Bidirectional Flyback Research Articles

Fast Battery Cell Voltage Equalizer Based on the Bidirectional Flyback Converter

The prevalence of electromobility requires reliable battery energy storage systems that can assure the high demands for extended driving range of the electric vehicles. To meet this demand, the Battery Management System (BMS) plays a major role. The requirements for the BMS variate according to the specific needs for each application. In this paper, a high-equalisation current BMS with high efficiency is implemented, based on the bi-directional flyback converter. The modelling of the converter considering non-ideal elements is combined with the Genetic Algorithm to select the parameters of the converter that maximise the efficiency of the BMS. As a result, a BMS for high-capacity lithium cells is implemented, achieving a 91.73 % efficiency for a balancing current of 5 A, and a peak efficiency of 94.19 % for a balancing current of 2 A. The proposed BMS follows the bi-directional module-to-cell configuration and is intended for integration on independent cells. As a result, a smart cell is developed that can be used in second-life battery applications.

A Modular Differential Power Processing Converter Design with Simplified Voltage Equalization for Photovoltaic Systems

Partial shading in series-connected photovoltaic (PV) systems poses a significant challenge as it considerably restricts the system’s output power and has a notable impact on the overall efficiency. Differential power processing (DPP) has emerged as a widely employed solution to mitigate this effect. However, implementing DPP architectures introduces challenges such as system cost, reliability, control implementation, and modularity. This research proposes a simplified voltage equalization (VE) algorithm, executed on a low-cost and modular DPP architecture using bi-directional flyback converters. Notably, under light and moderate partial shading conditions, the PV system’s output power exhibits a significant increase compared to the traditional string configuration with bypass diodes. To further optimize the system performance, a methodology adapted to the VE algorithm is suggested, minimizing the processed power while increasing overall efficiency. The proposed solutions have undergone rigorous testing through simulations and experiments. The results validate that, under moderate shading conditions, the system efficiency reaches approximately 90%.

A virtual bus parallel differential power processing configuration for photovoltaic applications

Photovoltaic (PV) systems are often exposed to mismatch caused by partial shading, different mounting angles, dust accumulation, cell degradation, and so on. This paper proposes a novel parallel differential power processing (P-DPP) configuration to minimize mismatch-related losses among PV strings. The proposed configuration, called PV to Virtual Bus P-DPP, uses a virtual bus as an input for all P-DPP converters. Since the virtual bus voltage can be selected lower than the DC Bus voltage, components’ voltage rating can be reduced. An essential feature of the proposed configuration is the ability of the converters to generate both positive and negative output voltage. Therefore, a bidirectional flyback converter connected to a bridgeless converter is proposed as the P-DPP converter. To find the MPP of each PV string, the Perturb and Observe (P&O) algorithm is implemented. Moreover, a proportional–integral feedback controller controls the virtual bus voltage through the central converter. The benefits of the proposed configuration are discussed, and the operation of the proposed structure is further verified through simulations with the software PLECS.

Sliding mode controller for multiphase bidirectional flyback converter topology in hybrid electric vehicle applications

Day by day, the power electronics (PE) application is increasing in hybrid electric vehicles (EV). The power interfacing between the DC link drive and battery is the main issue of EVs. The best choice for this application is the bidirectional flyback converter (BFC). This can be used in a different interface, like load from the grid to the battery, external Genset to the battery, and battery to the load. In this work, a Multiphase BFC Topology is developed for Hybrid EVs. It includes the design of the Sliding mode controller (SMC), which offers superior performance to the existing controller. Due to its separated nature and smaller machinery, it is most favoured in high-voltage applications. The suggested work is executed in MATLAB/Simulink environment. The proposed method is compared with the current controllers like GA-PID, Fuzzy logic controller (FLC). From the experimental outcomes, it is observed that the proposed SMC technique gives better converter performance.

