Bidirectional Converter Research Articles

Design of a 350 kW DC/DC Converter in 1200-V SiC Module Technology for Automotive Component Testing

In this paper, the design and implementation of a DC/DC converter for automotive component testing with state-of-the art performance is described. The converter is the core of a battery emulator for the characterization and development of automotive batteries, electronic chargers, traction inverters, DC-DC converters, E-motors and E-axles. Cutting edge performance, flexibility and compactness are obtained by exploiting 1200-V SiC modules, high switching frequency, planar transformer technology, suitable topology solutions and fast digital control strategies. The implemented system is a liquid-cooled, bidirectional converter with galvanic isolation capable of 350 kW continuous output power, output voltage range 48–1000 V, continuous output current up to 800 A (1600 A peak), voltage/current ramp-up time below 10/2 ms and 0.1% current/voltage accuracy. The entire instrument is implemented in a standard full-height 19-inch rack cabinet.

양방향 경계모드 벅/부스트 컨버터의 디지털 제어기법

This paper presents the digital control techniques of a bidirectional CRM(critical-conduction mode) buck(boost) converter, a dead-time design method that optimizes ZVS(zero-voltage switching) and valley-switching operation, and a switching-frequency limitation that ensures stable converter operation. To verify the feasibility of the design, a Si-MOSFET-based bidirectional CRM buck(boost) converter is built with 260-430 V input, 160-240 V output, and 1.0 kW rated capacity. The bidirectional CRM converter achieves an efficiency of up to 99.6% at buck mode and 98.7% at boost mode under rated load conditions.

Design of International Airport Hybrid Renewable Energy System

This paper presents the design and simulation of a hybrid renewable energy system utilizing solar and wind energy sources with a backup generator. The demand for reliable electric energy in support of investments in large social and economic development activities such as airport operations has been an agenda worldwide. In Tanzania, Mwanza International Airport (MIA) expects to consume about 18 MVA of electric power annually to support its operations for the next 25 years. About 78-80% of the world's commercial energy comes from fossil fuels. Non-renewable fuels and other negative effects contribute to global warming through greenhouse gas emissions and carbon dioxide emissions. Additionally, most centralized conventional power generation methods require transmission systems, adding complexity and poor power quality. Therefore, the proposal to use a mixed-coupled hybrid renewable energy source to power the airport is necessary. The energy mix considered is solar photovoltaic (PV), wind, diesel generator and a battery. There is an average solar irradiation of 5.38 kWh/m2 and a wind speed average of 4.20 m/s that could be converted to electricity by installing a 10-kW wind turbine (this is enough to generate power for MIA). The diesel generator and the battery designed at 140 kVA and 400 Ah, respectively, take the intermittency. The project will be in operation for 25 years; hence its costs are reasonable, and the justification is the potentiality of harvesting that estimated energy output of 18 MVA, which will meet the load for MIA. Some mathematical computations were performed, and, in the end, simulation results displayed different techno-economic Hybrid Renewable Energy Source (HRSE) configurations. The selected system's complete design would include a 78.48 kW PV system comprising 314 pieces of 200 W poly-crystalline modules, 608 batteries of 83.4 Ah, 12 V rating, 140 kVA diesel generator, and 41.64 kVA bidirectional converter. The net present cost of the selected design is US$357,780.8, the energy cost is 0.93US$/kW, and the minimum renewable fraction is 40.2%.

Cascade Active Balance Charging of Electric Vehicle Power Battery Based on Model Prediction Control

As a bi-directional converter, the Buck-Boost converter, which has the advantages of simple structure and taking the SOC of the battery as the balance variable, is adopted as the balance topology in this paper. In view of the shortcomings of traditional balance topology, which can only balance two adjacent batteries, resulting in a long balance time and insufficient balance accuracy, a cascade active balance charging topology that can balance in intra-group and inter-group situations simultaneously is proposed. At the same time, the fuzzy control algorithm and model predictive control are used as the balance control strategies, respectively, to control whether the MOSFET is on or off in the balance topology circuit. The duty cycle is dynamically adjusted to the size of the balance current to achieve the balance of the battery pack. The results show that the cascade Buck-Boost balance topology based on model prediction control can accurately control the balancing current and improve the accuracy and speed of the balance, and it is more suitable for the actual working process.

