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Recent developments in renewable energy-based power systems and smart grids have brought challenges to designing new power conversion systems. On account of the intermittent nature of the renewable sources and unpredictability of the load demand, a combination of two or more energy sources and auxiliary storage systems is usually mandatory to meet the load demand, improve dynamic and steady-state characteristics, and reliability and availability of the system. Conventionally, SISO (single-input-single-output) DC/DC converters are arranged in parallel at a common DC bus to exchange power. In this scheme, separate conversion stages are employed for respective renewable energy sources (RES) and energy storage systems (ESS), and the converters would be controlled independently. However, the multistage configuration generally leads to a large size due to the large number of conversion stages, relatively high cost, and low efficiency and power density. Also, the independent control of several converters and communication among the sources make the system complex. In order to overcome these disadvantages, multi-port DC/DC converters (MPDC) have been proposed. MPDCs are preferred against several independent converters in terms of efficiency, component count, size, cost, and performance point of view. In addition to RES, MPDCs can be utilized in other applications such as electric/hybrid vehicles, telecommunication and satellites, and UPSs. This paper aims to consider the recent advances in MPDC from a topology and control point of view and provide a helpful framework and point of reference for future converter design and applications.

The broad demonstration of grid-forming converters (GFMs) in microgrid applications has been well documented. Following this, the idea of GFM was assessed for its potential use in large-scale linked networks that include transmission and distribution systems combined with renewable energy sources. As a result, a thorough examination of GFM performance became imperative. This study provides a comprehensive examination of GFMs, encompassing fundamental principles, control mechanisms, implementation strategies, operational aspects, and potential avenues for further research. The capacity of GFMs to withstand system disturbances is of utmost importance for ensuring the overall stability of the system, particularly in situations where inertial response is diminished. Classical control methods are inadequate in addressing transient stability circumstances, necessitating the development of current control approaches to overcome these limitations. The utilization of GFM control is becoming increasingly important in the global initiative to establish a sustainable energy system through the integration of renewable energy. GFM control is particularly significant as it determines the level of controllability over non-dispatchable and variable generation, especially on a larger scale, thus contributing to the practical realization of this initiative. Therefore, an extensive and evaluative examination of many control systems, control theories, and algorithms has been conducted in the last twenty years. This study provides a comprehensive classification of control objectives and applications, emphasizing their importance and effectiveness. The findings of this study are equally applicable to various interdisciplinary fields such as power system operation, power electronics, renewable energy integration, advanced control, and smart grids. [ABSTRACT FROM AUTHOR]

Long high voltage direct current (HVDC) transmission link is commonly used to transmit electrical energy via land or under-sea cable. The long HVDC avoids reactive power losses (RPL) and power stability problems (PSP). On the contrary, the RPL and PSP phenomena occur in long high voltage alternative current-link (HVAC) caused by the high reactive component in the HVAC-link. However, the HVDC produces a high and slow transient current response (TCR) on the high value of the up-ramp rate. Interval type-2 fuzzy (IT2F) control on converter-side HVDC is proposed to mitigate this TCR problem. The IT2F is optimized by grey wolf optimizer (GWO) to adjust input-output IT2F parameters optimally. The performance of IT2F-GWO is assessed by the minimum value of integral time squared error (ITSE), peak overshoot, and settling time of the TCR. The IT2FC-GWO performance is validated by the performance of IT2F control that is optimized by genetic algorithm (IT2F-GA) and proportional integral (PI) controller. Simulation results show that the IT2F-GWO performs better with small ITSE, low peak overshoot, and shorter settling times than competing controllers. [ABSTRACT FROM AUTHOR]

Grid forming control applied to power converters termed as grid forming converters (GFC) interfacing storage and renewable generation has been identified as a potential solution to facilitate a more significant penetration of converter-based renewable generation in the power system. The emulated electromechanical model in the GFC is also the synchronization unit which typically utilizes measured output active power from the GFC as the feedback variable. However, this feature has opened up a concern on the transient stability due to loss of synchronism under significant transient events in the power systems, which include frequency change, phase jump, and voltage dips. This paper presents a quantitative and illustrative analysis of the impact of the current limit in GFC on the transient stability of a system comprising of GFC. Furthermore, a solution based on virtual active power is proposed to improve the transient stability margin of the GFC when the GFC enters the current limit. Finally, the analysis and the proposed method to enhance the transient stability are verified by Power hardware in the loop (PHIL) experimental tests.

