DC Switching Modules With RC Snubbers for Soft Current Interruption
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Solution Overview
Problem
Existing switching apparatuses for disconnecting DC voltage networks with source-side and load-side inductances experience prolonged oscillating currents after switching-off, leading to high power losses and the need for expensive voltage-limiting components.
Innovation Solution
A switching apparatus with at least two series-connected switching modules, each containing a controllable semiconductor switching element and a parallel RC circuit, operates using a duty factor based on the voltage difference between the actual and setpoint voltages to reduce energy stored in inductances, thereby preventing abrupt current reduction and oscillations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a switching apparatus disconnects a current path with source-side and load-side inductances, then the current path is opened, but high voltages build up and oscillating currents occur after switching-off
Solution Approach 1:
The switching apparatus is divided into multiple switching modules connected in series, each with its own controllable semiconductor switching element and parallel RC circuit. This segmentation allows distributed control of the switching process, enabling softer commutation and reducing voltage spikes and oscillations that would occur with a single abrupt switching action.
Solution Approach 2:
The semiconductor switching elements are operated with a duty factor, switching on and off periodically during the disconnection process. This periodic action allows the inductive energy to be gradually transferred to the capacitors in the parallel RC circuits rather than being abruptly interrupted, thereby preventing high voltage build-up and oscillating currents.
2Productivity
If the current flow is reduced abruptly during switching-off, then the disconnection is fast, but high power loss occurs in the semiconductor switching element
Solution Approach 1:
The semiconductor switching elements are operated with a duty factor, switching on and off periodically during the disconnection process. This periodic action allows the inductive energy to be gradually transferred to the capacitors in the parallel RC circuits rather than being abruptly interrupted, thereby preventing high voltage build-up and oscillating currents.
Solution Approach 2:
The parallel RC circuits act as intermediary energy storage elements between the inductive current path and the semiconductor switching elements. The capacitors absorb the inductive energy during the switching-off process, mediating the energy transfer and preventing direct dissipation in the semiconductor elements, thus reducing power loss.
3Reliability
If voltage-limiting components are used to protect against high voltages, then component damage is prevented, but the apparatus becomes more expensive and occupies more space
Solution Approach 1:
The parallel RC circuits serve multiple functions: they store inductive energy during switching, limit voltage rise rates, dampen oscillations, and eliminate the need for separate voltage-limiting components like varistors. This multi-functionality reduces overall device complexity and cost while maintaining protection against high voltages.
Solution Approach 2:
The parallel RC circuits act as intermediary energy storage elements between the inductive current path and the semiconductor switching elements. The capacitors absorb the inductive energy during the switching-off process, mediating the energy transfer and preventing direct dissipation in the semiconductor elements, thus reducing power loss.
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 approach enables a 'soft' switching-off process that minimizes power loss in semiconductor elements, eliminates the need for expensive voltage-limiting components, and significantly reduces oscillations, ensuring safe and efficient disconnection of DC zones in medium-voltage networks.
Implementation Method 1
the high power loss in the event of switching-off is therefore not converted in the semiconductor switching element of the respective switching modules, but rather predominantly in the resistor of the respective switching modules
Implementation Method 2
Each of the switching modules comprises at least one controllable semiconductor switching element with which a series circuit comprising a resistor and a capacitor is connected in parallel
Data Source
AI summary
A switching device for opening a current path of a direct-voltage network, which current path has source-side and load-side inductors, the switching device includes at least two switching modules, which are connected in series, each of the switching modules having at least one controllable semiconductor switching element, in parallel with which a series circuit of a resistor and a capacitor is connected. During operation of the switching device in order to open the current path, the controllable semiconductor switching element of at least one of the switching modules is switched into a conductive state with a duty cycle until the energy stored in the inductors has been dissipated, the duty cycle being dependent on the difference between the actual voltage and a target voltage across the semiconductor switching element, the target voltage being calculated at least from the system voltage of the direct-voltage network and the number of switching modules.