Bidirectional Converter Research Articles

Design of Bidirectional Resonant Converter For EV Application

In this study, a novel LLC converter-based battery charger for EVs is presented. With this structure, the major switches may be switched at zero voltage over the whole charging profile. The suggested charger offers a flexible output voltage range suitable for the battery system. Additionally, storage battery-to-battery charging enables the sharing of charge between two batteries if one battery becomes stranded far from a charging station, hence maintaining high-efficiency undercharging. Various types of vehicle-to-vehicle chargers have been examined by researchers. A major drawback of conventional chargers is the inefficiency caused by the several power conversion steps they use. The study describes a DC source to a battery charger that operates independently from the vehicle. The paper discusses the operation modes of DC source-storage battery chargers.

A Scalable Matrix Integrated Transformer With Controllable Leakage Inductance for a Bi-Directional Resonant Converter

Integrated transformer with built-in leakage inductors is a good approach for simplifying the whole system, as it integrates discrete leakage inductors into the transformer with printed circuit board (PCB) windings for a single-phase CLLC (1PCLLC) resonant converter. The EI-core-based integrated transformer can integrate adjustable leakage inductance into the transformer. Series or parallel connections of EI-core-based integrated transformers offer a possible solution for high-voltage and high-power applications: however, the penalty of more considerable core loss by the induced leakage flux is problematic. This paper proposes a matrix integrated transformer with controllable leakage inductance for a 1PCLLC resonant converter. Three EI-core-based elemental integrated transformers can be integrated into one three-UI-core-based integrated transformer with built-in leakage inductance, and the benefits of evenly distributed flux inside the core and much-reduced core loss can be achieved. An asymmetrical winding structure and asymmetrical core structure were proposed to adjust the built-in leakage inductance for the proposed matrix integrated transformer. An 11-kW 1PCLLC resonant converter for 800-V onboard-charger application was built to verify the proposed novel matrix integrated transformer. The designed converter can achieve a power density of 250W/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> power density and 98.4% peak efficiency.

A Grid Connected PV Array and Battery Energy Storage Interfaced EV Charging Station

In this work, a charging station for EV (Electrical Vehicle) integrated with a BES (Battery Energy Storage) is presented with enhanced grid power quality. The positive sequence components of the three phase grid voltages are evaluated for the estimation of the unit templates and the reference grid currents. The EV and battery energy storage are connected at DC link using a bidirectional buck-boost converter. During the daytime, EV takes power from the solar array while in its absence it consumes the power from the grid. Additionally, when the system is connected to the grid, the point of common coupling voltages synchronizes with the voltages of the grid. Tests are conducted on a hardware prototype developed in the laboratory for the validation of the satisfactory response under different dynamics conditions.

Active disturbance rejection control of an islanded PV/wind/battery microgrid with power quality enhancement by SAPF

&lt;p&gt;&lt;span lang="EN-US"&gt;The focus in this study is on an islanded microgrid based on hybrid renewable energy sources and storage systems. This latter is considered as an essential element for all off-grid autonomous systems to offer a reliable and stable operation. The proposed system is composed of a photovoltaic system, a wind power system based on a synchronous generator and a storage system. The proposed control strategy is intended to control, through the load side converter (LSC), the AC bus voltage in terms of amplitude and frequency under different operating conditions, and to obtain, through the bi-directional battery side converter (BSC), a better regulation between the available production and the global load demand. The proposed strategy also contributes to the power quality improvement in the AC bus by controlling the PV inverter to work as a shunt active power filter to provide the required harmonic current component to non-linear loads. A new robust control strategy for internal current and voltage control loops is proposed in this research paper, it’s the active disturbance rejection control (ADRC) and it is based on the extended state observer which allows to estimate all disturbances affecting the control, such as modeling errors and parameter variations.&lt;/span&gt;&lt;/p&gt;

Investigation of Soft-Switching QSW Technique in DC/DC SiC-Based Flying Capacitor Converter With Q2L Control

This paper investigates the soft-switching quasi-square-wave (QSW) technique in DC/DC SiC-based flying capacitor converter with quasi-two-level (Q2L) control establishing design guidelines for constructing high-efficiency soft-switched bidirectional converters with low-voltage power transistors. The general idea behind the soft-switching in the proposed system is based on near-CRM (critical conduction mode) operation using TCM (triangular current mode) and Q2L control with the addition of auxiliary transistor capacitances. The soft-switching process is based on a resonance between the capacitances in parallel to each transistor, and the main inductor - ZVS at turn-on is ensured through proper modulation pattern according to TCM-Q2L control, and the turn-off soft-switching mechanism is assured through the novelty in the form of adding auxiliary capacitance in parallel to each of the SiC power MOSFETs according to QSW operation. Thus, the converter can reach very high efficiency (peak at 99.5%), maintaining soft-switching for a wide operating range, using only small auxiliary SMD capacitors and a low-volume flying capacitor, leading to high power density. The presented study is based on experimental tests using a 1.5 kV model at up to 15 kW and includes the impact of various auxiliary capacitance values and optimal capacitor value selection for maximizing the converter efficiency.

