High Transient Currents Research Articles

Supercapacitor-Assisted Energy Harvesting Systems

Energy harvesting from energy sources is a rapidly developing cost-effective and sustainable technique for powering low-energy consumption devices such as wireless sensor networks, RFID, IoT devices, and wearable electronics. Although these devices consume very low average power, they require peak power bursts during the collection and transmission of data. These requirements are satisfied by the use of energy-storage devices such as batteries or supercapacitors (SCs). Batteries offer significantly higher energy density but are subject to regular replacement, thermal runaway risk, and environmental concerns. On the other hand, SCs provide over a million-fold increase in capacitance compared to a traditional capacitor of the same volume. They are considered as the energy-storing devices that bridge the gap between conventional capacitors and batteries. They also offer fast charging times, a long lifecycle, and low equivalent series resistance (ESR). Most importantly, they are capable of handling the high transient currents produced by energy harvesters and provide a stable power source for external loads. This study encompasses a brief exploration of the three fundamental SC types. Then, the discussion delves into the integration of SCs into energy harvesting applications. The collective knowledge presented aims to guide future research endeavors fostering the development of novel energy harvesting systems using SCs.

Improved equation to describe the induction motor currents during nearby three‐phase short‐circuits

AbstractThis article shows an improved equation to describe the induction motor currents during a three‐phase short‐circuit near to motor terminals. The proposed equation considers three details which are not in the equation shown in the IEEE Std. 551: (a) the equivalent frequency of these currents is not strictly equal to the grid frequency; (b) the magnitude of the DC component is not strictly equal to the magnitude of the AC component; (c) an angle is included to consider the instant of fault occurrence. The proposed equation was verified by experimental results, which were also verified by simulations. It is shown that the equivalent frequency of analysed currents is not exactly the grid frequency due to the sudden change of the machine speed (caused by the high braking torque originated by high transient currents during the short‐circuit). This effect is larger in smaller motors. The AC and DC components of the analysed currents have their own time constants, which are usually estimated from motor equivalent circuit. The application of the improved equation was useful to demonstrate that such a procedure does not lead to accurate results in case of the DC time constants of small motors. Finally, an example illustrates a case that cannot be well described by the equation from the IEEE Std. 551, whereas the result from the proposed equation is very similar to the measured current.

Strategy to reduce transient current of inverter-side on an average value model high voltage direct current using adaptive neuro-fuzzy inference system controller

Growing-up of high voltage direct current (HVDC) penetration into modern power systems (PS) makes difficulty on the PS operation. The HVDC produces high and slow transient current (TC) at start-time, especially for higher up-ramp rate (Urr>20 pu/s). Its condition makes the HVDC cannot be linked and synchronized into the PS rapidly. A strategy to reduce the TC is proposed by an adaptive network based fuzzy inference system (ANFIS) control on inverter HVDC-link to cope up this problem. The ANFIS control is tuned with the help of conventional control in various train-data by using offline mode. Response of ANFIS scheme is improved by suppressing TC at the values of 3.75% for the both phases (A and C), and 3.95% for phase B, for the Urr=30 pu/s. While the conventional control achieved at 9.1% for the both phases (A and B), and 9.2% for the phase C. The ANFIS control gives shorter settling time (0.553 s) than the conventional control (0.584 s) for all phases. The proposed control is more effective than the conventional control at all the scenario.

