Management and control of energy storage systems for stationary and automotive applications

This PhD dissertation has presented a number of scenarios in which Energy Storage Systems (ESSs) can be usefully employed for increasing energy system performances. Particularly, after introducing the State-of-the-Art of ESS technologies (Chapter 1), reference has been made to some stationary and automotive applications. Stationary applications have regarded Renewable Energy Sources (RESs) exploitation issues and EV integration within micro-grids (Chapter 2). It has been shown that ESSs are particularly useful in compensating for RES forecasting errors, whereas they are much less effective as energy buffers. In addition, Vehicle to Grid (V2G) has also been revealed as an alternative and viable solution for increasing RES penetration level and micro-grid autonomy, even in presence of small EV fleets. The promising results obtained in the energy management of power systems by means of the use of V2G and G2V paradigm have suggested the integration of Electric Vehicles (EVs) into the power system. This requires that EV energy storage systems should satisfy both electric propulsion and power system requirements. With this aim, the design and management of a novel Hybrid Energy Storage System (HESS) for EVs has been considered (Chapter 3). Particularly, the proposed configuration allows the reduction of the peak current delivered by EV batteries, thus preserving their rated performances and increasing their lifetime. This goal has been achieved by means of a suitable management of the energy flows provided by the HESS, leading to a good exploitation of the proposed topology. The effectiveness of the proposed solutions has been verified through several extensive simulation studies, which have been carried out in the Matlab environment. In conclusion, it can be stated that all cases have revealed the need of carefully sizing and managing ESSs in order to achieve optimal results. In this context, it is worth noting that the employment of large ESS easily leads to enhanced performances but also to significant increased costs. This drawback cannot be sustained, especially in automotive applications, in which EV competitiveness is strictly related to a decrease of ESS size, weight and costs. On the other hand, small ESSs do not generally guarantee the same performances but they can be quite similar if optimal management and control strategies are employed. These last thus will cover a fundamental role in making ESS more widespread, enabling an optimal trade-off among increased performances, costs, management and control issues

A Novel Highly Integrated Hybrid Energy Storage System for Electric Propulsion and Smart Grid Applications

This chapter addresses potentialities and advantages of a highly integrated hybrid energy storage system (HESS) for electric propulsion and smart grids. This configuration consists of a highly integrated battery-ultracapacitor system (HIBUC) and aims to benefit from the advantages of both passive and active HESS configurations. Particularly, the integration of the ultracapacitor module (UM) within the DC-link of the DC/AC multilevel converter enables the decoupling between DC-link voltage and energy content without the need for any additional DC/DC converter. As a result, HIBUC benefits from simplicity and energy flow management capabilities very similar to those achieved by passive and active HESS configurations, respectively. This is highlighted properly by a theoretical analysis, which also accounts for a comparison between HIBUC and both passive and active HESS configurations. Some HIBUC application examples are also reported, which highlight the flexibility and potentialities of HIBUC for both electric propulsion systems and smart grids

suppression of dc link voltage unbalance in three level neutral point clamped converters

Abstract Two different control approaches for suppressing DC-link voltage unbalance in Three-Level Neutral-Point Clamped Converters (NPCs) are presented in this paper. They both guarantee DC-link voltage equalization over any NPC operating conditions, i.e. when the NPC feeds or is supplied by the main AC grid at different active and/or reactive power rates. The proposed control approaches consist of either a hysteresis or a proportional regulator, each of which synthesizes the most suitable control action based on the actual DC-link voltage unbalance. Particularly, two different PWM techniques have been developed in order to achieve DC-link voltage equalization successfully, preserving NPC voltage and current waveforms at the same time. The performances achievable by means of both the proposed control approaches have been compared to each other through an extensive simulation study in order to highlight their most important advantages and drawbacks, as well as their effectiveness over any operating conditions. Particularly, both control approaches are validated in the Matlab-Simulink environment referring to DC-link voltage equalization of an NPC that represents the point of common coupling between a DC microgrid and the main AC grid

Energy Management and Control System Design of an Integrated Flywheel Energy Storage System for Residential Users

This paper presents the energy management and control system design of an integrated flywheel energy storage system (FESS) for residential users. The proposed FESS is able to draw/deliver 8 kWh at 8 kW, and relies on a large-airgap surface-mounted permanent magnet synchronous machine, the inner rotor of which integrates a carbon-fiber flywheel, leading to a compact and efficient FESS. The proposed energy management system is based on four different operating modes, which are defined and can be selected in accordance with FESS speed and/or user’s preference, while FESS control system is devoted to power/current tracking at both machine- and grid-side converters. The effectiveness of the proposed solutions, as well as the overall energy performance of the proposed FESS, are verified by real-time simulations, which regard different operating conditions and/or realistic scenarios

Design of flux-weakening space vector control algorithms for permanent magnet brushless DC machines on suitable synchronous reference frames

The design of Space Vector Control (SVC) systems suitable for flux-weakening operation of Permanent Magnet Brushless DC Machines (PMBDCMs) is presented in this paper. The proposed design approach enables overcoming the critical issues arising from the non-linearities of PMBDCM voltage and torque equations; these issues derive from the trapezoidal shapes of back-emfs and affect PMBDCM constraint management significantly. The SVCs presented in this paper have been developed within two different synchronous reference frames, both of which enable distinguishing torque and demagnetizing current components clearly. Therefore, reference torque current component is determined in accordance with PMBDCM torque demand, while reference demagnetizing current component is computed through a voltage follower PI regulator, which processes the voltage deficit detected on the DC-link. In this regard, a novel synchronous reference frame is proposed in this paper, which improves PMBDCM constraint management and results into a wider constant-power speed range, but at the cost of some torque ripple. The enhanced performances achievable by SVC approaches are highlighted by numerical simulations, which regard the comparison among the SVCs and an SVC with no flux-weakening capability, at different operating conditions

