Research On Virtual-Flux Based Model Predictive Direct Power Control Strategy Of Three-Level PWM Rectifier

The three-level PWM rectifier has many advantages such as adjustable DC side voltage,bidirectional energy flow and high sinusoidal network side current.It can operate in unit power factor and it is suitable for high-power occasions.It is widely used in active filtering,electrical transmission and new energy power generation.At the same time,many applications and fields also put forward higher requirements for PWM rectifier technology.In this paper,NPC type three-level PWM rectifier is taken as the research object,and the model predictive direct power control algorithm without grid side voltage sensors is studied.The main work is as follows:The topology of NPC rectifier is described,and mathematical model in three different coordinate systems is given.The traditional voltage and current double closedloop control is simulated and analyzed.The problem of neutral point potential imbalance in DC side of NPC three-level rectifier is studied,and a neutral point potential balance control scheme is presented.The traditional direct power control of PWM rectifier is simulated and analyzed.Because of the hysteresis control,there are some problems such as unfixed switching frequency of rectifier bridge,high dependence on sensor conversion accuracy and sampling frequency,and abnormal fluctuation of reactive power in traditional direct power control.Aiming at the above problems,this paper combines model predictive control(MPC)control with direct power control(DPC)to form model predictive direct power control(MPDPC).MPDPC can make the switch frequency fixed and the abnormal fluctuation of reactive power disappear.Based on MPDPC,this paper analyzes the model predictive direct power control strategy based on virtual flux(VF-MPDPC)without voltage sensors on the AC side.The basic principle of virtual flux observer is analyzed,and a new flux observer is proposed.By using the switch function of rectifier bridge,AC side current and DC side voltage,the concept of virtual flux in the motor is introduced to reconstruct the AC side voltage.Then the simulation of MPDPC and VFMPDPC of three-level PWM rectifier is built in Matlab/Simulink environment.The simulation results show that VF-MPDPC control strategy can achieve good control effect.Finally,the experimental platform of NPC three-level PWM rectifier is built,and the relevant content of this paper is verified.There are 54 figures,11 tables and 99 references in this paper.