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This paper proposes a novel method to locate faults in an AC‐meshed microgrid. To this end, a set of features is first extracted and selected from the measured signals and fed to a Support Vector Machine (SVM) to detect the occurrence of fault. Then, the Distributed Generator (DG) with the lowest amount of fundamental voltage, which is the closest one to the fault, injects an appropriate voltage/current harmonic. As the faulted section has the lowest impedance value from the Point of Common Coupling of the DG, the harmonic current of the corresponding line has the highest value. Based on this fact, the first candidate DG sends a notification signal to the second candidate DG, in which the fault occurs between them. Finally, the impedances in the injected frequency are measured from these two DGs and fed into a multi‐class SVM to locate the faulted line. The proposed method has the ability to locate faults for islanded and grid‐connected microgrids with variable configurations. Real‐time simulation results are taken by OPAL‐RT to show the effectiveness of the proposed method in the meshed microgrid. [ABSTRACT FROM AUTHOR]

Microgrid, which is one of the main foundations of the future grid, inherits many properties of the smart grid such as, self‐healing capability, real‐time monitoring, advanced two‐way communication systems, low voltage ride through capability of distributed generator (DG) units, and high penetration of DGs. These substantial changes in properties and capabilities of the future grid result in significant protection challenges such as bidirectional fault current, various levels of fault current under different operating conditions, necessity of standards for automation system, cyber security issues, as well as, designing an appropriate grounding system, fast fault detection/location method, the need for an efficient circuit breaker for DC microgrids. Due to these new challenges in microgrid protection, the conventional protection strategies have to be either modified or substituted with new ones. This study aims to provide a comprehensive review of the protection challenges in AC and DC microgrids and available solutions to deal with them. Future trends in microgrid protection are also briefly discussed. [ABSTRACT FROM AUTHOR]

This paper identifies the characteristics of a current source inverter operating in discontinuous conduction mode, and proposes a new multiobjective pulse-width modulation (PWM) method to mitigate voltage boosting and harmonic distortion effects. The method takes into account load impedance effects. Controls are also developed to enable transition between the multiobjective PWM method and conventional PWM as the current source inverter operates in discontinuous and continuous modes of operation. The concept is verified experimentally on a 3 kW test bed. [ABSTRACT FROM AUTHOR]

The benefits of variable-frequency drives (VFDs) have not been fully realized in many applications because they compete in the power density of legacy equipment, such as electromechanical motor controllers. This is particularly the case in Navy shipboard systems where sensitive equipment is in close proximity to VFDs. This paper compares the power densities, efficiency, and costs of both voltage-source- and current-source-based VFDs. A meaningful comparison is made based on actual hardware implementations that meet stringent power quality and electromagnetic compatibility requirements. The hardware results of a current-source-rectifier (CSR)-fed voltage-source inverter (VSI), or a CSR–VSI-based VFD, are provided in order to support the findings of this paper. Special consideration is given to operation at light loads. [ABSTRACT FROM AUTHOR]

Although the operation of a three-phase current source rectifier (CSR) for ac-to-dc conversion using phase control or low-frequency pulse control is well established in a wide variety of applications, CSR realization using high-frequency pulsewidth-modulation control has been recently studied as a potentially competitive alternative to a voltage source rectifier. In the CSR, reverse blocking gate turn-off switches are realized using series-connected diodes, which prevent any reversal of the dc-link current. A significant consequence of this limitation occurs at light load conditions. The dc-link inductor current enters the discontinuous mode of operation and leads to the loss of the control of the output voltage and a highly distorted input current, which compromise the potential advantages of the approach. This paper characterizes the CSR while operating in the discontinuous conduction mode and proposes a modulation strategy that restores the control of the output voltage and ensures a nearly sinusoidal current at light loads. Simulation and hardware results are provided for a 3-kW laboratory-scale prototype system. [ABSTRACT FROM AUTHOR]

A variable-frequency drive (VFD) having a 440-V front-end current source rectifier (CSR) interface to a voltage source inverter (VSI) feeding a Permanent-Magnet Axial-flux Air Core motor combination is a solution for low-horsepower pump and fan control that is both power dense and compatible with a shipboard environment. This paper describes the control and power platforms for the CSR/VSI and provides experimental results for a 250-V 3.3-kW system. Power density and efficiency comparisons are made between equivalent CSR/VSI- and voltage-source-conversion-based VFDs to demonstrate that the CSR/VSI-based VFD is more power dense. [ABSTRACT FROM AUTHOR]

