Bidirectional Isolated DC-DC Converter Research Articles

Vector Reconfiguration on a Bidirectional Multilevel LCL-T Resonant Converter

With the development of distributed energy technology, the establishment of the energy internet has become a general trend, and relevant research about the core component, energy router, has also become a hotspot. Therefore, the bidirectional isolated DC–DC converter (BIDC) is widely used in AC–DC–AC energy router systems, because it can flexibly support the DC bus voltage ratio and achieve bidirectional power flow. This paper proposes a novel vector reconfiguration on a bidirectional multilevel LCL-T resonant converter in which an NPC (neutral-point clamped) multilevel structure with a flying capacitor is introduced to form a novel active bridge, and a coupling transformer is specially added into the active bridge to achieve multilevel voltage output under hybrid modulation. In addition, an LCL-T two-port vector analysis is adopted to elaborate bidirectional power flow which can generate some reactive power to realize zero-voltage switching (ZVS) on active bridges to improve the efficiency of the converter. Meanwhile, due to the symmetry of the LCL-T structure, the difficulty of the bidirectional operation analysis of the power flow is reduced. Finally, a simulation study is designed with a rated voltage of 200 V on front and rear input sources which has a rated power of 450 W with an operational efficiency of 93.8%. Then, the feasibility of the proposed converter is verified.

Isolated bidirectional DC-DC Converter: A topological review

Bidirectional DC-DC converters (BDCs) are certainly an important power electronic converter for managing bidirectional power flow in various applications. It offers the ability to flow power in both directions, which is useful in systems with renewable energy sources and energy storage. BDCs are becoming increasingly important in various applications, including renewable energy systems, electric vehicles, and energy storage. The development of new BDC topologies and control strategies is expected to further improve their efficiency and performance. Non-Isolated Bidirectional DC-DC Converters (NBDCs) and Isolated Bidirectional DC-DC Converters (IBDCs) are the two main types of BDCs with different isolation properties and trade-offs in terms of size, cost and performance. Topological classification of BDCs further distinguishes various BDC types based on their configurations and voltage-boosting techniques. IBDCs are preferred over NBDCs due to high-power applications, and wide voltage range with higher efficiency; the performance of IBDCs is improving day by day. To provide a framework for comparison in implementing novel configurations or identifying the best converter for a given application, this study is concentrated on each topology and its usual applications. Soft switching converters are also discussed pointed to Resonant Power Converters (RPCs) for the application into Electric Vehicles (EVs). It is worth noting that the choice of BDC depends on the specific requirements of the application, such as power level, voltage range, efficiency, and cost. A detailed comparison, application, advantage and disadvantage table can be useful in comparing the characteristics of different BDCs and selecting the most suitable one.

Integrated on-board electric vehicle battery charger with multifunctional features

ABSTRACT Because of the continuous demand for reliable, efficient, small-size, light weighted, and low-cost Electric Vehicle (EV) battery charging systems, an integrated on-board charger is proposed with a high-power propulsion motor drive. It utilises stator windings of motor, the 6-leg Voltage Source Converter (VSC), DC-DC converter, and feedback sensors to facilitate vehicular battery charging. With this system, soft switching technique based bidirectional isolated DC-DC converter is proposed that offers the advantage of simple circuitry design due to no usage of extra passive or active components. This paper presents mathematical modelling, analysis, and controller design of this proposed configuration under various operating modes. The complete system is developed in Sim Power system toolbox of MATLAB software and tested in real-time environment. The performance investigations of proposed system are carried out for three operating modes like Grid-to-Vehicle (G2V), Vehicle-to-Grid (V2G), Vehicle-to-Vehicle (V2V) under Constant Current (CC) and Constant Voltage (CV) battery charging modes. Furthermore, the investigations ensure the system’s excellent efficiency, less THD, and nearly unity power factor operation under all operating conditions.

