Dual Phase Shift Research Articles

A Novel Feedforward Scheme for Enhancing Dynamic Performance of Vector-Controlled Dual Active Bridge Converter with Dual Phase Shift Modulation for Fast Battery Charging Systems

This paper proposes a novel feedforward control scheme to achieve a very smooth transition from Constant Current (CC) to Constant Voltage (CV) charging modes, the commonly used method for electric vehicle charging applications. Furthermore, a three-loop model-independent Linear Active Disturbance Rejection Control (LADRC)-based system is proposed, replacing the traditional two-loop Proportional-Integral (PI) control system. The extra loop performs a decoupled dq vector control of the inductor current, which is typically not used in single-phase Dual Active Bridge (DAB) systems. This additional loop not only facilitates the optimal determination of both internal and external phase shift angles of a Dual-Phase Shift (DPS) modulator but also lowers the peak input current of the converter, allowing for lower-rated switches. Numerical simulations using MATLAB/Simulink demonstrate the robustness of the proposed control strategy against both input voltage disturbances and load disturbances during the transition from CC to CV charging modes. Hence, the dynamic performance of the charging system is significantly improved with minimal controller effort.

Circulating power flow restricted operation of the isolated bi-directional dual-active bridge DC-DC converter for battery charging applications

This paper presents the Non-Circulating Power Flow (NCPF) enabled Dual Active Bridge (DAB) converter controller strategy. The proposed DAB controller eliminates the non-circulating power flow for all the four conventional modulation algorithms, i.e., Single Phase Shift (SPS), Extended Phase Shift (EPS), Dual Phase Shift (DPS) and Triple Phase Shift (TPS) modulation schemes. This leads to lesser current stress and power loss across the DAB converter switches due to reduced peak inverse current. The proposed controller strategy finds various applications, such as in a Solid-State Transformer (SST) enabled microgrid, or for Electric Vehicle (EV) Energy Storage Unit (ESU: battery, supercapacitor) integrations, etc. The proposed NCPF operation reduces battery (and supercapacitor) current stress by upto 71.8 %, and improves operative environment, thus fostering its health and lifecycle. In NCPF mode, if the rating of installed switches (current and voltage ratings) remains unchanged, its power transfer capability is marginally reduced by mere 10.0 %. In addition to this, the operating range (i.e., controlling range of phase shift (Φ) and modulation index (m)) remains unaffected. This paper summarizes the DAB NCPF operation in restricted power flow mode as a function of Φ and m through 3-D and 4-D graphs. Finally, working of NCPF DAB is tested via both simulation and hardware platforms. Comparative results are shown for conventional and proposed modulation schemes on hardware platform, to showcase the elimination of circulating current in both forward and reverse DAB operating modes. It is inferred that proposed controller is worthy of real-world implementations.

Phase shift control of dual active bridge DC‐DC converter based on feedforward compensation and transient optimization strategy

SummaryIn the context of the dual active bridge (DAB) bidirectional DC‐DC converter using the traditional dual‐phase‐shift (DPS) control method, a transient DC bias occurs during power co‐direction and commutation conversion. This bias negatively impacts the converter's transient performance and can lead to harsh effects, such as hard switching problems, resulting in power loss and excessive current stress. In a closed‐loop control system, poor transient response may destroy the stability of the converter. In this paper, the transient‐optimized‐dual‐phase‐shift (TODPS) control strategy is proposed to eliminate the transient DC bias and to maintain soft switching during transient states. It reduces power loss, eliminates excessive current stress, and allows for smooth transitions between single‐phase‐shift (SPS) and DPS control strategies without introducing DC bias. A closed‐loop control system based on TODPS control is established with feed‐forward compensation to adjust the primary‐side current and modify transmission power. This adjustment enhances the transient performance of the DAB converter. The proposed strategy is versatile and applicable to various power conversion scenarios involving DAB converters. It enables quick switching of the magnitude and direction of the primary‐side current during transient states, resulting in a smooth transient effect without noticeable overshoot or oscillation. The experiment results verify the effectiveness of the proposed transient optimization strategy.

