Turn-off Current Research Articles

A single-stage soft-switching LED driver based on CLCL resonant converter and BCM circuit for lighting application

This paper proposes a single-stage LED driver based on the CLCL resonant circuit and boundary conduction mode (BCM) boost circuit. The input voltage of an LED driver is categorized into two capacitors, which will reduce the input peak voltage by making a single-stage LED driver to work under maximum input voltage modes. The proposed CLCL resonant circuit contains a soft-switching feature where the major and minor area works under zero voltage and zero current phases, respectively. Moreover, this approach has reduced very small turn-off loss, turn-off current of a switch, which in turn proves the system efficiency. In this paper, the proposed BCM circuit, as well as CLCL resonant converter circuit, has been explained with five operational phases, and experimentation and analysis were made for proposed and existing methodologies. For validation of the proposed system, a 100 W investigational prototype is used, and experimental results were analyzed with the theoretical result.

An Optimal Variable Frequency Phase Shift Control Strategy for ZVS Operation Within Wide Power Range in IPT Systems

In inductive power transfer (IPT) systems, zero-voltage-switching (ZVS) operation within wide power range is an urgent requirement to improve system efficiency and reduce electromagnetic interference. The combination of phase shift (PS) control and variable frequency control is usually adopted to realize ZVS operation. However, in inductor-capacitor-capacitor-series (LCC-S) systems, the abovementioned hybrid strategy cannot be used directly due to nonnegligible harmonics, which result in detection difficulties or imprecise calculation of turn-off current. To solve this problem, this article proposes an optimal variable frequency phase shift (VFPS) control strategy for LCC-S systems to realize ZVS operation within wide power range. The universal harmonic-considered time-domain model of LCC-S system is deduced, and thus, the switching-moment current of power switches can be calculated accurately. Based on this value, an optimal working trajectory for ZVS operation with minimum frequency variation is presented. Finally, a 2.2-kW IPT prototype is built up to verify the universality of the deduced model and the validity of the proposed optimal VFPS control. Compared with PS control and the VFPS control based on fundamental-harmonic-approximation method, the systems realizes ZVS operation under wide power range with efficiency increase of 2.6%-6.9% and 0.8%-8.8%, respectively, and a peak efficiency of 96.4% is achieved.

A High Efficiency Model-Based Adaptive Dead-Time Control Method for GaN HEMTs Considering Nonlinear Junction Capacitors in Triangular Current Mode Operation

Gallium nitride (GaN) high-electron-mobility transistor (HEMT) has the advantages of high switching speed and low ON-resistance, which make it widely used in high-frequency applications to realize high power density. Triangular current mode (TCM) modulation has been used in GaN-based converters to simultaneously achieve high power density and high efficiency through full-range zero voltage switching (ZVS). However, as switching frequency increases, the effect of dead time becomes more significant. Meanwhile, because of the junction capacitors of GaN HEMTs, the optimum dead time changes greatly with the turn-off current. Inappropriate dead time will induce extra loss that goes against the further improvement of power density. In order to minimize the dead-time loss in GaN HEMT-based TCM converter, this article proposes a strategy of adaptive dead-time control. An accurate turn-off transient model is proposed to calculate optimal dead time with consideration of the nonlinear capacitors. Based on this model, a loss model is established to evaluate the effect of dead time involving the short circuit in dead time. A new method of drive signal generation in TCM is proposed to increase the accuracy of dead-time control and reduce the current ripple. By reusing the detection signal in TCM, the adaptive dead-time control is realized without extra sensors. The proposed model is verified by a dual-pulse test, which shows the maximum error between the calculated and the experimental turn-off time is below 3 ns. The proposed adaptive dead-time control is implemented in a GaN HEMT-based boost converter. The experimental results show that the adaptive dead-time control can improve the efficiency over all operation conditions compared with using the fixed dead time, and the total loss is reduced by 26.7% at 800-W load and 70.8% at 50-W load.

