-level inverter are analyzed on the basis of the mathematical model of PMSM is established and the theory and implementation method of direct torque control are grasped. In order to decrease the torque and flux ripple, direct torque control strategy based on the predicted voltage space vector is discussed in detail, and aiming at neutral-point voltage unbalanced issue, the centrosymmetric seven-segment modulation strategy starting with negative small vectors is adopted. Then the accuracy of space vector pulse width modulation(SVPWM) algorithm and the superiority of three-level inverter are confirmed using Matlab/Simulink, which is contrasted with two-level inverter.The cost of the overall system is increased as well as the reliability is reduced because of the presence of mechanical sensors. To overcome those problems, sensorless control method of PMSM based on sliding mode observer(SMO) is proposed to realize position and speed estimation with the traditional sign function replaced by a saturation function in this paper.In this paper, the validity of the proposed control scheme for the closed-loop control system of PMSM is verified through simulation preliminarily based on the theory of three-level inverter and direct torque control, combining with sensorless control technology.Finally the experiment platform of three-level inverter for AC speed regulation is designed and built, and software control procedures are written based on the TMS320F2812, the experiment is carried out of PMSM fed by a three-level inverter, whose results are consistent with the theoretical analysis and simulation results, verifying the control strategy is feasible.