Model Analysis And Transient Simulation Of AC Distributed Energy Resources And Micro-grid

In the distributed energy resources powered micro-grid with a large number ofDG sources and power electronics devices, the AC distributed energy resources suchas microturbine generation system and wind power system are very important. Thetransient modeling methods of machines in distributed generation systems, the modelimprovement of microturbine generation system and micro-grid control strategies arestudied in this dissertation for the transient simulation of micro-grid, and the transientsimulation is achieved. The work in this dissertation is summarized as follows:1) The mathematical modeling methods and iterative solutions for various typesof machines are studied, focusing on the decoupling of electrical equations andmechanical equations in the different modeling coordinate system and solvingframework. The dynamic simulation results of the different machine models in thesame simulation scenario is compared using a variety of simulation softwarepackagescontaining PSCAD, EMTP, MATLAB/SimPowerSystems and self-developed TSDG.2) The microturbine generation system is modeled and simulated in the paper,which is composed of microturbine, high speed permanent magnet synchronousgenerator, converter, inverter, controller and filter. The simulation model is improvedboth in steady operating points and transient process with the experimental data of apractical microturbine generation system. The relevant parameters of microturbineinput can be calculated through data fitting based on the input-output relationship toenhance the microturbine output accuracy in steady state. The rate limiter, whichreflects the delay characteristic of thermodynamic process, is applied in the powercommands of the microturbine and inverter to improve the dynamic characteristics.3) The micro-grid control strategies when operating modes change aresummarized. And the typical droop control based on P-f and Q-V characteristics isimproved to achieve constant power control. And the parameter automatic adjustmentis applied to reduce the voltage fluctuation caused by the power mismatch in themicrogrid. At the same time, the method of grid synchronization control based on thepositive feedback is analyzed to achieve micro-grid reconnection to the network whilemaintaining the output power of DGs, using the information of voltage applitude andphase at the PCC to move the micro-grid operating point. 4) The transient simulation modeling methods of wind power system is studied.Based on self-developed transient simulation program TSDG, the transient simulationof micro-grid with various DG sources is achieved in a typical medium-voltage andlow-voltage micro-grid system. The results comparision with the commercialsimulation tool have verified the accuracy and effectiveness of the machine modelsused in this dissertation.