System configuration, fault detection, location, isolation and restoration: a review on LVDC Microgrid protections

Low voltage direct current (LVDC) distribution has gained the significant interest of research due to the advancements in power conversion technologies. However, the use of converters has given rise to several technical issues regarding their protections and controls of such devices under faulty conditions. Post-fault behaviour of converter-fed LVDC system involves both active converter control and passive circuit transient of similar time scale, which makes the protection for LVDC distribution significantly different and more challenging than low voltage AC. These protection and operational issues have handicapped the practical applications of DC distribution. This paper presents state-of-the-art protection schemes developed for DC Microgrids. With a close look at practical limitations such as the dependency on modelling accuracy, requirement on communications and so forth, a comprehensive evaluation is carried out on those system approaches in terms of system configurations， fault detection, location, isolation and restoration

Utilising SMES-FCL to improve the transient behaviour of a doubly fed induction generator DC wind system

Wind energy is seen as one of the main pillars of renewable energy. However, the intermittent nature of these sources still poses as a major challenge. Moreover, sensitivity to grid faults and response to load changes are also main concerns. Superconducting devices have been introduced to solve grid faults and energy storage problems associated with renewable energy sources. Nevertheless, the cost of superconducting materials was still a major drawback for their application in power grids. In this paper, a novel power electronics circuit is used to connect the superconducting magnetic energy storage (SMES) to a DC system based on a doubly fed induction generator wind turbine. The proposed system merges energy storage function and the fault current limiting function into one device which is referred to as SMES-FCL in this paper. The role played by the SMES-FCL is studied under various scenarios that may affect the whole system. The study of the system is carried in MATLAB/SIMULINK where the system is simulated in standalone and grid-connected modes. In the end, the proposed SMES-FCL control circuit is tested in a small-scale DC system experimentally

A multi-inductor h bridge fault current limiter

© 2019 by the authors. Current power systems will suffer from increasing pressure as a result of an upsurge in demand and will experience an ever-growing penetration of distributed power generation, which are factors that will contribute to a higher of incidence fault current levels. Fault current limiters (FCLs) are key power electronic devices. They are able to limit the prospective fault current without completely disconnecting in cases in which a fault occurs, for instance, in a power transmission grid. This paper proposes a new type of FCL capable of fault current limiting in two steps. In this way, the FCLs’ power electronic switches experience significantly less stress and their overall performance will significantly increase. The proposed device is essentially a controllable H bridge type fault current limiter (HBFCL) that is comprised of two variable inductances, which operate to reduce current of main switch in the first stage of current limiting. In the next step, the main switch can limit the fault current while it becomes open. Simulation studies are carried out using MATLAB and its prototype setup is built and tested. The comparison of experimental and simulation results indicates that the proposed HBFCL is a promising solution to address protection issues

Contribution for the Study of the Integration of Inductive Superconducting Fault Current Limiters in Electrical Distribution Grids

