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This paper presents a control strategy for voltage source converters connected to weak grids. The proposed approach is based on slight modifications to the conventional vector current control strategy, including the use of two degrees of freedom proportional-integral controllers, with reference weighting factors, in the inner current loop and a proportional controller in the outer loop, resulting in the introduction of only three additional parameters. The paper analyses the effect of these additional design parameters on the robustness improvement and studies the limitations of the proposal, providing design steps to achieve given performance prescriptions such as speed response, noise amplification, delays and phase-locked loop bandwidth, and the ability to face weak grids. Simulations are conducted to evaluate the effectiveness of the proposed approach, which demonstrates that it is possible to achieve a more robust behaviour compared with the conventional vector current control strategy when facing weak grids. • Control strategy in grid supporting converters connected to weak grids. • P and V outer control loop , inner current loop (2DOF-PI) and current saturation. • Only three additional design parameters are included w.r.t. the conventional VCC. • Design balances performance, robustness against weak grids, delays, and noise. • The proposal allows enhanced robustness and improved grid connectivity. [ABSTRACT FROM AUTHOR]

This paper proposes a voltage compensator for converters in multi-converter DC microgrids (MG), which enhances the DC-MG behavior under fault conditions. Among the four existing categories in the classification of the faults, this paper focuses on those faults that affect voltage generation of converter-based distributed generation units (DGUs). Such faults conceptually occur from the terminal voltage reference to actual voltage generated by DGUs. To compensate the adverse effects of the faults, an adaptive scheme is proposed, which considers the most general case of the faults by using the time-varying multiplicative and additive fault models. The proposed scheme benefits from an integrated structure, which does not require separate fault detection, isolation, and identification blocks. As an advantage of the proposed approach, it is designed independent of the primary and secondary controllers of DGUs, and hence its performance is not affected by using different primary and secondary controllers. The effectiveness of the proposed scheme is verified under various fault conditions and uncertainty in the system parameters. Using the proposed scheme, the results show that the performance of system under the fault condition is similar to that of the normal operation. • An adaptive voltage control compensator scheme is proposed for DC microgrid. • The considered faults affect the voltage generation of DGUs. • The faults are modeled by time-varying multiplicative and additive components. • The proposed scheme does not need any separate fault detection and isolation modules. • To validate the conducted analysis, various case studies are provided. [ABSTRACT FROM AUTHOR]

• Propose a SMPC based voltage regulation scheme to coordinate DG, OLTC, SVR and CBs considering uncertainty of DG outputs. • Use the time-correlated scenario generation method in the proposed SMPC framework. • Consider the single-phase regulation effect of OLTC, DGs and CBs. With the increasing penetration of renewable energy resources, the uncertainty of renewable energy resources output introduces challenges to voltage control in distribution networks (DNs). To solve these problems, this paper proposes a double-time-scale voltage control scheme for unbalanced DNs based on stochastic model predictive control (SMPC) to coordinate multiple voltage control devices. In fast-time-scale control, the active and reactive power outputs of distributed generators (DGs) are optimized to minimize voltage deviation, active power curtailment and reactive power fluctuation. In the slow-time-scale control, optimal tap changes of on-load tap changers (OLTC), step voltage regulators (SVR), and switched capacitor banks (CBs) are calculated to reduce voltage deviation and tap operations. Additionally, in the fast-time-scale control, the SMPC-based scheme adopts a scenario generation approach to represent the uncertainty of DG output. Considering the temporal correlation of the DG output, different prediction scenarios and scenario probabilities are obtained by the empirical cumulative distribution function fitted by the historical measurement data. In this paper, the effectiveness of the proposed double-time-scale voltage control scheme is verified by the unbalanced IEEE123 node system. The case study demonstrates that the proposed voltage scheme can effectively keep the three-phase voltages in unbalanced DN within the secure operation range and achieve better voltage profiles. [ABSTRACT FROM AUTHOR]

