Soft-switching dual Active Bridge Converter-based Bidi-rectional On-Board Charger for Electric Vehicles under Vehicle-to-Grid and Grid-to-Vehicle Control Optimization

. Electric Vehicles (EVs) are rapidly replacing conventional fuel vehicles, o ff ering powerful, emission-free performance. This paper introduces an innovative three-phase bidirectional charger for Grid-to-Vehicle (G2V) and Vehicle-to-Grid (V2G) applications, strengthening the connection between EVs and the power grid. The charger employs a two-stage power conversion approach with advanced converters and a simplified dq-based charging control strategy. An e ffi cient AC-DC converter facilitates smooth transitions between modes, responding to grid directives for active and reactive power. A Soft Switching Dual Active Bridge (SS-DAB) DC-DC converter optimally interfaces with the EV battery pack, while dual active LCL filters suppress harmonics, enhancing system performance. Simulated results confirm the charger’s e ff ective-ness in a 3.5kW prototype using MATLAB / Simulink.

approaches, examines user behavior, driving patterns, batteries, and charging stations, and offers study on distribution implications, emergency charging, rebate equity, and big data in transportation management.Analyzing user behavior and driving behaviors, clustering approaches help power networks integrate electric vehicles (EVs).Patterns in huge datasets help estimate charging requests and optimize grid management.Clustering allows infrastructure design by categorizing customers by billing choices and consumption patterns.Anticipating peak demands ensures effective distribution and reduces power system pressure.EV usage increases and clustering lets utilities respond to shifting needs, making power infrastructure more robust and sustainable.These methods improve EV incorporation with developing power networks.The article emphasizes the need for EV-grid integration optimization using electric vehicle behavior modeling.It provides insights and integration solutions for diverse circumstances with a complete model selection methodology [4].In [5] discusses PV-grid charging profit potential, infrastructure, grid integration, economic constraints, capacity, and intermittency.A novel sliding mode controller (SMC) outperforms existing controllers in high-voltage power interface difficulties [6].
In [7] examines V2G bidirectional converter topologies for grid-to-EV battery energy transmission.Using a modified single-ended main inductor converter, a bidirectional battery charger charges 48 V and 120 V battery-powered automobiles effectively.Experimental findings show enhanced bidirectional operation and simpler switch ratings, improving performance and productivity [8].Power factor correction, voltage regulation, and dynamic adaptation are implemented via an onboard charging unit with an adaptive sliding mode controller [9].Genetic algorithms reduce chattering and improve parametric fluctuation adaptability by optimizing controller gains.MATLAB/Simulink simulations show that a state-of-charge-based high-level controller for smart V2G and G2V operations outperforms sliding mode and finite time synergetic control.A single-stage three-phase bidirectional AC-DC inductive power transfer converter for V2G applications [8] offers low input current distortion, high efficiency, output short-circuit protection, and soft-switching.

Literature review
In [10], a three-level dual-active-bridge converter for bidirectional EV charging is suggested with four modes of operation to accommodate a broad variety of EV voltages.Experimental data confirm its efficacy.Algorithms are employed to dynamically select the optimal operating mode in real time, reducing the transformer's RMS current in electric vehicle charging.Experimental results support the feasibility and advantages of the proposed dual-active-bridge (DAB) converter.In three-level DAB converter's four operating modes allow bidirectional EV charging at different voltages.The softswitching dual-active-bridge converter has zero voltage, zero current, and combinations of these modes.The converter optimizes power transmission by matching the EV's voltage during unidirectional charging.In reverse power flow for vehicle-to-grid applications, the converter smoothly switches modes to accommodate EV battery voltage changes.This flexibility boosts converter efficiency and reduces switching losses.Soft-switching reduces electromagnetic interference, improving system dependability.These modes provide robust and adaptive bidirectional EV charging across varied voltage settings.In [11], introduce a fault-tolerant method for currentfed dual active bridge (CF-DAB) converters equipped with blocking capacitors.The approach addresses open-circuit and frozen-phase faults, providing practical and low-loss fault isolation and ensuring the dependability of multiphase converters [12] presents a cost-effective bidirectional off-board electric vehicle charger utilizing a multilevel topology and dual active bridge configuration.
It incorporates a novel control method involving synchronous reference frame control for active rectification and dual-phase shift control in the DC-DC stage to enable safe zero voltage switching operation.Optimal control settings are determined through particle swarm optimization.Simulations and a 3.3-kW laboratory prototype confirm the charger's performance under various voltage and loading conditions.In [13], a comprehensive design methodology for a resonant dual active bridge (R-DAB) converter tailored for Li-ion battery charging is introduced.The methodology optimizes resonant tank parameters using pulse frequency modulation and phase-shift modulation to minimize switching losses.

