Bipolar dc microgrids have been increasingly adopted in different applications due to their versatility in scaling to higher power levels while maintaining the same safety requirements as lower voltage unipolar ones. On the other hand, power imbalance, commonly faced in bipolar systems, can lead to undesirable voltage deviations that may trigger protection devices, cause corrosion, and increase risks of electric shock. To address this issue, several voltage balancing solutions have been proposed, including self-balancing dc-dc converters, and others active balancers. Both approaches are different in terms of hardware implementation, efficiency, and complexity. In this paper, a two-switch buck/boost voltage balancer and a self-balanced current-fed dual active bridge (CF-DAB) converter are experimentally compared for applications in bipolar dc microgrids. Experimental results are presented using a 5-kW prototype. The results demonstrate that both solutions offer different opportunities for system optimization. However, the processed rms current analysis shows the self-balanced solution providing advantages in terms of efficiency, while the conventional buck/boost balancer offers a more cost-effective solution.

The increasing demand for efficient and resilient renewable-based energy systems is driving research towards hybrid ac/dc microgrids (HMG), offering a practical pathway to future dc-dominant grids by directly integrating a wide range of dc-operated resources. This paper proposes a model-free real-time control strategy for coordinating distributed generators (DGs) to achieve dynamic global power sharing in an islanded HMG. Conventional model-based controllers are replaced with a deep reinforcement learning agent based on the deep deterministic policy gradient (DDPG) algorithm. Unlike most existing studies that rely on offline training through computer simulations, the proposed agent is trained online during normal operation, without requiring predefined system models or manual controller tuning. The effectiveness of the method is validated through hardware-in-the-loop (HIL) experiments under different load variation scenarios, demonstrating robust dynamic response and accurate global power sharing.

To keep up with the rising demand for electricity, renewable energy sources, including solar and wind power, are being increasingly utilized. However, grid stability is compromised by the intermittent nature of renewable energy resources. Technologies for energy storage provide a solution by enhancing system flexibility. As prosumer-based electrical systems and distributed energy resources expand, energy management systems are becoming more essential for optimizing system functionality and efficiency by coordinating the operation of various devices. This paper deals with a genetic algorithm-based energy management system consisting of PV generation, household load, electric vehicle, and energy storage system. The objective is to reduce electricity costs by defining the objective function and related constraints. The main novelty of this paper is the study of different parameters used in a genetic algorithm, and to find out the best set of parameters in terms of electricity cost reduction, that can be later used as guidelines to design similar types of systems.

This paper presents the design and implementation of a grid-forming control for a dual-purpose dc-dc/ac PWM modular power converter tailored for three-phase three-wire ac conversion in nanogrid applications. The study emphasizes the integration of grid-forming and droop control mechanisms to ensure system stability and controlled power sharing. Extensive simulations and analyses demonstrate the effectiveness of the proposed control strategy, yielding swift and precise responses to dynamic power demand changes. The research offers valuable insights into the operation and functionality of this power converter topology within ac nanogrids, contributing to enhanced grid flexibility and reliability in renewable energy systems.

DC-DC converters are widely used to provide power conversion in electrical/electronic appliances and portable electronic devices. Over the last few decades, they also have been played a key role in the integration of renewable energy sources into the electric power grid or as standalone power sources. However, to achieve proper integration of certain electric/electronic devices/drives or photovoltaic power in shadowing conditions, it is frequently imperative to employ DC-DC converters that possess enhanced voltage amplification, a capability that standard DC-DC converters lack. According to this need, this paper proposes a new DC-DC Buck-Boost converter using a single power semiconductor switch. The proposed topology provides wide conversion voltage ratio, reduced voltage stress in the power semiconductor and reduced ripple of the input current. The operation principle of the proposed converter and the static gain will be discussed through a theoretical analysis. The performance of this power converter will be tested through simulations and experiments.

The smart transformer (ST) will become a fundamental element in the future of smart distribution grids. STs allow energy management by facilitating the connection between high and low voltage electric grids points, renewable energies, and energy storage devices. Multiport transformers have multiple windings for inputs and outputs, allowing different loads and generators to be connected to the same device. Multiport transformers combined with solid-state transformers (SST) could be an optimal solution for smart grids, as they can configure their operation mode on each port in accordance with the desired control strategy. This work proposes the use of a Multiport ST (MPST) in a residential building, which has batteries, photovoltaic panels, and electronic drivers to power the elevators. The paper proposes a coordination strategy for the different ports and tests its operation in different simulation cases.

This paper describes a prototype of a solar inverter based on qZS network that is designed as a competitive solution to the available on the market commercial solutions. Passive and active components selection guidelines are analyzed. It is based on the target efficiency profile and theoretical losses model for active and passive components. Experimental results confirm theoretical predictions. The results and feasibility for commercial application of the proposed solution is discussed.

