Short-circuit Events Research Articles

Short-Circuit Protection Circuits for Silicon-Carbide Power Transistors

An experimental analysis of the behavior under short-circuit conditions of three different silicon-carbide (SiC) 1200-V power devices is presented. It is found that all devices take up a substantial voltage, which is favorable for detection of short circuits. A transient thermal device simulation was performed to determine the temperature stress on the die during a short-circuit event, for the SiC MOSFET. It was found that, for reliability reasons, the short-circuit time should be limited to values well below Si IGBT tolerances. Guidelines toward a rugged design for short-circuit protection (SCP) are presented with an emphasis on improving the reliability and availability of the overall system. A SiC device driver with an integrated SCP is presented for each device-type, respectively, where a short-circuit detection is added to a conventional driver design in a simple way. The SCP driver was experimentally evaluated with a detection time of 180 ns. For all devices, short-circuit times well below 1 $\upmu\text{s}$ were achieved.

A Structural Based Thermal Model Description for Vertical SiC Power MOSFETs under Fault Conditions

The accurate prediction of the SiC MOSFET withstanding time for single fault events greatly influences the requirements for device protection circuits for these devices in power converter applications, like voltage source inverters or power electronic transformers. For this reason, a thermal model, based on the structural design and the physical dimensions of the chip as well as material properties of 4H-SiC, is proposed. This article gives a general description of the thermal behaviour of vertical SiC MOSFET under various driving and boundary conditions in case of a short-circuit event. The thermal model substitutes destructive tests of a device for an individual set of boundary conditions of an occurring fault event. The validity of the analytically parametrised thermal model is verified by experimental short-circuit tests of state-of-the-art vertical SiC MOSFETs for a set of various boundary conditions. The investigated thermal model can furthermore be used to standardise different gate-oxide degradation values from the literature for means of lifetime prediction of the gate oxide for an individual application under repetitive occurring fault or overload conditions. These manufacturer specific reported values measured with no standardised testing procedures can be translated into a maximum junction temperature, which is repeatedly reached. The thermal model therefore provides a unifying parameter for the gate-oxide lifetime calculation for an individual chip and application.

Reaction temperature sensing (RTS)-based control for Li-ion battery safety.

We report reaction temperature sensing (RTS)-based control to fundamentally enhance Li-ion battery safety. RTS placed at the electrochemical interface inside a Li-ion cell is shown to detect temperature rise much faster and more accurately than external measurement of cell surface temperature. We demonstrate, for the first time, that RTS-based control shuts down a dangerous short-circuit event 3 times earlier than surface temperature- based control and prevents cell overheating by 50 °C and the resultant cell damage.

Robustness of MW-Level IGBT modules against gate oscillations under short circuit events

The susceptibility of MW-level IGBT power modules to critical gate voltage oscillations during short circuit events has been evidenced experimentally. This paper proposes a sensitivity analysis method to better understand the oscillating behavior dependence on different operating conditions (i.e., collector–emitter voltage, gate-emitter voltage and temperature). A study case on 1.7kV/1kA IGBT power modules is presented. The proposed study helps to understand the oscillation mechanism by revealing its relationship with different working conditions. Moreover, the study can be helpful to understand the oscillation phenomenon, as well as to further improve the device performance during short circuit.

In Situ Diagnosis and Control of Li-Ion Batteries for Enhanced Safety

Safety of Li-ion batteries remains a critical challenge due to their high energy density and use of flammable electrolyte. The challenge is further propelled by their ever-increasing and demanding applications in electric vehicles (EVs). Recent high-profile events involving electric cars and airplanes that employ Li-ion batteries as main or auxiliary power sources lend further urgency to enhanced Li-ion battery safety. We obtained insights of nonuniform temperature distributions in Li-ion battery cells through in situ diagnosis1. Inspired by those insights, we developed a reaction temperature sensing (RTS)-based control technique to enhance Li-ion battery safety. The RTS-based control is demonstrated to shut down an external short circuit event 3 times earlier than conventional surface temperature- based control and effectively prevent cell damage2. We will apply the RTS-based control and in situ diagnosis of temperature distributions to other challenging safety scenarios including internal short circuit. The progress will be presented. Reference 1. G. Zhang, L. Cao, S. Ge, C.Y. Wang, C. E. Shaffer, C. D. Rahn, In situ measurement of radial temperature distributions in cylindrical Li-ion cells, Journal of The Electrochemical Society,2014, 161 (10): A1499-A1507 2. G. Zhang, L. Cao, S. Ge, C. Y. Wang, C. E. Shaffer, C. D. Rahn, Reaction temperature sensing (RTS)-based control for Li-ion battery safety, Scientific Reports, under review

