Research On AGC Capacity Requirement And Control Strategies Of Interconnected Power Systems

Automatic generation control (AGC) is one of the main technical means for the control of the modern power grid operation. To AGC real-time control, the control center must in advance determine AGC regulation capacity that should be reserved for regional system. Reasonable determined regulation certainty can ensure an adequate adjustable capacity, while reduce the cost of as much as possible. when AGC regulation capacity is determined, the control center would assigned the control tasks to each AGC power plant through AGC control strategy, and each AGC power plant would execute the instruction and regulate in accordance with appropriate control strategy. Reasonable AGC capacity reserve and effective AGC control strategy would significantly reduce adjustment costs and strengthen the AGC regulating effect. Since AGC costs account for a large part of the grid operating costs, effective AGC regulation has positive significance for energy-saving emission reduction and can make good economic and social benefits. However, existing study of the AGC control can not solved the corresponding problem. To this end, AGC capacity requirement and control strategy issues related are explored further and more systematically in this paper.Firstly, a more complete model of the history of AGC capacity needs is put forward based on the existing research on AGC capacity. The model comprehensively considers the impacts of the alternate track omission, AGC units cooperation and wind power generation units into the grid and other factors in the process of determining the real time history of AGC capacity needs, which allows determining the capacity requirements more in line with objective reality. The model, as a basis for forecasting demand for AGC to buy, is necessary for decision making to ensure that the AGC system put in or capacity purchased and actual demand achieve real-time balance.Then, the paper analyzes the following problems:the secondary regulation order for the power plant and the demand are reverse, the control cycles of the plants are not synchronized and the AGC support among regions are needed under large perturbations. Focusing on these problems, the paper proposes a series of more reasonable control strategies, including in-power plant, inter- power plants, and inter- areas three aspects.In AGC power plants, based on the analysis to the adjustment process of secondary regulation, the paper points out that as the longer cycle of secondary regulation, it often appears contradiction between the order of secondary regulation and the secondary demand during practical application in power plant, and under the contradictory situation the plant may execute the reverse order. Therefore, this paper presents that under the premise of being authorized by control center in advance and confirmed the need for changing secondary regulation order, the plant performs two new control strategies, real-time suspension of secondary regulation and real-time update of secondary regulation. The two control strategies could be selected flexibly at different requirements to ensure the plant have a corresponding capacity to respond a mutation in the secondary demand.In the process of AGC power plants implementing AGC orders from the control center, each power plant's cycle of AGC effective order is quite different. It results that the acceptation of effective order is not synchronized, which would make the traditional control strategy which assigns the total adjustment quantity according to the distribution coefficient can not effectively coordinate the AGC power plants. Meanwhile, control performance standard (CPS) indicator can be just controlled within the requirements. Moreover, the control strategy which pursues the best indicator will increase the amount of unnecessary regulation. This paper proposes a new AGC control strategy based on ultra-short term load forecasting and considering the AGC unit control command cycle to flexibility adjust the CPS indicator. The mathematical optimization model is established, which is solved by the optimization method combined Newton's method and SUMT interior-point method. The example indicated that the strategy can reach higher authorities to the better control effect on the reduced active control instruction.It is considered that the quality of frequency control differs between Chinese grid and other advanced grids, for giving full play to the advantages of interconnected power grid and ensuring the quality of frequency, a new method of AGC regulation responsibilities assignment among several regions is proposed. The principle is that when the frequency deviation |â–³f| is small, using the current type of regulation responsibilities assignment in order to ensure the fairness and reduce the bias of tie-line scheme; and when |â–³f| is larger, for the better frequency of the system, using the method presented in this paper to pursue the objective of frequency quality, not rigidly stick to a particular area load disturbance. By reunification of AGC responsibilities, it is guaranteed that the frequency could quickly recover and amount of AGC regulation and every region's reserve capacity is reduced.In short, this paper studies on the AGC capacity requirement and control strategies. Based on the existing related research, new AGC capacity requirement and control strategies which contain in- power plant, inter- power plants, and inter- areas are proposed. In accordance with the methods proposed to control and coordinate AGC action, it helps to AGC resources rational use, thus ensuring the quality of the frequency of the system to meet the requirements. This study would provide a theoretical basis for more secure, economic and quality operation of the interconnected power system.