ANPC Crowbar Module for Transient Current Sharing
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Solution Overview
Problem
Existing power conversion systems in wind turbines face challenges with high power mismatches during transient events, leading to excessive DC link voltage and stress on switching devices due to large current transients, which can exceed current or voltage ratings.
Innovation Solution
An active neutral point clamped three-level power conversion system with AC terminals crowbarred via two sets of middle point switching devices, utilizing a crowbar algorithm to bifurcate current into multiple paths, directing it through different sets of IGBTs based on temperature thresholds to manage transient events effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fast acting shorting means (crowbar circuit) is used to absorb excess power during transient events, then DC link voltage is lowered, but large current transients are created that stress the switching devices beyond their current ratings
Solution Approach 1:
The patent divides the single crowbar circuit into multiple parallel crowbar circuits (first crowbar circuit and second crowbar circuit), each handling a portion of the transient current. This segmentation distributes the current stress across multiple switching devices, preventing any single device from exceeding its current rating while maintaining effective DC link voltage control.
2Reliability
If the transient event duration is extended to allow switching devices to handle the current, then voltage rating is exceeded, but if the duration is reduced, then the switching devices cannot dissipate the energy
Solution Approach 1:
The patent segments the transient current handling into multiple parallel paths with independent timing control. Each crowbar circuit can be activated with optimized timing, allowing the system to manage the transient duration effectively while distributing the stress across multiple devices, thus protecting both voltage and current ratings.
Solution Approach 2:
The patent implements dynamic control of multiple crowbar circuits with independent activation timing. The controller can adjust the duration and timing of each crowbar circuit's operation based on real-time conditions, optimizing the balance between voltage protection and current dissipation capability during transient events.
3Device complexity
If a single crowbar circuit is used, then the system structure is simple, but the switching devices must handle the full transient current which exceeds their ratings
Solution Approach 1:
The patent divides the crowbar function into multiple parallel circuits, each with its own switching device. This segmentation reduces the current magnitude on each individual device while maintaining the overall crowbar functionality. The increased device count is offset by the reduced current stress and improved reliability.
Data Source
AI summary
A method for operating a multi-level bridge power converter of an electrical power system connected to a power grid includes receiving, via a controller of the power converter, an indication of a transient event occurring in the power grid or the electrical power system. The power converter has a plurality of switching devices arranged in an active neutral point clamped topology. Accordingly, upon receiving the indication, the method includes activating a crowbar algorithm programmed in the controller of the power converter to bifurcate a current received by the power converter into a plurality of different current paths defined by the plurality of switching devices.