Research On Power System Load Flow, Reliability And Stability Containing Distributed Generation

In recent years, with the rapid growth of energy consumption, the centralized and single power supply mode has caused many environmental issues, energy problems, as well as economic issues, which have aroused extensive concern in the international community. At the same time in order to effectively improve energy efficiency and realize sustainable development of the electric power industry, our country must step up the development and use of Distributed generations (DG). DGs include photovoltaic cells, wind generation, battery storage, fuel cell, etc. These units are usually sited at or near consumers to meet specific needs, low investment cost, be able to track the load changes in time, as well as improve system reliability, etc.With the penetration of DG technologies, DGs have good application foreground in power systems.Based on the introduction of various types of DGs, a systematic study on planning for grid-connected DG system and its impact on the power system has an important practical significance and theoretical value.This dissertation devoted to the research on load flow, power system planning, reliability, and stability studies containing DG (mainly wind and solar energy). The major research work is outlines as follows:(1) How to forecast wind speed accurately is a difficult problem to evaluate the status of wind energy resources.The paper takes wind speed as investigative object. Wind speed forecast model is built on the base of Auto-Regressive and Moving Average time series model by virtue of wind speed's time-sequential and self-correlation. A long autoregressive residual error checking algorithm is applied for estimating parameters and calculating the model's order. Based on an actual wind speed data for testing, the proposed method for wind speed forecast is analyzed to exhibit the effectiveness. (2) Wind and solar power are two types of DG most widely used at present. When wind and solar power are integrated into distribution network, it has great effect on load flow.Therefore, it is necessary that wind and solar power be integrated in research in order to enhance the accuracy of the load flow calculation model. The paper presents an AC-DC parallel iteration algorithm of load flow. First of all, the main problems of load flow are concerned when wind turbines and solar battery are integrated into distribution network, and then, the power flow calculation model is built including DG. On the basis of them, the sensitivity analysis method for distribution network is simplified in order to analyze the state of system in fault mode. The effectiveness of the proposed method is verified by the test system calculation analysis.(3) On the basis of analysing the influence of network loss when DG access to distribution network, the site and size of DG in distribution network expansion planning is researched.The paper presents a new algorithm to optimize the site and size of DG based on integrating the use of Simulated Annealing (SA) and Particle Swarm optimal (PSO) algorithm.The proposed algorithm adopts Metropolis criterion to search for individual optimum value in the individual optimization process and its result becomes basis for the individual optimal solutions of next-generation groups.With the search for the progressive position, the optimal solution is gradually located in the vicinity of the optimal solution, and can get the optimal solution of the site and size problems of DG quickly.With two numerical examples the superiority of the proposed algorithm is demonstrated in comparison with the genetic algorithms, simulated annealing algorithm. The calculation results show that the feasibility and good searching performance of the proposed algorithm.(4) On the basis of considering the time sequence and self-correlation of the wind speed, a reliability evaluation model of wind farms integration in power systems based on the Monte-Carlo simulation approach is proposed in this paper. Basing on these, a new reliability evaluation model in generation and transmission systems containing wind farms is proposed on the premise of the power system safety operation, in which the maximum load supplying capacity of transmission systems is used as the objective function, and the proposed model can be used to assess the influence when wind farms are integrated into transmission systems. Some reliability indices are analyzed and calculated to reflect the effects of wind farms. (5) The paper builds a divided island model including DG of distribution network. The breadth-first search technology are used to solve the problem.In addition, the paper presents a new reliability evaluation model considering the DGs, which can handle the influence of DGs on the distribution system through failure mode and effect analysis method and the minimal path method for the calculation of the distribution system with DGs.The calculating results indicate that the distributed generation connected to distribution network can improve the reliability of the distributed system.(6) The impact of large scale wind power integration on small signal stability problem is studied. The paper takes the wind generator as investigative object. A mathematical model of wind power generation sets for small signal stability analysis is established, which could consider its shaft and pitch control.With the solution of the eigenvalues, the analysis of oscillation modes, damp ratios are performed when operation parameters change such as the output of wind power, the distance to integration and so on.