Short-circuit Conditions Research Articles

Control Strategy for Line Overload and Short Circuit Current of Networked Distribution Systems

The expected increase in renewable energy sources (RESs) and electric vehicles (EVs) connected to distribution systems will result in many technical constraints. A meshed network is a promising solution; however, some remarkable challenges must be overcome. Among these, this paper mainly focuses on the line overload and short circuit current of a networked distribution system (NDS) in Korea, an advanced form of meshed network. An NDS refers to a system in which there exists permanent linkages between four feeders and N × N communication-based protection. We propose a method, which employs the tap changing control algorithm of the series reactor to control line overload and short circuit current. MATLAB/Simulink was used to evaluate the proposed method. Three different types of distribution system were employed. First, the utilization rate and feeder imbalance were analyzed in steady-state condition. Subsequently, the short circuit current was analyzed in short circuit condition. The results revealed that the proposed method can effectively prevent line overload in up to 82.7% of cases, enhance the utilization rate by up to 79.9%, and relieve the short circuit current; that is, it can contribute to system stability and the economic operation of an NDS.

Bandgap and mode shape tuning of piezoelectric metamaterial

The mode shape of piezoelectric metamaterials is tuned by manipulating spatially the electrical boundary conditions of the piezo-elements, in a desired and controlled manner, in order to tailor the wave propagation characteristics through these metamaterials. The proposed concept relies on the fact that open-circuit piezo-elements made of lead-zirconate-titanate (PZT4) are twice as stiff as the same piezo-elements when operating under short-circuit conditions. Appropriate switching of the boundary conditions of the different piezo-elements between open and short-circuit conditions results in any desirable spatially distribution of the stiffness over the entire metamaterial volume. With such capabilities, it would be possible to control the bandgap characteristics of the metamaterial. But, more importantly, it would also be feasible to alter the mode shape characteristics of the metamaterial in order to control the magnitude and direction of wave propagation. This in effect enables controlling or breaking the reciprocity characteristics of the metamaterial. A finite element model (FEM) is developed to model the bandgap and mode shape characteristics of one-dimensional piezo-metamaterial. The effect of various switching strategies on the location and spectral width of the bandgap characteristics is illustrated. Furthermore, the switching strategies are also shown to influence the mode shapes, energy flow, and reciprocity characteristics of the piezo-metamaterial.

Circuit and control strategy optimization of solid-state power controller for all-electric system

Solid-state power controller (SSPC) have been received increasing attention as it is vital to ensure the reliability and safety in All-electric System (AES). However, the traditional SSPC is easy to misjudge the high instantaneous current generated when capacitive or inductive load is started as load short circuit, activate tripping protection and cause misprotection. It also does not have the ability to suppress large current under short-circuit conditions. The short-circuit current may exceed the safe working range of MOSFET or generate high heat, resulting in damage to MOSFET. Therefore, this paper proposes a new SSPC circuit and control strategy to prevent false tripping protection caused by high instantaneous current and protect the device from thermal damage. In addition, this paper establishes three circuit models of capacitive load, motor and short circuit, carries out simulation analysis, and compares the traditional SSPC with the improved SSPC. The experimental results show that the method in this paper suppresses the large instantaneous current to 10A or the set value within tens of microseconds of instantaneous start-up, while the traditional method will have a steep peak and false protection. Finally, by summarizing the research results, a new anti time curve suitable for airborne equipment distribution control system is proposed.

A Nonintrusive Current Sensor Gain Tuning Method for Interior Permanent Magnet Synchronous Motor Drives Using Controlled Short-Circuit Tests

This paper presents a simple and nonintrusive method to identify and compensate for current measurement errors in interior permanent magnet synchronous motor (IPMSM) drives. Each IPMSM has a distinct steady-state short-circuit current characteristic. By controlling the motor to operate at its steady-state short-circuit current during coasting down, the inverter can be used to smoothly switch the IPMSM into three-phase short-circuit state. Then the d-q axis measured currents are compared with the true short-circuit characteristic of the IPMSM. The distortion pattern in the d-q axis currents contains all the needed information to correct for current sensor errors in IPMSM drives. For a three-phase motor, the proposed method can correct for single-current-sensor error or dual-current-sensor error with good accuracy. The effectiveness of the method is validated by both simulation and experiment.

