HVDC Semiconductor Switching Assembly Reverse Recovery Management
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Solution Overview
Problem
Semiconductor switching elements in HVDC power converters experience reverse recovery currents during turn-off, leading to non-ideal turn-off characteristics and potential adverse effects on DC and AC currents, which existing technologies fail to adequately manage.
Innovation Solution
A semiconductor switching assembly with an active auxiliary circuit, including an auxiliary semiconductor switching element and a current capture element, is used to divert and manage reverse recovery currents, with a control unit coordinating the switching to store or dissipate these currents, thereby maintaining an almost ideal turn-off characteristic and reducing the risk of adverse impacts on the power converter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the main semiconductor switching element is turned off, then the normal current conduction is interrupted, but the reverse recovery current continues to flow and adversely influences the DC and AC currents in the HVDC power converter
Solution Approach 1:
The harmful reverse recovery current is extracted from the main current path by diverting it through the auxiliary semiconductor switching element into the current capture element. This separates the harmful current component from the main DC and AC currents in the HVDC power converter, preventing adverse influences while maintaining reliable turn-off characteristics.
Solution Approach 2:
The auxiliary semiconductor switching element and current capture element serve as intermediary components that mediate the reverse recovery current. Instead of allowing the reverse recovery current to directly affect the main power converter circuits, it is channeled through this intermediary path, isolating the harmful effects from the main system.
2Ease of operation
If the reverse recovery current is allowed to flow freely, then the main semiconductor switching element maintains simple operation, but the reverse recovery current escapes and adversely influences the HVDC power converter currents
Solution Approach 1:
The auxiliary circuit acts as an intermediary that automatically captures the reverse recovery current without requiring complex control of the main switching element. The main semiconductor switching element continues its normal operation while the auxiliary element handles the reverse recovery current management, maintaining ease of operation while preventing current escape.
Solution Approach 2:
The auxiliary semiconductor switching element and current capture element form a self-service mechanism that automatically diverts and manages the reverse recovery current. The control unit detects when the main element turns off and automatically activates the auxiliary path, eliminating the need for complex external intervention while preventing harmful current escape.
3Reliability
If an auxiliary circuit is added to manage reverse recovery current, then the reverse recovery current is effectively diverted, but the device complexity increases
Solution Approach 1:
The current management function is segmented into separate components: the main semiconductor switching element for normal operation and the auxiliary semiconductor switching element with current capture element for reverse recovery current management. This segmentation allows each component to be optimized for its specific function, improving overall reliability while keeping the auxiliary circuit structure manageable through clear functional separation.
Data Source
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Figure 2(a)~2(e)
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AI summary
In the field of HVDC power converters there is a need for an improved semiconductor switching assembly which obviates the difficulties associated with main semiconductor switching elements having inherent limitations in their performance. A semiconductor switching assembly (10; 110) comprises a main semiconductor switching element (12, 112) that includes first and second connection terminals (14, 16) between which an active auxiliary circuit (20) is electrically connected. The auxiliary circuit (20) includes an auxiliary semiconductor switching element (22; 32; 38; 40; 42) and current capture element (24) that are connected in series with one another. The auxiliary semiconductor switching element (22; 32; 38; 40; 42) has a control unit (26; 126) operatively connected therewith. The control unit (26, 126) is configured to switch on the auxiliary semiconductor switching element (22; 32; 38; 40; 42) to divert into the current capture element (24) a reverse recovery current (IRR1, IRRn) that flows through the main semiconductor switching element (12; 112) while it turns off.