Fast DC Research Articles

Design and Implementation of Single-Phase Grid-Connected Low-Voltage Battery Inverter for Residential Applications

Integrating residential energy storage and solar photovoltaic power generation into low-voltage distribution networks is a pathway to energy self-sufficiency. This paper elaborates on designing and implementing a 3 kW single-phase grid-connected battery inverter to integrate a 51.2-V lithium iron phosphate battery pack with a 220 V 50 Hz grid. The prototyped inverter consists of an LCL-filtered voltage source converter (VSC) and a dual active bridge (DAB) DC-DC converter, both operated at a switching frequency of 20 kHz. The VSC adopted a fast DC bus voltage control strategy with a unified current harmonic mitigation. Meanwhile, the DAB DC-DC converter employed a proportional-integral regulator to control the average battery current with a dynamic DC offset mitigation of the medium-frequency transformer’s currents embedded in the single-phase shift modulation scheme. The control schemes of the two converters were implemented on a 32-bit TMS320F280049C microcontroller in the same interrupt service routine. This work presents a synchronization technique between the switching signal generation of the two converters and the sampling of analog signals for the control system. The prototyped inverter had an efficiency better than 90% and a total harmonic distortion in the grid current smaller than 1.5% at the battery power of ±1.5 kW.

Surrogate-Assisted Combinatorial Optimization of EV Fast Charging Stations

In this work, an artificial neural network surrogate model-based method is proposed to assist the optimal design of the modular electric vehicle fast DC charging station. This is a typical combinatorial optimization problem, which is hard to solve analytically as the key design parameters are discrete, e.g. the numbers of charging poles, power electronic converter modules, and switching contactors. In the first part of the paper, the details on how to generate the expected charging power demand of the charging station are presented, where characteristic electric vehicle charging curves are considered. The charging station is designed to operate under a modified first-come-first-serve policy to maximize the quality of service to the customers. The system time ratio, energy efficiency, and capital expenditure are then taken as the performance indicators to evaluate different designs in correlation to expected charging demand. By varying the design parameters, we generate a group of datasets from an adjustable charging station simulation model, which is then used for supervised training of an artificial neural network. As a surrogate model of the charging station, the trained neural network is finally used to quickly map the design parameters into the performance indicators, where optimal design parameters are found by evaluating the proposed cost function.

Design of a Level-3 electric vehicle charging station using a 1-MW solar system via the distributed maximum power point tracking technique

Abstract Solar power is mostly influenced by solar irradiation, weather conditions, solar array mismatches and partial shading conditions. Therefore, before installing solar arrays, it is necessary to simulate and determine the possible power generated. Maximum power point tracking is needed in order to make sure that, at any time, the maximum power will be extracted from the photovoltaic system. However, maximum power point tracking is not a suitable solution for mismatches and partial shading conditions. To overcome the drawbacks of maximum power point tracking due to mismatches and shadows, distributed maximum power point tracking is utilized in this paper. The solar farm can be distributed in different ways, including one DC–DC converter per group of modules or per module. In this paper, distributed maximum power point tracking per module is implemented, which has the highest efficiency. This technology is applied to electric vehicles (EVs) that can be charged with a Level 3 charging station in <1 hour. However, the problem is that charging an EV in <1 hour puts a lot of stress on the power grid, and there is not always enough peak power reserve in the existing power grid to charge EVs at that rate. Therefore, a Level 3 (fast DC) EV charging station using a solar farm by implementing distributed maximum power point tracking is utilized to address this issue. Finally, the simulation result is reported using MATLAB®, LTSPICE and the System Advisor Model. Simulation results show that the proposed 1-MW solar system will provide 5 MWh of power each day, which is enough to fully charge ~120 EVs each day. Additionally, the use of the proposed photovoltaic system benefits the environment by removing a huge amount of greenhouse gases and hazardous pollutants. For example, instead of supplying EVs with power from coal-fired power plants, 1989 pounds of CO2 will be eliminated from the air per hour.