This paper describes the implementation of a four-pole neutral-point-clamped (NPC) three-phase inverter that produces virtually no common-mode voltage. The low common-mode voltage output is achieved by constraining the switch states of the NPC inverter to only those states that produce zero common-mode voltage in dead-time compensation, which enhances the capability of the circuit to produce low common-mode voltage by compensating common-mode voltages produced by reverse diode commutations. The low common-mode voltage performance is achieved at the expense of reduced voltage utilization and loss of dc-link voltage balance control. In order to overcome this limitation, a fourth pole and associated control are added to balance the upper and lower dc-link voltages. This paper describes the control implementations and simulation results compared to measured results used in tuning and commissioning of the system. A 450-V 78-kW system is implemented in hardware, and experimental results are provided, showing its differential mode transient and steady-state harmonic performance as well as its common-mode output voltage. [ABSTRACT FROM AUTHOR]

A mathematical model that is developed for a generalized drive system, including common-mode passive and active elements, is used to explore the issues of paralleling soft-switched resonant dc-link drive systems. Differences between the modulation pattern for each drive system cause common voltage disturbances, which lead to significant circulating currents between the drive systems. Control methods for actively compensating for common-mode circulating currents or reducing the common-mode voltage disturbances are investigated. Practical modifications to the drive system controls are implemented to reduce the circulating currents between paralleled systems. [ABSTRACT FROM AUTHOR]

Evaluates the suitability of a soft-switched actively clamped resonant direct current-link (ACRDCL) inverter for low-output harmonic distortion high-power-density power conversion. Details on the ACRDCL inverter; Discussion of system design issues; Comparisons of hard-switched inverters.

The availability of fossil fuels in the future and the environmental effects such as the carbon footprint of the existing methodologies to produce electricity is an increasing area of concern. In rural areas of under-developed parts of the world, the problem is lack of access to electrification. DC microgrids have become a proven solution to electrification in these areas with demonstrated exceptional quality of power, high reliability, efficiency, and simplified integration between renewable energy sources (principally solar PV) and energy storage. In the United States, a different problem occurs that can be addressed with the same DC microgrid approach that is finding success internationally. In disinvested, underserved communities of with high unemployment and low wages, households contribute a significant portion of their income toward the fixed cost of their electrical utility connection, which by law must be supplied to every household. This paper analyzes a residential DC microgrid in an urban, underserved area that enables the sharing of renewable and stored energy resources between dwellings. The goal of the residential DC microgrid is to drive down to fixed costs of utility-provided electricity to all participants, such that the percentage of utility cost to total household income comes can be made comparable to that of more advantaged communities. A group of renovated dwellings constitute the community which the DC microgrid would serve. The distributed installation of solar panels and battery storage among dwelling locations are optimized based upon varying consumption patterns. Also, consumption patterns during different seasons of the year are considered. Electrical distribution architectures within the dwellings are based upon conventional AC. Each dwelling has a DC interface to the residential microgrid and progressive insertion of DC loads, with associated household DC distribution, is considered. [ABSTRACT FROM AUTHOR]

US households consume more electricity compared to other developed countries due to the fact that majority of the US household loads are inefficient. As a result, deployment of residential solar PV cost is increased given the high-power consumption and becomes less viable. Utilities are also increasingly applying surcharges to customers with solar PV installations because of direct impacts to the grid, making purely solar PV installations unattractive. This is especially in the case for low-income households, where they are seemingly shut out from participating in the energy economy given the penalties and the costs. This research primary focus is to make Installed Cost Benchmarks for Residential Solar Photovoltaic with Energy Storage costs more affordable for an average-income home owner in the USA; one approach is to reduce power consumption within the household by adapting DC appliances. So, a compelling means towards reducing household load is to convert a portion of household electrical loads such as LED lighting, air conditioning, ceiling fans, and electronic loads to DC. Secondly, optimizing size of solar panels and battery and without the need for energy export, it compensates for surcharges and recover return on solar investment. Data provided in this paper gives an insight into adapting suitable hybrid DC/AC architecture for three different types of households associated with five different geographical regions based of different climactic conditions spread across the USA. The systems are distinguished by the degree to which redundant AC to DC conversion stages are reduced, which will be inversely proportional to cost. This paper shows that deployment of DC distribution within the house will result in lower average cost and better returns on solar and battery investment than revealed by the NREL study. Also, outlines the costs and savings of different architecture that can be adaptable based on the type of the house, location, savings, and affordability. Only this paper shows the benefits occur due to the reduced number of solar panels and battery storage required when compared to conventional AC powered households. The end goal of this work is to increase the adoptability of solar PV across a more diverse population with a particular focus on low-income households. [ABSTRACT FROM AUTHOR]

