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Along with the rapid integration of distributed generation units (DGUs) into the power grids is the rise in unconventional and unpredictable patterns of the undesirable cyber–physical intrusions and faults; this drastically increases the risk of islanding possibilities and threatens the sustainability of the energy delivery infrastructure. Classification of cyber–physical events and developing solutions to mitigate their impacts before rising to an islanding situation is a critical monitoring task in DGUs. Passive islanding detection has been widely applied to studying the behavior of voltage signals at the point of common coupling, which is a sophisticated challenge due to cross similarity among fault (event) patterns and their fast dynamics. In this article, a novel quadratic time–frequency decomposition, namely HSS-transform, is applied over an alternative complex representation of three-phase signal defined by the synchronous reference frame transformation. We further exploit the principles of informative sparse representation-based classification (TISC) to develop a comprehensive artificial intelligence framework for fast and reliable classification of DGU islanding and nonislanding events with the focus on practical limitations and requirements of a smart power electronics inviter as the desirable observational site. Different from the state-of-the-art techniques, TISC does not need any training procedure, while due to its linear mathematical formulation acts inherently fast with low computational burden on the inverter processing unit. Moreover, the simultaneous three-phase feature extraction strategy ensures preservation of the between-phase information.

Geomagnetic Disturbances (GMDs) are the result of solar storms or a high-altitude nuclear detonation. On the power systems, they might lead to the flow of quasi-DC currents referred as Geomagnetically Induced Currents (GICs). These currents cause the AC current offset that may drive the power transformers into saturation. This leads to large draw of reactive power, causes transformer internal heating and increased noise level, damage to shunt capacitors, harmonic filters and maloperation of power system protection equipment. This paper reviews the state-of-the-art of the GIC mitigation and elimination strategies and their respective limitations. It also introduces converter-based strategies as a new avenue of power system protection against GICs by presenting novel strategies that involve the integration of the proposed schemes between the neutral and ground of power transformers. One of the proposed schemes is a contribution to the approaches solely focused towards GIC mitigation, whereas, the other provides a variety of grid-support functions in addition to GIC elimination. The simulations performed in a Controller Hardware-in-the-Loop (C-HIL) environment verify the proposed schemes as a promising alternative to the current GIC mitigation approaches.

The dc in a power network might be caused by geomagnetic disturbances that result from either a geomagnetic storm or a high-altitude nuclear detonation. The augmenting trend of inverter-based resources is also acting as a source of small dc injection into the power systems. As the resultant, dc could lead toward a possible power system failure, a myriad of neutral blocking devices (NBDs) have been proposed, where, these devices are installed between the neutral and ground of wye-grounded transformers. However, the electrical safety assessment of these devices is critical prior to adding them to the grid as they might raise serious concerns both for the power equipment and the power system maintenance staff. This work is the first effort toward hazard identification and quantitative risk assessment associated with NBDs. It proposes a risk management framework for augmented electrical safety pertinent to these devices. Later, it analyzes the proposed neutral blocking strategies and highlights the associated risks to the operational safety of these installations, particularly concerning electromagnetic pulse (EMP) attacks, cyber threats, and equipment malfunction. Finally, an ideal NBD operational design is proposed incorporating a variety of risk reduction measure to avoid any hazardous situation arising from such installations. This work could provide a guideline for the electric utilities and academic researchers to consider these safety implications prior to proposing or installing these devices.

The dc in a power system may be caused by geomagnetic disturbances that are the result of solar storms and high-altitude nuclear detonations. Increased inverter-based generation is also contributing to small dc injection into the power systems. The resultant dc could have serious consequences for the power systems as it may drive power transformers into saturation, cause transformer internal heating, cause large draw of reactive power, and misoperation of protective relays. This letter proposes a novel power electronics-based dc mitigation approach that involves a transformerless series active filter integrated between the neutral point and ground of power transformers serving multiple purposes. The first objective is to surpass the effect of dc injection, the second goal is voltage regulation, and the third is to provide harmonic isolation or impedance balancing. The proposed device is currently being developed on a 7.2-kV/240-V single-phase transformer; however, the solution is also relevant for 24–500-kV networks. The system circuitry, operation, and control are implemented and verified for this letter in a controller hardware-in-the-loop (C-HIL) test setup using a Typhoon HIL-402 simulator. Results indicate that our approach is a promising alternative to traditional neutral capacitor-blocking strategies.