Fast low bias pulsed DC transport measurements for the investigation of low temperature transport effects in semiconductor devices

We present a setup for fast, low-bias (≤1mV) DC transport measurements with μs time resolution for high ohmic resistance (≈20kΩ) semiconducting samples. We discuss the circuitry and instrumentation for the measurement approach that can be applied to any kind of semiconductor device or (gated) two-dimensional material and demonstrate the main measurement artifacts in typical measurements by means of circuit simulation. Based on the latter, we present a simple two-step protocol for eliminating the measurement artifacts reliably. We demonstrate the technique by measuring the transitions between quantum Hall plateaus in the HgTe quantum wells and resolve plateaus as short-lived as 100 μs.

Fast DC Charging Infrastructures for Electric Vehicles: Overview of Technologies, Standards, and Challenges

This paper is an overview of fast charging for electrical vehicles. Specifically, it analyzes the impact of Ultra-Fast Charging Stations (UFCSs) on the distribution grid and their role in the smart grids. Moreover, the paper defines the framework of UFC, its diffusion and the associated new trends. The most frequently used converters in the conversion stages of DC charging stations with integrated generation are analyzed. To achieve this goal four active front end AC-DC converters (unidirectional and bidirectional), three isolated DC-DC converters as well as two control architectures are explored. In comparing the targeted configurations, the main target is set on categorizing them based on supply voltage level, type of smart grid, and power flow of the converters. Further, the paper outlines a broad overview of main standards for UFCSs and evaluation of the reliability, data collection, and operation of UFCSs. The paper aims to to link the needs of the designers of charging stations to preferences of the commercial market.

Fast and robust DC link voltage control of single-phase grid-connected converters supporting 50 Hz and 60 Hz mains with universal magnitudes range

It is well-known that dynamics of single-phase grid-connected power converters employing PI or type-II DC link voltage controllers is limited by the maximum tolerable value of utility-side current total harmonic distortion (THD). Moreover, universal DC link voltage controller must be capable of supporting both 50 Hz and 60 Hz utilities and universal range of magnitudes (85Vrms–265Vrms). As a result, DC link crossover frequency value (and hence corresponding settling time) may vary significantly in case grid voltage magnitude variations are not compensated in the controller. In order to cope with the above-mentioned deficiencies, the paper suggests a design methodology for a novel dual-frequency-tuned utility magnitude insensitive plug-in disturbance observer (DOB), supporting universal utility frequencies and magnitudes so that the transient response of a grid-connected converter is improved without altering the existing PI or type-II DC link voltage controller coefficients. These characteristics are attained by robust modification of DC link voltage loop plant to possess notch-like properties around two frequencies of interest and treating the grid voltage magnitude value as non-measurable uncertainty translated into input disturbance and subsequently cancelled. Analytical design guidelines for obtaining PI + DOB controller coefficients are provided for desired values of utility-side current THD and DC link voltage loop phase margin (PM). Simulations and experimental results are provided to validate the feasibility of proposed design methodology.

Production of high-density metastable argon atoms with periodic fast pulsed DC discharge.

Optically pumped metastable rare gas laser (OPRGL), as a potential high-energy laser has attracted much attention. During extensive research on OPRGL, the realization of volume discharge with high-metastable density has always been a priority and is essential to the efficient lasing of OPRGL. A large-volume plasma of He/Ar with high metastable density at atmospheric pressure can be generated by applying peaking capacitors near the electrodes. In this article, 0.8 cm3 of He/Ar plasma at a pressure of 900 mBar, with a peak value of metastable argon density higher than 1014 cm-3 was realized. The metastable density was measured by absorption spectroscopy based on the absorption bandwidths acquired at a pressure range of 400-900 mbar where a probe beam at a weak line with wavelength 772.38 nm was applied. Furthermore, the high metastable density was verified by the laterally-observed laser-induced fluorescence, as well as the laser oscillation of 100 mW under a longitudinal pumping with a short gain length of 8 mm.