[Display omitted] • A physics-informed fast voltage control method of distribution network is proposed. • It develops a novel deep reinforcement learning algorithm with graph knowledge. • The proposed algorithm uses multiple agents with continuous action space. With the recent rapid uptake of photovoltaic (PV) resources, the overvoltage condition during low load periods or intermittent renewable generation is one of the most critical challenges for electricity distribution networks. Traditional model-based local or centralized control methods that rely on proper system parameters are difficult to mitigate rapid changes in power systems. Utilizing model-free/data-driven multiagent deep reinforcement learning (MADRL) has been recognized as an effective solution to active voltage control. However, existing MADRL-based control approaches trained solely on data are agnostic to the underlying real-world physics principles. Therefore, this paper aims to incorporate physical knowledge of regional distribution networks into MADRL's decision-making. The main contributions of this paper are summarized as follows. First, a novel physics-informed MADRL -based distributed voltage control method is proposed, which is still under a centralized training and distributed execution framework and only requires local measurements. Second, graph neural networks are employed to help MADRL agents learn graph knowledge (node features and topological information). Further, transformer is introduced to extract discriminative representations and ensure agents' cooperative control. Third, we adopt a physics-guided architecture of neural networks in the actor network to stabilize the training process and improve sample efficiency. Finally, simulation results based upon modified IEEE 33-bus and 141-bus networks validate the proposed method's effectiveness, robustness and computation efficiency. [ABSTRACT FROM AUTHOR]

• The proposed voltage control method provides optimal voltage profiles in various LVDC and MVDC electric railway systems by minimizing inter-area voltage drops. • The proposed voltage control method maximizes the release of the line capacity and minimizes the power losses by minimization of inter-area current. • The proposed voltage control method is a decentralized and distributed voltage control method that employs the DC voltage of DC electric railway networks rather than telecommunication systems. • The proposed voltage control method benefits from simplicity, cheapness, high reliability, expandability and modularity. • Any changes in the power, number and location of trains, traction substations, distributed generators, ESS's and the length of electric lines in LVDC and MVDC electric railway systems cannot perturb the performance of the proposed voltage control method. The medium voltage DC (MVDC) electric railway system is one of the most interesting options for future high-speed rail (HSR) lines. The dc voltage control is one of the most critical challenges of MVDC electric railway systems due to various reasons such as simultaneous, continuous and considerable changes in the power and location of trains, regenerative brake energy of trains, long power lines, the application of ESS's and RES's. In this paper, a voltage control, i.e., the optimal-voltage voltage-power (OVVP) control method, is presented for MVDC electric railway systems. OVVP control method is a practical, reliable, automatic, and modular distributed voltage control method. The proposed voltage control method satisfies the nearest voltage to the nominal value in each node and the smoothest voltage profile in different MVDC electric railway systems. Although the analyses carried out in this paper analytically prove the significant performance of the presented voltage control method, different challenging scenarios are considered to verify OVVP control method more. In addition, the results of the proposed voltage control method are successfully validated by GAMS software. [ABSTRACT FROM AUTHOR]

• A fast excitation structure has been proposed that can reduce the transient time of MCR from 400 ms to 37 ms. • The new structure proposed in the article can simultaneously reduce the time required for the excitation and demagnetization stages. • The fast excitation structure proposed in this article does not require additional circuit structures and retains the reliability of the original MCR. • The fast excitation structure proposed in this article has been verified through both simulation and experimental verification. With the increasing proportion of renewable energy usage, the randomness and volatility of renewable energy have led to a corresponding increase in the demand for reactive power regulation in the power system. Magnetic controlled reactor (MCR) is one of the technical and economic means used to solve problems such as reactive power compensation and voltage regulation in the power system. However, the transient time of traditional MCR is relatively long compared to other reactive power compensation devices, which limits the further application of MCR. At present, most methods for optimizing the dynamic response time of MCR are to add additional circuits or change control strategies, which will increase the difficulty of MCR control and reduce stability. Therefore, without adding additional circuit structure and control difficulty, this paper proposes a three-phase MCR fast excitation structure that changes the winding connection method, which can improve the DC voltage in the control circuit and reduce the transient time of the MCR. A magnetic circuit model in the MCR core under the fast excitation structure is built and analyzed, based on which, the transient time of the MCR is mathematically calculated. A fast excitation MCR simulation model was constructed based on MATLAB/Simulink platform for dynamic response test simulation. Compared with typical MCR simulation results, the transient time was reduced from 400 ms to 37.1 ms. Dynamic response tests were conducted on a three-phase MCR prototype of 35 kV/18 Mvar, and drop test indicates that the fast excitation structure could reduce the transient time of the three-phase MCR prototype to 36.6 ms, which substantiate the precision of mathematical and simulation results and the efficacy of the fast excitation structure. [ABSTRACT FROM AUTHOR]