The per-phase leg of an improved active-neutral-point-clamped (I-ANPC) multilevel converter is realized by the cascaded connection of the standard ANPC topology and the concatenated H-bridge modules consisting of the flying-capacitors (FCs). This article proposes an innovative approach for the active control of the I-ANPC inverters. The introduced methodology is developed on the basis of the logic-equations set for the active voltage balancing of the FCs within the H-bridge modules, and controlling the generated output voltage. It derives logic-variables employing the direction of the output current, and the deviation of the FCs’ voltages from their target operating levels in the H-bridge cells. These logic-variables are fed into a set of logic-equations derived for the control of the I-ANPC inverter. The regulation of the floating-capacitor voltages at their reference values along with synthesizing the required pulsewidth modulation voltage-level at the output having fast dynamics are the control objectives to achieve. The derived logic-equations and the proposed control method are explored and verified by the experimentally measured results obtained from the 5-kW prototype of a five-level converter.

The flow of DC in AC networks leads to half-cycle saturation of power transformers that causes their internal heating, large draw of reactive power and ultimate grid collapse. Transformerless power electronics-based module integrated between the neutral and substation ground of traditional transformers has previously been proposed that provides power system protection against DC flow in grid along with a variety of advanced grid-support features. The technique has already been tested and verified on a controller hardware-in-the-loop (C-HIL) platform. In this paper, the proposed strategy is evaluated on a laboratory scale hardware prototype utilizing Typhoon power hardware-in-the-loop (P-HIL) strategy. The experimental results verify the promising performance of the proposed scheme in nullifying the effect of DC injection, performing harmonics isolation and voltage regulation. Also, an effective transformer and converter protection scheme utilizing a hybrid AC/DC solid-state switch has been proposed and evaluated in this paper.

Energy sustainability and sustainable energy systems play a major role in the long-term sustenance of human existence and the environment, and improve the coexistence between technology and nature. Cyber-physical systems are one of the means for achieving energy sustainability. The physical layer comprising of power/energy and the cyber layer comprising of control, communication, and computation needs to be designed to achieve the overall goals of energy sustenance such as integration of renewable energy to the grid, reliable control power converters, microgrid control and protection, energy harvesting from nonconventional sources and efficient power circuit topologies. The confluence of the cyber and physical layers is seen in a multitude of applications such as smart connected and self-sustainable electronic grids; smart cities, centers, buildings, and villages; electronically controlled mobility, transportability, and energy transformation (e.g., electric vehicles and locomotives, electronically controlled semiconductor-based transformers); healthcare and biomedicine; cognitics, robotics, and wearables; lighting; telecommunications; aerospace, avionics, and space applications; off-grid and rural-electrification applications; and network-on chips, edge computing, and the Internet of Things (IoT).

In this article, a broad overview of the current research trends in power-electronic innovations in cyber-physical systems (CPSs) is presented. The recent advances in semiconductor device technologies, control architectures, and communication methodologies have enabled researchers to develop integrated smart CPSs that can cater to the emerging requirements of smart grids, renewable energy, electric vehicles, trains, ships, the Internet of Things (IoT), and so on. The topics presented in this article include novel power-distribution architectures, protection techniques considering large renewable integration in smart grids, wireless charging in electric vehicles, simultaneous power and information transmission, multihop network-based coordination, power technologies for renewable energy and smart transformer, CPS reliability, transactive smart railway grid, and real-time simulation of shipboard power systems. It is anticipated that the research trends presented in this article will provide a timely and useful overview to the power-electronics researchers with broad applications in CPSs.

The current and future growth in the penetration of the solar photovoltaic (PV) power generation and electric vehicle (EV) charging infrastructure across legacy distribution networks may cause numerous system vulnerabilities. In this paper, an approach is presented to evaluate a distribution system in terms of PV and EV penetration, as well as natural load growth based on a 2025 projection. The system vulnerabilities are identified in worst-case operation scenarios using time-series power flow analysis and load hosting capacity studies. Then, the negative impacts associated with PV and EV penetrations are mitigated using distributed energy storage deployment along the feeders. Finally, a business case and value proposition for the distributed energy storage is developed based on their applications and valuation in a regulated utility environment. The approach and findings of this paper may provide inputs to regulated utilities as they plan for the anticipated growth in PV and EV infrastructure on their legacy distribution networks.

Compared with the traditional power grid, the Microgrid with high penetration of converter-based renewable energy faces different protection challenges, e.g., different short-circuit levels in different operating modes, bidirectional fault coordination, ride-through capability, etc. Thus, the traditional mechanical circuit breaker with a relatively slow response time, requirements to operate at high fault currents and the single directional characteristic based protection system cannot satisfy the modern Microgrid demand. Accordingly, a new protection system to solve the new problems in Microgrid is essential. Fortunately, with the development of power electronics, circuit breakers (solid-state circuit breaker, hybrid circuit breaker) with fast response time and bidirectional characteristics gradually emerge. With these new breaker options, this paper proposes a novel hierarchical protection scheme based on the different response times among the solid-state circuit breaker, the hybrid circuit breaker, and the traditional mechanical breaker to better protect a campus Microgrid. The campus Microgrid is studied to verify the effectiveness of the proposed hierarchical Microgrid protection scheme.

