Isolated Power Converter Research Articles

Modeling, Analysis and Mitigation of Radiated EMI Due to PCB Ground Impedance in a 65 W High-Density Active-Clamp Flyback Converter

This paper first reviewed the modeling and prediction techniques for the radiated electromagnetic interference (EMI) in active-clamp Flyback (ACF) power converters. An improved radiated EMI model was then developed including the PCB ground impedance based on the ACF converter under investigation. Next, the improved radiated EMI model was quantified and experimentally verified. Two mitigation techniques were developed for the radiated EMI based on the improved model. Experiments were conducted to verify the developed analysis and mitigation techniques for the radiated EMI. The proposed modeling and mitigation techniques were finally extended to other isolated power converter topologies.

A Variable-Mode Bidirectional Isolated Power Converter for Wide Voltage-Transfer Ratio Applications

Lithium battery charging require a wide voltage gain range. Due to the limited voltage gain range of LLC converter, it is limited in battery storage application scenarios. In this paper, A interleaved parallel LLC converter is proposed to realize the charging and discharging processes of bidirectional battery energy storage systems. The converter extended range of voltage gain required for battery recovery area by mode switching control. For the interleaved parallel mode power equalization problem, a gain compensation control strategy is proposed to solve the power equalization problem of the converter in this mode. This results in more uniform thermal and current stresses on the charger, as well as smaller input and output ripple. Moreover, with the proposed variable-mode control strategy, the efficiency of the charging process remains above 90%. A 1.5-kW experimental platform was developed to validate the performance of the proposed converter.

Design of a Power Converter for Solar Energy Storage System

This paper presents a single-stage three-port isolated power converter that enables energy conversion among a renewable energy port, a battery energy storage port, and a DC grid port. The proposed converter integrates an interleaved synchronous rectifier boost circuit and a bidirectional full-bridge circuit into a single-stage architecture, which features four power conversion modes, allowing energy adjustment for both the renewable energy and the battery storage energy ports when power is supplied by the renewable energy port. It also features bidirectional functionality that allows the battery storage energy port to provide energy storage through the DC grid port, thereby providing uninterrupted power supply functionality. The converter uses four power switches and two inductors to boost and convert energy from the renewable energy port to the battery storage energy port or to the DC grid port through the bidirectional full-bridge circuit. The converter is also capable of 1 kW power energy conversion by utilizing an adjustable duty cycle with a fixed frequency of 100 kHz and phase-shift control through a built-in pulse width modulation control module of a TMS320F28 series digital signal processor. According to the experimental results, the converter developed in this study can achieve a conversion efficiency of up to 94%.

AC Resistance and Leakage Inductance Estimation for Planar Transformers With Parallel-Connected Windings

Regarding the ever-increasing switching frequency of power converters, there is a lack of tools to perform a quick and effective optimization of the high-frequency transformers embedded in isolated power converters. Indeed, at high operating frequency, the geometry of the core and windings deeply impacts the overall transformer performance. Specifically, assessing accurately the current distribution in parallel-connected windings is a challenging and key issue. Winding parallelization, frequently implemented in low-voltage and high-current applications so as to decrease Joule losses, may be an ineffective solution because of skin and proximity effects. They create an unbalanced current distribution in the parallel-connected windings, which greatly impacts the ac resistance and leakage inductance of the transformer. This article proposes an innovative frequency analytical model permitting to simply and accurately compute the current distribution in the transformer windings, the ac resistance, and the leakage inductance. The proposed approach is comprehensively presented, validated using both measurements and two-dimensional finite element analysis and analyzed giving guidelines to engineers designing high-frequency transformers.

Quantitative analysis of common‐mode current in flyback converter with balance winding

AbstractThe balance winding of the transformer is a compact and flexible technique for the common‐mode (CM) noise reduction of isolated power converters. A proper design of the grounding and turn number of the balance winding will generate an inverse displacement current to balance the CM noise flowing through the transformer. However, a trial and error process to find the optimum design is necessary for practical applications due to the unexplored source of calculation errors. In this paper, a quantitative analysis method of CM currents flowing through all the paths between windings is proposed for error quantifications. Based on an interleaved transformer, the capacitances are extracted with the help of electric field simulations, and the contribution of each path to the CM noise is analysed. Although the paths between adjacent layers are dominant in the CM noise, it is proved that ignoring non‐adjacent inter‐layer paths will lead to calculation errors due to the high voltage difference even with low capacitances. As both the application and verification of the proposed quantitative analysis method, the accurate evaluation of noise reduction effects and determination of the optimum balance winding turns can be achieved in experiments.

