Hybrid Fuel – Solar Powered Bidirectional Charging System for Electric Vehicles

Hybrid Fuel – Solar Powered Bidirectional Charging System for Electric Vehicles

Dr. V. Senthil Nayagam, Steve Ishan. Y, Daniel. J

Department Of Electrical And Electronics Engineering Sathyabama Institute Of Science And Technology, Chennai, India

Abstract: This study focuses on the development of an effective closed-loop control scheme for a bidirectional DC DC converter employing a phase-shift controlled, high- frequency full-bridge resonant architecture. The converters performance is analyzed under two different control approaches, namely proportionalintegralderivative (PID) control and sliding mode control (SMC). The transient and steady-state characteristics of the system are comparatively evaluated in terms of rise time, peak overshoot, settling duration, and steady-state regulation accuracy. A small- signal representation of the converter is derived to support controller synthesis and stability evaluation. The proposed converter topology and control methodologies are validated through MATLAB/Simulink-based simulations and experimental testing across multiple operating scenarios.

Keywords: Bidirectional DCDC converter, Phase-shift modulation, Sliding mode control, PID controller, Electric vehicle charging.

1. INTRODUCTION

   The rapid growth of electric vehicles (EVs) has intensified the demand for efficient, reliable, and flexible power conversion systems capable of supporting diverse energy sources and operating conditions. To address challenges related to energy efficiency, charging speed, and grid interaction, bidirectional DCDC converters have emerged as a key enabling technology in modern EV charging and energy management systems. These converters allow controlled power flow between batteries, renewable energy sources, and the utility grid, thereby supporting advanced functionalities such as vehicle-to-grid (V2G), grid-to- vehicle (G2V), and hybrid energy storage integration [1], [6].

   Recent research has focused extensively on improving converter topologies to achieve high efficiency, reduced switching losses, and enhanced power density. Isolated and non-isolated bidirectional DCDC converter structures, including resonant, multilevel, and high-gain configurations, have been proposed for EV and renewable energy applications [1], [9], [12]. Resonant and soft-switching techniques are particularly attractive due to their ability to minimize switching stress and electromagnetic interference while enabling high-frequency operation [10], [17]. Such characteristics are essential for compact onboard chargers and fast-charging infrastructure.

   In addition to hardware advancements, control strategy plays a crucial role in determining the dynamic and steady- state performance of bidirectional converters. Conventional proportionalintegralderivative (PID) controllers remain widely adopted due to their simplicity and ease of implementation; however, their performance may degrade under parameter variations, nonlinear operating regions, and rapid load changes [15], [19]. To overcome these limitations, advanced nonlinear control techniques, especially sliding mode control (SMC), have gained significant attention. SMC offers strong robustness against disturbances and uncertainties, making it well suited for EV charging systems operating under fluctuating source and load conditions [2], [5], [14].

   Several recent studies have demonstrated that SMC-based bidirectional converters exhibit superior transient response, reduced steady-state error, and improved stability compared to traditional linear controllers [2], [13], [20]. Furthermore, hybrid control approaches combining SMC with adaptive or intelligent methods have been proposed to enhance system robustness while mitigating chattering effects [3], [11]. Accurate small-signal modeling has also been emphasized as a vital step in controller design and stability analysis, enabling systematic comparison between different control strategies [4], [16].

   The integration of renewable energy sources such as solar photovoltaic (PV) systems with EV charging infrastructure has further increased the complexity of power conversion and control. Bidirectional DCDC converters facilitate efficient energy exchange between PV sources, battery storage, and the EV powertrain, thereby improving system flexibility and sustainability [4], [7], [8]. Recent works highlight the importance of coordinated control schemes that ensure stable operation under varying irradiation, battery state-of-charge, and grid conditions [6], [11], [18].

   Motivated by these developments, this paper investigates a closed-loop bidirectional DCDC converter based on a phase-shift modulated high-frequency full-bridge resonant topology for hybrid EV charging applications. The dynamic performance of conventional PID control is systematically compared with sliding mode control in terms of rise time, overshoot, settling time, and steady-state error. A small- signal model is developed to support controller design and stability evaluation. The effectiveness of the proposed approach is validated through MATLAB/Simulink

   simulations and experimental results under different operating modes.

