Research On Cooperative Control Of Renewable Energy Generators In Active Distribution Network And Micro Grid

In order to meet the requirements of social development, a lot of renewable generators are introduced into the power grid, which is become the inexorable trend of renewable energy development. The high penetration of new energy integration has been considered as an important feature of future smart grid. As the intermittent and randomness of new energy units like wind and photovoltaic (PV) generators, new energy generators don’t be considered as the friendly units to the grid. In this context, the cooperative control methods of high-destiny new energy generators are studied in this paper under active distribution network and micro grid environment respectively. The main work is as follows:1. Cooperative control problem of high-destiny new energy generators in active distribution networkThe high-destiny new energy generators are integrated into distribution network as distribution sources, which make the traditional distribution network become an active distribution network. In this environment, the main problem is how to achieve the cooperative control of output power of high-destiny new energy generators. At the meantime, the high demand of communication network caused by centralized control should be avoided. In this theme, the main work is as follows:1) Based on the distribution control, a cooperative control strategy is proposed. The total output power of PVs is controllable and the output power of each PV is distributed equally. In the proposed cooperative control strategy, only the local communication network is used, and only some PVs need to communicate with the upper level controller. So, the the high demand of communication network caused by centralized control can be avoided. At last, the requirement of communication network to make strategy validness is presented. The flexibility and self-organization of the proposed strategy is proved when some PVs connect or disconnect form the grid.2) Based on the above centralized control method, a free-center centralized control method is proposed. This strategy not only avoids the global information acquirement, but also can embedding the upper level controller into PV self-controller. So, the goal of free-center is achieved. In addition, an estimation method is proposed to get the maximum available power of PV, so the complex calculation for the maximum available power is avoided. Finally, based on the classical distribution network, the adaptability of the proposed free-center method on complex distribution network is proved.2. Cooperative control problem of high-destiny new energy generators in micro gridWhen the high-destiny new energy generators are introduced into micro grid which is on islanded mode, the stability of micro grid like frequency/voltage stability is decided by the characters of new energy generators because of the lack of synchronous generators. So the main problem in micro grid environment is to study the control strategy of new energy generators from the view of system stability. A wise method is to make the new energy generators have the characters like synchronous units. In this theme, the main work is as follows:1) A synchronized control strategy of double fed induction generator (DFIG) that can provide reserve capability and primary frequency support for micro grid is firstly developed. The proposed strategy doesn’t need measure external frequency and can make DFIG become a reliable frequency supporting point of micro grid. In addition, the proposed method can also cooperative with other distributed units conveniently. Finally, some time domain simulations also valid the effectiveness of the proposed method.2) The effect of synchronized control strategy on small signal stability is studied. A simple micro grid is considered as the study object. The micro grid based small signal stability performance is investigated under multiple operating conditions. The dominant eigenvalues which affect the small signal stability mostly is observed. Also, the effect of key controller parameters on dominant eigenvalues is studied. Furthermore, a method is proposed to identify the key controller parameters under the limits of system small signal stability. This method has strong robustness and avoids the frequent changing of parameters values under multiple operating conditions.