Electric vehicles (EVs) are rapidly becoming the future of transportation, and one of the most important features contributing to their efficiency is regenerative braking. This concept allows energy to be recaptured during braking and returned to the battery. In this blog post, we’ll explore a MATLAB simulation of a battery-driven electric vehicle that incorporates regenerative braking, demonstrating how this process works in real-time and how it improves the vehicle’s overall energy efficiency.
Overview of the Simulation Model
The simulation model represents a battery-powered electric vehicle consisting of several key components: a battery, a bidirectional DC-DC converter, and a DC motor. The motor’s speed is carefully controlled through a feedback system, using a Proportional (P) controller to compare the actual speed of the motor to a reference speed. This setup ensures the motor runs at a desired speed, allowing for precise control during both normal driving and braking.
The Role of Regenerative Braking
Regenerative braking is a crucial feature in modern electric vehicles. When the vehicle is braking, energy that would normally be lost as heat in traditional braking systems is instead captured by the motor. This captured energy is converted back into electricity and stored in the battery.
In this simulation, when the vehicle decelerates, the direction of current flow reverses in the motor. The negative torque generated during braking forces the motor to act as a generator, converting kinetic energy into electrical energy. This energy is then stored in the battery, contributing to the vehicle’s overall efficiency and extending its driving range.
System Components and Parameters
To better understand how the system operates, here’s a breakdown of the main parameters:
Battery: The battery has a voltage of 60V and a rated capacity of 400 Ah.
Motor: A 240V DC motor with a rated speed of 1,750 RPM and a power rating of 5 HP is used.
Load Torque: The system operates with a fixed load torque of 10 Nm.
Speed Control: The motor’s speed is initially set to 120 RPM and is monitored by the simulation to maintain the desired speed.
The system uses a bidirectional DC-DC converter to control the energy flow between the motor and the battery, allowing the vehicle to either consume or regenerate energy depending on the driving situation.
Operating the Motor: Forward Motoring Condition
During normal operation, the motor draws power from the battery to propel the vehicle. In this phase of the simulation, the system maintains a constant speed of 120 RPM. The battery supplies the required power to the DC motor, and the torque remains steady at 10 Nm.
As the vehicle runs, the battery current decreases due to energy consumption by the motor. The battery voltage and current are continuously monitored, and this data provides valuable insights into the power consumption of the motor.
Implementing Regenerative Braking
The regenerative braking operation is triggered by a change in the motor's speed reference. Initially, the motor operates at a constant speed of 120 RPM. After 2 seconds, the reference speed is reduced to 50 RPM to simulate the application of brakes.
As the motor slows down, it enters a generator mode, where the kinetic energy of the vehicle is converted back into electrical energy. The current direction reverses, and the electromagnetic torque changes from positive to negative. This causes the motor to generate power, which is fed back into the battery.
Energy Regeneration and Battery Charging
As the braking process progresses, the battery current shifts from positive to negative. The negative current indicates that the motor is generating power, which is then directed back to the battery. In this regenerative braking scenario, the battery voltage increases, and the state of charge (SOC) of the battery rises. This process not only replenishes the battery but also reduces the overall energy loss during braking, enhancing the efficiency of the electric vehicle.
Conclusion
The MATLAB simulation of a battery-driven electric vehicle with regenerative braking demonstrates the significant advantages of energy recovery in EVs. By using regenerative braking, the vehicle can recapture energy during braking events, extending the driving range and improving overall system efficiency. The bidirectional DC-DC converter plays a vital role in managing energy flow, ensuring that the energy captured during braking is safely returned to the battery.
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