The Generalization of Bidirectional Dual Active Bridge DC/DC Converter Modulation Schemes: State-of-the-Art Analysis under Triple Phase Shift Control

The main objective of this paper is to provide a thorough analysis of currently used modulation control schemes for single-phase bidirectional dual active bridge DC/DC converters. In this article, it will be shown that single phase shift, extended phase shift and dual phase shift modulation schemes are special cases of the triple phase shift (TPS) modulation scheme. The article aims to highlight six TPS switching modes and their complements with operational constraints. Unlike previous studies that regarded TPS as a complex scheme, this paper simplifies the analysis of each mode and aims to standardize the understanding of TPS modulation for dual active bridge (DAB) converters. Power equations, range of power transferred and zero-voltage switching (ZVS) are derived for all the modes under TPS without assuming fundamental component analysis. Additionally, a generic optimization algorithm is developed to show the advantages of TPS modulation, and thus, the analysis in this paper offers a valuable insight for single-phase DAB converter designers in identifying a wide range of optimization algorithms to achieve higher efficiency under TPS modulation. This analysis contributes to the advancement of bidirectional DAB converter technology and facilitates its application in various power electronic systems.

A series inductance based three-port isolated hybrid DC–DC converter for microgrid applications

The paper proposes a series inductance based three-port isolated hybrid converter (3PIHC) for wide change in voltage transformation ratio (VTR) which supports DC microgrid applications. Three-ports in the proposed converter is integrated by means of a three-winding high frequency transformer (HFT). The leakage inductance of three-winding HFT acts as an energy transfer element between the ports. The factors which need to be considered for designing the leakage inductance are power transfer flexibility and limits of current transfer at wide change in VTR. In a feasible scenario, the intricate aspects such as inconsistency of leakage inductance, requirements of power flow variability and current restrictions necessitates auxiliary inductors in series with the three-winding HFT. This paper focuses on selecting appropriate value of series inductance for 3PIHC based on the application demand and minimized converter losses. Study and analysis are carried out to evaluate the converter performance at certain values of series inductance which is the sum of leakage inductance of HFT and auxiliary inductance. A hybrid configuration is adopted in the proposed converter where the primary port holds multi-level half bridge structure which reduces the voltage stress across the transformer primary winding and semiconductor switches. The secondary and tertiary port occupies H-bridge circuit topology. Converter analysis is presented for both conventional phase-shift modulation (CPM) and dual phase shift modulation (DPM). A simple computational method for obtaining the phase-shift variables at minimum value of current stress is developed. Evaluated the converter current stress for various values of series inductance and at wide change in VTR. A prototype of the proposed converter is implemented and examined. The experimental results demonstrated authenticates the accuracy of theoretical analysis.

The Effect of Cross-Coupling on the Dynamic Performance of a Dual Phase Shift Controlled BiWPT System

In a bidirectional wireless power transfer (BiWPT) system, dual phase-shift (DPS) control is used to maintain the optimal efficiency at constant output power over varying misalignment. The presence of multiple control and output variables in DPS control creates cross-coupling between transmitter and receiver side, making BiWPT a multiple-input multiple-output (MIMO) system. Due to cross coupling, any change in control variable in one side of the BiWPT system will affect the output of the same side as well as output and control input in the other side. This results in an uncertain dynamic behaviour of the output response. The cross-coupling effect has not been adequately researched in the literature. Hence, this paper presents an accurate dynamic model using a generalized state-space averaging approach (GSSA) and an extended describing function (EDF) method for a multivariable control of the S-S compensated BiWPT system. This model is used to derive the system’s relative gain array (RGA), which is used to study the effect of cross-coupling terms on the output variables. A 1 kW S-S compensated BiWPT experimental set-up is used to validate the effect of cross-coupling on the dynamic behavior of the system by comparing DPS and single phase-shift (SPS) controlled experimental waveforms. The steady-state and transient behavior of the BiWPT system has also been investigated with simulation and experimental results.

