Research on the rectifier control method in drive system

The selection of oriented vector control method for three-level PWM rectifier is an important factor for getting stable DC voltage. Because the observer has an uncertain initial value, and the rectifier has a large start-up current which may lead to the system failure, while using the virtual flux oriented vector control method for three-level PWM rectifier. For this reason, the grid voltage oriented vector control strategy was adopted to achieve a more effective control on the rectifier. However, the complex mathematical model of this method makes the controller designed difficultly. As the neutral point voltage balance of three-level rectifier can get a good control effect throughout the entire control process, the average current of the neutral point was regarded as zero. Besides, transforming symmetric three-phase parameter to constant DC parameter through appropriate coordinates transform can change the three-phase nonlinear system with time-variable issue into two-phase linear system, and the rational simplification of rectifier model was presented according to the project requirement, which has laid a foundation for the design of controller so as to make it easy for the selection of the PID controller parameters. At last, an effective control on the DC bus voltage and the grid power factor was achieved.