Overview of the Model
The simulation demonstrates how a solar PV system and a battery work together to power an electric vehicle. The solar array and the battery serve as input power sources, feeding energy to a BLDC motor. The primary goal of this model is to maintain a constant power supply to the motor, irrespective of fluctuations in solar radiation or battery charge levels.
The PV Array: Power Generation
The model incorporates a solar PV array, which consists of one parallel string and eight series-connected modules. Under optimal conditions (1000 W/m² radiation), the PV system generates a maximum power output of 2 kW. The PV array is connected to a boost converter to step up the voltage, which is then used to supply power to the system.
The PV array operates based on the available sunlight intensity, meaning its power output can vary depending on the weather and time of day. To extract maximum power from the array, the system employs an Incremental Conductance Maximum Power Point Tracking (MPPT) algorithm. This ensures that the PV system continuously operates at its most efficient point, adjusting the duty cycle of the converter to match changing sunlight conditions.
The Battery: Energy Storage and Supply
In addition to the PV array, a lithium-ion battery with a 48 Ah capacity and a 240 V nominal voltage is used to store excess energy. The battery is connected to the common DC link through a bidirectional DC-DC converter, which allows both charging and discharging based on the system’s needs.
When the solar PV system generates excess power, the battery is charged. Conversely, when the PV power drops due to weather conditions or time of day, the battery discharges to maintain a constant DC link voltage, ensuring a steady supply of power to the EV.
Voltage Control and Power Management
The primary challenge in this system is maintaining a stable DC bus voltage, which is crucial for ensuring a consistent power supply to the EV. A voltage control loop is employed in the bidirectional DC-DC converter to regulate the battery's charging and discharging cycles.
The reference voltage is set to 400 V, and the system continuously monitors and adjusts the voltage to maintain stability. The voltage error is processed by a proportional-integral (PI) controller, which generates a duty cycle that controls the switching of the converter. This ensures that the battery operates efficiently and the DC link voltage remains constant.
Electric Vehicle Motor: Operation and Control
The electric vehicle in the simulation uses a BLDC motor, which operates in three different modes: acceleration, constant speed, and deceleration. These modes are controlled based on the motor’s speed, which is adjusted from 0 to 2000 RPM.
Acceleration Mode: The motor starts from zero speed and accelerates to 2000 RPM.
Constant Speed Mode: Once the motor reaches 2000 RPM, it operates at a constant speed.
Deceleration Mode: The motor then slows down from 2000 RPM to zero.
The motor’s speed is controlled through a closed-loop system that adjusts the duty cycle of the pulse width modulation (PWM) generator. The error between the desired and actual speed is processed by the PI controller, which generates control signals for the motor’s inverter.
Simulation: Power Fluctuations and Battery Response
In the simulation, the solar radiation intensity is varied, ranging from 1000 W/m² down to 100 W/m² and back up to 800 W/m². As the radiation decreases, the PV power output drops, and the battery compensates by supplying power to the DC link, ensuring that the motor receives a stable power supply.
The system’s ability to maintain the DC bus voltage at 400 V, regardless of the fluctuations in solar power, is key to ensuring the EV runs smoothly. As the battery discharges to support the system, its state of charge (SOC) decreases, but it continues to supply power when needed.
Motor Performance: Speed and Torque
The simulation also monitors the motor’s performance, including current, electromotive force (EMF), torque, and speed. During acceleration, the motor’s speed increases from zero to 2000 RPM, and torque reaches a peak value. In constant speed mode, the motor runs at a steady 2000 RPM, and in deceleration mode, the speed gradually decreases to zero.
This detailed control of motor speed and torque ensures that the electric vehicle operates efficiently across different driving conditions.
Conclusion
This MATLAB simulation of a solar PV battery-powered electric vehicle demonstrates the effective integration of renewable energy sources with electric mobility. By using a combination of a PV array, lithium-ion battery, and BLDC motor, the system ensures a stable and continuous power supply, even in the face of fluctuating solar radiation.
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