Improved high‐speed de‐excitation system for brushless synchronous machines tested on a 20 MVA hydro‐generator

Synchronous machines with brushless excitation have the disadvantage that the field winding is not accessible for the de-excitation of the machine. This means that, despite the proper operation of the protection system, the slow de-excitation time constant may produce severe damage in the event of an internal short circuit. A high-speed de-excitation system for these machines was developed, and this study presents the continuation of a previously published study. This study presents the design by computer simulation and the results of the first commissioning of this de-excitation system in a commercial 20 MVA hydro-generator. The de-excitation is achieved by inserting resistance in the field circuit, obtaining a dynamic response similar to that achieved in machines with static excitation. In this case, a non-linear discharge resistor was used, making the dynamic response even better.

Performance of a Polycrystalline SmBaCuO Superconducting Fault Current Limiter

This study has assessed the performance of a resistive superconducting fault current limiter based on polycrystalline SmBa2Cu3O7−d (Sm-123) subjected to 750 short-circuit events with acting time 80 ms. Preliminary results indicate that polycrystalline Sm-123 cuprates can be used to build superconducting fault current limiters. The results of this study have demonstrated that after 616 short-circuit repetitions, the superconducting element was able to limit the fault current without degradation on low-level fault current density J < 3.7 kA/cm2.

Live Grid Field-Testing Final Results of the First Italian Superconducting Fault Current Limiter and Severe 3-Phase Fault Experience

The first Italian Superconducting Fault Current Limiter 9 kV/3.4 MVA was developed and lab tested by Ricerca sul Sistema Energetico S.p.A. and then installed in the Milan distribution grid belonging to A2A Reti Elettriche S.p.A. This resistive-type SFCL device was operational since March 2012 and hence has been field tested for more than two years, providing a large amount of experimental data with a significant experience gaining. Some preliminary results were already presented; however, this paper reports on the main outcomes of the field testing activity including the effective short-circuit current limitation provided by this SFCL prototype during a severe real three-phase short-circuit event in the Milan distribution grid. The SFCL device showed to behave as expected, promptly limiting the short-circuit current by a factor of about 2. This is the first SFCL limiting action in Italy and one of the very first worldwide. Further to this first successful installation, the hosting utility A2A agreed to install in the same substation a new SFCL device protecting four different feeders, therefore implying a SFCL upgrading up to 15.6 MVA. Therefore, this paper also anticipates the key steps towards the development of the upgraded SFCL prototype to be commissioned in early 2015.

Stochastic modeling of power system faults

Correct modeling of power system faults is a key issue in a diversity of power system studies, such as in network planning, equipment specification and protection systems coordination. The present paper addresses the probabilistic description of faults, based on available data collected by transmission system operators for different voltage levels. Fault rate and individual fault characteristics are stochastically modeled, namely fault location, type and resistance. A fault resistance model is suggested, based on Weibull distribution, which parameters are set per voltage level. The proposed fault description is a useful tool for power system planning and design, when a stochastic approach of the power system faults characteristics is adopted. Time series of fault input data and simulation results are presented in a common format, so to allow using the same statistical tools as used in power system monitoring and field data reporting. The model is able to reproduce atypical years, as happen in real transmission networks. The developed fault model is used to generate stochastic short-circuit events, which are then used for short-circuit current computation. The methodology is applied to the IEEE RTS and simulation results are shown for the probability of amplitude and time constant values. These results are prone to be used to specify network circuit breakers and current transformers using a probabilistic approach.

Characterisation of gas turbine dynamics during frequency excursions in power networks

Gas turbines inherently depict unique frequency response characteristics compared with other conventional synchronous generation technologies as their active power output is not entirely determined by the governor response during frequency deviations of the power network. Thus, gas turbine dynamics significantly influence on system stability during frequency events in power networks. Power system and power plant operators require improved understanding of the gas turbine characteristics during various frequency events in order to mitigate adverse impact on power system. Therefore a comparative analysis has been performed between combined-cycle gas turbines (CCGTs) and open-cycle gas turbines (OCGTs) in order to characterise the dynamic behaviour considering different types of frequency events in power networks. Study has shown that CCGTs result in significant frequency variations in power networks in comparison with OCGTs because of the temperature control action performed by the fast acting inlet guide vanes at the combustor. In particular, they are susceptible to lean blowout during large frequency increase events such as short-circuit faults in power networks. Furthermore, a case study was developed based on the New England-39 bus system in order to illustrate the impact of gas turbine dynamics on network frequency during short-circuit events in power networks.

