This paper sets out a systematic modeling approach for determining the parameters of a three-winding high-frequency transformer (3W-HFT) equivalent circuit. The aim is to mimic its electromagnetic and electrostatic behavior in a multi-active bridge design framework. Starting from a reference lumped elements circuit, the proposed methodology extracts the key transformer parameters. This is achieved by performing short-circuit and open-circuit tests in a range of frequencies between 20 Hz and 13 MHz using an impedance analyzer. The accuracy of the proposed methodology for modeling 3W-HFT has been verified by comparing the short and open circuit impedances evaluated by the proposed equivalent circuit with the experimental ones, resulting in a significant overlap. Furthermore, a co-simulation model developed using MATLAB and PLECS software is presented, and the results exhibit a significant matching with the experimental data, validating the proposed modeling methodology.

The performance of zero-sequence voltage compensation algorithms in a three-phase neutral point clamped (NPC) converter acting as an interface between a DC charger for electric vehicles and the grid has been modelled, simulated and experimentally validated. In particular, the analysis of zero-sequence voltage methods has been investigated, as they provide an effective solution to this problem regardless of the modulation technique used. This study focuses on the development of an electric vehicle charging station supplied by an NPC converter, where both the linear control of the DC voltage unbalance and the optimal zero-sequence voltage detection methods are studied. Finally, the results obtained from the implementation of linear control of the DC voltage unbalance is reported.

This paper proposes a DC/DC isolated conversion system based on the Triple-Active Bridge (TAB) topology for green hydrogen production. Specifically, the configuration involving a Photovoltaic (PV) power plant and an Energy Storage System (ESS) is investigated. The TAB’s quasi-inherent decoupling feature and the use of Virtual Direct Power Control (VDPC) enable effective and independent management of power flows from the PV and ESS, even in the event that one of the sources fail and the ESS is charging due to PV overproduction. A simulation study on PLECS demonstrates the efficacy of the proposed configuration and shows that the system can manage the power flow of the TAB ports independently.

The papers in this special section focuses on the development of modeling the charging loads and behaviors of electric vehicles (EVs) and on the novel control methods for navigating and charging/discharging EVs. Due to the energy demand growth and environmental concerns, EVs have received a prominent interest by academia, industry, and government. This has attracted in recent years the study on the integration of EVs in the market. To make this integration widespread, several challenges need to be addressed and various shortcomings require solutions.

The paper reports the evaluation of a SiC-based three-phase inverter for the energy management of Sodium Metal Halide battery oriented to manage the power intermittency of renewable energy sources (RES). The power converter was firstly designed referring to a specific case study and subsequently prototyped. The control algorithm for managing the power flow was first developed and then tested. The performance in terms of current THD and energy efficiency has been evaluated. The experimental results confirm the expected design performances and the feasibility of using the proposed ESS configuration for managing power intermittency generation of RES-based microgrid

This paper presents the development of a characterization tool for innovative batteries intended for space applications. i.e. an innovative Lithium-Ion battery equipped with a nanostructured germanium anode. Particularly, a second-order equivalent circuit model and the test campaign required to identify all model parameters are introduced. Subsequently, the battery characterization tool developed on LabVIEW environment for the automatic implementation of the test campaign is described. The battery characterization tool has been experimentally tested on a battery prototype.

The energy storage sizing procedure for an all-electric aircraft, characterised by vertical take-off and landing (VTOL), is presented in the paper. In order to define the energy consumption, the propulsion system model has been developed and simulated, referring to a specific configuration of VOLT obtained by the transformation of a very light twin-propeller aircraft named Tecnam P2012 T. Specifically, a flight mission-oriented to air city taxing has been considered. The simulation results highlight the presence of significant peak power during take-off and landing. At the aim of optimising the weight and the volume of the energy storage systems (ESSs), considered a critical issue in all-electric aircraft (AEA), the sizing of electrochemical and Supercapacitors (SCs) hybrid ESS configurations have been investigated. In particular, the use of SCs is devoted to the smooth peak power demand of VTOL-AEA. A comparison between the simulation results of an electrochemical battery and hybrid ESSs, designed on the test mission of Tecnam P2012 T power demand, has been developed and presented.

This paper deals with electromagnetic loss analysis and minimization in an integrated Flywheel Energy Storage System (FESS). The FESS consists of a large-airgap Surface-Mounted Permanent Magnet Synchronous Machine (SPM), whose inner rotor integrates a carbon-fiber flywheel, leading to a compact and efficient FESS. Electromagnetic losses minimization is achieved through an accurate SPM modelling, which accounts for both Joule and core losses, as well as for flux-weakening operation. Consequently, SPM maximum efficiency is obtained by injecting a proper demagnetization current component at each operating condition, which guarantee the optimal trade-off among the different losses’ contributions. The effectiveness of the proposed approach is validated through numerical simulations.