Semiresonant Half-Bridge Zeta Converter With Reduced Turn-OFF Currents for High-Efficiency Power Supply

This article presents a semiresonant half-bridge zeta (HBZ) converter for high-efficiency power supply. Since the proposed converter utilizes a primary inductor and secondary capacitor as a resonant tank, it can make a resonant operation during the on-state of a low-side primary switch. Therefore, the proposed converter can effectively reduce turn-off currents of the low-side primary switch and the secondary diode without any additional component and control scheme, which decreases turn-off switching loss and reverse-recovery loss. Moreover, the proposed converter can maintain advantages of the conventional HBZ converter such as high input/output (I/O) voltage gain and wide zero-voltage-switching (ZVS) range with the proposed design procedure. As a result, the proposed converter can improve its efficiency over the entire load conditions compared to the conventional HBZ converter. A 250 W, 300-400 V input, and 56 V output prototype has been built and tested to verify the effectiveness of the proposed converter.

Applying Stray Inductance Model to Study Turn-off Current in Multi-Turn Loop of Shallow Transient Electromagnetic Systems

The multi-turn, small loop is usually used as the transmitting loop for shallow transient electromagnetic (TEM) surveying. As an inductive load of the current inverter of the TEM system, it finds that there are serious oscillations at early part of the turn-off current. However, the existed RLC equivalent model of the loop alone fails to explain this phenomenon. In this paper, a novel current inverter for shallow TEM survey is designed and analyzed. The passive constant voltage clamping technology is used to achieve fast linear turn-off current. Furthermore, a novel stray inductance model of the current inverter is first proposed and utilized to analyze the serious oscillations of turn-off current. Based on this model, the turn-off current of the current inverter is simulated, and the simulated results agree well with the measured results of the experiment, which verifies that the proposed stray inductive model is effective and reasonable. According to the TEM principle, the high-frequency oscillations of the early part turn-off current will badly influence the shallow transient electromagnetic response. In order to suppress the oscillations of the turn-off current, two effective suppressing methods are proposed and analyzed. It will effectively enhance the electromagnetic data interpretation quality for shallow TEM survey.

A Novel Zero-Current-Switching PWM Buck Converter with Magnetic Coupling Effect

In this paper, a novel zero current switching PWM buck converter with magnetic coupling effect is proposed. The main switch in this topology turns on with zero current switching and turns off with zero current transition condition. Furthermore, the auxiliary switch turns on and turns off with zero current switching condition as well. And the main diode operates at zero voltage switching turn-on and zero current switching turn-off. In addition, extra efficiency is improved because part of the resonant energy stored in auxiliary windings of the coupled inductor could be transmitted to output load, and the resonant current is also suppressed. The soft-switching operation of the proposed converter is realized in a wide load range. The operating principles and the soft-switching conditions are analyzed in detail. Finally, a 1-kW experiment prototype is set up to validate the theoretical analysis. The related experiment results at 50 and 100 kHz are also given to verify the proposed topology.

Effect of Transmitter Current Waveform on Transient Electromagnetic Responses

Abstract —The theoretical studies and methodological guidelines for transient electromagnetic (TEM) surveys assume an ideal step turn-off of transmitter current. Yet, the pulse duration in the survey practice is nonzero: It depends on penetration depth and has economic or logistic limitations. The turn-off time, which cannot be too short for technical reasons, affects especially the late-time transient responses, while the transmitter waveform is more essential at early times. Therefore, forward calculations of voltage decay should take into account the real parameters of the turn-off ramp. Earlier it was suggested to use transmitter current of a special waveform to improve the resolution of TEM soundings, e.g., in the designed and successfully tested compensation method. In this study the problem is treated from a broader perspective, in terms of TE and TM polarization of the TEM field. The two components are excited by different sources and behave in different ways in responses of a two-layer earth with a resistive lower layer to transmitter current of different waveforms.

