Research On PWM Rectifier Of Three-Phase Four-Wire UPS

UPS is used to supply stable and reliable power for important loads in many industrial filed. High-powered UPS configuration usually consists of three phase PWM rectifier at the front-end and three phase inverter at the back-end. This paper mainly researched on the front-end PWM rectifier in online double conversion UPS.Firstly, this paper compared various PWM topologies and their applications, and then summed up the control strategies. Three-phase four-leg PWM rectifier is suitable to high power and high reliability required system for its strong fault-tolerance ability. Hereby, this paper chose the three-phase four-leg configuration for the front-end rectifier. The rectifier is controlled with direct current control strategy plus harmonic injection modulation.Secondly, this paper set up the mathematic modules of the three-phase four-leg PWM rectifier in a-b-c nature coordinate frame,α-β-γstable coordinate frame, and d-q-0 synchronous rotating coordinate frame respectively based on the on-off state space averaging method. And then these modules in different coordinate frame are comparatively analyzed.Then according to the modules in different coordinate frame, various control strategies of the adopted PWM rectifier are investigated. This paper particularly stressed on analyzing the control effect of the Proportion controller and Proportion-Integration controller. An adjusting method of PI parameters by Bode-diagram is proposed in connection with the PWM rectifier. Controllers are designed in d-q-0 coordinate frame.In addition, based on the instantaneous power theory, the paper redefined the virtual power to make it compatible with traditional power theory. And then the power flow in UPS is analyzed according to the virtual power. Control method of the three-phase four-leg rectifier is researched for the UPS application. An averaging power control method is proposed to realize the rectifier always working symmetrically even when the inverter works with asymmetrical loads. By the characteristic of PWM modulation, a research focused on the harmonic injection of the federal control between rectifier and inverter. The voltage utility ratio is improved through instantaneous extremum averaging injection manner.At last, the design procedure of the main parameters of the three-phase four-leg rectifier was given in detail. And then a bench test is set up based on the design.Simulation and experiment results are both given to verify the validity of the control strategy adopted in the paper.