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MATLAB Simulation of Battery-Driven Electric Vehicle with Regenerative Braking Operation

Electric vehicles (EVs) are rapidly gaining popularity due to their eco-friendly nature and energy efficiency. One of the key features that enhance the performance and efficiency of electric vehicles is regenerative braking. In this blog post, we’ll explore the concept of regenerative braking in battery-driven electric vehicles and how MATLAB simulation can be used to model and analyze this process.

Introduction to Regenerative Braking in EVs

Regenerative braking is a technology used in electric vehicles to recover kinetic energy that would otherwise be lost during braking. When the vehicle slows down, the motor acts as a generator, converting the kinetic energy back into electrical energy, which is then stored in the vehicle’s battery. This process helps improve the vehicle's energy efficiency and extend the driving range by reducing the energy demand from the battery.


The MATLAB Simulation Model for EVs

In this simulation, a model for a battery-powered electric vehicle is created using MATLAB. The setup includes a battery, a bidirectional DC-DC converter, and a DC motor. These components work together to simulate the operation of the vehicle under different driving and braking conditions.

  • Battery: The power source of the vehicle.

  • Bidirectional DC-DC Converter: This converter is crucial for both supplying power from the battery to the motor and reversing the current to store energy back into the battery during braking.

  • DC Motor: The motor that drives the wheels of the electric vehicle, converting electrical energy into mechanical energy for motion.

How the System Works

The MATLAB model uses a Proportional (P) Controller to manage the speed of the DC motor. The speed of the motor is continuously compared to a reference speed. The controller adjusts the duty cycle of the DC-DC converter based on the difference between the actual and reference speeds.

  • Speed Control: When the vehicle accelerates, the motor speed increases, and the controller adjusts the power supplied from the battery.

  • Regenerative Braking: When the vehicle slows down, the direction of current in the motor is reversed, and the motor acts as a generator, converting the kinetic energy into electrical energy and sending it back to the battery.

The Role of the Bidirectional DC-DC Converter

The bidirectional DC-DC converter plays a critical role in the regenerative braking process. During normal driving conditions, the converter transfers power from the battery to the motor, providing the necessary torque to propel the vehicle. However, when the driver applies the brakes and the vehicle slows down, the motor acts as a generator.

The converter allows the current to flow in the opposite direction, which enables the motor to feed the generated energy back into the battery. This conversion of energy during braking is what we refer to as regenerative braking.

Simulation Parameters and Motor Behavior

In this simulation, several parameters are considered:

  • Battery Voltage: 60V with a rated capacity of 4,400 Ah.

  • DC Motor: 240V motor with a rated speed of 1,750 RPM, delivering 5 horsepower (HP).

  • Load Torque: A constant load torque of 10 Nm.

  • Reference Speed: Initially set to a constant speed of 120 RPM.

Under normal operation (motoring), the DC motor runs at a constant speed, with the battery supplying power to the motor. The voltage and current from the battery are monitored as the motor operates.

Regenerative Braking in Action

When the driver applies the brakes, the reference speed is reduced from 120 RPM to 50 RPM. This change in speed prompts the motor to switch from driving the wheels to generating electricity, which is sent back to the battery.

  • Speed Reduction: As the reference speed decreases, the actual speed of the motor also reduces.

  • Current Reversal: The current flows in the reverse direction, and the motor generates electrical power, which is stored in the battery.

  • Electromagnetic Torque: During braking, the motor experiences negative torque, indicating that energy is being regenerated and sent back to the battery.

Energy Recovery and Battery Charging

The regenerative braking process helps recover energy that would otherwise be lost during traditional braking. As the motor generates electricity, the battery current changes from positive to negative, indicating that energy is being stored back in the battery. This process not only conserves energy but also increases the state of charge (SOC) of the battery, which in turn improves the vehicle’s overall range.

The voltage across the battery also increases as it receives the regenerated energy, demonstrating the effectiveness of regenerative braking in extending the driving range of electric vehicles.

Conclusion

Regenerative braking is an essential technology for improving the efficiency and sustainability of electric vehicles. Through the use of MATLAB simulations, we can effectively model and understand the processes involved in both motoring and regenerative braking. By converting kinetic energy into electrical energy during braking, EVs can operate more efficiently, reduce energy consumption, and increase their range.

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