Hybrid AC/DC microgrid architecture is emerging as an interesting and attractive approach since it combines the prominent benefits of both AC and DC networks. In Hybrid Microgrids (HMGs), AC and DC networks are interconnected with each other through power converters. Therefore, power converters play a very important role in HMG operation, as their functionality is not only limited to interconnection but also provides power flow control and improves the power quality through different ancillary services. Moreover, due to intermittency of Renewable Energy Resources (RESs), synchronization, load variation, availability of both AC and DC networks, etc., the controllability of the power converters, power management, and protection become very complex in HMG. This paper initially provides a comprehensive review of different interconnection methods and then presents an overview of different control strategies for HMG and Inter-Linking Converters (ILCs). Moreover, power management in different operating modes, including mode transition, is discussed in detail. This paper also provides a critical assessment of the available protection challenges of HMG and provide a comprehensive review of different available protection schemes and devices is provided. Moreover, the highlights and recommendation regarding interconnection methods, control, and protection schemes are presented.

Electromagnetic interference poses enormous challenges for feedback-controlled systems, especially at medium-voltage levels. As power converters are increasingly utilized for medium- and high-voltage applications, optically-based measurement methods must be explored. This paper investigates current measurement via electroluminescence from silicon carbide semiconductor devices. A SiC half-bridge MOSFET module, provided by Powerex, is manufactured with fiber optic cables placed against the semiconductor junctions. The new fiber ports are employed to characterize the light spectrum as a function of conducted current and junction temperature for the body diodes. Most of the light energy is concentrated around peaks at 390 nm and 500 nm. It is observed that although the energy at the 390 nm peak increases with rising temperature, the energy at the 500 nm peak decreases. Therefore, the total light output is seen to only slightly vary with temperature and mostly depends on conducted current. A function is fitted to the light transducer output as a in relation to the on-state current. This function is utilized in a microprocessor that implements feedback current control in a buck converter. This type of control forms the basis of torque regulation in a motor drive or an “inner-current loop” of motor drive speed control or converter voltage control. The new electroluminescence control was demonstrated in the laboratory on a prototype system where the current command is stepped from 0 to 25A, showcasing the effectiveness of the new optical sensing method.

Electric vehicles (EVs) are an alternative to fossil-fuel-powered vehicles. However, high prices make them inaccessible for mass market adoption. Power electronics are a key enabler of vehicle electrification. In this work, the design of a bidirectional converter control is performed for application in EVs. A bidirectional topology with step-up and step-down capabilities is designed. Proportional-Integral-Derivative (PID) is the elementary control method and the most popular in power converters due to its ease of implementation, scalability, low hardware-resources requirement, and high switching frequency capability. New Wide Band Gap semiconductor devices allow to increase switching frequency to reduce the size of the converter. Design validation through in-the-loop methodologies verify that algorithms are ready for chip deployment identifying design flaws early through its development. In this work, the control algorithm for a bidirectional DC-DC converter employing WBG devices at EV power ratings is implemented. Step-up and step-down modes of operation in a cascaded bidirectional topology are analyzed with input voltage of 400 VDC, 13kW power rating, 500 kHz switching frequency and FPGA-in-the-loop (FIL) validation. FIL methodology proved a cost-effective approach to verify that control algorithms are capable for hardware deployment without the need for expensive hardware setups. [ABSTRACT FROM AUTHOR]

The grid-forming （GFM） control technology is instrumental in enabling converters to provide frequency and voltage support response akin to synchronous generators， thus bolstering the stability of the new power system. Nonetheless， a notable challenge lies in delivering grid support during fault current limiting. To this end， a strategy for fault current limiting in GFM converters based on measuring terminal and internal differential voltage orientation is proposed. In this approach， the angles of the positive and negative sequence current commands lag 90° behind the positive and negative sequence voltage differences. Additionally， the maximum magnitude of the synthesized vector of the current commands aligns with the converter’s overcurrent capability， which is equivalent to the generation of positive and negative sequence adaptive virtual inductance by control， respectively. This method obviates the need for direct virtual inductance value calculations and can maximize the maximum support capacity of the converter to realize the fault current characteristics resembling those of synchronous generators. The proposed fault current limiting strategy is validated by a simulation system built through PSCAD/EMTDC. The simulation outcomes affirm the strategy’s efficacy in delivering substantial grid support to the AC system while limiting fault currents.

