DFIG Rotor-Side Converter Overmodulation Control

Solution Overview

Problem

Doubly-fed induction generator (DFIG) systems in wind turbines face challenges in efficiently regulating power output across varying rotational speeds and grid frequencies, leading to increased harmonics and energy losses due to the use of conventional power conversion methods.

Innovation Solution

Implementing a power converter with a rotor-side converter operating in an overmodulation regime, utilizing switching elements like IGBTs, and an active filter to mitigate harmonic contributions, thereby enhancing voltage gain, reducing energy losses, and improving controllability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If conventional power conversion methods are used in DFIG systems, then the system can regulate power output, but harmonics and energy losses increase

Engineering Contradiction:

Improvepower regulation capabilityVSAvoidenergy losses

Core Design Contradiction:

Ease of operationVSLoss of energy

Solution Approach 1:

The patent changes the modulation parameters by operating the rotor-side converter in an overmodulation regime where the modulation index exceeds 1.0. This parameter change allows the system to maintain power regulation capability while reducing energy losses and improving voltage gain, as the overmodulation technique optimizes the switching patterns and reduces harmonic content compared to conventional modulation methods

Inventive Principle:

Principle #35Parameter changes

2Ease of operation

If conventional power conversion methods are used in DFIG systems, then the system can regulate power output, but harmonic propagation to the grid increases

Engineering Contradiction:

Improvepower regulation capabilityVSAvoidharmonic propagation

Core Design Contradiction:

Ease of operationVSObject-generated harmful factors

Solution Approach 1:

The patent changes the modulation parameters by operating the rotor-side converter in an overmodulation regime where the modulation index exceeds 1.0. This parameter change allows the system to maintain power regulation capability while reducing energy losses and improving voltage gain, as the overmodulation technique optimizes the switching patterns and reduces harmonic content compared to conventional modulation methods

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent converts the potential harm of overmodulation (which can increase harmonics) into a benefit by carefully controlling the modulation index and using it to achieve superior voltage gain and reduced losses. The controlled overmodulation regime transforms what could be a harmful condition into an advantageous operating state that improves overall system performance while maintaining grid compatibility

Inventive Principle:

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

3Productivity

If the operational range of the generator is increased, then more power can be extracted from wind, but system complexity increases

Engineering Contradiction:

Improvepower extraction capabilityVSAvoidsystem complexity

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The patent changes the modulation parameters by operating the rotor-side converter in an overmodulation regime where the modulation index exceeds 1.0. This parameter change allows the system to maintain power regulation capability while reducing energy losses and improving voltage gain, as the overmodulation technique optimizes the switching patterns and reduces harmonic content compared to conventional modulation methods

Inventive Principle:

Principle #35Parameter changes

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

This approach increases the operational range of the generator, reduces energy losses, and minimizes harmonic propagation to the grid, while maintaining efficient power regulation and high-voltage ride-through capabilities.

Implementation Method 1

the switching elements are controlled according to an overmodulation regime to produce the AC signal on the rotor-side converter

Methodology Applied

Scientific EffectOvermodulation:

Implementation Method 2

The switching elements are controlled to convert a DC signal on the DC link to an AC signal for the rotor of the DFIG, using, for instance, pulse width modulation

Methodology Applied

Scientific EffectPulse width modulation:

Implementation Method 3

an active filter to mitigate harmonic contributions, thereby enhancing voltage gain, reducing energy losses, and improving controllability

Methodology Applied

Scientific EffectHarmonic filtering: Filter (electronic)

Data Source

PatentEP3484007B9DFIG converter overmodulation

Publication Date: 2023.04.19 GENERAL ELECTRIC CO

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AI summary

Systems and methods for operating a power system 100 having a doubly fed induction generator 120 are provided. In example implementations, a power system 100 can include a power converter 130. The power converter can include a line-side converter 134, a DC link 135, and a rotor-side converter 132. The rotor-side converter 132 is configured to convert a DC power on the DC link 135 to an AC signal for a rotor bus 124. The system 100 can include a control system 140 having one or more control devices. The one or more control devices are configured to operate the rotor-side converter 132 in an overmodulation regime to provide the AC signal for the rotor bus 124.