Virtual Impedance Power Control for Low-Order Harmonic Damping

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Solution Overview

Problem

Existing systems for compensating low-order harmonics in power systems, such as those generated by electrical arc furnaces, require large and costly devices due to the need for numerous converter cells, increasing overall system costs.

Innovation Solution

A power supplying and/or absorbing device with a virtual impedance-based control system that uses a higher virtual reactance and lower virtual resistance to dampen voltage fluctuations and harmonics, allowing for effective compensation without the need for increased device size.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If the number of converter cells is increased to improve low-order harmonics compensation, then the compensation effectiveness is improved, but the device size and cost increase

Engineering Contradiction:

Improveharmonics compensation effectivenessVSAvoiddevice size

Core Design Contradiction:

Manufacturing precisionVSVolume of stationary object

Solution Approach 1:

The patent changes the control parameters of the power supplying and/or absorbing device by introducing virtual impedance (virtual reactance and virtual resistance) to achieve effective harmonics compensation. This allows the device to compensate for low-order harmonics without increasing the number of converter cells, thus avoiding device size expansion while maintaining compensation effectiveness.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces the traditional physical expansion approach (adding more converter cells) with a control-based approach (virtual impedance control). This substitution allows the same compensation function to be achieved through software/control algorithms rather than hardware expansion, resolving the contradiction between compensation effectiveness and device size.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Manufacturing precision

If the number of converter cells is increased to improve low-order harmonics compensation, then the compensation effectiveness is improved, but the system cost increases

Engineering Contradiction:

Improveharmonics compensation effectivenessVSAvoidsystem cost

Core Design Contradiction:

Manufacturing precisionVSEase of manufacture

Solution Approach 1:

By changing the control parameters to include virtual impedance characteristics, the system achieves effective harmonics compensation without hardware expansion. This parameter-based control approach maintains compensation effectiveness while avoiding the increased costs associated with adding more converter cells.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent substitutes hardware expansion with control algorithm implementation. Instead of investing in additional physical converter cells, the system uses virtual impedance control strategies to achieve the same compensation effect, thereby reducing system cost while maintaining compensation performance.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Stability of the object's composition

If virtual reactance is increased and virtual resistance is decreased, then voltage fluctuations and harmonics are damped more effectively, but the control complexity increases

Engineering Contradiction:

Improvevoltage stabilityVSAvoidcontrol system complexity

Core Design Contradiction:

Stability of the object's compositionVSDevice complexity

Solution Approach 1:

The patent introduces virtual impedance as an intermediary control mechanism between the power supplying and/or absorbing device and the power system. This virtual impedance (comprising virtual reactance and virtual resistance) acts as a mediator to dampen voltage fluctuations and harmonics effectively, while the control complexity is managed through structured control algorithms.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The control unit continuously monitors voltage conditions and adjusts the virtual impedance parameters accordingly. This feedback mechanism allows the system to maintain voltage stability by dynamically optimizing the virtual reactance and virtual resistance values, managing control complexity through adaptive control strategies.

Inventive Principle:

Principle #23Feedback

Data Source

PatentUS20250233416A1Apparatus and method for supplying power to or absorbing power from a load

Publication Date: 2025.07.17 HITACHI ENERGY LTD

AI summary

An apparatus is configured to supply power to a load or absorb power from the load, the load being connected or connectable to a load conductor. The apparatus comprises a power supplying and/or absorbing device, configured for selectively supplying power to the load conductor or absorbing power from the load conductor, and a control unit configured to control the power supplying and/or absorbing device. The control unit is configured to determine, based on at least one value indicative of voltage of the load conductor and a virtual impedance of the power supplying and/or absorbing device, a voltage reference value for the power supplying and/or absorbing device, and control the power supplying and/or absorbing device to supply power to the load conductor, and thereby supply power to the load, or absorb power from the load conductor, and thereby absorb power from the load, based on the determined voltage reference value.