An Improved Sliding Mode Control with Integral Surface for a Modular Multilevel Power Converter

This paper presents a novel method for current control for a modular multilevel converter (MMC). The proposed current control methodology is based on a modified sliding mode control (SMC) with proportional and integral (PI) sliding surface which allows fast transient responses and improves the robustness of the MMC control performance. As the proposed method is derived via Lyapunov direct method, the closed-loop stability is ensured and results in globally asymptotically stable. Furthermore, the reaching time is also guaranteed by the proposed method, leading to fast transient responses. The proposed method is validated by comparing with some existing methods, which are proportional integral controller and conventional SMC, via offline and hardware-in-loop (HIL) simulations where a 10 MW, medium-voltage MMC system is tested. According to these results, the proposed method is able to provide fast transient responses, zero overshoot, and robustness to the weak grid and short-circuit conditions.

Experimental Analysis of Short-Circuit Scenarios Applied to Silicon-Graphite/Nickel-Rich Lithium-Ion Batteries

Short-circuit incidents pose a severe safety threat to lithium-ion batteries during lifetime. Understanding the underlying electrochemical behavior can help to mitigate safety risks. The electrochemically-caused rate-limiting behavior is analyzed using a quasi-isothermal test-bench, where external and local short-circuit conditions are applied to single-layered pouch cells (<50 mAh). The cell voltage, the heat generation rate, and either the short-circuit current or a local electrical potential are measured and used to characterize the short-circuit intensity. The results of 35 custom-built silicon-graphite SiC/NCA and SiC/NMC-811 cells with 2.5 wt.-% silicon are benchmarked to previously studied graphite G/NMC-111 cells. An additional current plateau appears for the silicon-graphite/nickel-rich cells, which is ascribed to the anode-limited electrode balancing. At a maximum, 29% of the total dissipated heat is caused during over-discharge. The effect of cyclic aging on the impact of the short-circuit behavior is investigated with aged single-layered pouch cells (SoH < 80%), which revealed nearly the same levels of over-discharge as non-aged cells. A lithium reference electrode is used to visualize polarization effects in the anode during ESCs and to evaluate the onset of copper dissolution (>3.2 V vs Li/Li+), which could be estimated up to 20% of the negative current collector mass.

Research on Single-phase Power Supply in Short-circuit Test of Transformer on Magnetic-force Coupling Field

The short-circuit test is a test of the comprehensive technical ability of transformer manufacturing. The three-phase power supply is usually used for short-circuit test of transformer. To investigate the feasibility of using a single-phase power supply in the short-circuit test of transformer, in this paper, we modeled a 200 kVA power transformer in three dimensions, using the finite element method to calculate the short-circuit current and short-circuit electromagnetic force of the windings under different excitation modes when the three-phase short-circuit occurs in the low-voltage windings. Analyze and compare the short-circuit current and short-circuit electromagnetic force distribution characteristics of windings under different working conditions. The results show that when the three-phase short-circuit condition occurred in the low-voltage windings, regardless of the three-phase excitation or single-phase excitation exerted on the high-voltage windings, the short-circuit current and the short-circuit electromagnetic force of the voltage zero-crossing closing phase is basically the same. This proves that a single-phase power supply can be used instead of a three-phase power supply for short-circuit tests. the analysis result has certain reference significance for improving the short-circuit test of transformer.

Investigation of SiC Trench MOSFETs' Reliability under Short-Circuit Conditions.

