Short Circuit Analysis Of Distribution System With Distributed Generation

For less pollution during the process of generating power, higher efficiency and easier installation procedure, the Distributed Generation has been widely used in the power system. For the interconnection of distribution generation, the distribution system has changed from a single power and weakly meshed network to a multi power and multi loop one. Thus, the traditional short circuit calculation method of distribution system is no longer applicable. In the short circuit calculation, the distributed generation is only equivalent to the synchronous generator is inappropriate. As the output short-circuit current of the distributed generation and the load current is not very different, the load current can not be ignored during the short-circuit calculation. Therefore, studying the algorithm of short-circuit current calculation of the distribution system with distributed generation has some theoretical significance and practical value.Distributed generation can be divided into conventional generators and inverter-based generators, by its interface where it was connected to the distributed system. The equivalent model of short circuit calculation of conventional generators can be a equivalent impedance in series with a voltage source. There are mainly two control schemes used in practice of the inverter based distributed generation, the voltage control-based scheme and the current control-based scheme. Under the voltage control-based scheme, the generator can be equivalent by a impedance in series with a voltage source. Under the current control-based scheme, the generator can be equivalent by a current source.The virtual port is built in the point of failure, and the simulation circuit is connected to the virtual port to simulate a variety of short-circuit fault conditions. At the port the network is divided into a symmetric asymmetric network and a fault simulation network, and according to the circuit equations of the virtual port the equations for calculating short-circuit current is derived. Constant impedance is modeled of the load, combines the impedance of generator and the impedance of branch, the bus impedance matrix is formed. Based on the bus impedance matrix, the port impedance matrix is formed. Based on the bus admittance matrix of the fault simulation circuit, the bus admittance matrix of the fault simulation network is formed. In associated with open-circuit voltage of the virtual port, the short circuit current can be solved out. Then the bus voltages and branch currents can be calculated. The complex connection of sequence network can be avoid, and metallic short-circuit fault can be simulated accurately, and arbitrarily complex fault can be simulated using the proposed algorithm. The distributed generation has been fully considered in this paper. Ultimately, a short-circuit calculation of a33bus distribution system has been carried out, and the results demonstrated that the proposed algorithm is effective.