Annular Capacitor Segmentation for Low Inductance Power Conversion
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Solution Overview
Problem
In power conversion systems, the DC link capacitor experiences uneven current distribution and high temperature rises due to proximity to switching semiconductor devices, leading to reliability issues and limited current carrying capacity.
Innovation Solution
An annular form factor capacitor with power semiconductor switches arranged to evenly distribute current around its perimeter or within its center, reducing current density and temperature rises, and minimizing inductance connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the DC link capacitor is placed close to the switching semiconductor devices, then the impedance of the DC source is reduced and voltage rise during switch turn-off is minimized, but the capacitor experiences uneven current distribution and high temperature rises
Solution Approach 1:
The patent segments the capacitor into multiple distributed elements arranged in a specific geometric pattern around the semiconductor devices. This segmentation allows the current to be distributed across multiple capacitor elements rather than concentrated in a single location, reducing the temperature rise in any one capacitor while maintaining low overall impedance to the switching devices.
Solution Approach 2:
The patent transitions from a conventional single-point capacitor connection to a distributed multi-point arrangement in a two-dimensional plane. By arranging capacitor elements at multiple locations around the semiconductor devices and connecting them through a planar conductor structure, the system achieves both low inductance (by maintaining proximity) and uniform current distribution (by spreading connections across multiple points).
2Device complexity
If the capacitor is placed close to the switching semiconductor devices, then the inductance connection is reduced, but the current distribution becomes uneven and reliability decreases
Solution Approach 1:
The capacitor system is segmented into multiple elements distributed around the semiconductor devices, each carrying a portion of the total current. This segmentation ensures that no single capacitor element is overloaded, improving reliability while maintaining simple low-inductance connections to the switching devices.
Solution Approach 2:
Multiple capacitor elements are merged into a unified distributed capacitor system that functions as a single low-inductance connection to the semiconductor devices. The planar conductor structure merges the multiple capacitor connections into one integrated assembly, achieving both simplicity and reliability.
3Productivity
If multiple capacitor windings are interconnected to meet voltage and current requirements, then the DC link capacitor can handle higher currents, but it becomes difficult to ensure equal current distribution and temperature control becomes problematic
Solution Approach 1:
The high-current capacitor system is segmented into multiple parallel winding elements distributed around the semiconductor devices. Each winding element carries a portion of the total current, and the distributed arrangement ensures uniform current distribution across all elements, preventing any single element from overheating while maintaining high overall current capacity.
Solution Approach 2:
Each capacitor winding element is positioned at a specific location around the semiconductor devices to optimize local current distribution. This local quality approach ensures that each element operates under similar electrical and thermal conditions, achieving uniform temperature across all elements while collectively handling high currents.
Data Source
Figure 1~1B
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AI summary
The formation of an assembled unit consisting of an annular capacitor [a wound, metallized dielectric capacitor in the shape of a closed path ring] with other power conversion components arranged and attached in manners uniquely allowed by the ring design will allow higher density converter designs [power/unit volume]. The resulting short connection paths between the capacitor element and the switching semiconductors also provide a very low inductance path that minimizes voltage spikes on the switching semiconductors as a result of turn-off di/dt. The capacitor serves as a short time current source and sink for the switching semiconductors. With the described configuration the RMS current seen by the capacitor can be made more volumetrically uniform enabling more uniform capacitor rise. The single capacitor configured as described also mitigates bus resonance problems often observed in prior art when multiple discrete capacitors are connected in parallel.