Research On The Operating Characteristics And Controlling Technology Of The Low Voltage Microgrid

At present, issues about energy and environment have become a key factor restricting social development. Distributed generation can achieve the win-win situation of energy saving and being environmentally friendly; therefore, it gradually becomes an important research orientation of the power industry. However, distributed generation has many deficiencies. The concept of microgrid was brought into being to solve the contradiction between the power system and the connection of distributed generation, and to give full play to the potential of distributed generation, and it has gradually become a hot topic of research at home and abroad. This paper mainly focuses on the research into the operating characteristics and controlling technology of low-voltage microgrid, and the main contents are as follows:First, the operation mode and controlling requirements of a typical microgrid are deeply analyzed, and a brief introduction of the distributed generator, energy storage devices, switches, power electronic devices, communications technology and characteristics of load is given.Second, on the basis that most of the distributed generators in microgrid are of the inverter-type, this paper mainly focuses on three commonly used controlling methods of distributed generators:constant power control, constant voltage/constant frequency control and drooping control. The conclusion is that different distributed generators and different operating mode of the microgrid system require different controlling methods. On this basis, three commonly used microgrid system controlling modes are researched, i.e. master slave control, peer-to-peer control and hierarchical control, with detailed analysis of implementation methods of the three controlling methods and their characteristics. Built on the basis of theoretical analysis, and based on Matlab/Simulink simulation platform, the simulation model of V/f control and PQ control system of microsources are built. Besides, a simple structure of microgrid simulation model containing two microsources is established. Simulation about part of the characteristics of grid-connected mode and islanded mode of microgrid is made using master slave control, and the simulation data verifies the effectiveness of the microsources controlling method and the microgrid controlling strategy.Finally, the necessity and feasibility of the development of DC microgrid are analyzed aiming at the problems of AC microgrid operational control. This paper researches on operating characteristics of the DC microgrid on the basis of analyzing the basic structure of the DC microgrid. The control of energy storage devices and appropriate use of load shedding measures in the system have an important significance to the stable operation of the DC microgrid. In this paper relevant research has been deeply made, and in different operating modes the paper provides controlling strategy of the energy storage system and specific method of load shedding in DC microgrid when the storage is inadequate or the system is in a long period of island running. It is found in this research that there are also certain disadvantages in the development of DC microgrid, while the development of hybrid microgrid has its advantages. Therefore, there is brief description in the end of this paper about the concept, structure, characteristics of hybrid microgrid.