In order to meet the environmental and economic targets set by many governments, massive

amounts of distributed generation (DG) units, often fed by renewable energy sources, are being

integrated in the electric power system. However, the grids are designed for the integration of large

central generators at the highest voltage levels, not for integrating many small DG units at lower

voltage levels. Also, many DG units generate power in an intermittent manner with low

predictability. This poses challenges on the grid operation, such as an increased occurrence of

voltage problems. Therefore, the DG units will need to contribute in the grid control. By providing

ancillary services to the system operators, the integration of DG in the network could become more

smooth and less expensive.

This research focuses at the provision of ancillary services, mainly highlighting voltage control in the

medium and low-voltage networks. The developed control strategy will firstly, be effective and

generic in the sense that with the same control strategy, multiple grid elements can assist in the grid

control, e.g., not only renewable sources but also controllable loads. Secondly, the actions of these

grid elements will be coordinated in order to avoid oscillations and to capture as much of the

renewable energy as possible at minimal network losses. The results will be a higher production of

renewable energy, while maintaining a resilient, robust and efficient power system operation.