In this paper, the short-circuit robustness of 1200 V silicon carbide (SiC) trench MOSFETs with different gate structures has been investigated. The MOSFETs exhibited different failure modes under different DC bus voltages. For double trench SiC MOSFETs, failure modes are gate failure at lower dc bus voltages and thermal runaway at higher dc bus voltages, while failure modes for asymmetric trench SiC MOSFETs are soft failure and thermal runaway, respectively. The shortcircuit withstanding time (SCWT) of the asymmetric trench MOSFET is higher than that of the double trench MOSFETs. The thermal and mechanical stresses inside the devices during the short-circuit tests have been simulated to probe into the failure mechanisms and reveal the impact of the device structures on the device reliability. Finally, post-failure analysis has been carried out to verify the root causes of the device failure.

Electrodynamic Forces in a High Voltage Circuit Breakers With Tulip Contact System—FEM Simulations

Paper concerns the effects of electrodynamic forces that act on the contacts of the tulip contact system that is often implemented in high voltage circuit breakers. The high voltage circuit breaker often consists of two such systems. One of the systems is treated as an arcing one - made of tungsten coated elements. Capable of implementing the phenomenon of thermal-expansion. The second is made of one or two crown laces. The first system consists of a single piece of large mass, cut in such a way as to obtain the effect of increasing the contact surface. The second is a system, often of several dozen contacts, so as to increase the contact area and reduce the transition resistance. The main problem of actual validation through dynamic measurements (electrodynamic forces) is the specificity of the circuit breaker operation. The contact system is located directly in the switch chamber filled with CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> or SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> gas. Hence, tests under normal working conditions are very difficult - even impossible. Therefore, the authors proposed employment of FEM (Finite Element Method) in order to obtain values of electrodynamic forces acting on the contact system by executing the detailed 3D coupled simulation. The analysis of the results brought interesting conclusions that concerned operation of such contact layouts in short circuit conditions.

Optimal Coordination of Protection Devices in Distribution Networks With Distributed Energy Resources and Microgrids

Microgrids are promising to enhance power distribution systems’ efficiency, quality, sustainability, and reliability. However, microgrids operation can impose several challenges to traditional protection schemes, like changes in the power flow direction and an increase in short-circuit currents. Microgrids can include several distributed generation technologies with different behaviours during short-circuit conditions, requiring additional protection schemes and devices. In this way, the optimized coordination of reclosers and fuses in distribution networks with directional overcurrent relays, which operate as interconnection devices, might overcome many imposed protection challenges. Regarding to different generation technologies, voltage-restrained overcurrent relays and frequency relays are presented as local microgrid protection for rotative and inverter-based distributed generators, respectively. The optimized coordination of these protection devices maximizes microgrid benefits and minimizes operation drawbacks by reducing interruptions impacts and energy not supplied to consumers. This work proposes, thus, a mathematical model for the optimal coordination of protection devices in distribution networks with distributed energy resources operating in grid-connected and islanded modes. The minimization technique of operating times using an elitist genetic algorithm with variable crossover and mutation processes is proposed, as well. The results show adequate coordination using passive and low-cost protection devices.

Multistep Soft Turn-Off Time Control to Suppress the Overvoltage of SiC MOSFETs in Short-Circuit State