Performance analysis of GaN based dual active bridge converter for electric vehicle charging application

<p><span>The research work proposes a Gallium Nitride (GaN) based dual active bridge (DAB) converter for electric vehicle (EV) charging applications. The wide bandgap semiconductor device, GaN is implemented in the DAB topology of an Isolated Bidirectional DC-DC converter (IBDC). GaN-based DC-DC converters lead to higher efficiency, smaller size, faster charging, and reduced heat generation improving the overall performance of the EV charging system. The performance characteristics of GaN based DAB converter is analyzed both in simulation and hardware for EV charging application. The same analysis is extended to a Si based DAB converter and comparative results are presented. A 14.25 kW GaN based DAB and <br /> 10.5 kW Si based DAB is designed and evaluated using LTspice XVII software and a scaled-down prototype of 0.612 kW GaN based DAB and 0.25 kW Si based DAB is presented for experimental validation. Result analysis under similar operating conditions indicated an improvement of 36% more output power transfer on the GaN based DAB over the traditional Si based DAB. The developed prototype showcased improved levels of power, voltage, and current under same operating conditions. The power transmission in the developed DAB based IBDC topology is controlled using the single-phase-shift (SPS) control strategy.</span></p>

Efficiency-Oriented Parameter Design and Comparison of Medium Voltage Isolated Bidirectional DC/DC Converters

In a medium voltage (MV) solid state transformer(SST), the isolated bidirectional DC/DC converter (IBDC) is the core circuit for controlling power flow and galvanic isolation. Current research works on MV single-cell IBDC mainly focus on two directions: resonant and non-resonant topologies. However, for different scenarios with various voltage regulation ranges and power ranges, which topology should be adopted to achieve better efficiency performance is unclear. To effectively illustrate the two IBDCs’ respective benefits, a comparison between the two IBDCs is conducted in this study along with the optimization design method. For resonant IBDC, a complex objective optimization-based parameter design strategy is developed to realize rapid automatic design under various operating conditions. For non-resonant IBDC, a multi-phase modulation scheme aimed at minimizing the current stress under different voltage and power ranges is introduced. The optimal operating range of the two IBDCs has been derived. A 4 kV/1 kV 200 kW non-resonant IBDC experimental prototype has been built and its efficiency is tested under various operating conditions. The test data were compared with the established power loss model to derive the converter's full range efficiency, and the efficiency of the converter over a wider power range could then be projected.

Comparative Study of Control Methods for Bidirectional Isolated Dual Active Bridge DC-DC Converter

Comparative Study of Control Methods for Bidirectional Isolated Dual Active Bridge DC-DC Converter

High Efficiency and Voltage Conversion Ratio Bidirectional Isolated DC-DC Converter for Energy Storage System

This paper proposes a high efficiency and conversion ratio bidirectional isolated DC-DC converter with three-winding coupled inductor, which can fulfil storage system charging and discharging. The proposed topology is improved from traditional Buck-Boost converter. By integrating coupled inductor and switched-capacitor into power stage, the proposed converter can achieve the merits of isolation and bidirectional power flow. The proposed topology has only four switches and a common core coupled inductor, which greatly reduces design costs and achieves high step-up/step-down voltage gain without excessive duty cycles or high turns ratios. In addition, the proposed also has the function of leakage inductance energy recovery, which can recover all the energy stored in the leakage inductance to improve efficiency, and the main switches has a zero voltage switching (ZVS) feature. This paper implements a 500 W converter to verify the feasibility of the proposed topology through software simulation and experiment results, and conducts theoretical analysis, formula derivation, operation principle analysis, and non-ideal analysis. Finally, the experimental results show that the highest efficiency of the step-up and step-down modes are 96.8% and 96.4%, respectively.