Validation of a balancing model based on master-slave battery management system architecture

The battery management system (BMS) performs the monitoring and control of the charging/discharging process of the cell, state of charge estimation, battery safety and protection, state of health estimation, cell balancing, and thermal management. These control operations ensure accurate, safe, and reliable operating conditions, individual cell damage on battery string, and increase the cell life. Battery balancing is one of the key technologies in the BMS, which affects the actual usable capacity range, performance, and lifetime of the entire battery module. However, it is difficult to evaluate or compare the performance of the overall BMS under the multi-series battery module structure. Most of the proposed battery energy storage system (ESS) models focus on energy distribution and system estimation (microgrid or renewable energy). This study develops a balancing model for estimating the balancing performance of the BMS. A Master-Slave BMS (MS-BMS) is proposed to validate the balancing model. The Master and Slaves of the BMS employed a traditional flyback converter with a MOSFET switching array and bidirectional flyback converters with photoMOS arrays, respectively, to perform the balancing behavior. The balancing skill, balancing circuit power, equalization speed, control simplicity, modularization simplicity, and cost has been considered in designing the proposed BMS. The simulation results are verified with the experimental results, which are then compared with the balancing model's results under the five balancing conditions, and the average absolute error of the balancing duration results is 3.12%. The performance of the proposed BMS is also compared with the existing modular BMS architecture, which validates the advantages of the proposed BMS including equalization speed, control simplicity, modularization simplicity, and cost.

Balanced Control System Based on Bidirectional Flyback DC Converter

The inconsistency of the battery pack will cause the “barrel effect“ when the battery pack is working. The battery with lower power will first reach the discharge cut-off condition, resulting in the battery pack not being fully discharged, reducing the battery utilization rate. This paper uses the state of charge (SOC) as an equilibrium variable and the forgetting factor recursive least square–extended Kalman filter (FFRLS-EKF) method to estimate the SOC. Using a balanced topology based on a bidirectional impact direct current (DC) converter, the energy transfer can occur between any battery and only between batteries that need to be balanced, increasing energy utilization and the effect of equalization. The equalization system is simulated under various conditions, which proves the effectiveness of the equalization control system.

A Multifunctional, Non-Constant Current Charger Based on a Dual-Switching, Bidirectional Flyback Converter

This study implements a multifunctional charger based on a dual-switching, bidirectional flyback converter (DSBFC). The proposed charger adopts seven charging methods, including the incremental-current charging, constant-voltage (CV) charging, constant-current (CC) charging, pulse-current (PC) charging, triangular-current (TC) charging, sinusoidal-current (SC) charging, and positive/negative pulse-current (Reflex) charging methods. The charging process of a lithium-ion battery is divided into three stages: an initial term, a mid-term, and a final term. In the initial term, the incremental-current charging method is used in the initial term of charging for a soft start and to inhibit an increase in temperature. In the mid-term, five charging methods, including CC, PC, TC, SC, and Reflex-current charging, are used for charging. The CV charging method prevents overcharging the lithium-ion battery in the final term. Based on our experimental results, this study compares the four charging methods (PC, TC, SC, and Reflex-current) with the CC charging method to verify their improvement of the charging speed and increase in temperature in the mid-term. The charging speeds increased by 14.38%, 14.04%, 16.36%, and 27.27%, respectively, and the rise in temperature decreased by 37.8%, 40.5%, 48.6%, and 13.51%, respectively; all performed better than the CC charging method. Finally, users can adjust the charging method of the proposed DSBFC according to the needs of batteries so as to achieve excellent performance.

Sliding-Mode Control of Bidirectional Flyback Converters with Bus Voltage Regulation for Battery Interface

Energy storage systems are essential for multiple applications like renewable energy systems, electric vehicles, microgrids, among others. Those systems are responsible of regulating the dc bus voltage using charging-discharging systems which are mainly formed by a power converter and a control system. This work focuses on the control system of a flyback converter. A detailed design procedure of an adaptive sliding-mode controller (SMC) and its parameters is presented. The proposed procedure was validated through simulations which allow to confirm its good performance in terms of global stability providing the desired dynamic of the dc bus voltage regulation.

