| When DGs are introduced in distribution network,the network structure and load flow distribution of distribution network have been greatly changed.The randomness and intermittency of DGs make operational state of distribution network uncertain.Only optimize a certain state of system can't meet the requirements.More ever,in addition to the economy of the system,the reliability and security of the grid should be taken into account.It is difficult to obtain probability distribution of random variables,membership function and probability of scene in reactive power optimization base on probabilistic power flow,fuzzy mathematics or scene analysis.The interval analysis method,by contrast,can easily gain the interval parameter,with little subjective factor influence.However,in the current research of interval reactive power optimization,only the halfway point of network loss is optimized or only one objective is optimized,which can't make full use of interval information or can't make the system voltage quality meet the requirements.This paper analyze the uncertainty of the grid with interval mathematics and affine mathematics and propose an interval power flow algorithm base on complex affine arithmetic and Ybus gauss iteration method.The current interval multi-objective optimization algorithm is improved and be applied to the distribution network with DGs.Not only the network loss interval but also the voltage deviation interval is optimized,which can reduce the system-running cost as well as improve the voltage quality.Firstly,according to the demand of interval multi-objective reactive power optimization,this paper propose an interval power flow algorithm base on complex affine Ybus gauss iteration.The uncertainty of the DG output and state variables are described by complex affine and the interval power flow iterative equation in the form of complex affine is constructed by Ybus gauss method.Similar noise elements are merged,which can reduce the number of noise elements that come into being in the iteration process and improve the calculation speed,while maintaining the calculation precision.The method that can gain the affine polygon is proposed,through which amplitude and phase Angle angle interval of voltage complex affine can be figured out.Secondly,this paper improves the interval multi-obj ective optimization algorithm.On the basis of the mathematical model and algorithm of deterministic multi-objective optimization problem,the general mathematical model of interval multi-objective optimization problem is established.For the problem that the interval crowded distance calculation method in some research of interval NSGA-? algorithm would make faultage of the solution set happen,this paper propose a new method to calculate the interval crowded distance.At the first,calculate the crowded distance of each solution by NSGA-II algorithm as the initial value.Than take individual volume and overlap volume between individuals into consideration and amend the initial value.As a result,the final interval crowded distance is obtained.Lastly,the paper realizes interval multi-objective reactive power optimization in the distribution network with DGs.The mathematical model of interval multi-objective reactive power optimization of distribution network with DGs is established and the parallel PSO optimization method,whose accuracy is verified,is came up with as a reference method to calculate the objective function interval.Analyze the problem that deviation of interval center would happen when calculate loss interval and voltage deviation interval through voltage complex affine and amend the result by adjusting the complex affine multiplication.The example analysis shows that the methods proposed by this paper can not only take the nondeterminacy of DGs into consideration but also optimize the network loss and voltage,making the operating state of distribution network with DGs tend to be more economic,safe and reliable. |
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