In this paper a detailed analysis of a bidirectional buck boost converter used for charging/discharging a supercapacitor is carried out. The analysis takes into account conduction parameters of semiconductors and resistances of inductors, determining the variation of different performance indeces when the charge (and voltage) of supercapacitor varies.

This paper studies an operation strategy for a single-phase grid-connected 3LT-type qZSI to regulate the active and reactive power flows. This topology is quite promising in photovoltaic system. The different elements are properly calculated, providing simulation results with a good concordance with the theoretical predictions.

In this paper buck-boost inverter based on unfolding circuit is discussed as novel solution for photovoltaic application. Simple control system is proposed and discussed for output voltage control in grid-off mode. Experimental results are presented for wide range of input voltage and power. The main advantage and potential problems are discussed in conclusions.

This work presents an energy management strategy based on scheduling battery operation in prosumer systems, according to forecast data available 24 hours in advance. The proposed method seeks to reach a beneficial compromise between prosumers and distribution grid operators, independently of specific economic context or technical regulations. An improvement to deal with forecast inaccuracy is carried out. Results demonstrate that it offers good properties regarding energy management, with a stored energy reserve estimation, battery lifetime preservation and self-consumption and self-sufficiency enhancement.

This paper proposes a new modulation technique for an interleaved H-bridge qZS inverter that is intended for the single-phase photovoltaic systems. The potential benefits of this topology are reduced passive components and improved quality of energy generation. The modulation technique developed allows the maximum boost control for a better utilization of the dc-link. It is developed with the required phase-shifted carrier signals and wider shoot-through state generation than in simple boost control approach.

The upgrade of power systems in the last years due to the proliferation of distributed generation with renewable energy sources, active users and electric vehicles has become a challenge. In this new scenario, prosumers play an important role in order to buffer the consumption curve and, therefore, contributing to the grid requirements. Special attention is attracted by photovoltaic (PV) arrays integrated in residential buildings, because they can be complemented with energy storage systems (ESSs), such as batteries or ultracapacitors (UCs) or even a combination of both, with the aim to achieve that customers could manage their energy. The above reasons justify the need of an energy management system (EMS) that coordinates the operation of the energy storage devices in an optimized way, as they are expensive. In this paper, a comprehensive control system is proposed to exchange energy between the hybrid storage devices (batteries and UCs) of two dwells with PV installations in order to increase the availability of their ESSs and support the energy requirements during the most time possible, optimizing sizes and costs and avoiding saturation.

This paper presents a four wire dual-buck inverter integrated in a photovoltaic system with grid support capabilities. In the context of smart-grids this kind of systems can play an important role. In this particular case the system will supply the ancillary services for unbalanced loads and reactive power compensation. A dual-buck inverter is adopted in order to ensure a higher reliability. This kind of inverter is characterized by the non-existence of shoot-through problems and by the possibility of the using power MOSFETs as active switches. The control system for the dual-buck inverter with the ancillary service functions is also presented. In order to verify the performance of this system several simulation results are presented and discussed.

This paper presents the design for the control scheme of a three-level three-phase neutral-point-clamped quasi-Z-Source inverter which employs an LCL filter for the connection to the grid. A state-feedback based control is developed so as to attain a fully decoupled control of the active and reactive power exchanged with the grid. In addition, a PI regulator is tailored in order to control the dc-link voltage of the inverter. The complete control strategy, along with the inherent capabilities of the quasi- Z-Source inverters, signifies that this kind of power converters is suitable for renewable energy source applications.

The current project was originally initiated by the marine industry, where bulky low-frequency transformers have become a growing problem and the need for a more flexible solution is growing. The active power electronic transformer (APET) is likely to be the most suitable candidate. Modular power electronic building blocks (PEBB) enable complex power electronics systems to be built and reconfigured quickly and reliably. As a result, reduced costs, losses, weight, size and less engineering effort could be achieved. In this paper a new type of the PEBB for the APET is proposed. The input and output stages were constructed from the half-bridge sub-modules of the modular multilevel converter while the isolation stage consists of the conventional dual half-bridge. To balance the voltage of input capacitors a simple control algorithm was proposed. The performance of the system was verified by computer simulations using PSIM simulation software. Finally, a 3D model of the demonstrator is presented.

This paper presents an experimental investigation of a single phase three-level neutral-point-clamped quasi-Z-source inverter for photovoltaic application. The prototype and the case study system are described. Experimental results along with theoretical losses analysis are discussed. The implemented maximum power point tracking algorithm was verified in a real photovoltaic system.