Scaling of Time-Dependent Tunneling Current in Terahertz Scanning Tunneling Microscopes

Terahertz scanning tunneling microscopy (THz-STM) has enabled spatiotemporal imaging with femtosecond temporal resolution and angstrom spatial resolution. In THz-STMs, the junction bias is modulated by coupling THz pulses, which results in transient voltage bias and extremely high transient tunneling currents. In order to have efficient imaging of the sample surface, it is important to understand the nonlinear tunneling current response and its parametric dependence. In this work, we theoretically investigate the basic scaling of rectified electrons in a THz-STM junction. We use a self-consistent quantum model that includes both space-charge potential and exchange-correlation potential, which were ignored in previous studies. Since THz-STMs are operated at high transient voltage in field emission regime, the effects of exchange-correlation potential become crucial. We validate our calculation with recently reported experimental data and investigate the rectification property of the tip-sample junction for different parameters. We find that the time-dependent tunneling current and the electron transport can be manipulated by varying the dc bias voltage (polarity, amplitude), incident THz field (polarity, shape, peak amplitude), work functions of STM tip and sample---especially their difference $\mathrm{\ensuremath{\Delta}}W$, and the tip-sample separation. Our study provides an important framework that can be used in the future to characterize, control, and improve THz-induced currents and probing techniques at the nanometer scale over subpicosecond time periods.

Synchronous Converter Role in a Grid Forming System

There is a greater acceptance of the connection of an increasing share of renewable energy sources to electrical power networks at either grid or local utilization voltage levels as the electrical power network operators contend with the competing challenges of changing and increasing load demands, and continuing pressures to reduce net carbon footprint. Renewable energy resources are highly dynamic and somewhat intermittent compared to more traditional generation sources. Hence, they pose a challenge to the electrical network operator in terms of effectively managing their resources to maximize energy transfer while maintaining a stable interconnected network. Further, there is an increasing percentage of electrical energy generation that is connected at the utilization end of the electrical power network which poses challenges for energy flow, voltage stability and protection systems. This paper will initially discuss the concept of a grid forming system that forms the reference point of future embedded electrical power systems. The role that grid forming converters could have in future very weak system is discussed A traditional synchronous compensator forms part of the grid forming system and provides some limited energy input during energy transients, some reactive VAr capability, but importantly, high transient fault currents, which will strengthen the system and help it maintain stability.

Analysis of Single Event Effects in Capacitor-Less 1T-DRAM Based on an InGaAs Transistor

In this work, the study of the single event effects (SEEs) in capacitor-less one-transistor dynamic random access memory (1T-DRAM) based on an indium gallium arsenide on insulator (InGaAs-OI) transistor is conducted for the first time. The electrical properties of the 90-nm device are numerically simulated to determine appropriate operation condition. The successful memory behaviors are observed due to the gate-induced drain leakage (GIDL) programming method. The impacts of different linear energy transfer (LET) values, high-energy particle (HEP) strike positions and directions, and HEP hitting moments on the memory performance are investigated via simulations. Unlike the conventional SOI device, the source and drain in 1T-DRAM cells are found to be sensitive to SEEs with a higher transient current. The single event upsets (SEUs) are found to occur only when the HEP hits the device at reading “0” state and holding state before read “0.” An increased read-out current is obtained after the HEP strike due to the GIDL- and SEE-induced accumulative floating holes. The related mechanisms are discussed in detail. These results and discussions are useful for the development of the SEE hardening of 1T-DRAM-based embedded memory for space applications in the future.

Capacitive Power Transfer System with Double T-type Resonant Network for Mobile Devices Charging/Supply

In the applications of wireless power transfer for mobile devices, the pick-up of the wireless power transfer system often needs to be moved in and moved out. A sudden change in the system structure will cause high transient voltages or currents, which could damage the power electronic device of the capacitive power transfer (CPT). In addition, the standby power of the system will be too high to work after removing the pick-up. A CPT system with double T-type resonant networks has been proposed to address these problems. The steady-state models of the system without the pick-up and normal state conditions of it are established. The relationships between the resonant network parameters are analyzed, and a systematic circuit parameter design method is provided. The proposed CPT topology and the parameter design method have been verified by simulation and experiment. The system not only achieved self-protection under severe load change but also entered standby mode automatically after the pick-up was moved out. Besides, the system is restored to the normal state condition when the pick-up is moved in without additional detection and control circuitry.

