Högskolan i Skövde

This study analyzes an underwater inductive wireless power transfer (UIWPT) to be used in offshore vehicles. Fixating on inadvertent eddy current losses (ECLs), this study offers an approach to tackle this concern based on the optimal selection of main design parameters of Archimedean magnetic coils. An accurate analytical electromagnetic field model is derived for directly calculating ECLs, and based on the ECL model, the main design parameters of coils are selected. The electrical fundamental components of coils are calculated as a function of the selected design parameters. A numerical metaheuristic optimization method along with the formulation of a multi-objective function and inequality constraints is utilized to estimate the selected parameters of coils. This function addresses various design objectives simultaneously, considering the water medium and inequality constraints. For optimization purposes, an electrical equivalent circuit model is derived, considering the ECLs impact by reflecting these losses in the equivalent circuit model. The ECL model is verified through Finite Element Analysis (FEA). Finally, a laboratory scale setup is developed and UIWPT experiments are conducted to validate the equivalent circuit and analytical modeling, the calculation of components, and the simulation study. 

In recent years the development of LVDC distribution networks is under consideration. DC electrical distributions offer several advantages compared to AC ones in many applications, in particular in the presence of energy storage systems and distributed generation like high efficacy, flexibility and simple integration of renewables. The DC distribution allows to integrate in a more efficient “microgrid” different sources with DC/DC converters. The article proposes an innovative model of microgrid configuration for aggregations of end-users able to share the power produced by common generators and energy services named by the authors Power Sharing Model (PSM) using a DC bus that connects in a one way approach, the common generators to the end-users. The article investigates on the different suggested configurations of the PSM, with the converter characteristics and controls. A simplified case study is analyzed to test the performance of the sharing model and the stability of the control in different scenarios. The article compares the PSM based on a LVDC grid with existing approaches of virtual aggregations, and it highlights the main differences between the currently existing methods and our new LVDC microgrid approach. The suggested PSM appears more efficient, convenient and flexible than the existing virtual models, because users physically self-consume and share the energy locally generated.

This paper proposes a novel energy and reserve scheduling model for power systems with high penetration of wind turbines (WTs). The objective of the proposed model is to minimize the total operation cost of the system while static and dynamic security is guaranteed by preserving the frequency nadir, RoCoF, and quasi-steady-state frequency in the predefined range. Likewise, a supervisory, control, and data acquisition (SCADA) system is developed which allows Vanadium Redox Flow Batteries (VRFBs) to continuously communicate and participate in the primary frequency response. To cope with the uncertainties, adaptive information gap decision theory is used that ensures a target operating cost for the risk-averse operator of the power system. The proposed scheduling model is applied on a modified IEEE 39 bus test system to verify the impacts of the fast reserve provided by the VRFBs in the dynamic frequency security enhancement of the power system with high penetration of WTs.

Co-designing energy systems across multiple energy carriers is increasingly attracting attention of researchers and policy makers, since it is a prominent means of increasing the overall efficiency of the energy sector. Special attention is attributed to the so-called energy hubs, i.e., clusters of energy communities featuring electricity, gas, heat, hydrogen, and also water generation and consumption facilities. Managing an energy hub entails dealing with multiple sources of uncertainty, such as renewable generation, energy demands, wholesale market prices, etc. Such uncertainties call for sophisticated decision-making techniques, with mathematical optimization being the predominant family of decision-making methods proposed in the literature of recent years. In this paper, we summarize, review, and categorize research studies that have applied mathematical optimization approaches towards making operational and planning decisions for energy hubs. Relevant methods include robust optimization, information gap decision theory, stochastic programming, and chance-constrained optimization. The results of the review indicate the increasing adoption of robust and, more recently, hybrid methods to deal with the multi-dimensional uncertainties of energy hubs.

Nowadays, the local distribution grids have been facing technical, economic, and regulatory challenges, because of the increased integration of renewable energy sources (RESs) and electrification of vehicles. The traditional solutions to the grid expansion, e.g., to build an additional power line, are utility-centered solutions, i.e., the distribution grid operators (DSOs) are the only party involved to tackle grid issues. The DSOs have to engage grid users with technology providers to develop innovative solutions that tackle one problem and overcome several cost-effectively. This paper presents a holistic solution to optimally control cross-sectoral energy flow between interconnected microgrids (MGs) consisting of different RESs, hydroelectric power plant (HPP) and wind turbines (WTs) to meet electric vehicles (EVs), residential, commercial and industrial demands with the main grid contribution. This issue will provide the advantages of community-based MGs for local energy trading which causes for an active and engaged system, however, an adequate control strategy for proper operation is required. The proposed solution is based on a new interconnection line between two MGs through a multiport converter (MPC) with the techno-economic consideration of newly installed components such as MPC, cables and the required battery energy storage system (BESS). The proposed case study is evaluated under three different conditions e.g., load increment, demand response (DR) and N-1 criterion in separate, interconnect and island modes. The CPLEX solver of GAMS software is employed to solve the mixed-integer linear programming model. The results show that the applied interconnection line for MGs compared to the separated operation mode can decrease the system's total costs, reduce the applied peak to the upstream grid, and enhance the system's reliability under different conditions. Furthermore, the applied solution provides the ability for MGs operation even in island mode under different conditions for a full day (24 h).

