DFIG Rotor-Side Converter Fault Protection via Dynamic Brake
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Solution Overview
Problem
Wind turbine DFIG systems face challenges in protecting power converters from excessive energy during fault events like grid under-voltage or over-voltage conditions, which can lead to damage due to uncontrolled current and voltage levels.
Innovation Solution
The method involves detecting fault events based on current levels in the power converter, disabling bridge switching when current exceeds a threshold, and employing a dynamic brake to dissipate energy, with a crowbar as a last resort, allowing for higher voltage utilization and reduced peak current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a crowbar or brake chopper is utilized to prevent excess energy from reaching the power converter during fault events, then the power converter is protected from overvoltage conditions, but the current level quickly rises and may exceed component limitations
Solution Approach 1:
The patent applies preliminary action by disabling bridge switching of the rotor-side converter before excessive current can damage the power converter. The controller detects fault conditions and proactively disables the switching elements, preventing the harmful current surge that would otherwise occur when using traditional crowbar or brake chopper methods.
Solution Approach 2:
The patent employs dynamics by selectively disabling only the rotor-side converter bridge switching while maintaining line-side converter operation. This dynamic, selective approach allows the system to protect the power converter from overvoltage while avoiding the excessive current rise that occurs when completely disconnecting the rotor, thus adapting the protection level to the specific fault condition.
2Reliability
If the rotor is open-circuited during a fault event to protect the power converter, then overvoltage conditions are prevented, but the voltage may rise to the locked rotor voltage of the generator exceeding current and voltage limitations
Solution Approach 1:
The patent applies dynamics by selectively disabling only the rotor-side converter bridge switching while maintaining line-side converter operation. This dynamic, selective approach allows the system to protect the power converter from overvoltage while avoiding the excessive current rise that occurs when completely disconnecting the rotor, thus adapting the protection level to the specific fault condition.
Solution Approach 2:
The patent changes the operational parameters of the converter by disabling bridge switching, which alters the electrical characteristics of the rotor circuit. This parameter change enables the system to limit voltage rise during fault events while maintaining controlled current levels, avoiding the locked rotor voltage condition that would occur with complete rotor open-circuiting.
3Object-affected harmful factors
If bridge switching is disabled and dynamic brake is gated on to dissipate energy, then peak current is reduced and voltage utilization is improved, but the system complexity increases
Solution Approach 1:
The patent applies self-service by using the existing dynamic brake component already present in the power converter system. The controller simply gates on the dynamic brake and disables bridge switching, allowing the existing hardware to dissipate energy and limit peak current without requiring additional external components or complex external protection circuits.
Solution Approach 2:
The patent employs feedback by continuously monitoring system conditions and using this information to control the dynamic brake and bridge switching operations. The controller adjusts the duty cycle of the dynamic brake based on real-time measurements, creating a closed-loop control system that automatically responds to changing fault conditions without requiring complex external intervention.
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 effectively reduces the risk of damage to power converters by managing peak current and energy dissipation during faults, enhancing the operational safety and efficiency of wind turbine electrical power systems.
Implementation Method 1
employing a dynamic brake to dissipate energy
Data Source
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AI summary
A method 300 for operating an electrical power system includes disabling 330 bridge switching of one of the rotor-side converter 132 or line-side converter 134. The method 300 further includes gating 335 on the dynamic brake after the disabling occurs, comparing 400 a power converter input variable to a primary predetermined variable threshold, and forcing 410 the gated-on dynamic brake 180 to a 100 percent duty cycle when the power converter input variable exceeds the primary predetermined variable threshold.