Short Circuit Pulses Research Articles

Experimental Investigation of the Effect of EDM Debris Particles Mixed into the Dielectric Fluid on Tool Feed Rate in Drilling-EDM

In this paper the potential of the recirculation of the EDM debris particles of the workpiece material into the dielectric fluid to increase the tool feed rate vf in drilling Electrical Discharge Machining (drilling-EDM) is experimentally investigated. Two-Channel electrodes made of copper (Cu) and brass (CuZn) in the range from 1.0 mm to 2.5 mm were used. The effect of the EDM debris particles in the dielectric fluid was investigated at a discharge current ie of 25 A, a discharge duration te of 50 μs and a duty cycle of 80 % by comparing the EDM pulse characteristics and the feed rate vf of the EDM process with and without debris particles added to the dielectric fluid (particle concentrations C1 = 2.5 g/l and C0 = 0 g/l, respectively). By the recirculation of EDM debris particles the feed rate could be increased up to 36 % depending on the machining conditions. Furthermore, it was observed that the increase in the feed rate is due to the increase of the percentage of discharge pulses and the decrease of short-circuit pulses as well as a more stable machining process.

Performance monitoring and failure prediction system for wire electric discharge machining process through multiple sensor signals

This study aims to develop a pulse classification algorithm to understand wire electric discharge machining (wire EDM) process stability and performance based on the discharge pulse characteristics. Also, a process data driven failure prediction system is proposed. The wire EDM monitoring system includes high sampling rate differential probes and current probes. The features extracted through pulse train analysis were spark discharge energy, ignition delay time, spark frequency and proportion of various discharges. A pulse discrimination algorithm was proposed, which classifies the discharges into open circuit sparks, arc discharges, short circuit sparks and normal sparks. It was observed that higher proportions of short circuit pulses resulted in inferior part quality. The differences in the pulse cycle during stable and unstable machining were studied based on the extracted features. It was found that the discharge frequency and the proportion of arc and short circuit pulses were extremely high before the wire breakages. An artificial neural network (ANN) model was developed to predict the process responses, like cutting speed and surface roughness, from the process data. Also, an intelligent algorithm was developed based on the extracted in-process data to predict the unstable conditions, leading to machining failures. The accuracy of the algorithm was confirmed to be very high by conducting confirmation tests.

Novel Advances in Machine Tools, Tool Electrodes and Processes for High-Performance and High-Precision EDM

High-performance electrical discharge machining (EDM) is a key technology for manufacturing high-precision components in a broad range of industrially relevant applications. Formation of debris in the working gap leads to arcing and short-circuits on the surface as well as related inaccuracies and process instabilities. Despite decades of research in the field of EDM excessive tool wear and limited process performance are still challenging. In order to overcome highly complex state-of-the-art challenges, dedicated processes, machine tools, peripheral systems, software, tool electrodes and technologies for the application of alternative dielectric fluids have been developed. Within this work novel advances in the development of a sophisticated dry EDM machine tool, including generator and process control technology based on open architecture, open source software, and commonly available machine tool components, are presented. Solutions for challenges regarding remaining debris and gas bubbles as well as related arc discharge and short-circuit pulses in sinking EDM are presented by new flushing methods, technologies and devices. A new system for inverted pressure flushing of a dielectric fluid in ED-drilling enables a highly efficient removal of debris and gas bubbles through the interior channels of the tool electrode. A new multi-fluidic spindle system for EDM provides the ability to use performance- and material-related application of gaseous, near-dry and liquid dielectric fluids sequentially within a single machining process. Recent advances in tool electrode design, tool electrode material application, modification and production have led to essential process improvements. A helical tool electrode design significantly improved flushing conditions and related material removal rate in ED-drilling. Modification of ED-drilling tool electrode surfaces by thermal oxidation of copper reveals a promising approach to minimize ineffective discharges. Application of a specific mesophase-pitch carbon fiber with a diameter of df = 10 µm using a new process and handling technology enabled drilling holes with a diameter of dh = 25 µm. Next to the shown advances in EDM, efficient development of new process technologies could be enabled by using a specially adapted natural analogue algorithm software tool.

