| Due to the rapid development of human civilization,the traditional single energy network gradually can not meet the needs of production and life.Smart distribution grid is one of the hot spots in power system research,and it is the future development trend of power grid.A fundamental feature that differentiates smart distribution grid from traditional distribution network is that it supports a large number of distributed generation access to and the structure,power loss and voltage distribution in distribution network have undergone great changes.Power flow calculation is one of the basic electrical calculations keen on power system operation dispatchers and plays an important role in the stable operation of power system.Therefore,power flow calculation is the basis for the study of smart distribution grid with a high proportion of clean energy.Firstly,the impact of distributed generation on the distribution network is studied in this thesis,and the power flow calculation models of various electrical components and distributed generation in the distribution network are established.The application of Newton’s method in traditional power grids and power grids with distributed generation and its advantages and disadvantages are analyzed.The sensitivity of Newton’s method to initial values is studied.The convergence theorem of Newton’s method of power flow calculation is put forward to determine whether the initial value can make the power flow equation convergence.If the initial value is feasible,the number of iteration times of the power flow calculation is estimated by the maximum iteration number estimation theorem.According to the two theorems,whether the selected initial value can make the power flow calculation converge can be judged by the two theorems to avoid the redundant calculation caused by the random selection of the initial value.Through the simulation on the IEEE standard node system and the actual power grid,the correctness and practicability of the proposed theorem are verified.Secondly,aiming at the complex Jacobian matrix and the slow convergence rate of the traditional Newton’s method,a new improved Newton’s method is proposed for power flow calculation and a detailed derivation of the algorithm is given.The proposed improved Newton’s method has the following advantages:most of the non-zero elements in the Jacobian matrix of the algorithm are constant,which not only reduces the amount of memory occupied by the algorithm,but also greatly reduces the calculation of the Jacobian matrix in each iterate.And further improves the convergence rate of power flow calculation.Taking the Tongliao Naiman 16-node distribution network as an example,the improved Newton’s method is better than the traditional Newton’s method in terms of convergence and calculation speed by simulating the two methods.Finally,the question of power flow calculation when a large number of distributed generations are connected to the distribution network is studied,and the processing methods of distributed generation with different node types in the improved Newton’s method are given.The power flow calculation of improved Newton’s method with a large number of distributed generations is proposed,and verified the correctness and superiority in USA PG&E69 nodes.Then,taking Tongliao Naiman distribution network as an example,the influences of the different number,location and type of distributed generations on the proposed algorithm and the traditional Newton’s method are compared.It is verified that the improved Newton’s method not only has fast convergence but also has good robustness,not only has fast convergence but also has good robustness,can better deal with the smart distribution grid with high proportion of clean energy. |
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