Research On Optimization Algorithm In The Operation Of Distribution Systems

The implemention of automation control has a great significance on improving security reliability and economy level in distribution system operation. Against the background, this paper studies the basic theory and algorithm in distribution automation control, such as distribution power flow, network reconfiguration, capacitor switching. It hopes to enrich the theory and pratice in the field of distribution automation.This dissertation studies the method for weakly meshed distribution networks. For pure meshed networks, if the joint points (the first or end node of a branch) are given, the branches with a joint point are treated as link branches. With other branches treated as tree branches, an incidence matrix is formulated. Then the basic loop matrix is formulated by incidence matrix. If the joint points are not given, this dissertation uses the breadth-first search algorithm to get link branches. Then the first or end node of a link branch is appointed as joint point. With the same method as above, the basic loop matrix is formulated. So the joint points and independent loops formed mannually is avoided and it is convenient for practical applications. The logical distance (branch numbers) between the two end of joint points to the source node is nearly the same. The voltage difference of the two end of the joints is nearly zero and the algorithm can convergence in a few iteration number of times.For the capacitor problem, two algorithms are proposed. One is the action scope algorithm for capacitor switching. Firstly, based on the idea that optimal capacitor switching is Mvar balanced locally and radial operating in distribution networks, this dissertation proposes the node optimal condition and treats it as a heuristic rule. Not considering the capacity constraints of capacitors, this dissertation gets the action scope of each source and each capacitor. Secondly, according to two capacitor compensation basic rules, based on the action scope of source and each capacitor the real reactive injection current of capacitor is calculated with the capacity constraints. Finally, the capacitor switching banks are obtained. The other is an optimal capacitor switching algorithm based on the idea of backward/forward sweep algorithm. Firstly, radial distribution network is divided into many local trees by the breadth-first algorithm. For local trees the optimal solution can be obtained quickly by utilizing the local Mvar balance rule that reduces the solution space. Secondly, it gives an efficient algorithm considering the influence of local trees by analyzing its rule. Finally the optimization process is embedded in backward/forward sweep algorithm. For the above two algorithm, the first one is helpful for justification of installation banks and capacitor compensation by means of its action scope. The second one is faster than the first one and is suitable for practical application.For network reconfiguration problem, this dissertation presents a distribution network optimal reconfiguration algorithm of reducing the number of spinning trees. The result of distribution network reconfiguration must be a radial network and can be determined by the spinning tree method. Under this idea, a method that uses spinning trees and seeks an optimal reconfiguration result is proposed. Based on the optimal flow pattern, a feasible reference network configuration is determined. The ideal network and the method of determining it are also given. Based on these results, the rule that those switches must be closed is deduced while not affecting the optimal solution. Then, the number of spinning trees is notably deduced by dint of Minty algorithm. The time cost of finding the optimal solution can satisfy the needs for real-time operation. It avoids the local optimal solution in contrast to the heuristic method and is more efficient than artificial intelligence algorithm.A joint optimization algorithm of combining network reconfiguration and capacitor control is proposed for loss reduction in distribution systems. After network reconfiguration by reducing spinning trees, the capacitor switching is carried out for all the remaining trees by capacitor switching based on backward/forward theory instead of a minimum loss tree. By doing so, the optimization results may be obtained with high probability. After capacitor switching, the equation of estimating the loss change resulting from branch exchange is used to avoid the network reconfiguration after the capacitor switching in the alternate method. Then the calculation efficiency is improved. Based on the joint optimization algorithm, the action scope algorithm for capacitor switching is used to just if the rating capacity of capacitors can satisfy Mvar needs in their action scope. This can help for optimating the network and minimize the network loss.Finally, the distribution power flow containing wind turbines is introduced. Based on this, both network reconfiguration and capacitor switching with wind turbines are studied via the Monte-Carlo simulation.