The high penetration of renewable fed decentralized generation has paved the way for realizing microgrids that can offer better resiliency and reliability than traditional distribution systems. This paper discusses the modeling and operation of a hybrid AC-DC microgrid for the Clemson University Campus. Various inverter-based Distributed Energy Resources(DERs) models are developed to accomplish the task and presented in the paper. The central controller for the hybrid microgrid is designed to correctly dispatch DERs and Battery Energy Storage Systems(BESS) in regulating voltage and frequency to nominal values as per IEEE 2030.7-2017 std. The campus microgrid is sized to work in grid-connected and islanded modes of operation with a load shedding scheme. The results for different dynamic events in both AC and DC microgrids depict a seamless operation between the two modes with the proper voltage and frequency regulation. Finally, a cost analysis is performed to look at the financial viability of implementation.

Due to the rapid transformation of traditional grid into a complex meshed network along with an exponential integration of volatile distributed energy resources (DERs); wind and photovoltaic (PV) farms, and converter-based loads; electric vehicles (EVs) etc., traditional grid operation strategies are stressed, and mitigation measures are required. Accordingly, a myriad of dynamic mitigation devices have been proposed in the last few decades where these devices are installed at strategic points in the grid. Transformer-less power electronics-based modules, integrated between the neutral and substation ground of traditional transformers, have been proposed introducing a variety of advanced grid mitigation and support features; DC elimination, voltage regulation, voltage and impedance balancing, harmonics isolation and power flow control. However, the protection of these series-connected modules against high voltage development during ground faults or inrush currents is critical as it could damage these converter-based mitigation devices or exceed the transformer BIL rating, thus, severely threatening the energy security. This paper presents an effective transformer and the module protection scheme utilizing a hybrid AC/DC solid-state switch. The proposed scheme is evaluated on an emulated 25-kVA, 7.2kV/240V single-phase hybrid smart transformer (HST), utilizing Typhoon HIL that verifies its promising performance.

Distributed energy resources (DERs), bulk grid events, grid stability and resilience, microgrids, standards, power quality, and high-voltage dc (HVDC) technologies were among the topics of interest at the third IEEE International Workshop on Electronic Grid (eGrid). IEEE eGrid 2018, hosted by Clemson University in Charleston, South Carolina, 12-14 November 2018, provided a platform for examining the role of power electronic applications in modern electric utilities. Power electronics is currently changing from an enabling technology for renewable generation and energy efficiency to an underpinning technology for grid modernization, electronic transmission, and distribution grids that can effectively manage electricity among many power electronic-based sources and loads. Power electronicbased sources and loads will be prominent in the grid of the future.

The solar storm or a high-altitude nuclear detonation leads to geomagnetic disturbance (GMD) that causes the flow of geomagnetically induced current (GIC) in the power systems. The GIC leads to half-cycle saturation of generator step-up (GSU) transformers that causes negative-sequence currents to flow in the generator's stator windings. This in turn leads to excessive rotor vibration, heating and generation fluctuations, thus threatening the grid reliability and resiliency. This paper performs the vulnerability assessment of the most-widely utilized power generation resource i.e. synchronous generators against GIC by performing a detailed harmonic analysis and depicting the resultant mechanical, electrical and thermal repercussions. The simulation is performed in PSCAD/EMTDC for a 13.8kV/120MVA grid-tied synchronous hydro-generator impacted by a GMD. The simulation results highlight the significant threat facing the highly prevalent generation facilities that are largely unprotected against the adverse effects caused by the GMD on power systems.

The HVDC transmission is typically utilized for connecting long distance or asynchronous AC networks. The two most common HVDC technologies are voltage source converter HVDC (VSC-HVDC) and line commutated converter HVDC (LCC-HVDC). Although VSC-HVDC has enhanced control features along with non-dependence upon synchronous machines for commutation, it suffers from higher cost and higher losses due to the involvement of high-speed switching, requires sophisticated gate driver circuitry, has a weak overload capability and suffers from lower reliability due to higher component count. This paper focuses on the highly mature LCC-HVDC technology and aims at enhancing its reliability along with reduced control complexity by proposing a novel transformerless power electronics-based module integrated between the neutral and ground of HVDC inverter-side transformer. The module introduces a variety of smart features in conventional converter transformer, such as, harmonics isolation, voltage regulation, voltage and impedance balancing. This enhances LCC-HVDC robustness against commutation failure, reduces DC power recovery time and control complexity while protects it against certain natural and man-made disturbances, such as, solar storms and high-altitude nuclear detonations. The proposed approach is evaluated in PSCAD/EMTDC for the CIGRE HVDC benchmark model that highlights its promising performance.