High‐frequency‐link DC solid state transformer based on voltage self‐balancing control for MVDC power distribution application

This paper presents a novel voltage self-balancing converter (VBC) applied to DC solid-state transformer (DCSST), analyzes the operating principle of the proposed VBC, and proves the voltage balance performance. Based on this converter, a novel DCSST topology is proposed, which can be used in medium and low voltage DC distribution application, microgrid and medium and low voltage energy storage system. Compared with the previous work, under the same voltage level, it can effectively reduce the number of transformers and switches, reduce the voltage level of switches, and realize the soft switching of the VBC switches, so as to improve the system efficiency and power density, and then improve the system reliability. Meanwhile, the fault handling ability and fault tolerance ability of DCSST are improved, which makes DCSST more reliable when multiple isolated bi-directional DC/DC Converters (IBDC) are connected in series. In addition, with this topology, the input voltage self-balancing control strategy of the IBDC is not needed because of the voltage self-balancing characteristic of VBC, which simplifies the control complexity and greatly improves the control accuracy of the control system. Experimental results agree well with the accuracy and correctness of the proposed topology.

Distribution Network Hierarchically Partitioned Optimization Considering Electric Vehicle Orderly Charging with Isolated Bidirectional DC-DC Converter Optimal Efficiency Model

The access of large-scale electric vehicles (EVs) will increase the network loss of medium voltage distribution network, which can be alleviated by adjusting the network structure and orderly charging for EVs. However, it is difficult to accurately evaluate the charging efficiency in the orderly charging of electric vehicle (EV), which will cause the scheduling model to be insufficiently accurate. Therefore, this paper proposes an EV double-layer scheduling model based on the isolated bidirectional DC–DC (IBDC) converter optimal efficiency model, and establishes the hierarchical and partitioned optimization model with feeder–branch–load layer. Firstly, based on the actual topology of medium voltage distribution network, a dynamic reconfiguration model between switching stations is established with the goal of load balancing. Secondly, with the goal of minimizing the branch layer network loss, a dynamic reconstruction model under the switch station is established, and the chaotic niche particle swarm optimization is proposed to improve the global search capability and iteration speed. Finally, the power transmission loss model of IBDC converter is established, and the optimal phase shift parameter is determined to formulate the double-layer collaborative optimization operation strategy of electric vehicles. The example verifies that the above model can improve the system load balancing degree and reduce the operation loss of medium voltage distribution network.

Modelling of DC-DC Converter for Solar Based Electric Vehicle

Presently a days we are searching for substitute sources like electric vehicles, to chop down the contamination from cars which are developing quickly. In electric vehicles, A DC-DC converter is used to boost the voltage from solar photo voltaic (PV) array and isolated bidirectional DC-DC converter (IBDC) is used to charge and discharge the battery. In this paper, the proposed utilization of quadratic twofold lift converter (QBC) instead of DC-DC converter, which has high increase when contrasted and ordinary converter. In disengaged bidirectional DC-DC converter, delicate exchanging is accommodated lessen the turning misfortunes and weights on switches. The proposed two DC-DC converters are demonstrated and mimicked utilizing MATLAB Simulink and results are appeared in this paper.

A Novel Bidirectional Isolated DC-DC Converter With High Voltage Gain and Wide Input Voltage

This article proposes a novel bidirectional isolated dc-dc converter with high voltage gain and wide input voltage, which can be applied to bidirectional power conversion systems. The proposed topology is composed of a bidirectional buck-boost converter and a forward-flyback converter; it has the advantage of higher voltage gain and has continuous current characteristic of the low-side port in step-up and step-down mode. In addition, the proposed topology also has the function of leakage inductance energy recovery, which can improve the efficiency of the converter, reduce the voltage surges on switches, and have the characteristics of zero voltage switching on certain switches. Finally, this paper implements a 500-W bidirectional dc-dc converter to verify the feasibility of the proposed topology. The low-side voltage of the proposed topology is 24, 48, and 55 V; the maximum efficiency in step-up mode are 94.2%, 95.6% and 96.9%, and the maximum efficiency are 92.6%, 94.2% and 94.5% in the step-down mode, respectively.

