Direct current distribution systems (DCDS) are a promising alternative to alternating current (AC) systems because they remove AC--DC conversion between sources and loads that cause energy losses. Compared to AC systems, a DCDS has higher power capacity, energy efficiency and reliability, and no need for synchronisation---suitable where a large amount of renewable power is generated and consumed locally in DC. A DCDS has unique features that affect its implementation: low system inertia, strict power limits and power--voltage coupling. Hence, simply applying markets designed for AC cannot guarantee a DCDS's supply security and voltage stability. This dissertation aims to identify DC-tailored local market designs that facilitate a DCDS's operational efficiency and reliability under uncertainty. To identify promising DCDS market designs from all feasible options, we developed and applied a comprehensive design framework for local electricity markets. It is based on an engineering design process of identifying goals, determining design space, testing and evaluation. Whereas previous studies focused on individual commodities, we widened the scope to include the role of market architecture. Its main element is the choice of sub-markets for energy delivery, the provision of DC-substation capacity, and voltage regulation. For each selected sub-market, we analysed the design options for the general organisation, bid format, allocation and payment, and settlement. Considering the design complexity, we performed three rounds of market design according to the agile development principle: a qualitative assessment, a quantitative analysis without uncertainty, and a quantitative analysis under uncertainty. In Step 1, we analysed the design options and identified three types of DCDS market designs according to the above framework, each featuring a unique architecture. First, the integrated market (IM) design explicitly links three sub-markets (for energy, substation capacity and voltage regulation) to incorporate all system costs into energy prices. It aims to create price signals that encourage prosumers to resolve congestion and voltage issues, but the challenges are privacy concerns and sophisticated market clearing. Second, the locational energy market (LEM) design relieves congestion with nodal prices--by linking the energy and substation capacity markets--whereas a system operator regulates the voltage. Third, the wholesale energy price (WEP) market design passes such prices directly to local prosumers, whereas the system operator resolves all network issues. In Step 2, we quantitatively analysed how the market design addresses DC technical characteristics, such as volatile energy prosumption that challenges DC-substations. We built a deterministic optimisation model to evaluate three market designs, with a one-minute resolution to reflect the local prosumption volatility. Recognising that both total demand and demand flexibility may increase significantly in the future, we included a high share of electric vehicles (EVs) to test the market robustness. Simulations of a realistic urban DCDS demonstrated that the IM and LEM designs manage network congestion and voltage deviation even with a large share of EVs. It is found out that the main challenge to distribution-level market design is network congestion, mainly due to flexible prosumption at low-price hours. Voltage deviation and cable power capacity are not limiting factors of an urban DCDS market design. However, simply passing wholesale prices to local prosumers (like in the WEP design) is discouraged, as it may cause severe congestion and substantial flexibility investments. In Step 3, we demonstrated the economic efficiency and reliability of the LEM design also under uncertainty. The performance of a local energy market is dominated by the uncertainty from stochastic local power prosumption, fluctuating wholesale energy prices, and unforeseen EV availability. We presented a novel agent-based model to evaluate the LEM design's performance in realistic scenarios. This model describes typical electric-vehicle user preferences and their bidding strategies with different levels of range anxiety. To stress-test LEM, we created challenging scenarios with a high share of solar generation and EVs. It performed efficiently and reliably in simulations, based on the high-resolution 2018 Pecan Street database and the IEEE European Low Voltage Distribution Test Feeder, even with a high share of EVs. We demonstrated that regardless of the bidding strategy, the LEM achieves efficient DCDS operation, as long as the network constraints are not too tight. Hence, we conclude that the simple LEM design---with only price--quantity bids and DC-substation capacity constraints---is the best feasible option among the three designs. Although both DCDS technologies and the concept of local energy markets are still under development, we presented viable market solutions based on the best practices in the emerging DC technology, thereby clearing its market-side implementation barrier. The most economically-efficient yet technically feasible market design, at least in urban DCDS applications, is the LEM design. It supports fast market clearing and real-time control over flexible devices to resolve DC substation congestion. Other market designs, namely the IM and WEP, were proven to have practical limitations. In the future, we recommend testing, improving and verifying the LEM design in field tests with real prosumers and various flexibility sources. This dissertation made assumptions and simplifications on both the technical system and the market operation, thereby leaving room for further development. First, the optimisation model and the agent-based model could be improved to enable more realistic market simulations. Second, a simple, user-friendly yet efficient agent module should be developed to enable high-frequency energy transactions in a DCDS. Third, follow-up research should estimate upon prosumers' bidding and investment incentives: the impact of additional price components---transmission and distribution system costs, national taxes and levies. Fourth, we should also evaluate the influence of prosumer values---including privacy, energy equality and energy self-sufficiency---on the local energy market design. ... Read more

DC distribution systems are a promising alternative to existing AC distribution systems. They connect customers to local energy sources without conversion, thus reducing power losses. However, the unique features of DC impose strict requirements for system operation compared to AC. Within the context of a liberalized energy market, this article demonstrates three promising market designs—an outcome of a comprehensive engineering design framework—that meet those DC requirements. They are an integrated market design, which incorporates all system costs into energy prices; a market design that passes wholesale energy prices directly to prosumers; and a locational energy market design that relieves congestion with nodal prices. An optimization model estimates the three market designs’ performance by simulating a realistic DC distribution system, featuring a high share of electric vehicles. Results indicate that the integrated market design is optimal in theory but computationally infeasible in practice. The wholesale energy price design aiming at constraint-free energy trading requires substantial investments in flexibility. The locational energy market design yields nearly optimal operation in urban networks and is considered the best feasible market design for DC distribution systems. ... Read more