Fast Harmonic Rejecting Control Design to Enable Active Support of Charging Stations to Micro-Grids Under Distortion

This paper proposes a fast harmonic rejecting control design to enable active support of electric vehicle (EV) charging stations to micro-grids under distortion. The proposed harmonic rejecting strategy is applied to control bidirectional converters and storage elements in charging stations to improve performance of charging stations under various distorted conditions. In this approach, power quality of both ac- and dc-grids is improved by actively rejecting unwanted harmonic components in voltages, currents, and powers. A fast dynamic control design can actively reject harmonic components where harmonic filters are used to eliminate unwanted components in signals. The paper shows that the proposed harmonic rejecting method can result in a simple control design in stationary frames without any phase-lock-loop ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">PLL</i> ) blocks. A two-stage optimization method is introduced under the predictive control fashion, i.e., optimizing vector angle for control performance and then modulating vector magnitude by coordinating one active- and one zero-switching state. The comparative results prove that not only control performance is resilient under distorted conditions but also the power quality on both ac- and dc-grids is actively improved. Both MATLAB/Simulink and real-time experimental platforms are used to verify the efficacy of the proposed approach in terms of compensating the reactive power, rejecting the imbalance harmonic distortions, and smoothing the dc-voltage.

Power Quality Improvement of a Hybrid Renewable Energy Sources Based Standalone System Using Neuro-Fuzzy Controllers

Wind and Photovoltaic (PV) based hybrid standalone systems for supplying electricity to remote consumers are becoming increasingly popular around the world. In general, power generation from both PV and wind is always variable due to irradiance and speed fluctuations. Furthermore, the load is unpredictably variable and changes at random. As a result, one of the main challenges in such standalone micro grids is maintaining power quality. To maintain power quality in such standalone systems, a novel controller should be developed. Furthermore, due to the unpredictable random changes in wind speed, solar irradiance, and load, a battery bank must be integrated into the standalone system via a bidirectional converter. Furthermore, the interconnection of multiple wind turbines and PV panels can create a powerful hybrid system. This paper examines a 1 MW stand-alone power generation system using numerous PV and wind systems. Maximum power points tracking devices with perturbed and observe algorithms are used to optimize the utilization of individual PV modules and wind turbines. Because of its superior priority over conventional PI controllers, a Neuro-Fuzzy integrated controller-based novel control scheme for both inverter and bidirectional converter is proposed to achieve precise response while maintaining power quality. This paper discusses extensive results obtained by establishing hardware-in-the-loop on the OPAL-RT platform to evaluate the responses of proposed controllers. The experimental results also included to provide strength to the paper.

ДВОНАПРАВЛЕНИЙ КАСКАДНИЙ ПЕРЕТВОРЮВАЧ ПОСТІЙНОЇ НАПРУГИ ДЛЯ ПОТУЖНОЇ СИСТЕМИ ЕНЕРГОНАКОПИЧЕННЯ В МЕРЕЖАХ ЕЛЕКТРОПОСТАЧАННЯ SMART GRID

Electromagnetic processes in a bidirectional cascade DC converter with the possibility of increasing and decreasing the output voltage levels in both directions of energy transfer for electric power storage systems are considered. Using the method of averaging in the state space, a mathematical model of the pulse converter was obtained. Analytical ex-pressions for calculating the ripple characteristics of a bidirectional cascade converter have been determined, with the help of which you can calculate the main parameters of the constant voltage converter, which provide permissible volt-age ripples on the DC buses and power choke current. To illustrate the developed calculation methodology, the ripple characteristics and parameters of a 30 kW converter for various load modes with 400V and 700V DC busbars for use in energy storage systems are determined. The bidirectional converter was calculated, analyzed and simulated in Math-cad/PSim packages at idle speed and at different load levels in order to confirm the effectiveness of the conducted re-search. Ref. 7, fig. 2. Keywords: method of averaging in state space, electric power storage systems, bidirectional constant voltage converter, non-isolated four-quadrant bidirectional converter.