The HVDC systems are typically utilized for long distance power transmission due to their advantages like minimal-loss bulk power transmission, advanced control features and capability to interconnect asynchronous AC networks. Among the two most common HVDC technologies; voltage source converter HVDC (VSC-HVDC) and line commutated converter HVDC (LCC-HVDC), the former has enhanced control features along with non-dependence upon synchronous machines for commutation. However, it suffers from higher losses due to the involvement of high-speed switching, involves sophisticated gate-driver circuitry, has a weak overload capability, suffers from non-availability in higher ratings and lower reliability due to higher component count. This paper is focused on enhancing the reliability along with reduced control complexity of the highly mature LCC-HVDC technology by converting the inverter-side transformer into smart one through integration of a power electronics-based module between its neutral and converter-station ground. The module enables the conventional converter transformer to perform voltage regulation, harmonics isolation, voltage and impedance balancing. This leads to enhanced robustness of LCC-HVDC against commutation failure, minimization of DC power recovery time and protection against disturbances, such as, solar storms and high-elevation nuclear explosions. The proposed approach is also depicted to introduce power flow control capabilities in AC-tie lines for parallel AC/DC transmission. The PSCAD/EMTDC is utilized to evaluate the proposed approach on the CIGRE benchmark model and the results verify it as a promising solution to multiple HVDC problems.

The electric grid is rapidly evolving by incorporating advanced equipment that bears a variety of smart features in addition to their traditional functionalities. The power transformers are the most significant equipment in the substation and have been traditionally performing voltage conversion and isolation. However, the modern grid dynamics demand a variety of smart control features at strategic locations of the grid for which the most appropriate candidate are the transformers. Accordingly, the idea of solid-state transformers (SST) was conceived but they are still far from integration into grid due to their poor lifetime and reliability concerns. Also, the investment on existing infrastructure demands introduction of smart features into already installed traditional transformers. This paper proposes a converter-based intelligent transformer configuration that utilizes conventional transformers and introduces smart features into them through a power electronics-based module integrated between neutral and substation ground. The device introduces a variety of advanced features in traditional transformers that include voltage regulation, voltage balancing, harmonics isolation, supporting voltage ride through (VRT) capabilities of distributed energy resources (DERs) and avoiding grid collapse due to certain natural or man-made disturbances, such as, solar storms and high-altitude nuclear explosions. The proposed scheme is evaluated utilizing Typhoon hardware-in-the-loop (HIL-604) real-time simulator for a modified IEEE-9 bus benchmark system. The results verify the promising performance of the proposed scheme to enhance grid reliability, resiliency and power quality.

In the era where there is a huge demand to curtail the power plants with conventional sources of energy owing to their higher generation costs and carbon emissions, the Combined Heat and Power (CHP) units are still gaining a wider popularity. This is due to the intermittent nature of renewable energy sources that impedes their full share in the current energy mix and the lower emissions along with the higher efficiency levels associated to the CHP units when compared with units utilizing conventional sources. The inverter interface of CHP units further enabled their integration in advanced grid environment. This paper reviews the enabling framework, role and significance of the inverter-interfaced CHP units in the modern grid concept of microgrids. A case study of a variable speed inverter-interfaced CHP unit in a planned campus microgrid environment is also presented.

Microgrids are a promising alternative to the traditional distribution systems due to their highly desirable features, such as, reliability, resiliency, and efficiency. This paper covers the design, simulation, and economic analysis of a theoretically designed modern, mixed-use commercial and residential building on a feeder in Charleston, SC, USA. The designed system is simulated in PSCAD/EMTDC. The system combines a natural gas CHP turbine and generator block set, solar photovoltaics (PV), and a battery energy storage system (BESS). It is planned to provide power through a DC lighting bus and an AC to several different commercial load profiles as well as 40 apartments of varying sizes. Additionally, a comprehensive economic analysis is completed with available or estimated pricing to prove the feasibility of such a project.

