SiC Converter Circuit Short-Circuit Protection
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Solution Overview
Problem
The use of normally-on type SiC JFETs in converter circuits poses challenges due to their inherent characteristics, including the need for negative voltage to turn off and the risk of short-circuit faults when auxiliary power is lost, requiring additional protection and startup circuits, which increase complexity and component count.
Innovation Solution
A converter circuit design that employs a parallel connection of controllable switches and resistive components at the input/output and a series connection with the DC link capacitor, along with a normally-off-type gate driver, to prevent short-circuit paths and maintain safe operation by ensuring switches remain off after auxiliary power loss, thereby reducing the number of components and minimizing losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If normally-on type SiC JFETs are used in converter circuits, then high voltage, high frequency and high temperature operation capability is improved, but additional protection circuits and startup circuits are required to prevent short-circuit faults
Solution Approach 1:
The patent combines the protection function and startup function into the normally-on switch itself by utilizing its inherent characteristics. The normally-on switch automatically provides protection during faults and startup operations without requiring separate dedicated circuits, thereby merging multiple functions into a single component and reducing overall circuit complexity.
Solution Approach 2:
The normally-on switch serves itself by providing both power conversion and protection functions. During fault conditions or startup, the switch automatically enters a protective state without requiring external control, enabling the device to protect itself and eliminating the need for separate protection circuits.
2Reliability
If additional protection circuits are added to prevent short-circuit faults, then reliability is improved, but the total number of components increases
Solution Approach 1:
The normally-on switch is designed to perform multiple functions: power conversion during normal operation, automatic protection during faults, and startup control. This multi-functionality eliminates the need for separate protection components, reducing the total component count while maintaining high reliability.
Solution Approach 2:
The protection mechanism is built into the normally-on switch itself, which automatically provides fault protection without requiring external protection circuits. This self-service approach maintains reliability while minimizing the number of additional components needed.
3Reliability
If auxiliary power supply is lost in normally-on type switches, then the switch turns on automatically, but short-circuit paths are created
Solution Approach 1:
The patent converts the potentially harmful automatic turn-on during auxiliary power loss into a beneficial protection mechanism. By designing the circuit to utilize the normally-on characteristic, the automatic turn-on actually provides fault protection by blocking short-circuit paths, transforming what could be a harmful effect into a protective feature.
Solution Approach 2:
Instead of trying to prevent the automatic turn-on during auxiliary power loss, the patent inverts the approach by designing the circuit to expect and utilize this behavior. The circuit is configured so that the automatic turn-on actually protects against short-circuits rather than causing them, reversing the conventional protection approach.
Data Source
Figure 1~2
Figure 3~4
Figure 5(a)~5(b)
AI summary
A converter circuit with short-circuit protection comprising a plurality of phase legs having a series connection of normally-on switches (JH1, JL1, JH2, JL2, JH3, JL3), the phase legs being connected between positive and negative voltage rails of a DC voltage link, a DC link capacitor (CL), AC voltage connection points formed of the connection points between the normally-on switches. Converter circuit further comprises phase-to-phase short-circuit protection circuits comprising each a parallel connection of a resistive component (RG1, RG2) and a controllable switch (SG1, SG2), the phase-to-phase short-circuit protection circuits comprising each first and second terminals and the first terminal being connected to an AC voltage connection point and the second terminal forming an input or an output of the converter circuit, and a phase leg short-circuit protection circuit comprising a controllable switch (SL) connected in series with the DC link capacitor, the series connection of the controllable switch and the DC link capacitor being connected between the positive and negative voltage rails of the DC voltage link, wherein in case of lack of control of the normally-on switches the controllable switch of the at least one phase-to-phase short-circuit protection circuit and the controllable switch of the phase leg short-circuit protection circuit are adapted to be controlled to a non-conductive state.