ДОСЛІДЖЕННЯ ДВОНАПРЯМНОГО ПЕРЕТВОРЮВАЧА ПОСТІЙНОЇ НАПРУГИ ДЛЯ ЗАСТОСУВАННЯ В СИСТЕМАХ НАКОПИЧЕННЯ ЕНЕРГІЇ

Electromagnetic processes in a bidirectional DC converter with the possibility of increasing and decreasing output voltage levels using an asymmetric inverter for a battery energy storage system when operating in difficult conditions with a short conversion period and determining its parameters are considered. Bidirectional DC converters are widely used in hybrid energy storage systems and in DC distribution power systems. This non-isolated bidirectional boost-buck converter is designed to control the flow of energy between sources with different voltage levels due to the use of low-voltage batteries in these systems. Thanks to the ability of these converters to quickly redirect electrical energy both in one and the other direction, it became possible not only to charge the battery from stationary sources of electricity, but also to charge the battery during the operation of the generator from the internal combustion engine and regenerative braking. The results of calculations of the prototype of a bidirectional DC converter with a 14 V battery, a 200 V DC bus and an output power of 3500 W are given. A prototype was made to confirm the possibility of rapid energy conversion. Ref. 9, fig. 6. Keywords: electric power storage systems, bidirectional DC voltage converter, fast energy conversion, hybrid electric vehicle.

Voltage-Oriented Control-Based Three-Phase, Three-Leg Bidirectional AC–DC Converter with Improved Power Quality for Microgrids

Renewable energy sources (RESs) and energy storage schemes (ESSs) integrated into a microgrid (MG) system have been widely used in power generation and distribution to provide a constant supply of electricity. The power electronics converters, particularly the bidirectional power converters (BPCs), are promising interfaces for MG infrastructure because they control the power management of the whole MG system. The controller of BPCs can be designed using several different control strategies. However, all the existing controllers have system stability, dynamics, and power quality issues. Therefore, this study demonstrates the development of an LCL-filtered grid-connected bidirectional AC–DC converter’s (BADC) control strategy based on voltage-oriented control (VOC) to overcome these issues. The proposed VOC-based inner current control loop (ICCL) is implemented in synchronous dq-coordinate with the help of proportional-integral (PI) controllers. An observer-based active damping (AD) is also developed in order to estimate the filter capacitor current from the capacitor voltage instead of directly measuring it. This developed AD system helps to damp the resonance effect of the LCL filter, improves system stability, and also eliminates the practical challenges of measuring capacitor current. The proposed controller with AD is able to realize bidirectional power transfer (BPT) with reduced power losses due to the elimination of passive damping and improved power quality, system dynamics, and stability. The mathematical modeling of the suggested system was developed, and the structure of the system model was established in the MATLAB/Simulink environment. The performance of the proposed system was validated with real-time software-in-the-loop (RT-SIL) simulation using the OPAL-RT simulator for a 16 kVA converter system. The real-time (RT) simulation results show that the BADC with the proposed control scheme can provide better dynamic performance and operate with tolerable total harmonic distortion (THD) of 2.62% and 2.71% for inverter and rectifier modes of operation, respectively.

Optimizing a Green and Sustainable Off-Grid Energy-System Design: A Real Case

In recent years, unquestionable warnings like the negative effects of CO2 emissions, the necessity of utilizing sustainable energy sources, and the rising demand for municipal electrification have been issued. Therefore, users are encouraged to provide off-grid and sustainable energy systems for their own homes and businesses, especially if they are located rurally and far from grids. Hence, this study aims to design an off-grid hybrid energy system, in order to minimize both the baseline cost of energy and the net current expenditure in the desired system. To construct such a system, wind generators (WG), photovoltaic arrays (PV), battery banks, and bi-directional converters are considered in the real case of a supermarket with a 20-year lifespan in Malmö, Sweden. Some significant assumptions, such as the usage of renewable energy resources only, electricity production close to the business location, and a maximum allowance of 0.1% unmet are incorporated. To optimize the considered problem, a particle swarm optimization (PSO) approach as developed to provide the load requirements and establish the number of WGs, PVs, and other equipment. Moreover, to verify the obtained results, the developed system was simulated using HOMER Pro software, and the results are compared and discussed. The results indicated that the designed hybrid energy system is able to perform completely off-grid, while satisfying 99.9% of the yearly electricity demand. The best results obtained by the proposed PSO offered 160, 5, and 350 PVs, WGs, and batteries, respectively, while the best solution found by the simulation method was the use of 384 PVs, 5 WGs, and 189 batteries for the considered off-grid system. This study contributes to decentralized local electrification by utilizing renewable energy sources that have the potential to revolutionize green energy solutions.