Copyright of Zhejiang Electric Power is the property of Zhejiang Electric Power Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Grid-forming converters are considered a key technology for electrical grids with a high share of renewable energy. However, there is a lack of a general, robust and verifiable definition of what constitutes this behaviour. Therefore, this paper presents three simple scenarios that enable such a definition. They are based on simple black-box simulations that allow manufacturers to protect their development work. It can be shown that grid forming can be clearly distinguished from grid-following controls by their grid behaviour in the proposed scenarios. Extensive results illustrate this and also provide suggestions to deepen the understanding of grid-forming grid behaviour and its impact on system inertia. These findings should inspire the development of a clear definition and ultimately new requirements for converter systems. [ABSTRACT FROM AUTHOR]

This work is devoted to possible implementation of tunable magnetic devices in electrical systems with adaptive properties. The basic idea, underlying operation of the presented magnetic device, depends on interaction of two (or more) magnetic fluxes in a quasi-linear range of ferromagnetic core characteristics. This is a new approach to the design of such magnetic elements; typically, saturation phenomenon of the ferromagnetic core of an inductor is used to change a value of its inductance. The good examples of adaptive electrical power systems can be devices for improving a quality of electrical energy. When used in compensators of reactive and a distortion power (or a reactive power only), tunable magnetic devices clearly offer wider possibilities for the compensation, compared to solutions, using compensators based on fixed magnetic elements. However, the application of the proposed tunable device in an adaptive compensator is only one example of its possible use in an electrical power area. In this work, the following issues are presented: exemplary solution of the adaptive passive compensator, basics of operation of tunable magnetic device, and test results of the experimental model of an electrical system with such a device. [ABSTRACT FROM AUTHOR]

This paper presents a novel integration scheme of solar Photovoltaic (PV) with a large-capacity Doubly Excited Induction Generator (DFIG)-based wind energy system. The proposed scheme leverages both the grid and rotor-side power converters of the DFIG to inject PV power into the grid, eliminating the need for a dedicated converter for PV power processing and offering a cost-effective PV-grid integration solution. The system effectively delivers a substantial amount of PV power to the grid when compared to an equivalent rating inverter used in conventional PV-grid systems. Moreover, the proposed scheme prevents circulating power during sub-synchronous operation in the presence of solar radiation, enhancing overall system efficiency. Additionally, the system's stability benefits from turbine inertia, allowing for higher PV penetration into the power grid. The intermittent complementary nature of solar PV and wind energy sources significantly improves the utilization of the converters. Furthermore, the proposed scheme minimally impacts Maximum Power Point Tracking (MPPT) for PV and wind sources, except in rare environmental glitches, which the PV power control algorithm is adept at handling. The study provides a comprehensive system model used to design the control strategy, supported by analysis, simulations, and experiments conducted on a laboratory prototype. [ABSTRACT FROM AUTHOR]

This paper presents a live field experience of creating an isolated microgrid for the Expoelectric fair during 2018 and 2019. The islanded microgrid comprises a Master Inverter with grid-forming capabilities and fault management. The Master Inverter and stationary batteries, and EVs with V2G capabilities provide storage. A PV generation system supplies the microgrid. The loads are the fair booths, mainly lighting and chargers for personal mobility vehicles. All the equipment used in the experimental microgrid is from different manufacturers. The operation and control of the islanded microgrid are based on the VDE-AR-N-4105 standard. The paper also presents the operation of the Master Inverter during faults. The live field experience shows that the proposed operation method is valid for operating different converters from different manufacturers without needing any communication layer between them. The experimental results also show that faults can be handled correctly by the Master Inverter to operate the entire microgrid safely. In conclusion, islanded microgrids based on power electronics are feasible to replace diesel generators in faires, conventions or temporary events.

Grid-connected permanent magnet synchronous generator (PMSG) wind farms may be susceptible to oscillation when connected to weak grids. This paper explores the root causes of the oscillations from two perspectives: the model and the oscillation frequency band. First, the small signal model of PMSG wind farm grid-side system is established, and the small disturbance comparison with the PMSGA full-order electromagnetic transient model in MATLAB/Simulink is carried out. Then, we calculatue the eigenvalues of the small signal model and use model analysis techniques such as participation factors calculation and root locus method to identify the critical factors that cause the oscillation modes to be dominant. Finally, time-domain simulation is used to verify the theoretical analysis. Two dominant modes are identified: the subsynchronous oscillation mode and the low-frequency oscillation mode. The subsynchronous oscillation mode is closely related to the direct current (DC) voltage control and the dynamics of DC link. The low-frequency oscillation is significantly weakened with the decrease in grid strength, and it is closely related to the phase-locked loop (PLL) control. The conclusions can provide a reference for tuning the control parameters of PMSG converter.