A Single-Stage LED Driver Based on Half-Bridge $CLCL$ Resonant Converter and Buck–Boost Circuit

A single-stage light-emitting diode driver based on interleaving buck–boost circuit and CLCL resonant circuit is proposed in this paper. The two circuits achieved an effective integration as well as kept their respective working conditions through the switch integration. Interleaving buck–boost circuit with symmetrical structure worked in discontinuous-conduction mode, achieving high power factor and low harmonic distortion. This structure can reduce the input current ripple and balance the current stress of switch at the same time. Besides, the bus voltage was also reduced. The CLCL resonant circuit has a soft-switching characteristic, the primary side operates in zero voltage mode and the secondary side operates in zero current mode. In addition, due to the small turn-OFF current, the turn-off loss of switch was also reduced. Therefore, the system efficiency was high. This paper elaborated the working mode, analysis and design method of the proposed topology. Finally, a 100-W experimental prototype was built, and the experimental results were corresponded with the theoretical analysis.

Reprocessing strategy to obtain quantitative early time data from historic VTEM surveys

While data in AEM systems such as VTEM is continuously sampled at 5 or 10 microsecond intervals, conventional processing steps in the past have not provided useful data close to transmitter current turnoff. In historic VTEM data for example, delivered data usually starts many tens or even a hundred microseconds or so after turnoff. Experiments in deconvolution of early time data at high altitude identified that the symptoms of problem early-time data were that the underlying cause had a linear phase response, resulting in a consistent exponential response in time-domain. This unwanted or spurious response is experimentally determined to be of variable amplitude, and of either sign, usually reducing the data at early delays, but occasionally enhancing the combined response. A change in processing strategy to specifically identify and subtract this additive spurious response from a valid earth response has led to the extraction of quantitative AEM data at early delays in the 10 to 20 ?s range. The process can be applied to historic data. System bandwidth limitations do of course provide a limit to the accurate sampling of the earth response at extremely early delays. More recently, hardware changes have increased the system bandwidth and reduced the need for software corrections to acquired data.

Analysis and design of a high gain non-isolated zero current switching bidirectional DC–DC converter for electric vehicles

ABSTRACTThis paper presents a dual inductor based current-fed bidirectional non-isolated DC–DC converter for energy storage applications. The main idea of this converter is to achieve a higher voltage conversion ratio by obtaining the operation of zero current switching. The proposed soft-switching bidirectional DC–DC converter reduces the turn-off switching losses with the aid of auxiliary network, where, the auxiliary network comprised with the resonant inductor and the resonant capacitor. This converter operates under two different operating modes such as a boost (discharge) and buck (charge) modes. In both the modes of converter operations, the IGBTs are operating under zero current turn-off in order to minimize the switch turn-off losses and to improve the efficiency of the converter. The principle of the operations and its theoretical analysis are validated by the experimental results using a 300W (50 V/250 V) converter system.

A 5-kW Isolated High Voltage Conversion Ratio Bidirectional CLTC Resonant DC–DC Converter With Wide Gain Range and High Efficiency

This paper presents a novel high voltage conversion ratio (HVCR) bidirectional CLTC resonant dc-dc converter. Based on inductor-inductor-capacitor (LLC), series resonant converter, and capacitor-inductor-inductor-capacitor (CLLC), the novel CLTC structure is proposed. With the use of auxiliary transformer and extra resonant capacitor, a CLTC resonant dc-dc converter can achieve zero voltage switching in all load ranges. Also, CLTC has a good gain characteristic with high power load. In this study, a review of the statuses for the isolated HVCR bidirectional converters is made. The operating principle of a bidirectional power flow in two directions is analyzed in details. In addition, by changing ac output resistance, a modified fundamental harmonic analysis (FHA) method makes the calculated gain curve more accurately than traditional FHA. Also, voltage and current stresses of power switches and resonant capacitors are given. A parameter optimization method is proposed to minimize the impedance angle of CLTC, which corresponds to less reactive power and turn-off current. The optimal parameters show advantages in voltage and current stresses. Moreover, power losses are analyzed in this study, showing advantage of CLTC in efficiency. At last, the experimental results based on a 5-kW prototype converter are presented to validate the theoretical analyses.