Stability Control Strategies for Bidirectional Energy Storage Converters Considering AC Constant Power Loads

In islanded AC microgrids, negative impedance characteristics of AC constant power loads (AC CPLs) easily introduce large signal instability to the system, while energy storage systems sometimes compensate for the dynamic characteristics of AC CPLs, and increase the system stability. Although energy storage control techniques and characteristics have gained a lot of attention, few studies have derived quantitative design guidelines for energy storage systems from the aspect of stability improvement. In order to fill this gap, this paper proposes stability control strategies for bidirectional energy storage converters considering the characteristics of AC CPLs to guarantee large signal stability of islanded AC microgrids. The presented control techniques create quantitative limits for the DC bus voltage loop control parameters of the energy storage DC/DC converter and the integral control loop control parameter of the energy storage DC/AC converter, and also interpret the positive stability influence of energy storage systems and the negative stability influence of AC CPLs. The structure of the paper is as follows. Firstly, DQ coordinate transformation is adopted, and AC microgrid nonlinear models with the energy storage system in charging and discharging states are constructed. Then, large signal models are constructed depending on mixed potential theory. Stability control strategies for bidirectional energy storage converters are obtained, and AC CPLs power, storage system equivalent resistor, and micro power source power are all taken into account. Finally, based on simulation and experimental results, it is obvious that regulating the control parameters of the energy storage converter significantly increases the large signal stability of islanded AC microgrids without extra equipment. The method is very simple and easy to implement.

Power Management in Three-Phase Grid-Integrated PV System with Hybrid Energy Storage System

The management of energy in distribution networks has been gathering attention in recent years. The simultaneous control of generation and demand is crucial for achieving energy savings and can further lower energy pricing. The work aims to develop a control scheme for a hybrid microgrid that can provide stability to the bus voltage and effectively manage the power flow. Solar energy is the current trend in renewable energy sources (RES). There is a surge in the installation of solar PV systems both on a large scale and on a small scale, such as rooftop PV systems. Installation of RES at residential premises has to be conducted with a proper power management scheme. The hybrid microgrid for this work consists of a PV system with a boost converter to extract maximum power, a DC-DC bi-directional converter to charge or discharge the hybrid energy-storing devices, and a three-phase AC-DC interlinking converter for exchange of energy with the utility grid. The control and power management scheme checks the voltage of each unit and maintains the power flow according to operating conditions. Disturbances are introduced in the form of load switching and irradiance variation to check the system performance. The system is tested on the MATLAB (R2021a) Simulink platform for varying its different modes of operations. An experimental set-up has been developed with hardware-in-the-loop to validate the simulation results.

Influence of Switching on the Aging of High Energy Lithium-Ion Cells

An AC-battery or multilevel inverter used to increase safety and flexibility is realizable by switching the cells and modules on and off in a defined way and thus can replace the bidirectional converter. Assessing possible additional aging due to switching, the results of a previous study for a high-power optimized cell showed no influence on the current rates or the switching. In this paper, a highly energy-optimized LG 18650-cell is investigated to discuss the influence of switching during the charge and discharge process, respectively, as well as combining both processes together with clear performance differences when applying higher charge and discharge currents. Moreover, the influence of switching is discussed for the two frequencies (50 Hz and 10 kHz) and different duty cycles. The aging is analyzed by capacity loss and resistance increase, by dV/dQ analysis, and by electrochemical impedance spectroscopy. We found no clear negative influence of switching but a positive effect if the cells are switched during charge. The best performance is found for switching during charge as well as during discharge. The cell aging during switching is clearly determined by the average and not the maximum current applied. This work shows no negative effects of multilevel inverter applications on the tested cells.

A Center-Tapped Transformer Based Multifunctional Single-Phase Converter with Wide DC-Bus Control.

Alongside the rapid increase in distributed power generation and load, the demand for highly efficient and reliable power converters is increasing. This has resulted in the rise of grid interfaced renewable energy sources (RES), rapid deployment of battery energy storage systems (BESS) coupled with energy managment systems (EMS), and DC based grid. This paper presents a center-tapped transformer-based single-stage single-phase full-bridge (FB) bidirectional AC-DC converter and its control strategy to improve controllability and reliability in applications such as DC distribution, PV/BESS grid interfacing, vehicle to grid (V2G), and so on. In contrast to conventional galvanically isolated topologies, a single-phase center-tapped transformer is introduced. It links and galvanically isolates the converters and the grid and provides its leakage inductance as the needed inductor required for current control (depending on the design). Furthermore, it reduces the number of conventionally required power conversion stages by employing a wide DC-bus voltage control strategy, resulting in a single converter that undergoes a single power conversion. Additionally, the voltage level can be increased to further enhance the output quality by cascading multiple converters (Multi-Level). The structure, operation, and basic control scheme are discussed in detail. Verification through a 220 Vrms, 1.8 kVA, and 45∼100 VDC simulation and small-scale experimental prototype (60∼100 VDC voltage) for practical validation of the topology is also presented.

