Turn-off Current Research Articles

A small-loop double-coil decoupling transient electromagnetic device for high-sensitivity near-surface detection

Small-loop transient electromagnetic (TEM) devices, several meters in size, are increasingly applied to near-surface geophysical exploration in space-limited environments. But the transmitter (TX) coil significantly affects the early time data acquisition of the receiver (RX) coil during current turn-off, resulting in the loss of shallow signals and creating a significant blind zone problem. We report a double-coil decoupling TEM (DCDTEM) device to solve this problem. The novel DCDTEM device ensures a weak primary magnetic flux region between the two coplanar TX coils with the same current direction and different radii. Simulation results indicate that the transmitting field of the DCDTEM device is more focused than the traditional central loop device, ensuring a stronger coupling with the target. The 3D TEM forward-modeling results show that the DCDTEM device has the highest detection sensitivity, together with a relatively high lateral resolution compared with other small-loop TEM devices. We further carry out several physical experiments to test the response characteristics of the DCDTEM device with reference to the offset and the ratio of turns between the TX and RX coils. The experimental results ensure that the position of the zero magnetic flux point can be accurately calibrated and mitigate interference from TX coils. Our DCDTEM device is also applied in a field test on water pipe detection, demonstrating its practicality in near-surface detection.

Phase-Shifting Adaptive LLC Resonant Converter with Reduced Turn-Off Loss in Wide Voltage Application

In this paper, a hybrid control method with adaptive phase-shifting modulation (PSM) and pulse-frequency modulation (PFM) is proposed to optimize the steady-state performance of an LLC resonant converter in wide voltage-gain range application. For the primary-side switches under the hybrid control method, zero-voltage switching (ZVS) performance is maintained over wide voltage-gain range and the turn-off loss is reduced; therefore, the converter reconciles wide voltage-gain range and high efficiency. Mode characteristics under different phase-shifting-angle-θ and switching-frequency-fs combinations is analyzed, and then the soft-switching characteristic is revealed. By introducing time domain analysis, the turn-on current of the primary-side switches is calculated, and thus the ZVS boundary of different θ and fs combinations is inferred. In addition, to acquire the optimum steady-state operation of the converter, the turn-off current is calculated; by making the converter work near to the minimum turn-off current operating point, the turn-off loss can be reduced greatly. With the principles of achieving ZVS performance and minimizing turn-off current, the phase-shifting angle θ of PSM is designed to be adaptive to the reference output voltage, no additional circuits are needed, and the two control degrees (θ and fs) are simplified to one (fs). The simulation and experiment are developed to verify the feasibility and effectiveness of the hybrid control method; the results show that ZVS performance is maintained at wide voltage-gain range and the turn-off current of the hybrid control method is reduced to that of the single PFM, and thus the turn-off loss is reduced. The efficiency comparison validates the fact that the hybrid control method has less power loss than single PSM and single PFM.

Turn-Off Current and TEM Field Based on Distributed Capacitance Model of Multiple Coils in Helicopter Transient Electromagnetic System

For compensating the primary field coupling from the transmitting coil and the sensing coil, the bucking coil is often used to achieve pure secondary field for the helicopter transient electromagnetic (HTEM) system. Traditionally, the distributed capacitance of the bucking coil and the transmitting coil is ignored and pay few attentions to study it. In fact, it has very important influence on the turn-off current of the transmitter and the transient electromagnetic (TEM) field of the system. In this paper, a novel distributed capacitance model of the HTEM coils is theoretically established at the first time, its effects on the turn-off current and the TEM field are analyzed in detail. It finds that the turn-off current in the transmitting coil and the bucking coil are not equal caused by the distributed capacitance although they are connected in series. The field experiments are completed and proved that the measured TEM fields agree very well with the simulated results based on the distributed capacitance model. This is very helpful to optimize the early-time TEM field and promote the shallow TEM data interpretation capability for the HTEM surveying.

