Battery driven Electric vehicle with regenerative Braking operation
Electric vehicles (EVs) have become an increasingly popular mode of transportation due to their eco-friendliness and efficiency. One of the critical technologies that enhance the performance of electric vehicles is regenerative braking. This concept helps in reusing energy that would otherwise be lost during braking. In this blog post, we’ll explore a simulation model of a battery-driven electric vehicle with regenerative braking using MATLAB. The model integrates various components like a battery, DC motor, and bi-directional DC-DC converter, demonstrating how energy is captured and stored back into the battery during braking.
The System Setup
The system used in the simulation includes the following components:
Battery: Supplies power to the DC motor.
DC-DC Converter: A bi-directional converter that controls the flow of power from the battery to the motor and vice versa.
DC Motor: Powers the vehicle’s wheels. The motor speed and torque are crucial for simulating the vehicle's operation.
Speed Control: The system uses a PID (Proportional-Integral-Derivative) controller to maintain the desired motor speed by comparing it with a reference speed.
How Regenerative Braking Works
Regenerative braking is a method of slowing down a vehicle while simultaneously recovering energy. During normal braking, energy is typically lost as heat. However, in regenerative braking, this energy is converted back into electrical power and stored in the battery. Here’s how it functions:
When the vehicle slows down (such as when the brake is applied), the DC motor operates in reverse, converting the kinetic energy into electrical energy.
This electrical energy is sent back to the battery, which then stores it for later use.
During motoring operation (accelerating or driving), the battery provides power to the motor, allowing the vehicle to move forward.
Key Simulation Results
In the simulation, the following parameters were set to simulate both normal driving and regenerative braking:
Battery Voltage: The initial battery voltage was set at 60V, with a state of charge (SOC) of 50%.
DC Motor: The DC motor used had a rated voltage of 240V, with a rated speed of 10,750 RPM and a power output of 5 horsepower (HP).
Torque and Speed: A load torque of 10 Nm was applied to the system, and the reference speed was initially set at 120 rad/sec.
Normal Driving Operation
During normal motoring operation, the motor speed was maintained at a constant 120 rad/sec. The system tracked the battery voltage, current, and state of charge (SOC), and these parameters showed a decrease as the motor drew power from the battery.
The battery voltage, current, and SOC were displayed in real-time.
The motor speed remained stable at 120 rad/sec.
Battery current was recorded at around 27.5 amps as the battery supplied power to the motor.
Regenerative Braking Process
When the speed reference was reduced from 120 rad/sec to 50 rad/sec, regenerative braking occurred. Here’s how the system responded:
The speed of the motor decreased, and the current direction reversed.
The motor, now acting as a generator, produced negative electromagnetic torque, causing the current to flow back into the battery.
As a result, the battery current shifted from 27.5 amps to a negative value of around -18 amps.
This negative current indicated that energy was being transferred back to the battery, increasing its SOC.
Energy Recovery and Battery Recharging
One of the main advantages of regenerative braking is the recovery of energy during braking, which helps recharge the battery. The simulation confirmed that as the motor slowed down, the following changes occurred:
Battery Voltage: Increased due to the power being returned to the battery.
SOC: Improved as the energy generated from the braking was stored back in the battery.
Current Direction: The current flowing to the battery reversed, indicating energy recovery.
Electromagnetic Torque: Shifted from positive to negative, which is characteristic of regenerative braking.
Conclusion
This simulation demonstrated the importance and efficiency of regenerative braking in electric vehicles. By recovering energy during braking, electric vehicles can improve their overall energy efficiency and extend the range of their batteries. The bi-directional DC-DC converter plays a crucial role in this process by managing the energy flow between the motor and the battery. With technologies like regenerative braking, electric vehicles become even more sustainable and cost-effective.
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