Optimal Energy and Flexibility Dispatch of Grid-Connected Microgrids
Doctoral thesis, 2022

This thesis proposes an optimization model to efficiently schedule energy and flexibilities of a grid-connected microgrid (MG) with non-dispatchable renewable energy sources and battery energy storages (BESs). The model can also be used to coordinate the MG operation with the connected upstream distribution grid and to assess the MG flexibility considering economic viability, technical feasibility, and BES degradation. The performance of the model was tested for both deterministic and stochastic formulations using two solution approaches i.e., day-ahead and rolling horizon, in different simulation and demonstration test cases. In these test cases, the model optimizes the schedule of the MG resources and the energy exchange with the connected main grid, while satisfying the constraints and operational objectives of the MG. The flexibilities from the MG would also be optimized when the MG provided flexibility services (FSs) to the distribution systems. The coordination with the distribution system operator (DSO) was proposed to ensure that the microgrid operation would not violate the technical constraints of the distribution grid.

 

Two types of test systems were used for the simulations studies: 1) distribution grids with grid-connected MGs and 2) building MGs (BMGs). The distribution test systems included the 12-kV electrical distribution grid of the Chalmers campus and a 12.6-kV 33-bus standard test system, while the BMGs were based on real residential buildings i.e., the HSB LL building and the Brf Viva buildings. Results of the Chalmers’ test case showed that the MGs’ economic optimization could reduce the annual cost for the DSO by up to 2%. Centralized coordination, where the MG resources were scheduled by the DSO, led to an even higher reduction, although it also led to sub-optimal solutions for the MGs. Decentralized coordination was applied on the 33-bus network with a bilevel optimization framework for energy and flexibility dispatch. Two types of FSs were integrated in the bilevel model i.e., the baseline (FS-B) and the capacity limitation (FS-C). The latter has found to be more promising, as it could offer economic incentives for both the DSO and the MGs. In the studies of the BMGs, the BESs were modeled considering both degradation and real-life operation characteristics derived from measurements conducted at the buildings. Results showed that the annual building energy and BES degradation cost could be reduced by up to 3% compared to when the impact of BES degradation was neglected in the energy scheduling. With the participation of the BMG in FS-C provision, the building’s operation cost could be further reduced depending on the flexibility price. A 24-h simulation of the BMG’s operation yielded an economic value of flexibility of at least 7% of its daily energy and peak power cost, while the DSO could benefit from the FS assuming that the dispatched flexibility could be used to reduce the subscription fee that guarantees a certain power level. For frequent flexibility provision i.e., multiple times within a year, the value of flexibility for the MG operator could be reduced due to the BES degradation.

 

To demonstrate the practical use of the proposed model, an energy management system was designed to integrate the model and employ it to optimize the energy schedule of the BMGs’ BESs and energy exchange with the main grid. The energy dispatch was performed in real-time based on the model’s decisions in real demonstration cases. The demonstration results showed the benefits of the model in that it helped reduce the energy cost of the BMG both in short term and in long term. The model can also be used by the MG operators to quantify the potential and assess the value of microgrid flexibility. Moreover, with the help of this model, the MG can be employed as a flexible resource and reduce the operation cost of the connected distribution grid.

flexibility

microgrids

Battery energy storage

optimization.

energy scheduling

energy management

distribution network

EA lecture hall
Opponent: Birgitte Bak-Jensen, Aalborg University, Denmark

Author

Kyriaki Antoniadou-Plytaria

Chalmers, Electrical Engineering, Electric Power Engineering

Effect of Short-term and High-resolution Load Forecasting Errors on Microgrid Operation Costs

IEEE PES Innovative Smart Grid Technologies Conference Europe,; Vol. 2022-October(2022)

Paper in proceeding

Scenario-based Stochastic Optimization for Energy and Flexibility Dispatch of a Microgrid

IEEE Transactions on Smart Grid,; Vol. In press(2022)

Journal article

Values and Impacts of Incorporating Local Flexibility Services in Transmission Expansion Planning

Electric Power Systems Research,; Vol. 212(2022)

Journal article

Market-based Energy Management Model of a Building Microgrid Considering Battery Degradation

IEEE Transactions on Smart Grid,; Vol. 12(2021)p. 1794-1804

Journal article

Energy Scheduling Strategies for Grid-connected Microgrids: A Case Study on Chalmers Campus

Proceedings of 2019 IEEE PES Innovative Smart Grid Technologies Europe, ISGT-Europe 2019,; (2019)

Paper in proceeding

Chalmers Campus as a Testbed for Intelligent Grids and Local Energy Systems

IEEE International Conference on Smart Energy Systems and Technologies (SEST),; (2019)

Paper in proceeding

The transition to the future electricity distribution grid, which will host a high number of local energy resources, motivates studies of microgrids, which represent clusters of these resources, to investigate the benefits and challenges associated with their operation. This thesis proposes an optimization model to efficiently schedule energy and flexibilities of a grid-connected microgrid, coordinate the microgrid operation with the connected upstream distribution grid, and assess the microgrid flexibility considering techno-economical feasibility and battery degradation.

Two types of test systems were used for the simulations studies: 1) distribution grids with grid-connected microgrids, including the electrical distribution grid of the Chalmers campus, and 2) building microgrids based on real residential buildings i.e., the HSB LL building and the Brf Viva buildings. The buildings were also used to demonstrate the practical use of the model, which was integrated in an energy management system designed to control in  real-time the power of the buildings’ batteries according to the model’s decisions.

The thesis’ results showed that the model can reduce the microgrid’s operation costs, which can offer financial benefits to the electricity customers if the model is used by future microgrid and building operators. It was also shown that the model can accurately quantify and reliably dispatch the microgrid’s flexibility. Therefore, distribution grid operators can also use the model to take advantage of the microgrid’s flexibilities and reduce the operation costs of their distribution grids.

Subject Categories

Electrical Engineering, Electronic Engineering, Information Engineering

ISBN

978-91-7905-700-8

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5166

Publisher

Chalmers

EA lecture hall

Online

Opponent: Birgitte Bak-Jensen, Aalborg University, Denmark

More information

Latest update

3/30/2023