Abstract
With the great increase of renewable generation as well as the DC loads in the distribution network; DC distribution technology is receiving more attention; since the DC distribution network can improve operating efficiency and power quality by reducing the energy conversion stages. This paper presents a new architecture for the medium voltage AC/DC hybrid distribution network; where the AC and DC subgrids are looped by normally closed AC soft open point (ACSOP) and DC soft open point (DCSOP); respectively. The proposed AC/DC hybrid distribution systems contain renewable generation (i.e., wind power and photovoltaic (PV) generation); energy storage systems (ESSs); soft open points (SOPs); and both AC and DC flexible demands. An energy management strategy for the hybrid system is presented based on the dynamic optimal power flow (DOPF) method. The main objective of the proposed power scheduling strategy is to minimize the operating cost and reduce the curtailment of renewable generation while meeting operational and technical constraints. The proposed approach is verified in five scenarios. The five scenarios are classified as pure AC system; hybrid AC/DC system; hybrid system with interlinking converter; hybrid system with DC flexible demand; and hybrid system with SOPs. Results show that the proposed scheduling method can successfully dispatch the controllable elements; and that the presented architecture for the AC/DC hybrid distribution system is beneficial for reducing operating cost and renewable generation curtailment.
Highlights
The power system has been dominated by the AC grid for a long time, since AC voltage can be changed by transformers, and the power supply radius [1] of the AC system is larger
These results show that the proposed method is still applicable in a larger system
This study is focused on the operation strategy of the distribution system, with the assumption that the cost of renewable generation is low enough to compete with traditional energy in the future
Summary
The power system has been dominated by the AC grid for a long time, since AC voltage can be changed by transformers, and the power supply radius [1] of the AC system is larger. The progress in the power electronic area has made DC voltage transformation [2] much easier and more effective. The adoption of DC loads [3] (e.g., electric vehicles, data centers) and DC based sources (e.g., photovoltaic systems, fuel cells) has increased greatly in recent years [4,5]. The DC/AC and AC/DC conversion stages in the AC systems can be avoided in the DC systems, because many renewable energy sources (RESs) like wind power and photovoltaic (PV) generation usually produce DC power directly, or produce DC first it is converted to AC. Considerable emerging new loads like electric vehicles are using DC systems. DC distribution systems can improve system efficiency by reducing conversion losses. The disadvantages of AC systems, including frequency reactive power flow, synchronization, and harmonics can be eliminated in DC systems
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