Algorithim to control output voltage and reduce the ripple of input current in quasi switched boost inverter

In recent years, the quasi -switched boost inverter uses widely in electrical systems. This paper proposes a method to control the AC output voltage and reduce the current ripple of the booster inductor in the quasi-switched boost inverter (QSBI). The proposed technique base on carrier pulse width modulation with two triangles with phase shifts 90◦. This technique uses the offset function to expand the modulation index and the algorithm for output voltage stabilization based on the adjustment of the boost ratio. The modulation index expansion will reduce the stress voltage on the switches by an average of 16.5% under the simulated conditions. The boost factor base on the short circuit time on the DC / DC booster and the inverter on the zero vectors. So, the duty ratio (of the boost DC / DC) can reduce by the short-circuit pulses that insert in the position of zero vectors, so the inverter is responsible for both boosting and inverting. The combination helps to reduce the current ripple on the boost inductor. Besides that, reducing the short-circuit ratio of DC / DC booster will also reduce the capacity of the booster switch and thereby reduce the production cost. The analysis clarifies the proposed technique. Simulations and experiments evaluate the proposed method.

Analysis of trap and recovery characteristics based on low-frequency noise for E-mode GaN HEMTs with p-GaN gate under repetitive short-circuit stress

In this letter, the degradation and recovery characteristics of E-mode AlGaN/GaN high-electron mobility transistors (HEMTs) were investigated under repetitive short-circuit (SC) stress. Output, transfer, transconductance and gate-leakage characteristics were analyzed in detail before and after repetitive SC stress. After stress, the electrical characteristics of the devices gradually degraded as the SC pules increased. Low-frequency noise measurements are performed over the frequency range of 1 Hz–10 KHz by increasing SC pulses. Furthermore, the recovery tendency of DC characteristics and trap density is observed between repetitive SC measurements, and this physically confirms that the mechanism of the performance degradation could be attributed to the trapping and releasing processes of electrons in the p-GaN layer and AlGaN barrier layer of AlGaN/GaN HEMTs, which change the electric field distribution under the gate.

Study on Adaptive Servo Control Strategy of WEDM Based on Discharge State Detector

In wire electrical discharge machining (WEDM), with changes in the gap state or in workpiece thickness, the servo feedrate often fluctuates and the cutting process becomes unstable, thereby resulting in a decrease in machining efficiency and a degradation in surface roughness. In order to address the problems of unstable and inefficient cutting in WEDM, the servo control system in WEDM is studied in this paper. Firstly, the discharge state detector is designed and implemented based on a programmable System-on-Chip (PSoC), in which every single discharge pulse is discriminated by preprogramed FPGA logical circuit with adjustable thresholds. The thresholds of short circuit pulses and open circuit pulses are adjusted according to parameters of the pulse power supply. As each single pulse is precisely identified and counted, this device provides more accurate feedback information to the servo control system through a CAN bus. Secondly, based on the WEDM model obtained by online identification, a two-degree-of-freedom controller and an adaptive controller are designed respectively. With adaptive control, servo feedrate is adjusted based on the information provided by the newly designed discharge state detector in real time. The two-degree-of-freedom controller and adaptive controller are implemented in the Microcontroller Unit (MCU) of the WEDM numerical control system to realize the servo feedrate control in WEDM processes. Finally, experiments are conducted on the WEDM machine for verification. Compared with the conventional servo control methods, the proposed adaptive control with discharge state detector improves the cutting stability and efficiency significantly.

Investigation of repetitive short-circuit operation of 1200 V IGBTs in the IC-VCE phase space

This work shows an investigation of repetitive Short-Circuit (SC) operation of 1200 V–15 A IGBT far above the Short-Circuit Safe Operating Area (SC-SOA). The goal behind this work was to perform repetitive SC tests with test conditions provoking the formation of current filaments in the short-circuit pulse, which leads to a non-homogeneous heating but not to a destruction. The target was to investigate unknown physical effects that lead to device degradation during the repetitive SC test. The IGBT device shows strong deterioration in its blocking characteristic after it was subjected to several 1000 SC pulses at extremely high SC levels.

