Bidirectional Converter Research Articles

A novel control strategy for dual active bridge bidirectional converter for electric vehicle application

AbstractEnvironmental issues and the depletion of fossil fuel resources cause increased demand for electric vehicles. An electric vehicle consists of two main components: a propulsion system and a battery charger. The design of an efficient, fast and economical charger is key to its success. Therefore, this paper presents a novel design of a dual active bridge‐based bidirectional converter with logical control for an electric vehicle application. The logical control of the converter enables the power flow between the grid and the electric vehicle and vice versa. The power flow is based on the single‐phase shift method. The converter selects the mode of operation based on the battery's state of charge and the user command using a binary switch. The power requirement influences the design of the circuit's parameters of the electric vehicle battery. A 50 V, 100 Ah, and 5 kW Li‐ion battery and AC power source of 230 V, 50 Hz are used in the simulation work. The circuit performance is verified in the SIMULINK/MATLAB environment. The analysis of the converter gives better control for various state‐of‐charge levels of electric vehicle batteries.

A Coupled Inductor-Based Bidirectional DC-DC Converter with Step-Up Step-Down Operation for Electric Vehicle Applications

A coupled-inductor-based high step-up high step-down DC-DC converter with bidirectional capability suitable for electric vehicle (EV) applications is proposed in this paper. The voltage gain in both step-up and step-down operations is increased by a two-winding coupled inductor. The current ripple in the low-voltage port is low making it suitable for renewable energy sources. In addition, the low number of components causes the efficiency of the proposed converter to be competitive with similar topologies in the literature. Due to the use of only three bidirectional switches with low voltage stress, the cost and volume of the converter are reduced. To demonstrate the performance of the proposed bidirectional converter, an analysis of the operation modes in the steady state is presented. Also, a comparison between the suggested converter and other similar converters in the literature is provided. The results of these comparisons show that the proposed converter has a lower number of components and higher efficiency than the others. In addition, lower voltage stress and noticeable voltage gain in comparison with others are further results of these comparisons. Eventually, the experimental results in step-up and step-down operations are presented. In step-up operation, the experimental prototype is tested under fs = 50 kHz, VLow = 20 V, VHigh = 110 V, rated power = 120 W, with 94.60% efficiency. Furthermore, VHigh is considered 100 V with VLow = 33 V and 94.43% efficiency at 50 W rated power in step-down mode operation.

Review on modeling and control of megawatt liquid flow energy storage system

Flow battery has recently drawn great attention due to its unique characteristics, such as safety, long life cycle, independent energy capacity and power output. It is especially suitable for large-scale storage system and has a good application prospect. In this paper, the overall structure of the megawatt-level flow battery energy storage system is introduced, and the topology structure of the bidirectional DC converter and the energy storage converter is analyzed. Secondly, the influence of single battery on energy storage system is analyzed, and a simulation model of flow battery energy storage system suitable for large power grid simulation is summarized. The model of the whole system of flow battery is summarized from the grid-connected side and the energy storage system itself. The model of flow battery energy storage system should not only accurately reflect the operation characteristics of flow battery itself, but also meet the simulation requirements of large power grid in terms of simulation accuracy and speed. Finally, the control technology of the flow battery energy storage system is discussed and analyzed. The multi-DC/DC control strategy on the DC side and the parallel operation control strategy of the energy storage converter on the AC side are compared and analyzed. The advantages and disadvantages of each control method are analyzed accurately, which can provide reference for the modeling and control strategy of the megawatt flow battery energy storage system.

Design of a 7.5 kW Dual Active Bridge Converter in 650 V GaN Technology for Charging Applications

High-voltage GaN switches offer low conduction and commutation losses compared with their Si counterparts, enabling the development of high-efficiency switching-mode DC–DC converters with increased switching frequency, faster dynamics, and more compact dimensions. Nonetheless, the potential of GaN switches can be fully exploited only by means of accurate simulations, optimal switch driving, suitable converter topology, accurate component selection, PCB layout optimization, and fast digital converter control. This paper describes the detailed design, simulation, and implementation of an air-cooled, 7.5 kW, dual active bridge converter exploiting commercial 650 V GaN switches, a compact planar transformer, and low ESL/ESR metal film capacitors. The isolated bidirectional converter operates at a 200 kHz switching frequency, with an output voltage range of 200–500 V at nominal 400 V input voltage, and a maximum output current of 28 A, with a wide full-power ZVS region. The overall efficiency at full power is 98.2%. This converter was developed in particular for battery charging applications, when bidirectional power flow is required.

A Comprehensive Review of the Bidirectional Converter Topologies for the Vehicle-to-Grid System

Over the past decade, there has been a great interest in the changeover from cars powered by gasoline to electric vehicles, both within the automotive industry and among customers. The electric vehicle–grid (V2G) technology is a noteworthy innovation that enables the battery of an electric vehicle during idling conditions or parked can function as an energy source that can store or release energy whenever required. This results in energy exchange between the grid and EV batteries. This article reviews various bidirectional converter topologies used in the V2G system. Additionally, it can reduce the cost of charging for electric utilities, thus increasing profits for EV owners. Normally electric grid and the battery of an electric vehicle can be connected through power electronic converters, especially a bidirectional converter, which allows power to flow in both directions. The majority of research work is carried out over the converters for V2G applications and concerns utilizing two conversion stages, such as the AC-DC conversion stage used for correcting the power factor and the DC-DC conversion stage for matching the terminal voltage. Furthermore, a bidirectional conversion can be made for an active power transfer between grid–vehicle (G2V) and V2G effectively. This review explores and examines several topologies of bidirectional converters which make it possible for active power flow between the grid and the vehicle and vice versa. Moreover, different types of charging and discharging systems, such as integrated/non-integrated and on/off board, etc., which have been used for electric vehicle applications, are also discussed. A comparison study is carried out based on several other factors that have been suggested. The utilization of semiconductors in power converters and non-conventional resources in charging and discharging applications are the two improving technologies for electric vehicles.