A Modular Multifunction Power Converter Based on a Multiwinding Flyback Transformer for EV Application

In this article, a revolutionary and novel single-stage, multiport power conversion block is proposed. The power conversion concept is based on a bidirectional flyback converter with four-quadrant switches that permit us to seamlessly control the direction of the energy flow and to select which ports are active. This approach, denominated as multicell multiport bidirectional flyback (M2BF), can be used as a modular and a multifunction building block interfacing ac and dc sources and loads in complex conversion systems like the one we can encounter in electric vehicle (EV) applications. The multiport property is obtained due to the multiwinding flyback transformer that interfaces different sources and loads in a simple and effective way. We present and analyze this concept in detail, focusing on different operation modes it can provide (multiport dc–dc conversion, ac–dc conversion, vehicle-to-grid, grid-to-vehicle, and so on) and their possible implementation in the energy distribution network of an EV, where this unique multifunction multiport converter could bring an important breakthrough. The operating principles of the M2BF for different operating modes are described and analyzed, placing emphasis on the modularity of the proposed concept. The overall concept is evaluated and quantified using a gallium nitride (GaN)-based prototype achieving efficiencies higher than 91% that additionally validates the proposed idea experimentally. The presented analysis and experimental results clearly identify the advantages and limitations of the presented concept leaving no doubt about its usefulness to the future EV distribution network.

슈퍼커패시터 전압 밸런싱을 위한 디지털 제어기 개발

In this paper, a digital controller is developed to perform voltage balancing of the supercapacitor cells. The bidirectional flyback converter which has a simple structure and is frequently used in charging and discharging circuits is used to charge and discharge the supercapacitor cells. The balancing circuit with the controller constructed in this paper uses the capacitor placed on the rectifier circuit of the input ac source to exchange energies among supercapacitor cells instead of auxiliary capacitors or batteries which are usually used in active shuttling battery cell balancing circuits. The validity of the controller developed for the supercapacitor voltage balancing is shown through experimental results.

A Reduced-Component-Count Centralized Equalization System for Series-Connected Battery Packs Based on a Novel Integrated Cascade Topology

In this article, a reduced-component-count centralized equalization system based on a novel integrated cascade equalization topology is proposed to achieve the equalizing of series-connected battery packs. The proposed converter topology is the integration of the polarity switches and the bidirectional converter in traditional centralized battery equalization systems, and can also be regarded as a cascade structure composed of a bidirectional buck-boost and a bidirectional flyback converter. Compared with existing centralized equalizers, the number of components applied on the proposed scheme is significantly reduced, which obtains higher cost performance and reliability, and is more suitable for the equalization of large-capacity battery packs. Meanwhile, this integrated cascade structure enables the proposed topology to achieve an ultra-high voltage conversion ratio; hence, the efficiency can be significantly enhanced by employing a transformer with a smaller turns ratio and reduced leakage inductance. Furthermore, the operating principles, design considerations, and comparative analysis are presented in detail. Finally, an experimental prototype based on a 13-cell lithium-ion battery pack is established to verify the superior performance of the proposed equalization system.

Ultra-High-Voltage (7-kV) Bidirectional Flyback Converter Used to Drive Capacitive Actuators

Dielectric elastomer actuators (DEAs) have extremely advantageous characteristics such as lightness, compactness, flexibility, and large displacements. However, in order to operate, they can require voltages in the order of several thousands of volts. Thus, to unleash the full potential of DEAs, it becomes essential to be able to generate and manipulate such voltages with an electronics as compact and efficient as possible. While previous works showed that it was possible to implement a system capable of supplying voltages of up to 2.5 kV and recovering part of the energy stored in DEAs (due to their capacitive nature), no work managed to go over that threshold for two main reasons: first, due to the absence of switches capable of withstanding more than 4.5 kV, and, second, due to parasitic capacitances of the flyback's coupled inductor, which steal an increasingly large part of the energy destined for the load when the output voltage is higher. This article, therefore, proposes a global design, where the factors limiting the increase in the output voltage have been mastered. Through a careful design of the coupled inductor combined with the use of mosfets put in series, thanks to the pulsed transformer gate drive topology to handle the high voltages, this work goes beyond the current state of the art. Indeed, here, we present various strategies undertaken, which led to the manufacture of a bidirectional flyback converter capable of amplifying an input voltage of 12 V to more than 7 kV across a capacitive load and recuperating parts of the energy stored. A preliminary study of the efficiency shows an approximate 58% efficiency during the charge phase from 0 V to 7 kV and a 54% efficiency during the discharge phase.