A wider adoption of distributed generation sources and an increased interconnection of networks tend to increase the complexity of electric power grids, thus causing a surge in failures, especially short-circuits. The conventional solution against short-circuit currents, for example, the construction of new substations, splitting of busbars, even updating the technology of the existing current limiters may prove either economically or technically unfeasible. Fault current limiters, mainly the superconducting fault current limiters, have already demonstrated their viability in electric power grids. Fault current limiter devices at normal operation are invisible to the grid, acting almost instantly upon a fault, returning to their normal state upon its correction. To disseminate these technologies, the development of straightforward design tools is required. These tools must consider the properties of the available constitutive elements of the devices. Behind these design tools, the integrity of the fault current limiter should be assured during its operation. Problems regarding the electrodynamic forces developed under short-circuit events must be properly characterized because they can damage windings, causing device breakage and affecting the power grid. In this thesis, a design methodology that intends to model and optimise saturated cores superconducting fault current limiters is presented. This methodology considers the characteristics of each constitutive element of the limiter while addressing utility requirements and power grid characteristics. Genetic algorithms are used both to optimise the constitutive elements of the limiter and its performance in the power grid. In order to validate the present methodology, a three-phase superconducting fault current limiter is designed/optimised, built and tested. The electrodynamic forces analysis developed in superconducting tapes of an inductive transformer type superconducting fault current limiter, under short-circuit conditions is performed.A crescente adoção de fontes de geração distribuída e o aumento das ligações internas entre redes de energia levou ao aumento da complexidade das redes elétricas, causando um provável aumento do número de falhas, especialmente os curto-circuitos. Soluções convencionais para lidar com curto-circuitos, como por exemplo, a construção de novas subestações, a divisão dos barramentos, ou a atualização tecnológica dos limitadores de corrente existentes, podem se mostrar muito dispendiosas ou tecnicamente inviável. Os limitadores de corrente de defeito, principalmente os dispositivos supercondutores, têm vindo a demostrar a sua viabilidade em redes de energia elétrica. Estes dispositivos são considerados invisíveis para a rede, quando em operação normal. Quando uma falha na rede ocorre, estes agem instantaneamente, retornando ao seu estado normal após a falha terminar. De modo a disseminar estas tecnologias, é necessário o desenvolvimento de ferramentas de projeto e modelação, de fácil uso. Essas ferramentas devem considerar as propriedades dos elementos que constituem os dispositivos de proteção. Por detrás dessas ferramentas de projeto, a integridade do limitador deve ser assegurada durante todo o seu funcionamento. Problemas relacionados com forças eletrodinâmicas desenvolvidas sob eventos de curto-circuito devem ser devidamente caracterizados, pois podem danificar os enrolamentos, e por sua vez o equipamento e afetar a rede elétrica. Nesta tese, é apresentada uma metodologia de projeto, que visa modelar e otimizar limitadores de corrente de defeito supercondutores, do tipo núcleos saturados. Esta metodologia considera as características de cada elemento constitutivo do limitador enquanto aborda os requisitos da concessionária da rede de distribuição de energia e as características da rede elétrica. Algoritmos genéticos são usados para otimizar os o limitador e o seu desempenho na rede elétrica. A fim de validar a metodologia atual, um limitador trifásico é projetado/otimizado, construído e ensaiado. É ainda realizada a análise das forças eletrodinâmicas desenvolvidas em fitas supercondutoras de um limitador de corrente de defeito, do tipo transformador, em condições de curto-circuito

A compound current limiter and circuit breaker

© 2019 by the authors. Licensee MDPI, Basel, Switzerland. The protection of sensitive loads against voltage drop is a concern for the power system. A fast fault current limiter and circuit breaker can be a solution for rapid voltage recovery of sensitive loads. This paper proposes a compound type of current limiter and circuit breaker (CLCB) which can limit fault current and fast break to adjust voltage sags at the protected buses. In addition, it can act as a circuit breaker to open the faulty line. The proposed CLCB is based on a series L-C resonance, which contains a resonant transformer and a series capacitor bank. Moreover, the CLCB includes two anti-parallel power electronic switches (a diode and an IGBT) connected in series with bus couplers. In order to perform an analysis of CLCB performance, the proposed structure was simulated using MATLAB. In addition, an experimental prototype was built, tested, and the experimental results were reported. Comparisons show that experimental results were in fair agreement with the simulation results and confirm CLCB’s ability to act as a fault current limiter and a circuit breaker

Architecture, Voltage and Components for a Turboelectric Distributed Propulsion Electric Grid

The development of a wholly superconducting turboelectric distributed propulsion system presents hide unique opportunities for the aerospace industry. However, this transition from normally conducting systems to superconducting systems significantly increases the equipment complexity necessary to manage the electrical power systems. Due to the low technology readiness level (TRL) nature of all components and systems, current Turboelectric Distributed Propulsion (TeDP) technology developments are driven by an ambiguous set of system-level electrical integration standards for an airborne microgrid system (Figure 1). While multiple decades' worth of advancements are still required for concept realization, current system-level studies are necessary to focus the technology development, target specific technological shortcomings, and enable accurate prediction of concept feasibility and viability. An understanding of the performance sensitivity to operating voltages and an early definition of advantageous voltage regulation standards for unconventional airborne microgrids will allow for more accurate targeting of technology development. Propulsive power-rated microgrid systems necessitate the introduction of new aircraft distribution system voltage standards. All protection, distribution, control, power conversion, generation, and cryocooling equipment are affected by voltage regulation standards. Information on the desired operating voltage and voltage regulation is required to determine nominal and maximum currents for sizing distribution and fault isolation equipment, developing machine topologies and machine controls, and the physical attributes of all component shielding and insulation. Voltage impacts many components and system performance