Leakage Inductance Research Articles

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.

Forward-Based DC-DC Converter With Eliminated Leakage Inductance Problem

Forward-Based DC-DC Converter With Eliminated Leakage Inductance Problem

Magnetic Integration for a Dual Active Bridge Converter Planar Transformer with Accurate Leakage Inductances Estimation

Magnetic Integration for a Dual Active Bridge Converter Planar Transformer with Accurate Leakage Inductances Estimation

A new soft‐switching high gain DC/DC converter with bipolar outputs

AbstractThis paper introduces a new single‐input multi‐output step‐up DC/DC converter with soft‐switching performance and low input current for renewable energy applications. The proposed topology uses a three‐winding coupled‐inductor (TWCI) and voltage multiplier circuits to achieve high voltage gains. The bipolar output voltages of the proposed converter can be varied independently by tuning the turns ratios of the TWCI. Due to the semi‐trans‐inverse specification of the suggested topology, high voltage gains can be obtained under a lower number of turns ratio in the magnetic device. Furthermore, a regenerative passive clamp technique mitigates the voltage stress on the single power switch. Additionally, the power dissipations are further reduced by considering a resonant tank in the circuit. In the converter, the parasitic leakage inductances of the TWCI windings help to provide the soft‐switching conditions for the switch and also to eliminate the reverse‐recovery loss for all converter diodes. The operating mode of the presented converter has been introduced and the steady state, along with the main operating equations have also been derived. Finally, the theoretical analysis is verified by a sample prototype 235 W at the input voltage 25 V and outputs of 200 V and −200 V.

Design and implementation a novel single switch high gain DC-DC converter based on coupled inductor with low-ripple input current

A novel high-gain and high-efficiency direct current to direct current (DC-DC) converter is introduced in this paper. The presented converter is suitable for low-voltage renewable energy resources such as photovoltaic (PV) and fuel cell (FC). The existence of series inductance with the input source ensures continuous and low-ramp input current, which is important for extracting maximum power from resources. Using coupled inductor technology and an intermediate capacitor in the suggested converter leads to a high gain voltage. In the presented topology for recovering energy from the leakage inductor, reducing voltage stress on the power switch, and so decreasing overall converter losses, a passive clamp circuit is used. The suitable operation range of duty cycle in the converter, besides the leakage inductor, decreases the problem of reverse recovery in diodes. The low value of the leakage inductor and the low volume and cost of the proposed converter are due to the low turn ratio of the coupled inductor. Details of the operation principles of the proposed converter have been discussed in this paper. The presented simulation and laboratory prototype results verify the theoretical analysis and performance of the suggested topology.

Analytical Double-2D Frequency-Dependent Leakage Inductance Model for Litz-Wired High-Frequency Transformer

Accurate and fast calculation of frequency-dependent leakage inductance is critical for the optimization of the high-frequency transformer with Litz wire winding. The analytical method is widely used due to its high computation speed. However, its computation accuracy is limited due to the following factors. i) One-dimensional (1D) or two-dimensional magnetic field model (2D) has unsatisfying accuracy for the transformer with a rotationally asymmetric structure. ii) The skin and proximity effect factors based on the multilayer foil winding are inaccurate for the Litz wire winding in the calculation of frequency-dependent magnetic energy. This paper proposes a double-2D frequency-dependent leakage inductance model for the transformer with Litz wire winding. It uses the image method to calculate the 2D leakage magnetic field inside and outside the core window, respectively, which considers the rotationally asymmetric structure in leakage inductance calculation. The round conductor model is proposed for the frequency-dependent magnetic energy calculation. The single strand in a Litz wire is taken as the basic modeling object of the round conductor model, which is more detailed than the multilayer foil winding model for the Litz wire winding. The comparison between the experiment, FEM, state-of-the-art models and the proposed model is conducted for eight transformers with E-core, U-core, round or rectangular Litz wire winding. The proposed model shows satisfying computation accuracy in the whole frequency band. And the computational speed of the proposed model is 100 times that of the FEM.

Grid‐tied PEMFC power conditioning system based on capacitor voltage thorough feedback procedure in a weak and harmonics‐polluted network

