Bridging Unit With Bistable Relay For Converter Cells
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Solution Overview
Problem
Existing bridging units for converter cells are non-resettable, time-consuming, and costly to replace, and thyristors return to an open state without external power, leading to inefficiencies in handling overcurrent and overvoltage situations.
Innovation Solution
A bridging unit incorporating a bistable mechanical relay and a power-electronic switch, driven by an energy store and passive overvoltage detection, which remains stable without external power and allows for resettable operation, enabling efficient handling of overcurrent and overvoltage conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If non-resettable bridging units (pyrotechnic make contact or broken-down components) are used, then the converter cell can be permanently bridged in case of internal fault, but the removal and replacement process is highly time-consuming and costly
Solution Approach 1:
The patent applies the dynamics principle by implementing a resettable bridging unit that can transition between open and closed states. The bistable mechanical relay and power-electronic switch enable the bridging unit to be opened after a fault condition is resolved, allowing the converter cell to be restored without physical replacement. This dynamic state change capability directly addresses the time-consuming replacement issue while maintaining reliable fault protection.
2Productivity
If thyristors are used for bridging, then surge currents can be bypassed in external faults, but the bridging unit returns to open state without external power, causing complete power failure to switch bridging units back to switched-off state
Solution Approach 1:
The patent applies the self-service principle through passive overvoltage detection that automatically charges the energy store when overvoltage is exceeded. This self-charging mechanism eliminates the need for external power to operate the bridging unit. The system serves itself by using the overvoltage condition to charge the energy store, which then powers the bistable mechanical relay and power-electronic switch to close the bridging path, enabling autonomous operation during fault conditions.
Solution Approach 2:
The patent applies the composite materials principle by combining a mechanical relay with a power-electronic switch to create a hybrid bridging unit. This composite structure integrates the advantages of both mechanical reliability and electronic speed. The mechanical relay provides robust, power-independent switching capability, while the power-electronic switch enables fast response to surge currents. Together, they create a bridging unit that handles surge currents effectively while remaining operable without external power.
3Reliability
If a bistable mechanical relay and power-electronic switch are used together, then the bridging unit remains stable without external power and allows resettable operation, but the device complexity increases
Solution Approach 1:
The patent applies the merging principle by integrating a bistable mechanical relay and a power-electronic switch into a single coordinated bridging unit. Both components work together to achieve the same function of bridging the converter cell, providing redundancy and complementary advantages. The mechanical relay ensures stable, power-independent operation, while the power-electronic switch provides fast response capability. This merging of components achieves reliable stable operation without external power while managing complexity through functional integration.
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 provides a maintenance-friendly and reliable bridging unit that remains stable without external power, allowing for efficient handling of overcurrent and overvoltage conditions, reducing replacement costs and time, and offering redundant paths for fault situations.
Implementation Method 1
The bistable mechanical relay is configured to electrically connect the first input to the second input
Implementation Method 2
The power-electronic switch is configured to electrically connect the first input to the second input
Implementation Method 3
an energy store for supplying power to the mechanical relay, the power switch and the drive
Implementation Method 4
The drive includes passive overvoltage detection configured to charge the energy store if the overvoltage is exceeded
Implementation Method 5
the drive is configured to supply current from the energy store to at least one of the bistable relay and the power-electronic switch
Data Source
AI summary
A converter cell of a modular converter is provided. The converter cell includes a bridging unit which has a mechanical bistable relay, an electronic switch, a drive for switching the relay and the electronic switch, and an energy store for supplying power to the mechanical relay, the electronic switch and the drive. The drive includes passive overvoltage detection configured to charge the energy store if the overvoltage is exceeded. The drive includes an additional switch which is closed when a voltage on the energy store exceeds a predefined value, and the drive supplies current from the energy store to at least one of the relay and the electronic switch. The drive has hysteresis, such that, if the voltage on the energy store is undershot, at least one of the relay and the electronic switch is still supplied with current from the energy store.