Study On Reliability Evaluation And Reconfiguration Of Distribution System With Microgrids

In recent years, with the increasing depletion of conventional energy sources, the transformation of the "energy" is in full swing around the world. Electrical power, as the most widely used energy, is difficult to stay out. Under the current circumstances, smart grid becomes one of the means in this power reform wave.The optimal combination of renewable energy generation and power grid is one of the symbols of the smart grid. Limited by the diversification of renewable energy generation in the form, as well as the complexity of the control mode, however, distributed generation technology has always been difficult for the promotion and application of large area use. It is still far away from the green energy target. In this background, in order to maximize the use of the advantages of distributed generation technologies in economic, energy and environment, advanced power electronic technology and control theory are introduced to establish microgrid concept.Microgrid is a complete subsystem with power generation and distribution system, which is generally managed and controlled as a whole self-controlled unit in the distribution network. Microgrids are characterized by autonomy, stability, compatibility, flexibility and economy, it can be connected to or isolate from large power grid in a rapid and seamless fashion. Large power grid and the DGs in microgrid supply electrical energy to loads jointly, but once there are failures or power quality problems in large power grid, microgrid will isolate itself from large power grid by its central control system and slip into an autonomous operation mode, then only DGs provide loads power supply. Microgrid can be automatically connected to large power grid until the problem resolved.To achieve fast and flexible transition between these operation modes, microgrid is equipped with a large number of static, power electronic based switches. Similarly, there are a lot of sectionalizers and tie switches for realizing flexible operation and reducing the range of failures. This paper has done some studies on the reliability assessment and reconfiguration of distribution system with micro-grid based on these switches, the main study can be summarized as follows:⑴The micro-grid components, and the structure, control, operation mode and their characteristics of distribution system with microgrids are analyzed. The intrinsic relationship between the reliability indexes of distribution system with microgrids is analyzed.⑵There are a lot of equipments in the distribution system. Among them, switch has different functions in the procedure of reliability evaluation. A switch factor model is built based on its characteristic and influence scope in reliability evaluation process, then the conceptions of rank and zone are defined to reduce the complex distribution system, a switch oriented simplified topography of distribution system is built, and a new numbering principle and a switch auto generating algorithm are raised according to the switch oriented simplified topography of distribution system with microgrids.⑶A switch oriented simplified model of reliability evaluation of complex distribution system with microgrids is discussed based on the switch factor model. The minimal path method and the switch auto generating algorithm are used to calculate load point reliability indices directly without network-wide computing, when we only care about the level of a load point reliability and not want to know the status of the other load point reliability, the method is relatively simple and effective.⑷Micro-grid contains many types of micro-source, their control methods are different from each other. The reliability evaluation of distribution system with microgrids considering its power control mode is discussed in this paper. The positive effect of microgrid power control mode to the distribution system reliability is analysd.⑸The wind-solar hybrid power system(WSHPS) is generally used in the off-grid microgrid. This paper presents a probability tree method to evaluate the reliability of WSHPS in which its operation and control mode, configuration are fully considered. Then the monte-carlo simulation method is used to evaluate the reliability of the off-grid microgrid based on the FMEA method.⑹A reliability based reconfiguration model and algorithm of distribution system with microgrids is discussed. The model is eatablished based on a weighted combination of the specific system reliability index which is used as the objective function in the model. A new switch exchange algorithm based on the reliability is designed, and the reconfiguration of distribution network with microgrids based on this algorithm is studied.