Deadbeat Power Control Strategy Of PWM Rectifiers Under Unbalanced Grid Voltages

Pulsewidth modulation (PWM) rectifiers with the characteristics of sinusoidalgrid-side currents, controllable power factor, and bi-directional power flow, arewidely used in static reactive power compensators, active power filters, new energypower generation systems, etc. In practical applications, the access of single phasehigh power load and unbalanced distribution of three-phase loads will lead to theunbalanced grid voltages in power system. At this point, the control strategies whichare designed under balanced grid voltages will fail, and cause the grid-side currentsdistortion and dc-side voltage fluctuation. In more serious conditions, the unbalancedgrid voltages can cause system performance to deteriorate sharply, and even damagethe devices. Therefore, this paper conducts researches on the control strategy of PWMrectifiers under unbalanced grid voltages.According to the PWM rectifier topology structure, the mathematical model instationary frame is established. The traditional proportional resonant control strategyand its problems are researched. For the existing problems of the traditional controlstrategy, the deadbeat power control scheme under unbalanced grid voltages isproposed in this paper. Based on the proposed instantaneous power analysis method,both the novel grid-side power control (GPC) and novel grid-side and alternation-sidepower control (GAPC) are researched, which can avoid the positive and negativesequence decomposition of every unbalanced variables, and improve the systemperformance in certain extent. But the problems of the poor control effect of GPC andthe complicated calculation process of GAPC still exist. To solve these problems, thealternation-side power control (APC) calculation method is further proposed, whichcan simplify the calculation and improve the system steady state performance. At thesame time, in order to improve the system dynamic performance, the fully digitaldeadbeat controller is designed as the current inner controller, which can makegrid-side currents quickly track the reference currents. To improve the performance ofthe controller, analysis of the time delay influence on the controller is conducted andcorresponding compensation scheme is proposed.On the simulation and experiment platforms, both the traditional proportionalresonance control strategy and the proposed deadbeat power control strategy are verified. Simulation and experimental results show that compared with the traditionalproportional resonance control strategy, the proposed deadbeat power control strategycan effectively suppress grid-side currents distortion and dc-side voltage fluctuation,and have fast dynamic response. It demonstrates that the proposed scheme canguarantee good dynamic and static performance of the PWM rectifiers underunbalanced grid voltages.