top of page
Search

# Three-Phase Grid-Connected Inverter Using MATLAB with Decoupling Control

## Introduction

We will explore the real and reactive power control of a three-phase grid-connected inverter using MATLAB. This post will guide you through the simulation model and the implementation of decoupling control for effective power management.

## Simulation Model Overview

The simulation model used for testing the three-phase grid-connected inverter includes several key components:

• LCL Filter Design

• Inverter and Grid Connection

• Feed Forward Decoupling Control

### LCL Filter Design

The design of the LCL filter is crucial for the proper functioning of the grid-connected inverter. The design is based on the following parameters:

• DC Source Voltage: 1000V

• Grid Voltage: 480V (divided by âˆš3 for single phase)

• Grid Frequency: 50Hz

• Switching Frequency of the Inverter: 5kHz

• Power Rating: 20kVA

Using these parameters, the values for L1, L2, and C are calculated to ensure that the resonance frequency lies between the grid frequency (fg) and the switching frequency (fs).

### Inverter and Grid Connection

The inverter model uses a universal three-phase IGBT diode inverter, with the following setup:

• DC Voltage: 1000V

• Grid Voltage: 480V, 50Hz

The inverter voltage and current are measured to control the real and reactive power supplied to the grid.

### Measurement Units

• Inverter Real and Reactive Power: Measured using the inverter current and grid voltage.

• Load Real and Reactive Power: Measured separately to ensure the load requirements are met.

## Feed Forward Decoupling Control

The inverter is controlled using feed forward decoupling control, which involves the following steps:

### PLL and DQ Transformation

• Phase-Locked Loop (PLL): Used to generate the phase angle (Ï‰t) of the grid voltage.

• DQ Transformation: Converts the grid voltage and inverter current from ABC to DQ0 form to facilitate control.

### Control Signal Generation

• Reference Currents: Generated based on the load's real (P) and reactive (Q) power demands.

• PI Controllers: Used to control the D and Q axis currents, generating control signals.

### Feed Forward Compensation

• Compensation Components: Added to the control signals to account for the decoupling of D and Q axes.

• Conversion to ABC: The final control signals in DQ form are converted back to ABC form.

### PWM Generation

• PWM Generator: Generates the pulse signals for the IGBT inverter based on the control signals.

## Simulation Results

Initially, we tested the model with a real power load of 10kW. The simulation results show that the inverter supplies 10kW of real power to the load with no reactive power. The voltage and current are in phase, indicating purely real power supply.

### Real and Reactive Power Load Condition

Next, we added a reactive power load of 10kVAR. The simulation results show that the inverter supplies 10kW of real power and 10kVAR of reactive power to the load. The voltage and current have a phase difference, indicating the presence of reactive power.