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MATLAB Simulation of a 5 kW Single-Stage Grid-Connected PV System

👋 Introduction

MATLAB/Simulink implementation of a 5 kW single-stage grid-connected photovoltaic (PV) system. The key objective of this system is to convert DC power generated by the PV array directly into AC power and inject it into the utility grid using a single power-conversion stage, ensuring simplicity, high efficiency, and reduced system losses.

☀️ PV Array Configuration

The PV array is designed to generate approximately 5 kW under standard test conditions (STC).

🔹 Array configuration

  • 🔗 Parallel strings: 1

  • 🔢 Series-connected modules: 24

  • 🔋 Single PV module rating: 215.17 W

🔹 Electrical characteristics at MPP

  • ⚡ Voltage at MPP (V_MPP): 28.96 V

  • 🔌 Current at MPP (I_MPP): 7.43 A

  • 🌞 Total rated PV power: ≈ 5.16 kW

📉 The PV output power and voltage vary dynamically with changes in solar irradiance, highlighting the need for an MPPT algorithm.

🔄 Single-Stage Grid-Connected Topology

Unlike two-stage PV systems, this model uses a single-stage topology, where:

✔️ The PV array is directly connected to a three-phase voltage source inverter (VSI)✔️ No intermediate DC–DC converter is used✔️ DC–AC conversion and MPPT are handled together

This approach reduces:

  • ❌ Converter count

  • ❌ Switching losses

  • ❌ System complexity

⚙️ Inverter and Grid Interface

  • 🔁 A universal bridge is used as a three-phase VSI

  • 🔌 The inverter output is connected to the grid through an LCL filter

  • 🌐 Grid specifications:

    • Voltage: 400 V

    • Frequency: 50 Hz

The LCL filter ensures:

  • ✔️ Harmonic reduction

  • ✔️ Smooth grid current injection

  • ✔️ Compliance with grid standards

🎯 MPPT Using P&O Algorithm

To extract maximum power from the PV array, a Perturb and Observe (P&O) MPPT algorithm is implemented.

📥 Inputs to MPPT

  • PV voltage

  • PV current

📤 Output of MPPT

  • Reference PV voltage (V_ref)

🧠 Working principle

  • PV power is calculated continuously

  • Changes in voltage (ΔV) and power (ΔP) are evaluated

  • Based on four P&O rules, the reference voltage is incremented or decremented

  • This ensures PV operation near the maximum power point under varying irradiance

🔋 DC-Side Voltage Control

The reference voltage generated by the P&O MPPT is compared with the actual PV voltage.

⚙️ A PI controller acts as a PV voltage controller, regulating the operating voltage of the PV array so that maximum power is extracted without instability.

🔄 Power-to-Current Conversion

The measured PV power is converted into a reference current for grid injection.

📐 This is achieved by:

  • Multiplying PV power by 2/3

  • Dividing by the direct-axis grid voltage (Vd)

📌 This step ensures proper synchronization between DC power generation and AC current injection.

🧭 Grid Synchronization Using PLL

To synchronize inverter operation with the grid:

  • 🔍 Grid voltages (V_abc) are measured

  • 🧠 A Phase-Locked Loop (PLL) extracts the grid angle (ωt)

  • 🔄 Park transformation converts abc quantities into d-q components

This allows precise control of:

  • Direct-axis current (Id)

  • Quadrature-axis current (Iq)

⚡ Feed-Forward Decoupling Current Control

To achieve fast and stable current control, a feed-forward decoupling strategy is used.

🔹 Id control

  • Id reference is derived from PV power

  • Compared with actual Id

  • Processed through a PI controller

  • Decoupling terms (ωL Iq + Vd) are added

🔹 Iq control

  • Iq reference is set to zero (unity power factor operation)

  • Compared with actual Iq

  • Processed through a PI controller

  • Decoupling terms (ωL Id + Vq) are included

This ensures:✔️ Independent control of active and reactive power✔️ Unity power factor grid injection

🔁 PWM Generation and Inverter Switching

The final control voltages (Vd and Vq) are:

  • Converted back to abc frame using inverse Park transformation

  • Fed to a sinusoidal PWM generator

🎛️ The generated PWM pulses control the inverter switches, enabling smooth DC–AC power conversion.

📊 Simulation Results and Performance

🔹 At 1000 W/m² irradiance

  • PV voltage: ~695–700 V

  • PV power: ~5.1 kW

  • Grid receives nearly the same power

🔹 At 0.3 s, irradiance drops to 500 W/m²

  • PV power reduces to ~2.5 kW

  • Inverter and grid power reduce proportionally

📌 At all operating points:

  • Power balance between PV and grid is maintained

  • No intermediate storage is required

  • All generated PV power is injected into the grid

✅ Key Advantages of the Single-Stage System

✔️ Reduced system complexity✔️ Higher efficiency✔️ Lower cost and losses✔️ Effective MPPT and grid synchronization✔️ Suitable for medium-scale grid-connected PV plants

🏁 Conclusion

This blog presented a detailed explanation of a 5 kW single-stage grid-connected PV system implemented in MATLAB/Simulink. By combining P&O MPPT, feed-forward decoupled current control, and PLL-based synchronization, the system efficiently injects maximum available solar power into the grid under varying irradiance conditions.

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