Overview of the Solar PV EV Charging Station
The model consists of several key components: a solar PV array, an electric vehicle (EV) battery, a stationary battery, and a single-phase grid. All these components are interconnected through a common DC link, ensuring smooth power flow and energy exchange. The solar panel, along with the batteries, supplies power to the EV and the grid, with the system dynamically adjusting based on energy availability.
The Solar PV Array
The solar PV array is made up of parallel strings of solar modules, with each string containing 16 series-connected modules. Under maximum solar radiation (1000 W/m²), the PV array produces 4 kW of power. The power output from the solar panel can fluctuate with varying solar radiation conditions, making it essential to regulate the power flow efficiently.
To minimize energy loss and ensure consistent power delivery, the solar PV array is connected to the common DC bus via an interleaved buck converter. This converter is crucial as it reduces the ripple content in the output, offering smoother and more reliable power.
MPPT Control with Incremental Conductance
The operation of the solar PV array is controlled using the Incremental Conductance Maximum Power Point Tracking (MPPT) algorithm. This algorithm adjusts the duty cycle of the interleaved buck converter based on the voltage and current of the PV array to operate at the maximum power point (MPP). A PWM (Pulse Width Modulation) generator processes the duty cycle and controls the converter’s switching to ensure efficient power extraction from the solar panels.
Grid Integration and Control Logic
The solar PV system is integrated with a single-phase grid through an inverter, which is connected via an LCL filter to the common DC bus. The inverter allows for bidirectional power flow, converting AC power from the grid into DC power for the battery, or vice versa. The inverter's operation is controlled using a sophisticated logic system that decides whether the system should supply power to the grid or draw power from it, based on the availability of solar power and the state of the batteries.
If the solar PV array cannot meet the load demand, the system draws power from the grid. Conversely, when excess power is available from the solar panels, the system can supply power back to the grid.
Battery Management: EV vs. Stationary Battery
The system features two types of batteries: an EV battery and a stationary battery. Both are connected to the common DC bus through a bi-directional DC-DC converter. This converter operates in two modes: buck mode (charging) and boost mode (discharging). The selection of either the EV battery or the stationary battery is based on a control logic system that switches between the two, ensuring that the appropriate battery is used for energy storage depending on the circumstances.
In situations where the EV battery is available, it is connected to the system to store energy. However, when the EV battery is not available, the stationary battery is used instead, ensuring continuous energy supply to the grid or the EV.
Voltage Control and Power Flow Regulation
The bi-directional DC-DC converter operates under a voltage control mechanism, where the reference voltage is maintained at 400 V. This ensures that the system’s DC bus voltage remains constant, even as the irradiation levels change and solar power output fluctuates. The power flow is adjusted to ensure that the load demand is met, and the batteries are charged or discharged accordingly.
Energy Flow in Varying Irradiation Conditions
The power output from the PV array varies significantly with changing solar radiation levels. During high radiation (1000 W/m²), the solar panel generates maximum power, but as radiation decreases (to 500 W/m² or zero), the power output drops as well. The system dynamically adjusts to these changes, maintaining a constant DC bus voltage while managing the load and battery charging.
In cases where the PV power is insufficient, the system draws power from the grid to meet the load demands and charge the batteries. The grid acts as a backup, ensuring uninterrupted power supply to the system.
Vehicle-to-Grid and Grid-to-Vehicle Operation
One of the most innovative aspects of this solar PV EV charging station model is its ability to perform Vehicle-to-Grid (V2G) and Grid-to-Vehicle (G2V) operations. In V2G mode, the EV battery can supply power back to the grid when necessary, contributing to the grid's energy pool. Similarly, in G2V mode, the grid can supply power to the EV battery to ensure it remains charged, particularly during periods of low solar energy generation.
Conclusion
This MATLAB-based Solar PV EV Charging Station model offers a comprehensive solution for integrating renewable energy into EV charging infrastructure. With efficient control of solar power generation, battery management, and grid interaction, the system optimizes energy use while maintaining stable voltage and power levels. Whether utilizing the EV battery or a stationary battery, the system ensures a reliable energy supply to the grid and the electric vehicle. The incorporation of V2G and G2V capabilities further enhances the flexibility of the system, enabling a truly sustainable and efficient energy network.
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