Grid-Forming Inverter Control for Renewable Microgrid Frequency Stability

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Solution Overview

Problem

Isolated electrical grids relying on renewable energy sources face challenges in maintaining stable voltage and frequency without combustion engine-driven alternators, necessitating a system that can ensure grid stability with maximum renewable energy penetration.

Innovation Solution

A method and system utilizing a controllable inverter coupled to an electric battery, operating as a master controller to adjust grid frequency by supplying or withdrawing power from the grid based on frequency deviations, combined with an energy bank and alternators to stabilize frequency and voltage, ensuring optimal operation of renewable energy sources.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If combustion engine-driven alternators are used to ensure stable voltage and frequency in isolated grids, then grid stability is maintained, but reliance on non-renewable energy sources increases

Engineering Contradiction:

Improvegrid stabilityVSAvoidrenewable energy penetration

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The patent replaces the mechanical combustion engine-driven alternator system with an electronic inverter-based grid-forming system. The inverter uses power electronic components to synthesize stable voltage and frequency from renewable energy sources and battery storage, eliminating the need for mechanical prime movers while maintaining grid stability requirements.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the control parameters and operating modes of the inverter to provide grid-forming functionality. By dynamically adjusting the inverter's output voltage, frequency, and reactive power based on grid conditions, the system can stabilize the isolated grid without combustion engines, enabling higher renewable energy penetration.

Inventive Principle:

Principle #35Parameter changes

2Adaptability or versatility

If maximum renewable energy penetration is achieved without combustion engines, then carbon emissions are reduced, but grid frequency and voltage stability become difficult to maintain

Engineering Contradiction:

Improverenewable energy penetrationVSAvoidfrequency stability

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent implements preliminary action by using battery storage systems charged during periods of high renewable generation to prepare for periods when renewable output fluctuates. The inverter is pre-configured with grid-forming control algorithms that activate when combustion engines are removed, enabling the system to maintain frequency stability proactively rather than reactively.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent employs feedback control mechanisms where the inverter continuously monitors grid frequency, voltage, and power balance, then adjusts its output accordingly. This closed-loop control enables the inverter to maintain stable grid parameters despite the variability of renewable energy sources, replacing the inherent mechanical stability of combustion engines.

Inventive Principle:

Principle #23Feedback

3Speed

If inverter-based systems replace combustion engine alternators, then response time to frequency deviations improves, but system complexity increases

Engineering Contradiction:

Improveresponse timeVSAvoidcontrol system complexity

Core Design Contradiction:

SpeedVSDevice complexity

Solution Approach 1:

The patent makes the inverter a multi-functional device that simultaneously performs power conversion, grid-forming control, frequency regulation, and voltage stabilization. By consolidating these functions into a single electronic device with integrated control, the system achieves fast response times without proportionally increasing overall system complexity compared to mechanical alternatives.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentUS12451698B2Method and system for operating an electrical grid

Publication Date: 2025.10.21 VESTESEN HYBRID ENERGY APS

AI summary

A power supply system and method for operating an electrical grid having coupled thereto at least one fluctuating source of AC power generated from renewable energy, consumers creating a fluctuating AC power demand, at least one grid forming controllable inverter coupled to an electric battery, and the power supply system including a controller. The controller being configured to perform a method of:operating the at least one fluctuating source of AC power as a slave to the grid, measuring grid frequency,controlling grid frequency with the controllable inverter as master controller to obtain a desired grid frequency,supplying power from the electric battery through the controllable inverter to the grid when the measured gridfrequency is below the desired grid frequency by more than a first lower margin, and withdrawing power through the controllable inverter from the grid to the electric battery when the measured grid frequency is above the desired grid frequency by more than a second first upper margin.