Novel mapping tool to identify drivers in persistent atrial fibrillation: first clinical experience

Abstract Funding Acknowledgements Type of funding sources: None. Background Developing ablation strategies beyond pulmonary vein isolation (PVI) in persistent atrial fibrillation (persAF) is still a challenge. To date, few diagnostic tools have allowed identification of potential drivers during AF, with questionable results. There is a need for a tool that allows to consistently display and detect EGMs and identify optimal ablations targets. A novel mapping tool can provide algorithmic detection of ablation targets based on EGM properties specific to relatively stable localized rotational activations. Objective Describing an initial series of patients (pts) where Ockham mapping was used during AF to identify ablation targets and treat PersAF. Methods PersAF pts presenting in AF for were mapped using an ultra-high density mapping system (RHYTHMIA). A novel PersAF mapping feature (Ockham) was used to detect ablation targets by calculating local cycle length (LCL) and local spread of activation time within that LCL (Duty Cycle) for consistent EGMs. A scatterplot tool (F1 A) was used to identify regions of consistent (relatively stable) local activation. Among these areas, those with fast CL and high DC (>90%) were used to guide the optimal PVI line placement. Additionally, during remapping the same approach was used to target ablation beyond PVI.RF was delivered at 40-45 W via a StablePointTM IntallaNav OI catheter aiming at the maximum impedance drop (30 ohms).Durable PVI was verified by EGM visualization. In case of ongoing AF at the end of the procedure patients were monitored for 48 h before eventual cardioversion. Follow-up was by Holter every 3 months (more if symptoms). Data are median [IQR]. Results The novel mapping tool was used on 31 PersAF pts (68±9.5 years, 71% male, 20 De Novo).A median of 41228 [32789-46512] EGMs was collected before PVI. After PVI, 3 de novo pts had AF terminate into AT. Additional targets were identified in the other ones from a second post-PVI map. 81% of the extra-venous potential drivers identified on the post-PVI maps were already present on the pre-PVI map, supporting the reproducibility of the tool. Pts had a median of 3 [1-4.25] extra-PV drivers targets. Across all pts, following PVI and targeted ablation, there was progressive AF organization demonstrated by global activation slowing (a rightward shift of CL; F1 B), which in approximately half of the patients formed bi-modal curves clustered around 2 discrete CL values. Acutely, 88% of patients had AF terminate to SR or AT. At 10 months [5.75-13] follow-up, 3 (15%) patients had recurrence of persAF, and 2 (10%) patients had AT recurrences. No complication occurred. Discussion This clinical experience demonstrates that this tool can identify limited, but highly selective, reproducible extra-PV AF drivers. Since PersAF pts have high variability in arrhythmogenic sites, this novel tool allows efficient identification of ablation targets based on EGM properties for an individualized approach to ablation beyond PVI.

Adaptive Interval Type II Fuzzy Logic Controller with Interface Inductor Bank Pulse Generator Based Three-Phase Four-Wire DSTATCOM Device for Power Quality Improvement

It goes without saying that the electrical distribution system is facing many power-quality issues these days. The main cause of these issues is the wide spread of nonlinear load integrated with the electrical distribution system. Moreover, the DSTATCOM device with interface inductor has different control algorithms. These encompass proportional integral controller, Interval type I fuzzy logic and interval type II fuzzy logic along used for improving the power quality issues. Before integration with the electrical distribution grid, these controllers need the tune processing. The combination of DSTATCOM with the load, which is different from the tuned one, and the wrong selection of the interface inductor leads to the failure of DSTATCOM device in the mitigation of source current harmonics. This study suggests that the use of adaptive interval type II fuzzy logic with the interface bank pulse generator based DSTATCOM device with self-tunning process and self-selection of the interface inductor would be suitable for all load types integrated into the distribution system within the rated power of DSTATCOM device. The adaptive interval type II fuzzy logic with the interface bank pulse generator based DSTATCOM device mitigates the source current harmonics and gives fast DC capacitor bus voltage response. Employing the suggested control algorithm based DSATCOM device makes the DC capacitor voltage signal settling time at almost 50 ms and total harmonic distortion of the source current at almost 4% for all cases of the load connected with the distribution system within the rated power of DSTATCOM device.