AC Grid–DC Microgrid Coupling with High-Performance Three-Phase Single-Stage Bidirectional Converters

This paper discusses bidirectional step-down topologies that enable the interface of the 400V unipolar DC microgrid with the European low-voltage three-phase AC grid. The study compares three single-stage non-isolated topologies, namely, the seven-switch buck converter, Swiss converter, and Y-converter, based on semiconductor stresses and losses, magnetic component sizes and losses, and heat sink sizes. The analysis is conducted for a 10kW converter designed for small commercial or residential use. The results indicate that the Y-converter has superior overall performance compared to the other topologies, making it a potentially better candidate for this application. A 10kW prototype of the Y-converter is constructed. It is demonstrated to have a peak efficiency of 99.26% and an efficiency of 97.47% at the rated output power.

A novel bridgeless flying capacitor multilevel rectifier

SummaryA novel transformerless three‐phase unidirectional bridgeless flying capacitor (UBFC) rectifier for medium‐voltage and high‐voltage applications is presented in this paper. The rectifier consists of three single‐phase rectifiers in wye connection; the DC outputs of the three single‐phase rectifiers are connected in parallel to provide a high common DC‐link bus, which makes it convenient to connect with neutral point clamped (NPC) or flying capacitor (FC) multilevel inverters. To avoid phase‐to‐phase current circulation, an additional inductor and diode are added to each single‐phase rectifier. Compared with conventional bidirectional multilevel converters, only half IGBTs are used, the voltage stress is lower, and the line‐frequency transformers are no longer required, which makes the proposed rectifier has a series of advantages such as reduced cost, simplified control complexity, increased reliability and improved overall efficiency. The basic operating principle of the proposed rectifier in continuous conduction mode is discussed; an improved carrier‐based level‐shifted pulse‐width modulation (PWM) method integrated with voltage balancing and the double closed‐loop control strategy are proposed to achieve more voltage levels and keep the flying capacitors in balance. The feasibility of the proposed rectifier is verified by the simulation and experimental results.

A virtual inertial control strategy for bidirectional interface converters in hybrid microgrid

Insufficient inertia is one of the urgent problems to be solved in the stability of AC-DC hybrid microgrid. In order to improve AC bus frequency and DC bus voltage inertia in hybrid microgrid, a virtual inertia control strategy for bidirectional interface converter (BIC) based on virtual synchronous generator (VSG) is proposed. The virtual inertia equations on both sides of the AC and DC are used to slow down the variation of the DC voltage and the AC frequency. When the load fluctuates, the dynamic response of the DC voltage, the AC frequency and the power transmission between the AC and DC subnets is improved, thus improving the stability of the system. This control strategy enables BICs to share active power equally under stable conditions, prevents circulating power, and achieves accurate power sharing among parallel BICs. The small signal model of BIC under virtual inertia control is established, the dynamic characteristics of the system under different control parameters are analyzed, and the influence of the control parameters on the system is discussed. The simulation model is established in PSCAD/EMTDC software to verify the correctness of the proposed control strategy.

Design of an energy management system applied to an electric power plant based on a biomass gasifier

Biomass gasification plants for electricity generation are an environmentally friendly technology. One of their main problems is their poor responsiveness to load variations when the plant operates off-grid. For this reason, they are usually grid-connected systems.Therefore, as a solution, an energy management system that allows the plant to operate off-grid is proposed. The system has been obtained through the optimal design of unidirectional and bidirectional Z-source converters and their coupling with their series outputs. This approach has been applied to a biomass gasification power plant.To validate the system, the results of an experimental 10 kW gasification plant are presented. With the plant working off-grid, there is a sudden load increase of 2.5 kW, and due to the proposed system performance, there is only an output voltage oscillation of less than 1%, preserving a stable power supply.This proposed system allows the plant to work isolated or coupled to a weak micro-grid of renewable energies. Obtaining a permanent supply of quality and also improving its efficiency. Thus, the gasification technology can be used for electricity generation in isolated areas of many developing countries, where the electrical grid is not totally developed, but there are available biomass sources.