Contribution and paper organization
Validation through simulations and a 1 kW/30A laboratory prototype affirms the effectiveness of the dual control method and the proposed design approach [14] present a rapid phase-shift control approach for bidirectional dual active bridge (DAB) DC-DC converters, enhancing transient response during power-changing operations.By combining pulse-width modulation (PWM) with pulse frequency modulation (PFM), this method enables effective phase-shifting without causing DC imbalances or other adverse effects.This paper is to analyze and model the three-phase bidirectional charger which can operate in G2V and V2G mode.The main contributions of this paper are as follows: • The charger module employs a two-stage power conversion process for efficient energy transfer or conversion, commonly used in modern charger designs.
• Advanced power converters are employed for improved efficiency and performance during the conversion stage, enhancing energy transfer and management.• Simulation environments enable the observation of V2G (vehicle-to-grid) and G2V (grid-to-vehicle) charging effects and their impacts on power systems.
The current paradigm of electric vehicle (EV) integration with the grid demands efficient bidirectional power flow.However, conventional on-board chargers face challenges in achieving optimal vehicle-to-grid (V2G) and grid-to-vehicle (G2V) control.The softswitching dual active bridge converter (SS-DAB) emerges as a promising solution.This research addresses the critical problem of enhancing bidirectional on-board charging for EVs, focusing on V2G and G2V control optimization.The aim is to develop an innovative SS-DAB-based charger system that optimally manages power flow in both directions, ensuring efficiency, reliability, and seamless integration between EVs and the grid.The main contribution lies in the soft-switching dual active bridge converter's advanced technology, enabling bidirectional power flow in on-board chargers for electric vehicles.This innovation enhances vehicle-to-grid (V2G) and grid-to-vehicle (G2V) control, optimizing energy transfer efficiency, reducing losses, and fostering a more resilient and integrated electric vehicle ecosystem.This paper is organized as follows: Ev's impact on the distribution grid and exploration of three-phase bidirectional charging is delved in the "Methods" section.Moving to the "Results and discussion" section, simulation results for the proposed SS-DAB-based bidirectional charger are detailed.Finally, the "Conclusions" section encapsulates the research work's summary.

Methods
According to [15], choosing an electric automobile (EV) battery is difficult.EVs cut urban pollution and operate quietly, making them a popular public transit option.Their environmental effect is negligible when fuelled by renewable energy or modern, ) of root mean square error (RMSE) and root mean square percentage error (RMSPE) were used to assess battery models.Equations ( 2) and ( 3) define RMSE and RMSPE.
The RMSE and RMSPE of the battery voltage are 0.0328 V and 0.85% in the high SoC zone, and 0.0245 V and 0.61% in the low SoC region.