• A novel hierarchical control method for EVCSs in an unbalanced distribution network. • A three-phase EV charging scheduling optimization model to maximize PV hosting capacity. • Ancillary service functions of active power transfer and voltage droop control. PV hosting capacity of a practical three-phase unbalanced distribution network is expected to increase, thus increasing safe PV penetration and speeding up the decarbonization of power systems. However, power unbalances and bus voltage violations are two major obstacles limiting further increases in the PV hosting capacity. With the popularization of electric vehicles (EVs), EV charging stations (EVCSs) as controllable loads can effectively provide grid ancillary services, which helps enhance the PV hosting capacity. In this regard, this paper proposes a hierarchical control method for EVCSs in an unbalanced network, consisting of central day-ahead scheduling and local real-time dynamic control. It is novel that the local control capability of EVCSs is reserved in the central scheduling. A three-phase day-ahead EV charging scheduling optimization model is developed to reduce the power unbalance and the bus voltage violation, and in turn, improve the PV hosting capacity. Moreover, active power transfer and voltage droop control are developed as two ancillary service functions for local real-time control responding to dynamic network operating conditions. Numerical simulations verify the effectiveness of the proposed method in enhancing PV hosting capacity and providing grid ancillary services. [ABSTRACT FROM AUTHOR]

• The core of the novelty of NV-MAIS approach relies on the fact that we are using shunt reactors for both voltage regulation and frequency oscillation damping. To the best knowledge of the authors, there has not been reported the use of the shunt reactors in frequency oscillation damping and the NV-MAIS strategy is the first of a kind of such an approach with grid commissioning and installation in high voltage 735-kV transmission level. The Hydro-Québec transmission system is among the most extensive and complex power grid in North America due to its very long lines (over 1000 km) joining the generation facilities in the north of the Québec province to the main centers of consumption in the south. Since the 1990s, Hydro-Québec has adopted a defense plan, consisting of various types of protection solutions including different remedial action schemes (RAS) and automatic action strategies, to increase the stability and reliability of its transmission system against extreme contingencies. One of these protection strategies is the automatic switching of shunt reactors (MAIS) 1 MAIS is the acronym of the French name of the project as M anoeuvre A utomatique d' I nductance S hunt (MAIS). which has been in operation since 1997. The goal of the MAIS system is to keep the voltage profile of the whole 735-kV grid in an acceptable range to increase the transmission capacity. The MAIS system at each substation is entirely independent from neighbour substations and will close or trip shunt reactors just based on local measurements. As a periodical upgrade in all existing protection solutions in the Hydro-Québec power system, new functionalities have been added into the existing MAIS system to develop its new version to improve both the voltage profile and the frequency response. This paper presents this new version including the algorithm and the concept behind the new additional functionalities. The simulation results show the efficiency and performance of the proposed method. On that basis, a deployment on Hydro-Québec's grid to replace almost all the existing MAIS system with this new version will be realized by 2030. [ABSTRACT FROM AUTHOR]

