DC Breaker Bridge Circuit for High-Speed Fault Cutoff
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Solution Overview
Problem
Current direct-current circuit breakers require significant time to cut off fault points due to the need for current oscillation and require separate charging circuits for forced commutation, leading to increased size and cost.
Innovation Solution
A direct-current circuit breaker configuration using a bridge circuit with anti-parallel series circuits, where oscillating currents generated by capacitors and reactors create current-zero points for rapid fault cutoff, eliminating the need for separate charging circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the self-commutation method is used to form a current-zero point, then the circuit breaker can block DC current, but a considerable amount of time is required to completely cut off a fault point from the occurrence of a fault
Solution Approach 1:
The capacitor in the commutation circuit is charged in advance before fault occurrence. When a fault occurs, the pre-charged capacitor can immediately discharge to generate oscillating current, forming a current-zero point rapidly without waiting for charging cycles. This preliminary charging action resolves the time delay issue of the self-commutation method.
Solution Approach 2:
The invention uses forced commutation with a resonant circuit that generates periodic oscillating current. By controlling the timing of capacitor discharge and utilizing the natural oscillation period of the LC circuit, the system can reliably create current-zero points at predictable intervals, enabling fast and controlled fault cutoff.
2Speed
If the forced commutation method is used to form a current-zero point, then the DC current can be blocked at high speed, but a separate charging circuit that includes an AC power supply and a rectifier is required, increasing the size and cost
Solution Approach 1:
The invention merges the charging function into the main circuit topology by using the DC line itself to charge the capacitor through the reactor during normal operation. The commutation circuit shares components with the main power path, eliminating the need for separate AC power supply and rectifier circuits. This integration reduces device complexity while maintaining fast fault cutoff capability.
Solution Approach 2:
The reactor and capacitor serve multiple functions: the reactor limits fault current and enables oscillation, while the capacitor provides both the charging function (replacing separate charging circuits) and the commutation function for generating current-zero points. This multi-functionality reduces the overall component count and system complexity.
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
Enables faster fault cutoff and reduces the size and cost of the circuit breaker by generating current-zero points without additional charging circuits, achieving high-speed fault isolation.
Implementation Method 1
a resonant circuit constituted by a capacitor and a reactor is connected to a blocking unit in parallel, and the current oscillation is increased by the interaction between the resonant circuit and negative arc characteristics
Implementation Method 2
a resonant current from a commutation circuit constituted by a capacitor and a reactor is superimposed on the DC current, and at the current-zero point, the DC current is blocked
Data Source
Figure 1
Figure 2(a)~2(c)
Figure 3(a)~3(c)
AI summary
To obtain a direct-current circuit breaker that is capable of cutting off a fault point at a higher speed and that can achieve downsizing and cost reduction. The direct-current circuit breaker includes a bridge circuit 6 that is configured by connecting two series circuits 6a and 6b in anti-parallel with each other, each of the series circuits being configured from a reactor 2 and a commutation unit 3 that includes a capacitor 5, a first blocking unit 1 that is connected between connection points, each of which is between the reactor 2 and the commutation unit 3 in each of the series circuits 6a and 6b, that is in a closed state at a normal time when a steady-state current flows through a DC line, that is controlled so as to be opened after occurrence of a fault in the DC line, and that is disconnected at a current-zero point at which a current flowing through the reactors 2 and a current flowing through the commutation units 3 cancel each other out, and a second blocking unit 4 that is connected to the bridge circuit 6 in series, that is in a closed state at a normal time, that is controlled so as to be opened after the first blocking unit 1 is disconnected, and that is disconnected at a current-zero point at which currents flowing respectively through the series circuits 6a and 6b cancel each other out.