This document presents a three-phase grid-connected power injection system for a photovoltaic power source with control of the injected active power through an energy storage system based on ultracapacitors. The ultracapacitor technology offers high power density that matches properly in a Smart-Grid scenario with the need of active power regulation for quasi-manageable energy ability. A voltage source inverter injects the power into the grid, while a bidirectional direct current converter regulates the charge of the ultracapacitor. In this way, the ultracapacitor could be charged when the active power needed in the grid is below the photovoltaic power, it could be discharged in the opposite case, and, if the ultracapacitor is saturated the power point tracked depends on the reference, injecting the desired active power in every assumption. The system has been implemented in a prototype through a FPGA/processor controller, so the hardware/software co-design is detailed. Finally, the performance of the configuration is exposed via experimental tests.

Distribution Grid is evolving into the Smart Grid and users are playing a key role more and more. An efficient network is the aim and Energy Management Systems are being utilized in residential areas in order to contribute to reach this final mentioned goal. The Local Energy Management Unit is presented in this paper, which allows an optimized constant power demand to the Grid, demanding sinusoidal currents to the Grid which are in phase with the Grid voltage. Communications by using TCP and X10 protocols are used to control the whole system and a prototype, which is presented in this paper together with the obtained experimental results, is built to demonstrate the presented efficient energy management conclusions.

Smart grid structure could be very complex. Active power electronic transformers (APETs), composing an important part of the smart grid, could have many roles in that stochastic and variable system. Modular structure is the key to flexibility, reduced costs and losses. We propose a base module of the APET consisting of modular building blocks, also known as power electronics building blocks (PEBBs). PEBBs have plug-and-play functionality and can be connected together in various ways. Therefore, it is easy to adapt the APET to any kind of voltage level and type. To guarantee power quality, the base module has the functionality of power factor correction and active power injection. The performance of the base module was verified by computer-aided simulations.

This paper describes the operation of a grid-connected PV system based on a single-phase 3L-NPC qZSI using PSCAD as simulation tool for modelling the system: PV array, single-phase 3L-NPC qZSI, filter stage and electrical grid. The control system considers a maximum power point tracking algorithm, a phase loop locked for synchronization with the grid voltage, a control strategy to inject current in phase with the voltage at the point of common coupling and the modulation technique that also take into account shoot-through duty cycle. Simulation results are provided in order to show the viability of using this topology for PV energy systems connected to the electrical grid.

In this paper a low-power wind generation grid-connected system for domestic consumers with two control modes (Maximum Power Point Tracking (MPPT) and Power Control (PC)), will be presented. The MPPT mode will be active when the home's load is higher than the wind generator's maximum available power and the PC mode will be active when the home's load is lower than the wind generator's maximum available power. These two techniques will be adopted to both optimize the wind system performance and to prevent power injection into the electrical grid. Hence, the PC mode will be a particularly important part of this system. It will also be crucial to assure that the controller decides correctly on which control mode should be active, given the current grid supplying power.

This paper describes a new modulation technique for a single phase three-level neutral-point-clamped qZS inverter. The proposed converter is intended for applications that require input voltage gain and high quality of the output voltage. The simulation and experimental results are presented and discussed.

This paper presents a study about the power injection of grid connected photovoltaic plants when there are non-linear loads connected to the point of common coupling. The smart grid scenario suggests that the photovoltaic energy should take care not only about the active power, but also about the reactive power. The study compares the last years criteria of injecting the maximum active power, with the expected tendency of providing reactive power in an active filter way for avoiding currents harmonics in the grid. The topology used is a traditional three-phase inverter controlled by a power balance technique through a synchronous hysteresis band. First of all, a power injection system that do not care about the loads connected into the grid is developed, then the loads are taken into account to improve the grid operation by supplying them. Both configurations are implemented in a prototype to compare the results via experimental tests.

The idea of power electronic transformer is known already over 20 years. There are numerous papers written about power electronic transformers. In the literature one can find tens on different topologies, control methods, standards, requirements etc. It is easy to loose insight what topology to use and where. In this paper a general overview of the power electronic transformer technology in terms of smart grids is presented. The information collected from the literature is classified and organized. In conclusion some generalizations are made and development trends are shown.

High penetration levels of distributed photovoltaic inverters on electrical distribution grids and due to the main points demanded in the latest issues of grid codes such as the reactive power injection during transient grid faults (voltage sags) and their disconnection in order to avoid the islanding phenomena, a suitable control algorithm combination is needed to provide an optimum operation at the electrical grids where they are connected, improving the power quality and the power supply continuity. This paper is devoted to the comparison through simulation of two power flow control strategies for 100 kW photovoltaic inverters in order to analyze the advantages and disadvantages of each one. The first one is based on the modulation index and the disphase controls of the reference signal face to the point of common coupling voltage. The second one is based on a synchronous reference frame with the voltage at the point of common coupling using idand iqcurrent component controllers.