The design of an Inner-Rotor Large-Airgap Permanent Magnet Synchronous Machine (IRLA-PMSM) is presented in this paper, whose distinctive feature consists of integrating a thick carbon-fibre cylindrical layer that acts as both a sleeve and a flywheel. This results in large airgap and makes simplified mechanical modelling generally used for sleeve design no more suitable. Therefore, an advanced mechanical modelling is presented in the paper, which is combined with an electromagnetic and energy modelling in order to make the analytical design procedure compliant with all the design targets and constraints. The proposed IRLA-PMSM is validated through finite element analyses, which regard both mechanical and electromagnetic aspects at different operating conditions.

An optimization study to reduce the harmonic components of the magnetic flux density due to the modulation effect in a coaxial Magnetic Gear Transmission system (MaGT) is presented in this paper. The results of the harmonic content analysis of a MaGT are used to optimize the design of a double-stage MaGT configuration for automotive applications presented in previous works. In particular, pole arc to pole pitch ratios of the two rotors and of the modulation ring have been tuned in order to reduce the harmonic content of the magnetic flux density. The comparison between two different case studies is presented in regard to core losses, maximum temperatures and overall MaGT efficiency. These analyses have been carried out by means of analytical formulations and finite element simulations using the FEMM software.

The papers in this special section explore the resilience in the energy markets. The transformation of energy infrastructure is making the resilience a fundamental topic for the definition of future configuration of the energy systems. This is due to the increased penetration of renewable energy sources (RES), the distributed energy management, the change in the power demand, the integration between energy and mobility sectors, the progressive liberalization of energy markets, the increased probability of extreme weather events, and the occurrence of errors in the interaction between humans and machines.

In this paper a model suitable for representing the electrical dynamic behaviour of Sodium Metal Halides Batteries (SMHBs) has been reported. In particular, the Thévenin circuit approach has been investigated considering the equivalent circuit parameters depending on the State Of Charge (SOC). The proposed SMHB model has been developed referring to the experimental tests conducted on a commercial module with a capacity of 23.5 kWh and a rated discharge power of 7.8 kW. In order to develop the identification of the Thévenin circuit parameters, a numerical processing of the specific measurements of a SMHB test-bench, considering the dynamic analytic solution of Thévenin circuit battery voltage, has been carried out and discussed in detail. The proposed approach allows a significant reduction of steady state errors respect to the numerical fitting procedure. Finally, the optimization of the first step identification process has been performed obtaining a very small variation in the values of the identified parameters by means of the proposed approach. The comparison between the experimental and simulation results has confirmed the good accuracy of the proposed model in a defined SOC range.

In this paper a Genetic Algorithm (GA) is used to partition a distribution network with the aim to minimize the energy exchange among the microgrids (i.e. maximize self-consumption) in presence of distributed generation. The proposed GA is tested on the IEEE prototypical network PG & E 69-bus. The microgrid partitioning is tested over a period of one year with hourly sampled data of real household consumption and real distributed generation data. The proposed GA approach is compared with a Tabu Search (TS) method already presented in the scientific literature. Results show that both GA and TS lead to the identification of equivalent microgrids. However, the GA based approach achieves better convergence results allowing for a reliable network partitioning with less CPU effort. Moreover, the histograms of the power unbalances of the microgrids show unimodal and skewed distributions offering an interesting starting point for the appropriate deployment of storage and control systems.

Modelling, sizing and control of a Hybrid Energy Storage System (HESS) made up of Batteries (B) and Supercapacitors (S) is presented in this paper. The HESS is characterized by an integrated topology through a Three-level Neutral-Point Clamped Converter (NPC), leading to a highly-integrated electric propulsion system. Accurate modelling of both B and S are considered at first, although some simplifications are introduced due to automotive application. Then, a suitable sizing procedure is introduced and discussed in detail, which is based also on an experimental S characterization. The HESS control approach is described as well, which is quite robust against the non-linear model of S due to the integrated topology. The effectiveness of all the design solutions has been validated through a simulation study, which refers to a vehicle start and stop.