An Active Clamp Flyback Converter With High Precision Primary-Side Regulation Strategy

The active clamp flyback (ACF) converter has been widely adopted because of the feature of isolation, soft-switching, and high conversion efficiency. On the other hand, due to the characteristic of the circuit cost reduction and the fast control response, the primary-side regulation (PSR) has become a popular control method for isolated power converters. However, high precision PSR strategies for ACF converters are not exposed. Therefore, the aim of this article is to propose a high precision PSR strategy for the ACF converter. Relations between the primary-side current and the secondary-side current are analyzed and derived. Both of the continuous conduction mode operation and the discontinuous conduction mode operation will be considered. The output voltage control mode or the output current control mode can be selected via the proposed strategy. In addition, a secondary-side losses compensation (SSLC) strategy is developed to deal with the non-ideal circuit characteristics as well as to enhance the control accuracy. Operational principles and thorough mathematical derivations will also be revealed. Finally, both simulation and experimental results obtained from a 100 W prototype circuit demonstrate the performance and feasibility of the proposed PSR and SSLC strategy. Validations show that the control accuracy of the output voltage and the output current are 98.54% and 98.42%, respectively.

Evaluation of Transformer Leakage Inductance Using Magnetic Image Method

Leakage inductance is a critical design element of a transformer in a galvanically isolated power converter. For multi-objective optimization-based designs of power converters, analytical leakage inductance models that are computationally efficient and accurate are preferred over the finite element methods (FEMs). In this article, three new analytical models are proposed—triple-2-D, double-2-D, and single-2-D—that are formulated using the magnetic image method. These 2-D models are used to calculate the leakage inductance of a partially filled shell-type transformer having a circular center leg, and the resulting errors are less than 1.25% for each model when compared to the 3-D FEM simulated value of the leakage inductance. Additionally, three different conductor models are considered, and their relative accuracies and computational efficiencies are investigated. Furthermore, a variable inductance transformer (VIT) is designed, whose leakage inductance can be modified by moving one of the windings vertically along the central core leg. The analytically evaluated variable leakage inductances of the VIT are in good agreement with the 3-D FEM simulated and experimentally measured values.

Advances in High-frequency Isolated Power Converters

Advances in High-frequency Isolated Power Converters

Hybrid Passive Cancelation Method for Reducing Common-Mode Noise in Isolated Power Converters

The shielding technique is an effective method for reducing the common-mode (CM) electromagnetic interference in an isolated power converter. However, the interwinding capacitance between the shielding layer and its adjacent winding provides the path for CM noise current. This CM noise current can be suppressed by making the averaged electric potential (AEP) of the shielding layer and its adjacent winding be equal. In this article, a balancing winding is introduced to be connected with the shielding layer for adjusting the AEP of the shielding layer to be equal to that of its adjacent winding and, thus, canceling the CM noise current. Furthermore, the hybrid passive cancelation (HPC) method is proposed in which the balancing winding is reused as the compensation winding to generate the compensation voltage for canceling the noise current flowing through the parasitic capacitance between the high dv / dt node in the primary circuit and protective earth. The proposed shielding technique with balancing winding and the HPC method are verified by the experimental results.

Design and characterisation of advanced magnetic material‐based core for isolated power converters used in wave energy generation systems

The oceanic wave energy generation has been drawn significant attention in the field of power engineering recently. These generation systems are basically direct drive electrical power generators connected to the wave energy devices with the variable frequency drives (VFDs). This study proposes an application of high-frequency transformers at the output stages of VFDs for the galvanic isolation purpose among multiple output ports of VFDs in a wave farm. The design process of a high-frequency magnetic link involves multiphysics problems that entail complex tradeoffs between electrical and magnetic properties including efficiency. Moreover, the performance of the magnetic link depends on the switching characteristics of the power switching devices and various excitation signals. Therefore, extensive multiphysics research in the field of design and optimisation of magnetic links is needed to develop next-generation technologies. In this study, a finite-element method-based systematic process is presented for the design of amorphous alloy-based core of the high-frequency magnetic link. Two cores are developed and characterised in the laboratory. The characterised data obtained from the experiment can be used in the future design optimisation of other high-frequency magnetic links.

Independent high voltage DC source development for renewable-grid integration interface

<span>Recent advancement in renewable-grid integration research, due to the concern on the environmental impact, leads to extensive study in isolated power converter as their interface. As part of isolation capability in power converter interface, extensive study of magnetic component has been carried out, especially on the design, construction and optimisation to achieve optimal operation. One of the main issue in verifying the analytical power loss model is to have independent HVDC link power source for an experimental validation work. This paper focus on the design and construction of DC link source, to be use in the experimental rig setup. Several DC link source option has been evaluated, and TDK-lambda PF500-360A power supply was selected due to the availability and excellent energy efficiency offered, at better price. External circuit is designed and implemented to achieve desired voltage and current supply characteristic. At the end, the voltage and current of the DC link supply for Dual H-bridges is obtained and shown promising result for experimental rig measurement and data collection work.</span>