A Modified Transient Current Limiter to Mitigate Energization Inrush Current in Wind Turbine Transformers

Energization of wind turbine transformers (WTTs) in wind power plants (WPPs) leads to high transient inrush current, which imposes high mechanical and thermal stresses on transformer windings and voltage sag problems at grid connection point (GCP). Therefore, to solve these problems, the inrush current should be suppressed during the energization time. The current research presents a modified transient current limiter (MTCL) for suppressing WTTs’ inrush current. Two types of MTCL such as resistor type (R-type) and reactor type (L-type) are considered for this purpose. To investigate the efficiency of the MTCL, a WPP includes five wind turbines which are simulated by PSCAD/EMTDC software. The simulation results reveal that the MTCL is an effective means for suppressing the WTTs’ inrush current and mitigating GCP voltage sag during energization. Besides, to show the effectiveness of the proposed MTCL, the performance of the MTCL is compared with the conventional TCL through simulation.

Removal of Initial Phase Transient Current in DC-DC Boost Converter using Modified Switched Inductor

This paper presents the removal of initial phase transient currents in an existing dc-dc boost converter topology with the help of a modified switched inductor cell. In an earlier proposed topology, a novel single switch boost converter was proposed with high voltage gain, which however gave a high initial transient current of the order of 26kA on simulating in MATLAB Simulink environment. This initial phase current was removed by placing a small valued inductor and a freewheeling diode in series with boost capacitor. The inductor is placed in parallel with the diode and creates an open circuit initially, this arrangement limits the current to a bearable value, i.e. approximately 180A, without compromising with the high gain of the cell. The results of the proposed modifications are validated using MATLAB Simulink.

A Multi-Stage Approach to a Hybrid Lead Acid Battery and Supercapacitor System for Transport Vehicles

Lead Acid Batteries (LABs) are used for starting, lighting, and igniting, as well as in air conditioning systems and to supply power to electric engines in transport vehicles (TVs). However, the application of LABs for TVs has faced a number of market challenges, mounted by the upcoming high energy density and long lifespan batteries, such as lithium ion. LABs, on the other hand, are inexpensive. The key research question is, how can the lifespan of LABs used in automotive industries be increased, while still ensuring a low cost solution? Thus, integrating LABs with the supercapacitor (known as an electric double layer capacitor—EDLC) is likely to outperform the competing alternative batteries for TVs. This paper proposes a multiple stage approach to hybrid lead acid batteries and a supercapacitor system for TVs that is capable of maintaining the battery state-of-charge (SOC) at statistically high limits, ranging between 90% and 95%. This SOC target will likely ensure that the lifespan of the hybrid battery system can be elongated (extended) more than its competitors. In this study, the multiple stage approach of concatenated converters has been designed in order to satisfy all energy storage requirements for different characteristics of LABs and the supercapacitor. The designed hybrid system has been simulated using Matrix Laboratory (MATLAB/Simulink (version R2016a, MathWorks, Natick, MA, USA)). The simulated results show that high transient currents from the direct current (DC) bus of LABs, caused by the regenerative braking or deceleration of the TVs, reduce the battery lifespan and induce mechanical stress. The supercapacitor reduces the stress on the LAB by absorbing high transient currents. This, in turn, keeps the LABs’ SOC between 90% and 96% and the voltage at 12 V. As indicated by the simulated results, the hybrid battery SOC is maintained at 90–96% and the terminal voltage is approximately 12 V.

Bridge-arm current reduction in DC-AC inverter

ABSTRACTWhen building single-phase inverter with power Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET), switching action may cause poor reverse recovery characteristic due to body parasitic diode of MOSFET, which can produce peak current in the circuit loop and the high transient voltage and current (dv/dt, di/dt) during the turning-on period. In this article, a novel method to reduce the bridge arm current spike in DC-AC inverter is proposed. The presented method uses the improved and simplified coupled inductor which is connected between the upper and lower power devices. The parasitic capacitors of MOSFET are charged and discharged by the coupled inductor and the energy is released in the new loop; therefore, the bridge peak current is diminished. The time-domain model of transient-state analyses is given in detail. The current spike of the main switch is clamped efficiently. By increasing switching frequency, the volume of the magnetic core can be further reduced which is resulted from reduction in the reverse recovery current in parasitic diode. Because of the suppression of the spike current via the device, the switch-on loss of the power loss is reduced, and low on-state resistor of the power device can be adopted to suppress the conduction loss. The proposed approaches are validated with experimental results.

