Research On The Coordinated Control Between AC/DC Grid And AGC

Compared to traditional AC transmission, DC transmission has been used widely in power system because of its controllability and application in the case of long-distance and high-capacity transmission. AC/DC grid, combined the advantage of AC and DC transmission, has been put into operation gradually. AGC(Automatic Generation Control), as an important method to keep the frequency stable, has been widely applied in interconnected power grid. To utilize DC transmission's controllability to improve the performance of AGC, researching the coordinated control between AC/DC grid and AGC will make great significance. For the coordination between AC/DC grid and AGC, the main results of this paper are as follows:1. The method of HVDC's participation in primary frequency control has been discussed. When the frequency deviation of the area that DC joins in exceeds the threshold value, then DCs participation in primary frequency control is launched. A proportional component is placed after frequency deviation of one area. Its output, as the deviation signal of HVDC power modulation, accumulates the reference value of HVDC power and then turns to be total signal. Finally, the validity of this mode has been verified by simulation.2. The mode that HVDC assists AGC has been proposed. When the disturbance of one area took place, HVDC would participate the secondary frequency regulation of the area after its primary frequency control finished. The AGC of disturbed area assigns part of its instruction to HVDC, that is to say HVDC delivers part of disturbance to another area, which makes both ends of HVDC share the perturbation. Related model has been constructed and strategy has been discussed for this mode. Furthermore, it has been studied that if the area that doesn't has disturbance should be informed in advance while the instruction is being dispatched to HVDC. Simulation has indicated that the result of the mode that HVDC assists AGC under the case that other area is informed is better.3. In order to make HVDC take multiple areas into account, an upper coordinated controller is designed above HVDC. The upper controller considers the unbalance of both areas, and then assigns the power deviation instruction to HVDC. Meanwhile, the instruction is informed to both areas to improve their response speed. Besides, for the coordination with the effect of the upper DC controller, the AGC of these areas uses PROP to distribute its order to those generators that belong to the same area as AGC, Finally, the results of those modes in different situations were compared by simulations, and the conclusion was drawn that the mode that HVDC is dispatched by the upper coordinated controller can not only make the active power output of these generators in respective area change synchronously, but also improve the dynamic performance of power system and be suitable for more cases.