Load Sharing in Microgrids with Renewable Energy Sources

The reliable operation of microgrids can be achieved by properly sharing the load demand among available generators within microgrids. The load sharing depends on the types of energy sources and characteristics of microgrids where most of these energy sources are based on renewable power generation. The grid integration of renewable energy sources (RESs) increases the uncertainties as the power generation from RESs heavily relies on the natural resources (sun light, wind speed) which are unpredictable. In such cases, load sharing becomes more challenging as the reliability of the grid degrades. Moreover, microgrids are low- or medium-voltage networks which have resistive transmission lines and their generators are distributed throughout the network which creates complexities and reduces the accuracy of load sharing. A proper load-sharing control technique is necessary to enhance the reliability of a microgrid system. In this thesis, the effect of renewable energy penetration is analysed and two different techniques for load sharing in microgrids with RESs, which overcome the limitations of the techniques in the existing literature for improving sharing accuracy, are proposed.In the first technique proposed in this thesis, a central power management unit and local controllers work together to share the load of a microgrid with its available generators. The central control unit is able to estimate the load deviations for each node centrally by using node voltages. This control scheme considers both resistive and inductive transmission lines and works well in a microgrid environment with RESs. Simulation results show that load-sharing errors from this technique are negligible and all node voltages are within the permissible limits.The second approach is a decentralised control technique which works without any central controller and introduces a new term called demand factor to calculate the load demand for each generator. The benefit of using the demand factor is that each controllable generator can calculate the load demand itself without communicating with other generators or load centres. Only a very low-bandwidth one-way communication link is needed if the system contains a battery for utilising the maximum power from RESs. Simulation results show that the load-sharing performance of this control scheme is reasonably good and maintains the system voltage within permissible limits