A Genetic Algorithm for the Definition of Nodal Load Time Evolutions in Micro Grids Assessment

One of the on-going research topic in smart grid planning and assessment is the definition of suitable time evolution of load profiles in micro grids by using the information about the network topology and the available electrical measurements. This paper presents an approach for a heuristic definition of nodal load profiles in micro grids when the available measurements are not exhaustive for its state evaluation. In particular, in order to develop the preliminary micro grids assessment, a Genetic Algorithm (GA) has been employed to determine possible evolution of nodal load profiles that satisfy the power system constraints and input measurements. In order to verify the effectiveness of proposed methodology a real micro grid has been considered as case of study. The micro grid has been simulated in Digsilent and the used GA has been implemented in Matlab environment. Finally, Digsilent Programming Language (DPL) has been employed for interfacing the GA with Digsilent

A Forecasting-Based Control Algorithm for Improving Energy Management in High Concentrator Photovoltaic Power Plant Integrated with Energy Storage Systems

The High Concentrator Photovoltaic (HCPV) technology, due to its high efficiency, is considered one of the most promising solutions for the exploitation of sun-irradiation-based Renewable Energy Sources (RES). Nevertheless, the HCPV production is strictly connected to the Direct Normal Irradiation (DNI) making this photovoltaic technology more sensible to cloudiness than traditional ones. In order to mitigate the power intermittence and improve production programmability, the integration between Energy Storage Systems (ESSs) and HCPV, resorting to forecasting algorithms, has been investigated. Specifically, a local weather forecasting algorithm has been used for estimating the daily time evolution of DNI, air Temperature (T), Wind Speed (WS), and Air Mass (AM). These data are subsequently processed by means of an accurate HCPV model for the estimation of one day-ahead daily power production profile. The processing of HCPV forecasted generation by means of a properly tuned filter-based algorithm allows one day-ahead the definition of power profiles of ESS and power plant respectively, considering also the ESS constraints and the characteristic of the implemented real-time control algorithm. The effectiveness of the proposed forecasting model and control algorithm is verified through a simulation study referring to the solar power plant constituted by HCPV and ESS installed in Ottana, Italy. The results highlight that the application of the proposed approach lessens the power fluctuation effect caused by HCPV generation preserving the batteries at the same time. The feasibility and advantages of the proposed approach are finally presented

Vehicle-to-Grid Technology: State-of-the-Art and Future Scenarios

An overview of V2G (vehicle-to-grid) technology is presented in this paper. It aims to highlight the main features, opportunities and requirements of V2G. Thus, after briefly resuming the most popular charging strategies for PEVs (plug-in electric vehicles), the V2G concept is introduced, especially highlighting its potentiality as a revenue opportunity for PEV owners; this is mainly due to the V2G ability to provide ancillary services, such as load leveling, regulation and reserve. Such solutions have been thoroughly investigated in the literature from both the economic and technical points of view and are here reported. In addition, V2G requirements such as mobility needs, charging stations availability and appropriate PEV aggregative architectures are properly taken into account. Finally, future developments and scenarios have also been reported

Design of a High-Speed Ferrite-based Brushless DC Machine for Electric Vehicles

In the present paper an analytic procedure for the preliminary design of a High-Speed ferrite-based Brushless DC Machine (HS-BLDC) has been proposed. In particular, mechanical and electromagnetic modeling have been developed in order to take into account their mutual influence in the definition of the geometry of the electrical machine. In addition, suitable design targets have been imposed in accordance with electric vehicle application requirements. Hence, several mechanical and electromagnetic constraints have been introduced in order to comply with high-speed operation, preventing demagnetization issues of ferrite magnets as well. Subsequently, an HS-BLDC characterized by an inner rotor configuration has been designed in accordance with the proposed methodology. The analytical procedure and the corresponding results have been reported and validated by means of Finite Element Analyses (FEAs), highlighting the effectiveness of the proposed configuration and design solutions

A Methodological Approach For The Effective Infiltration Assessment In A Coastal Groundwater

Accurate estimates of spatial and temporal distribution of groundwater recharge are of utmost importance to protect groundwater systems. In coastal areas, the fragility of the systems makes such estimates critical for the correct management and protection of water resources from saltwater intrusion. The Muravera coastal plain, in the south-eastern Sardinia, has been studied since 1960, due to important saltwater intrusion phenomena. Since the early fifties, the natural hydrodynamic equilibrium between groundwater, surface-water and seawater has been deeply modified by the construction of four dams across the Flumendosa river and the development of agriculture, tourism and aquaculture activities along the coast. To implement an integrated and sustainable management system addressed to slow down the process of saltwater intrusion and, on the other, satisfy human requirements, it is important to develop a flexible scenario analysis system that considers changes of land-use and inputs to the hydrogeological system, also in relation to climate change. In this study, the innovative Soil Water Balance code (SWB) has been applied to the Muravera plain groundwater body to calculate spatial and temporal variations of groundwater recharge. The code calculates the recharge (R) by using geographic system (GIS) data layers in combination with tabular climatological data. It is based on a modified Thornthwaite - Mather soil water balance approach, with components of the soil water balance calculated at a daily time-step. A combined experimental approach of hydrogeological, satellite remote sensing and pedological methodologies has been applied to derive data layers describing local features of: (1) land-use classification, (2) hydrologic soil group, (3) flow direction, and (4) soil-water capacity. The code has proved to be promising for the effective infiltration assessment and it can be easily updated with high resolution data acquired in the field and from satellite images