This paper deals with a novel hybrid transformer configuration for MV/LV three-phase distribution systems. The configuration involves a standard distribution transformer with an open-end secondary winding, which is connected to the LV grid and a four-legged inverter with a floating DC bus. Unlike previous hybrid transformers, the proposed configuration eliminates the need for a bidirectional converter and auxiliary transformer windings as well. The fourth leg of the inverter is exploited to manage the neutral line current. The main advantage of the proposed configuration is its ability to provide phase voltage control at the distribution grid edge. This enables the compensation of various grid voltage anomalies such as sags, swells and some kinds of interruptions. The effectiveness of the proposed configuration is demonstrated through simulation and experimental results, highlighting its promising performance in real-world scenarios. [ABSTRACT FROM AUTHOR]

• An unprecedented very large-scale T&D dataset covering Texas is made publicly available. • The sheer size of this dataset is intended to provide a challenge for the scientific community. • This lays the foundation for demonstrating the coordination of T&D. • It can help foster the improvement of algorithms and tools for years to come. Distributed energy resources, such as rooftop solar, have rapidly expanded in recent years, given declining costs and the desire to reduce carbon emissions. With more energy resources located in the lower-voltage distribution system, it is increasingly helpful to utilize combined transmission and distribution (T&D) system models to analyze interactions between these normally-distinct subsystems. This paper proposes a methodology for creating very large-scale, highly detailed, combined T&D systems that are synthetic—that is, free from non-public data—yet still realistic. The methodology creates very large-scale combined T&D systems by merging the most up-to-date techniques for creating synthetic distribution feeder networks with the latest methods for building synthetic, meshed bulk-power transmission networks. This methodology is demonstrated on a T&D system geolocated in Texas, and benchmarked with co-simulation results. Validation demonstrates that the resulting syn -texas-TDgrid synthetic test system realistically represents characteristics found in actual networks, addressing the lack of available T&D test systems. With over 15,000 feeders and 46 million electrical nodes, this T&D dataset has applications for research in optimal power flow algorithms, voltage control, reconfiguration, and T&D coordination schemes under high adoption of distributed energy resources. [ABSTRACT FROM AUTHOR]

Previous research indicates that post-fault grid-forming (GFM) converters only work in current limiting control (CLC) mode. However, converters integrating the current saturation algorithm (CSA) can operate in both constant voltage control (CVC) and CLC modes. This paper firstly derives the angle-switched model of the grid-connected system governed by CSA and virtual synchronous generator (VSG). Then, combining the fault and three types of post-fault trajectories, critical clearing angle is analytically formulated through the Segmental Equal Area Criterion (SEAC). Finally, a range of values for the saturated current angle is proposed to ensure that the system is stabilized in CVC mode. Notably, the optimal saturated current angle, which is the minimum value within the range, provides the maximum critical clearing angle. • An angle-switched model for a virtual synchronous generator equipped with the current limit is established. • Segmental equal area criterion is proposed and analytical formulations are derived for the critical clearing angle under three post-fault operational states. • Optimal saturated current angle control is proposed to enhance transient stability by configuring the saturation current angle. [ABSTRACT FROM AUTHOR]

• Propose a new real-time distributed voltage control scheme for MV&LV DNs based on ATC method. • Coordinate multiple DGs at different voltage levels to guarantee secure operation of the entire DN. • Design a dynamic allocation approach to determine the weighting factors for the optimization problem of MV&LV DNs. This paper proposes a new real-time distributed voltage control (RTDVC) scheme for medium and low voltage (MV&LV) distribution networks (DNs) based on the analytical target cascading (ATC) method. In this scheme, photovoltaic (PV) units at the LV level, on-load tap changer (OLTC) and distributed generation (DG) clusters at the MV level are optimally coordinated to regulate the bus voltages in MV&LV DNs to be close to the nominal value while minimizing the number of operations of OLTC and smoothing the reactive power outputs of DGs. Based on the ATC method, the large-scale strongly coupled voltage control problem of MV&LV DNs is decomposed into several subproblems while guaranteeing the optimality of the primal voltage optimization problem. The decomposed subproblems are iteratively solved in parallel in the MV and LV controllers, which achieves optimal voltage control in a distributed manner and effectively reduces the computation burden. An MV&LV test system with two 20 kV feeders and 39 0.4 kV LV grids was simulated to demonstrate the control performance of the proposed distributed voltage control scheme. [ABSTRACT FROM AUTHOR]