Ports play an undeniable role in people's lives. The energy consumption of large ports has an increasing rate worldwide and it has become a new challenge. The specific types of loads such as cranes, in particular, ship to shore, rubber tyred gantry, rail-mounted gantry, and cold ironing system in the ports present a distinctive load profile due to their sudden peak load demand. To deal with the problem and avoid extra costs, it is possible to apply a delay time management to cranes operation and/or to implement energy storage systems (ESSs) to take benefit of regenerative energy. At this aim, the load profile characteristics require both energy storage with high power and energy densities and fast response time. Peak shaving (P^S) can optimize the load demand and facilitate the participation of small power generation units based on renewable energy resources. In this regard, many approaches are introduced such as energy management strategies, modern technologies, and installing high-tech devices such as battery energy storage, ultracapacitors, and flywheel energy storage acting as ESS. Therefore, the goal of this article is to deal with an investigation for an integrated vision and a combination of ESSs application in the ports’ loads. Since the ports cannot persist to have independent and uncontrolled power systems, hence, the article proposes the organization of their global design in a microgrid approach and the coordinated management for all the services such as cranes, reefers, col ironing, trucks, and offices to increase the operation and energy performance. The statistical results show that the integration of ESSs can provide P^S, energy saving, and cost reduction in ports.

Energy transition toward smart grids with deep impact of renewables, energy storage systems, and electric vehicle charging stations will increasingly promote the establishment of energy communities that own portions of the electricity grid. The energy communities will consist of clusters of multiunit buildings and or single residential units aggregated sharing a common or multiple medium and low voltage (MV/LV) electrical substations. The size and impact of the location of these MV/LV substations can constitute a barrier especially for highly urbanized contexts where it is very complicated to provide technical spaces inside buildings for large technical systems like transformers, MV switchgear, etc. The idea of this work consists of developing a compact outdoor MV/LV substation to reduce the overall dimensions and to make the execution modularized to facilitate management and maintenance. Also an investigation of energy exchange between multiunit buildings, which are considered as the real energy community case study. The main objective for this case study is to minimize the operation cost of the system by maximizing the self-consumption.

This article presents the application of cluster analysis (CA) to data proceeding from a testbed microgrid located at Sapienza University of Rome. The microgrid consists of photovoltaic (PV), battery storage system (BESS), emergency generator set, and different types of load with a real-time energy management system based on supervisory control and data acquisition. The investigation is based on the area-related approach - the CA algorithm considers the input database consisting of data from all measurement points simultaneously. Under the investigation, different distance measures (Euclidean, Chebyshev, or Manhattan), as well as an approach to the optimal number of cluster selections. Based on the investigation, the four different clusters that represent working conditions were obtained using methods to define an optimal number of clusters. Cluster 1 represented time with high PV production; cluster 2 represented time with relatively low PV production and when BESS was charged; cluster 3 represents time with relatively high PV production and when BESS was charged; cluster 4 represents time without PV production. Additionally, after the clustering process, a deep analysis was performed in relation to the working condition of the microgrid.

The modularization of industrial plants concerns the decomposition of the system into multiple subsystems that are built in yards located in different areas of the world and then assembled on the construction site. This design philosophy allows for the reduction of construction costs and schedules. Unconventional plant solutions can make the most of this system concept in the electrical sector. In this article, an alternative architecture for electrical distribution is proposed. The suggested scheme allows the reduction in the number of items of equipment and the weight of the system, resulting in an optimal solution for a modularized system. The results are achieved by decreasing the required installed power and the weight of the copper used for the cables.

Due to the dramatic growth of the global population, building multi-story buildings has become a necessity, which strongly requires the installation of an elevator regardless of the type of building being built. This study focuses on households, which are the second-largest electricity consumers after the transportation sector. In residential buildings, elevators impose huge electricity costs because they are used by many consumers. The novelty of this paper is implementing a Hybrid Energy Storage System (HESS), including an ultracapacitor Energy Storage (UCES) and a Battery Energy Storage (BES) system, in order to reduce the amount of power and energy consumed by elevators in residential buildings. The control strategy of this study includes two main parts. In the first stage, an indirect field-oriented control strategy is implemented to provide new features and flexibility to the system and take benefit of the regenerative energy received from the elevator’s motor. In the second stage, a novel control strategy is proposed to control the HESS efficiently. In this context, the HESS is only fed by regenerated power so the amount of energy stored in the UC can be used to reduce peak consumption. Meanwhile, the BES supplies common electrical loads in the building, e.g., washing machines, heating services (both boiler and heat pump), and lighting, which helps to achieve a nearly zero energy building.