Interconnected High-Voltage Pulsed-Power Converters System Design for H− Ion Sources

This paper presents the design and experimental validations of a system of three new high-voltage (HV) pulsed-power converters for the H sources. The system requires three pulsed voltages (50, 40, and 25 kV to ground) at 2-Hz repetition rate, for 700 μs of usable flat-top. The solution presents ripple-free output voltages and minimal stored energy to protect the ion source from the consequences of arc events. Experimental results on the final full-scale prototype are presented. In case of short-circuit events, the maximal energy delivered to the source is in the Joule range. HV flat-top stability of 1% is experimentally achieved with a simple Proportional-Integral-Derivative regulation and preliminary tuned H source (e.g., radio frequency control, gas injection, and so forth). The system is running since more than a year with no power converter failures and damage to the source.

Characterization of Gas Turbine Lean Blowout During Frequency Excursions in Power Networks

While gas turbines are popular in power networks due to reduced emissions and economical operation, their frequency response characteristics are substantially different from other conventional generation technologies; hence, gas turbine dynamics may influence system stability during significant frequency excursions. This study characterizes the impact of gas turbine combustor lean blowout (LBO) while considering large frequency excursions and, in particular, during short-circuit faults. Studies have shown that combined-cycle gas turbines are more vulnerable to an LBO condition during short-circuit events when they operate at rated power output. A sensitivity analysis was also carried out against a number of factors influencing the LBO, revealing that generator loading and rate-of-change-of-frequency are the main contributing factors for the LBO. Furthermore, mitigation strategies are also proposed to alleviate the LBO condition during large frequency excursions.

A di/dt Feedback-Based Active Gate Driver for Smart Switching and Fast Overcurrent Protection of IGBT Modules

This paper presents an active gate driver (AGD) for IGBT modules to improve their overall performance under normal condition as well as fault condition. Specifically, during normal switching transients, a di/dt feedback controlled current source and current sink is introduced together with a push-pull buffer for dynamic gate current control. Compared to a conventional gate drive strategy, the proposed one has the capability of reducing the switching loss, delay time, and Miller plateau duration during turn-on and turn-off transient without sacrificing current and voltage stress. Under overcurrent condition, it provides a fast protection function for IGBT modules based on the evaluation of fault current level through the di/dt feedback signal. Moreover, the AGD features flexible protection modes, which overcomes the interruption of converter operation in the event of momentary short circuits. A step-down converter is built to evaluate the performance of the proposed driving schemes under various conditions, considering variation of turn-on/off gate resistance, current levels, and short-circuit fault types. Experimental results and detailed analysis are presented to verify the feasibility of the proposed approach.

3.3 kV PT‐IGBT with voltage‐sensor monolithically integrated

An intelligent insulated gate bipolar transistor (IGBT) suitable to be used in remote-controlled on-load tap changers and traction applications is analysed in this study. An anode voltage sensor monolithically integrated in the active area of a 3.3 kV–50 A PT-IGBT is introduced to enhance the robustness of the IGBT against short-circuit events. The operation mode of the anode voltage sensor is described and TCAD simulations are performed to describe the static and dynamic performance together with the interaction between the sensor and the IGBT core cells. The study of the anode voltage performance under inductive turn-off conditions is also included, comparing the behaviour of IGBTs with and without anode voltage sensor.

Novel short‐circuit protection technique for DC–DC buck converters

This study presents a novel short-circuit protection technique for DC-DC buck converters. The required short-circuit operating frequency is derived in order to avoid the effect of inherent propagation delay in the controller and power transistors. In this design, the short-circuit switching frequency is approximately 31% of the normal value. Simultaneously, the peak current limit is decreased to about 40% of the normal value to lower the power dissipation when a short-circuit event occurs. Once the fault condition is removed, the converters can automatically return to normal operation smoothly by clamping the soft-start signal using the feedback voltage of the output. A buck converter with the proposed technique has been successfully simulated and verified by a 0.6-μm CDMOS technology. The simulation results show that the power loss is only 17.1% of the constant current limit during the prolonged short-circuit situation, which significantly enhances the reliability of the chip. Furthermore, the converter is able to achieve smooth self-recovery as soon as the fault status is released.

