Research On Power Supply Capacity Of Distribution Network With Distributed Generation

The rapid development of economy makes power grid construction in China face dual pressure of energy crisis aggravating and load growth accelerating. Many provinces and cities usher peak load every summer. Although higher capacity-load ratio was adopted in the planning and design of distribution network, the phenomenon of loss of load still occurs during peak load periods. This is because load is uncertain and can not be predicted accurately. On the other hand, power supply bottlenecks exist in distribution network, as a result of which the power supply capacity can not meet the needs of users. The access of distributed generation(DG) can increase the power supply capacity of distribution network and relieve its power supply pressure to a certain extent. But because of the randomness of DG output, the connected DG will bring a series of uncertainty to distribution network. Therefore, it is necessary to research the power supply capacity in depth so as to ensure the safe and reliable operation of distribution network.Firstly, a multi-objective planning method for locating and sizing of multi-type DG is proposed based on the analysis of the investment and income brought by many types of grid-connected DG. This method analyses the timing characteristics of load and DG output as well as the environmental benefits of DG. The typical daily load sequence and the typical daily output sequence of DG per capacity have been calculated on the basis of the classification of daily load sequence. The mathematical planning model with the location, capacity and type of DG as the optimization variables is established and it can not only measure the economic benefits of DG objectively but also help different groups make decisions on the planning scheme of DG according to their own interests.Secondly, based on the uncertainty of DG output and the cyclical change characteristics of power grid load, this paper proposes a real-time evaluation method for power supply capacity of distribution network with DG. The method considers the situation that various types of DG in distribution network generate electricity complementally and obtains the future load and DG output through prediction technology. The optimization model is established using the maximum load that can be supplied by distribution network as objective function and the safe operation requirements of the system as constraint conditions. The model can give change curves of power supply capacity and power supply margin of distribution network for a period of time in the future, which allows dispatchers to take corresponding measures in advance according to the evaluation results to ensure the safety and reliability of power grid operation. Considering the situation that load growth in the same proportion may result in large errors, the relative growth rate is used here to construct load growth mode and a practical example is employed to verify the feasibility and effectiveness of the proposed method and model.Finally, from the perspective of the long-term growth of load, a calculation method for power supply capacity of distribution network based on mid-long term load forecasting is proposed. First, test various prediction models respectively with the historical data of different load points to find out the best prediction model of each load point. Then, superimpose the best prediction models to get the superposition model of the full load in distribution network. Finally, establish the mathematical model for the calculation of power supply capacity with the superposition model as the growth mode of load. Calculating the power supply capacity repeatedly using the model and eliminating the power supply bottlenecks in turn, the power supply bottleneck sequence which limits the improvement of the power supply capacity of distribution network can be obtained. The sequence can provide important recommendations for the planning and upgrade of distribution network.