Single-ended DC line protection scheme based on first peak time of current-limiting reactor voltage

Fast and sensitive DC line protection is an important guarantee for the security of the flexible DC grid. However, the reliability and sensitivity of the DC line protection are greatly affected by the high fault resistance. To overcome this problem, this paper proposes a novel single-ended line protection scheme for multi-terminal flexible DC grid. Firstly, the propagation characteristics of traveling wave after the internal and external faults are analyzed. Furthermore, a single-ended protection criterion based on the first peak time of current-limiting reactor transient voltage is proposed to distinguish the internal and forward external faults, which is independent of simulation. Then, based on the change characteristics of fault component current, a fault direction criterion and fault pole identification criterion are constructed to identify the backward fault and fault pole, respectively. Finally, extensive simulations and experiments show that the proposed protection scheme can identify the fault quickly and sensitively even for the internal remote-end fault with high fault resistance.

Dynamic State Estimation Based Protection for Flexible DC Grid

Fast and reliable dc line protection is one of the key techniques for flexible dc grid with the development of flexible dc transmission technology. However, the serious overcurrent caused by dc faults has a prominent contradiction with the weak overcurrent capability of power electronics. In this article, the high-fidelity dynamic model of the transmission line is first established based on the frequency-dependent characteristic of line parameters. Then, a new dynamic state estimation based protection (DSEBP) scheme is proposed, which uses the redundancy feature of state estimation to improve the dependability of protection. Finally, the actual measurements and the estimated states are compared with the similarity to identify the fault by the chi-square distribution. The proposed method's effectiveness is verified through simulations power systems computer aided design (PSCAD)/electromagnetic transients including DC (EMTDC) and experiments, and the factors affecting the performance of DSEBP are analyzed. Compared with the existing protection methods, the proposed method is more dependable, more sensitive, and available for actual projects.

Rotating Phase Shedding for Interleaved DC–DC Converter-Based EVs Fast DC Chargers

Fast dc chargers are the key enablers for the massive rollout of electric vehicles due to the reduced charging time. On the other hand, the rapid growth in battery technology with different voltages and charging requirements has imposed additional hurdles on the charger design to meet the efficiency requirements. Multiphase interleaved converters with conventional phase-shedding control improve the efficiency for a wide range of operations. However, they tend to operate certain phases, resulting in uneven thermal stress among the converter phases. This article proposes a rotating phase-shedding control to distribute the switching activities among all phases, enhancing the system's reliability while retaining the efficiency improvement. The proposed technique selects the proper number of active phases based on the required charging profile and periodically swaps them with other phases to even out the stress. The thermal profile is extracted to assess the thermal damage of the power switches. The performance of the proposed approach is evaluated and compared with the conventional phase shedding. The simulation and experimentally validated results confirm that the proposed technique achieves a better even distribution of the thermal damage between the phases compared with the conventional one. This will ultimately extend the lifetime of the system.

Fast Y-Type Thyristor-Based DC SSCB Using Complementary Commutation in a Capacitor–Capacitor Pair Structure

This article proposes a new thyristor-based dc solid-state circuit breaker (SSCB) named Y-type. Main contributions focus on a new complementary commutation circuit including a capacitor–capacitor pair, which features three remarkable advantages. First, a fast commutation is achieved using a countercurrent pulse injection by the capacitor–capacitor pair structure. Second, metal-oxide varistors (MOVs) are disconnected from the power line when SSCB is <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> , which solves the reliability issue due to the MOV degradation and enhances the voltage utilization rate of the main switch. Third, benefiting from the capacitor–capacitor pair structure, reliable reclosing and rebreaking are obtained for practical applications. Experiments are conducted on a 400 V/120 A prototype to validate the proposed Y-SSCB. The peak voltage on the main and auxiliary thyristors reaches 773 and 400 V, respectively. Also, the peak voltage on the auxiliary capacitors pair reaches 740 and 400 V. The Y-SSCB achieves a fast reaction time of 80 μs in interrupting 120 A short-circuit fault current.