This paper presents a live field experience of creating an isolated microgrid for the Expoelectric fair during 2018 and 2019. The islanded microgrid comprises a Master Inverter with grid-forming capabilities and fault management. The Master Inverter and stationary batteries, and EVs with V2G capabilities provide storage. A PV generation system supplies the microgrid. The loads are the fair booths, mainly lighting and chargers for personal mobility vehicles. All the equipment used in the experimental microgrid is from different manufacturers. The operation and control of the islanded microgrid are based on the VDE-AR-N-4105 standard. The paper also presents the operation of the Master Inverter during faults. The live field experience shows that the proposed operation method is valid for operating different converters from different manufacturers without needing any communication layer between them. The experimental results also show that faults can be handled correctly by the Master Inverter to operate the entire microgrid safely. In conclusion, islanded microgrids based on power electronics are feasible to replace diesel generators in faires, conventions or temporary events. [ABSTRACT FROM AUTHOR]

Copyright of e & i Elektrotechnik und Informationstechnik is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This manuscript describes the operation of a droop-based controller for three-phase converters in the case of the absence of a neutral connection to the grid. The controller is capable of output power tracking and smooth transitions into the islanded operation. While independent per-phase control of the converter output power is possible if a neutral connection is present, its absence implies additional constraints to be considered. Focusing on this latter case, the controller described herein allows the independent control of the active power at the output of each phase of the converter and a smooth transition to the islanded operation. These features are paramount in future smart power systems, such as smart microgrids, for implementing demand–response, power-flow management, and uninterrupted power operation. [ABSTRACT FROM AUTHOR]

Grid-forming converters are considered a key technology for electrical grids with a high share of renewable energy. However, there is a lack of a general, robust and verifiable definition of what constitutes this behaviour. Therefore, this paper presents three simple scenarios that enable such a definition. They are based on simple black-box simulations that allow manufacturers to protect their development work. It can be shown that grid forming can be clearly distinguished from grid-following controls by their grid behaviour in the proposed scenarios. Extensive results illustrate this and also provide suggestions to deepen the understanding of grid-forming grid behaviour and its impact on system inertia. These findings should inspire the development of a clear definition and ultimately new requirements for converter systems.

Wide-scale adoption and projected growth of electric vehicles (EVs) necessitate research and development of power electronic converters to achieve high power, low-cost, and reliable charging solutions for the EV battery. This paper presents a comprehensive review of EV off-board chargers that consist of ac-dc and dc-dc power stages from the power network to the EV battery. Although EV chargers are categorized into two types, namely, on-board and off-board chargers, it is essential to utilize off-board chargers for dc fast and ultra-fast charging so that volume and weight of EV can be reduced significantly. Here, we discuss the state-of-the-art topologies and control methods of both ac-dc and dc-dc power stages for off-board chargers, focusing on technical details, ongoing progress, and challenges. In addition, most of the recent multiport EV chargers integrating PV, energy storage, EV, and grid are presented. Moreover, comparative analysis has been carried out for the topologies and the control schemes of ac-dc rectifiers, dc-dc converters, and multiport converters in terms of architecture, power and voltage levels, efficiency, bidirectionality, control variables, advantages, and disadvantages which can be used as a guideline for future research directions in EV charging solutions.

A single-switch N-stage Z-network high-gain boost converter is proposed in this study, which can be applied in the field of chip etching for bias provision. The circuit topology, operation mode, voltage gain and the control strategy are analyzed. Thereafter, the steady-state performance of the circuit is analyzed with small signal stability modeling. A simulation model is built using Simulink and compared with the traditional quadratic circuit. Combined with the control strategy, the circuit can obtain better steady-state performance by controlling the number of working N-networks and adjusting the duty ratio in the case of high voltage, wide range of voltage output and dynamic voltage output. The simulation model and hardware prototype of the single-switch four-stage Z-network high-gain boost circuit are built and tested, which have verified the effectiveness of the proposed design. [ABSTRACT FROM AUTHOR]

This work focuses on the possibility of using a tuned inductor in electric power systems with adaptive features. The presented idea of inductor operation, using an interaction of the magnetic fluxes, is a new approach to designing such devices. Examples of power adaptive systems are devices for improving the quality of electricity. Therefore, various types of 'compensators' of reactive power (or both reactive and distortion power) are used in electrical systems as a preventive measure. The tuned inductor, presented in this work, offers wider possibilities for power compensation in electric systems, compared to the classic solutions of compensators based on fixed inductors. Another possible implementation of such an inductor solution is in static power electronic devices, installed in AC transmission grids to increase power transfer capability, stability, and controllability, through a series and/or shunt compensation. Nevertheless, the use of the proposed device in the aforementioned electric systems is only one example of the possible implementations in the power electronics area. In this work, the following issues are presented: exemplary solutions of compensators with the adaptive features, rules of the tuned inductor operation, test results of the 3D field model of the inductor, and test results of the laboratory model of the electric system with this device. [ABSTRACT FROM AUTHOR]

