Grid-Forming Inverter Control With Virtual Inertia for Frequency Stability

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Solution Overview

Problem

Grid-following inverters lack the inertia provided by traditional synchronous generators, leading to instability in power grids as the proportion of renewable energy sources increases, which can result in frequency and voltage variability and potential grid failures.

Innovation Solution

A grid-forming inverter system that includes a power stage, control circuit, and capacitors to provide virtual inertia, using pulse width modulation (PWM) for frequency and voltage control, and a source-side converter that adjusts power output based on weather conditions and grid stability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If grid-following inverters are used to convert renewable energy to grid-compatible power, then installation and operation are simple with low maintenance costs, but the inverter does not provide inertia to the grid and may deteriorate grid stability

Engineering Contradiction:

Improveinstallation and operation simplicityVSAvoidgrid stability

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent copies the inertia characteristic of synchronous generators by implementing a virtual inertia control algorithm in the inverter's control circuit. The control circuit calculates a frequency command value that includes an inertia component proportional to the rate of change of grid frequency, thereby replicating the inertial response of traditional generators without requiring physical rotating mass.

Inventive Principle:

Principle #26Copying

Solution Approach 2:

The patent changes the control parameters of the inverter from passive grid-following mode to active grid-forming mode. By introducing virtual inertia parameters and adjusting the frequency command value dynamically based on grid conditions, the inverter transforms its operational characteristics to provide stability support while maintaining electrical energy conversion functionality.

Inventive Principle:

Principle #35Parameter changes

2Productivity

If the proportion of renewable energy sources increases, then sustainable energy generation improves, but grid frequency stability deteriorates due to lack of inertia

Engineering Contradiction:

Improverenewable energy generation proportionVSAvoidfrequency stability

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

Inventive Principle:

Principle #26Copying

Solution Approach 2:

The patent replaces the mechanical inertia of synchronous generators with an electronic control mechanism. The virtual inertia is achieved through software-based frequency regulation that responds to grid frequency changes with a time delay characteristic similar to mechanical systems, effectively substituting physical mass with computational control.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Ease of operation

If grid-following inverters automatically synchronize with grid voltages and frequencies, then connection to the grid is easy and load on the grid is minimized, but the inverter becomes a burden for grid management during variability situations

Engineering Contradiction:

Improvegrid connection easeVSAvoidresponse to grid variability

Core Design Contradiction:

Ease of operationVSAdaptability or versatility

Solution Approach 1:

The patent transforms the inverter from a static grid-following device to a dynamic grid-forming device. The control circuit continuously adjusts the frequency command value based on real-time grid conditions and virtual inertia calculations, enabling the inverter to actively adapt to and stabilize the grid during variability situations rather than passively following grid fluctuations.

Inventive Principle:

Principle #15Dynamics

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The system stabilizes grid frequencies and addresses instability from intermittent renewable energy sources by mimicking the inertia of synchronous generators, enhancing grid stability and maintaining voltage levels.

Implementation Method 1

a control circuit to calculate a frequency command value in proportion to a direct current input voltage and to control the switching devices using pulse width modulation (PWM) according to the frequency command value

Methodology Applied

Scientific EffectPulse Width Modulation (PWM):

Implementation Method 2

A capacitor may be disposed in an input side of the power stage and the direct current input voltage may be formed in the capacitor

Methodology Applied

Scientific EffectCapacitance: Capacitance

Data Source

PatentUS20250330022A1Grid-forming inverter and grid-forming inverter system for distributed power sources based on intermittent renewable energy sources and control method thereof

Publication Date: 2025.10.23 KOREA INST OF ENERGY RES

AI summary

An embodiment of the present disclosure provides a grid-forming inverter comprising: a power stage to convert electric power according to on/off controls of switching devices and to output the converted electric power to a grid; and a control circuit to calculate a frequency command value in proportion to a direct current input voltage and to control the switching devices using pulse width modulation (PWM) according to the frequency command value.