Suppression for DC Magnetic Flux for a Current-Fed Bi-Directional Isolated DC-DC Converter under Boost Mode

Suppression for DC Magnetic Flux for a Current-Fed Bi-Directional Isolated DC-DC Converter under Boost Mode

Evaluation of a Three-Phase Bidirectional Isolated DC-DC Converter with Varying Transformer Configurations Using Phase-Shift Modulation and Burst-Mode Switching

This paper presents the performance of a three-phase bidirectional isolated DC-DC converter (3P-BIDC) in wye-wye (Yy), wye-delta (Yd), delta-wye (Dy), and delta-delta (Dd) transformer configurations, using enhanced switching strategy that combines phase-shift modulation and burst-mode switching. A simulation verification using PSCAD is carried out to study the feasibility and compare the efficiency performance of the 3P-BIDC with each transformer configuration, using intermittent switching, which combines the conventional phase-shift modulation (PSM) and burst-mode switching, in the light load condition. The model is tested with continuous switching that employs the conventional PSM from medium to high loads (greater than 0.3 p.u.) and with intermittent switching at light load (less than 0.3 p.u), in different transformer configurations. In all tests, the DC-link voltages are equal to the transformer turns ratio of 1:1. This paper also presents the power loss estimation in continuous and intermittent switching to verify the modelled losses in the 3P-BIDC in the Yy transformer configuration. The 3P-BIDC is modelled by taking into account the effects that on-state voltage drop in the insulated-gate bipolar transistor (IGBTs) and diodes, snubber capacitors, and three-phase transformer copper winding resistances will have on the conduction and switching losses, and copper losses in the 3P-BIDC. The intermitting switching improves the efficiency of the DC-DC converter with Yy, Yd, Dy, and Dd connections in light-load operation. The 3P-BIDC has the best efficiency performance using Yy and Dd transformer configurations for all power transfer conditions in continuous and intermittent switching. Moreover, the highest efficiency of 99.6% is achieved at the light power transfer of 0.29 p.u. in Yy and Dd transformer configurations. However, the theoretical current stress in the 3P-BIDC with a Dd transformer configuration is high. Operation of the converter with Dy transformer configuration is less favorable due to the efficiency achievements of lower than 95%, despite burst-mode switching being applied.

An Integrated Cascade Structure-Based Isolated Bidirectional DC–DC Converter for Battery Charge Equalization

In this article, an isolated bidirectional dc-dc converter with an integrated cascade structure is proposed for a centralized charge equalization system. Compared with existing architectures, the proposed converter structure is equivalent to the integration of polarity switches and a bidirectional dc-dc converter. Equalization of cells with different voltage polarities can be realized by controlling the working state of the converter, which further improves the reliability and integration of the equalization system. The integrated cascade structure can not only increase the equalization current and make it work in a continuous state but also achieve a high voltage conversion ratio to improve the efficiency of the transformer. Theoretical derivations of the converter and the conditions of soft-switch implementation are analyzed in detail. Finally, equalization experiments on a 13-cell lithium-ion battery string are carried out, and a quantitative and comprehensive comparison of different centralized equalizer is conducted. The experimental and comparison results validate the superiorities of the proposed equalizer and demonstrate obvious performance enhancement over the conventional method.

Ultra-Fast DC Charger with Improved Power Quality and Optimal Algorithmic Approach to Enable V2G and G2V

In existing electric vehicle (EV) charger topology, due to the presence of line frequency transformer and bidirectional DC-DC/AC converters, the circuit complexity in the structure gets increased in EV charger; thereby, it results bigger in size for high capacity. Moreover, due to rectification mode, it consumes the power with poor power quality. To overcome these drawbacks, this paper proposes a single input-dual port (SIDP) isolated bidirectional DC-DC converter (IBDC) to achieve ultra-fast EV charging of the battery. Also, to improve the power quality, a novel DC-link-fed PFC control strategy is proposed in this paper. Moreover, enabling grid to vehicle (G2V) and vehicle to grid (V2G) operation at bidirectional way depends on the situation such as state of charge (SOC) levels, off-peak and peak hours and user-defined data, which have been implemented using optimal algorithmic approach (OAA). The closed-loop control strategies are implemented to transfer the power at an accurate range using PWM plus phase-shifting approach. Moreover, it has the advantages of smaller in size due to the presence of medium frequency transformer and power quality gets improved without any additional converter stage. Finally, to validate the proposed operation, the results are observed under various case studies and conditional input from the customer and presented in this paper. Furthermore, the experimental results have been presented to validate the operation.