Simulation analysis of the switching of $$230\hbox { kV}$$ 230 kV substation shunt capacitor banks with a 6% series reactor for limiting transient inrush currents and oscillation overvoltage

This paper presents the simulation and investigation of switching large shunt capacitor banks in a $$230\hbox { kV}$$ Thailand substation system. Simulations are performed using PSCAD/EMTDC to determine the peak of the transient inrush currents, the oscillation overvoltage and the frequency of the inrush current. The inrush current is generated by energizing the $$4 \times 72$$ Mvar, $$230\hbox { kV}$$ shunt capacitor banks. The purpose is to observe and investigate the behaviour of transient inrush currents and oscillation overvoltages to ensure the safe and successful operation of shunt capacitor banks. The methodology of inrush current transient analysis and transient reduction control was studied. The proposed method for controlling system transients during capacitor energization is through the use of a switching shunt capacitor bank with a series 6% reactor. The simulation cases for transient mitigation are numerically conducted for six different cases: a base case, with a pre-insertion resistor, with a pre-insertion inductor, with a current-limiting reactor, with a series 6% reactor and using synchronous closing control. The effects of parameters such as the sizing of the current-limiting reactor, the capacitor bank rating and the short-circuit impedance of the system are investigated. The simulation results demonstrate that the switching shunt capacitor bank with a series 6% reactor is effective in reducing the high transient inrush currents and oscillation overvoltages.

Uncontrolled Generator Operation of PM Synchronous Machine Drive With Current-Source Inverter Using Normally on Switches

This paper investigates the uncontrolled generator (UCG) operating characteristics of permanent magnet (PM) synchronous machine drives using current-source inverters (CSIs) with normally on switches. This special mode occurs when a PM machine is spinning at a high speed and gating signals are simultaneously removed from all of the inverter switches. This investigation shows that the UCG operating characteristics are quite different when the PM machine is combined with a CSI that uses normally on switches, compared to the use of a conventional voltage-source inverter (VSI). The presence of the stiff dc-link current prevents high transient currents from being developed in the machine phases that can expose the machine's rotor magnets to significant demagnetization risks. As a result, the UCG characteristics of the CSI-based PM machine drive with normally on switches are more benign than those of comparable VSI-based drives, representing an advantage of the CSI drive configuration during fault-mode operation. Experimental test results for UCG-mode operation with a 2.6-kW current-source PM drive are included that exhibit good agreement with the analytical predictions.

The New Technique of Shunt Active Power Filter Employing Kalman Filter Estimator for Photovoltaic Grid Connected System

Background/Objectives: The field of power electronics now has evolved to encompassed green technology in its approach. In this case, PV-grid connected system is being evaluated with a new approach of shunt APF that manipulate KF technique. Methods/Statistical Analysis: Introducing new technique of reference currents generation for shunt APF using KF. Conventionally, Butterworth low-pass filter is used to filter the unwanted signal which produces time delay and high transient thus degrades the overall performance of the shut APF. Therefore, to reduce the drawbacks produce by conventional method, the proposed technique using KF estimator is proposed for generating the reference current. Results: To demonstrate the proposed system performance, the simulation has been carry-out using MATLAB/Simulink (MLS) platform. The proposed technique reduced the delay time and high transient current that occur in the conventional technique. Thus, it also improves 6% of the power factor and 1.1% improvement for the THD. Conclusion/Application: Results from the study shows that KF estimator was an alternative technique in generating the reference current for shunt APF to improve the time delay, transient current, power factor and THD of the system.