Fully Soft Switched Bidirectional Buck–Boost Converter With Improved Voltage Conversion Ratio and Single Auxiliary Switch

In this paper, a fully soft-switched bidirectional buck/boost converter with improved voltage conversion ratio (VCR) and minimum semiconductor devices is proposed. An auxiliary circuit which employs only one active switch along with coupled inductors technique is utilized to increase VCR and provide soft switching condition for all semiconductor devices. Soft switching condition is provided at a wide power range while the leakage inductance energy of coupled inductors is absorbed in both power flow directions. The main switches are turned on at zero voltage-zero current switching and turn off at zero voltage switching, while the switches body diodes used as the converter diodes turn off at zero current switching which alleviates the diodes reverse recovery problem. Soft switching operation and low component count especially the active switches have contributed to realize a proper converter efficiency. Moreover, the converter has maintained continuous current at low voltage side, common ground between the high and low voltage sides and switches voltage stress similar to the basic bidirectional buck/boost topology. A converter prototype at 300W and 100kHz is implemented to confirm the converter theoretical operation and analysis.

Enhancing Turn-off Performance in IGCT-Based High Power Applications—Part I: Anomalous High Current Turn-Off Mode and Safe Operating Area Expansion at Ultra-Low Voltage

Enhancing Turn-off Performance in IGCT-Based High Power Applications—Part I: Anomalous High Current Turn-Off Mode and Safe Operating Area Expansion at Ultra-Low Voltage

A 6-in Integrated Emitter Turn-OFF Thyristor With 17.5 kA Turn-OFF Current

The demand and requirement for high-capacity power electronic devices increase rapidly, and Integrated Emitter Turn-off Thyristor (IETO) has excellent performance in both on-state voltage drop and turn-off capability. An advanced 6-inch 4.5kV IETO device is proposed and developed, including optimized package and driver unit. A low thickness package with compact disc spring assemblies is put forward, which achieved excellent pressure distribution with the same thickness as IGCT for complex IETO structure. A composite signal extraction structure without hindrance for ceramic seal is also proposed. Several electromagnetic transient problems during large current turn-off are analyzed, such as the emitter voltage oscillation during commutation, the damping characteristics of gate control signals, and the induced voltage on signal extraction structure. Based on the analysis, a new external driver unit with higher reliability for large current is designed. After optimization, a prototype was developed with all problems solved. According to the experiments, the 6-inch 4.5 kV IETO achieved 17.5 kA turn-off current, and the transient characteristics were verified. The commutation time is less than 300ns, which has enormous potential for larger turn-off current with better GCT wafers. Compared to the other GCT based devices, the IETO in this paper reaches the maximum turn-off current.

The defects of reported TID reinforced structures and the improved structure

We find that the previously reported P-edge N-Metal-Oxide-Semiconductor Field-Effect Transistor (NMOSFET) and dummy gate-assisted (DGA) NMOSFET, to resist the total ionizing dose (TID) effect, have a fatal drawback in that they can only work under a very low drain voltage (Vdd). This paper proposes and demonstrates an improved structure, called P+ edge source NMOS (PES-NMOS), in which the heavily P+ doped belts are only formed on both sides of the source region close to the shallow trench isolation (STI). Both the TCAD software simulations and radiation experiments show that the turn-off current (Ioff) of the PES-NMOS device under 1.8 V Vdd is about 4 to 5 orders of magnitude smaller than that of the control group without reinforcement structure at 300 krad(Si) TID. This result proves that the PES-NMOS can well resist the TID effect and solve the fatal drawback of the reported structures. With the continuous progress of the CMOS process, the thickness of gate oxide becomes very thin, while STI is relatively thick, so the total dose effect on STI is still significant. Therefore, the importance of using the PES-NMOS to suppress the parasitic channel of STI and overcome the shortcomings of the ELT is increasing. Index termsP+ edge source NMOS, total ionizing dose(TID) effect, radiation experiments, radiation hardening by design(RHBD).

Testing transient electromagnetics systems on the ice cover of Lake Baikal

Currently, sites well studied by geological and geophysical methods are used as natural reference models for testing measurement systems used in the transient electromagnetic (TEM) method. However, the electrical properties of these models are rarely known in such detail that the difference between the measured and modeled transient responses can be safely attributed to the measuring system's intrinsic response, rather than the properties of a reference model. In this article, we present and discuss the results of testing TEM systems on Lake Baikal. The measurements were taken in early spring when the lake was covered with ice. More than 1000 m deep, homogeneous and isotropic water column of the lake is a unique natural model with precisely known properties. Testing works on Lake Baikal answered the question why, when using small central loop arrays in resistive environment, an anomalously slow decrease in transient EMF (long tail) is observed at late times. As it turned out, long tails are a slowly decreasing component of the input amplifier's intrinsic response to a voltage pulse induced in the receiving loop during transmitter current turn-off. As for measurements at early times, it was shown how delay effects in turning off the transmitter current manifest themselves in the early-time loop-loop TEM data.

