Research Of Three-level PWM Rectifier Based On Improved Direct Power Control

Compared with the traditional diode rectifier, the PWM rectifier has many advantages such as sinusoidal and low harmonic of grid side current,adjustable power factor, reversibility of energy, DC voltage controlled, and so on.These features makes it have a good prospect in high-voltage transmission and distribution, frequency control for high voltage and power motor.In this thesis, the neutral point clamped three-phase and three-level SVPWM rectifier is studied.Firstly, based on the research of the model of PWM rectifier circuit, the operation state and control principle were analysised. At the same time, aiming at the topology of neutral point clamped three-phase and three-level rectifier, the principle of main circuit is analyzed in depth. On this basis, mathematical model of the three-level rectifier is established in three-phase static abc coordinate、two-phase static αβ coordinate and two-phase rotating dq coordinate. Then, deriving a diode-clamped three-level PWM Rectifier mathematical model based on the instantaneous power theory for the design, which provides theoretical basis for the design and optimization of three-phase three-level rectifier control system.Secondly,with the the three-level PWM rectifier based on the basis of a mathematical model of the instantaneous power control having been established, the traditional direct power control system architecture based on hysteresis is studied seriously. Then, for lack of this method, the new power control model to analyze ways to improve the hysteresis switching table design is used, thereby improving the control effect. However, the use of hysteresis comparator will make the rectifier switching frequency is not fixed, this thesis proposes a prediction based on direct power space vector control strategies to overcome this shortcoming. The control strategy combines power predictive control theory with space vector modulation technologies to replace the original comparator with hysteresis switching table to achieve a fixed frequency.Then, a three-phase three-level PWM rectifier control system is simulated in the PLECS simulation software and each of the three control methods is used in the simulation. The simulation results were in-depth comparative analysis.Finally, based on the above theoretical analysis, the validity of direct power is verified by experiment control strategy based on predictive, by experimental platform based on TMS320F28335. And through analyzing and solving the problems met in the debugging process, the indexes of the system performance was further improved.