Construction of graphite/TiO2/nickel foam photoelectrode and its enhanced photocatalytic activity

Graphite/TiO2/nickel foam photoelectrode was constructed through a modified sol-gel method, followed by coating procedure. Morphology, structure and optical property of the as-prepared photoelectrode was characterized via transmission electron microscopy (TEM), scanning electrons microscopy (SEM), X-ray photoelectron microscopy (XPS), X-ray diffraction (XRD) and UV–vis diffuse reflection spectroscopy (DRS). Results indicated that nickel foam framework was partly covered by graphite/TiO2 and the crystallite sizes of anatase TiO2 were found to be about 10nm.C elements were incorporated into the lattice of TiO2 nanoparticles through replacing titanium atom. Graphite/TiO2/nickel foam photoelectrode showed the enhancement of light absorption in entire UV–vis regions. Besides, the photoelectrochemical performances of the graphite/TiO2/nickel foam electrode were studied by transient photocurrent response (TPR), open circuit voltage (OCV) and electrochemical impedance spectroscopy (EIS). Moreover, photodecomposition properties of the electrode were evaluated by the generation of hydroxyl (OH) radicals, photocatalytic (PC) and photoelectrocatalytic (PEC) degradation of methyl orange (MO). The graphite/TiO2/nickel foam electrode revealed high transient photogenerated current of 0.054mAcm−2, open circuit photovoltage of −0.32mVcm−2, yield of OH radicals, PC activity of 85.1% and PEC activity of 99.8% for removal of MO. The improved PEC efficiency could be mainly ascribed to the coupled graphite, nickel foam support and applied bias voltage, which could not only enhance the UV–vis light absorption, but also accelerate the charges separation and transfer.

Symmetrically biased T/R switches for NMR and MRI with microsecond dead time

For direct NMR detection and imaging of compounds with very short coherence life times the dead time between radio-frequency (RF) pulse and reception of the free induction decay (FID) is a major limiting factor. It is typically dominated by the transient and recovery times of currently available transmit–receive (T/R) switches and amplification chains.A novel PIN diode-based T/R switch topology is introduced allowing for fast switching by high bias transient currents but nevertheless producing a very low video leakage signal and insertion loss (0.5dB). The low transient spike level in conjunction with the high isolation (75dB) prevent saturation of the preamplifier entirely which consequently does not require time for recovery.Switching between transmission and reception is demonstrated within less than 1μs in bench tests as well as in acquisitions of FIDs and zero echo time (ZTE) images with bandwidths up to 500kHz at 7T. Thereby the 2kW switch exhibited a rise-time of 350ns (10–99%) producing however a total video leakage of below 20mV peak-to-peak and less than −89dBm in-band.The achieved switching time renders the RF pulse itself the dominant contribution to the dead time in which a coherence cannot be observed, thus making pulsed NMR experiments almost time-optimal even for compounds with very short signal life times.

One-step construction of N/Ti3+ codoped TiO2 nanotubes photoelectrode with high photoelectrochemical and photoelectrocatalytic performance

In this study, we reported a facile strategy to fabricate N, Ti3+ codoped TiO2 nanotubes (N-Ti3+/TiO2 NTs) photoelectrode through one-step solution reduction process. The hydrazine hydrate treatment induced the simultaneous formation of Ti3+ species and N-doping in the lattice of TiO2 NTs. In addition, the N-Ti3+/TiO2 NTs photoelectrode exhibited intense visible light absorption ranging from 400 to 800nm, high transient photoinduced current of 0.213mAcm−2, charge carriers concentration of 0.92×1019cm−3, generation of hydroxyl radicals and PEC efficiency of 100% for the degradation of diclofenac solution within 4h visible light irradiation. The enhanced-visible-light PEC performance was mainly attributed to the enhancement of visible light absorbance, narrow band gap energy and high separation efficiency of photoinduced charge carriers. This study provides a facile strategy to construct intense visible light active catalyst, which could be applied in the fields of wastewater/air purification, solar energy conversion and water splitting.

