Design and Simulation of a 6.5 MW Grid-Connected PV System in MATLAB

lms editor
Aug 4
3 min read

📌 PV Module Configuration and Array Sizing

The system begins by selecting a single PV module rated at 360 W, with a maximum power point (MPP) voltage of 38.6 V and MPP current of 9.33 A. To achieve the required system voltage and power:

Number of series-connected panels (Ns) = 130→ Total string voltage ≈ 130 × 38.6 V ≈ 5018 V
Required system power = 6.5 MW
Number of parallel strings (Np) =6.5 × 10⁶ / (130 × 38.6 × 9.33) ≈ 13.83 → Rounded to 139 strings

Thus, the entire PV array is built by configuring 130 panels in series and 139 strings in parallel, delivering approximately 6.508 MW at 5018 V under standard test conditions (1000 W/m², 25 °C).

⚡ DC Link Voltage and Boost Converter Design

To interface with an 11 kV grid, the inverter needs a well-regulated DC link voltage. Here's how it's designed:

Convert 11 kV line-to-line to phase voltage:11,000 / √3 ≈ 6.35 kV
Find peak phase voltage: 6.35 × √2 ≈ 8.98 kV
Set DC link voltage ≈ 2 × peak ≈ 17.96 kV → Rounded to 20 kV

A boost converter is used to step up the PV voltage (~5.02 kV) to the DC link voltage (20 kV). Using input voltage, output voltage, power (6.5 MW), and switching frequency (10 kHz), the inductor (L) and capacitor (C) values are calculated using standard design equations. This ensures stable power conversion and minimized ripple.

🔍 Maximum Power Point Tracking (MPPT) Control Logic

To extract the maximum power from the PV array under dynamic conditions, an Incremental Conductance (INC) MPPT algorithm is implemented.

The MPPT logic includes:

Parameters:
- Initial duty cycle: 0.8
- Maximum: 0.9
- Minimum: 0.1
Continuously monitors:
- ΔP (change in power)
- ΔV (change in voltage)

The control logic adjusts the duty cycle of the boost converter based on whether the operating point lies on the left or right side of the MPP on the P-V curve, ensuring convergence to maximum power in real-time.

🔁 Inverter Design and Control Strategy

A three-phase inverter is employed to interface the DC link with the 11 kV, 50 Hz grid. The control architecture consists of:

Synchronization via Phase Locked Loop (PLL):Determines the phase angle of the grid voltage for accurate synchronization.
Voltage and Current Control Loops:
- Compares measured DC link voltage with a reference (20 kV) and normalizes it.
- A PI controller regulates this voltage and generates a current reference (Id_ref).
- Since only real power is injected, Iq_ref = 0 (no reactive power).
Park Transformation:Converts grid currents from ABC to DQ frame for comparison and control.
Inverse Park Transformation:Converts control voltages back to ABC to drive the PWM generator, which sends gate signals to the inverter switches.
Filter Inductor Design:The value is calculated based on PV power, DC link voltage, grid voltage, switching frequency, and modulation index to limit current ripple.

🧪 Simulation and Performance Validation

Upon simulation:

PV output voltage stabilizes around 5,000 V
Current is approximately 1300 A
Power output reaches 6.5 MW, effectively transferred to the grid via the inverter
Grid and inverter voltages and currents are accurately synchronized and controlled

🌥️ Response to Changing Irradiance

The system is further tested under varying irradiance levels:

At 800 W/m² → PV output ≈ 5.2 MW
At lower irradiance → Output drops to ≈ 3.27 MW

In all cases, the MPPT algorithm tracks the maximum power point accurately, and the inverter dynamically adjusts to feed the available power into the grid. Grid current amplitude varies accordingly, reflecting the real-time power changes.

✅ Conclusion

This MATLAB/Simulink-based model of a 6.5 MW grid-connected PV system effectively demonstrates:

Accurate PV array sizing
Boost converter design with MPPT
Real and reactive power control using DQ transformations
Successful grid synchronization and dynamic power delivery

Such systems are crucial for integrating renewable energy into the grid reliably and efficiently.