AbstractProton exchange membrane fuel cells (PEMFC) have been noticed by researchers due to their high efficiency, low pollution, and high‐power density in distributed generation systems. In this paper, an LCL‐type grid‐tied PEMFC fuel cell power conditioning system is evaluated in a harmonics‐polluted low‐voltage grid. The LCL‐filters can lead to resonance and instability despite their capability to attenuate harmonics. In this research, a transformer has been used to connect the fuel cell inverter to the grid. The grid‐side inductor of LCL‐filter is realized by the leakage inductance of the transformer. In addition, for more effective resonance damping and attenuation of current ripples caused by the grid voltage harmonics, a capacitor voltage comprehensive feedback control has been designed and investigated. The comprehensive feedback control of the capacitor voltage contains proportional, first and second‐order derivative terms. In the proposed control scheme, the capacitor‐current‐feedback is opposed by the capacitor voltage derivative term due to reverse loop gain, which leads to deleting both of these loop gains. As a result, there is no need to utilize a current sensor in this control method. Consequently, the proportional and second‐order derivative terms of the capacitor voltage attenuate the LCL‐filter resonance. A low‐pass filter is also considered in the second‐order derivative loop in the controllable frequency range to ensure system stability. The simulation results of the PEMFC power conditioning system in different conditions confirm the proper attenuation of LCL resonance of grid‐tied inverter, high‐quality current injection to the harmonics polluted grid, the suitable stability, and the appropriate dynamic response for the proposed system. Under the proposed control scheme, the fuel cell power conditioning system demonstrates satisfactory stability. Even when reducing the LCL filter values by 5%–20%, the system maintains its stability effectively. Moreover, the THD of the injected current into the grid, employing the proposed control strategy, has been successfully reduced to an impressive value of 1.97% in a weak and harmonical grid.

Soft switching modulation strategy based on bipolar (PSM) with improved efficiency in high-frequency link inverters

High Frequency-Link (HFL) Inverters have been employed to integrate renewable energy sources into utility grids and electric vehicles. The soft-switching range of High-Frequency Link Inverters (HFLI) is increased using auxiliary inductors and capacitors. The application of auxiliary components increases the conduction loss and the complexity of the circuit. The literature indicates that the existing soft-switching methods suffer from higher duty cycle loss, voltage spikes, and lower efficiency owing to the resonance between the parasitic capacitance of switches and the leakage inductance of the transformer. Therefore, it is imperative to develop a modulation strategy that can improve the efficiency of HFLI. In this context, the proposed study develops a cycloconverter-type High-Frequency Link Inverter (CHFLI) based on a Bipolar Phase Shift Modulation (BPSM) strategy without the use of auxiliary components. The proposed modulation strategy enables the semiconductor switches to operate under zero voltage switching. The full-bridge inverter and Full Bridge Active Clamper Circuit (FBAC) switches operate at the same gating signals with a constant duty cycle of 50%. The proposed topology uses built-in magnetizing inductance to achieve zero voltage switching and reduce the duty cycle loss. The leakage energy is recycled from the output filter inductor to the load side using the FBAC. The results indicate that the proposed modulation strategy achieves ZVS and simultaneously achieves an efficiency of 95%. The proposed modulation strategy is easy to implement and does not require complex circuitry.

A New Soft-switched Flyback Converter with a Minimum Number of Elements and High Efficiency

Background: This paper proposes a new soft-switching flyback converter with a simple structure and high efficiency. The proposed converter has zero current switching conditions for the turning-on distance and zero voltage switching conditions for the turning-off distance of the switch. Objective: With a minimum number of elements, a soft switching condition is created for all semiconductor devices, and high efficiency is obtained. Methods: To create the ZCS condition, an inductor is used, and when the switch is turned on, the current due to the existence of this inductor increases slowly. But when the switch is turned off, this inductor has an energy that suddenly discharge on the switch, which is then controlled by a capacitor and discharged in capacitor. Then when the energy is discharge in capacitor, this capacitor is connected to the switch, which increases the voltage of the switch slowly and ZVS condition is stablished. Also the energy of leakage inductance in this state is discharged in that same capacitor which eliminates destructive effect of this inductor. Results: A prototype of the proposed converter is implemented and tested in 60 W power. The experimental results verified theoretical analysis and shown that soft switching condition is established. Also 92% efficiency at full load is obtained, which shows the efficiency has increased. The current of the diodes in experimental results shows that when the diodes are turned off, ZCS condition is created, therefore reverse recovery problem of the diodes does not exist. Conclusion: Therefore, the proposed converter has high efficiency and simple structure, which is suitable to convert AC voltage to DC voltage for the devices power supply.

Performing Wind System with Rectifier with Near Sinusoidal Input Current

The RNSIC-1 (rectifier with near sinusoidal input currents converter), is the foundation of a wind generator system that is presented. The three inductances that make up a traditional RNSIC–1 converter are eliminated in the proposed arrangement, and the SCIG generator's leakage inductances fill their place. This is what makes it new. The wind system's role in the load currents is discussed. Lower power losses, smaller harmonic input currents, fewer EMI issues, excellent dependability, and cheaper costs are characteristics of the new wind system. This new wind system could be used for partial variable speed wind turbines (usually 70% to 100% synchronous speed) and lower hydro connector squirrel cage induction generators (SCIG).