Current stress optimization control of isolated AC-DC matrix converter

The Isolated AC/DC matrix converter realizes bi-directional energy transmission through phase shift control. The existing control schemes do not coordinate the modulation coefficient and phase shift ratio well, which will cause large current stress to the converter, resulting in low efficiency. To solve this problem, this paper analyses the working mechanism of IAMC under dual phase shift control. It constructs a mathematical model under dual phase shift control to calculate the current stress. An optimal control method for the current stress of isolated AC/DC matrix converter is proposed. The current stress is suppressed by coordinating modulation coefficient and internal and external phase shift ratio. Finally, a simulation platform is built to verify the proposed method.

Perturbation Observation Method-Based Optimization Seeking Control of Soft-Switching and No Backflow Power for LCL Resonant-Type Dual Active Bridge DC–DC Converters

LCL-type resonant dual active bridge (LCL-DAB) DC-DC converters feature high gain, high power density, and low reactive current. To further improve the efficiency, based on the dual-phase shift (DPS) modulation method, the operating characteristics are firstly derived and the design regions of soft-switching and no backflow power are established, and then a perturbation observation method based optimization seeking control of soft-switching and no backflow power is proposed in this paper. In the starting process, the system firstly tracks the reference voltage according to the relationship between the inner and outer phase shift ratio obtained by the first harmonic approximation. Then, the outer phase shift ratio is perturbed based on the characteristics of soft-switching and backflow power, approaching the target phase shift ratio stepwise, while the inner phase shift ratio is calibrated to hold the output voltage. Both H bridges can operate in soft-switching mode, and on this basis, the backflow power was eliminated to the maximum extent. Finally, the simulation and experimental results verified the feasibility and effectiveness of the proposed method.

Improved Triple-Phase-Shift Modulation for Bidirectional CLLC Converters

CLLC resonant converters are an attractive option for battery charging applications due to their bidirectional power flow and high efficiency. Pulse frequency modulation (PFM) is the simple method to drive CLLC converters. However, PFM cannot regulate the output voltage under the light-load condition properly, which leads to high switching and core losses. Phase shift modulation techniques like dual-phase shift (DPS) modulation can overcome this challenge. However, more improvements are demanded due to high circulating currents in phase shift modulations. In this paper, an improved modulation technique based on triple-phase shift (TPS) has been applied in CLLC converters to improve the light-load efficiency. TPS modulation like any other phase-shift modulation, keeps the switching frequency of CLLC converters fixed at the resonant frequency under the light-load condition and regulates the output voltage by its three phase shift parameters. The improved TPS modulation has lower circulating current at the same average output current compared to DPS modulation. Therefore, higher efficiency, smaller peak, and RMS current values can be achieved under the light-load condition. In addition, the proposed TPS modulation has a better flexibility in regulating the output voltage under the light-load condition due to an extra phase shift parameter compared to DPS modulation. The proposed TPS modulation has been analyzed thoroughly in this paper and a proper selection of phase shift values has been explained to improve the efficiency of the converter. Finally, advantages of the improved TPS modulation have been validated by simulation and a 1 kW experimental setup.

Dual Polarization DQPSK ROF System with Duo Binary Precoding and Hybrid Amplification for Effective Hybrid SMF FSO Transmission Medium

This article demonstrates the utilization of a hybrid amplification technique on the transmission part of the proposed hybrid medium transmission system which includes both using Single Mode Fiber (SMF) with 60 km and Free Space Optic (FSO) with a range between 5 km and 25 km. It has included four weather situations with an investigation of the FSO medium-based system performance. The system uses 64 channels based on Dual Polarization-Differential Quadratic Phase Shift Keying (DP-DQPSK) Dense Wavelength Division Multiplexing (DWDM) for the Radio over Fiber (RoF) system using the Duo Binary coding scheme to improve the system efficiency in general and the cross-talk in particular. The investigations will include using the hybrid amplifiers of Erbium Doped Fiber Amplifier (EDFA) and Optical Amplifier (OA) for transmission. The analysis results show that using the hybrid amplification could improve the transmission to reach 25 km for light air case, meanwhile, for light haze, it could reach up to 20 km. Moderate haze could improve transmission efficiency for a distance of 7 km. Finally, for moderate rain situations, the transmission could be further improved to cover a distance of up to 5 km.