Fast protection strategy for monopole grounding fault of low-voltage DC microgrid

• This paper presents a low-voltage DC microgrid ground short-circuit fault protection system based on positive channel metal oxide semiconductor (PMOS). • In case of ground short-circuit fault in DC microgrid, the coupling energy of the short-circuit current makes the PMOS to be turned off reliably. • In addition, because the primary inductance of the transformer plays a certain current limiting role, the turn-off current of PMOS will not increase sharply. Low voltage DC microgrid has attracted more and more attention in smart grid with its advantages such as low network loss, large transmission capacity and easy direct access to distributed power supply. However, compared with the traditional AC microgrid, the DC microgrid lacks inertia support and the fault develops rapidly, which makes the existing short-circuit current protection technology difficult to meet the requirements of accurate and efficient troubleshooting. Therefore, this paper presents a low-voltage DC microgrid ground short-circuit fault protection system based on positive channel metal oxide semiconductor (PMOS) self-powering DC solid-state circuit breaker protection elements, and verifies the feasibility and effectiveness of the protection system through simulation experiments. The experimental results show that the proposed protection system based on solid state circuit breaker will not affect the voltage of DC microgrid when it is normally on; In case of ground short-circuit fault in DC microgrid, the coupling energy of the short-circuit current makes the PMOS to be turned off reliably. In addition, because the primary inductance of the transformer plays a certain current limiting role, the turn-off current of PMOS will not increase sharply. The solid-state circuit breaker can effectively block the fault without a buffer circuit, which has a good application prospect.

Study on failure mechanism caused by voltage leap of SGT-MOSFET during UIS testing

During the unclamped inductive load switching (UIS) testing or system application of power SGT-MOSFET, it is found that the step leap of drain voltage occurs during clamping at high avalanche current. This voltage leap eventually leads to the failure of device. In this paper, the structural modeling and simulation analysis of the related products reveal that the drain voltage leap is ultimately caused by the turn-off of the triggered npn transistor. By comparing the static with the dynamic avalanche characteristic curves, it is found that the robustness of SGT-MOSFET during self-clamping is limited by the different differential resistance branches on the static avalanche breakdown curve. It is pointed out that the negative differential resistance branch is the primary cause of the parasitic npn transistors triggering. When the device structure parameters are determined, the current that causes the parasitic transistor to be triggered has a certain value, so the higher the turn-off current is, the longer the duration of voltage leap during clamping is. Theoretically, the avalanche ruggedness of SGT-MOSFET can be estimated by the snapback current on the static avalanche breakdown curve.

Zero voltage switching high step‐up boost converter with coupled inductor for renewable energy applications

AbstractThis paper proposes a zero‐voltage switching high step‐up boost converter with coupled inductor for renewable energy applications. In this proposed circuit, main and auxiliary switches are turned ON at zero voltage switching to reduce switching losses. The voltage gain of the converter is increased by varying the turns ratio between primary and secondary of the coupled inductor (CI). The voltage spikes at the main switch are mitigated by using active clamping technique. The reverse recovery problem in diodes is alleviated due to leakage inductance of the CI. Zero current switching turn OFF in output diode is achieved, which can enhance the efficiency of the converter. A real‐time model for 100 W proposed converter circuit is developed to verify the theoretical analysis.

A modular isolated battery‐integrated multiport step‐up DC–DC converter for hybrid energy applications

In this paper, a modular isolated battery-integrated multiport step-up dc–dc converter is designed for simultaneous energy transfer from multiple renewable energy sources (RESs) to a load. The proposed converter offers a plug-and-play capability of input sources where each input can be connected to and disconnected from the converter. The power generation shortage/surplus can be managed by a battery inserted into a bidirectional port. Also, charging/discharging durations of battery are independent of switching duty ratios for input sources. In the presented converter, inputs are connected in parallel with a common ground through individual step-up dc–dc cells while outputs are connected in series with voltage doubler rectifiers (VDRs) to achieve higher voltage gains and lower voltage stress on output capacitors. Moreover, the leakage inductances of the isolated transformers with dc blocking capacitors provide quasi-resonant operation to alleviate high turn-off currents of switches and hard-switching in VDR diodes. Due to interactions of converter control loops, a MIMO closed-loop control system is designed to regulate the output voltage and output power of input sources at references. The simulation and experimental results obtained for three inputs verify performance of the developed converter in different modes.