The DC currents might flow in a power system due to Geomagnetic Disturbances (GMDs) that result from either a solar storm or a high-altitude nuclear detonation. The increasing inverter-based generation is also injecting small DC currents into the power systems. These currents could have serious implications for the power systems as they drive the transformers towards saturation, cause massive draw of reactive power, cause transformers internal heating and maloperation of protection equipment. This paper studies the impact of the DC currents flowing in a power transmission network on a 50MVA grid-tied solar farm. A variety of loading conditions that include both local and remote loads have been considered. A detailed harmonic analysis is performed and evaluated against IEEE-519. Also, the limitations imposed by the DC current flow in a power grid on the solar farm capabilities have been highlighted. Finally, the effectiveness of a Neutral Blocking Device (NBD) in restoring the normal operation of a solar farm has been evaluated. The PSCAD/EMTDC has been utilized as the simulation platform and the associated results are presented.

Geomagnetically Induced Currents (GIC) are the significant effects of the Geomagnetic Disturbances (GMDs) on power systems. GICs typically appear in the form of DC components in the current wave forms of high voltage transmission lines and may lead to transformer saturation, so-called DC saturation. Such saturation scenarios, if experienced, can result in severe damages to the transformer core and significantly increase the system-wide risk of major blackouts. It calls for developing detection and classification mechanisms for GICs in power systems so they can be prevented or interrupted before emerging as a threat. A major challenge associated with GIC detection is the presence of similar events, resulted from faults and other distortions, such as AC saturation caused by harmonics. The current signals recorded by current transformers can be analyzed to classify these events. In this paper, the time-frequency S-Transform is integrated with a sparsely-enhanced version of the collaborative representation-based classification to implement a fast, reliable, and adaptive GIC events classification approach. Unlike usual techniques, the proposed mechanism does not need any training procedure while, due to its linear formulation, acts inherently fast and is adaptable to recognize the challenging scenarios of combined events.

Geomagnetic Disturbances (GMDs) have long been the cause of various power system failures thus affecting the power system stability and security. Their major effect on power systems is the injection of Geomagnetically Induced Currents (GICs) among the long length transmission lines. This phenomenon, particularly, leads to transformers saturation and consequent damages. This paper proposes a novel power electronic-based GICs mitigation approach for utility transformers that involves a transformerless series active filter integrated between the neutral point and earth ground serving multiple purposes. The first objective is to surpass the effect of GICs, while the second goal is voltage regulation and the third is to provide harmonic isolation. The system circuitry, operation and control are implemented and further verified in a Controller Hardware-in-the-Loop (C-HIL) test setup with Typhoon HIL 402 simulator. Results indicate that our approach is a promising alternative to traditional neutral capacitor blocking strategies.

Geomagnetic Disturbances (GMDs) can cause the flow of Geomagnetically Induced Currents (GICs) in a power system. The GICs can affect the power systems reliability through maloperations of associated protection equipment. This can lead to a wide area system blackout, thus, augmenting the chances of a catastrophe. This paper analyses the influence of GICs on the most commonly utilized transmission system protection equipment that includes Current Transformers (CTs) and protection relays i.e. distance, differential, inverse-time over-current (ITOC) and undervoltage (UV) relays. The simulation is performed in PSCAD/EMTDC for a 230kV test transmission system to show the variation in performance of the associated protection equipment under influence of GICs. Some recommendations are also provided to avoid the chances of protection equipment maloperation due to GICs for enhanced grid reliability.

Geomagnetic Disturbances (GMDs) lead to the flow of Geomagnetically Induced Currents (GICs) in power systems. The GICs compromise the reliability of a power network by causing mis-operation or even damage to certain power equipment. The wye-grounded three-phase power transformers in transmission network provide the most appropriate path for the flow of GICs. This paper proposes a novel GIC mitigation approach that utilizes a power electronic circuitry integrated between the neutral point and earth ground of power transformers. In addition to automatic GIC mitigation, the device provides voltage regulation, voltage unbalance removal and harmonic isolation as added features. The proposed approach converts the traditional transformers into smarter one, thus, providing a step forward towards realization of the much-needed smart grids. The simulation results in Typhoon Hardware-in-the Loop (HIL) real-time simulator verify the efficacy of the proposed approach on a 765kV/345kV power transformer.

This paper proposes a decentralized control scheme for controlling active and reactive power of grid-tied ac-stacked photovoltaic (PV) inverter architecture using single member phase compensation. Reactive power control is required for the next generation of grid-tied smart PV inverter systems in power networks with high PV penetration. The decentralized control scheme proposed in this paper allows for a fully distributed architecture, both in terms of active and reactive power control and physical implementation of a PV system. This will result in higher reliability and potentially lower cost with minimum communications requirements. A decentralized controller enables higher switching frequencies that can shrink passive components. Therefore, string voltage variations due to voltage drop across passive components will be negligible and the system will be controlled with minimum communications requirement. The relative gain array approach has been used to study the feasibility of the decentralized control scheme. Detailed modeling and analysis are provided to show the effectiveness of the proposed decentralized approach and the effect of this approach on control implementation. Finally, effectiveness of the proposed decentralized approach is verified using mathematical modeling, simulation, and a lab-scale experimental setup in different operation conditions.