Short‐circuit current difference of parallel strands in winding turns and its influence on the distribution of electromagnetic force

AbstractTransformer winding turns often consist of multiple parallel strands. The spatial position variation of each strand affects the leakage inductance of each branch, resulting in an uneven distribution of short‐circuit currents within the winding turns. And this unevenness persists even when transposition structures are implemented. Traditional methods in transformer analysis frequently overlooked the distribution characteristics of short‐circuit currents when calculating electromagnetic forces. A frequency‐domain calculation method for analysing the current distribution in winding turns was proposed, with a deviation of less than 3% compared to existing analysis methods. Two typical 110 kV transformer models were utilised to investigate the influence of uneven current distribution on the spatial distribution of electromagnetic forces. The spatial distribution of short‐circuit electromagnetic forces in low‐voltage (LV) windings exhibited significant changes, with maximum change rates of 10% and 61.2% for axial and radial electromagnetic force, respectively, in a LV winding with 4 parallel strands. The research also analysed how strand radial width and axial height affect current distribution unevenness and proposed specific design principles to mitigate these disparities in winding design. The findings offer valuable insights for selecting structural parameters and assessing short‐circuit stability during transformer design.

A series inductance based three-port isolated hybrid DC–DC converter for microgrid applications

The paper proposes a series inductance based three-port isolated hybrid converter (3PIHC) for wide change in voltage transformation ratio (VTR) which supports DC microgrid applications. Three-ports in the proposed converter is integrated by means of a three-winding high frequency transformer (HFT). The leakage inductance of three-winding HFT acts as an energy transfer element between the ports. The factors which need to be considered for designing the leakage inductance are power transfer flexibility and limits of current transfer at wide change in VTR. In a feasible scenario, the intricate aspects such as inconsistency of leakage inductance, requirements of power flow variability and current restrictions necessitates auxiliary inductors in series with the three-winding HFT. This paper focuses on selecting appropriate value of series inductance for 3PIHC based on the application demand and minimized converter losses. Study and analysis are carried out to evaluate the converter performance at certain values of series inductance which is the sum of leakage inductance of HFT and auxiliary inductance. A hybrid configuration is adopted in the proposed converter where the primary port holds multi-level half bridge structure which reduces the voltage stress across the transformer primary winding and semiconductor switches. The secondary and tertiary port occupies H-bridge circuit topology. Converter analysis is presented for both conventional phase-shift modulation (CPM) and dual phase shift modulation (DPM). A simple computational method for obtaining the phase-shift variables at minimum value of current stress is developed. Evaluated the converter current stress for various values of series inductance and at wide change in VTR. A prototype of the proposed converter is implemented and examined. The experimental results demonstrated authenticates the accuracy of theoretical analysis.

Interturn Fault Detection in Induction Machines Based on High-Frequency Injection

An interturn short-circuit in the stator windings can lead to the breakdown of electrical machines. In the case of induction machines, several fault detection methods and faulted models have been developed in the recent decades. These models differ mainly in how the leakage inductances of the faulted winding are modeled. This work provides a generalized model for interturn short-circuit faults, using different assumptions for the leakage inductances. The model is validated with experimental results for an exhaustive set of fault parameters, and the leakage inductances influence is analyzed. Moreover, the model is used to analyze the drawbacks of the negative-sequence fundamental current as a traditional fault signature. A high-frequency injection method for converter-fed machines is presented to overcome these limits. The proposed fault signature is the negative-sequence current at the injection frequency and it is evaluated experimentally at different operating conditions. The fault severity and its location are proved to be related to the proposed fault signature.

A Novel Isolated High-Step-Up Interleaved Converter for Renewable Energy Systems

In this paper, an isolated high step-up interleaved converter for renewable energy systems is proposed. The input-parallel configuration introduced by two energy storage inductors, which can disperse the input current, reducing conduction losses and also improve the conversion efficiency. In order to improve the voltage gain and recover the energy stored in the leakage inductance, the auxiliary step-up structure is utilized in the proposed converter, that including an auxiliary inductor, an auxiliary capacitor, a voltage multiplier capacitor and two switches which serve to exchange the energy stored in auxiliary capacitors and inductors. On the secondary side, a voltage-doubler circuit is used to extend the voltage gain. Finally, a 48V-input, 400V-output and the rated power of 500 W prototype is implemented to verified the effectiveness of the proposed converter. The experimental results shows that the maximum efficiency is 95.97%, and the efficiency of full-load is 93.27%.

Comparative Analysis and Optimization of Triple Active Bridge Transformer Configuration With Integrable Leakage Inductance

Comparative Analysis and Optimization of Triple Active Bridge Transformer Configuration With Integrable Leakage Inductance

Study of the Protection and Energy Transmission Modes of One Phase Short Circuit to Ground in Inverters.