• An accurate admittance model for the grid-connected converter with droop control is proposed. • The frequency coupling phenomenon is induced by the asymmetry of the droop controller for the grid-connected converter. • The outer control loop will impact the frequency-coupled phenomenon, but has slight effects on positive and negative sequence admittance of VSCs. • The proportional gain of the current control loop impacts obviously the frequency coupling phenomenon. The droop control scheme is widely applied for the paralleled operation of the grid-connected converter. Yet, the frequency-domain admittance model for the grid-connected converter with droop control is still inaccurate due to the complex coupling relation of the droop control loop, the voltage control loop, and the current control loop. To address this problem, the coupling relationship of these control loops is analyzed in this paper, and then an accurate admittance model for the grid-connected converter with droop control is proposed based on the complex vector modeling method in both dq -frame and αβ -frame. The influence of different control parameters on the admittance model is analyzed further. The proposed model accurately describes the admittance characteristics of the grid-connected converter with droop control, and reveals the frequency coupling phenomenon caused by the droop control loop. The frequency response measured by frequency scan and simulation results verify the effectiveness of the established model. Finally, the impedance interactive stability analysis results show that the grid-connected converter with droop control is prone to instability in stiff grid conditions. © 2017 Elsevier Inc. All rights reserved. [ABSTRACT FROM AUTHOR]

For islanded microgrids with inverter-based distributed generators (DGs), this article focuses on the fast finite-time secondary voltage and frequency control problem considering system uncertainties. The distributed controller is designed based on the command filtered backstepping procedure, and a disturbance observer is constructed to estimate the lumped system uncertainties (including parameter perturbations, unmeasurable variables, etc.). In addition, the singularity issue derived from differentiating the virtual control law is avoided by using a smooth switch function. The proposed controller guarantees that the tracking errors of voltage and frequency converge to a small region around the origin in a finite time, while achieving desired active power sharing ratio. Case studies are conducted on a microgrid system to demonstrate the effectiveness of the proposed strategy in the presence of load changes and parameter perturbations. • This paper aims at achieving fast finite-time secondary control of islanded microgrids. • The proposed method is free of chattering and singularity issues. • The disturbance observer is constructed to enhance the robustness of voltage control. • Case studies are conducted to verify the effectiveness of the proposed strategy. [ABSTRACT FROM AUTHOR]

This paper proposes a new real-time distributed voltage control (RTDVC) scheme for medium and low voltage (MV&LV) distribution networks (DNs) based on the analytical target cascading (ATC) method. In this scheme, photovoltaic (PV) units at the LV level, on-load tap changer (OLTC) and distributed generation (DG) clusters at the MV level are optimally coordinated to regulate the bus voltages in MV&LV DNs to be close to the nominal value while minimizing the number of operations of OLTC and smoothing the reactive power outputs of DGs. Based on the ATC method, the large-scale strongly coupled voltage control problem of MV&LV DNs is decomposed into several subproblems while guaranteeing the optimality of the primal voltage optimization problem. The decomposed subproblems are iteratively solved in parallel in the MV and LV controllers, which achieves optimal voltage control in a distributed manner and effectively reduces the computation burden. An MV&LV test system with two 20 kV feeders and 39 0.4 kV LV grids was simulated to demonstrate the control performance of the proposed distributed voltage control scheme.

• Impacts of stator voltage, DC voltage and magnetic flux on transient stability are analyzed. • VSynC-DFIG model is simplified as a well-studied synchronous generator. • A new procedure to calculate critical clearing angle of VSynC-DFIG is proposed. Transient stability of virtual synchronous controlled (VSynC) equipment is usually analyzed without considering the dynamics of the AC voltage controller. However, neglecting the impact of stator voltage controller dynamics in doubly fed induction generator (DFIG) wind turbine can lead to inaccurate stability assessment results. In this paper, the quantitative analysis of the impact of non-forced magnetic flux and DC voltage fluctuations on transient stability is conducted. Based on these analyses, a simplified DFIG model is proposed, which is approximately equivalent to a synchronous generator with excitation regulator. Then, a discretized step-by-step calculation procedure is introduced for the proposed model. Moreover, the influence of controller parameters on transient stability is analyzed based on the calculation results. Finally, simulations and experimental validations are carried out to demonstrate the effectiveness of the proposed model. [ABSTRACT FROM AUTHOR]