This article presents a deep theoretical analysis of the Active Disturbance Rejection Control (ADRC) regulator for the control of first-order systems, directly compared to a "traditional" Proportional Integral (PI) regulator. To complete the theoretical study, ADRC and PI are implemented into the model of a single-phase Dual Active Bridge (DAB) converter to regulate the voltage of a Direct Current (DC) network. Facing different types of disturbances and DC network parameters variations, strengths and weaknesses of the two controllers are highlighted. ADRC and PI controls are discretized and implemented in Control Hardware In the Loop (CHIL) simulations of a single-phase DAB converter to regulate the voltage of a node of multi-terminal and multi-level DC network. By changing the DAB connection points along the MVDC network, the controlled system is stressed with different disturbances, extending the result of single-terminal network software simulations. [ABSTRACT FROM AUTHOR]

The resiliency of a standalone microgrid is of considerable issue because the available regulation measures and capabilities are limited. Given this background, this paper presented a new mathematical model for a detailed photovoltaic (PV) module and the application of new control techniques for efficient energy extraction. The PV module employs a single-stage conversion method to integrate it with the utility grid. For extraction the maximum power from PV and integrate it to power grid, a three-phase voltage source converter is used. For obtaining the maximum power at a particular irradiance a maximum power point tracking (MPPT) scheme is used. The fuzzy logic control and adaptive network-based fuzzy inference system are proposed for direct current (DC) link voltage control. The proposed model and control scheme are validated through a comparison with the standard power-voltage and current–voltage charts for a PV module. Simulation results demonstrate that the system stability can be maintained with the power grid and in the island mode, in contrast with the MPPT.

This work is devoted to possible implementation of tunable magnetic devices in electrical systems with adaptive properties. The basic idea, underlying operation of the presented magnetic device, depends on interaction of two (or more) magnetic fluxes in a quasi-linear range of ferromagnetic core characteristics. This is a new approach to the design of such magnetic elements; typically, saturation phenomenon of the ferromagnetic core of an inductor is used to change a value of its inductance. The good examples of adaptive electrical power systems can be devices for improving a quality of electrical energy. When used in compensators of reactive and a distortion power (or a reactive power only), tunable magnetic devices clearly offer wider possibilities for the compensation, compared to solutions, using compensators based on fixed magnetic elements. However, the application of the proposed tunable device in an adaptive compensator is only one example of its possible use in an electrical power area. In this work, the following issues are presented: exemplary solution of the adaptive passive compensator, basics of operation of tunable magnetic device, and test results of the experimental model of an electrical system with such a device.

This work focuses on the use of a one-phase direct current (DC) power supply equipped with a shunt active filter feature, which enabled the possibility of compensation (minimisation) of reactive and distortion power, generated by a group of loads, that was connected to the same power grid node as the power supply. A tuned inductor, which was included at the input of the controlled current source (constituting the main part of the power supply) allowed for an improvement in the quality of the compensation process, compared to a device with a fixed inductive filter This resulted in a visible reduction of the nonlinear distortions of the grid current. The improvement was made possible by extending the frequency response of the current source, which allowed to increase the dynamics of the current changes at the input of the power supply. This solution represents a new approach to such power devices. This work describes the principle of operation of the proposed converter solution and presents selected test results for a laboratory model of an electric system with this device. [ABSTRACT FROM AUTHOR]

This paper concerns the maximum power extraction of a photovoltaic generator system (PGS). The PGS consists of single photovoltaic (PV) cells. To improve the efficiency of a PGS, it is necessary to work within its maximum power point (MPP). In a PGS, output power is dependent on solar irradiance and the operating temperature and, therefore, MPP would be varied. To address this problem, a converter should be placed after the PGS and a smooth control signal should be used to adjust its duty cycle. The other challenge of a total system, i.e., PGS and converter, is the uncertainty involved. To overcome this uncertainty, a dynamic sliding mode control (SMC) can be used to regulate the smooth duty cycle. The low-pass integrator before the system can remove the chattering in dynamic SMC. However, due to the integrator, the states of the system increase and, hence, we propose a dual sliding observer (DSO) to estimate this added state. For a reliable comparison with the conventional SMC, the same proposed DSO can be applied in both dynamic and conventional SMC. The provided comparison shows the effectiveness of dynamic SMC in chattering suppression and real implementation with respect to conventional SMC. [ABSTRACT FROM AUTHOR]

In view of global targets to expurgate the carbon foot prints, presently major focus is on integrating prosumer renewable energy sources (RES). This has caught more interest in studying the impacts of AC and DC micro grid. Looking at the advantages of power transformers for stepping up and down the voltages, AC grids seem favorable for transmitting power over long distances, but AC grids are also often subjected to difficulties associated with them such as frequency dip, voltage drop due to line impedance, skin effect and Ferranti effect etc. Most of the sources and loads, particularly the renewables like solar, battery etc., in a micro grid are basically DC in nature and their operating voltages are low. Considering the conversion losses and transformer cost combined with problems of AC grid, DC micro grids are catching attention and their analysis is thus required. This paper presents the controls of various types of distributed generation sources (DGs) including renewable energy sources (RES) so as to integrate them to form a micro-grid. The AC and DC micro-grid models have been developed and its performance is assessed. Stability analysis is performed on both AC and DC micro-grid during permanent faults, temporary faults and sudden load variations to have a comparative outcome for selection of a better micro-grid.