A Data-Driven Convex Model for Hybrid Microgrid Operation With Bidirectional Converters

Bi-directional converters (BDCs) facilitate the high efficiency of hybrid AC/DC microgrids (HMs). However, the HM operation is rather challenging due to the non-convex system model. This letter develops a data-driven convex model for HM operation involving BDCs. First, a least squares approximation method with data-driven weight functions is proposed to linearize BDC efficiency behavior. Then, the convex linear HM model is formulated by combining this linearized model with an analysis of the conditions ensuring non-simultaneous BDC inverting and rectifying operations. The low approximation error and high computational efficiency of the proposed model are demonstrated based on an analysis of numerical studies.

Stability Analysis of Bidirectional Dual Active Bridge Converter With Input and Output LC Filters Applying Power-Feedback Control

This article analyzes the dynamic characteristics of a dual active bridge (DAB) converter with input/output LC filters connected and power-feedback control applied, and then discusses an impedance stability criterion about both side LC filters and the converter. Power control is suitable as a control method for grid-connected converters because of its affinity with the energy management system, which is being introduced as a new way to operate power systems in recent years. In order to provide stable power supply, it is necessary to ensure the stability of the converter, and information on dynamic characteristics is essential for the design and development of converters. Since there are no previous papers found yet where the impedance stability criterion is applied when LC filters are connected to both ends of a bidirectional DAB converter, this article discusses the procedures and key points to be considered to apply the criterion. Based on the analysis, the design guidelines of the system will be discussed.

An Efficient Supervisory Power Management Scheme for a Wind–Battery-Assisted Hybrid Autonomous System

This article presents an efficient power management and protection scheme for a wind–battery-assisted hybrid autonomous system. To operate the wind power generation system at the maximum power point (MPP), a drift-free perturb and observe algorithm is adapted. A unified controller for a bidirectional converter (BDC) is incorporated for the dc-bus voltage regulation along with the charge/discharge control of the battery. The small-signal analysis of the BDC and the buck converter is presented in detail. The performance of the proposed power management scheme (PMS) is validated through a time-domain simulation in MATLAB/Simulink along with the hardware implementation using the DS1103 digital platform. Initially, the PMS with only maximum power point tracking (MPPT) and pitch controller is unable to maintain the dc-bus voltage during the battery overcharge or deep-discharge condition. To address this issue, an <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> -MPPT controller is proposed to regulate the dc-bus voltage. The effectiveness of all the operating modes of the proposed PMS is verified in the developed laboratory prototype, and the performance is also compared with that of the classical droop control method. The experimental results confirm the ability of the PMS to handle power sharing and dc-bus voltage fluctuation during wind speed and load change and satisfy the load demand. This ensures that the improved performance of the developed hybrid autonomous system and changeover from the MPP to the generator or battery protection mode is seamless and fast.

Inertia Droop Control and Stability Mechanism Analysis of Energy Storage Systems for DC-Busbar Electric Vehicle Charging Station

Although the photovoltaic (PV) integrated dc-busbar electric vehicle charging station (EVCS) is a promising energy supply form for EVs, its inertialess and poor damping always lead to the potential system instability. In this article, inertia droop control (IDC) strategies are, thus, proposed for a bidirectional dc converter (Bi-C) to improve dynamic stability and provide a high-quality power supply for EVs. Compared with the virtual inertia and damping control (VIDC), the proposed IDC can be implemented by easily modifying conventional droop control, avoiding complex control structures. First, virtual inertia is achieved in the proposed IDC strategies in two ways: 1) dynamic virtual impedance and 2) adaptive droop algorithm. Damping support comes from the redesigned damping term featuring secondary voltage regulation to eliminate the voltage deviation. Then, a feedback analytic method is proposed to comprehend stability mechanisms from multiview, and a double-coordinate-based phasor diagram is developed as its analytical tool to observe the interaction among variables intuitively. Accordingly, IDC’s negative feedback property is revealed, and the impactors of system inertia, stiffness, and dissipation properties are explored. Dynamic performance and small-signal stability analysis are also presented to guide parameter selection and optimize the transient response. Experiment results verify that IDC has similar effects to VIDC while simplifying the control structure.

Design and Control of a Novel Wireless Energy Router With Independent Power Transmission Channels

Energy routers are intelligent power electronic systems that enable energy sharing and flexible power flow regulation among various distributed energy sources. Combining the excellent feature of wireless power transfer technology for contactless transmission of electrical energy, this article proposes a novel wireless energy router to realize the power exchange of multiple energy storage devices, such as various mobile electronics, electric vehicles, and energy storage stations. Independent power transmission channels with specific operating frequencies are built between any two of the power-exchanging units. The multiple resonating decoupling compensations are designed and implemented, which offer each power-exchanging unit and various resonate operating frequencies while suppressing the frequency components from irrelevant channels. Moreover, through generation by the bidirectional multilevel converter, the drive voltage of each unit can naturally realize the synthesis of multiple-frequency voltage components. In addition, the decoupled dual-side phase-shift control with capacitor voltage balancing strategy is proposed to regulate the power flow in each power channel. As a result, simultaneous energy sharing among power storage devices can be achieved. And the power flows can be adjusted independently without cross interference. Finally, both simulation and experimental results are presented to verify the effectiveness of the proposed wireless energy router.

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.