Short Circuit Capability and Short Circuit Induced $V_{\mathrm{TH}}$ Instability of a 1.2-kV SiC Power MOSFET

The withstand capability and threshold voltage ( $V_{\mathrm {TH}}$ ) instability of 1.2-kV silicon carbide (SiC) MOSFETs under repetitive short circuit (SC) tests are investigated. An SC test system is constructed to apply repetitive SC stress to SiC MOSFETs and measure the transfer $I$ – $V$ characteristics and gate-to-source leakage current ( $I_{\mathrm {GSS}}$ ) after each set of SC tests. To evaluate the SC capability, repetitive SC tests with different SC durations ( $t_{p}$ ) are conducted until device failure. The SC withstand time (SCWT) at 1000 SC cycles is found to be $\sim 3.3~\mu \text{s}$ . $V_{\mathrm {TH}}$ instability under repetitive SC tests prior to the device failure is characterized. A bidirectional $V_{\mathrm {TH}}$ shift behavior, i.e., negative shift at shorter $t_{p}$ and positive shift at longer $t_{p}$ , was revealed. The $V_{\mathrm {TH}}$ shifts under repetitive SC tests are attributed to the SC pulse process according to the results of high-temperature reverse bias (HTRB) and dynamic high-temperature gate bias (HTGB) tests. The underlying mechanisms of the complex $V_{\mathrm {TH}}$ shift behavior are explained in a unified framework by taking into account the junction temperature ( $T_{j}$ ) increase with longer $t_{p}$ . TCAD device simulation is used to help analyze the mechanisms.

Fuel-to-air ratio control under short-circuit conditions through UEGO sensor signal analysis

The impact of short-circuit pulses on the after-treatment system of a spark-ignited engine must be taken into account to keep the fuel-to-air equivalence ratio within the three-way catalyst window, thereby reducing pollutant emissions. The fuel-to-air equivalence ratio overestimation that suffers the wide-range λ-sensor upstream three-way catalyst in the presence of short circuit is especially relevant. In this study, a novel approach to deal with the fuel-to-air equivalence ratio control under short-circuit conditions is introduced. Under this scope, this work proposes a strategy for the on-board correction of the aforementioned fuel-to-air equivalence ratio overestimation, by means of the information regarding short-circuit level that provides the frequency content of the λ-sensor at the engine frequency. Finally, the potential of this approach to minimize pollutant emissions, in particular the NO x penalty arisen as a consequence of running the engine under leaner conditions than expected, is assessed through experimental tests.

Short-circuit effects on spark ignition engine after-treatment and fuel-to-air ratio control

The short circuit of fresh air is a more and more extended strategy to deal with low-end torque issues, very common in small turbocharged and spark-ignited four-stroke engines. Therefore, from the author’s point of view, it is interesting to check whether the after-treatment system can work properly under these conditions. In the present study, the effect of the fresh air short-circuit on engine emissions has been assessed through its impact on the wideband [Formula: see text] sensor and the three-way catalyst behaviour, which are the key elements of the fuel-to-air ratio control strategy. In particular, the analysis of the sensor dynamic response shows that the [Formula: see text] sensor overestimates the fuel-to-air ratio under short-circuit conditions. The sensor overestimation leads the actual fuel-to-air ratio out of the proper three-way catalyst window; in this sense, results show a non-negligible emissions increase, especially in terms of NOx. Regarding the impact on the three-way catalyst behaviour, the study shows how short-circuit pulses change the exhaust gas composition for a given fuel-to-air ratio at catalyst inlet, which also contributes to a penalty in the three-way catalyst efficiency.

Short-Circuit Degradation of 10-kV 10-A SiC MOSFET

The short-circuit behavior of power devices is highly relevant for converter design and fault protection. In this paper, the degradation during short circuit of a 10-kV 10-A 4H-SiC MOSFET is investigated at 6 kV dc-link voltage. The study aims to present the behavior of the device during short-circuit transients as it sustains increasing short-circuit pulses during its lifetime. As the short-circuit pulse length increases, degradation of the device can be observed in periodically performed characterizations. The initial degradation seems to be associated with the channel region, and continuous stressing leads to an overall increase in device on-state resistance at the end of the degradation study. Thermal simulation shows that the surface aluminum metalization reached its melting temperature and the top part of the device reaches temperatures above the rated junction temperature. Scanning electron microscope investigation shows aluminum reconstruction and cavities at the contact interface between the aluminum surface metalization and source contacts.