This paper develops a new control strategy for voltage source converter (VSC) based multi-terminal high voltage dc (MT-HVDC) grids for enhancing the mutual frequency support between MT-HVDC interconnected asynchronous ac systems. The existing droop control structure of VSCs is augmented with an additional feedback voltage-based loop that generates a voltage shifting term to be added to the original dc voltage reference. The addition of this integrator-based controller nullifies the difference between voltage errors seen at adjacent converter stations. This action helps to overcome inaccuracies in the mutual frequency support caused by the uneven voltages across a dc system. The proposed strategy uses only local variables for the continuous-time control; thus, it does not rely on a high-bandwidth communication network, and its performance is not affected by the change of ac systems’ parameters. Modal analysis is carried out to investigate the stability of the proposed controller. Finally, comprehensive simulation studies are used to verify the proposed strategy’s performance and compare it with recently reported alternative controllers. [ABSTRACT FROM AUTHOR]

Conventional power management methods of networked microgrids (NMGs) are limited to the failure of pinned communication terminals and heavy communication burdens. This paper proposes a multilevel dynamic master-slave control strategy via two-level dynamic leaders to realize the resilience enhanced power management of NMGs. The first level dynamic leader with considerations of distributed energy resources (DERs) feature is selected to guide the output of DERs and achieve the power management within individual microgrid (MG). Subsequently, the secondary level leader considering each MG feature is selected among the bidirectional interlinking converters (BICs), whose signals would be shared with other BICs by communication to achieve power management among MGs. Moreover, the local weight selecting method (LWSM) is proposed to automatically select the two-level dynamic leaders according to the real-time system operation state. Compared with conventional methods, the communication among MGs is essentially realized through the dynamic DER leaders instead of pinned ones. Therefore, unreliability issues in the event of pinned terminal outage and converters' communication failure can be fully addressed and the communication bus within each only needs to transmit one DER's signals. The proposed strategy can be also extended to NMGs with various topologies and provide the "plug and play" capabilities of DERs or MGs. Finally, the effectiveness and feasibility of the proposed strategy are verified through the PSCAD/EMTDC platform. [ABSTRACT FROM AUTHOR]

One of the major failure causes in the power modules comes from the severe thermal stress in power semiconductor devices. Recently, some local control level methods have been developed to balance the power loss, dealing with the harsh mission profile, in order to reduce the thermal stress. However, there is not any specific system level strategy to leverage these local control level methods responding to the multiple inverters situation. Besides, the impacts of these methods on the thermal cycle and lifetime of the power modules in the long-term time scale have not been evaluated and compared yet. Hence, in this article, a centralized thermal stress oriented dispatch (TSOD) strategy is proposed to take full advantage of these local control level methods, including the switching frequency variation and the reactive power injection, to reduce the thermal stresses for multiple inverters. In addition to the PI controller, the finite control set model predictive control (FCS-MPC) is also explored to synergize with the proposed strategy. The results from the real-time model-in-the-loop testing on a four-paralleled-inverters platform, the reliability assessment, and the experiments all validate the effectiveness of the proposed centralized TSOD strategy on the thermal stress reduction.

This paper presents a droop-based controller for grid-tied three-phase inverters. The controller allows to regulate the inverter output power while operating grid-tied, to support the local grid voltage while operating islanded, and to seamlessly transition into this latter mode of operation. Remarkably, the use of the traditional droop control scheme for per-phase power control would lead to unequal frequencies among the phase voltages, which is not acceptable. Instead, the proposed controller allows independent power references tracking at each of the phases of a three-phase inverter while grid-tied and a proper transition into the islanded operation. Per-phase power control is crucial for several services in modern smart power networks, like demand-response and distributed unbalance compensation. The paper also reports the stability analysis of the whole control system and outlines a procedure for the design of the involved regulators. Simulation and experimental results considering a laboratory-scale prototype are reported and discussed to validate the proposed controller.

