Synchronous Speed Avoidance Controller for DFIG Thermal Management

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Solution Overview

Problem

Variable speed power generation systems face operational issues due to high power transistor junction temperatures, particularly when the rotor side converter operates at or near zero rotor frequency, leading to potential semiconductor failure from temperature stress.

Innovation Solution

Implementing a synchronous speed avoidance (SSA) controller that regulates the electrical torque and rotor speed of doubly-fed induction generators, creating an unstable operating range around synchronous speed to prevent excessive junction temperatures, thereby protecting power semiconductors.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If power semiconductors with oversized current ratings are used to handle temperature fluctuations, then reliability is improved, but device cost increases significantly

Engineering Contradiction:

Improvepower semiconductor reliabilityVSAvoidsystem cost

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The control system proactively detects when rotor frequency approaches zero and executes avoidance maneuvers before excessive temperature rise occurs. By performing the speed adjustment in advance, the system prevents thermal stress accumulation without requiring oversized semiconductors, thus maintaining reliability while avoiding increased component costs

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The control system continuously monitors rotor frequency and junction temperature, using this feedback to dynamically adjust rotor speed and avoid operating conditions that cause excessive heating. This closed-loop control enables the use of optimally-sized semiconductors rather than oversized components, reducing system cost while maintaining reliability

Inventive Principle:

Principle #23Feedback

2Productivity

If rotor side converter operates at zero rotor frequency, then power generation efficiency is improved, but power transistor junction temperature increases excessively

Engineering Contradiction:

Improvepower generation efficiencyVSAvoidpower transistor junction temperature

Core Design Contradiction:

ProductivityVSTemperature

Solution Approach 1:

When the rotor frequency approaches zero, the control system rapidly adjusts the rotor speed to skip through the dangerous operating zone before excessive temperature can develop. This quick maneuver allows the system to maintain efficient operation while avoiding the thermal stress that would occur with prolonged operation at zero frequency

Inventive Principle:

Principle #21Skipping (Rushing through)

Solution Approach 2:

The control system implements periodic monitoring of rotor frequency and applies corrective speed adjustments at appropriate intervals to prevent junction temperature from rising excessively, allowing efficient operation while managing thermal conditions through rhythmic control actions

Inventive Principle:

Principle #19Periodic action

3Stability of the object's composition

If rotor operates at synchronous speed, then operational consistency is improved, but power semiconductor reliability deteriorates due to thermal stress

Engineering Contradiction:

Improvegenerator operational consistencyVSAvoidpower semiconductor reliability

Core Design Contradiction:

Stability of the object's compositionVSReliability

Solution Approach 1:

The control system dynamically adjusts the rotor speed parameter to maintain operational consistency while avoiding synchronous speed conditions. By changing the speed parameter slightly above or below synchronous speed, the system achieves stable operation without subjecting power semiconductors to excessive thermal stress from zero-frequency operation

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS8035240B2Systems and methods for synchronous speed avoidance in doubly-fed induction generators

Publication Date: 2011.10.11 NORDEX ENERGY SPAIN SAU

AI summary

The disclosure details implementations of apparatuses, methods, and systems for facilitating efficient operational characteristics for wind turbine generators. The system includes features that facilitate protecting the power semiconductors used in the power converters of variable speed power generation systems from excessive junction temperatures. These features may be achieved by implementing a synchronous speed avoidance (SSA) controller implemented to facilitate a determined active control range as an electrical torque/power-generator rotor speed controller. The determined active control range may be centered around a generator synchronous speed. The upper and lower bounds of the active control range are determined based on operational junction temperature characteristics of power semiconductors used within a power converter, reliability characteristics of the power semiconductors and/or current ratings of the power semiconductors.