Modeling Of Distributed Generators And Control And Protection Of Micro-grid

Distributed Generator (DG) becomes an important supplement for power grid, when thedisadvantages of the traditional one-way power grid is more and more obvious, and the globalenergy and environment problem is more and more pressing. The Distributed Generation iseco-friendly, high efficiency and has advantage in installation location of localization. Moreover, itcan reduce the transmission and distribution line loss, lower the operation cost, guarantee basicenergy supply when the power grid power has malfunction. However, there also somedisadvantages for the distributed power generation, such as randomness, small capacity, smallinertia, low overload ability, the influence of Distributed Generation access to power grid and so on.Many factors restrict the application and promotion of distributed power generation technology.Microgrid technique is developed to solve the above problems. In this study, the simulationenvironment is Matlab/Simulink, demonstrative research project of the grid-connection Microgridsystem works as a platform. Take the relevant technology of Distributed Generator and Microgridas application background, the modeling of Distributed Generator, inverter technology ofDistributed Generator and the control strategy and protection of Microgrid is discussed.Firstly, establish the model of Photovoltaic cells, Micro-turbines, Batteries and ElectricalDouble-Layer Capacitors according to their mathematical principles or engineering models. Withthese models, we study their relevant output performance by simulations. The experimental resultsshow that these models could reflect the characteristics of above Distributed Generators, and havesignificance to future research.Secondly, considering the problem of Distributed Generator interface to feeder connections,the difference between Distributed Generator and the traditional synchronous generator is discussed.Afterward, the interface technology of inverter, including phase lock loop technique (PLL), pulsewidth modulation (PWM) technology, inverter principle and power control are simulated andanalyzed. Finally, the three-phase inverter PQ power control is realized in the simulation.And then, three-phase inverter control technologies, including PQ power control, V/f controland Droop control are discussed. The mainstream control strategy of Microgrid is introduced. TheDroop controller is designed, with which the power grid-connection simulation experiments areimplemented. These simulation results demonstrate the validity of the designed controller. Then, theMicrogrid active isolated from grid and in the state of island operation inputting or cutting loadsimulated, in which, the results demonstrate that the grid power quality requirements can besatisfied by appropriate control strategy, even there is load wave. And then, the PCC’constant power control methods based on PID control are detailed. The control strategy of PCC’constantpower is tested by simulation, which proved the validity of this strategy.At last, the influence to the relay protection when Distributed Generator is applied to thetraditional power grid is discussed. Based on the above discussion, this thesis expounds theMicrogrid relay protection approaches in the state of connection and isolated to grid. According tothe protection of the empirical Microgrid system, the Microgrid platform’s protective hierarchy,protective logic and protection in the state of island are discussed.