The use of Distributed Energy Resources (DER) has been proposed as one of the possible solutions to today's energy and environmental challenges. The optimal integration of DER in distribution networks is essential to guarantee the best of resource, i.e. maximize their benefits, such as reduction of carbon emissions, reduction of network energy losses and to minimize the negative impacts, which can affect the network quality, cause network sterilization and increase investment and operation costs. Hence, DER planning is a multi-objective problem in which many objectives of interest, sometimes conflicting, need to be optimized simultaneously, and where a compromise for different perspectives (DER developer, Distribution System Operator, regulator) needs to be found. Appropriate multi-objective planning methods that consider technical, environmental and economic impacts of DER integration, and that are able to support a suitable model of stochastic DER and active networks, can provide a deep insight into the case specific and general advantages and drawbacks of DER. Consequently, the interest in multi-objective DER planning has increased in recent years, and a number of novel methods have been proposed in this area. This paper provides a timely review of the state-of-the-art in multi-objective DER planning, and discusses in detail the challenges, trends and latest developments in this field.

Multi-objective planning of distributed energy resources: A review of the state-of-the-art

Microgrid systems show great promise for integrating large numbers of distributed energy resource (DER) systems into future power networks. This paper provides a brief overview of current microgrid technologies and issues associated with their implementation. The case is made for a real-time power management and control system that attempts to optimize microgrid systems based on multiple objectives, such as power demands, fuel consumption, environmental emissions, costs, dispatchable loads, etc. A multi-agent based control architecture that can ensure robust, stable, and optimal microgrid operation is also addressed. In addition to the discussion of power management and control topics, a qualitative classification tool has been proposed for assisting system planners in assessing the impact of microgrid systems on broader grid operations.

A review of challenges to real-time power management of microgrids

Marginal-cost-based dynamic pricing of electricity services, including real power, reactive power, and reserves, may provide unprecedented efficiencies and system synergies that are pivotal to the sustainability of massive renewable generation integration. Extension of wholesale high-voltage power markets to allow distribution network connected prosumers to participate, albeit desirable, has stalled on high transaction costs and the lack of a tractable market clearing framework. This paper presents a distributed, massively parallel architecture that enables tractable transmission and distribution locational marginal price (TD electric vehicle (EV) battery charging and storage; heating, ventilating, and air conditioning (HVAC) and combined heat & power (CHP) microgenerators; computing; volt/var control devices; grid-friendly appliances; smart transformers; and more. The proposed iterative distributed architecture can discover T&DLMPs while capturing the full complexity of each participating DER’s intertemporal preferences and physical system dynamics.

Co-Optimization of Power and Reserves in Dynamic T&D Power Markets With Nondispatchable Renewable Generation and Distributed Energy Resources

This paper considers the effects of various voltage control solutions on facilitating an increase in allowable levels of distributed generation installation before voltage violations occur. In particular, the voltage control solution that is focused on is the implementation of ‘soft’ normally-open points (SNOPs), a term which refers to power electronic devices installed in place of a normally-open point in a medium-voltage distribution network which allows for control of real and reactive power flows between each end point of its installation sites. While other benefits of SNOP installation are discussed, the intent of this paper is to determine whether SNOPs are a viable alternative to other voltage control strategies for this particular application. As such, the SNOPs ability to affect the voltage profile along feeders within a distribution system is focused on with other voltage control options used for comparative purposes. Results from studies on multiple network models with varying topologies are presented and a case study which considers economic benefits of increasing feasible DG penetration is also given.

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Increasing distributed generation penetration using soft normally-open points

A multistage active distribution network (ADN) planning model that is integrated with the application of energy storage system (ESS) is presented in this paper. Both the long-term investment cost and short-term operation conditions of ADN are considered in the proposed model. The power supply reliability improvement brought by ESS is also analyzed. At each planning stage, the operation conditions are divided into several typical day scenarios and an extreme condition scenario which are based on the load forecast data. The long-term expansion planning decisions including those for replacing and adding circuits, introducing ESS, and considering ADN short-term operation strategies for the ESS charging and discharging are optimized together in the proposed model. The ESS benefits pertaining to peak load shaving and power reliability enhancement are demonstrated using numerical cases, in which the centralized and the distributed ESS are considered as options for the ADN implementation. The effectiveness of the proposed model is demonstrated through various discussions in the paper.

Expansion Planning of Active Distribution Networks With Centralized and Distributed Energy Storage Systems

Until now, distribution networks are regarded as a passive termination of the transmission network, with a radial structure, unidirectional power flows, and a simple and efficient protection scheme. In presence of a large amount of distributed generation (DG), distribution networks will gradually, but ineluctably, change towards a new kind of active networks. The most revolutionary change, needed to efficiently allocate so much DG, could be represented by the adoption of a meshed network architecture. For this reason, in the paper new possible arrangements for distribution networks have been deeply investigated and compared with the radial scheme. Steady state and dynamic simulations have been performed, considering a portion of the real Italian distribution network, and voltage profile, power losses, short circuit currents and grid reliability have been analyzed.

Meshed vs. radial MV distribution network in presence of large amount of DG

Despite the radical changes that the electricity distribution system is currently facing and will have to face in the next decade, utilities still adopt a traditional approach for the expansion planning of their networks, based essentially on the fit and forget concept (only network reinforcements to cope with the worst case scenario) Although innovative solutions have been proposed in the last decade at the electricity distribution level (distributed energy storage, active management of distributed generation, demand side integration, etc) and are becoming technically and economically feasible, they are not yet considered as viable planning alternatives The reasons of this reluctance are the lack of ad hoc planning tools and business cases In the paper, a novel planning tool for Active Distribution Networks is applied to a real MV distribution network of the A2A utility sited in the district of Brescia in order to prove the benefit of energy storage devices

A comparison of distribution network planning solutions: Traditional reinforcement versus integration of distributed energy storage

The most innovative concept in the nowadays distribution system is that Distributed Energy Resources (DERs) are active subjects of the system with new business opportunities from the active management but with the responsibility to assure a proper work of the system working in coordination with DSOs. The Civil Society, the DSO and DER owner are clearly the stakeholders of the systems, that have contrasting and opposite goals; in the paper, the points of view and the needs of system stakeholders has been simulated. For this reason, MultiObjective approach are used to capture the relationship among players in order to constitute an objective basis to define a regulatory environment with fair incentives for those distribution operators who invest in innovative distribution operation.

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R. Cicoria

Papers

Meshed vs. radial MV distribution network in presence of large amount of DG

A comparison of distribution network planning solutions: Traditional reinforcement versus integration of distributed energy storage

Active distribution network cost/benefit analysis with multi-objective programming