Switching Device for Precharging DC Networks
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Solution Overview
Problem
In large DC voltage networks, pre-charging resistors often overheat due to excessive capacitance, leading to limitations in system configuration and increased costs with conventional solutions, which restrict flexibility and performance.
Innovation Solution
Divide the DC voltage network into sub-networks using switches to limit the current through the resistor during pre-charging, allowing each sub-network to be pre-charged sequentially, giving the resistor time to cool down, and using a switching device to manage the pre-charging process, including a main switch that operates in a clocked manner to prevent overheating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the total capacitance of all connected loads is increased to expand system capacity, then the power supply can serve more loads, but the pre-charge resistor overheats during pre-charging
Solution Approach 1:
The patent divides the DC network into multiple partial networks, each with its own pre-charge switch (S1, S2, S3, etc.). This segmentation allows the pre-charge resistor to serve multiple smaller groups of capacitors sequentially rather than all capacitors simultaneously, preventing overheating while supporting large total capacitance
Solution Approach 2:
The patent implements periodic pre-charging cycles where switches are closed successively rather than simultaneously. Each switch remains closed only for the duration needed to pre-charge its associated capacitors, then opens to allow the resistor to cool down before the next cycle, creating a rhythmic pre-charge pattern that prevents thermal overload
2Temperature
If conventional project planning is used to limit maximum capacity, then resistor overheating is avoided, but system configuration flexibility is severely restricted
Solution Approach 1:
The patent replaces static capacity planning with dynamic control through programmable switches. The system can adapt its pre-charge configuration in real-time based on which loads are actually connected, allowing flexible system expansion without re-planning. The controller can dynamically adjust which switches close and when, providing versatility while maintaining temperature control
3Temperature
If thyristors are used for pre-charging instead of contactor and resistor, then resistor overheating is avoided, but the power supply performance is limited and costs increase
Solution Approach 1:
The patent uses simple, inexpensive mechanical or electronic switches instead of expensive thyristors. These switches are designed for brief, intermittent use during pre-charging only, then remain open during normal operation. This approach achieves temperature control without the high cost and performance limitations of thyristor-based solutions
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 prevents resistor overheating, allows for easier planning of DC voltage networks without additional pre-charging units, and maintains system flexibility while reducing energy losses and costs.
Implementation Method 1
During pre-charging, the same amount of energy is converted into heat in a pre-charge resistor as is stored in the capacitors
Data Source
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AI summary
The invention relates to an electrical power supply system, comprising: a transformer (0) from a medium voltage level to a low voltage level; at least one electrical resistor (3), which is electrically connected to the secondary winding of the transformer (0) and which acts as a precharging resistor, a bypass switch (5) being electrically connected in parallel with each resistor (3); a rectifier module (9) connected electrically in series with each resistor (3), for feeding a direct voltage grid (11), to which electrical loads (17), in particular electrical motors, are electrically connected by means of respective capacitors (19) or electrical stores (20). During precharging of the capacitors (19), the through-current through the resistor (3) can be limited by means of a switching device (21).