Investigation of Radiated Electromagnetic Interference for an Isolated High-Frequency DC–DC Power Converter With Power Cables

To analyze the radiated electromagnetic interference generated by isolated power converters, this paper proposes a technique to develop a general radiation model for the converters. The radiated electric field can be predicted from the developed model. The interaction between the impedance of the converter and the undesired antenna in the converter's power delivery paths is explored in detail based on the developed model. Moreover, a dual active bridge converter is taken as an example to demonstrate the developed modeling technique based on the converter's topology. The radiated electric field of the dual active bridge converter is predicted from the developed model. Experiments are conducted to validate the developed model and the predicted interaction between the converter impedance and the undesired antenna impedance in the power delivery paths.

DC-AC Isolated Power Converter Array. Focus on Differential Mode Conducted EMI

This paper introduces the implementation of a DC–AC step up isolated converter from associations of bidirectional Conversion Standard Cells (CSCs). The designed multi-cell converter is an array of standardized converter cells. It is described and then compared to a reference converter with respect to differential mode conducted electro-magnetic interference (EMI). The paper outlines the motivation for developing a generic multi-cell approach before underlining the benefits from the point of view of conducted EMI when implementing power converter arrays (PCAs). In particular, it is shown that in PCAs, the differential mode (DM) EMI filter can advantageously utilize distributed CSCs, making it possible to use very low value AC inductors to filter the AC current ripple. Experimental results are provided to validate the analysis carried out in the paper.

Design optimisation of an inductor‐integrated MF transformer for a high‐power isolated dual‐active‐bridge DC–DC converter

Medium-/high-frequency isolated power conversion systems are continuously evolving towards higher power densities. A comprehensive design strategy is required to find a medium-frequency (MF) transformer design that maximizes efficiency and power density while complying with material, electrical, and temperature limits. The proposed approach takes the optimum size of winding conductor conducting harmonic currents into account. The influence of the winding interleaving configuration on the leakage magnetic field is discussed and a method to tune the leakage inductance in a transformer is proposed. A novel semi-empirical expression providing an improved accuracy of an AC resistance factor is introduced. Two well-known configurations of transformers utilised in MF high-power applications are also investigated, namely shell type and core type. The design methodology is established based on the parameter sweep method, and many candidate solutions are enumerated and tested one by one to determine the solution set that satisfies various constraints. Two prototypes of 5 kHz/10 kW nanocrystalline-based transformers are designed and manufactured. The results show that the natural-cooled shell-type prototype can reach a power density of 17.6 MW/m 3 at an efficiency of 99.36%, and the natural-cooled core-type prototype can reach a power density of 14.2 MW/m 3 at an efficiency of 99.33%.

PV Micro-Inverter Topology Using LLC Resonant Converter

In this paper, a DC–single-phase AC power converter with an LLC resonant converter is presented for a photovoltaic (PV) micro-inverter application. This application requires the leakage current suppression capability. Therefore, an isolated power converter is usually combined for DC/AC systems. The LLC resonant converter is the one of the isolated power converter topologies, and it has good performance for conversion efficiency with easy control. On the other hand, a double-line frequency power ripple has to be compensated for in order to improve the performance of the maximum power point tracking (MPPT). Therefore, a bulky electrolytic capacitor is usually necessary for the power converter. However, the electrolytic capacitor may limit the lifetime of the micro-inverter. This paper introduces the PV micro-inverter with a LLC resonant converter. In addition, the active power decoupling circuit is applied in order to compensate the double-line frequency power ripple by the small capacitor in order to eliminate the electrolytic capacitor. Finally, the transformer design is considered in order to reduce the transformer losses. As a result, the conversion efficiency of the LLC converter is improved by 1% when the litz wire has many strands.

A Combined Topology With Coupled LLC Resonance for Wide-Range Operation

This paper proposes a topology combination scheme to achieve wide-range operation for LLC resonant converters. Instead of directly adding an auxiliary current injection circuit for each individual LLC converter, the proposed scheme combines two LLC converters through coupled resonance. Then, one LLC circuit can be utilized to adjust the equivalent resonant parameters of the other LLC circuit. By only controlling the phase delay between the mosfet bridges, output voltage regulation is properly maintained without changing the switching frequency. Since the total power rating does not change and each converter can share the load, it does not have any extra cost of power components. The advantages of this design include higher power efficiency, smaller size, and optimized utilization of each converter at different load, since both converters can fulfill isolated power conversion with independent control. Also, by taking the benefit of suppressed frequency variation, a smaller leakage inductance and a lower ratio between the leakage inductance and the magnetizing inductance are allowed, so that the coupling of transformer windings and transformer efficiency just improve. In addition to detailed theoretical analysis, experimental results verify the feasibility and effectiveness of the proposed concept.