Research indicates that phase-to-ground short-circuits in a frequency converter can subject the rectifier diode and IGBT to excessive voltage and current, potentially causing damage if the component selection margin during hardware design is insufficient. In order to solve the above problems, this paper studies the design of the LCL filter and ground short circuit problem of the hundred-kilowatt inverter. Firstly, an analytical method for calculating the DC bus capacitance and reactor of the inverter is proposed. The interaction between the DC bus capacitance and the reactor parameters and performance is considered in the implementation process. The parameters of the DC bus capacitor and reactor are given. Secondly, the one-to-ground short circuit of the inverter is studied, and the energy flow mode and mathematical expression of the double boost circuit, considering the influence of the leakage inductance of the power transformer, are given. Based on the above analysis, a method for determining the rectifier diode and IGBT, considering the one-to-ground short circuit of the inverter, is proposed. Finally, a one-hundred-kilowatt inverter is developed, and the corresponding experiments are carried out. The feasibility of the proposed scheme is verified by simulation and experiment.

High-frequency transformers optimized design for power electronic transformers

Because of its small size, high frequency transformers are widely used to maximize energy transfer. However, the leakage inductance and distributed capacitance of high frequency transformer can not only cause resonance, but also lead to transient changes of voltage and current in high frequency, which can lead to voltage spike, so that the switch tube is damaged. For transformers with the same output power, high-frequency transformers are much smaller and have lower calorific value than low-frequency transformers. Therefore, at present, many consumer electronics and network product power adapters are switching power supplies, and the internal high-frequency transformer is the most important component of switching power supplies. The basic principle is to turn the input alternating current into DC first, and then turn it into high frequency through a transistor or FET, etc., through a high-frequency transformer to change voltage, and then rectify the output again, plus other control parts, and stabilize the output DC voltage. In this thesis, we choose a more rational and cost effective winding structure, choose a more appropriate core material based on the comparison of different core materials, research on the insulation and cooling properties of transformer so as to improve the insulation properties of the transformer, make it safer and more efficient. The study has important significance to decrease the power loss of high frequency transformer and decrease the size of high frequency transformer.

Isolated high step‐down DC–DC converter with current‐doubler rectifier for ultracapacitor charger applications

SummaryAn isolated high‐efficiency, high step‐down converter for ultracapacitor charger is presented. The proposed converter utilized the structure of switched inductors and combined the current‐doubler synchronous rectifier, which can reduce the secondary circulating currents. In addition, the energy of the leakage inductance can be recycled to reduce the voltage stresses of the switches. Therefore, the proposed converter can supply the requirement of charging high current, and keep converting high efficiency at the same time. The maximum efficiency of the proposed converter reaches 96.53% at 350 W, and the full load 1 kW is 94.31%, in the case of input voltage 380 V and output voltage 14.6 V. Finally, a 250 F ultracapacitor is charged by the proposed converter from 0 to 14.6 V with constant current (CC) and constant voltage (CV) modes in 1 min. The proposed converters can prove their feasibility by experimental results.

Toward a simple topological model of a three-phase transformer including deep saturation conditions

PurposeThis paper aims to propose a method of parametrizing topological transformer model at high flux densities in the core.Design/methodology/approachThe approach proposed is based on terminal voltages and currents measured in a special purpose saturation test whose data are combined with typical saturation curves of grain-oriented electrical steels; the modeling is carried out in the ATPDraw program.FindingsThe authors corroborate experimentally the necessity of dividing the zero sequence impedance between all transformer phases and propose a method of the individual representation of the legs and yokes. This eliminates the use of nonexistent leakage inductances of primary and secondary windings.Practical implicationsThe presented modeling approach can be used for predicting inrush current events and in the evaluation of the impact caused by geomagnetically induced currents (GICs).Originality/valueThe proposed approach is completely original and will contribute to a better understanding of the transients occurring in a transformer under abnormal conditions, such as inrush current events and GICs.

Design and analysis of quasi-resonant high-gain impedance source DC–DC converter for DC microgrid

ABSTRACT This paper presents a quasi-resonant, isolated, high-gain, Y-source, DC/DC converter for a DC microgrid. Here, quasi-resonance is obtained by the LC tank during the shoot through period, resulting in natural commutation at the turn-off instant of the MOSFETs. The LC tank is formed by an additional parallel capacitor and transformer leakage inductance. The high voltage gain is obtained by including an isolation transformer with lower turns ratio, coupled inductor and voltage doubler. Here, frequency is modulated to regulate the output voltage with ON period constant. This converter’s zero current switching feature allows it to operate at a higher switching frequency and thus enhances the power density and efficiency. This converter’s continuous input current feature is an added advantage. The proposed converter inherits all the benefits of traditional impedance source converters. Finally, a 250 W hardware prototype is developed, and its performance is tested in the laboratory.