Wide-bandgap (WBG) devices, such as silicon carbide (SiC) MOSFETs and gallium nitride (GaN) FETs, have replaced silicon insulated gate bipolar transistors (Si-IGBTs) in recent years, because WBG devices can achieve fast switching frequencies and improved temperature variation reliability with better characteristics. However, this fast-switching operation can cause a substantial drain-source voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{\mathrm {DS}}$ </tex-math></inline-formula> ), which can damage the WBG switch device in the short-circuit state because the gate driver turns off the device extremely quickly, resulting in a substantial <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta I / \Delta t$ </tex-math></inline-formula> owing to the large drain current. Therefore, this study presents a multi-step soft turn-off time control method capable of changing the turn-off time according to the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{\mathrm {DS}}$ </tex-math></inline-formula> variation using one external capacitor and simple control blocks. The proposed multi-step soft turn-off method suppresses the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{\mathrm {DS}}$ </tex-math></inline-formula> variation under the setup voltage regardless of changes in the operating conditions and device characteristics by using a simple structure. An entire control block fabricated using a 180 nm BCDMOS process achieved real-time <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{\mathrm {DS}}$ </tex-math></inline-formula> sensing with only one external capacitor to control the number of ON/OFF MOSFETs for the 9-level soft turn-off operation and suppressed the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta V_{\mathrm {DS}}$ </tex-math></inline-formula> voltage under 60 V with a 1200V/25A SiC MOSFET power module.

Influence of the Magnetic Field on the Diffusion Capacitance of a Serial Vertical Junction Silicon Solar Cell in Frequency Modulation

In this work, a theoretical study of the effect of the magnetic field on the minority charge carrier density and the diffusion capacity of a silicon solar cell with vertical junction in series in dynamic frequency regime, is done. From the relative continuity equation of the minority charge carriers’ density we establish the boundary condition at the junction and the base medium. The expression of the density of minority carriers of charges in the base, allows us to determine the capacity of diffusion of the solar cell according to the magnetic field, the frequency of modulation, the wavelength of illumination and a junction recombination velocity. The profile of the diffusion coefficient allowed us to make a choice on the values of the magnetic field. These values of the magnetic field intensity will be fixed throughout this article. Each value of the magnetic field strength corresponds to a well-defined value of the resonance frequency. We obtained two ranges of illumination wavelengths from the minority charge carrier’ density profile. The influence of the magnetic field on the diffusion coefficient, of the density of minority charge carriers in short-circuit and open-circuit conditions and of the diffusion capacity, for a specific wavelength, is theoretically studied.

Effect of Position-Dependent Doping on Intermediate Band Generation-Recombination Rate in InAs/GaAs Quantum Dot Solar Cell

InAs/GaAs quantum dot solar cells (QDSCs) with <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> -type delta-doped quantum dots (QDs) have gained immense interest due to their improved open-circuit voltage. Here we report the effect of position-dependent doping on the intermediate band generation-recombination rate through theoretical modelling to analyze the reduced short-circuit current density ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J_SC</i> ) due to doping. A 1-D drift-diffusion model was used to obtain the photovoltaic characteristics. Simulations suggest that the intermediate band's contribution reduces by almost three orders of magnitude for the doped case near the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> -doped base at short-circuit conditions compared to the undoped case. We utilized these findings to develop spatially varying doping conditions. The structure with doped QDs exhibit the highest power conversion efficiency (PCE) but minor <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J_SC</i> enhancement. Comparatively, when the QDs near the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> -doped base are kept undoped, better results are obtained at low bias, and a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J_SC</i> enhancement of 0.322 mA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> is observed. With the increase in bias above 0.68V, recombination becomes dominant in the proposed partially doped structure. These observations are backed by the occupation probability of the QDs, electron and hole carrier dynamics, and electric field distribution along the intrinsic region. With such an arrangement, PCE is enhanced by 0.69% compared to that of the undoped QDSC.

Frequency Analysis of Partial Short-Circuit Fault in BLDC Motors with Combined Star-Delta Winding

This paper analyses the condition of a partial short-circuit in a brushless permanent magnet motor. Additionally, the problem was analysed for three stator winding configurations: star, delta and star-delta connection. The paper presents an original mathematical model allowing a winding configurations to be analysed. What is more, the said mathematical model allows taking account of the partial short-circuit condition. Frequency analysis (Fast Fourier Transform—FFT) of the artificial neutral point voltage was proposed for the purpose of detecting the partial short-circuit condition. It was demonstrated that a partial short-circuit causes a marked increase in the diagnostic frequencies of the voltage signal. The proposed brushless permanent magnet motor diagnostic method is able to detect the fault regardless of the stator winding configuration type.

