Active Damping for LCL Filter Resonance in Grid Converters

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Solution Overview

Problem

Grid-connected converters with LCL filters experience instability due to resonance phenomena, which existing damping methods either increase system dimensions and cost or require expensive sensors, leading to performance degradation and noise amplification.

Innovation Solution

A damping apparatus and method that compensates the input voltage reference and capacitor voltage in a harmonic filter using the ratio between inductances of inductors, generating a final voltage reference to prevent resonance without needing expensive sensors or complex calculations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a passive damping method adds a resistor to the capacitor end of an LCL filter, then resonance phenomenon is attenuated, but system dimension and manufacturing cost are unnecessarily increased

Engineering Contradiction:

Improveresonance attenuationVSAvoidsystem dimension

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent extracts the damping function from a separate physical component (resistor) and integrates it into the existing control system through software/algorithms. The active damping controller implements virtual resistance through control signals, eliminating the need for additional passive damping components and reducing system dimension while maintaining resonance attenuation capability

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent replaces the mechanical/electrical passive damping approach (physical resistor) with an active control system that uses sensing and processing elements. The active damping controller measures capacitor voltage and generates compensating control signals to achieve damping effect without physical energy dissipation components, thereby reducing system dimension and manufacturing cost

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Reliability

If a passive damping method adds a resistor to the capacitor end of an LCL filter, then resonance phenomenon is attenuated, but manufacturing cost is unnecessarily increased

Engineering Contradiction:

Improveresonance attenuationVSAvoidmanufacturing cost

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Reliability

If an active damping method uses information related to capacitor current, then damping is achieved without physical loss, but expensive current sensor is required

Engineering Contradiction:

Improvedamping performanceVSAvoidsensor cost

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent substitutes expensive current sensors with inexpensive voltage sensors. By measuring capacitor voltage instead of current and using the known capacitance value to derive current information through calculation, the system achieves the same damping function using cheaper sensing components, thereby reducing manufacturing cost while maintaining damping performance

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

4Ease of manufacture

If an active damping method uses information related to capacitor voltage, then inexpensive voltage sensor is used, but noise component is amplified when implementing differential term

Engineering Contradiction:

Improvesensor costVSAvoidcontrol stability

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent applies preliminary filtering or preprocessing to the voltage signal before implementing the differential operation. By preparing the signal in advance through filtering or smoothing operations, the system prevents noise amplification that would otherwise occur during differentiation, thereby maintaining control stability while using inexpensive voltage sensors

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent implements feedback mechanisms that monitor the differentiated voltage signal and adjust control parameters to compensate for noise effects. Through feedback control, the system can maintain stability by detecting and correcting noise-induced deviations, thereby achieving reliable damping performance with inexpensive voltage sensing

Inventive Principle:

Principle #23Feedback

Data Source

PatentUS9923449B2Damping apparatus and damping method of converter system

Publication Date: 2018.03.20 LSIS CO LTD

AI summary

The present disclosure relates to a damping apparatus of a converter system, which compensates an input voltage reference being transmitted to a converter to damp an output current of a harmonic filter that is connected between an output end of the converter and a system, including a voltage reference compensation unit configured to compensate for the input voltage reference using a ratio between inductances of inductors included in the harmonic filter; a capacitor voltage value compensation unit configured to compensate for a voltage value of a capacitor included in the harmonic filter using the ratio between the inductances of the inductors; and a voltage reference generation unit configured to generate a final voltage reference by subtracting the compensated voltage value of the capacitor from the compensated input voltage reference.