• Voltage control plays a crucial role in the restructuring of modern power systems especially with high share of renewables and controlled resources. • An optimal control is proposed based on a proper linear quadratic integral control. • Voltage time response of aperiodic type without oscillations is assured. • Feasibility and robustness analyses on actual regional networks and test systems. The network voltage control together with the regulation of reactive power, has always been recognized as vital feature of power systems. It is aimed at containing the bus voltage within acceptable limits for guaranteeing system security, first and then assessing power quality. The voltage control is a key field in which several Transmission System Operators are currently investing resources to be well prepared in managing power systems with a high share of renewable energy sources, overcoming the drawbacks of the existing architectures. As is well known the voltage control is realized through a hierarchical structure, which is based on classical primary control, secondary control, and tertiary optimization. The secondary control is concerned with the regional level, implying proper coordination at both the geographical and temporal level. Due to its central role in power system operation, the secondary voltage control cannot be excluded from the effects of the dramatic changes that power systems are experiencing worldwide, even though regulators work by implementing well consolidated methodologies and strategies which show excellent performances. The motivation for this study in fact relies on the observation of some oscillatory phenomena in some areas of the Italian power system characterized by a high number of regulating resources highly coupled each other on the basis of the grid topology: despite these oscillatory phenomena are not so frequent, with the increasing of regulating resources enslaved by secondary regulation (such as renewable-based power plants) could potentially be worsened in the near future. Thus, in this paper, an optimal control strategy is proposed by tailoring a proper linear quadratic integral control which allows guaranteeing the desired profile for pilot buses voltage, ensuring a time response of aperiodic type without any oscillations. The aim of the proposed approach is to preserve the strengths of the existing secondary voltage regulation while enhancing the overall stability so enabling the progressive large penetration of renewable energy sources-based power plants and minimize the occurrence of oscillatory phenomena especially in highly electrically coupled areas. The robustness of the proposed regulation is verified first with respect to the WSCC 9-bus test system and successively on an actual regional area of Italian transmission network. [ABSTRACT FROM AUTHOR]

This paper focuses on the voltage control of grid-forming Voltage Source Converters (VSCs) connected to AC networks. The work aims to identify the best pairing between voltage control structures and usual ac filter topologies. The two filter topologies considered are the inductive (L) and the inductive–capacitive (LC) filter. The control structures studied are the Cascaded Control (CC, cascaded voltage and current loop) and the direct Voltage Control (VC, without current loop). To select the best control-filter pair, the following methodology is suggested. First, for each pair, a voltage control parameter sweeping methodology is developed to find suitable designs considering the following limits: minimum bandwidth, maximum converter voltage, point of connection voltage deviation and maximum current. Second, this action is repeated for different filter parameters and network Short-Circuit Ratios (SCRs). Finally, based of the obtained results, the most relevant control-filter pairs can be selected, prioritizing them according to the fulfilment of the defined limits. To conclude, time-domain simulations are carried out to validate pairing selection. • The paring of voltage control and AC filter for grid-forming converters is presented. • The tuning method optimizes control against disturbances within converter limits. • The analysis considers several SCR, filter parameters and converter limits. [ABSTRACT FROM AUTHOR]