Parameter Optimization of Thyristor Snubber Circuit in LSTF Quench Protection System

The Large-scale Superconductor Test Facility (LSTF) is an important part of comprehensive research facilities in support of China Fusion Engineering Test Reactor (CFETR). In order to protect the superconducting magnets from being damaged in quench accident, the Quench Protection System (QPS) should be designed to commutate the energy stored in the coils. The snubber circuit is used to reduce the reverse recovery current and voltage of thyristor in QPS, and it can impact the reliability and stability of the QPS. In general, the studies of snubber circuit are focused on the DC turn-off process of thyristor used in HVDC, which has small turn-off current. However, the turn-off current can reach to 100 kA in the QPS of LSTF. In this paper, a thyristor reverse recovery model is described, and the key parameters of reverse recovery current are obtained from the testing experiment. Based on the transient analysis of snubber circuit, a systematic approach is used to minimizing the resistance and capacitance of snubber circuit of QPS working condition is proposed. By the MATLAB simulation and comparison, minimum parameters of snubber circuit were obtained, and proved that the approach can improve the reliability and stability of system, while reduce the cost of QPS.

A Hybrid Resonant ZCS PWM Converter for Renewable Energy Sources Connecting to MVDC Collection System

To relieve the tail current effect of insulated-gate bipolar transistors which are preferred in high-power applications, an approach of zero-current-switching (ZCS) for main switches is presented in this paper. Different from the large turn-off current of the main switches of the conventional zero-voltage and zero-current-switching (ZVZCS) full-bridge (FB) dc-dc converter, small turn-off current of auxiliary circuit is introduced to achieve ZCS for main switches, where the auxiliary circuit also delivers a small portion power and can realize ZVZCS. Hence, high efficiency can be achieved with the switching loss lowered remarkably. Furthermore, a hybrid resonant FB dc-dc converter is proposed, the operation principle and parameters design rules of which are analyzed in detail. A 200 V-2 kV/3 kW experimental platform has been built to verify the feasibility and performance of the proposed ZCS approach, as well as the proposed converter.

Minimum resonant capacitor design of high‐power LLC resonant converter for comprehensive efficiency improvement in battery charging application

Here, a minimum resonant capacitor design approach is proposed for the insulated-gate bipolar transistor (IGBT)-based high-power LLC resonant converter to improve its comprehensive efficiency in the electric vehicle (EV) battery charging application. The mathematical model of LLC resonant converter is established by using the first harmonic approximation (FHA) method. Then, the switching losses of IGBT-based high-power LLC resonant converter are analysed. Also, the relationship between predominant turn-off losses and turn-off current of power device IGBT is derived. To improve the comprehensive efficiency, the minimum resonant capacitor is proposed to reduce the turn-off losses, avoiding complex control or auxiliary circuit. Finally, the proposed approach is verified by a 2 kW LLC resonant converter prototype with 690 V DC input voltage and 75–150 V DC output voltage. Experimental results show the comprehensive efficiency of the prototype is up to 93.7%.

Voltage slope‐based zero voltage switching detection method for wireless power transfer systems

A zero voltage switching (ZVS) detection method, which relies on the half-bridge output voltage slopes during the MOSFET turn-on and turn-off transient processes, is proposed for the wireless power transfer (WPT) systems in this Letter. A voltage slope detection circuit and its active control method are also proposed to convert the nanosecond transient signal to a steady voltage level, which can be handled by the microcontroller easily. By having the information of the turn-on and turn-off voltage slopes, the state of ZVS can be evaluated to optimise the switching losses. A 500 kHz, three-coil resonant WPT system is built in order to evaluate the performance of the proposed detection method. Experimental results show that the ZVS state can be detected effectively. Also, the turn-off current can be controlled to a constant value to optimise the switching losses under the load and parameter variations.

