Introduction to Grid-Connected PV Systems
A grid-connected PV system comprises several components including the photovoltaic panel, a DC link, an inverter, and coupling inductors. The inverter plays a crucial role in converting the DC power generated by the PV panel into AC power that can be fed into the electrical grid. In this setup, the PV panel is connected to the grid through a single-stage power conversion system, where the primary objective is to manage power flow effectively.
PV Panel and Power Characteristics
The PV panel used in this system consists of 18 parallel strings and 25 series-connected strings. The output power of the PV panel varies with changes in temperature. For instance, at 25°C, the power output is different from that at 45°C. By studying these variations, we can understand how temperature fluctuations affect the performance of the PV panel.
Inverter Control Logic: Voltage and Current Control
For optimal performance of the grid-connected system, precise control of the inverter is necessary. This is achieved using two main control strategies:
Voltage Control: The DC link voltage (VDC) is regulated by comparing it with the reference voltage. The error in the voltage is processed through a Proportional-Integral (PI) controller to ensure stability.
Current Control: To determine the output current, several parameters such as the phase currents (I_da, I_db, I_dc) are calculated. These are determined using a frequency-locked loop (ISO), which helps in deriving the load current (IL) and other related variables.
Unit Vector Calculation for Load Current
A key step in controlling the inverter is calculating the load current. To do this, unit vectors (UPA, UPB, and UPC) are computed using phase and terminal voltages. These unit vectors play a critical role in determining the power exchanged between the PV system and the load. Once the unit vectors are calculated, the inverter is able to output the appropriate switching pulses for efficient power conversion.
PSO-Tuned ANFIS for MPPT
The MPPT technique is crucial for maximizing the power output from a PV panel. In this system, the ANFIS model is tuned using PSO to track the maximum power point effectively. PSO is employed to optimize the fuzzy inference system by adjusting the parameters to minimize the error between the target and actual outputs. After running the PSO code, the best cost function is calculated, resulting in an optimized ANFIS model.
This optimized ANFIS model is integrated into the MPPT algorithm to calculate the reference voltage (V_ref). The main goal of this model is to maintain the DC link voltage constant, regardless of fluctuations in solar irradiation, thus ensuring a stable and efficient energy conversion process.
Model Operation and Power Variations
Once the system is implemented, the behavior of the PV system under varying irradiation conditions can be observed. For example, when the irradiation changes from 1000 W/m² to 500 W/m², the output power from the PV panel reduces accordingly. This reduction in PV power impacts the system’s overall performance, but the PSO-tuned ANFIS MPPT controller ensures that the DC link voltage remains nearly constant, only showing minor variations in response to these changes.
Grid Power Management
The power that the grid receives is determined by the difference between the power produced by the PV panel and the power consumed by the load. During periods of low irradiation, the PV power decreases, and the grid compensates by supplying additional power. The balance between PV output, load power, and grid power is constantly monitored to ensure efficient energy flow.
Inverter and Grid Power Interaction
The inverter plays an important role in managing the power exchange between the PV system and the grid. The inverter adjusts its output voltage and current based on the irradiance conditions, ensuring that the system operates efficiently. When the irradiation is high, the inverter sends more power to the grid, while in low irradiation conditions, the amount of power sent to the grid is reduced. This efficient management helps optimize grid stability and reduces energy loss.
Conclusion
In this post, we explored the working principle of a grid-connected PV system using PSO-tuned ANFIS for MPPT. By using this approach, we can effectively track the maximum power point of the PV system and ensure stable operation of the DC link voltage under varying environmental conditions. The integration of PSO for tuning the ANFIS model enhances the MPPT performance, making the system more efficient and responsive to changes in solar irradiation.
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