• A frequency regulation method for a two-stage PV system by controlling DC voltage is proposed, which is coordinated with the enhanced virtual inertia control (VIC) of the DC capacitor. • An active DC voltage recovery control is designed at the inverter to restore the frequency support ability after primary frequency modulation. • The proposed method can fully use the available power to improve the frequency nadir, rate of change of frequency, and voltage recovery ability. The current frequency regulation methods for a photovoltaic (PV) system cannot balance frequency support and primary control performances. This paper proposes a frequency regulation method for a two-stage PV system by controlling DC voltage, which is coordinated with the enhanced virtual inertia control (VIC) of the DC capacitor. The power reserve control of the PV arrays is improved considering the characteristics of the VIC, thereby strengthening the frequency regulation ability of the PV system. An active DC voltage recovery control is designed at the inverter to restore the frequency support ability after primary frequency control. With MATLAB/Simulink software, the performance of the proposed method in dealing with different load sizes, load change trends, and DC voltage recovery coefficient is verified by comparing it with other traditional methods in different scenarios. The proposed method can fully use the available power to improve the frequency nadir, rate of change of frequency, and voltage recovery ability. [ABSTRACT FROM AUTHOR]

• New soft-switching Dual-input DC-DC boost converter. • Checking the voltage gain and getting an acceptable result. • Converter load voltage control. • Experimental verification is provided. This paper proposes a new non-isolated dual-input zero-voltage switching (ZVS) dc-dc boost converter with medium voltage gain. Two input ports of the converter are current-fed and suitable for a unidirectional dc power source, and a chargeable dc energy storage. The proposed converter basic circuit composed of three cascaded power switches, which at their connection points join to the converter three inductors and a switched capacitor voltage multiplier (VM) cell is accompanied. Using this VM cell the converter voltage gain achieves two times of that in the conventional boost converter and also half voltage stress across the power switches. Through the converter two input inductors powers from a unidirectional source (like PV) and a chargeable battery source can be accepted. Taking a triangular resonant current at the switching frequency, the converter third inductor aids to reach ZVS for the power switches. The converter power switches turn-on with ZVS and the power diodes stop conducting with ZCS in all operation conditions. As a result, low switching power losses, reduced reverse recovery issue, and high efficiency are accessible especially for higher input and output powers. The converter power switches are switched in PWM manner with two individual duty ratios, allowing to regulate the output voltage and control the extracted power from the input unidirectional port. The proposed circuit has been analyzed in detail to find its different operating modes, determine its capacitor currents, estimate its power losses components and design its control system. Behavior of the proposed system is also examined by a low-power laboratory prototype tested under four different practical operation conditions. The proposed converter benefits from simple and compact structure, current-fed input ports, low number of power switches and magnetic elements, low voltage stress across the power switches, medium voltage gain and high efficiency. [ABSTRACT FROM AUTHOR]

The usage of distributed generation sources and the segmentation of power systems into microgrids brings several advantageous features, such as energy independence, lower transmission losses, and improved energy management flexibility. Still, the expected steady abolition of traditional centralized networks and their centralized control schemes introduces several operational difficulties, that can compromise (micro)grid's stability and reliability. Consequently, several approaches to how microgrids should be operated have been proposed, albeit with several salient deficiencies. Precise power exchange, control of frequency and voltage excursions, applicability on different grid topologies, and the possibility to integrate grid codes, which are very important control aspects, are not jointly enabled in a general case. This paper proposes a novel approach, based on a specific goal function and corresponding decentralized control that addresses the mentioned problems and guarantees the microgrid's stability by constraining the frequency and node voltage deviations, simultaneously supporting the desired active power exchange between prosumers. Unlike droop-based and droop-derived control schemes, the proposed approach aims to inherently preserve the frequency and voltage levels within the limits defined by the grid operator or future microgrid codes, thus preventing the generation unit's unwanted disconnection during transients and disturbances. In addition, the control algorithm is independent of network topology, can be applied in both islanded and non-islanded microgrids, and secures system scalability. To confirm the effectiveness of the proposed control strategy, a number of simulation results are presented and thoroughly discussed. • A novel seamlessly scalable self-stabilizing microgrid control framework is proposed. • Guaranteed upper bounds on deviations of node frequencies and voltages are provided. • Precise active power exchange between nodes is enabled. • Priorities of the proposed scheme can be adjusted according to user preferences. • Comprehensive tests in relevant operational scenarios are performed. [ABSTRACT FROM AUTHOR]