Isolated microgrid stability reinforcement using optimally controlled STATCOM

This paper presents optimal control of static synchronous compensator (STATCOM) intended for the application in isolated microgrids using genetic optimizers. The main objectives are to enhance the microgrid stability and reduce the oscillations in voltage, power, and frequency at different operating conditions. The proposed microgrid is a hybrid power system consisting of a diesel generator and a wind turbine each rated at 500 kW. The microgrid is supplying standalone static/dynamic loads rated at 500 kW. The wind turbine unit is controlled to operate at maximum power point tracking (MPPT). The diesel unit is used for ensuring the generation-demand equilibrium is maintained particularly under low wind speeds. The paper mainly discusses the voltage and frequency regulation of the isolated microgrid at different conditions such as: sudden changes in wind speed and/or load variations. Moreover, the proposed microgrid operation is examined under abnormal three-phase short circuit condition at the point of common coupling (PCC). To guarantee the microgrid voltage and frequency regulation at these diverse operating conditions, an optimally controlled STATCOM is considered as a reactive power source. The multi-objective genetic algorithm (GA) is used to obtain the optimal scheduling of the STATCOM controller’s gains without any delay in the control signal. From the simulation results, using Matlab™, the performance of the microgrid is improved and the oscillations in voltage, frequency, and power are reduced. The microgrid stability is enhanced using STATCOM device.

A Multi-Output Multi-String High-Efficiency WLED Driver Using 40 nm CMOS Technology

In this work, a multi-independent-output, multi-string, high-efficiency, boost-converter-based white LED (WLED) driver architecture is proposed. It utilizes a single inductor main switch with a common maximum duty cycle controller (MDCC) in the feedback loop. A simple pulse skipping controller (PSC) is utilized in each high-side switch of the multiple independent outputs. Despite the presence of multiple independent outputs, a single over-voltage protection (OVP) circuit is used at the output to protect the circuit from any voltage above 27 V. An open circuit in any of the strings is addressed, in addition to the LED’s short-circuit conditions. Excellent current matching between strings is achieved, despite the low ON-resistance (Rdson) of transistors used in the 40 nm process. Most circuits are designed in digital CMOS logic to overcome the extreme process variations in the 40 nm node. Compared to a single output parallel strings topology, a 50% improvement in efficiency is achieved relative to extremely unbalanced strings. Three strings are used in this proposal, but more strings can be supported with the same topology. Each string is driven by a 25 mA current sink. An input voltage of 3.2–4.2 V and an output voltage up to 27 V are supported.

Multi-carrier switching strategy for high-bandwidth potential balancing control of multilevel inverters

&lt;span lang="EN-US"&gt;This paper confers on investigation of a direct torque control (DTC) of induction motor drive by 3 level neutral point clamp (NPC) multilevel inverter. The imbalance problem may deteriorate the electric drive performances which might cause a short circuit condition. Various balancing control strategies were proposed, however, most of them employed complex space vector modulation (SVM) and hysteresis-based controller that generates variable switching frequencies. The proposed method will offer a reliable balancing control strategy with a constant switching frequency, and moreover, it will provide excellent electric drive performances. This research proposed a new multi carrier switching modulation strategy that establish a high-band-width control for neutral point potential in the NPC inverter. Potency of the proposed high-bandwidth potential balancing strategy is validated through the MATLAB/SIMULINK environment.&lt;/span&gt;

Effect of illumination and applied potential on the electrochemical impedance spectra in triple cation (FA/MA/Cs) 3D and 2D/3D perovskite solar cells

