Introduction to the 5 MW Grid-Tied PV System
A 5 MW grid-tied PV system is designed to convert solar energy into electrical power and inject it into the grid. This system uses 11 solar panels connected in series, with a total of 213,325 panels arranged in parallel strings. The rating of each panel is set at 23.15 watts, with a maximum power point (MPP) voltage of 29 volts and a current of 7.35 amps at full power.
Key Specifications of the PV Panels
Open Circuit Voltage (Voc): 36.3 V
Short Circuit Current (Isc): 7.84 A
Voltage at Maximum Power Point (Vmp): 29 V
Current at Maximum Power Point (Imp): 7.35 A
These parameters ensure that the system is optimized for energy generation based on ideal standard testing conditions (STC). The system is designed to operate efficiently by maintaining the voltage at a set point, and this is done by controlling the output using a boost converter.
Boost Converter Design and MPPT Algorithm
The boost converter in the PV system is designed to step up the output voltage of the solar panels to the required voltage levels for grid connection. The terminal voltage is determined by the voltage rating of the panels, while the boost converter increases the voltage to match the grid voltage, which is maintained at 800V. The boost converter is controlled by the Incremental Conductance MPPT algorithm.
The MPPT algorithm continuously adjusts the duty cycle of the boost converter to ensure the PV system operates at the maximum power point. It receives inputs from the panel's voltage (Vpv) and current (Ipv), calculating the changes in voltage and current to track the maximum power point. The algorithm uses the principle that the ratio of the change in voltage to the change in current (dV/dI) can help identify the point of maximum power.
Working of Incremental Conductance MPPT
The Incremental Conductance MPPT works by comparing the current rate of change of voltage and current with the instantaneous conductance of the PV system. The algorithm checks:
If the rate of change of voltage is zero, indicating that the system is at the maximum power point.
If the rate of change of current is zero, which also indicates the maximum power point.
If either condition isn't met, the algorithm adjusts the duty cycle of the boost converter to move the system closer to the maximum power point.
The adjustment of the duty cycle ensures that the system continually operates at optimal power output, even when environmental conditions such as solar irradiation change.
Control of the Inverter for Grid Integration
The inverter plays a critical role in converting the DC power from the PV system to AC power, which is required for grid injection. To control the inverter, a combination of voltage control and current control is used.
Voltage Control: This control mechanism ensures that the DC voltage is maintained at a reference value (800 V in this case). It compares the measured voltage with the reference voltage and adjusts the inverter’s output accordingly.
Current Control: The current control mechanism is used to manage the real power output of the inverter, ensuring that the power sent to the grid matches the demand. This is done by comparing the actual current with the reference current and adjusting the inverter’s output to match the required values.
The system uses Park’s Transformation to convert the grid voltage and current from the three-phase system (ABC form) to a two-phase (DQ form) system, which simplifies the control process.
Simulation Results and System Performance
The system was simulated under standard conditions of 1000 W/m² irradiation. In this scenario, the PV system operated near its maximum power output of 5 MW, with the voltage maintained at approximately 319 V, and the current output reached around 15,000 A.
As part of the simulation, the system’s performance was monitored in real-time, with key parameters such as PV voltage, current, inverter current, grid current, and power output being tracked. The voltage remained stable at 800 V across the system, and the power output was successfully injected into the grid.
Impact of Changing Irradiation Conditions
To test the system's adaptability, the irradiation level was reduced to 500 W/m². Under these conditions, the PV system’s power output decreased to around 2.5 MW. The voltage remained steady around 300 V, while the current dropped to around 7.5 kA, reflecting the decrease in available solar energy. Despite the lower power generation, the system maintained optimal operation thanks to the dynamic adjustments made by the Incremental Conductance MPPT algorithm.
Conclusion
This MATLAB simulation demonstrates the effective operation of a 5 MW grid-tied PV system with Incremental Conductance MPPT. By using this advanced algorithm, the system continuously tracks the maximum power point, ensuring efficient energy conversion and grid integration, even under varying environmental conditions. The simulation results highlight the flexibility of the system in adjusting to different irradiation levels and maintaining stable power output.
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