A General Method for Analyzing Resonant and Soft-Charging Operation of Switched-Capacitor Converters

Traditionally, switched-capacitor (SC) converters have suffered from high transient currents, which limit both the efficiency and power density of such converters. Soft-charging operation can be employed to eliminate the current transients and greatly improve the power density of SC converters. In this approach, a second-stage magnetic converter is cascaded with the SC stage to act as a controlled current load. Another approach is to use resonant SC converters with zero-current switching. This paper shows that resonant and soft-charging operations of SC converters are closely related, and a technique will be proposed, which achieves either operation by adding a single inductor to existing SC topologies. In addition, since most preexisting resonant or soft-charging SC converters were devised in an ad-hoc manner, this paper formulates an analytical method that can determine whether an existing conventional SC converter topology is compatible with the proposed approach. A number of common SC topologies are analyzed, including Dickson, series-parallel, ladder, Fibonacci, and doubler configurations. Through comparison to simulated results, as well as experimental work, the proposed method is validated and a family of high-performance SC converters is obtained.

Low voltage ride through of doubly-fed induction generator connected to the grid using sliding mode control strategy

Wind Energy Conversion System (WECS) based on Doubly Fed Induction Generator (DFIG) connected to the grid is subjected to high transient currents at rotor side and rise in DC-link voltage during voltage sag at stator/grid side. To secure power system operation wind turbines have to meet grid requirements through the Low voltage ride through (LVRT) capability and contribute to grid voltage control during severe situations. This paper presents the modeling and control designs for WECS based on a real model of DFIG taking into account the effect of stator resistance. The non-linear control technique using sliding mode control (SMC) strategy is used to alter the dynamics of 1.5 MW wind turbine system connected to the grid under severe faults of grid voltage. The paper, also discusses the transient behavior and points out the performance limit for LVRT by using two protection circuits of an AC-crowbar and a DC-Chopper which follow a developed flowchart of system protection modes under fault which achieved LVRT requirements through results. The model has been implemented in MATLAB/SIMULINK for both rotor and grid side converters.

Bending phenomenon of temperature calibration curve in junction temperature measurement by the high transient current

To measure the junction temperature of diodes under operating conditions, the temperature calibration curve is studied under large current conditions. To avoid the self heating by the large current conditions, pulsed currents are used in the paper. The temperature calibration curve of TO-247-2L fast recovery diode is investigated in this paper. The 0-1.5 A pulse current, of which the pulse width is 250 μs and the duty cycle is 5%, is chosen to study the temperature calibration curves under 50, 70, 90, 110, 130 ℃ respectively.#br#The results show that under the large current condition, the temperature calibration curve bends. The main reason for the bending phenomenon is that the series resistance changes with temperature increasing, which is affected by the mobilities of electrons and holes in semiconductor material. With the temperature rising, the mobility decreases, which results in the increasing of series resistance. Due to the series resistance increasing The voltage on p-n junction will be reduced. For this reason, a higher voltage is needed to obtain the same current, and the temperature calibration curve will bend.#br#There are two reasons which will lead to the temperature rising. The first reason is self-heating of devices by the power dissipation, and the second reason is that the temperature of device is heated by ambient temperature. Under the same temperature, self-heating behaviors of device by different currents will result in different series resistances. But in the paper, the results show that the series resistances under different currents are the same, which illustrates that self-heating is not the key reason for the change of series resistance. So, the temperature changing of the diode is caused by the ambient temperature rising, which verifies that the bending phenomenon of the temperature calibration curve of TO-247-2L fast recovery diode is caused by the ambient temperature rising.#br#Then, through experimental measurements and theoretical calculations, the accurate nonlinear temperature calibration curve is acquired, which can reduce the measurement errors of high current transient junction temperature.