Adaptive Neural Network Q-Learning-Based Full Recurrent Adaptive NeuroFuzzy Nonlinear Control Paradigms for Bidirectional-Interlinking Converter in a Grid-Connected Hybrid AC-DC Microgrid

The stability of a hybrid AC-DC microgrid depends mainly upon the bidirectional interlinking converter (BIC), which is responsible for power transfer, power balance, voltage solidity, frequency and transients sanity. The varying generation from renewable resources, fluctuating loads, and bidirectional power flow from the utility grid, charging station, super-capacitor, and batteries produce various stability issues on hybrid microgrids, like net active-reactive power flow on the AC-bus, frequency oscillations, total harmonic distortion (THD), and voltage variations. Therefore, the control of BIC between AC and DC buses in grid-connected hybrid microgrid power systems is of great importance for the quality/smooth operation of power flow, power sharing and stability of the whole power system. In literature, various control schemes are suggested, like conventional droop control, communication-based control, model predictive control, etc., each addressing different stability issues of hybrid AC-DC microgrids. However, model dependence, single-point-failure (SPF), communication vulnerability, complex computations, and complicated multilayer structures motivated the authors to develop online adaptive neural network (NN) Q-learning-based full recurrent adaptive neurofuzzy nonlinear control paradigms for BIC in a grid-connected hybrid AC-DC microgrid. The proposed strategies successfully ensure the following: (i) frequency stabilization, (ii) THD reduction, (iii) voltage normalization and (iv) negligible net active-reactive power flow on the AC-bus. Three novel adaptive NN Q-learning-based full recurrent adaptive neurofuzzy nonlinear control paradigms are proposed for PQ-control of BIC in a grid-connected hybrid AC-DC microgrid. The control schemes are based on NN Q-learning and full recurrent adaptive neurofuzzy identifiers. Hybrid adaptive full recurrent Legendre wavelet-based Neural Network Q-learning-based full recurrent adaptive NeuroFuzzy control, Hybrid adaptive full recurrent Mexican hat wavelet-based Neural Network Q-learning-based full recurrent adaptive NeuroFuzzy control, and Hybrid adaptive full recurrent Morlet wavelet-based Neural Network Q-learning-based full recurrent adaptive NeuroFuzzy control are modeled and tested for the control of BIC. The controllers differ from each other, based on variants used in the antecedent part (Gaussian membership function and B-Spline membership function), and consequent part (Legendre wavelet, Mexican hat wavelet, and Morlet wavelet) of the full recurrent adaptive neurofuzzy identifiers. The performance of the proposed control schemes was validated for various quality and stability parameters, using a simulation testbench in MATLAB/Simulink. The simulation results were bench-marked against an aPID controller, and each proposed control scheme, for a simulation time of a complete solar day.

An Isolated Three-Port Power Converter with 2C3L and 2C2L Resonant Circuits

This study proposed an isolated three-port bidirectional resonant converter that combines 2C3L and 2C2L resonant circuits for application in power dispatching. The proposed converter improves the bidirectional power dispatch capabilities of conventional three-port converters and utilizes different resonant converters to complete the energy charge–discharge through ports of different voltage levels. By modulating the frequency alone, bidirectional power regulation and electrical isolation were achieved among the three ports with different voltage levels. The converter involves the use of resonance techniques to enable the power switch to perform soft switching during bidirectional power transmissions, reducing switching loss and electromagnetic interference. The system control of the circuit was a Texas Instruments TMS320F28335 microcontroller. By simulating a DC grid port with a fixed voltage of 400 V, a vehicle battery port with a variable voltage of 280–403 V, and a battery charging port with a variable voltage of 180–213 V, an experimental platform with a rated output of 3 kW was built to determine the accuracy of the proposed theoretical analysis and design method.

Bidirectional Power Converters for EV Battery Chargers

The introduction of electric mobility into the transport sector has significantly contributed to the mitigation of environmental issues [...]