An advanced Frequency-Based energy Management (FBM) suitable for Hybrid Energy Storage Systems (HESSs) in Microgrids (MGs) is presented in this paper. The HESS is made up of Batteries (B) and Supercapacitors (S) and it has to provide both peak shaving and power quality. A frequency-based power split criterion is introduced, namely the B power profile is synthesized through an appropriate low-pass filter, while S has to cope with sudden and fast power fluctuations. In addition, in order to enable a suitable peak shaving capability, an appropriate management algorithm is developed based on the forecasted MG power profile. As a result, suitable B power thresholds can be defined in accordance with both B power and energy constraints over a given time horizon. This can be adapted also in real-time in order to benefit from more accurate forecasting and B energy status. The effectiveness of the proposed FBM is proved by numerical simulations, which refer to the MG of the German island of Borkum.

This paper presents a smart energy management of a Hybrid Energy Storage System (HESS) that supplies a highly integrated electric propulsion system. The HESS consists of Batteries (BT) and Supercapacitors (SC), which are integrated to each other through the traction inverter, namely a Three-level Neutral-Point Clamped Converter (NPC). The proposed management strategy consists of exploiting SC over the low-speed operating range, thus coping with vehicle acceleration and deceleration needs for urban mobility mostly. Consequently, BT is preserved successfully from excessive cycling, it being also supported over the mid speed range. Both these goals are achieved by suitable SC sizing, which accounts for both energy and voltage constraints. The proposed energy management is validated through a simulation study, which refers to vehicle acceleration and stop.

An optimal control strategy devoted to manage the daily charging/discharging profiles of Energy Storage Systems (ESSs) is described in the present paper. The proposed approach aims to minimize Microgrids (MGs) daily electricity costs considering both the real-time price evolution and the effects of intermittent Renewable Energy Sources (RESs). Referring to MGs and electricity market modeling as well as to their main physical and economic constraints, an optimal ESS charging/discharging strategy has been developed. The effectiveness of the proposed ESS management is verified on a MG case study. Particularly, the electricity demand and RES production measured on a small-scale MG are used to compare the daily MG electricity costs and energy balances with and without the proposed optimal control strategy of ESS.

A novel Hybrid Energy Storage System (HESS) for Electric Vehicles (EVs) is proposed in this paper. It consists of a battery pack and an ultra-capacitor module (UC), which are suitably coupled through a Three-Level Neutral-Point Clamped Converter (NPC). Particularly, although the UC is integrated within the DC-link, its voltage can be varied within a wide range, thus assuring its full exploitation without the need of any DC-DC converter. This is achieved by means of an appropriate HESS control system, which also prevents the battery pack from handling sudden power fluctuations. The effectiveness of the proposed HESS is verified through a simulation study, which refers to an electric propulsion system based on a Surface-Mounted Permanent Magnet Synchronous Machine (SPM), which is supplied by the proposed HESS through the NPC.

In this paper the integration between the Vehicle to Grid technology and a stationary energy storage system in a Virtual Power Plant (VPP) has been investigated. In order to evaluate the effects of such energy storage systems in an autonomous VPP, an Energy Management System (EMS), oriented to improve the local matching between electrical energy demand and production, has been proposed. To achieve this target and optimize the local energy production exploitation, an energy system design procedure, based on the minimization of the VPP total cost through an annual emulation of the VPP's EMS strategy, has been applied. The proposed methodology, tested on a benchmark VPP, considers the contribution of both electric vehicles and stationary battery in different possible configurations. The comparison among three different cases of study has finally presented at the aim of pointing out the technical and economic benefits.

A novel DC-link voltage and current control algorithm for Three-Level Neutral-Point-Clamped converters (NPCs) is proposed in this paper. It is developed with the aim of sharing the overall DC-link voltage among DC-link capacitors as needed, without impairing NPC load performances. The proposed algorithm consists of an external DC-link voltage control loop, which synthesizes an appropriate reference DC-link current profile on the basis of the reference DC-link voltages. Such a current profile is then tracked by means of an inner DC-link current control system. This last synthesizes the most suitable PWM pattern for DC-link voltage regulation, prioritizing NPC load requirements at the same time. The effectiveness of the proposed DC-link voltage and current control algorithm is verified through extensive simulations, which refer to the case study of a three-phase NPC that feeds a Surface-Mounted Permanent Magnet Synchronous Machine.

In the present paper a novel configuration of high concentrator photovoltaic (HCPV) systems based on Cassegrain optics has been presented. The proposed system has been designed in order to be suitable for the implementation of both multi-junction and spectrum splitting configurations. The Cassegrain optic design, the components and material choices for the development of HCPV receivers have been described. Subsequently, the proposed HCPV system has been implemented considering a multi-junction and dichroic photovoltaic solar cells configurations. Finally, the outdoor characterization of the two receiver prototypes has been carried out in order to determine their energy conversion performances. The obtained outcomes are then compared and discussed in order to highlight the worth, and the effectiveness of the proposed HCPV configurations.