Review on Unidirectional Non-Isolated High Gain DC–DC Converters for EV Sustainable DC Fast Charging Applications

Modern electrical transportation systems require eco-friendly refueling stations worldwide. This has attracted the interest of researchers toward a feasible optimal solution for electric vehicle (EV) charging stations. EV charging can be simply classified as Slow charging (domestic use), Fast charging and Ultrafast charging (commercial use). This study highlights recent advancements in commercial DC charging. The battery voltage varies widely from 36V to 900V according to the EVs. This study focuses on non-isolated unidirectional converters for off-board charging. Various standards and references for fast off-board charging have been proposed. Complete transportation is changed to EVs, which are charged by the grid supply obtained by burning natural fuels, contributing to environmental concerns. Sustainable charging from sustainable energy sources will make future EV completely eco-friendly transportation. The research gap in complete eco-friendly transit is located in interfacing sustainable energy sources and fast DC EV charging. The first step towards clean, eco-friendly transportation is identifying a suitable converter for bridging the research gap in this locality. A simple approach has been made to identify the suitable DC-DC converter for DC fast-charging EVs. This article carefully selected suitable topologies derived from Boost, SEPIC, Cuk, Luo, and Zeta converters for clean EV charging applications. A detailed study on the components count, voltage stress on the controlled and uncontrolled switches, voltage gain obtained, output voltage, power rating of the converters, switching frequency, efficiency obtained, and issues associated with the selected topologies are presented. The outcome of this study is presented as the research challenges or expectations of future converter topologies for charging.

Design and Analysis of a DC Solid-State Circuit Breaker for Residential Energy Router Application

Energy routers act as an interface between the distribution network and electrical facilities, which meet the requirements of clean energy substitution and achieve the energy sharing and information transmission in the energy network. However, the protection of the dc load side of residential energy routers including interruption and isolation of short-circuit fault currents is vital for discussion. Since the traditional mechanical and hybrid circuit breakers for dc fault protection have the drawback of slow operation, a solid-state circuit breaker (SSCB) is an optimal solution for fast dc fault interruption. In this paper, a dc SSCB is proposed that uses an RCD + MOV snubber circuit, which is considered the best and most complete circuit used in common SSCBs. There are two main contributions in this paper: First, a dc SSCB is designed, which isolates both positive and negative terminals of a circuit and its working principle and operating modes along with the formulas for calculation of crucial time intervals, voltages, and currents along with the design procedure are provided. Second, a soft turn-on auxiliary is designed to prevent a high current surge caused by the capacitance difference between the source and the load. The experimental results demonstrate the proper performance of the topology and the validity of the findings.

ESPSim: An Efficient Scalable Power Grid Simulator Based on Parallel Algebraic Multigrid

Fast verification for the extremely large-scale power grid is demanding as CMOS technology advances consistently. In this work, we propose ESPSim, an efficient scalable power grid simulator based on a parallel smoothed aggregation-based algebraic multigrid technique. ESPSim has the ability to do fast DC and transient analysis through MPI and adaptive timestep control mechanism. Thanks to the smoother applied on the prolongation operator, ESPSim copes well with the convergence rate on extremely large-scale power grid transient analysis. Extensive experiments are conducted with a variety of serial/parallel solvers. The runtime of ESPSim is linear with case size. With 16 processors, 1,000 timesteps transient analysis of 63.4M nodes can be completed in 22.1 min. Over 22× speedup compared to the well-known direct solver Cholmod is observed.