An islanding condition refers to an undesired event in which a portion of utility system, including both distributed generator(s) (DG) and local loads, remains energized while the main grid is disconnected. Unintentional islanding incident can result in serious personnel safety issues, interference to grid-protection facilities, power quality degradation, and equipment damage. Accordingly, anti-islanding protection for DG system is required by standard and utility codes. In this paper, an active islanding protection method is proposed called locking frequency band detection. The proposed method functions by introducing a virtual detection band only based on local grid frequency measurements at the point of common coupling. Hence, it has little or no impact on DG output and its power quality, and it does not get affected by a number of DGs. In addition, the proposed protection method eliminates the dreaded nondetection zone for DG systems typically observed during most severe power system transient conditions. In this paper, detailed description of the algorithm is explained and its performance and efficacy are evaluated through simulation and hardware experiments for different load quality factors.

This paper summarizes workforce development efforts that are underway in the Carolinas with the help of a regional industry-led consortium, namely, “The Center for Advanced Power Engineering Research (CAPER).” The three CAPER university members, Clemson University, NC State University, and UNC Charlotte, have met on a number of occasions to discuss the different aspects of workforce development efforts. We describe the entire process, from core competencies needed to how and where the training should be done. For individuals aspiring to work in the power industry, in addition to possessing a strong knowledge in the fundamentals of power engineering, there are several other attributes that the industry looks for in a potential candidate. While industry is mostly clear on what attributes they look for in their new employee candidates, the challenge for universities is to build the right curriculum, offer opportunities to develop the soft skills, provide interaction with industry and build a spirit of collaboration among students in order to prepare them for future careers in power engineering. This paper also discusses a variety of university perspectives and experience with developing the curriculum and the different ways to involve all industry stakeholders in the educational process.

Multilevel voltage-source converters are well-suited for power conversion applications demanding higher power density, reliability, efficiency, and power quality. An unremitting and persistent research for developing advanced multilevel converter topologies with improved characteristics, performance, modulation techniques, and control methods continues. This paper proposes duo-neutral-point-clamped (D-NPC), duo-active-neutral-point-clamped (D-ANPC), and duo-neutral-point-piloted (D-NPP) multilevel voltage-sourced converter topologies. The D-NPC, D-ANPC, and D-NPP converters phase-leg is realized by adding low-frequency semiconductor power switches to their structures. This results in a substantial reduction in the number of the high-frequency pulsewidth-modulation insulated-gate bipolar transistors and clamping passive devices including diodes as well as flying-capacitors (FCs). Moreover, a drastic abatement in the total voltage rating and total stored energy of the FCs within the D-ANPC topology is achieved compared to the classic ANPC configuration. The experimental results are provided for D-NPC, D-ANPC, and D-NPP converters to validate the feasibility of their topology and modulation method for control of the multilevel converters.

Microgrids with Distributed Energy Resources (DERs) have proved to be a propitious alternative to the traditional distribution systems. This is due to the increased resiliency, efficiency and reliability offered by these grids. This paper discusses the design and operation of a microgrid and its associated controller for the Clemson University main campus. The virtual inertia has been emulated in the microgrid to make it closely resemble the one emulating a synchronous generator. A coordination controller has been developed for the systematic dispatch of Photovoltaic (PV) and Battery Energy Storage System (BESS). The microgrid has been sized to perform both grid-connected and two days of islanding operation. The designed grid exhibits a nearly seamless transition from the grid-connected mode to the islanded mode and vice versa. The system also successfully satisfies the IEEE Std 1547.4. A business case has also been developed for the proposed microgrid that suggests its implementation due to economic viability.

The prevailing business, policy, and regulatory environment for electric utilities has evolved over the last century in response to certain broadly accepted attributes of the electric system?that steady growth in electric consumption and economies of scale necessitate investment in large, central, long-lived generating assets that deliver electricity, as a commodity, to consumers through a unidirectional transmission and distribution system. Today, this paradigm is challenged by a combination of technological and behavioral factors.

This paper presents a new wind farm control framework for inertial and primary frequency response for a high wind integrated power system. The proposed architecture is unique in the sense that the methodology can be used for frequency regulation support during subsynchronous and super-synchronous operation of the wind turbines (farm). The architecture work with existing wind farm controllers thus avoiding any additional replacement or tuning. The methodology depends on reduced order modeling based on model order reduction (MOR) and subsequent online controller design. The approach is tested on a smaller wind farm and further evaluated on a larger reduced power grid with 39 buses and ten generators. The results show that the proposed architecture provides greater flexibility in wind farm control towards frequency oscillations.