Gate Unit With Improved Short-Circuit Detection and Turn-Off Capability for 4.5-kV Press-Pack IGBTs Operated at 4-kA Pulse Current

This paper presents a gate unit with short-circuit protection for a 4.5-kV press-pack insulated gate bipolar transistor (IGBT) designed for pulsed applications and operated at a pulse current of 4 kA and the results of short-circuit tests performed with the mentioned switch and the gate unit. Initially, an overview of the gate unit, the implemented gate boosting as well as the two-stage turn-off and active clamping is given. An over- di/dt as well as an over-current detection using a printed circuit board (PCB) Rogowski coil is used in the gate drive to protect the IGBT during operation. Then, the design of the PCB Rogowski coil is introduced including partial element equivalent circuit simulations to predict the coil parameters. Measurements were made to verify these simulations. Afterward, two types of short-circuit tests were performed. First, the over- di/dt detection was tested by turn-on into a short circuit. The tests show that the over- di/dt detection reacts very fast. The IGBT was always able to turn off the short-circuit current. The maximum short-circuit current was 4.4 kA. Second, tests using an auxiliary switch were made to investigate the short-circuit events during pulse top. The IGBT was able to turn off a maximum short-circuit current of 8.7 kA.

Building a “smart nail” for penetration tests on Li-ion cells

Nail penetration is one safety test that Li-ion cells experience in order to simulate some aspects of an internal short circuit event. To our knowledge, nail penetration is usually performed with an ordinary steel nail. Normally, the only data gathered has been a simple pass/fail result depending on whether or not the cell emitted smoke or flame, along with a thermocouple on the surface of the cell. A “smart nail” has been developed to allow the collection of temperature versus time data at the point of nail penetration. This nail, in conjunction with a thermocouple on the cell surface and tabs on the ends to measure voltage, should provide some new insights into the behavior of cells during this type of abuse testing as well as aid in the developing of safer Li-ion cell chemistries.

Anti-islanding Protection of Distributed Generation Using Rate of Change of Impedance

Abstract Distributed Generation (DG), which is interlinked with distribution system, has inevitable effect on distribution system. Integrating DG with the utility network demands an anti-islanding scheme to protect the system. Failure to trip islanded generators can lead to problems such as threats to personnel safety, out-of-phase reclosing, and degradation of power quality. In this article, a new method for anti-islanding protection based on impedance monitoring of distribution network is carried out in presence of DG. The impedance measured between two phases is used to derive the rate of change of impedance (dz/dt), and its peak values are used for final trip decision. Test data are generated using PSCAD/EMTDC software package and the performance of the proposed method is evaluated in MatLab software. The simulation results show the effectiveness of the proposed scheme as it is capable to detect islanding condition accurately. Subsequently, it is also observed that the proposed scheme does not mal-operate during other disturbances such as short circuit and switching event.

Short Circuit Tests on a Coreless HTS Synchronous Generator

A series of short circuit tests have been performed on a coreless (air-core) high-temperature superconducting (HTS) rotor, installed inside a conventional stator. The machine was driven like a generator using an 11 kW drive motor, to a maximum frequency of 20 Hz. The short circuit was activated at the stator terminals using a three-phase contactor switch and a remote trigger. Tests were conducted with a range of values for each of the following parameters: i) initial frequency, between 4 and 20 Hz; ii) operating field current, between 5 and 80 A; and iii) external resistance, between 14 and 160 mΩ. For each investigation, the other parameters were fixed. Large current surges were observed in both the stator (3 times its nominal current) and in the rotor (1/4 of the initial operating current). Some localized thermal measurements of a coil in the HTS winding were also recorded but, during the transient events, these measurements are invalidated by inductive voltages. The temperature is believed to remain steady during the short circuit event. The rotational kinetic energy of this rotor was almost half of its counterpart, but it was the power supply and the series resistor that absorbed most of the magnetomotive energy after the short-circuit. These components are essential parts of the HTS generators' overall system and their operating limits must also be considered in new designs.

Contribution of synchronous condensers for the energy transition

In recent years a revival of rotating synchronous condensers could be seen all over the world. This trend is mainly driven by the introduction of enduring energy production. The change in energy mix is leading to the replacement of conventional energy production with synchronous machines by “low inertia” and “low thermal time constant” power park modules. Power park modules are represented by wind farms and registrable solar power plants. Compared to power park modules synchronous machines have a high thermal time constant and must therefore not be limited during short circuit events in its reactive power capability. Additionally, synchronous condensers have a natural mechanical inertia, which cannot be reached by modern power park modules. Therefore synchronous condensers complement power park modules for transmission upgrade projects and help to improve reliability, preserve future energy options and contribute to economic stability. Different design considerations are discussed.