A wide zero-voltage-switching range with low reactive power modulation strategy for LCL resonant three-phase dual active bridge DC–DC converter in renewable energy generations

LCL resonant three-phase dual active bridge (LCL-TPDAB) dc–dc converter is progressively used in renewable energy systems due to the advantages of low circulating reactive power and wide voltage regulation. Conventional dual-phase-shift (DPS) modulation can effectively reduce the circulating reactive power of the converter, but it cannot achieve zero-voltage-switching (ZVS) of all switches, which increases switching losses and generates electromagnetic interference. To solve the above problems, an optimized modulation strategy based on phase-shift plus duty cycle (PSPDC) control is proposed in this paper. Firstly, the mathematical model of the LCL-TPDAB converter with the PSPDC modulation is established by harmonic analysis. Then, the relationship between the ZVS boundaries and the control variables is determined by analyzing the soft-switching characteristics. In order to accurately describe the ZVS boundaries, the impact of switch junction capacitance is considered in the analysis. Further, an optimized modulation strategy is proposed, which can achieve ZVS for all switches and low reactive power in the whole operating range. Furthermore, the offline particle swarm optimization (PSO) algorithm is introduced to acquire the optimal control variables in the operation of the converter. Finally, a 1.5 kW experimental prototype is applied to verify the effectiveness and excellence of the proposed optimized modulation strategy, where the efficiencies are improved in the whole operating range.

Control and Study of the Three-Phase Three-Level Dual Active Bridge DC Converter

Multilevel DAB converters can share more effectively the reverse voltage compared to conventional dual active full-bridge converters, reducing the cost of switching tubes at the same power and voltage levels. At the same time, the increased control freedom of multilevel makes the control objectives more flexible, combining optimization objectives such as soft switching and inductor current reduction. In this paper, we propose a three-phase three-level dual active converter, based on the power transfer characteristics of dual phase shift control in the time domain, deriving the effect of inductor current with phase shift angle and variable voltage ratio, and determining the conditions for the switching tubes to work in soft switching, which effectively reduces the DC bus current fluctuation. Finally, the correctness of the theoretical analysis is verified by simulation.

A Three-Parameter Adaptive Virtual DC Motor Control Strategy for a Dual Active Bridge DC–DC Converter

Increasingly more power electronic devices are being connected to DC microgrids, which reduces the inertia of a DC microgrid, and the DC bus voltage has poor resistance to disturbance. Adding a virtual DC motor control to the converter can effectively suppress the fluctuation of the DC bus voltage; however, due to the fixed inertia and damping parameters, the system cannot attain a good dynamic performance. On this basis, a two-parameter adaptive virtual DC motor control is proposed to realize flexible change both in terms of inertia and damping, which improves the stability of the DC bus, and the system has good dynamic performance under this control. To further improve the stability of DC bus voltage and the flexibility of the microgrid control, in this paper, a dual active bridge (DAB) DC–DC converter controlled by dual phase shift (DPS) is taken as the research object, a three-parameter adaptive virtual DC motor control strategy is proposed to realize the flexible adjustment of inertia, damping, and armature resistance at the same time, and meanwhile, optimize the backflow power and inductor current stress of the converter. Finally, simulation and experiment results show that the proposed three-parameter adaptive control strategy compares with the two-parameter adaptive control strategy, and it can further reduce DC bus voltage fluctuation and recovery time, which improve the stability of the DC bus and the dynamic performance of the system. The DC bus voltage fluctuation rate under the three-parameter adaptive control is reduced to 9%, and the voltage recovery time is only 0.18 s; the optimization strategy can also effectively reduce the backflow power and inductor current stress.