Adaptive estimation-based hierarchical model predictive control methodology for battery active equalization topologies: Part II - equalizer control

In the first paper, a model predictive control (MPC) balancing strategy as the superior control is developed based on a universal equalization plant with balancing efficiency. Herein, two typical active equalization topologies, i.e., bidirectional adjacent, and bus-based, are considered to design the low-level controller, and the bidirectional flyback converter is selected as an individual cell equalizer (ICE). First, the extended Kalman filter (EKF) state-of-charge (SOC) estimation is presented to develop a unified ICE model. Then, an adaptive estimation-based control is proposed to track the optimal balancing reference current yielding from the superior control MPC formulation under the charge/discharge disturbance and parameters uncertainties. The current/voltage adaptive sliding-mode tracking control of the ICE is derived through the defined Lyapunov function, and the results are compared with a PI controller. Combined with the MPC balancing strategy, the EKF and adaptive-based controls are utilized to perform a balancing task for a 5-series battery cells module, which reduced the unbalanced SOC from 13% to 1%. To conclude, with the proposed superior control MPC strategy yielding optimal current targets, the low-level adaptive estimation-based controller for the ICE can effectively balance the inconsistent series-connected cells in typical active equalization systems by taking disturbance and uncertainty into consideration.

An active parallel power decoupling circuit with a dual loop control scheme for micro‐inverters

AbstractAn important challenge in single‐stage single‐phase micro‐inverters is reducing required capacitance by various active power decoupling (APD) techniques in order to use film capacitors with a longer lifetime instead of electrolytic capacitors. In this paper, a photovoltaic (PV)‐side parallel APD circuit based on a bidirectional flyback converter is proposed. This topology is able to increase the average and ripple voltages for the capacitor due to having a transformer and thus can reduce the required capacitance. In the control scheme, dual control loops on the main and decoupling circuits manage the micro‐inverter operation. The primary control loop is based on the instantaneous active and reactive power theory and a proportional resonant (PR) controller that is responsible for delivering the PV panel energy to the grid. The secondary control loop regulates the pulsation power on the dc‐link capacitor through the PR controller. Simulation results demonstrated that the proposed APD circuit and the control method could properly damp the pulsation power in the normal and reference tracking operations. Furthermore, the good robustness of the micro‐inverter was confirmed in shutdown and start‐up. Finally, the experimental results with a 180‐W single‐phase micro‐inverter prototype are presented, which validates the advantages of the proposed configuration.

Bidirectional Isolated Single-Stage Single-Phase AC–AC Converter

The objective of this paper is to propose a bidirectional isolated single-stage single-phase ac-ac converter (BISS-converter) with quasi-resonant (QR) topology. The proposed converter is composed of multiple bidirectional flyback type dc-dc converters (BFDCs) and two bidirectional dc-ac unfolders. Because the unfolder only switches at the zero crossing of the ac line voltage, there is only one set of high-frequency pulse width modulation (PWM) signal, which is used to control the BFDCs to generate the desired rectified sinusoidal currents. Advantages of the proposed BISS-converter include high conversion efficiency, single-stage high-frequency power conversion, simple control circuit, flexible capacity, and bidirectional power flow capability. Moreover, the controller can maintain the zero voltage switching to reduce the switching loss without the need for valley detection. Also, with the interleaved operation between BFDCs, the current ripple of the output can be reduced greatly. The hardware experimental results are shown to verify the performance of the proposed BISS-converter.

An Active Equalization Method for Lithium-ion Batteries Based on Flyback Transformer and Variable Step Size Generalized Predictive Control

The inconsistency in large-scale battery pack significantly degrades the performance of electric vehicles. In order to diminish the inconsistency, the study designs an active equalization method comprising of equalizer and equalization strategy for lithium-ion batteries. A bidirectional flyback transformer equalizer (BFTE) is designed and analyzed. The BFTE is controlled by a pulse width modulation (PWM) controller to output designated balancing currents. Under the purpose of shortening equalization time and reducing energy consumption during the equalization process, this paper proposes an equalization strategy based on variable step size generalized predictive control (VSSGPC). The VSSGPC is improved on the generalized predictive control (GPC) by introducing the Step Size Factor. The VSSGPC surmounts the local limitation of GPC by expanding the control and output horizons to the global equalization process without increasing computation owing to the Step Size Factor. The experiment results in static operating condition indicate that the equalization time and energy consumption are reduced by 8.3% and 16.5%, respectively. Further validation in CC-CV and EUDC operating conditions verifies the performance of the equalizer and rationality of the VSSGPC strategy.