Ultra-low turn-off current 2D material heterojunction selectors: first-principle calculations

Selector is important for emerging non-volatile memory arrays to settle the sneak path problem and inhibit the array leakage current. The turn-off current of the selector determines the ability of selector to inhibit the leakage current. Here, selector models with the structure of graphene/g-GaN/graphene show ultra-low turn-off current. First, combining the plane electrostatic potential and the current–voltage characteristic of switch layers of heterojunctions, it can be concluded that the resistance switching mechanism is based on Schottky barrier at the interface. Moreover, three selector models with different switch layers (model A, B, C) are explored to study the influence of the switch layer structure on the device. The plane average electrostatic potential of selectors shows that the different structures of the switch layer result in the difference of the threshold voltage (V th), owing to the different interface barrier. Finally, the electronic transmission shows each selector have an ultra-low turn-off current (I off) and high nonlinearity, which could better suppress the leakage current in array. This work supplies a potential implementation scheme for the selector with ultra-low turn-off current.

A Dynamic Self-Clamping Caused by Dynamic Avalanche During the Turn-Off of PT-IGBT

A dynamic self-clamping is found during overstress turn-off of the PT-insulated gate bipolar transistor (IGBT) with a higher carrier lifetime. Theoretical analysis and numerical device simulation reveal that it is caused by the remaining plasma that cannot be completely removed due to dynamic avalanche injection. A 1-D physics-based analytical model for the self-clamping is established, and analytical results indicate that clamped voltage is inversely proportional to the initial turn-off current density and the carrier lifetime. When the dc-link voltage is larger than the clamped voltage of the device at a certain turn-off current, both terminal voltage and terminal current will be clamped, causing the device to lose control of the gate. Simulations of the multicell structure demonstrate that the avalanche-generated current filament under the self-clamping is stationary and may exist for a longer time, which is extremely likely to lead to local overheat and device destruction.

Optimal Design of LLC Resonant DC Transformer under Adaptive Frequency Tracking Strategy

In recent years, the LLC (inductor–inductor–capacitor) DC transformer has been widely used in communication and computer power supply because of its advantages of zero voltage conduction of primary switch and zero current turn off concerning the output rectifier diode. To obtain higher transmission efficiency and make the LLC DC transformer always run at the optimal operating point, the switching frequency of the LLC DC transformer should work at the resonance frequency of the circuit. In actual conditions, the optimal operating frequency of the LLC DC transformer will be changed due to the influences of the working condition on the circuit parameters and the load change. Therefore, the LLC DC transformer controlled by the fixed frequency mode will not be in the best working condition. In this paper, an adaptive frequency tracking method is used to control the circuit; when the circuit parameters change, the LLC DC transformer can always be in the best working state. Then, the influence of circuit parameters such as output power and excitation inductor on the optimal working point of the LLC DC transformer is analyzed in detail. Finally, a 1 kW LLC resonant converter prototype is designed under laboratory conditions to verify the feasibility of the control strategy.

Analysis of cyclic spontaneous switchings in GaN & SiC cascodes by snappy turn-off currents

This paper investigates the crosstalk-induced spontaneous switchings as continuous cycles of turn-on and turn-off transients as a key reliability criterion in SiC and GaN cascode power devices. The paper presents a wide range of measurements to describe the severity of unwanted switching cycles in presence of a few diodes with high turn-off dI/dt which results in a negative gate voltage induced by the source inductance. Modelling is performed which confirms the theory described to explain the root cause of the continued oscillatory transients and comparisons are made with standalone SiC power MOSFETs.

