Power Conversion Device Bypass Overcurrent Suppression
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Solution Overview
Problem
Existing power conversion devices face challenges in ensuring continuous operation when double abnormalities occur in cell converters, as the bypass portion can be damaged due to overcurrent, leading to unreliable operation.
Innovation Solution
A power conversion device design where the first and second conductor portions are formed in a bent shape to intersect with each other, allowing currents to flow in the same direction and partially overlap, thereby suppressing overcurrent to the bypass portion, ensuring reliable operation even with double abnormalities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a bypass portion is closed to exclude a failing cell converter from the series circuit, then continuous operation is guaranteed, but the bypass portion is subjected to harsh states involving overcurrent that may damage it
Solution Approach 1:
A semiconductor element is introduced as an intermediary component between the capacitor and the bypass portion. This intermediary element is selectively turned on to provide an alternative current path, preventing overcurrent from reaching the bypass portion while still enabling continuous operation when abnormality is detected
Solution Approach 2:
The semiconductor element is turned on simultaneously with or prior to the closing of the bypass portion. This preliminary action establishes a safe current path before the bypass portion closes, preventing overcurrent from damaging the bypass portion during the switching transition
2Object-affected harmful factors
If semiconductor elements are controlled to form a current path that does not include the bypass portion, then overcurrent protection is improved, but technologies to deal with double abnormalities in semiconductor elements are required
Solution Approach 1:
The control strategy changes based on the detected abnormality type. When abnormality is detected in both semiconductor elements and the bypass portion, the system switches to a control mode where the bypass portion remains closed and the semiconductor element is kept off, providing a different current path configuration to handle the double abnormality scenario
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 design results in a highly reliable, small-sized, and inexpensive power conversion device capable of continuous operation without increasing the size of cell converters, by effectively managing overcurrent and preventing bypass portion damage.
Implementation Method 1
the first and second conductor portions are each formed in a bent shape between the main circuit conductor and the bypass portion so as to, with respect to a first direction which is a direction of a path from the main circuit conductor to the bypass portion, have a portion that extends in a second direction intersecting with the first direction. A first portion, of the first conductor portion, that extends in the second direction and a second portion, of the second conductor portion, that extends in the second direction are disposed so as to at least partially overlap with each other in a third direction that intersects with the first and second directions. When current flows from the capacitor to the bypass portion, currents in a same direction flow in the first portion and the second portion.
Data Source
AI summary
In a power conversion device in which cell converters are connected in series, each cell converter includes: main circuit conductors connecting switching elements and a capacitor to each other; a bypass portion disposed between two external terminals connected to other cell converters; external output conductors connecting the external terminals and the main circuit conductors to each other; and bypass connection conductors connecting the external output conductors and the bypass portion to each other. The bypass connection conductors or the external output conductors are disposed so as to oppose each other at a high-potential side and a low-potential side thereof. The conductors are bent so as to have portions at which currents in parts of the conductors have the same direction. Thus, mutual inductances and self-inductances are increased, whereby short-circuit current flowing to the bypass portion at the time of double failures is suppressed.