2. SYSTEM DESCRIPTION

   Fig. 1 illustrates the overall architecture of the proposed hybrid fuelsolar powered bidirectional charging system intended for electric vehicle applications. The photovoltaic (PV) source serves as the primary energy input and is interfaced with Converter-1, which performs initial DC voltage regulation. This converter is operated using a pulse- width modulation (PWM) strategy to control the power extracted from the PV source.

   The basic idea behind a PID controller is to read a sensor, then compute the desired actuator output by calculating proportional, integral, and derivative responses and summing those three components to compute the output.

   Fig-2: Block diagram of PID controller

   2.2. Sliding Mode Controller

   The block–diagram of SMC is appeared in Fig-3. In SM, the preponderance of the controller comprise error of single or copious states of the-system in the sliding-surface.

   Fig-1: Closed loop simulation block diagram of onboard charging DC-DC converter with PID/SM controlled system

   The regulated DC output is supplied to a high-frequency transformer, which provides galvanic isolation between the source and load while enabling voltage matching through high-frequency operation. On the secondary side, Converter- 2 is employed as a bidirectional DCDC converter, allowing controlled power transfer in both forward and reverse directions, thereby supporting battery charging and discharging modes.

   A cascaded output filter is connected at the converter output to attenuate high-frequency switching ripples and improve the quality of the DC output voltage. The filtered output is delivered to the load, representing the EV battery or DC bus. The output voltage Vo is sensed and compared with the reference voltage Vref. The resulting error signal is processed by a hybrid PIDSliding Mode Controller (PID- SMC), which generates appropriate PWM signals for Converter-2. This control approach ensures accurate voltage regulation, fast dynamic response, and enhanced robustness against source and load disturbances.

   2.1.PID controller

   A proportionalintegralderivative controller (PID controller or three-term controller) is a control loop mechanism employing feedback that is widely used in industrial control systems and a variety of other applications requiring continuously modulated control. A PID controller continuously calculates an error value.

   Fig-: Block-Diagram of Slide Mode Controller.

   Furthermore, a few-controller comprise error &both of the time-derivatives and the -integral of the-error in the sliding-surface to stabilize the-system. In this-case, the sliding-surface can be symbolized as a 2nd-order deferential equation-for which broad numerical study is obliged to guarantee-system-steadiness. Another surface is characterized in for the enhancement in the steady-state- error& settling-time, which comprises voltage-error &square of the capacitor-current.

3. PROPOSED METHODOLOGY

A. Operating Principle of the Bidirectional Resonant Converter

The proposed system employs a phase-shift modulated full- bridge resonant DCDC converter to enable bidirectional power transfer between the renewable source and the electric vehicle battery. The converter operates in two modes depending on the direction of power flow:

cycle and transferred power are controlled by the phase difference between the gate signals.

• When switches S1 and S4 are ON, a positive voltage is applied across the transformer primary.
• When switches S2 and S3 are ON, a negative voltage is applied.
• The overlap period between switching states determines the energy transferred through the resonant tank.

Fig-4: Closed Loop Circuit Diagram Of Bi-Directional DC-DC Converter With PID Controlled System

The Proposed Circuit Diagram of closed loop PID/SM controlled Bi-Directional DC-DC Converter with Cascaded-Filter system is shown in fig 2.4 and fig 2.5.

By varying the phase shift angle , the output voltage and power flow direction are controlled without altering the switching frequency, which simplifies control and maintains soft-switching conditions.

C. Mathematical Model of the PID Controller

The error between the reference voltage and output voltage is expressed as

e(t)=VrefVo The PID controller output is given by

Fig-5: Closed Loop Circuit Diagram Of Bi-Directional DC-DC Converter With SM Controlled System

1. Forward Mode (Charging Mode):

   Power flows from the PV source to the load. The primary-side full bridge switches S1-S4operate as an inverter, generating a high-frequency AC voltage that is transferred through the resonant tank and transformer. The secondary-side bridge S5-S8 functions as an active rectifier to regulate the DC output voltage.