EV's impact on the distribution system
Transmission losses can be reduced by separating power production and distribution, however dispersed solar arrays change voltage and frequency.Since solar energy output fluctuates from 9 AM to 6 PM, feeder voltage might exceed acceptable values.To fix this, loads should use electricity during peak generation.Solar production normally increases from 9 to 10 AM, therefore EV charging coincides with this.Due to increased solar energy intake, feeder voltage rises.Optimal charging at peak solar generation between 10 AM and 12 PM reduces voltage oscillations.EV charging using extra solar power stabilizes feeder voltage.Maintaining EV charging from 12 to 2 PM uses high solar output to reduce feeder voltage swings.This noon-time has abundant sun energy.As solar output stays high between 2 and 4 PM, EV charging absorbs extra solar power to stabilize the system and avoid voltage spikes.Tapering EV charging from 4 to 6 PM matches declining solar input.Limiting feeder voltage fluctuations from peak solar output to lower levels is achieved by reducing solar generation gradually.Synchronizing EV charging with optimum solar output between 9 AM and 6 PM maximizes renewable energy use and reduces feeder voltage fluctuations.Electric vehicle (EV) charging patterns are unpredictable; thus, they must be aligned with peak generating periods.Smart grid technology, demand-side management, and enhanced control techniques reduce energy consumption, promote grid stability, and protect infrastructure during peak generation, ( 1) providing a smooth integration of renewables and EVs and avoiding voltage concerns [16].
Figure 3a shows that charging electric vehicles (EVs) during peak hours lowers line voltage, particularly as you go down the line.Smart charging and grid management solutions, especially in rural regions, are crucial to preventing power outages and network challenges during peak demand.In Fig. 3b, more EVs linked to phase a cause greater voltage drops than phases b and c.To balance phase-to-phase load, electric vehicles (EVs) must be used with bidirectional chargers.This transportation and energy transition greatly affects electric utility operations.As EV usage rises, grid support, demand response, and new business models give energy sector prospects.Grid management and infrastructure development are crucial to realizing this promise and transitioning to a sustainable and resilient energy system.

Three-phase bidirectional charger
Three-phase bidirectional charger design and grid integration control are covered in this section.EVs battery pack, three-phase AC, filter, AC-DC, and DC-DC converters make up the charger shown in Fig. 4.An AC-DC converter transports power from the AC supply to the DC bus, while a dq controller manages energy flow to the vehicle's battery pack for bidirectional energy exchange and grid integration.

AC-DC converter
A three-phase bidirectional AC to DC converter with switches S 1 -S 6 properly converts AC power to DC for EV charging.This converter rectifies three-phase AC voltage while charging and gives extra power to the grid in vehicle-to-grid situations.A switching  sequence control method ensures accurate and efficient energy conversion.Flexible for EVs and grid integration, this bidirectional converter dynamically controls power flow to optimize charging, discharging, and renewable energy consumption.The switching function is defined by Transistors and diodes behave as short circuits during conduction and open circuits during the blocking state.When switches are turned off, there is no tail current, and when diodes are reversed, there is no recovery current.Switches between the blocking and conducting phases are instantaneous.With a three-phase full-bridge in consideration, AC side current, i, is a DC quantity free of ripple throughout the switching cycle.
where d is the duty cycle, adjusting m from -1 to 1 causes a linear change in the average voltage at the AC-side terminal V t , where m = 0 represents the zero averaged voltage.The Voltage Source Converter (VSC) is a frequency converter that is provided by the power provider and is required to be used.To restate this, the time and frequency sinusoids that are imposed by the grid serve as a representation of the three-phase values.Power systems depend on the Voltage Source Converter (Vsc) to manage DC voltage and real (P s ) and reactive (Q s ) powers.A true reactive power controller, it uses grid-imposed frequency.At the Point of Common Coupling (PCC), the VSC system optimizes P s and Q s transmission for fast response.
Industrial applications now employ voltage-mode control, which was formerly used in FACTS controllers.The AC-side terminal of the VSC may be adjusted for phase angle and voltage amplitude relative to the PCC voltage to precisely regulate P s and Q s .In the Voltage Source Converter (VSC), the phase angle and magnitude of the VSC line current relative to the Point of Common Coupling (PCC) voltage regulate real (P s ) and reactive (Q s ) powers.Modern EV chargers use current-mode control to improve VSC and AC system stability and dynamic performance.Figure 5 shows how a dq-frame current controller controls reactive and actual power.The d-q controller precisely controls Ps and Q s by separating line current into i d and i q components.From altered feedback and feedforward signals, compensators create dq-frame control signals.

