Introduction to the Model
The focus of the simulation is on an electric vehicle powered by a combination of solar PV energy and a battery. The vehicle is equipped with a BLDC motor, and the power management system ensures that energy from the PV panel and battery is optimally used to keep the vehicle running smoothly. This model demonstrates how renewable energy sources can be integrated into an electric vehicle system.
Solar PV Panel Specifications
The solar PV panel in this model is composed of one parallel string and eight series-connected modules, with the ability to generate up to 2 kW of power when exposed to 1000 W/m² solar radiation under standard test conditions (25°C). The PV panel’s output depends on solar irradiance, which can vary throughout the day. The model includes an IV and PV characteristics plot that shows how the power output changes with different levels of irradiation.
Maximum Power Point Tracking (MPPT)
To efficiently extract power from the PV panel, a boost converter is employed. The boost converter helps regulate the voltage and current output from the PV system, ensuring that the power supplied to the battery and the electric vehicle remains stable. The converter is controlled using a Maximum Power Point Tracking (MPPT) algorithm, specifically the Incremental Conductance MPPT. This algorithm ensures that the PV system operates at its maximum power point, adjusting the duty cycle of the converter based on the variations in PV voltage and current.
Battery Storage and Control
The vehicle's power management system relies on a lithium-ion battery with a nominal voltage of 240V and a rated capacity of 48 Ah. The battery’s state of charge (SOC) starts at 50%, and it is connected to a common DC bus through a bidirectional DC-DC converter. This converter allows the battery to charge when excess PV power is available and discharge when the solar output is insufficient, ensuring the system's voltage remains stable.
The battery management system operates using voltage control. A reference voltage of 400V is compared with the actual DC bus voltage, and any discrepancies are corrected by a proportional-integral (PI) controller, which adjusts the duty cycle of the converter.
Electric Vehicle and Motor Control
The electric vehicle in this simulation uses a BLDC motor, which is controlled through a series of feedback loops to regulate speed and torque. A speed sensor continuously monitors the rotor speed of the motor, comparing it with the desired reference speed. The error is processed by a PI controller, which generates a duty cycle to control the inverter. The inverter converts the DC power from the PV panel and battery into AC power for the BLDC motor.
The motor’s operation can be categorized into three modes: acceleration, constant speed, and deceleration. The system efficiently manages transitions between these modes to maintain optimal performance while ensuring the battery is charged or discharged as needed.
Power Flow and Battery Operation
When the irradiation is high, the PV system generates sufficient power to charge the battery. However, when the irradiation decreases, the battery starts discharging to maintain a constant DC bus voltage. The battery ensures that the system always has the required power to operate the BLDC motor, even when solar input is low.
As the battery charges and discharges, its state of charge (SOC) fluctuates. When the PV power is abundant, the SOC increases, and when the system relies more on battery power, the SOC decreases. This power management ensures that the DC bus voltage stays constant, regardless of fluctuations in the PV output.
DC Bus Voltage Management
One of the primary objectives of this system is to maintain a stable DC bus voltage. The battery plays a crucial role in ensuring that the voltage remains constant, even when the solar irradiance changes. This stability is essential for the smooth operation of the electric vehicle's motor, as voltage fluctuations could lead to performance issues.
Motor Operation Modes
The BLDC motor operates in three distinct modes:
Acceleration Mode: The motor starts from zero speed and accelerates up to a specified maximum speed.
Constant Speed Mode: Once the motor reaches the desired speed, it operates at a constant speed.
Deceleration Mode: When the motor needs to slow down, the system transitions into deceleration mode.
The system smoothly transitions between these modes, ensuring the vehicle operates efficiently across different driving conditions.
Conclusion
This MATLAB simulation of a solar PV battery-powered electric vehicle provides valuable insight into how renewable energy can be integrated into electric vehicle systems. The combination of solar energy, battery storage, and efficient power management ensures that the vehicle operates smoothly while maintaining a constant DC bus voltage. The simulation also highlights the importance of technologies like MPPT and battery management in optimizing the performance of solar-powered electric vehicles.
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