Hybrid microgrids (HMGs) have shown great potential for the efficient integration of distributed energy resources and supporting reliable, flexible operation in standalone scenarios. In such systems, the secondary control is essential for restoring voltage and frequency deviations and ensuring accurate power sharing among distributed generators (DGs). While centralized control enables simple and cost-effective coordination, its vulnerability to controller or communication link failures can compromise global power sharing and system stability. This paper presents a resilient centralized secondary control architecture for standalone HMGs that preserves one-way broadcast coordination in normal operation while providing communication-free fault operation through locally deployed, online-trained artificial neural networks (ANNs). The ANNs are deployed at the DGs and the bidirectional interlinking converter (BIC) to predict point-of-common-coupling voltages using local measurements. These predicted values enable local controllers to emulate the behavior of the central secondary controller during system faults. This maintains accurate global power sharing during full centralized system failure and frequency/voltage regulation during isolated BIC operation, without introducing peer-to-peer coordination or additional distributed messaging. Furthermore, the ANNs are trained online during normal operation, allowing continuous adaptation to system changes. Real-time validation is carried out using a high-fidelity field-programmable gate array (FPGA)-based simulation platform with detailed power switching models. Results confirm the effectiveness of the proposed method in both seen and unseen scenarios, demonstrating improved resilience while retaining the low-overhead communication structure of centralized secondary control.

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.

The introduction of the three-phase dual-purpose dc-ac/dc power converter (PC), a recent addition to the universal converter family, holds significant promise for improving the reliability and flexibility of modern microgrids (MGs). This paper presents a novel energy management strategy for a flexible hybrid ac/dc MG architecture featuring dual-purpose dc-ac/dc power converters. These converters offer the capability of both dc/ac and dc/dc power conversion, allowing for connection to either the ac bus or the dc bus through simple reconfiguration, thereby providing enhanced modularity and operational adaptability to various MG conditions. Leveraging model-free reinforcement learning (RL) algorithms, the proposed strategy optimizes the operation mode of the dual-purpose converters to minimize the interlinking converter utilization based on historical MG operational data. The feasibility of the proposed MG architecture and the performance of the RL-based energy management strategy are verified by simulation results.

DC-DC converters play a crucial role in providing power conversion for the integration of renewable energy sources into the electric power grid or as standalone power sources. However, achieving proper integration of applications like photovoltaic generators often requires DC-DC converters with an enhanced voltage range due to conditions such as PV shadowing. This is a feature that is lacking in standard DC-DC converters. Addressing this need, this paper presents a novel transformerless buck-boost converter with a wide conversion voltage ratio. The proposed converter has only one active switch, simplifying the gate driver and control system implementation. The wide conversion voltage ratio is ensured by its quadratic voltage gain. Operates in both step-up and step-down modes, unlike most existing quadratic topologies, which are limited to either step-up or step-down operation, and shares a common ground between the input and output terminals. The operational modes of the proposed converter and its steady-state performance are thoroughly analyzed. Simulation and experimental tests were conducted to evaluate its performance.

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.

As power systems move towards decentralized models based on renewable energy sources with distributed generation, the role of power inverters in microgrids becomes increasingly important. In this paper, a three-level T-type quasi-impedance source inverter (3L-T-type qZSI) with a grid-forming control structure is studied for the first time in an islanded ac microgrid composed by three prosumers, supplying residential loads. The power sharing among prosumers is achieved through the well-known droop control method with virtual impedance, and proportional-resonant (PR) controller-based voltage and current control loops. A proportional-integral (PI) based control for regulating the dc-link voltage of the T-Type inverter was implemented making use of the boost ability of the qZS network. The proper operation of the microgrid has been tested by simulation with PLECS, demonstrating a robust behavior of the overall system and a good dynamic performance of the proposed control structure for the 3L-T-Type qZSI in different conditions.