This paper proposes an innovative active voltage control technique for flying-capacitor (FC) multilevel converters. The proposed active control method on the basis of the logic-equations exploits converter's measured variables including the capacitor voltages and output current to generate a switching state that regulates the FC voltages at reference values and also produces the commanded PWM voltage-level. Simulation results and experimental measurements are provided to confirm the introduced method and derived equations.

This paper introduces a new circuit topology for multilevel converters. The proposed multilevel converter circuitry is realized by the cascaded connection of a 2-level converter and modular-concatenated-cell (MCC) H-bridge cells. In the proposed MCC multilevel topology, the classic two-level converter functions as the main converter through generating the major voltage-steps, whereas auxiliary concatenated H-bridge cells produce the intermediate voltage-levels. The overall output voltage is formed by adding the intermediate voltage-levels to the major ones. The crucial distinction between the cascaded H-bridge (CHB) converters and proposed MCC multilevel converter topology is that the latter exploits flying-capacitors (FCs) instead of isolated dc-voltage sources, and uses per-phase redundant switching states to regulate FC voltages. The voltage rating of semiconductor power switches and FCs within the concatenated cells of the proposed MCC multilevel converter all are 1 p.u. that lead to a modular structure.

The scope of this paper composes of data collection and synthesis, system design, cost analysis, demonstration and grid-connected operation of diesel-gensets, forming a proposed microgrid. The solar resource in Clemson was analyzed through historical data. From the findings, the microgrid component sizing was designed so as to supply the campus with sufficient energy for two-day islanding event. Eventually, for operational performance analysis case study, a microgrid is formed from inertial prime mover gensets for Clemson University to be connected to the western main campus substation in order to support the critical loads. Parallel generator unit connection enables support of critical load during islanding-mode of operation. Results indicate autonomous operation of 1.8MW generator-based microgrid under various scenarios including load sharing, load and droop variations, gensets disconnection and grid islanding modes.

Microgrids have been considered an essential component for improving the efficiency, resilience and reliability of the evolving electric power grid. Their modularity adds to the operational flexibility of the system in addition to provision for multi-player energy markets and transactive energy framework. The value of microgrid based systems is evident from their growing implementations globally. This underscores the need for developing a skilled workforce at the confluence of power systems and power electronics. Based on this, a special course in virtual power plants and virtual inertia was introduced at Clemson for exploratory pedagogy and building foundations for scientific scholarship in this area. This paper introduces the objectives, major challenges, design, planning and modeling tools, project outcomes and lessons learned from the instructor's experience with this hybrid course.

For medium-voltage (MV) industrial applications such as the HVDC and adjustable-speed ac-motor drives, the multilevel voltage-source converters are deemed the predominant topologies. One of the promising derived-topologies from the neutral-point-clamped (NPC) configuration is the active NPC (ANPC) structure with an improved balanced lossdistribution performance. This paper introduces duo-ANPC (D-ANPC) converter topology, which is controlled with a new modulation technique. The suggested control method regulates the flying capacitor (FC) voltages naturally at their reference values and preserves the indispensable attribute of the natural balance in the FC-based ANPC inverters. The D-ANPC converter's phase leg is formed by equipping the classic ANPC converter with additional two low-frequency (LF) MV power switches, adding up to six in contrast to four LF power switches in the ANPC. The proposed D-ANPC converter has considerable advantages over the classic multilevel inverters that makes it a competitive topology for MV applications. The substantial reduction in the number of the high-frequency (HF) MV insulated-gate bipolar transistors (IGBTs) by 50% in comparison with the classic ANPC converter as well as a drastic abatement in the total voltage rating and the stored energy of the FCs are the main significant advantages offered by the D-ANPC multilevel converter over the flying-capacitor-based inverters. This study explores the fundamental circuitry of the proposed D-ANPC multilevel topology and provides an exhaustive comparison with classic FC-based inverters. The experimental results are presented to validate the proposed D-ANPC topology and its modulation.