Integration of SiC Devices and High-Frequency Transformer for High-Power Renewable Energy Applications

This paper presents a novel structure of Integrated SiC MOSFETs with a high-frequency transformer (I-SiC-HFT) for various high-power isolated DC–DC converters. Several resonant converters are considered for integration in this paper, including the phase-shift full-bridge (PSFB) converter, inductor–inductor–capacitor (LLC) resonant converter, bidirectional PSFB converter, and capacitor–inductor–inductor–capacitor (CLLC) resonant converter. The applications of I-SiC-HFT are focused on V2G EV battery charging systems, energy storage in DC and AC microgrids, and renewable energy systems. SiC devices, including MOSFETs, Schottky diodes, and MOSFET modules, are used in this novel structure of I-SiC-HFT. The high-frequency magnetic structure uses distributed ferrite cores to form a large central space to accommodate SiC devices. The optimized architecture of I-SiC-HFT and heatsink structure is proposed for thermal management of SiC devices. To prove the concept, a small-scale 1.5 kW prototype I-SiC-HFT is used to demonstrate the basic structure and various performance indicators through the FEM based electromagnetic simulation and DC–DC converter experiments.

Adaptive Bus-Impedance-Damping Control of Multi-Converter System Applying Bidirectional Converters

Modern dc-power-distribution systems utilizing energy storages are often dependent on the operation of bidirectional power-electronics converters. Such distribution systems typically consist of several feedback-controlled converters prone to experience stability issues due to cross-effects among the different converters. Studies have presented adaptive control-based techniques to prevent such stability issues, but most studies have not fully considered their implementation on a bidirectional converter. The system dynamics may vary significantly depending on the operating point and particularly the direction of the bidirectional power flow. Therefore, specific care should be taken in the design of the adaptive stabilizing control to guarantee that the system’s regular operation is not impeded when the stabilization is implemented on a bidirectional converter. This article proposes a procedure to implement an adaptive stabilizing control method on a bidirectional converter with minimal changes to the regular controller. We add an adaptive resonance term to the bidirectional converter’s voltage controller that enhances stability and damping around the identified resonance frequency without impeding the converter’s regular operation. The resonance term is adjusted periodically based on online impedance measurements and the chosen design criteria. As a result, the controller can dampen resonances and prevent adverse impedance-based interaction. Experimental measurements based on a multi-converter setup demonstrate the effectiveness of the proposed methods.

Non-Backflow-Power and Reduced-Switching-Loss Modulation for Bidirectional Series Resonant Converter With Wide Gain Range

In the achievement of high power efficiency over a wide gain range for a bidirectional series resonant converter (BSRC), conduction losses caused by backflow power and switching losses are two challenges. In this article, a novel modulation of the BSRC is proposed for a wide voltage gain range and high efficiency as well. With the proposed modulation, the BSRC can operate in both buck- and boost-like modes for a wide gain range. The resonant current is in phase with the terminal voltage on both primary and secondary sides, to eliminate the backflow power for the reduction of conduction losses. Hard turn-off problem is alleviated with a resonant current fully released before the completion of the switching cycle. Thus, the number of hard switching actions is significantly reduced compared with existing modulation schemes in the literature. A control scheme based on state-flowchart is also proposed to realize seamless transition among different working modes. To validate the proposed modulation, a 1 kVA prototype of BSRC is developed and interfaces a high-voltage bus ranging from 240 to 480 V and a low-voltage bus ranging from 24 to 56 V. Compared with conventional modulation schemes, efficiency enhancement can be observed over the whole operating range.

A Quasi-Two-Stage Isolated Bidirectional Buck-DAB Converter for Wide Input Voltage Range

In this article, a quasi-two-stage buck-DAB (QBDAB) converter is proposed for improving the performance of the conventional dual active bridge (DAB) solution under a wide voltage range. For the proposed QBDAB converter, the DAB can always work under voltage matching conditions for wide voltage range applications, and the gain is adjusted through the added front-end circuit. The front-end circuit is similar to a buck converter, while only part of the transmission power flows through the circuit, which could also reduce the burden of achieving ZVS of the front-end circuit. Therefore, compared with the traditional two-stage buck-DAB converter solution, the related loss for the buck circuit can be reduced. The working principle, power transfer characteristics, and full load range ZVS design are analyzed deeply in this article. A detailed comparison of the QBDAB and other related combined buck+DAB topologies is also presented. Finally, the effectiveness of the proposed QBDAB is verified through experimental results from a 1kW prototype.