Phasor representation of space in dq frame
Consider the space phasor f(t) = f α + f β the d-q to α-β frame transformation is defined as Which is a phase shift in −→ f (t) by -ρ(t) .The angle ρ(t) can be chosen arbitrarily.How- ever, if −→ f (t) = f (t)e j(ωt+θ 0 ) then choosing ρ(t) equal to ωt results in space phasors (4) The inverse transformation is When taken into consideration, the voltages of the three phases are as follows: where V s is the line to neutral voltage peak value, θ 0 is the source starting phase angle, and ω 0 is the frequency of the AC system.The space-phasor equivalent of V sabc is The dynamics of VSC are described by the following equation Substituting for V s , then Eq. ( 13) becomes Then by using i = i dq e jp and V t = Vs e j(ω 0 t+θ 0 ) provides ( 8) di dq e jρ dt = −Ri dq e jρ + V tdq e jρ − V s e j(ω 0 t+θ 0 )

Fig. 5 Vector representation of PLL
where f dq = f d + jf q and rewriting the above equation as The dq axis voltage equations are

Phase-locked loop
The phase-locked loop (PLL) comprises essential components: the phase detector, low pass filter, and voltage controlled oscillator (VCO) as depicted in Fig. 6.Maintaining V sq at zero is critical for synchronizing the dq-axis, achieved by modulating the dq-rotational frame's speed.Ultimately, ρ(t) = ω 0 (t) + θ 0 and V sd = V s .The VCO acts as a resettable integrator when its output reaches 2/pi, allowing precise synchronization.Bipolar sine triangle pulse width modulation generates pulses by comparing the carrier signal V tri to the reference signal V sine .PLL manages synchronization through V sdq manipulation, pulse generation using bipolar sine triangle modulation, and VCO precision, vital for applications requiring synchronous dq-axis rotation, such as motor control and power electronics.

Soft-switching dual active bridge DC-DC converter
In EV bidirectional charging, the soft-switching dual active bridge (SS-DAB) DC-DC converter with two LLC filters provides constant and dependable performance throughout operating modes.It supports soft-switching, resonant operation, high-frequency isolation, voltage control, and efficiency improvement.Square wave outputs are produced by regulating main and secondary bridges concurrently with 50% duty cycle.Key qualities make the soft-switching dual active bridge (SS-DAB) DC-DC converter efficient for bidirectional EV charging.Its soft-switching reduces switching losses, improving efficiency.Second, the converter's zero-voltage and zero-current switching modes maintain performance under different load circumstances.Two LLC filters reduce highfrequency components' electromagnetic interference and improve dependability.Both EV charging and discharging are stable with this dual-filter arrangement.Flexible operating modes and LLC filters make the SS-DAB efficient and reliable in bidirectional EV (15) 6 Phase-locked loop charging situations, meeting electric vehicle power system needs.Figure 7 shows that inductor current and voltage waveforms split the switching pattern into four time periods.Dual active bridge (DAB) converters measure primary and secondary voltages across the transformer's main and secondary windings, respectively.In Fig. 7, the transformer turns ratio (Np/Ns) is the primary-to-secondary turn ratio.The square root of the primary-to-secondary voltage ratio.This turn ratio affects voltage transformation and may determine DAB converter output voltage, affecting power conversion efficiency and performance.

