DFIG Rotor Protection Circuit for LVRT Miniaturization

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Solution Overview

Problem

Existing protection circuits for wind power generation systems with double-fed induction generators are large in size and unable to continuously operate during grid faults, such as low voltage ride through (LVRT), necessitating a miniaturized solution that can manage overcurrents and overvoltages effectively.

Innovation Solution

A protection circuit comprising a diode rectifier, a switching element (IGBT) connected in series with a resistor, and a control device that adjusts the switching element to consume current, allowing for the miniaturization of the circuit while enabling continuous operation during grid faults by controlling the flow of current and voltage.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a large-sized protection circuit is used to protect the converter from overcurrent during grid faults, then the converter is protected, but the circuit size becomes large and continuous operation during LVRT is not achieved

Engineering Contradiction:

Improveconverter protectionVSAvoidprotection circuit size

Core Design Contradiction:

ReliabilityVSVolume of stationary object

Solution Approach 1:

The invention extracts the essential protection function from the conventional large-sized protection circuit by using a simplified configuration with a switching element and resistor connected in series with the rotor winding, removing unnecessary components while maintaining overcurrent protection capability during grid faults

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The invention uses a simple switching element and resistor combination that can be quickly activated and deactivated during grid faults, providing temporary protection only when needed rather than requiring a permanently active large-sized protection circuit, enabling continuous operation during LVRT

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

2Reliability

If a protection circuit is provided to prevent overcurrent from rotor to converter, then converter damage is prevented, but the wind power generation system cannot continuously operate during grid faults

Engineering Contradiction:

Improveconverter protectionVSAvoidcontinuous operation duration

Core Design Contradiction:

ReliabilityVSDuration of action of stationary object

Solution Approach 1:

The invention dynamically activates the protection function only when grid faults occur by controlling the switching element based on grid voltage detection, allowing the system to operate continuously during normal conditions while providing on-demand protection during LVRT events

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The control device detects grid voltage levels and provides feedback control to the switching element, activating the protection circuit only when grid voltage drops below a threshold, thereby enabling continuous operation during LVRT while preventing overcurrent damage to the converter

Inventive Principle:

Principle #23Feedback

3Productivity

If the rotor is excessively speeded up by wind gust causing voltage rise on rotor side, then wind energy is captured, but overcurrent flows from rotor to converter

Engineering Contradiction:

Improvewind energy captureVSAvoidovercurrent

Core Design Contradiction:

ProductivityVSObject-generated harmful factors

Solution Approach 1:

The invention converts the harmful overcurrent effect into a beneficial protection mechanism by using the same rotor winding and switching element to dissipate excess energy during wind gusts, transforming the potential damage into a controlled energy dissipation process that protects the converter while allowing continued operation

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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 proposed solution allows the wind power generation system to maintain operation during grid faults by consuming excess current and stabilizing voltage, achieving miniaturization and enhanced protection of the rotor-side converter, thus enabling LVRT capability.

Implementation Method 1

a protection circuit which comprises a diode rectifier

Methodology Applied

Scientific EffectRectification: Diode

Implementation Method 2

a switching element which is connected in series with a resistor on a direct-current side of the diode rectifier

Methodology Applied

Scientific EffectJoule heating: Joule Heating

Data Source

PatentEP2378656B1Protection circuit used in wind power generation system including double-fed induction generator

Publication Date: 2018.04.04 TOSHIBA MITSUBISHI ELECTRIC IND SYST CORP

Figure 1~2
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Figure 4~5

AI summary

There is provided a protection circuit (10) that protects a rotor-side converter (2) connected to a secondary winding of a double-fed induction generator (6) including a diode rectifier (13), connected to the secondary winding, for rectifying an electric power coming through the secondary winding, a resistor (15) for consuming the electric power rectified by the diode rectifier (13), and a switching element (16), connected to the resistor (15) in series, for adjusting the electric power flowing into the resistor (15).