Converter Output Protection Circuit for Fast DC Fault Interruption
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Solution Overview
Problem
Existing converters used to supply DC grids face challenges in protecting the network from fault currents due to the discharge of output filter capacitors, leading to high and fast-rising current peaks, which conventional circuit breakers struggle to interrupt quickly and efficiently, resulting in additional losses and cooling issues.
Innovation Solution
A multifunction output protection circuit with an interruptible freewheeling path and a voltage clamping device is integrated into the converter, allowing for both current limitation and fast interruption of fault currents, using a freewheeling switch and diode in combination with a voltage clamping device to manage current flow and energy dissipation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a series semiconductor switch with parallel varistor is used for output protection, then fast current interruption is achieved, but excessive losses occur in the MOV when operated in chopping mode
Solution Approach 1:
The output protection function is divided into two distinct circuits: a first output protection circuit with a series semiconductor switch and parallel varistor for fast current interruption, and a second output protection circuit with a series semiconductor switch and parallel capacitor for current limitation. This segmentation allows each circuit to specialize in one function, reducing the losses associated with using a single circuit for both purposes.
Solution Approach 2:
The invention dynamically switches between different protection modes by controlling the semiconductor switches. The first switch operates for fast interruption when fault current peaks occur, while the second switch operates for sustained current limitation. This dynamic operation optimizes energy loss by using the appropriate protection mechanism at the appropriate time.
2Duration of action of moving object
If a series semiconductor switch with freewheeling diode is used, then current limitation is possible for extended time duration, but fast interruption of fault current is not possible due to long lasting tail current
Solution Approach 1:
The protection function is segmented into two circuits: the first circuit with freewheeling diode handles extended current limitation, while the second circuit with parallel capacitor provides fast interruption capability. This segmentation resolves the contradiction by assigning different time-scale functions to different circuits.
Solution Approach 2:
The invention merges two different protection topologies into a unified system. The first output protection circuit (with freewheeling diode) and the second output protection circuit (with parallel capacitor) are combined at the converter output, allowing the system to benefit from both extended current limitation and fast interruption capabilities simultaneously.
3Speed
If SSCBs are used at various places in the DC grid, then fault currents are interrupted quickly, but additional losses, cost, and cooling issues occur due to space limitations
Solution Approach 1:
The converter's output protection circuit performs multiple functions: it limits fault current, interrupts fault current, and protects downstream equipment. By making the converter itself multi-functional for protection, the need for multiple separate SSCBs throughout the DC grid is reduced, simplifying the overall system.
Solution Approach 2:
The output protection circuit performs preliminary current limitation before fault currents can propagate through the DC grid. By limiting current at the source (converter output), the system prevents the need for multiple downstream breakers, as the fault current is already controlled before it reaches other parts of the network.
4Ease of manufacture
If mechanical circuit breakers are used, then cost is reduced, but opening time increases to several to tens of milliseconds which is not fast enough to prevent short circuit peak currents
Solution Approach 1:
The invention merges mechanical circuit breakers with semiconductor-based output protection circuits. The semiconductor circuit provides fast current limitation and interruption for peak currents, while the mechanical breaker provides inexpensive sustained protection for tail currents. This combination allows the use of cheaper mechanical breakers without sacrificing fast protection capability.
Solution Approach 2:
The system dynamically transitions from semiconductor-based fast protection to mechanical breaker protection. The semiconductor switches operate during the critical fast transient period to limit peak currents, then the mechanical breaker takes over for the sustained tail current period. This dynamic handoff allows each component to operate in its optimal performance range.
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
The solution enables rapid current interruption and safe energy dissipation, reducing losses and enabling the use of cheaper mechanical breakers by quickly limiting fault currents, allowing for efficient protection coordination with mechanical contactors or relays.
Implementation Method 1
a voltage clamping device parallel to at least the interruptible freewheeling switch
Implementation Method 2
The freewheeling circuit comprises an interruptible freewheeling path including a freewheeling switch and a freewheeling diode
Data Source
Figure 1~2
Figure 3a~3c
Figure 4
AI summary
The invention relates to a converter (100) comprising a conversion stage (104) and an output protection circuit (106). The output protection circuit (106) comprises a first input terminal (201) and a second input terminal (202), and a first output terminal (203) and a second output terminal (204). The first input terminal and the first output terminal are on a first voltage level and the second input terminal and the second output terminal are on a second voltage level. The converter further comprises a switch S1 connected between the first input and output terminals or between the second input and output terminal, and an interruptible freewheeling circuit (120) between the first output terminal and the second output terminal. The freewheeling circuit comprises a freewheeling path (122) including a freewheeling switch and a freewheeling diode, and a voltage clamping device parallel to at least the freewheeling switch.