| A microgrid is a local electricity network with several distributed energy systems. Different strategies of power sharing in distributed generation are reviewed and the droop control approach for inverter based distributed generators is selected for further investigation due to its low cost and potential for performance enhancement. The inverters in a microgrid with droop control use a wireless control system which doesn't have any intercommunication cost and is not distorted by electromagnetic interferences. The control system is extendable to any number of distributed sources. Proper power sharing, which enables the energy sources (with energy storage units) to provide powers proportional to their apparent rated powers, is a very important property of the system. Hence, the collection of the distributed sources can deliver their maximum powers when there is full load demand, without overloading some and underutilizing others. The conventional droop control doesn't result in proper power sharing; especially when the sources have different rated powers or the feeders are unbalanced (have different impedances). This drawback has not been fixed in the other publications; either by using the power sources with equal apparent power or by ignoring the improper power sharing ratio. Also in some publications, there have been some poor load voltage regulations. In this thesis, a modified droop system has been used which will result in appropriate power sharing and load voltage regulation. Furthermore, the effects of the sources' voltages' magnitude, phase angle, and frequency on the system power sharing are considered. Moreover, the influences of the droop system's parameters on system's behaviour were evaluated in different cases of sources' apparent powers ratio and feeders' lengths ratio and a general rule is presented which shows how to choose the droop parameters for any isolated microgrid's control system. |
