Study And Simulation On Microgrid Operation Control

Under the background of emphasis on environment protection and fuel saving, distributed generations (DG), based on new energy and renewable energy, become most promising. Microgrid is an aggregation of some DG and some load, which can be regarded as a mini power system. The appearance of Microgrid can reduce the impact on the grid when lots of small-sized DG connecting to the grid, lower the loss of long distance transmission and improve the power supply reliability. So, the study of Microgrid control is hot in recent years.This paper established photovoltaic generation (PV), micro turbine generation (MT) model, and then the Microgrid system based on PSCAD simulation. After analysis of the characteristics of different DG, the scheme of grid connection is decided. PV is connected to the grid as a current source with MPPT, and MT as a voltage source with droop characteristic.The control methods of grid connetion as voltage source and current source are studied respectively. Voltage source control employs voltage as external loop and current as inner loop with instantaneous value as feedback. Inner control loop uses capacitor current as feedback to improve the dynamic characteristic. The paper studies the PI optimization considering the pole set method. Current source control employs the classic d-q current compenet to adjust the active power and reactive power outputs, obtaining power facter as 1. Employing the voltage forward feedback can reduce the haimonic current and the impact of the homonic current from CSI on voltage is studied.Then, power sharing between the parallel DGs is discussed. The paper analyses the advantage of frequency droop control in comparison with angle droop control in terms of active power sharing. The accuracy of reactive power sharing with voltage droop control is influenced by the line parameter, combined with droop coefficient. Considering both the line resistance and inductance, active power flow and reactive power would be coupling. In this condition, the method to insure the accuracy of power sharing is given.At last, the whole small-signal dynamic model, including the VSI, the line parameter and load parameter, is proposed, which can be used in stability analysis. Based on this model, eignvalue locus plots as a function of all kinds of parameters can be gained and so the relationship between system parameter and stability can be obtained, too. Simulation results prove that the conclusion is rational.