Synthetic Resilience Exploration and Economic Defense Strategy for Microgrid-Level AC/DC Hybrid Energy System

For the ac/dc hybrid energy system, a resilience-oriented defense strategy is developed for survivability enhancement when subject to severe energy disruptions. On account of heterogeneous components, an integration index of synthetic resilience (SR) is formulated to assess the resilience capability of hybrid energy systems in the event of sudden energy changes. The derived SR is systematically illustrated in this work, which not only reveals its convexity feature but also visualizes the inherent self-healing resources during the ac/dc energy interaction. Based on the proposed resilience index and interlinking bridge of bidirectional converter, an economic defense strategy concerning uncertainties from renewable energies and loads is developed and system resilience is consequently reinforced by dispatching distributed energies according to individual marginal cost. Without the global coordination and mode transition, the system resilience is significantly strengthened and assessed by the proposed index and defense strategy, which formulates an operational paradigm for the microgrid-level energy hybridization considering load variation and renewable energy penetration. To completely demonstrate the effectiveness of the proposed index and defense strategy for the hybrid energy system, the controller-hardware-in-the-loop experiment results have been provided from six aspects of steady-state operation, dc demand variation, ac demand variation, renewable energy fluctuations, dc energy source failure, and ac energy source failure.

Establishment of second-order equivalent circuit model for bidirectional voltage regulator converter: 48 V-aluminum-ion battery pack

The establishment of an equivalent circuit model for new-generation battery packs is an important issue related to the safety of future energy storage systems. In this study, an aluminum-ion battery pack model is accurately built by performing a hybrid pulse power characterization (HPPC) experiment, along with a synchronous regulator converter electric-circuit model of the resistor–capacitor (RC) equivalent circuit. This approach proves the feasibility of the proposed model via field testing and simulation, thereby underscoring its capability to precisely depict the exterior features of the battery discharging behavior and its advantages and disadvantages, as well as suggestions for improvement. From the analysis results, the convergent efficiency is found to exceed 90%. The simulation error was smaller than 0.08 V. The system can be incorporated with the function of current feedback to suppress current surge and stabilize battery output as well as to prevent voltage surges and damage to components caused by impulses when a load is applied.

A Fault-Tolerant Bidirectional Converter for Battery Energy Storage Systems in DC Microgrids

Battery energy storage systems (BESSs) can control the power balance in DC microgrids through power injection or absorption. A BESS uses a bidirectional DC–DC converter to control the power flow to/from the grid. On the other hand, any fault occurrence in the power switches of the bidirectional converter may disturb the power balance and stability of the DC microgrid and, thus, the safe operation of the battery bank. This paper presents a fault-tolerant topology along with a fault diagnosis algorithm for a bidirectional DC–DC converter in a BESS. The proposed scheme can detect open circuit faults (OCFs) and reconfigure the topology to guarantee the safe and continuous operation of the system while it is connected to the DC microgrid. The proposed method can be extended to multi-phase structures of interleaved bidirectional DC–DC converters using only two power switches and n TRIACs to support the OCF occurrence on 2 × n switches of n legs. The proposed fault diagnosis algorithm detects OCFs only by observing the current of the inductors and does not require any sensor. Hence, the cost, weight, volume and complexity of the system is considerably reduced. Experimental results show that the reconfiguration of the converter, along with its fast fault detection, leads to fewer switches overloading and less DC voltage deviation.

Fully soft switched high step‐up/down bidirectional buck/boost converter with reduced switch voltage stress

AbstractA fully soft switched high step‐up/down bidirectional converter is presented in this paper. The high voltage conversion ratio is achieved by a pair of coupled inductors along with a switched capacitor while all active switches operate at zero voltage switching. To provide soft switching condition for the main switches and absorb the leakage inductance energy of coupled inductors, active clamp circuits are utilized for both operating modes. Furthermore, all active switches body diodes which are utilized as converter diodes turn off at zero current switching (ZCS) and thus, the reverse recovery problem is eradicated. Additionally, the voltage stress of the main switches is reduced in comparison with the basic bidirectional buck/boost converter and thus, their drain‐source resistance is relatively lower which leads to considerably lower conduction loss. All the mentioned advantages along with relatively low number of components contribute to the converter efficiency. Theoretical analysis of the proposed converter is presented in detail for both operating modes and the experimental results from the implementation of a 300 W prototype circuit confirm the validity of the converter performance. A comprehensive comparison table between the proposed converter and the recent counterpart bidirectional converters is presented to demonstrate the converter advantages.

Parameters analysis and control strategy combined with synchronous rectification technology for bidirectional CLLC resonant converter

Parameters analysis and control strategy combined with synchronous rectification technology for bidirectional CLLC resonant converter