Converter Cell Thyristor Bypass for Overcurrent Protection
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Solution Overview
Problem
Existing power conversion devices, such as modular multilevel converters, lack effective protection for converter cells against overcurrents caused by faults like arm short-circuits and ground faults, beyond short-circuit faults in the DC voltage circuit.
Innovation Solution
Incorporating a thyristor in parallel with semiconductor circuits within converter cells and a control system that detects overcurrents, gate-blocking switching elements and controlling the thyristor to an ON state to divert current away from freewheel diodes, thereby protecting the elements from damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional protection methods are used that only detect DC voltage circuit short-circuits, then the control system remains simple, but converter cell elements are not protected against other overcurrent faults
Solution Approach 1:
Each converter cell is equipped with its own current detector that autonomously monitors current conditions within that cell. When an overcurrent condition is detected, the system automatically triggers the corresponding thyristor without requiring complex centralized control logic. This self-service approach maintains control system simplicity while achieving comprehensive protection coverage.
Solution Approach 2:
The current detectors are positioned to detect overcurrent conditions at the earliest possible moment within each converter cell. By detecting faults preliminarily before they can damage the freewheel diodes or other components, the system can immediately trigger protective thyristors to prevent damage. This preliminary detection action enables protection against all fault types before they escalate.
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 solution provides enhanced protection for converter cell elements by quickly diverting overcurrents, preventing damage and ensuring the continued operation of the power conversion device.
Implementation Method 1
controls the thyristor to be in an ON state
Data Source
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AI summary
A power conversion device (1) includes: a power converter (2) including a plurality of converter cells (7) connected in series; and a control device (3). Each of the plurality of converter cells (7) includes: a cell controller (35); a first semiconductor circuit (25A) including a first switching element (22) and a first diode (23A); a second semiconductor circuit (25B) including a second switching element (22B) and a second diode (23A); a power storage element (24) connected in parallel with a series body including the first semiconductor circuit (25A) and the second semiconductor circuit (25B) connected in series; and a thyristor (26) connected in parallel with the first semiconductor circuit (25A). When the cell controller (35) detects an overcurrent flowing to the first semiconductor circuit (25A), the cell controller (35) gate-blocks the first switching element (22A) and the second switching element (22B), and controls the thyristor (26) to be in an ON state.