This article deals with the impact of harmonic filters’ interactions in the aircraft grid, in particular, their influence on the control performance of each subsystem. The study has been carried out on a notional electrical system composed of two three-phase power converters—a voltage source inverter and an active front end. The beginning of the article presents the origin of the issue—trend of reducing the filter size and weight, which is especially true in the aircraft industry. Then, the roles of the filter and their design challenges are discussed. The next part of the article describes the controller’s constraints, its design, and the control system modeling approach, including a specially developed simulation tool used for the interactions analysis. Simulation results with the experimental verification are presented showing the interactions impact on the system dynamics. Finally, optimization of the filters under dynamic control constraints considering system’s components interaction are presented as the simulation tool application. [ABSTRACT FROM AUTHOR]

Solid-state transformer (SST) is an emerging technology integrating with a transformer power electronics converters and control circuitry. This paper comprehensively reviews the SST topologies suitable for different voltage levels and with varied stages, their control operation, and different trends in applications. The paper discusses various SST configurations with their design and characteristics to convert the input to output under unipolar and bipolar operation. A comparison between the topologies, control operation and applications are included. Different control models and schemes are explained. Potential benefits of SST in many applications in terms of controllability and the synergy of AC and DC systems are highlighted to appreciate the importance of SST technologies. This review highlights many factors including existing issues and challenges and provides recommendations for the improvement of future SST configuration and development.

This manuscript describes the operation of a droop-based controller for three-phase converters in the case of the absence of a neutral connection to the grid. The controller is capable of output power tracking and smooth transitions into the islanded operation. While independent per-phase control of the converter output power is possible if a neutral connection is present, its absence implies additional constraints to be considered. Focusing on this latter case, the controller described herein allows the independent control of the active power at the output of each phase of the converter and a smooth transition to the islanded operation. These features are paramount in future smart power systems, such as smart microgrids, for implementing demand–response, power-flow management, and uninterrupted power operation.

In High Voltage Direct Current (HVDC) grids, system parameter and/or topology changes following HVDC grid protection actions affect system dynamics and in combination with the existence of line inductors in series with HVDC circuit breakers (DCCB), pose a challenge to designing converter controls that satisfy desired performance and stability requirements. To date, several methods have been proposed for evaluating the influence of the line inductors on system stability; however, tuning of the MMC controls considering system parameter and/or topology changes following HVDC grid protection actions haven’t been studied in detail. This paper presents a systematic tuning procedure for a robust operation of MMCs in any HVDC grid configuration. The proposed method analyzes the impact of variations in HVDC grid system parameters and control bandwidths (BWs) using small-signal based stability analysis and Singular Value Decomposition (SVD)-based performance analysis methods. In addition, it considers the impact of line outages associated with HVDC grid protection actions in order to select optimal control gains that fulfill performance and stability requirements of the HVDC grid for given HVDC Circuit Breakers (DCCBs) line inductor values. To illustrate the proposed methodology, a detailed step-by-step stability analysis in a 4-terminal HVDC grid test system is presented. [ABSTRACT FROM AUTHOR]

This article presents an energy management strategy for a microgrid having solar PV arrays and a battery energy storage system (BESS). Most of the energy management strategy used for commercial photovoltaic (PV) inverters and battery inverters do not consider the future load behavior and cannot ensure the energy resiliency for a PV and battery storage based microgrid. This article proposes the use of a model predictive control strategy that considers future load behavior and energy cost profile to determine an optimum power flow trajectory to achieve energy resiliency, minimize the operating cost and maximize the profit of the microgrid. The proposed control strategy of the energy management system (EMS) is validated using both simulations in MATLAB/Simulink environment and by carrying out laboratory experiments on a developed laboratory test platform. For the converters of the test platform, this article develops a magnetically linked seven-level multilevel converter (acting as the solar PV inverter) and a full-bridge inverter with an advanced pulsewidth modulation technique (acting as the BESS inverter). Commercial inverters usually require large and bulky power frequency transformers for the grid integration of renewable energy sources. The high-frequency magnetic link-based power electronic converter can produce multiple balanced dc power sources with reduced size, ensures lower power losses during the energy conversion process and can also ensure galvanic isolation. The results from the simulation and experimental studies of the EMS demonstrate that the developed energy management strategy ensures both the minimization of the operating cost of the system and the increased resiliency of the whole system. [ABSTRACT FROM AUTHOR]

A single-switch N-stage Z-network high-gain boost converter is proposed in this study, which can be applied in the field of chip etching for bias provision. The circuit topology, operation mode, voltage gain and the control strategy are analyzed. Thereafter, the steady-state performance of the circuit is analyzed with small signal stability modeling. A simulation model is built using Simulink and compared with the traditional quadratic circuit. Combined with the control strategy, the circuit can obtain better steady-state performance by controlling the number of working N-networks and adjusting the duty ratio in the case of high voltage, wide range of voltage output and dynamic voltage output. The simulation model and hardware prototype of the single-switch four-stage Z-network high-gain boost circuit are built and tested, which have verified the effectiveness of the proposed design.

