Hybrid DC Switching Device for Fault Isolation
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Solution Overview
Problem
Current DC voltage network switching technologies face challenges in safely and rapidly controlling faults, particularly in high-voltage, long-distance HVDC networks, due to the limitations of mechanical switches and existing electronic solutions which incur high energy losses and complex semiconductor management.
Innovation Solution
A device comprising two hybrid switches connected in series with parallel uncontrolled and controllable switches, along with polarized attenuators and a current pulse generator, allows for efficient DC switching with reduced semiconductor cooling needs, self-sufficient energy supply, and optimized overvoltage management, enabling fast and reliable fault control without disrupting the power flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If mechanical switches are used for high-voltage DC networks, then the switching device can handle high fault currents, but the switch-off time is too long and switching overvoltages are disruptive
Solution Approach 1:
The patent replaces mechanical switches with a hybrid switching system combining semiconductor switches (IGBTs, diodes) and mechanical circuit breakers. The semiconductor switches perform rapid current commutation and fault isolation within milliseconds, while the mechanical breaker provides final isolation. This substitution eliminates the slow switch-off times of purely mechanical systems while maintaining high fault current handling capability through the coordinated action of both switch types.
Solution Approach 2:
The switching function is segmented into multiple stages: first, semiconductor switches (T1-T4) rapidly commutate the fault current; second, the mechanical circuit breaker isolates the faulty section. This segmentation allows each component to optimize its specific function - semiconductors for speed and control, mechanics for final isolation - resolving the contradiction between fast switching and high current handling.
2Loss of time
If semiconductor switches are used for fast switching, then the switch-off time is reduced, but energy losses increase and cooling requirements become complex
Solution Approach 1:
The patent employs periodic switching of semiconductor devices in bridge configurations (e.g., T1-T2, T3-T4 pairs) to control current flow. The semiconductors switch periodically at controlled frequencies, allowing them to operate in optimized conduction modes that reduce continuous conduction losses. The periodic action enables efficient current commutation while minimizing energy dissipation during switching transitions.
Solution Approach 2:
The patent introduces DC-side inductors and capacitors as intermediary energy storage elements that buffer power flow through the semiconductor switches. These intermediaries absorb and release energy during switching transitions, reducing the instantaneous power stress on semiconductors and thereby reducing their energy losses and cooling requirements.
3Power
If conventional thyristor converters are used for high power transmission, then the power transmission capability is achieved, but reactive power compensation and voltage stabilization are insufficient
Solution Approach 1:
The patent transitions from static thyristor converters to dynamic voltage-source converter (VSC) technology using IGBTs. The VSC system provides fully controllable, dynamic reactive power compensation through independent control of active and reactive power flows. The converter can rapidly adjust its output characteristics to stabilize voltage and provide reactive power support, making the system adaptable to varying grid conditions while maintaining high power transmission capability.
4Stability of the object's composition
If capacitor banks are used on the DC side, then voltage stabilization is improved, but the complexity of fault control increases
Solution Approach 1:
The patent extracts the voltage stabilization function from separate DC-side capacitor banks and integrates it into the control system of the VSC itself. The VSC's inherent ability to control output voltage and reactive power replaces the need for external capacitor banks, simplifying the overall system architecture and reducing fault control complexity while maintaining voltage stabilization capability.
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 solution achieves short switch-off times, reduces energy losses, and allows for economical insulation design, enabling reliable operation with shared components and improved switching speed, thus addressing the limitations of existing technologies in controlling faults in HVDC networks.
Implementation Method 1
a current pulse generator which—in response to a control command—is set up to generate a unipolar current pulse leading via the third connection and the polarized attenuators, so that the direction of the current in one of the hybrid switches can be reversed for a short time
Implementation Method 2
with two polarized attenuators, which are designed to absorb energy in only one polarity of the applied terminal voltage
Data Source
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AI summary
The invention relates to switching and switchover devices for DC networks which make it possible to realize - particularly in the event of faults - rapid and reliable switching processes in combination with good overvoltage damping and low energy losses during normal operation.