Analytical Dead-Band Compensation for ZCS Modulation Applied to Hybrid Si-SiC Dual Active Bridge

This paper proposes a triangular modulation with zero current switching (ZCS) for a hybrid Si-SiC isolated bidirectional DC-DC converter (IBDC). Three of the four legs in the IBDC operate at ZCS and use Si IGBTs, while the fourth operates at zero voltage switching (ZVS) and uses SiC MOSFET. In that case, the turn-off switching losses are concentrated regardless of the direction of the power. The main contribution of this paper resides in the proposed dead-band compensation mechanism. This dead-band compensation is crucial when addressing ZCS modulation and improves the overall efficiency of the full operating range. As a co-benefit, the proposed mix of semiconductor technologies can result in an effective cost reduction compared with a full SiC IBDC. The paper contains a detailed explanation of the implemented modulation applied to an IBDC. The paper contributes to deploy a theoretical implementation where the effect of parasitic capacitance on semiconductors during the dead-band is analytically considered. The presented method results are validated on a laboratory set-up using a 20 kW - 40 kHz hybrid Si-SiC IBDC.

Pre-charge Method Using a Bi-directional Isolated DC-DC Converter

Pre-charge Method Using a Bi-directional Isolated DC-DC Converter

Design-Oriented Comprehensive Time-Domain Model for CLLC Class Isolated Bidirectional DC-DC Converter for Various Operation Modes

A comprehensive time-domain model of a CLLC class isolated bidirectional dc–dc converter (IBDC) is proposed in this article. Based on the circuit analysis and the solution of the state equations, analytical expressions of the state variables are provided. The model is a piecewise time-domain analytical model and can accurately describe the transformer currents and capacitor voltages under almost all basic types of control strategies, e.g., phase-shift control and frequency modulation control. With the model, the steady-state analysis of the IBDC can speed up evidently (up to 330 times faster compared to MATLAB/Simulink and more than 10 times compared to SIMPLIS and PLECS), which gives great support to parameter sweep and case comparison in the design procedure. By assigning specific parameters, the presented model can also be applied to the analysis of the LLC resonant IBDC or typical DAB IBDC since the LLC converter and DAB converter are similar to the CLLC converter in the circuit topology. The transformation of the model from CLLC to LLC /DAB is provided and several application examples are given. Finally, the simulation and experimental results are presented, verifying the effectiveness of the model.

Efficiency Improvement and Transient Characteristics of the 750-V, 100-kW, 20-kHz Bidirectional Isolated DC-DC Converter

Efficiency Improvement and Transient Characteristics of the 750-V, 100-kW, 20-kHz Bidirectional Isolated DC-DC Converter

Low-load Efficiency Improvement of a Three-Phase Bidirectional Isolated DC-DC Converter (3P-BIDC) Via Enhanced Switching Strategy

This paper presents the system design, operation and enhanced switching strategy of a three-phase bidirectional isolated dc-dc converter (3P-BIDC). The paper discusses the operating modes of the 3P-BIDC using phase-shift modulation (PSM), with analysis on its soft-switching characteristics. The phase-shift modulation is the simplest modulation technique that can be applied to the 3P-BIDC. However, it comes with the consequences of low efficiency performance in the low-load conditions. Therefore, this paper investigates the improvement in efficiency of the 3P-BIDC during low-load condition using an enhanced switching strategy combining burst-mode switching and phase-shift modulation. The model of a 700-V, 100-kW, 20-kHz 3P-BIDC and the enhanced switching strategy are verified via simulation using PSCAD. The simulation results shows that the combination of burst-mode and phase-shift modulation technique improves the efficiency of the 3P-BIDC at low-load conditions.