This work focuses on the possibility of using a tuned inductor in electric power systems with adaptive features. The presented idea of inductor operation, using an interaction of the magnetic fluxes, is a new approach to designing such devices. Examples of power adaptive systems are devices for improving the quality of electricity. Therefore, various types of ‘compensators’ of reactive power (or both reactive and distortion power) are used in electrical systems as a preventive measure. The tuned inductor, presented in this work, offers wider possibilities for power compensation in electric systems, compared to the classic solutions of compensators based on fixed inductors. Another possible implementation of such an inductor solution is in static power electronic devices, installed in AC transmission grids to increase power transfer capability, stability, and controllability, through a series and/or shunt compensation. Nevertheless, the use of the proposed device in the aforementioned electric systems is only one example of the possible implementations in the power electronics area. In this work, the following issues are presented: exemplary solutions of compensators with the adaptive features, rules of the tuned inductor operation, test results of the 3D field model of the inductor, and test results of the laboratory model of the electric system with this device.

Although Switched Reluctnace Motors have many advantages, vibration is known as their most severe drawback acting as an impediment limiting their widespread use in industrial and domestic applications. Through electromechanical relationships, it is shown that the first-order time derivative of applied phase voltage and second-order time derivative of radial force directly affect the amplitude of generated vibration, especially at the beginning of demagnetization instance. Therefore, a set of criteria is stated in this paper meeting which ensures having low vibration intensity. In this paper, three types of demagnetization voltages are proposed which comprehensively meet the stated criteria. These voltages share the same characteristics contributing to the vibration reduction in Switched Reluctance Motor. Two vital parameters of Synchronous Counter and Coefficient are included in the proposed demagnetization voltages which must be meticulously chosen in order to be effective. Noticeable contribution of the proposed methods to the vibration alleviation is validated through simulation and experimental tests conducted under different working conditions. [ABSTRACT FROM AUTHOR]

This work focuses on an isolated offline driver to power LED lamps, realized with a high-power-factor quasi-resonant (Hi-PF QR) flyback converter with peak current mode control and employing constant-current primary-sensing regulation (CC-PSR). The converter is controlled with a recently introduced control technique that enables this kind of converter to ideally draw a sinusoidal current from the input source and, at the same time, to accurately regulate the dc output current using only quantities available on the primary side. The resulting absence of an optocoupler or other means crossing the isolation barrier to close a feedback loop not only reduces size and cost of the driver but also brings greater safety and reliability. The analysis addresses those factors inherent in the control method that affect the shape of the input current that have not been covered in the existing literature. The aim is to set up some design guidelines to minimize the Total Harmonic Distortion (THD) of the input current. The experimental work shows that using this technique enables the design of an LED driver for wide range mains (90 to 264 Vac) that achieves output current regulation better than ±2%, power factor close to unity and THD of the input current

This work focuses on the use of a one-phase direct current (DC) power supply equipped with a shunt active filter feature, which enabled the possibility of compensation (minimisation) of reactive and distortion power, generated by a group of loads, that was connected to the same power grid node as the power supply. A tuned inductor, which was included at the input of the controlled current source (constituting the main part of the power supply) allowed for an improvement in the quality of the compensation process, compared to a device with a fixed inductive filter This resulted in a visible reduction of the nonlinear distortions of the grid current. The improvement was made possible by extending the frequency response of the current source, which allowed to increase the dynamics of the current changes at the input of the power supply. This solution represents a new approach to such power devices. This work describes the principle of operation of the proposed converter solution and presents selected test results for a laboratory model of an electric system with this device.

Conventional power management methods of networked microgrids (NMGs) are limited to the failure of pinned communication terminals and heavy communication burdens. This paper proposes a multilevel dynamic master-slave control strategy via two-level dynamic leaders to realize the resilience enhanced power management of NMGs. The first level dynamic leader with considerations of distributed energy resources (DERs) feature is selected to guide the output of DERs and achieve the power management within individual microgrid (MG). Subsequently, the secondary level leader considering each MG feature is selected among the bidirectional interlinking converters (BICs), whose signals would be shared with other BICs by communication to achieve power management among MGs. Moreover, the local weight selecting method (LWSM) is proposed to automatically select the two-level dynamic leaders according to the real-time system operation state. Compared with conventional methods, the communication among MGs is essentially realized through the dynamic DER leaders instead of pinned ones. Therefore, unreliability issues in the event of pinned terminal outage and converters’ communication failure can be fully addressed and the communication bus within each only needs to transmit one DER’s signals. The proposed strategy can be also extended to NMGs with various topologies and provide the “plug and play” capabilities of DERs or MGs. Finally, the effectiveness and feasibility of the proposed strategy are verified through the PSCAD/EMTDC platform.