Solid State Circuit Breaker Control Using Direction-Based Trip Thresholds
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In DC power systems, solid state circuit breakers face challenges in selectively disconnecting devices close to a failure position without damaging themselves or affecting other devices, due to difficulties in accurately determining the direction and magnitude of fault currents.
Innovation Solution
A method and apparatus for controlling solid state circuit breakers that involve detecting current direction and setting a waiting period before disconnecting, using different breaking current values for forward and backward currents, and predicting current values to determine if the circuit should be disconnected to prevent damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the solid state circuit breaker immediately disconnects the circuit upon detecting a fault current, then the response speed is improved, but the selectivity is worsened causing excessive devices to be disconnected
Solution Approach 1:
The system performs preliminary actions by detecting current direction and predicting future current values before making the disconnection decision. The controller detects whether the fault current is forward or backward, predicts the current value in the next sampling period, and only then decides to disconnect. This preliminary analysis ensures fast response while maintaining selectivity by avoiding premature disconnection decisions.
2Measurement precision
If the solid state circuit breaker uses a low breaking current threshold, then the protection sensitivity is improved, but the risk of self-damage is worsened due to backward currents from loads
Solution Approach 1:
The breaking current threshold is made dynamic rather than fixed. The controller adjusts the threshold based on the detected current direction: a first breaking current threshold is used for forward currents and a second (higher) threshold is used for backward currents. This dynamic adjustment allows the system to maintain high protection sensitivity for forward faults while preventing self-damage from backward currents generated by loads such as motors.
3Reliability
If the solid state circuit breaker waits for other circuit breakers to detect the failure, then the selectivity is improved, but the response time is worsened
Solution Approach 1:
The system performs preliminary detection of current direction and prediction of current values in advance, so when the fault current exceeds the threshold, the disconnection can be executed immediately without waiting for other circuit breakers. This preliminary action eliminates the time delay while maintaining selectivity through accurate direction-based discrimination.
4Measurement precision
If the solid state circuit breaker uses direction-based breaking current values, then the protection accuracy is improved, but the device complexity is worsened
Solution Approach 1:
The patent replaces complex mechanical direction-sensing mechanisms with electronic control based on current polarity detection. The controller simply detects whether the current flows in the forward or backward direction and applies the corresponding breaking current threshold from stored values. This substitution of electronic detection and digital comparison for mechanical direction sensing significantly reduces device complexity while maintaining high protection accuracy.
Data Source
AI summary
A method for controlling a solid state circuit breaker includes detecting a direction of a current flowing through the solid state circuit breaker, obtaining a breaking current value of the solid state circuit breaker according to the detected direction of the current, obtaining a value of a maximum threshold current to flow through the solid state circuit breaker, obtaining a predicted current value within a next sampling period of a present sampling period of the solid state circuit breaker, comparing the predicted current value with the breaking current value, and upon the predicted current value being greater than the breaking current value, delaying the solid state circuit breaker, and upon the predicted current value being greater than the maximum threshold current value, controlling the solid state circuit breaker to disconnect a circuit in which the solid state circuit breaker resides.