Active Disturbance Rejection Control of DC-Bus Voltages Within a High-Speed Aircraft Electric Starter/Generator System

Wide-speed range operation capabilities in both motoring and generation modes are essential for an aircraft electrical starter/generator (ESG) drive system for more-electric aircraft applications. When running as a generator, the ESG is supplying power to the main HVdc bus within the onboard electrical system. A fast and robust dc bus voltage would be beneficial to electrical loads connected to it. In this article, an active disturbance rejection control (ADRC) is proposed to realize a fast and robust regulation of onboard dc bus voltages. The ADRC is achieved with a second-order extended state observer (ESO) to generate torque reference for the ESG. All the key characteristics, such as the stability of ESO, dc voltage tracking performance, and disturbance rejection capability of the ADRC for aircraft ESG applications, are thoroughly analyzed. To enhance system stabilities, an innovative and simple design method for the ADRC and ESO gains is introduced based on the gain-margin and phase-margin criteria. Experimental results have shown that, compared with the conventional PI-based dc voltage control, the proposed method can realize a faster and more robust dc voltage control.

Scheduling and Routing of Mobile Charging Stations With Stochastic Travel Times to Service Heterogeneous Spatiotemporal Electric Vehicle Charging Requests With Time Windows

This article presents an alternative service of mobile charging stations for the large-scale charging of electric vehicles, which consider the spatiotemporal heterogeneity of charging requests. As charging infrastructure is the key determinant for the large-scale adoption of electric vehicles, state-of-the-art scheduling and control strategies need to be explored. The charging of electric vehicles in a conventional charging station even with the fast dc–dc chargers takes around 30 min, which results in congestion and large waiting queues at public charging stations. To account for this issue, a novel strategy of routing and scheduling mobile charging stations to charge electric vehicles without the constraints of time and space is discussed in detail. Furthermore, the traveling times of mobile charging stations in reality are stochastic in nature. We formulate the optimization problem to minimize the cost of charging and show that the problem formulated is a combination of a bin packing problem and a multicity traveling salesman problem; hence, it is NP-hard and cannot be solved in reasonable CPU time, unless P = NP. We, thus, present modified saving’s heuristic and modified genetic algorithm metaheuristic to solve the optimization problem. Furthermore, numerical simulations show that the proposed scheduling and routing algorithm requires less number of mobile charging stations and can appreciably reduce the cost of charging.

In-motion charged vehicle simulation considering traffic and power grid interactions

When designing new electric vehicles for urban transport, both vehicle producers and operators need to establish and verify requirements that the vehicle has to fulfil regarding, e.g., energy storage capacity, driving range, or battery wear. These requirements are typically verified using simulation tools that concentrate mostly on electrical quantities, but disregard the influence of road infrastructure, surrounding traffic and detours. At the same time, an expansion of the electric vehicle fleet may have a negative impact on the existing power grid. Sufficient dimensioning of the grid elements and their verification are therefore necessary to keep the electric transport service reliable. This paper demonstrates a tool suitable for verification of battery-assisted trolleybus fleet and power infrastructure parameters, based on extensions to the SUMO traffic simulator. The tool carries out a joint simulation of electric and traffic-related quantities. It is demonstrated on seven use-cases inspired by real-life problems. • A tool to verify battery-assisted trolleybus fleet configuration is presented. • Includes fast DC power grid solver for electric grid analysis. • Combines traffic and electric circuit simulation to study mutual interactions. • The effect of surrounding traffic on vehicle power demands is considered. • Study of different parameters of a sample trolleybus network is presented.

Fast Charging of an Electric Bus Fleet and Its Impact on the Power Quality Based on On-Site Measurements

The subject of this study was a distribution substation that feeds 14 fast DC chargers (80 kW) located at the bus depot in Lublin, Poland. The voltage variations were determined to be within the PN-EN 50160 standard limit values (±10% Un). There were several events registered when 4th, 6th, 8th, and 10th voltage harmonics were above the PN-EN 50160 limit during the charging of the electric buses. The obtained maximum 10 min average values of the total voltage harmonic distortion (THD) were 3.36%, 2.27%, and 2.89% for the first, second, and third phase, respectively, i.e., below the limit value of 8% required by PN-EN 50160. Due to the exceedance of the 6th voltage harmonic, the PN-EN 50160 requirements were not met.