Short-Circuit Robustness Testing of SiC MOSFETs

This paper presents electrical results for two different commercial devices and one prototype 1.2 kV SiC power MOSFET device subject to short-circuit (SC) stress. Two failure modes were observed among the devices tested, with one mode of failure resulting in catastrophic device destruction and the other resulting in permanent damage of the insulating gate dielectric manifested as a leakage current of 400 mA. Short-circuit pulses of increasing time duration caused a reduction in the gate-to-source voltage toward the falling edge of the pulse. This phenomenon is a precursor to failure of SiC MOSFETs under SC stress, but this reduction in VGS is not known to occur in silicon-based devices. The measured short-circuit withstand times for commercial devices from group A and B MOSFETs were 8 us and 12 us, respectively. MOSFET-C devices had a withstand time of 7 us. A larger chip size improves robustness even for large values of peak short-circuit current.

On the short-circuit and avalanche ruggedness reliability assessment of SiC MOSFET modules

This paper provides an insight into the operational robustness of commercially available SiC MOSFET power modules, during short-circuit (SC) and unclamped inductive switching (UIS) test environments. A set of five different power modules from three vendors rated from 1.2–1.7kV and with various current ratings have been evaluated, where the possible failure mechanisms that cause the breakdown of the modules have been addressed. The SC pulse duration of the modules was gradually increased until the failure occurred. A critical short circuit energy in the order of 4.0–8.0J was observed at a supply voltage of 800V and a pulse duration of 4.0μs. At lower supply voltage of 500V, all modules survived until 10.0μs. One of the modules, rated at 1.7kV, survived SC tests at voltages up to 1000V for a pulse duration of 4μs, but failed when the supply voltage was increased to 1100V. Prior to failure, a gate-source voltage drop has been recorded, which is associated with a high G-S leakage current. The main failure mechanism, however, is the thermal runaway which leads the devices into avalanche breakdown mode. During the UIS tests, multiple samples from the three vendors of the power modules failed. The failure of the modules was always caused by the external diode connected in parallel with the MOSFETs. One of the modules from the same vendor which does not have external diode and another module from a different vendor with external diode survived the UIS tests under nominal test conditions.

Short Circuit Robustness of 1200 V SiC Junction Transistors and Power MOSFETs

Short-circuit (SC) robustness of 1200 V-rated SiC npn Junction Transistors (SJTs) and commercial power DMOSFETs is investigated. Due to low (2x) overdrive base currents and low short-circuit currents, SJTs demonstrate superior SC capability including: (a) minimum short-circuit withstand time (tSC) of 14 µs, even at VDS=1000 V (b) Perfectly stable output and blocking characteristics after 10,000, 10 µs long SC pulses at 800 V, (c) tSC ≥ 18 µs at 800 V up to (at-least) 175°C base-plate temperatures. In contrast, commercial (Gen-II) 1200 V/80 mΩ SiC MOSFETs exhibit catastrophic failure beyond tSC = 7 µs at 500 V, and tSC = 3 µs at 800 V, due to excessive SC currents of > 200 A resulting in junction temperatures in excess of 650°C. The MOSFET’s drain leakage current increases by a factor of 120, and the VTH reduces by 20%, after 7 µs-long SC pulses at 500 V.

Repetitive Short-Circuit Tests on SiC VMOS Devices

SiC MOSFET are now commercially available and show promising performances when considering static losses, commutations and long term reliability. The devices may face short-circuit conditions and knowing their capibility in terms of critical time and repetitive fault is mandatory before integration in commercial systems. This paper presents the short-circuit performances for two families of commercial devices in terms of critical energy, time and repetitve SC stress. It shows that both devices show similar critical time but very different behavior when stressed under repetitive SC pulses. These results demonstrate that SiC MOSFET reliability under repetitive short-circuit pulses strongly depends on the pulse length and device provider. This information will be crucial to design the system in order to limit the SC length depending on the application requirements.