Segmented Differential Power Processing Converter Unit and Control Algorithm for Photovoltaic Systems

Differential power processing (DPP) for photovoltaic (PV) systems can achieve high system efficiency and maintain maximum power production even under mismatched conditions. However, DPP converters applied to large-scale systems have challenges of complicated installation and high voltage ratings. The segmented DPP structure is introduced as a modular approach that utilizes groups of bidirectional DPP flyback converters to maximize PV power generation while minimizing converter power loss. Groups of four DPP converters are combined into a segmented DPP unit with maximum power point tracking (MPPT) control to maximize output power of the unit. The segmented DPP system and control algorithm are verified through simulation and hardware experimentation. Simulation results verify the effectiveness of the control algorithm with multiple segmented DPP units interacting with a typical inverter employing MPPT. Experimental results verify that system efficiency of the segmented DPP unit reaches 96.4% in even lighting conditions, reaches 92.7% in severe partial shading conditions, and shows an increase of up to 14.8% in uneven lighting conditions compared to an equivalent series-connected PV system.

An Active and Passive Hybrid Battery Equalization Strategy Used in Group and between Groups

Active battery equalization and passive battery equalization are two important methods which can solve the inconsistency of battery cells in lithium battery groups. In this paper, a new hybrid battery equalization strategy combinfigureing the active equalizing method with a passive equalizing method is proposed. Among them, the implementation of the active equalizing method uses the bidirectional Flyback converter and Forward converter. This hybrid equalizing strategy adopts the concept of hierarchical equilibrium: it can be divided into two layers, the top layer is the equalization between groups, and the bottom layer is the equalization of group. There are three active equilibrium strategies and one passive equilibrium strategy. For verification purposes, a series of experiments were conducted in MATLAB 2018b/Simulink platform. The simulation and experiment results show that this hybrid battery equalizing method is efficient and feasible.

Power Loss Analysis and a Control Strategy of an Active Cell Balancing System Based on a Bidirectional Flyback Converter

This research proposes a power loss analysis and a control strategy of an active cell balancing system based on a bidirectional flyback converter. The system aims to achieve an energy storage application with cells connected in 6 series and 1 parrarel (6S1P) design. To reduce the structural complexity, Metal-Oxide-Semiconductor Field Effect Transistor (MOSFET) array commonly used in balancing system is replaced with the photovoltaic Metal-Oxide-Semiconductor (photoMOS) array. Power loss analysis is utilized for the system operating in the proper current to reach higher efficiency. The proposed loss models are divided into conduction loss, switching loss, and copper and core loss of the transformer. Besides, the models are used to estimate the loss of converter operating in different balance conditions to evaluate the system efficiency and verified by the implemented balancing circuit. By way of the loss models, the balancing current can be determined to reach higher efficiency of the proposed system. For further improvement of the balancing process, the system has also applied a control strategy to enhance the balancing performance that reduces 50% maximum voltage difference than traditional cell-to-pack architecture, and 47% balancing duration than traditional pack-to-cell architecture.

Novel voltage equalisation circuit of the lithium battery pack based on bidirectional flyback converter

Lithium batteries have become the main power source for new energy vehicles due to their high energy density and low self-discharge rate. In actual use of series battery packs, due to battery internal resistance, self-discharge rate and other factors, inconsistencies between the individual cells inevitably exist. Such inconsistencies will reduce the energy utilisation rate and service life of the battery pack, and even endanger its battery system safety. To improve the inconsistency of series battery packs, this study innovatively proposes an equalisation method based on a flyback converter. The residual power of a single cell is used as an index of inconsistency. A simple and reliable flyback converter is used to achieve balanced energy in the entire group, which make the energy is transferred between any batteries. Compared with the traditional equalisation topology, the equalisation topology proposed in this study reduces the number of components and reduces the volume of the equalisation system. Moreover, the primary side of the energy transfer only needs a set of control signals, which reduces the control difficulty. A series of equalisation experiments were performed using 12 series of battery cells. The results show the effectiveness of the proposed new equalisation method.