A Bidirectional Fast EV Charger for Wide Voltage Range Using Three-Level DAB Based on Current and Voltage Stress Optimization

Converter cost is the crucial concern while designing off-board electric vehicle (EV) chargers for high-voltage charging applications using advanced high breakover voltage power semiconductor switches. To solve this problem, multilevel topology is used with the typical dual active bridge (DAB) for the development of high-voltage and high-power EV charging. It offers low cost, compact, less complex control, highly efficient, and reliable development. This article presents the design and development of bidirectional off-board fast EV charger with voltage and current stress optimization for wide voltage range. It is designed with two-stage power conversion. Here, active front-end converter is connected to three phase grid and controlled through synchronous reference frame (SRF) d-q control approach for active rectification. The large range of power and voltage variation in off-board EV charger design makes it challenging to develop a controller that allows the converter to operate inside the zero voltage switching (ZVS) operating region. In this context, a detailed circuit analysis of dc–dc stage with dual phase shift (DPS) control under different operating conditions is presented to identify the coordinates of safe operating region with reduced voltage stress. To select the converter control parameters with optimum current stress in conjunction with reduced voltage stress, particle-swarm-optimization technique is applied to the identified operating regions. This provides a unique selection criterion for both control parameters over wide voltage conversion ratio. A coordinated control is designed based on the identified boundaries for easy implementation and less computation burden on microcontroller units (MCUs). A 7.2-kW system is designed and simulated on MATLAB/Simulink. A 3.3-kW laboratory prototype is designed to validate the identified operating points with wide battery voltage range under varying source and loading scenarios.

A Load Adaptive Hybrid DPS Control for DAB to Secure Minimum Current Stress and Full ZVS Operation Over Wide Load and Voltage Conversion Ratio

Wide variations in voltage conversion ratio and loading are the most important parameters to consider when designing off-board EV chargers to achieve high power density and efficiency. Dual phase shift (DPS) modulation provides a better way for dual active bridge (DAB) DC-DC converter operation when load side parameter variation is utmost important. To accomplish this, conventional DPS control is modified to ensure zero voltage switching (ZVS) across the entire load range despite wide variations in voltage conversion ratio. The designed control provides ZVS of all FETs as compared to the conventional DPS control over full loading range. For this, magnetizing inductance of HF isolation transformer is utilized and designed to shape the secondary side current for getting ZVS for both active legs. The light loading performance of the converter is improved with the bidirectional conduction angle control. The hybrid utilization of DPS control is incorporated with minimum peak current stress considerations. A Karush-Kuhn-Tucker (KKT) method based on Lagrange's multipliers is used for mathematical derivation of optimized solution of both control parameters. Performance of designed control is verified using experimental results for wide variation in battery terminal voltage. For validation, a 1250 W laboratory prototype is developed. A comparison of ZVS regions among the conventional and designed modulation technique, shows the effectiveness under wide voltage and loading scenarios.

Comparison and Validation of Five Modulation Strategies for a Dual Active Bridge Converter

This paper addresses the comparison and validation of different modulations for an isolated dc-dc dual active bridge converter (DAB), namely, Duty-Cycle Modulation, Single Phase Shift (SPS), Dual Phase Shift (DPS), Extended Phase Shift (EPS) and Triple Phase Shift (TPS). Given the DAB’s applicability in a wide variety of power electronics branches, several control strategies are being studied to improve its efficiency, by mitigating circulating currents and reactive power. Regardless of the chosen architecture, appropriate modulations must be adopted, assessing which one presents the better cost-benefit ratio. This simulation-based analysis aims to investigate the DAB performance when controlled by the above-mentioned modulations and operating with a nominal power of 3.6 kW. Thus, simulation results show that only SPS, DPS, and TPS are considered suitable, while Duty-Cycle Modulation has time limitations during power transfer and EPS is more appropriate for dynamic power applications.