Half‐bridge flyback converter with lossless passive snubber and interleaved technique

Hard-switching flyback converters are widely used in the low power application but suffer from high electromagnetic emissions, current ripples, and low efficiency. To overcome these problems, a half-bridge flyback converter with a new lossless passive snubber is proposed using an interleaved structure. All switches of the proposed converter turn on under zero current switching and turn off under zero voltage switching which decreases the switching losses and electromagnetic interference (EMI). Theoretical analysis of the proposed converter is presented and verified by the experimental results of a 200 W prototype. In addition to the 7% efficiency improvement, the proposed converter has lower EMI in comparison with its hard-switching converter.

Investigation on Current Crowding Effect in IGBTs

This paper investigates the influences of various topside cell structures of insulated gate bipolar transistor (IGBT) on the current crowding effect during high current turn-OFF by symmetrical multicell numerical simulations. It is observed that lower breakdown electric field in the drift region can reduce the negative differential resistance in the forward blocking curve and therefore suppress the current crowding effect during high current turn-OFF. We refer to this characteristic as the self-suppressing current crowding effect (SSCCE). Different topside cell structures of IGBT have considerable influence on the SSCCE. A modest increment of the SSCCE by proper topside structure design provides an alternative solution to improve the ruggedness of IGBT, especially for the strong punchthrough or low current gain IGBTs.

Simulation and analysis of the effect of ungrounded rectangular loop distributed parameters on TEM response

An ungrounded loop in the shallow subsurface transient electromagnetic surveys has been studied as the transmission line model for early turn-off stage, which can accurately explicate the early turn-off current waveform inconsistency along the loop. In this paper, the Gauss-Legendre numerical integration method is proposed for the first time to simulate and analyze the transient electromagnetic (TEM) response considering the different early turn-off current waveforms along the loop. During the simulation, these integral node positions along the loop are firstly determined by solving these zero points of Legendre polynomial, then the turn-off current of each node position is simulated by using the transfer function of the transmission line. Finally, the total TEM response is calculated by using the Gauss-Legendre integral formula. In addition, the comparison and analysis between the results affected by the distributed parameters and that generated by lumped parameters are presented. It is found that the TEM responses agree well with each other after current is thoroughly switched off, while the transient responses in turn-off stage are completely different. It means that the position dependence of the early turn-off current should be introduced into the forward model during the early response data interpretation of the shallow TEM detection of the ungrounded loop. Furthermore, the TEM response simulations at four geometric symmetry points are made. It shows that early responses of different geometric symmetry points are also inconsistent. The research on the influence of turn-off current position dependence on the early response of geometric symmetry point is of great significance to guide the layout of the survey lines and the transmitter location.

Development and optimization of 4.5kV IGBT for power system

In this paper, a 4500V IGBT is investigated by device simulation. The substrate resistivity and thickness of 4500V IGBT are determined by simulation, and the appropriate implantation dose of field stop layer is determined by the simulation. The test results show that the device can not meet the application requirements of power system, so we optimize the key parameters such as saturation voltage and safe operating area. The optimized device was fabricated and the experimental results show that the breakdown voltage is 6110V, the saturation voltage is 2.6V, and the maximum controllable turn-off current is 160A, which can well meet the simulation expectation and application requirements of power system.

Modeling, control, and implementation of the soft switching dc-dc converter for battery charging/discharging applications

This paper presents a soft switching bidirectional buck-boost converter for battery charging and discharging systems. The proposed method comprises of Inductance Capacitance Diode combination of the bidirectional dc-dc converter with one more electric switch is presented to accomplish high efficiency, high conversion ratio and maximum output power compared to the other bidirectional converters. It works in both steps up and steps down conversions. The proposed converter has alleviated the switching stress problems in the conventional bidirectional dc-dc converter. It suppresses the switching losses by zero voltage and zeroes current turn ON and OFF all switches. The complete steady-state analysis of the proposed bi-directional converter has described with its operating modes. Design consideration of parameters also presented to realize the converter characteristics. The switching stress on the power semiconductor devices is given, and the comparisons between the proposed technique and other bidirectional converters are illustrated with some results. Finally, the experimental prototype of 20 kHz, 315 W output power converter developed, and its feasibility verified through computer simulation results.