Even though there has been numerous works performed based on electrochemical impedance spectroscopy (EIS) of perovskite solar cells (PSCs), however, many aspects of the obtained EI spectra are yet to be fully grasped. Moreover, the change of these spectra over the passage of time needs to be fully analysed and understood, therefore, this research aimed to perform a comparative study to provide a comprehensive understanding of the illumination and voltage dependence of impedence spectra of 3D & 2D/3D PSCs with aging time. The analysis was performed over the period of 5000 h of exposure of the PSCs to the ambient environment at room temperature (24 ± 1 °C). Complex EIS curves (nyquist plots and bode plots) have been investigated (with aging) in the dark, under 1 Sun illumination and at different applied potentials. Over the course of time, the charge transfer resistance (Rct) trend of both solar cells types was observed to be behaving oppositely in the dark and under illumination in the short circuit condition. Moreover, at high potentials in dark conditions, a negative capacitance feature was observed, while under 1 Sun illumination, this feature was realized even at low potentials. All of these complex observations have been interpreted and explained in terms of the charge dynamic in bulk and at the interfaces of 3D and 2D/3D PSCs. This study paves the way to understand further the complex charge dynamic processes within PSCs that evolve under different operating conditions with aging.

A Novel SiC MOSFET With Embedded Auto-Adjust JFET With Improved Short Circuit Performance

In this letter, a novel planar gate SiC MOSFET with embedded auto-adjust normally-on JFET (ADJ-MOSFET) is proposed and characterized to improve short circuit capability. The normally-on auto-adjust JFET (AD-JFET) is embedded in P-well region as the conduction path of electrons from N-type source to the channel region of SiC MOSFET. Meanwhile, the P-type source of device splits into two parts, one of which serves as the gate of AD-JFET. Under high DC bus voltage (short circuit) conditions, the effective channel width of AD-JFET will be reduced by the increased depletion charge. Therefore, the potential barrier of AD-JFET channel will increase rapidly, making it difficult for electrons transporting. The potential barrier of AD-JFET will be adjusted by that of the JFET region in drift region automatically, resulting in a reduction of the saturation (peak short circuit) current caused by the higher potential barrier of SiC MOSFET. Compared with conventional planar gate SiC MOSFET, ADJ-MOSFET not only reduces 33&#x0025; peak short circuit current, but also increases short circuit withstanding time from <inline-formula> <tex-math notation="LaTeX">$8~\mu \text{s}$ </tex-math></inline-formula> to 14 <inline-formula> <tex-math notation="LaTeX">$\mu \text{s}$ </tex-math></inline-formula> under 800 V DC bus voltage. Furthermore, an auto-adjust JFET barrier model is proposed for SiC ADJ-MOSFET.

Comparative study of dual 3‐phase permanent magnet machines with coil span of two slot‐pitches

In this study, the electromagnetic performances of dual 3-phase permanent magnet (PM) machines with coil span of two slot-pitches are comparatively investigated. It mainly focuses on two PM machines with different slot/pole number combinations (Ns/2p), that is, the 24-slot/10-pole and 24-slot/14-pole machines (2p = Ns/2 ± 2). First, winding configurations are illustrated for these two dual 3-phase machines with 30° angle displacement. Then, the winding factor, back electromotive force, average torque, torque ripple, iron and PM losses, short-circuit (SC) current, and PM irreversible demagnetisation are analysed and compared for both machines on the conditions of healthy operation and one set of three-phase fault, that is, SC or open circuit (OC), respectively. The comparative results show that on healthy condition the 14-pole PM machine has a slightly larger torque output. Besides, on 3-phase OC condition, the 14-pole machine also performs better over-rating torque capability. In terms of iron and PM losses, the 10-pole machine has smaller iron losses but larger PM losses than the 14-pole machine. Moreover, on 3-phase SC condition, the 14-pole machine has a significantly lower risk of PM irreversible demagnetisation than the 10-pole machine, although both machines have very similar SC currents. Finally, the 24-slot/10- and 14-pole dual 3-phase PM machines are both prototyped and some tests are carried out for validation.