ПРИМЕНЕНИЕ ТАСИТРОНОВ В СХЕМАХ С ИНДУКТИВНЫМ НАКОПИТЕЛЕМ ЭНЕРГИИ

Features of generating high voltage in a pulsed or weakly pulsating form for different applications with an inductive energy storage device are considered. High voltage (tens of kilovolts) is generated due to self-induction when the storage is disconnected using a high-voltage tacitron-type switch device from a low-voltage pumping current source (with voltage less than 1 kV). The tacitron is a gas-discharge triode with a dense control grid, which provides initiation of a discharge between the cathode and anode and pumping the storage at a positive voltage, and then disconnecting it from the pumping current source, when a negative voltage of 20-200 V is applied to the grid for the blocking of the electron flow to the anode. Tacitrons are able to turn-off currents from a few to hundreds of amperes in the presence of a high voltage between the cathode and anode that takes a time of the order of 1 μs. Diagrams of changes in time of the current and voltage of the tacitron and the load during the generation of both pulsed and weakly pulsating voltages are considered. In the latter case, an additional storage (filter) capacitor is connected in parallel with the load, supplying the load by energy during the pumping periods of the inductive storage, and a high-speed pulse gas-filled rectifier diode is proposed to use for the dynamic separation of the storage capacitor and tacitron circuits in the said periods. Formulas are given that allow one to evaluate the parameters of the high voltage generation process. It is proposed to use a combined switching device containing tacitron and pulse gas-filled diode in one envelope with a common cathode electrode to simplify the high voltage generator circuit.

Acoustic Emission-Based Experimental Analysis of Mechanical Stress Wave in IGBT Device

In this paper, based on acoustic emission (AE) monitoring and digital filtering technology, the low and high frequency components in the switching mechanical stress wave (MSW) of insulated gate bipolar transistor (IGBT) device were discovered for the first time. Then, the effects of turn-off current on the low and high frequency components were studied. The obviously linear relationship was found between the low frequency component and the turn-off current, and the low frequency component could closely follow the change of turn-off current, showing that the low frequency component was strongly related with turn-off current. The high frequency component contained two pulse waves with the inverse phase, single frequency and high similarity, and it was weakly linear related with or not linear related the turn off current, and it was insensitive to the change of turn-off current, proving that the turn-off current was not the main cause of the high frequency component. Besides, the repeatability test was performed on another IGBT device, showing good repeatability for the experimental results.

Improved MVDC Breaker Operation by Active Fault Current Sharing (FCS) of Existing Power Converters for Shipboard Applications

In this article, an active fault current sharing (FCS) strategy is proposed to improve the dc circuit breaker (CB) operation in a breaker-based medium-voltage dc (MVdc) system. The peak turn-off current of CBs can be decreased by controlling the existing converters located in parallel with activated CBs to share the fault current. This reduction effect can be amplified from the systematic perspective since one single converter with the proposed FCS can benefit different CBs in various fault scenarios. The short-circuit fault scenarios of a shipboard breaker-based MVdc system are analyzed and the corresponding fault equivalent circuits, including power converters adjacent to CBs, are developed. The device stress of voltage-fed (VF) and current-fed (CF) converters applying the proposed active FCS strategies during short-circuit faults is derived and compared with those of passively shutdown counterparts. Finally, a downscaled experimental test bed was built to emulate a 6-kV/6-MW MVdc system fault scenarios. The experimental results are provided to verify the proposed FCS.

Comparison and Discussion on Shortcircuit Protections for Silicon-Carbide MOSFET Modules: Desaturation Versus Rogowski Switch-Current Sensor

Survivability of silicon-carbide (SiC) mosfet modules during short circuit (SC) is essential for modern power electronics systems due to large economic implications. SiC mosfet modules exhibit narrow SC withstand times and generally much lower SC robustness than silicon (Si) insulated-gate bipolar transistors (IGBTs). This puts a critical concern on their utilization, further stressing the importance of reliable protection. This article presents a comprehensive analysis and discussion on the SiC mosfet module SC protection and performance comparison between conventional desaturation detection, previously used for Si IGBT protection, and Rogowski switch-current sensor (RSCS) detection. In addition, this article presents the experimental design for soft turn-off as a reaction to the SC detection to avoid excessive overshoots during the abrupt turn-off of the SC current. To perform different types of SC with various fault inductances on different temperatures, and for the sake of fair comparison under the same conditions, a gate-driver unit for 1.2 kV SiC mosfet half-bridge modules is developed containing both detection methods. The results demonstrate that both methods are successful in protecting the module in all SC types, with superiority of the RSCS detection and concerns for desaturation detection in high-inductance and high dc-bus voltage SC events.