2. Reverse Mode (Discharging Mode):

Power flows from the battery/load back to the source. The secondary bridge operates as an inverter, while the primary bridge performs rectification. The bidirectional nature of the switches enables seamless mode transition without additional hardware. Due to phase-shift control, the converter achieves zero-voltage switching (ZVS) for the power switches, resulting in reduced switching losses and improved efficiency.

B. Switching States and Phase-Shift Modulation

The full-bridge converter operates using phase-shift modulation between the two bridge legs. The effective duty

where Kp, Ki, and Kd represent the proportional, integral, and derivative gains, respectively. The integral term eliminates steady-state error, while the proportional and derivative terms improve dynamic response.

D. Sliding Mode Control (SMC) Design

To enhance robustness against parameter variations and load disturbances, Sliding Mode Control is integrated with the PID controller. The sliding surface is defined as

where is a positive constant that determines the convergence speed.

The SMC control law is expressed as

where Ks is the sliding gain. This term forces the system states to converge rapidly toward the sliding surface, ensuring stable operation under uncertainties.

1. Results and Discussion of resonant DC-DC converter.
   1. Open loop Proposed Bi-Directional DC-DC converter with cascaded filter for source Disturbance system

      . Simulation parameters are presented in table1.

      Table-1

      Simulation parameters of modified LLC Resonant Converter

      Vin	20V
      L2, L3	0.005µH
      L1	0.06µH
      C3	0.2µF
      C1,C2	4200 µF
      C2	1500 µF
      R	0.001
      Rload	10
      Mosfet	IRF840
      Diode	IN4007
      Vo	38V

      switching ripple, and measurement blocks are included to observe voltage, current, and power characteristics. This configuration is used to study the converter performance in open-loop operation. The input voltage waveform corresponding to this condition is presented in Fig. 7, with an input voltage of 18V.

      Fig-7: Input voltage across PV

      Fig-8: Voltage across battery Load

      Fig. 8 illustrates the output voltage across the battery load of the bidirectional DCDC converter under source disturbance conditions, with a measured value of 38 V. The corresponding output current delivered to the battery load is shown in Fig. 9 and is observed to be 2.5 A. Fig. 10 presents the output power of the bidirectional DCDC converter under the same operating condition, which is approximately 87W.

      Fig-9: Current through battery- load

      Fig-10: Output power

   2. Closed loop Proposed Bi-Directional DC-DC converter with cascaded filter for PID controlled system

      Fig-6: Proposed bidirectional DC-DC converter with soruce Disturbance

      Fig. 6 shows the open-loop configuration of the bidirectional DCDC converter with source disturbance. The input source is interfaced with a full-bridge converter, followed by a high-frequency transformer that provides electrical isolation and voltage matching. An LC output filter is used to reduce

      Fig-14: Current through battery- load

      Fig-11: Proposed bidirectional DC-DC converter with PID controller

      Fig-11 presents the circuit schematic of the proposed bidirectional DCDC converter operating under a closed-loop PID-controlled scheme. The output voltage and current are sensed and compared with reference values, and the resulting error signals are processed by PID controllers. The controller outputs are used to generate PWM signals for the power switches, ensuring regulated output and improved dynamic performance under varying operating conditions. The corresponding input voltage waveform is illustrated in Fig-12, where the input voltage is maintained at 18 V.

      Fig-15: Output power

   3. Closed loop Proposed Bi-Directional DC-DC converter with cascaded filter for Sliding Mode controlled system

      Fig-12: Input voltage across battery

      Fig-13: Voltage across battery Load

      The output voltage across the battery load of the proposed bidirectional DCDC converter with closed-loop PID control is depicted in Fig-13 and is maintained at 38 V. Fig-

      14 shows the output current flowing through the battery load, which reaches 2.8 A. The resulting output power of the converter is illustrated in Fig-15 and is measured to be 100 W.