High-efficiency bidirectional low-voltage power converter for fuel-cell electric vehicles

High-efficiency bidirectional low-voltage power converter for fuel-cell electric vehicles

Coordinated Power Management of a Laboratory Scale Wind Energy Assisted LVDC Microgrid With Hybrid Energy Storage System

The present work proposes a coordinated power management scheme (CPMS) of wind energy-fed self-excited induction generator (SEIG) based low-voltage direct current (LVDC) autonomous microgrid. The battery and supercapacitor (SC) based hybrid energy storage system (HESS) is interfaced with the common 48 V LVDC bus using a parallel-active configuration through two bidirectional converters. The central idea of hybridization is to mitigate the instantaneous surge current demand and alleviate the charge/discharge stress during transients, thus ultimately enhancing the cycle life of the battery. The experimental validation of the autonomous LVDC microgrid equipped with the CPMS is conducted for various operating modes. The dSPACE DS1103 digital controller is used for the real-time implementation of the complete system. The effectiveness of the proposed CPMS is supported by the analysis of comparative experimental results demonstrates its ability to incorporate seamless mode transition. The developed 48 V LVDC microgrid can be a promising solution for powering consumer electronics in homes/office spaces or other small-scale applications.

Analysis and Design of Bidirectional Parallel-Series DAB-Based Converter

Unprecedented expansion of renewable, energy storage and fast charger system applications has diversified the bidirectional converter designs over the past decade. This paper presents a new dual-active bridge (DAB) converter topology which employs parallel and series switches arrangements for low-voltage (LV) bridge configurations. The additional switch inclusion provides high dc conversion gain, which enables attractive fast charger applications. The performance of the proposed DAB-based converter with wide dc range has been investigated through several design techniques and comparisons. The use of use of silicon carbide devices (SiC) in higher power conversion significantly improves switching losses. However, unsupervised design will result in significant switching losses and increased electromagnetic emissions. Since the DAB-based converter's high switching frequency allows operation with smaller magnetics, the system stray capacitance plays a critical role. The common-mode current (CMC) propagated through the system's stray capacitance generates undesired electromagnetic interferences (EMI) and impacts the soft-switching achievable range. To overcome the common-mode current circulation issue, design solutions have been employed to reduce the emergence of system stray capacitance. A harmonic analysis is further discussed along with evaluation of transformer design comparisons. The experimental results show the performance of the DAB-based converter in bidirectional operation and improved common mode current generation with respect to EMI emissions. The simulation and experimental results have been performed using a 5kW rated power DAB-based converter with SiC power semiconductors.

Integrated bidirectional converter with voltage equalizer for energy storage system

SummaryIn energy storage systems, a voltage equalizer is always needed. The voltage equalizers often include a DC‐DC converter. In this paper, the DC‐DC converter in the voltage equalizer is saved by integrating the voltage equalization circuit into the bidirectional converter of the battery system, thus simplifying the system. The voltage equalization circuit in the integrated system is composed of a LC resonant circuit and a voltage multiplier, which has the advantages of simplicity and low complexity. This paper presents the design process based on the analysis model, which enables the equalizer to obtain the optimal parameter configuration. Test results show the proposed LC‐SVM can automatically realize voltage balance between energy storage cells without additional control.

Real-time implementation of sliding mode controller for standalone microgrid systems for voltage and frequency stabilization

This paper presents for stabilizing the output voltage and frequency of the hybrid source microgrid system (HSMG) and standalone solar photovoltaic microgrid system (SAPV), under varying source and loading conditions. An HSMG system consists of a solar, wind and battery system incorporated with a solar boost converter, wind rectifier/boost converter and bidirectional converter, respectively. These different dc level outputs are applied to the multiple input dc–dc converter for obtaining the constant dc level and then converted into three-phase power with suitable inverters. The source-side converters are designed to obtain the maximum output irrespective of the input conditions with PI controllers. The multiple input dc–dc converter controls the dc link voltage with the well-designed proportional, proportional integral, proportional integral derivative controller. The three-phase inverter is premeditated to obtain the constant voltage and frequency even under varying load patterns. The tuning of the PID controller is incorporated with Ziegler Nichols’s technique to reduce the frequency deviation and steady-state error. A SAPV microgrid system is developed with a high-capacity solar system incorporated with two-stage power conversion. Stage 1 and 2 are constant dc/constant ac obtained using suitable converters incorporated with an adaptive controller. The sliding mode controller (SMC) is an adaptive controller that performs better in dynamic operations. In this work, SMC maximizes the solar output and stabilizes the DC voltage using an appropriate PWM pulse to the boost converters. Also, the output voltage and frequency are maintained constant during the different operating situations. All simulations are carried out in MATLAB. PID and SMC controllers are implemented to the HSMG and SAPV microgrid systems in the OPAL-RT environment to validate the results in real-time applications respectively. The different operating conditions are tested for both the systems and the results prove that the chosen controllers are more suitable for these applications.