A model predictive control algorithm (MPC) suitable for Surface-Mounted Permanent Magnet Synchronous Machines (SPMs) is presented in this paper. It is based upon an accurate discrete-time model of the drive, accounting for both voltage saturation and current limitation constraints. It aims to properly manage these constraints in order to guarantee a good exploitation of both transient and steady state SPM performances, especially over flux-weakening operation. The effectiveness of the proposed MPC is first validated by a simulation study, in which the sensitivity of the proposed MPC against un-compensated inverter un-idealities and parameter uncertainties is properly highlighted and discussed, as well as the effects of sudden load torque variations. Then, an experimental study is performed on a radial-flux SPM driven by a Field Programmable Gate Arrays (FPGA) control board. The performances achievable by the proposed MPC are compared with those obtained by a conventional PI-based control system in order to highlight the improvements, especially regarding transient and flux-weakening operation.

A novel flux-weakening approach suitable for Surface-Mounted Permanent Magnet Synchronous Machines (SPMs) is presented in this paper. It consists in directly synthesizing the square magnitudes of the current and voltage vectors on the basis of an accurate SPM sampled-data model and of the reference torque profile. This enables optimal and easy management of SPM operating constraints, i.e. current limitation and voltage saturation, on the basis of which the dq reference current profile can be achieved, whatever the SPM speed and Constant Power Speed Ratio (CPSR) is, i.e. finite or infinite. The effectiveness of the proposed flux-weakening approach is highlighted by both simulation and experimental results, which refer to SPMs with finite and/or infinite CPSR and driven by a predictive control algorithm.

The continuing development and the increasing diffusion of concentrator photovoltaic (CPV) systems highlight the lack of specific international standards in the CPV power rating and characterization field. Presently, the only reference standard for CPV cells and modules is the IEC 62108, which does not impose minimum requirements for solar trackers and simulators used in the qualification process of CPV modules. Nevertheless, the overall quality of CPV tests is strictly associated to the technical specifications of these devices. The aim of this paper is to define optical and radiometric properties of solar simulators and the pointing accuracy of solar trackers, required for testing CPV devices and rating their performance. The results of experimental analyses on real CPV systems have been reported, highlighting the criticalities of indoor and outdoor CPV characterization. Finally an outdoor light soaking test, executed under MPPT conditions, has been proposed for the qualification process of high concentrating photovoltaic devices.

In this study, the characterization of a concentrator photovoltaic (CPV) system based on a Cassegrain-type optic is presented. The indoor and outdoor electrical parameters have been measured and analyzed. On the basis of the IEC 60891 standard, the acquired I-V characteristics have been reported under the CSTC defined in the CEI 82-25 and the electrical parameters deviations have been determined. The correlations among temperature, direct normal irradiance (DNI) and power have been discussed. The results of the absolute power test based on the ASTM E2527 standard and the values of power deviation are reported. Finally the rating power comparison between the two standard test procedures is performed.

This paper presents the preliminary design of a 10 MW permanent magnet synchronous generator (PMSG) for off-shore direct drive wind turbines (DDWT). In order to improve the DDWT torque quality, energy efficiency, power management, fault tolerance and reliability a twelve-phase PMSG made of four independent three-phase star connected subsystems has been considered. With the aim of satisfying the several constraints related to cogging torque reduction, stator and rotor diameter limitation, low speed operation and magnetic decoupling of four three-phase subsystems, a multi-star fractional-slot tooth concentrated winding PMSG has been designed. The analytical results have been validated by means of Finite Element Analysis (FEA) highlighting the worth and effectiveness of the proposed configuration.

A novel DC-link voltage equalization algorithm for Three-Level Neutral-Point-Clamped Converters (NPCs) is presented in this paper. It mainly consists of appropriate pulse width modulation patterns, which are alternatively employed in order to exploit the DC-link capacitors differently, for a given reference voltage space vector. Thus, the most suitable PWM pattern is chosen in each sampling time interval in accordance with DC-link voltage equalization needs, without affecting NPC performances in terms of output voltage and current waveforms. The worth and effectiveness of the proposed equalization algorithm are verified through a simulation study, which refers to the case of a Surface-Mounted Permanent Magnet Synchronous Machine (SPM) fed by a three-phase NPC.