Low-Inductance DC Switch Circuit for Fast Fault Current Turn-Off
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Solution Overview
Problem
Existing electronic switches in DC networks face challenges in quickly and reliably switching off high short-circuit currents due to the lack of effective overvoltage protection, which can lead to damage or reduced lifespan of semiconductor switches.
Innovation Solution
An electronic switch design featuring a switch-off semiconductor switch in parallel with a series circuit comprising a capacitor and bifilar resistance, which effectively absorbs energy from inductance during switching off, reducing overvoltages and enabling quick disconnection of short-circuit currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a turn-off semiconductor switch is used in a DC network, then fast switching speed (100ns) is achieved, but the switch is vulnerable to voltage spikes and overvoltages during turn-off that can damage the semiconductor switch
Solution Approach 1:
A parallel circuit comprising a capacitor and a bifilar resistor is connected across the turn-off semiconductor switch to provide overvoltage protection before damage can occur. The capacitor absorbs voltage spikes and the bifilar resistor dissipates energy, cushioning the semiconductor switch from damaging voltage transients during fast switching operations.
Solution Approach 2:
The parallel circuit with capacitor and bifilar resistor acts as an intermediary protective layer between the turn-off semiconductor switch and the damaging voltage spikes. This intermediary circuit absorbs and dissipates the harmful voltage transients, protecting the semiconductor switch while allowing fast switching to continue.
2Loss of energy
If DC networks use short cable lengths to reduce losses, then energy efficiency is improved, but series inductances become very small causing fault currents to exhibit very steep current increases
Solution Approach 1:
The bifilar resistor configuration converts the harmful effect of low inductance (which causes steep fault current rises) into a beneficial protective mechanism. By arranging two resistors in parallel with opposite current directions, the magnetic fields cancel each other, creating effectively zero inductance while the resistors dissipate fault energy, turning the low-inductance problem into a protective feature.
3Adaptability or versatility
If DC grids lack reactance to limit maximum current, then direct energy exchange between converters is enabled, but fault currents cannot be limited requiring very fast fault detection and shutdown
Solution Approach 1:
The absence of reactance in DC networks, which initially causes uncontrolled fault currents, is compensated by the bifilar resistor configuration. The resistors provide passive current limitation through energy dissipation while maintaining the DC network's reactance-free characteristics for normal operation, converting the harmful lack of current limitation into a controlled protective mechanism.
Solution Approach 2:
The electrical parameters of the protective circuit are specifically designed to change behavior based on operating conditions. During normal operation, the parallel circuit has minimal impact on the DC network's energy exchange capability. During fault conditions, the resistors activate to limit current through their resistive properties, changing the circuit's effective impedance from near-zero to a current-limiting value.
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 proposed electronic switch design provides reliable protection against overvoltages, allowing for fast and efficient switching off of high short-circuit currents, thereby extending the lifespan of semiconductor switches and ensuring safe operation in DC networks.
Implementation Method 1
a series circuit arranged parallel to the semiconductor switch and comprising a capacitor (3) for absorbing energy during the turn-off process
Implementation Method 2
The first and second resistors (4a, 4b) are constructed together as a bifilar resistor
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
The invention relates to a switch, in particular for use as a DC switch, composed of a semiconductor switch that can be switched off and a series circuit, the series circuit being arranged in parallel with the semiconductor switch that can be switched off and comprising a first resistor, a capacitor and a second resistor, the first and second resistors being jointly constructed as a bifilar resistor in order to form a particularly low-inductance commutation loop.