Overview of the Solar PV System
The solar PV-based EV charging system features a photovoltaic panel, a boost converter, and an inverter. The PV panel comprises eight series-connected modules per string, with one parallel string, designed to generate a maximum power output of 2,000 watts under optimal conditions. The solar panel operates under varying irradiation levels, meaning its power output fluctuates based on sunlight intensity.
To maximize the power extracted from the PV panel, the system employs a fuzzy MPPT algorithm, which adjusts the power converter's duty cycle based on the error and rate of change of error between the actual and maximum power points. This ensures the PV panel operates at its optimal power point, regardless of changes in sunlight.
Boost Converter and Fuzzy MPPT Control
The PV panel is connected to a boost converter that regulates the power generated by the solar panel. The fuzzy MPPT algorithm processes the input signals (error and rate of change of error) to generate the correct duty cycle. This duty cycle is then sent to the pulse-width modulation (PWM) generator, which controls the switching of the boost converter. By adjusting the converter’s operation, the system ensures that the maximum power is harvested from the PV panel.
The Role of the EV Battery and Bidirectional Converter
The heart of the system is the EV battery, with a maximum charging capacity of 2,000 watts. This battery is connected to a bidirectional DC-DC converter that allows both charging and discharging of the battery, depending on the system's needs. The converter operates in both buck and boost modes, ensuring that the battery is charged efficiently or discharged when needed.
The bidirectional converter is regulated using a voltage control mechanism. A reference voltage is compared to the actual battery voltage, and any difference (error) is processed using a proportional-integral (PI) controller. The PI controller adjusts the duty cycle of the converter, which is then used to generate switching pulses through the PWM generator. This ensures the battery receives consistent charging power, even when the PV power fluctuates.
Integrating Grid Power into the Charging System
One of the critical features of this system is its ability to integrate grid power when solar generation is insufficient. The grid is connected to the system through a single-phase inverter with an LCL filter to smooth the output. When the PV power output drops below the required charging power for the battery, the system uses the grid to supply the additional power necessary to charge the EV battery.
Inverter control plays a vital role in this process. The system continuously monitors the PV power, battery charging state, and grid power. It then dynamically adjusts the current flowing to the battery, ensuring that it receives consistent power. The system uses a reference current to regulate the power flow, with the current converted from the ABC form (three-phase) to the DQ form (two-phase). This conversion helps optimize the power flow between the grid, PV system, and battery.
Handling Power Flow with Varying Solar Irradiation
Solar power generation is highly dependent on sunlight intensity, and this system is designed to handle fluctuations in solar irradiance effectively. When the irradiation level changes, the power generated by the PV system varies accordingly. The system continuously monitors these fluctuations and adjusts the power flow to ensure the battery is consistently charged.
For example, when the solar irradiation drops from 1,000 watts per square meter to 500 watts per square meter, the power output from the PV panel decreases. During such times, the system compensates for the reduced PV power by drawing power from the grid. Similarly, when the irradiation increases, the PV system generates more power, and the grid may reduce its contribution.
Maintaining Constant DC Bus Voltage and Battery Charging
Throughout the system's operation, the DC bus voltage is carefully maintained at a constant 400 volts, irrespective of changes in irradiation or power flow. This ensures stability in the system and efficient power conversion. Even when the PV output decreases, the battery continues to receive a steady charging current, as the grid provides support when necessary.
The system also ensures that the battery receives constant power for charging, regardless of the changes in PV power. By balancing the power from the PV, grid, and battery, the system maintains a consistent charging rate, preventing overcharging or undercharging of the EV battery.
Efficient Grid Control and Power Balancing
One of the significant advantages of this system is its ability to manage and balance power between the grid, PV, and battery. When PV power is high, the grid may not need to supply any power. However, during periods of low solar generation, the grid will supply the necessary power to ensure the battery is charged correctly.
The inverter control system continuously monitors and adjusts the power flow to the battery, ensuring that the battery charges at the optimal rate, even during fluctuating solar conditions. The system dynamically adapts to changes in PV power and grid availability to maintain a stable and efficient EV charging process.
Conclusion
The solar PV-based EV charging system with fuzzy MPPT and bidirectional converter control offers an efficient and sustainable solution for charging electric vehicles. By integrating solar power, grid power, and advanced control systems, this model ensures consistent and reliable EV charging, even with fluctuating solar irradiance. This system not only maximizes the efficiency of solar energy use but also ensures that the EV battery receives optimal power, contributing to the broader goal of sustainable transportation.
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