Analysis of Losses in Two Different Control Approaches for S-S Wireless Power Transfer Systems for Electric Vehicle

This paper presents the study and detailed analysis of converter losses at different stages together with the series-series (S-S) compensating coils in wireless power transfer (WPT) systems, via two distinct approaches to control the power converters. The two approaches towards wireless DC–DC power flow control are termed as the Single Active High-Frequency Wireless Power Transfer (SAHFWPT) system and the Dual Active High-Frequency Wireless Power Transfer (DAHFWPT) system. The operation of converters in SAHFWPT and DAHFWPT are controlled by the extended phase shift (EPS) and dual phase shift method respectively. The general schematic of the SAHFWPT system consists of an active bridge and a passive bridge, while the schematic of the DAHFWPT system consists of both active bridges. The efficiency evolutions of ideal SAHFWPT and DAHFWPT are far away from the real ones. Moreover, this article analyzes the operation and losses of the uni-directional power flow of the WPT system, i.e., from the DC bus in the primary side to the battery load in the secondary side. The loss estimation includes high-frequency switching losses, conduction losses, hard turn on and turn off coil losses, etc. Moreover, the efficiency of the WPT system depends on operation of the converter. A 50 W–3600 W Power range system at a resonant frequency of 85 kHz is implemented in MATLAB/SIMULATION to demonstrate the validity of the proposed method.

A Virtual Direct Current Control Method of LCL-DAB DC-DC Converters for Fast Transient Response and No Backflow Power

The LCL-type dual active bridge (LCL-DAB) DC-DC converter is a promising part for DC micro-grids due to its high voltage gain and low bridge current, but the issues of backflow power elimination and transient response optimization deserve attention in its operation. In this article, a virtual direct current control (VDCC) method of the LCL-DAB converter for fast transient response and no backflow power is proposed, which can eliminate the backflow power and improve the transient response against the input voltage and load disturbances. With dual-phase-shift (DPS) modulation scheme, the voltage-current characteristics are first analyzed using the phasor method. The small-signal mathematic model of the LCL-DAB converter is then established. The power characteristic is derived so the design regions of no backflow power can be graphed. On this basis, an appropriate outer phase shift ratio can be estimated to ensure a wide range of no backflow power operation. Moreover, a virtual voltage is generated to compensate in the control loop, thus the transient response against disturbances of the LCL-DAB converter can be improved under no backflow power. Simulation and prototype experimental results are presented to verify the feasibility of the proposed VDCC method.

A Single-Stage Semi Dual-Active-Bridge AC–DC Converter With Seamless Mode Transition and Wide Soft-Switching Range

In this article, a novel single-phase single-stage ac–dc converter based on semi dual-active-bridge dc–dc converter is proposed for unidirectional power flow applications. Dual-phase-shift (DPS) and single-phase-shift (SPS) modes are adopted individually according to their operation. Only two control variables, which are primary side phase shift and the phase shift between the two bridges, are used. The optimal voltage and current waveforms in different operation modes are analyzed. The detailed transition process between the DPS mode and SPS mode is given, and the mode transition is seamless. The proposed converter can achieve high power factor correction without an inner current tracking loop. In addition, the switches can achieve zero-voltage switching <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> within a wide operating range and the rectifier diode can obtain zero-current switching <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> . The power transfer capability, mode transition mechanism, soft-switching range, mode operation range, and parameter design are analyzed. Besides, a 1 kW experimental prototype is built to verify the effectiveness of the proposed control strategy.

An Optimized Control Method of Soft-Switching and No Backflow Power for LLC Resonant-Type Dual-Active-Bridge DC-DC Converters

The LLC-type resonant dual-active-bridge (LLC-DAB) DC-DC converter with a high voltage gain, high power density, and low backflow power has attracted increasing attention in recent years. However, its soft-switching and backflow power problems are still not solved, so the improvements to these problems are studied in this paper. Based on the dual phase shift (DPS) modulation method, the operating characteristics are analyzed, and a soft-switching and no backflow power modulation curve is established based on the voltage-current time-domain characteristics. On this basis, a soft-switching and no backflow power optimized control method based on DPS modulation is proposed to achieve soft-switching operation and eliminate backflow power. Due to the complex time-domain characteristics of the resonant tank voltage and current, the relationship between the phase shift ratios is fitted and optimized with this method based on the soft-switching and no backflow power characteristic curve, and the optimized results of the phase shift ratio under different operating conditions are obtained. The simulation results indicate that the soft-switching operation of the LLC-DAB converter can be achieved with the optimized control method proposed in this paper, and the backflow power is effectively eliminated.