A single-phase single-stage flying inductor based buck-boost inverter (S2FIB2I) is presented in this paper. Operation in buck, boost and buck-boost modes gives the proposed topology the ability to inject power into the grid at a wide range of input voltages. In other words, the proposed inverter has a dynamic voltage gain. The direct connection of the negative terminal of the input source with the neutral terminal of the power grid causes that in photovoltaic applications, the problem of injecting even harmonics into the grid is solved and the leakage current is completely eliminated. The absence of electrolytic capacitors in the proposed converter increases the life and reliability of the system. Also, the ability to operate at nonnity power factor allows the proposed inverter to control the reactive power at its output terminals. Theoretical analysis, design of passive elements and 1 kW simulation results are given to prove the accuracy of the proposed inverter performance.

Due to the new paradigm in which AC grids must coexist with DC microgrids, new solutions to interlink those networks are required. In this context, a new interlink hybrid converter is presented in this paper. This solution is designed to interlink AC grids and bipolar DC microgrids or two DC microgrids. The simplest solution allows linking a three-phase AC grid using only two single-phase inverters. However, it can be extended with the purpose to make a multilevel converter. The solution allows to transfer the energy in a way that supports the attenuation of the voltage unbalance that can appear in the DC microgrid(s). This support is done by an independent transference of energy to the microgrid poles or microgrids. This concept and behavior of the interlink hybrid converter will be tested through simulation studies. The results obtained in these studies show the capability of the proposed solution.

Nowadays DC microgrids provide a valuable alternative to AC technology in the context of electrical energy distribution grids and increasing energy demand. One of the main structures of DC microgrids are the bipolar solutions. Although presenting several advantages over unipolar solutions, the major problem is the voltage imbalance that can appear. This paper presents a non-isolated bipolar DC-DC converter to be integrated in battery storage systems. The converter was designed to transfer energy between the DC microgrid and batteries, and at the same time, to support the balance of the bipolar DC microgrid. This support can be achieved in two ways, namely through the transference of the energy between the DC microgrid and batteries using only the pole that requires support for the balance or as a standalone voltage balancer. Simulations and experimental results of the DC-DC converter operating in bidirectional mode will be provided. From the presented results, it will be possible to verify the capability of the converter to operate as bidirectional interlink between the battery storage systems and the bipolar DC microgrid.

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.

This paper presents an intelligent energy storage system for NZEB buildings integrated in a smart grid context. The proposed methodology is suitable for NZEB buildings that include integrated renewable generation and storage capabilities, aiming at high load matching and low grid interaction, acting as a prosumer. The considered energy storage system is electrochemical storage (batteries) and the renewable production is based on PV panels. The energy storage management is based on a genetic algorithm approach that aims to increase the energy storage system return of investment by, at the same time, minimizing the grid energy consumption, on higher DSO tariff periods, and reducing the number of battery operating cycles. In this way the management system will increase the life time of the energy storage system and reduce the amount of money that the prosumer has to pay to the DSO operator.

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 study proposes a simple digital control strategy for a single-phase interleaved quasi-z-source inverter (QZSI) with active-power decoupling (APD). Requirements for QZSI and APD passive elements are presented and discussed. The QZSI-APD with the applied control features low input current and power ripples. Firstly, it was achieved by an interleaved approach; as a result, high-frequency ripples are partly compensated. Secondly, APD with a multi-resonant controller allowed a decrease in low-frequency input ripple. Thus, the proposed topology and control reduced the QZSI capacitors significantly. In addition, as compared to a Z-source inverter, QZSI capacitor sizes could be significantly decreased due to lower voltage levels. The study assumed a 2 kW photovoltaic string inverter; our results proved that the interleaved QZSI-APD is a suitable solution for kW-scale photovoltaic systems.

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.

This paper presents guidelines for component design of the three-level three-phase T-source inverter with continuous input current under maximum boost control proposed recently. Steady state analysis under low-frequency current and voltage ripples in the dc side was made. Component sizes for both with and without low-frequency ripples are estimated and compared. Simulation results have confirmed most of theoretical predictions.

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 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.

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.

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.