Solid-State Circuit Breaker Current Limiting With TVS and GaN HEMTs
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Solution Overview
Problem
In direct current (dc) electrical systems, the lack of zero current crossings and fast rising fault currents due to large dc-link capacitance and low fault impedance pose challenges for protection, particularly in solid-state circuit breakers (SSCBs).
Innovation Solution
The proposed solution involves using energy absorption components, such as TVS diodes, in conjunction with GaN HEMT switches to enhance current limiting capability in series-connected SSCB switching cells. This approach utilizes the high pulse power capability of TVS diodes to absorb a major part of the energy, allowing the GaN HEMTs to control the limited current level by operating in saturation mode and alternating between switches to distribute energy absorption effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If conventional current limiting methods are used in SSCBs, then the device complexity is reduced, but the current limiting withstand time is insufficient
Solution Approach 1:
The patent divides the current limiting function into two segments: (1) TVS diodes handle the initial high-power pulse energy absorption during fault onset, and (2) GaN HEMTs maintain saturation mode operation for sustained current limiting. This segmentation allows each component to operate in its optimal performance range, achieving extended withstand time without proportionally increasing overall device complexity
Solution Approach 2:
TVS diodes are pre-configured in parallel with the GaN HEMTs to automatically activate during fault conditions. The TVS diodes perform preliminary energy absorption during the initial fault surge, preparing the system for sustained current limiting by the GaN HEMTs, thereby extending the overall withstand time before trip operation is required
2Reliability
If high-frequency switching is used to achieve current limiting, then the current limiting capability is improved, but EMI issues increase
Solution Approach 1:
The patent employs periodic alternating operation of multiple GaN HEMTs in saturation mode, switching between devices in a controlled sequence. This periodic action distributes the energy absorption burden across multiple devices over time, maintaining effective current limiting capability while operating at lower switching frequencies that generate less EMI compared to continuous high-frequency switching of a single device
Solution Approach 2:
TVS diodes serve as intermediary components between the fault current source and the GaN HEMTs. They absorb the initial high-power pulse energy, acting as a buffer that reduces the immediate stress on the GaN HEMTs. This intermediary action allows the GaN HEMTs to operate in saturation mode with reduced switching frequency, thereby maintaining current limiting capability while minimizing EMI generation
3Duration of action of moving object
If energy absorption components are added to enhance current limiting, then the current limiting withstand time is improved, but the device complexity and hardware requirements increase
Solution Approach 1:
The patent integrates TVS diodes that serve multiple functions: (1) absorbing initial fault pulse energy, (2) protecting GaN HEMTs from voltage spikes, and (3) enabling extended current limiting withstand time. By making the TVS diodes multi-functional, the patent achieves enhanced performance without adding dedicated separate components for each function, thereby limiting the increase in device complexity
Solution Approach 2:
The patent merges the TVS diodes in parallel with the GaN HEMT switching cells, creating a unified current limiting structure. This merging allows the energy absorption components to work synergistically with the semiconductor switches, achieving extended withstand time while sharing common mounting and control infrastructure, thus reducing the overall complexity increase compared to separate independent systems
4Measurement precision
If GaN HEMTs operate in saturation mode for current limiting, then the current control precision is improved, but the energy dissipation and heat generation increase
Solution Approach 1:
The patent applies partial action by having multiple GaN HEMTs share the current limiting duty through periodic alternating operation. Each device operates in saturation mode for a portion of the total fault duration, maintaining precise current control during its active period while distributing the cumulative energy dissipation across multiple devices and time intervals, thereby reducing peak thermal stress on individual components
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 strategy significantly improves the current limiting withstand time by a factor of 3-4 compared to conventional methods, achieves compact implementation without additional hardware, and mitigates high-frequency switching-related EMI issues.
Implementation Method 1
The proposed solution involves using energy absorption components, such as TVS diodes, in conjunction with GaN HEMT switches to enhance current limiting capability
Implementation Method 2
allowing the GaN HEMTs to control the limited current level by operating in saturation mode and alternating between switches to distribute energy absorption effectively
Data Source
AI summary
Solid-state circuit breakers (SSB) have a fault current limiting function that limit the fault current in power applications. It allows sustained overcurrent for a certain period while preventing the fast fault current increase in dc systems. For the conventional method of using switches alone to limit the current, the high loss results in a short withstand time and low current limiting capability of the SSCBs. Disclosed are various embodiments for a control strategy to use one or more energy absorption components to handle the major part of the energy during a current limiting stage to increase the current limiting capability for series-connected SSCB switching cells.