A General Transformer Evaluation Method for Common-Mode Noise Behavior

In isolated power converters, the transformer is a key part of voltage transformation and isolation. Since common-mode (CM) noise is rather difficult to suppress compared with different-mode (DM) noise, more and more scholars are paying attention to the characteristics of CM noise, especially in high-frequency CM noise behaviors. CM noise can be further divided into conducted CM noise and radiated CM noise, and the main focus of this paper is on conducted CM noise. The CM coupling capacitance of the transformer is one of the main contributors of CM noise, which has been verified in many previous studies. Hence, eliminating the CM noise in a transformer coupling path can significantly lower the whole CM noise level of the converter. Professional conducted electromagnetic interference (EMI) testing instruments are quite expensive. In this paper, a general transformer evaluation technique for CM noise behavior is proposed. Only a signal generator and oscilloscope can achieve transformer CM noise behavior evaluation. PCB planar flyback transformers are designed, and a series of noise spectrums and voltage waveforms can verify the effectiveness of the proposed transformer evaluation method. The flyback adapter porotype can pass the EMI standard limited line EN55022 class B by the proposed evaluation method.

A Fully Isolated Amplifier Based on Charge-Balanced SAR Converters

A galvanic isolated amplifier based on SAR converters architecture is presented which realizes chip level isolation in both the power and signal domains. The compact IC package contains an integrated isolated power converter which includes on-chip transformer, oscillator and rectifier, digital isolators based on on-chip transformers, a front-end programmable gain amplifier, a SAR ADC, a complementary charge redistribution DAC, and post filters to reconstruct and smooth the linear signal. The symmetric implementation of the SAR ADC and DAC realizes the charge balance between the input side and the output side, where an inherent linear transfer function is achieved. The sampling clock comes from an on-chip oscillator of poor jitter performance which limits the SNR performance of the ADC. With the correlated clock for the DAC reconstruction, the close-in phase noise from the clock generator is attenuated so that the SNR performance of the overall isolated amplifier is not sensitive to the jitter from the sampling clock. This fully integrated solution displaces the traditional bulky hall-effect sensors, and enables precise and fast isolated voltage or current sensing applications such as photovoltaic inverters. The isolated amplifier, with the ability to measure both large currents and small dc injection currents in a single solution, can contribute compactly and efficiently to smart grid integration circuitry. The system-in-package achieves less than 1 mV total offset and 71.9 dBFS SNR in a bandwidth of 200 kHz. It achieves an isolation working voltage rating of 600 Vrms and 5 kVrms over 1 min duration.

A Bipolar Voltage Modulation Spectrum Analysis

Features of power grid based on renewable energy sources are described. The necessity of isolated power converters in the power grid is shown. Low harmonics negative impact in modulated AC voltage based on unipolar pulse width modulation for transformer weight of isolated invertors is underlined. An approach of bipolar voltage generation with inverting every second modulation pulse that significantly decreases the low harmonics amplitude and allows to decrease the transformer weight in several times is described. A double Fourier series implementation for bipolar voltage analysis that allows expressing a signal spectrum characteristic in compact form for any multiplicity parameter value is proposed. Representation of modulated signal based on two variables of carrier and modulation functions is considered. Two different cases of modulated voltage generation depending on multiplicity parameter value are described. Bipolar voltage signal representation based on the sum of two unipolar signals with two times lower carrier function frequency is proposed. Bipolar and unipolar modulated signals spectrum components of double Fourier series are calculated. Spectrum characteristic of bipolar voltage modulation is analyzed. Transmission of the significant energy amount of bipolar voltage by harmonics with frequencies near two times lower value than carrier function frequency is proved. A case with multiplicity parameter which is multiplied to number four is noted as more desirable due to decreasing the first harmonic value. A proposition about subsequent improvements of bipolar voltage modulation is given

Dyna-C: A Minimal Topology for Bidirectional Solid-State Transformers

This paper presents a topology for bidirectional solid-state transformers with a minimal device count. The topology, referenced as dynamic-current or Dyna-C, has two current-source inverter stages with a high-frequency galvanic isolation, requiring 12 switches for four-quadrant three-phase ac/ac power conversion. The topology has voltage step-up/down capability, and the input and output can have arbitrary power factors and frequencies. Further, the Dyna-C can be configured as isolated power converters for single- or multiterminal dc, and single- or multiphase ac systems. The modular nature of the Dyna-C lends itself to be connected in series and/or parallel for high-voltage high-power applications. The proposed converter topology can find a broad range of applications such as isolated battery chargers, uninterruptible power supplies, renewable energy integration, smart grid, and power conversion for space-critical applications including aviation, locomotives, and ships. This paper outlines various configurations of the Dyna-C, as well as the relative operation and controls. The converter functionality is validated through simulations and experimental measurements of a 50-kVA prototype.