Results and discussion
A simulation scenario is used to evaluate the charger's operation and grid compliance as utility-level circumstances cannot be replicated in real time.PLL is used to synchronize a locally produced signal with the grid frequency signal.The charger performs when the DC-link voltage decreases to 400 V in the simulation as shown in Fig. 8a-b.While this study focuses on V dc = 400 V, the results provide light on the charger's grid compliance and synchronization at other voltage levels.It is essential to examine the charger's utility compliance and grid interconnection capability.Figure 9a shows that the DC-Link voltage was in the V2G mode between 0 and 1 s when the soft-switching dual active bridge (SS-DAB) DC-DC converter was operating.The voltage difference facilitates power exchange between the DC-DC converter and AC-DC converter.
From 1 to 2 s, it transitions to G2V operation, functioning as a buck converter, and power exchange occurs in Fig. 9b.The dual LCL filter ensures smooth grid voltage and current Fig. 9c, nearly in phase with the grid voltage, achieving a near-unity power factor.Figure 9d illustrates the inverter terminal voltage and inverter-side current with ripples at the AC-DC converter's switching frequency, characteristic of the SS-DAB DC-DC A steady battery voltage is maintained by the system, which optimizes it for effective power exchange.At the same time, the system carefully regulates the flow of current to guarantee dependability and performance, which ultimately improves the overall functioning of electric vehicles within the grid.
In grid-to-vehicle (G2V) mode, the soft-switching dual active bridge converter (SS-DAB) based bidirectional on-board charger maintains efficient power transfer.The battery experiences a stable voltage of 400 V and a controlled current of 50A, ensuring optimal charging.This configuration enhances charging performance, minimizing energy loss and optimizing electric vehicle (EV) integration with the grid.Modulation signals (m d and m q ) in the dq-axis are converted to abc form to create a sinusoidal AC signal.Pulses from Sine Triangle Pulse Width Modulation control the switches.In the Sine Triangle Pulse Width Modulation technique, a pulse is generated when the sinusoidal reference signal (V sine ) exceeds the triangular carrier signal (V tri ).This pulse is then sent to one switch in the leg, while its complementary pulse is sent to the other switch.This process creates a modulated waveform.The resulting pulse train controls the operation of the switches in the power converter.A 180-degree phase shift in the current, typical for PWM applications, is essential for proper converter operation and achieving bidirectional power flow.Figures 11a and b depict the modulating signals and carrier signals, providing a comprehensive overview of their interaction.The modulating signals dictate when the power switches should be turned on or off, using the carrier signal as a reference for switching timing.Figures 12a and b illustrate the State of Charge (SoC) fluctuations during discharge and charge modes of the battery.In the discharge mode, as energy is released, SoC decreases from 50 to 49.996%.The constant discharge rate of 4.5A corresponds to a voltage drop from 400 to 376 V, aligning with the decreasing SoC.
Conversely, in the charge mode, SoC increases as the battery receives energy.The steady charging rate of 0.55 A leads to a voltage rise from 384 to 396 V, reflecting the growing battery capacity percentage.This behavior continues with a constant charging rate of 0.125A, resulting in voltage increasing from 394 to 396 V. Figure 12c provides insight into the power flow process.The active power supplied to the grid indicates the actual power transferred, contributing to total energy exchange.Simultaneously, the dual LCL filter consumes minimal reactive power.Reactive power is essential for voltage regulation and overall power system stability.The given system conforms to the fundamentals of PWM control, which enables accurate regulation of the flow of power.The fact that the battery and the grid engage in a two-way exchange  of power is reflected in the way that SoC fluctuates while switching between various modes.The electrical specifications of EV battery can be observed in Table 1. Figure 13a and b illustrate the active power and minimal reactive power drawn from the grid during V2G and G2V modes.The dual LCL filters consume only a small amount of reactive power.In Fig. 14a, voltage and current levels when EVs contribute reactive power to the grid are shown.A higher current voltage than grid voltage indicates the EV as the source of grid reactive power.Figure 14b displays the delivery of reactive power to the grid.The charging process can be optimized by using multistage constant current charging, which avoids the less efficient CC-CV charging method, where the remaining 20% of battery capacity is charged slowly in the CV mode after an 80% CC charge.

Conclusions
This research provides a powerful three-phase bidirectional charger that incorporates a battery pack, an AC-DC converter, and a DC-DC converter that is equipped with a soft-switching dual active bridge (SS-DAB).Both grid-to-vehicle (G2V) and vehicle-togrid (V2G) situations can benefit from the use of a unified Voltage Source Converter

Fig. 3
Fig. 3 EV penetration of a grid impedance and b phase interdependence

Fig. 4
Fig. 4 Structure of three-phase battery charger

Fig. 7 Fig. 8 a
Fig. 7 Transformer primary and secondary voltages, inductor current Figure 10 shows Bipolar Sine Triangle Pulse Width Modulation comparing the carrier signal (V tri ) to the reference signal (V sine ).

Fig. 9
Fig. 9 Simulation results of a grid voltage and current in V2G, b grid voltage and current in G2V, c inverter voltage and current in V2G, and d inverter voltage and current in G2V

Fig. 10
Fig. 10 Carrier signal and modulated reference signal

Fig. 11 aFig. 12 a
Fig. 11 a Bipolar SPWM for S 1 of phase-a, b bipolar SPWM for S1 of phase-b

Table 1
EV battery specifications