For medium-voltage (MV) high-power industrial applications including HVDC and variable-speed motor drives, multilevel converters are deemed predominant topology. One of the promising derived-topologies from neutral-point-clamped (NPC) configuration is active NPC (ANPC) inverter that offers improved characteristics. This paper proposes an improved ANPC (I-ANPC) converter controlled with an innovative logic-equation-based modulation method. The I-ANPC converter phase leg is realized by the cascaded connection of the single ANPC converter and one H-bridge cell. The H-bridge converter is formed by one flying-capacitor (FC) and four switches such as the insulated-gate bipolar transistors (IGBTs). The I-ANPC converter has considerable advantages over the classic multilevel inverters that makes it a preferable topology for MV applications. The substantial reduction in the number of cells in comparison with classic ANPC converter along with a drastic decrease in the total voltage rating and the stored energy of the capacitors are the main advantages offered by the I-ANPC multilevel converter over the FC-based inverters. This study explores the fundamental circuit of the proposed I-ANPC multilevel and its derived innovative logic-equation-based modulation technique, and provides an exhaustive comparison with FC-based classic converters. The simulation and experimental results are presented to validate the proposed I-ANPC topology and its logic-equation-based control strategy.

A Virtual Power Plant (VPP) composed of distributed energy resources (DER) with load and generation forecasting is presented in this paper. The large-scale integration of renewable energy and energy storage systems have introduced many technical and economic challenges to both customers and utilities. High levels of renewable power injection might reduce grid stability due to intermittencies. The proposed VPP mitigates these issues and can function as a major component of a utility grid with high levels of DER penetration. The VPP has two components: a forecast and analytics component, and an electrical systems control component. The forecaster generates the dispatch schedule for each player in the VPP e.g. a PV station, and the loads. This is done by taking historical load and weather data, models of the VPP players, and the weather forecast as inputs. The electrical systems controllers use the dispatch schedule to regulate power flows from each individual player and to the loads. Grid frequency and voltage support are also provided by the control, thereby improving system stability. An example VPP with three solar photovoltaic and two battery energy storage systems is presented and implemented using a real-time digital simulator. The results validate the VPP performance in load forecasting, power flow control and grid support. A dispatch schedule is generated for a 24-hour period and the VPP controller operation to service the loads and supply the power sold on the day-ahead market was verified.

The significant mechanical inertia of the rotor in a synchronous generator is crucial for facilitating the cooperative grid forming capability of multiple such generators on the transmission and distribution network. This paper demonstrates that the DC link capacitance in a PV inverter is the analogous form of inertia for such a system, albeit having much smaller magnitude. Furthermore it proposes using storage integrated on the DC link to synthesize extra inertia by programming the storage power electronics controller to achieve an emulated capacitance. Inertia added to distributed energy resources (DERs) in this manner is the first step towards mitigating the power quality issues arising from increased renewable penetration on the network. Demonstration of the acquired inertia dynamics and verification of the required controller design is shown through a detailed simulation model.

The main objective of this paper is to analyze the feasibility of decentralized control approach in providing smart inverter functions for grid-tied AC-stacked PV inverter architecture. Decentralized controller allows fully distributed architecture both in terms of control and physical implementation of a PV system, resulting in higher reliability and potentially lower cost. In this paper, Relative Gain Array concept has been used to determine the best locally measured input-output pairing sets for designing the proposed decentralized controller. Proposed approach by sending supervisory commands to only one inverter minimize the required communications for controlling reactive power and mitigating harmonics. Detailed modeling and analysis are provided to show the feasibility of the proposed decentralized approach. Proposed decentralized control scheme is verified by offline simulation and real-time hardware-in-the-loop setup.

Proliferation of distributed energy resources (DERs) on the low voltage network comes with a myriad of power quality problems such as voltage fluctuations and poor harmonic performance. Distributed mitigation solutions are being proposed for the low voltage network which are similar to state-of-the-art solutions in medium voltage networks. This paper presents a μ-STATCOM device as a distributed solution to interface with DER's at the leaf end of the network to achieve fine-tuned voltage regulation and mitigation of voltage harmonics. This solution combines the operation of low voltage grid-tied inverters (for both PV and battery systems) and passive or active voltage regulation devices. A general analysis of the effectiveness this solution along with simulation and experimental results are presented in this paper. A benchmark control algorithm has been designed to achieve the desired features of the proposed μ-STATCOM. The experimental setup consisted of a proof of concept hardware prototype rated at 5kW.

Existing photovoltaic (PV) power plants impact the power grid in a negative way due to a lack of voltage regulation, energy storage, forecasting and wide-area communications, measurement, and control. Currently utility-scale distributed solar PV plants on distribution networks have nominal capacities that are compatible with distribution substation MVA ratings e.g., between 5 and 30 MW. Furthermore, PV plants in the 30 to 100 MW power range are currently integrated in transmission networks. The system impacts are discussed, and mitigation solutions are proposed using advanced power converters, energy storage systems, as well as local and remote measurements and forecasting options. Case studies are provided.