Direct Current Distribution System (DCDS), a promising alternative to existing AC systems, connect customers to DC energy sources without AC/DC conversion. The unique features of DC, including the power-voltage coupling effect, impose different requirements to DCDS operation compared to AC. Addressing a liberalized energy market, this paper investigates the significant impact of market design on DCDS operation with an empirical analysis of electric vehicle charging. With an empirical analysis on EV charging, we investigate the level of efficiency a centralized market may theoretically reach, then compare it with a market based on prosumers’ local decision. ... Read more

DC distribution systems (DCDSs) are a promising alternative to AC systems because they remove AC-DC conversions between renewable sources and loads. Their unique features compared to AC include low system inertia, strict power limits and power–voltage coupling. In a liberalised electricity market, merely applying an AC market design to a DCDS cannot guarantee the latter’s supply security and voltage stability; new markets must be designed to meet DC challenges. This article identifies the key design options of DCDS electricity markets. To identify these options, we develop a comprehensive design framework for local electricity markets; to our knowledge, we provide the first such analysis. Whereas previous studies focus on separate aspects of DCDS markets, we widen the scope to include the role of market architecture and investigate the arrangements of sub-markets. As an illustration, we demonstrate three promising DCDS market designs that can be defined in our framework, and provide a first assessment of their performance. ... Read more

This paper studies the energy trading among flexible demand response aggregators (DRAs) and a distribution company (Disco) with self-owned generators. Instead of the conventional non-cooperative game based approach, the trading problem is formulated as a bargaining based cooperative model, where Disco and DRAs collaboratively decide the amounts of energy trade and the associated payments. This cooperative interaction can be beneficial to both Disco and DRAs, by reducing the aggregated peak demand and increasing the potential cost savings. The increased benefits from cooperation are fairly allocated among these participants, based on the Nash bargaining theory. Compared with the non-cooperative game based approach, the proposed bargaining cooperative model can further improve the benefits of Disco and DRAs. Moreover, the bargaining outcome can maximize the social welfare of the system. Considering the privacy and autonomy issues of participants, we utilize a decentralized solution to solve the bargaining problem, with minimum information exchange. Numerical studies demonstrate the effectiveness of the bargaining -based cooperative framework, and also show the improvement of benefits of the system. ... Read more

Battery energy storage (BES) and demand response (DR) are considered to be promising technologies to cope with the uncertainty of renewable energy sources (RES) and the load in the microgrid (MG). Considering the distinct prediction accuracies of the RES and load at different timescales, it is essential to incorporate the multi-timescale characteristics of BES and DR in MG energy management. Under this background, a hierarchical energy management framework is put forward for an MG including multi-timescale BES and DR to optimize operation with the uncertainty of RES as well as load. This framework comprises three stages of scheduling: day-ahead scheduling (DAS), hour-ahead scheduling (HAS), and real-time scheduling (RTS). In DAS, a scenario-based stochastic optimization model is established to minimize the expected operating cost of MG, while ensuring its safe operation. The HAS is utilized to bridge DAS and RTS. In RTS, a control strategy is proposed to eliminate the imbalanced power owing to the fluctuations of RES and load. Then, a decomposition-based algorithm is adopted to settle the models in DAS and HAS. Simulation results on a seven-bus MG validate the effectiveness of the proposed methodology. ... Read more

Direct current distribution systems (DCDS), which connect local prosumers directly to community grids without AC/DC conversions, are a promising alternative to AC systems. While regulations call for market-based operation, existing markets for AC systems do not meet DC requirements and cannot be applied to a DCDS. This paper develops a design framework for local electricity markets and with it explores possible DCDS market designs. We review the technical requirements and desired properties for DCDS operation, enumerate its market design goals, then identify the design variables influencing the short-term market efficiency. This paper is our first step towards a systematic DCDS market design, and it supports our future work on quantitative analysis of the design choices. ... Read more

Under the background of global energy conservation, the energy hub (EH)-based integrated energy system is becoming the transition direction of future energy structure. In this paper, we study the cooperative economic scheduling problem for multiple neighboring integrated energy systems on the basis of EH. Different with the traditional non-cooperative mode where each EH operates individually, these EHs constitute a cooperative community and can share energy among them. Considering the autonomy and selfinterest of different EHs, the coordinated management problem is modeled as a bargaining cooperative game, where involved EHs will bargain with each other about the exchanged energy and the associated payments. The bargaining solution can achieve a fair and Pareto-optimal balance among the objective functions of different EHs. A distributed optimization is applied to find the bargaining solution of the cooperative system, to guarantee the autonomous scheduling and information privacy of EHs. Numerical studies demonstrate the effectiveness of the bargaining-based cooperative economic scheduling framework, and also show the improvement of benefits of the community system. ... Read more

DC distribution systems (DCDS) connect local generators and loads directly. By avoiding unnecessary losses in AC-DC conversion, DCDS offers higher energy efficiency. Since different parties in a DCDS may have conflicting goals, matching between power supply and demand should be done with carefully designed allocation rules and monetary transfers, such that no one prefers to act otherwise than the outcome of the allocation. This paper reveals DCDS' unique operational requirements and indicates the challenges and opportunities they pose to market design. A design framework is introduced into DCDS electricity market, incl. tradable services, design goals, market participants, design options and performance criteria. We review the existing market models for AC and DC distribution systems and point out the direction for future work. ... Read more