Virtual Synchronous Generator Current Limiting With Virtual Impedance

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Power generating units, such as wind turbines, configured with virtual synchronous machines face damage from overcurrents during abnormal grid conditions, as they have low thermal capacity and are unable to sustain high currents effectively.

Innovation Solution

A method for controlling power generating units that determines a virtual impedance based on current differences and uses this impedance to reduce the acceleration of the virtual synchronous generator, thereby limiting the current delivered and preventing damage to electronic components. This involves determining a virtual resistance value through a control algorithm, which can include proportional and integral parts, and optionally a virtual reactance value, to manage grid currents during overcurrent situations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If power generating units are configured with virtual synchronous machines to enable grid-forming properties, then penetration of renewable energy sources into the electrical grid is improved, but the units become vulnerable to damaging overcurrents during abnormal grid conditions

Engineering Contradiction:

Improvegrid-forming capabilityVSAvoidovercurrent protection

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent introduces a virtual impedance element as an intermediary between the power converter and the grid. This virtual impedance acts as a mediator that limits the current flow during abnormal conditions while maintaining the virtual synchronous machine's grid-forming capabilities during normal operation. The virtual impedance is determined based on current magnitude and compared against threshold values to activate current limitation only when needed.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent implements dynamic adjustment of virtual impedance based on real-time current conditions. The virtual impedance value is not fixed but is dynamically determined by comparing the current magnitude against threshold values and adjusting the virtual resistance and reactance components accordingly. This allows the system to adapt its behavior from grid-forming mode to current-limiting mode as conditions change.

Inventive Principle:

Principle #15Dynamics

2Ease of operation

If virtual synchronous machine control is implemented to manage power output, then control of renewable power generating units is improved, but the low thermal capacity of power converters makes them unable to sustain overcurrents

Engineering Contradiction:

Improvepower controlVSAvoidthermal capacity

Core Design Contradiction:

Ease of operationVSTemperature

Solution Approach 1:

The patent applies preliminary anti-action by preemptively introducing virtual impedance before damaging overcurrents can occur. The control system continuously monitors current magnitude and activates the virtual impedance mechanism when current approaches threshold values, preventing the thermal damage that would otherwise occur during grid faults or abnormal conditions.

Inventive Principle:

Principle #9Preliminary anti-action

Solution Approach 2:

The patent changes the electrical parameters of the system by introducing adjustable virtual resistance and reactance components. These parameter changes are made dynamically based on operating conditions, allowing the power converter to maintain safe operating temperatures by limiting current while preserving full power control capability during normal operation.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If current limitation is implemented during overcurrent situations, then damage to electronic components is prevented, but the acceleration of the virtual synchronous generator is reduced

Engineering Contradiction:

Improvecomponent protectionVSAvoidgenerator acceleration

Core Design Contradiction:

ReliabilityVSSpeed

Solution Approach 1:

The patent applies partial action by implementing current limitation only to the extent necessary to prevent damage. The virtual impedance is adjusted to limit current to safe levels rather than completely blocking power flow, allowing the virtual synchronous generator to maintain some acceleration and power transfer capability while protecting components from damaging overcurrents.

Inventive Principle:

Principle #16Partial or excessive action

Data Source

PatentUS12176842B2Power generating unit with virtual synchronous generator with current limitation

Publication Date: 2024.12.24 VESTAS WIND SYSTEMS AS

AI summary

The invention relates to a method for controlling a power generating unit. The method includes determining a virtual impedance value, determining a virtual grid power based on the virtual resistance value and the grid current, determining a virtual synchronous machine rotational speed and/or a synchronous machine angle of a virtual synchronous generator, and determining a voltage reference for controlling a line side converter to generate the desired reactive power based on the virtual synchronous machine rotational speed or angle, a virtual voltage and the voltage magnitude reference.