Fault current limiters (FCLs) are one of the main solutions to upcoming challenges in the microgrid protection. Regarding the high penetration of distributed generations (DGs) in the future power system, designing cheap and effective FCLs is a necessity. This letter addresses this issue by proposing an embedded FCL operating based on modifying the secondary control of the inverter. As this method is presented for a four-wire system, besides very low implementing cost, it has independency and flexibility to only limit the current of the DG faulted phase. This letter also provides real-time simulation results by real time simulator (OPAL-RT) to compare the proposed method with a virtual-impedance-based FCL to validate its effectiveness. Finally, experimental results are presented to validate the effectiveness of the proposed FCL. [ABSTRACT FROM AUTHOR]

Microgrid, which is one of the main foundations of the future grid, inherits many properties of the smart grid such as, self-healing capability, real-time monitoring, advanced two-way communication systems, low voltage ride through capability of distributed generator (DG) units, and high penetration of DGs. These substantial changes in properties and capabilities of the future grid result in significant protection challenges such as bidirectional fault current, various levels of fault current under different operating conditions, necessity of standards for automation system, cyber security issues, as well as, designing an appropriate grounding system, fast fault detection/location method, the need for an efficient circuit breaker for DC microgrids. Due to these new challenges in microgrid protection, the conventional protection strategies have to be either modified or substituted with new ones. This study aims to provide a comprehensive review of the protection challenges in AC and DC microgrids and available solutions to deal with them. Future trends in microgrid protection are also briefly discussed. [ABSTRACT FROM AUTHOR]

This article identifies and validates the use of ultrafast silicon carbide (SiC) junction field effect transistor (JFET)-based self-powered solid-state circuit breakers (SSCBs) as the enabling protective device for a 340 Vdc residential dc community microgrid. These SSCBs will be incorporated into a radial distribution system in order to enhance fault discrimination through autonomous operation. Because of the nature and characteristics of short-circuit fault inception in dc microgrids, the time–current trip characteristics of protective devices must be several orders of magnitude faster than conventional circuit breakers. The proposed SSCBs detect short-circuit faults by sensing the sudden voltage rise between its two power terminals and draw power from the fault condition itself to turn off SiC JFETs and then, coordinate with no-load contacts that can isolate the fault. Depending upon the location of the SSCBs in the microgrid, either unidirectional or bidirectional implementations are incorporated. Cascaded SSCBs are tuned using a simple resistor change to enable fault discrimination between upstream high-current feeds and downstream lower current branches. Operation of one of the SSCBs and three in cascaded arrangements are validated both in simulation and with a hardware test platform. Thermal impact on the SSCB is discussed as well. The target application is a residential dc microgrid that will be installed as part of a revitalization effort of an inner city Milwaukee neighborhood. [ABSTRACT FROM AUTHOR]

In restructured power systems, Independent System Operator manages and handles the Reliability-Security Constraint Unit Commitment problems including reliability and security issues. In this paper, a novel two-level optimization approach is proposed to achieve reliable, secure, and optimal generation units' schedule while wind generation units are presents, in which the power system is divided to a number of zones. Uncertainties and time-dependent sources such as wind generation units are the most significant reasons for reliability challenges. In the proposed approach, load forecast and wind generation units' uncertainty have been considered. An intelligent search technique is implemented for reliability study. The proposed method is evaluated by simulation of the 6-bus, 118-bus, and 4672-bus test systems. The two-level optimization is compared to robust optimization and centralized methods. The results show the effectiveness and significance of this method. [ABSTRACT FROM AUTHOR]

Develops a soft-switched medium-voltage drive system utilizing series-stacked modules with low-voltage devices. Major restrictions to higher frequency high-power direct current (DC)-DC converters; Control of a resonant DC-link-based sinusoidal inverter; Implementation of medium-voltage inverter.