Comprehensive Documentation for Simulation of a Three-Phase Grid-Connected Inverter Using Direct-Quadrature (DQ) Control

System Overview

What is a Grid-Connected Inverter with DQ Control?

A grid-connected inverter converts DC power (from a renewable energy source or energy storage system) into AC power that is synchronized with the electrical grid. The Direct-Quadrature (DQ) Control method simplifies the control of active and reactive power by transforming three-phase AC variables into a rotating reference frame.

Purpose of the Simulation

The simulation aims to:

• Validate the performance of the grid-connected inverter under various grid conditions.
• Analyze the effectiveness of DQ-based current control for active/reactive power regulation.
• Evaluate power quality metrics such as Total Harmonic Distortion (THD) and power factor correction.

Key Features

DQ Synchronous Reference Frame Control

The system transforms three-phase AC signals into DC-equivalent DQ components, allowing precise control of grid-injected power.
➡️ HIL/PHIL Benefit: Enables real-time control validation and grid fault simulations.

Sinusoidal Pulse Width Modulation (SPWM)

SPWM is used for smooth inverter switching, reducing harmonic distortion and improving efficiency.
➡️ HIL/PHIL Benefit: Allows testing of different modulation strategies under real-time conditions.

Phase-Locked Loop (PLL) for Grid Synchronization

A PLL ensures phase and frequency synchronization between the inverter and the grid.
➡️ HIL/PHIL Benefit: Enables robust testing of grid synchronization algorithms under grid disturbances.

Simplified Control Design

 The transformation of AC quantities into DC quantities simplifies the control design and implementation.

Grid Compatibility

DQ control ensures compliance with grid codes and standards for voltage, frequency, and power factor.

Dynamic Performance

DQ control provides fast and accurate response to grid disturbances, enhancing system reliability.

Simulation Objectives

This simulation helps evaluate:

• Grid-synchronization performance using PLL techniques.
• Active and reactive power control capabilities using DQ control.
• Power quality improvements with SPWM-based inverter switching.
  ➡️ HIL/PHIL Benefit: Facilitates hardware-in-the-loop testing before grid integration.

Technical Description

System Configuration

• Input: DC power source (e.g., renewable energy, battery storage).
• Output: Three-phase AC power injected into the grid.
• Power Stage: IGBT-based three-phase inverter with LC filter.

Control Methodology

• DQ Transformation: Converts AC voltages and currents into DQ reference frame.
• Current Control Loop: Regulates active (d-axis) and reactive (q-axis) current components.
• Phase-Locked Loop (PLL): Ensures accurate grid synchronization.
  ➡️ HIL/PHIL Benefit: Enables real-time validation of inverter control strategies.

Advantages of DQ-Based Grid-Connected Inverter Control

• Precise Power Regulation: Independent control of active and reactive power.
• Improved Power Quality: Reduces harmonics and enhances grid stability.
• Fast Dynamic Response: Adapts quickly to grid disturbances and load variations.
  ➡️ HIL/PHIL Benefit: Provides a realistic testing platform for grid compliance verification.

Applications

Renewable Energy Systems

Solar Power Plants: Grid-connected inverters with DQ control are used in photovoltaic (PV) systems to convert DC power from solar panels into AC power for the grid. Simulations help optimize power injection and ensure compliance with grid codes.

Wind Turbines: DQ-controlled inverters are used in wind energy systems to manage power flow between the generator and the grid. Simulations ensure stable operation under varying wind conditions.

Hybrid Energy Systems: DQ control is used in hybrid systems combining solar, wind, and battery storage to ensure efficient power conversion and grid integration.

Energy Storage Systems (ESS)

Battery Energy Storage: Grid-connected inverters with DQ control are used in battery energy storage systems to manage charging and discharging. Simulations optimize power flow and ensure grid stability.

Grid Support: DQ-controlled inverters provide grid services such as frequency regulation, voltage support, and peak shaving. Simulations validate their performance under dynamic grid conditions.

Microgrids

Islanded Microgrids: DQ-controlled inverters are used in islanded microgrids to regulate voltage and frequency, ensuring stable operation without grid connection.

Grid-Connected Microgrids: Simulations help optimize the performance of DQ-controlled inverters in grid-connected microgrids, enabling seamless transition between grid-connected and islanded modes.

Electric Vehicle (EV) Charging Infrastructure

Bidirectional Chargers: DQ-controlled inverters are used in bidirectional EV chargers for Vehicle-to-Grid (V2G) applications. Simulations validate power flow control and grid interaction.

Fast Charging Stations: DQ control ensures efficient power conversion and grid compatibility in fast charging stations. Simulations optimize performance under varying load conditions.

Industrial Power Systems

Motor Drives: DQ-controlled inverters are used in industrial motor drives for precise speed and torque control. Simulations optimize performance and energy efficiency.

Uninterruptible Power Supplies (UPS): DQ control ensures stable power supply in UPS systems. Simulations validate performance during grid disturbances and outages.

Power Quality Improvement

Active Power Filters (APF): DQ-controlled inverters are used in APFs to mitigate harmonics and improve power quality. Simulations validate harmonic compensation and grid stability.

Static Synchronous Compensators (STATCOM): DQ control is used in STATCOMs for reactive power compensation. Simulations ensure stable voltage regulation and grid support.

Aerospace and Defense

Aircraft Power Systems: DQ-controlled inverters are used in aircraft to manage power flow between generators, batteries, and onboard systems. Simulations ensure reliable operation under extreme conditions.

Military Power Systems: DQ control is used in military applications for efficient power conversion and grid integration. Simulations validate performance in harsh environments.

Smart Grids

Grid Integration of Distributed Energy Resources (DERs): DQ-controlled inverters enable efficient integration of DERs like solar, wind, and storage into the grid. Simulations validate grid compatibility and stability.

Demand Response: DQ control helps manage power flow in demand response systems. Simulations optimize load balancing and grid support.

Simulation Benefits

With this simulation, users can:

• Optimize inverter control strategies for grid compliance.
• Analyze real-time grid interaction and power injection performance.
• Evaluate harmonic content and power factor improvement.
  ➡️ HIL/PHIL Benefit: Ensures seamless transition from simulation to real-world deployment.