      Fig-16: Proposed bidirectional DC-DC converter with sliding mode controller

      The circuit configuration of the proposed bidirectional DC DC converter employing closed-loop sliding mode control is shown in Fig-16. Fig-17depicts the input voltage applied to the converter, which is set to 18 V.

      Fig-17: Input voltage

      voltage error is reduced from 1.5 V to 0.92 V when compared to the PID-controlled system.

      Fig-18: Voltage across battery Load

      Fig-18 shows th output voltage across the battery load under closed-loop sliding mode control at 35 V. The corresponding output current is presented in Fig-19 with a magnitude of 2.8 A, while the output power of the proposed converter is illustrated in Fig-20 and is observed to be 100 W.

      Fig-19: Current through battery- load

      Fig-20: Output power Table -2

      Types of controller	Tr	Tp	Ts	Ess
      PID	1.60	2.00	3.50	1.50
      SMC	1.55	1.65	2.00	0.92

       

      Comparison of time domain parameters of voltage

      Table-2 summarizes the comparison of voltage time-domain performance parameters for the proposed closed-loop bidirectional DCDC converter employing PID and sliding mode control strategies. The corresponding bar-chart representation of these parameters is illustrated in Fig-21.

      It is observed that the implementation of the sliding mode controller based on the voltage reference significantly improves the dynamic response of the system. Specifically, the rise time is reduced from 1.6 s to 1.55 s, the peak time decreases from 2 s to 1.65 s, and the settling time is shortened from 3.5 s to 2 s. In addition, the steady-state

      Fig-21:Bar chart Comparison of time domain parameters of voltage

      Table -3

      Comparison of time domain parameters of current

      Types of controller	Tr	Tp	Ts	Ess
      PID	1.59	1.98	3.50	0.3
      SMC	1.55	1.64	2.00	0.1

      Table-3 provides a comparative analysis of the current time- domain response characteristics of the proposed closed-loop bidirectional DCDC converter using PID and sliding mode control approaches. The graphical comparison of these current performance indices is shown in Fig-22 in the form of a bar chart.

      The analysis indicates that the sliding mode controller referenced to current control yields improved transient and steady-state behavior. In particular, the rise time decreases from 1.59 s to 1.55 s, while the peak time is reduced from

      1.98 s to 1.64 s. Additionally, the settling time is shortened from 3.5 s to 2 s. A notable improvement is also observed in steady-state accuracy, with the current error reduced from

      0.3 A to 0.1 A when compared to the PID-controlled system.

      Fig-22: Bar chart Comparison of time domain parameters of current

2. CONCLUSION

The proposed bidirectional DCDC converter is simulated under three operating conditions: with source disturbance, with a closed-loop PID controller, and with a closed-loop sliding mode controller (SMC). The simulation results are used to evaluate and compare the dynamic and steady-state performance of the control strategies. When the proposed converter operates under closed-loop sliding mode control with a voltage reference, a noticeable improvement in transient response is observed in comparison with the PID- controlled system. Specifically, the rise time is reduced from

1.60 s to 1.55 s, the peak time decreases from 2.00 s to 1.65 s, and the settling time is shortened from 3.50 s to 2.00 s. In addition, the steady-state voltage error is significantly reduced from 1.50 V to 0.92 V. Similarly, under current reference control, the sliding mode controller demonstrates superior performance. The rise time improves from 1.59 s to

1.55 s, the peak time decreases from 1.98 s to 1.64 s, and the settling time is reduced from 3.50 s to 2.00 s. Furthermore, the steady-state current error is minimized from 0.3 A to 0.1 A when compared to the PID-controlled case. Overall, the simulation outcomes confirm that the proposed closed-loop bidirectional DCDC converter employing sliding mode control exhibits enhanced dynamic response, improved steady-state accuracy, and greater robustness against disturbances. These results clearly indicate that the sliding mode controller outperforms the conventional PID controller for bidirectional DCDC converter applications.

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