The increasing interest in integrating intermittent renewable energy sources into microgrids presents major challenges from the viewpoints of reliable operation and control. In this paper, the major issues and challenges in microgrid control are discussed, and a review of state-of-the-art control strategies and trends is presented; a general overview of the main control principles (e.g., droop control, model predictive control, multi-agent systems) is also included. The paper classifies microgrid control strategies into three levels: primary, secondary, and tertiary, where primary and secondary levels are associated with the operation of the microgrid itself, and tertiary level pertains to the coordinated operation of the microgrid and the host grid. Each control level is discussed in detail in view of the relevant existing technical literature.

Trends in Microgrid Control

Many areas in power systems require solving one or more nonlinear optimization problems. While analytical methods might suffer from slow convergence and the curse of dimensionality, heuristics-based swarm intelligence can be an efficient alternative. Particle swarm optimization (PSO), part of the swarm intelligence family, is known to effectively solve large-scale nonlinear optimization problems. This paper presents a detailed overview of the basic concepts of PSO and its variants. Also, it provides a comprehensive survey on the power system applications that have benefited from the powerful nature of PSO as an optimization technique. For each application, technical details that are required for applying PSO, such as its type, particle formulation (solution representation), and the most efficient fitness functions are also discussed.

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Particle Swarm Optimization: Basic Concepts, Variants and Applications in Power Systems

Carbon capture and storage (CCS) is broadly recognised as having the potential to play a key role in meeting climate change targets, delivering low carbon heat and power, decarbonising industry and, more recently, its ability to facilitate the net removal of CO2 from the atmosphere. However, despite this broad consensus and its technical maturity, CCS has not yet been deployed on a scale commensurate with the ambitions articulated a decade ago. Thus, in this paper we review the current state-of-the-art of CO2 capture, transport, utilisation and storage from a multi-scale perspective, moving from the global to molecular scales. In light of the COP21 commitments to limit warming to less than 2 °C, we extend the remit of this study to include the key negative emissions technologies (NETs) of bioenergy with CCS (BECCS), and direct air capture (DAC). Cognisant of the non-technical barriers to deploying CCS, we reflect on recent experience from the UK's CCS commercialisation programme and consider the commercial and political barriers to the large-scale deployment of CCS. In all areas, we focus on identifying and clearly articulating the key research challenges that could usefully be addressed in the coming decade.

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Carbon capture and storage (CCS): the way forward

This paper provides an overview of grid code technical requirements regarding the connection of large wind farms to the electric power systems. The grid codes examined are generally compiled by transmission system operators (TSOs) of countries or regions with high wind penetration and therefore incorporate the accumulated experience after several years of system operation at significant wind penetration levels. The paper focuses on the most important technical requirements for wind farms, included in most grid codes, such as active and reactive power regulation, voltage and frequency operating limits and wind farm behaviour during grid disturbances. The paper also includes a review of modern wind turbine technologies, regarding their capability of satisfying the requirements set by the codes, demonstrating that recent developments in wind turbine technology provide wind farms with stability and regulation capabilities directly comparable to those of conventional generating plants.

A review of grid code technical requirements for wind farms

Plug-in electric vehicles (PEVs) present environmental and energy security advantages versus conventional gasoline vehicles. In the near future, the number of plug-in electric vehicles will likely grow significantly in the world. Despite the aforementioned advantages, the connection of PEV to the power grid poses a series of new challenges for electric utilities. This paper proposes a comprehensive approach for evaluating the impact of different levels of PEV penetration on distribution network investment and incremental energy losses. The proposed approach is based on the use of a large-scale distribution planning model which is used to analyze two real distribution areas. Obtained results show that depending on the charging strategies, investment costs can increase up to 15% of total actual distribution network investment costs, and energy losses can increase up to 40% in off-peak hours for a scenario with 60% of total vehicles being PEV.

Assessment of the Impact of Plug-in Electric Vehicles on Distribution Networks

The integration of a significant amount of renewable and in particular wind energy in the Great Britain transmission system requires a fundamental review of the operational and market arrangements of the electricity transmission. The main reviews under way focus on transmission access arrangements (TAR), transmission security standards (GB SQSS) and transmission investment incentives. This paper presents the current arrangements for the aforementioned issues and analyses the drivers behind the reviews. Changes in the current arrangements are suggested and it is intended to identify the interactions between the reviews, which would result to an efficient short-term allocation of transmission resources and long-term least cost investment.

The new transmission arrangements in the UK

https://www.ofgem.gov.uk/sites/default/files/docs/2007/04/dti-centre-for-dg-and-sustainable-electrical-energy-paper.pdf

DTI Centre for Distributed Generation and Sustainable Electrical Energy

The paper proposes a model to determine the optimal strategy of offering electricity at the day-ahead market for a portfolio of Distributed Energy Resources. The stochastic nature of the problem is taken into account through uncertainty of generator output and forecasts of day-ahead and imbalance prices. The model attempts to maximise the expected profit of the portfolio when exposed to imbalance prices and output uncertainty. Portfolios analysed included conventional generators, wind generators, or both. The results indicate that the proposed approach is able to adapt the offering strategy to the risk profile in different times of the day. Also, significant synergic effects are demonstrated when wind and conventional generators are aggregated into a single portfolio, due to increased flexibility in internal portfolio balancing.

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Characterisation of portfolios of distributed energy resources under uncertainty

Work package 2 Impact analysis of increasing (intermittent) RES and DG penetration in the electricity system

Effective integration of distributed generation (DG) in distribution networks can be stimulated by providing adequate economic signals to inform DG developers and operators about the preferable locations and the value of DG in the context of providing network flow control services and deferring network reinforcement. DG which contributes positively in the reduction of network investment cost should be rewarded and DG which drives network reinforcement should be penalized. In that context, this paper discusses the importance of having cost reflective access and distribution network pricing and highlights the need for recognizing the link between network design and planning, drivers for investment and pricing.

Danny Pudjianto

Papers

The new transmission arrangements in the UK

DTI Centre for Distributed Generation and Sustainable Electrical Energy

Characterisation of portfolios of distributed energy resources under uncertainty

Work package 2 Impact analysis of increasing (intermittent) RES and DG penetration in the electricity system

Access and Pricing of Distribution Network with Distributed Generation