Experimental study on energy consumption of energy-saving pulse power for WEDM

Wire electrical discharge machining (WEDM) is widely used in aerospace, mold manufacturing, automotive, and other fields. But now, traditional WEDM pulse power contains current-limiting resistor, and its energy utilization rate is low. Meanwhile, discharge energy of WEDM pulse power cannot be accurately controlled, and there is no unified understanding of distribution about discharge energy. In this paper, the pulse power improves energy utilization rate by removing current-limiting resistor and adopting single-arm pulse width modulation control method which controls peak current and modulates long short-circuit pulse width. Experiments proved that the energy-saving pulse power improves energy utilization rate by, approximately, 67.6 % than traditional pulse power. The paper analyzed a single-pulse energy waveform of the energy-saving pulse power and calculated each spark pulse energy and total energy provided by pulse power. It found that gap spark discharge energy only accounted for about 51 % of the energy provided by the pulse power, and other energy was mainly consumed in switching loss of power switch and parasitic resistance of pulse power.

Junction Temperature Measurement of IGBTs Using Short Circuit Current as a Temperature Sensitive Electrical Parameter for Converter Prototype Evaluation

This paper proposes a method to measure the junction temperatures of insulated-gate bipolar transistors (IGBTs) during the converter operation for prototype evaluation. The IGBT short-circuit current is employed as the temperature-sensitive electrical parameter (TSEP). The calibration experiments show that the short-circuit current has an adequate temperature sensitivity of 0.35 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">${\rm A}/^{\circ}\hbox{C} $</tex-math></inline-formula> . The parameter also has good selectivity and linearity, which makes it suitable to be used as a TSEP. Test circuit and hardware design are proposed for the IGBT junction temperature measurement in various power electronics dc–dc and ac–dc converter applications. By connecting a temperature measurement unit to the converter and giving a short-circuit pulse during the converter operation, the short-circuit current is measured, and the IGBT junction temperature can be derived from the calibration curve. The proposed temperature measurement method is a valuable tool for prototype evaluation and avoids the unnecessary safety margin regarding device operating temperatures, which is significant particularly for high-temperature/high-density converter applications.

PULSE DISCRIMINATION FOR ELECTRICAL DISCHARGE MACHINING WITH ROTATING ELECTRODE

This article presents a new method for discrimination of various types of pulses generated during an electrical discharge machining process in presence of a rotating electrode. Existing pulse discrimination methods do not perform efficiently in an electrical discharge machine with rotating electrode, as arcs rarely occur during the machining process. Our method involves simultaneous comparison of the gap voltage and current signals with various thresholds. The main advantage of our proposed method is its efficient computation and significantly better accuracy in discriminating between various pulse classes for electrical discharge machining devices with rotating electrode. Experimental studies demonstrate a superior performance of our method in distinguishing normal pulses from harmful arcs, open circuit and short circuit pulses, compared with the state-of-art methods.

Pulse train data analysis to investigate the effect of machining parameters on the performance of wire electro discharge turning (WEDT) process

This paper aims at giving an insight into the wire electro discharge turning (WEDT) process, by analyzing the effect of machining parameters on material removal rate (MRR), surface roughness and roundness error, using the pulse train data acquired at the spark gap. To achieve this objective a simple and cost effective spindle is developed for the WEDT process. Pulse train data are acquired with a data acquisition system developed in the present work. A pulse discrimination algorithm has been developed for classifying the discharge pulses into open circuit, normal, arc and short circuit pulses. With the help of algorithm the number of arc regions, average ignition delay time, the width of the normal and arc regions in the data acquired can also be obtained. It has been observed that the rotation of the workpiece has significant influence on the type of the discharges occurring at the spark gap. Preliminary experiments conducted to compare the WEDM and WEDT processes disclosed that MRR is less in WEDT and the number of arcs and arc regions are more in WEDT. It has been observed that the surface roughness and roundness error of the WEDT components are influenced by the occurrence of arc regions, width of arc and normal discharge regions and average ignition delay time.

Effect of Ultrasonic Vibration of Tool on Electrical Discharge Machining of Sintered NdFeB Magnet

Sintered NdFeB magnet is widely used in many areas because of its excellent magnet. This paper studies the effect of ultrasonic vibration of tool on electrical discharge machining of it. Experiments were carried out on self-made equipment and material removal rate(MRR) against pulse-on time, MRR versus peak current and machined surface results with and without ultrasonic employment were analyzed. Results show that MRR of the ultrasonic assisted electro-discharge machining would be up to five times higher than MRR of the conventional EDM for small pulse durations and low discharge currents. The machined surface of US/EDM is finer than EDM because of less arcing and short circuit pulses. There are less cracks on the surface.