High-Voltage DC Bus Parallel Connection Without Current Spikes
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Solution Overview
Problem
Adding a second high voltage DC source to an aircraft's DC bus in parallel can cause a significant current spike, potentially damaging contactors and reducing their lifespan, due to voltage differences across capacitors on the bus.
Innovation Solution
The solution involves temporarily lowering the voltage of the incoming high voltage DC source and using a pair of diodes and an auxiliary contactor to make the parallel connection, ensuring equal capacitor voltages and avoiding current spikes by natural commutation, followed by closing the main contactor when current is detected through both diodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a second high voltage DC source is connected in parallel to the DC bus, then power supply capability and system redundancy are improved, but a significant current spike occurs that can damage contactors and reduce their lifespan
Solution Approach 1:
The patent applies preliminary action by pre-charging the capacitors of the incoming DC source to match the voltage of the existing DC bus before closing the main contactor. This is achieved through a sequential connection process where auxiliary contactors first connect the incoming source to a pre-charge circuit, allowing capacitors to charge to equal voltage levels, thereby eliminating voltage difference and preventing current spikes when the main contactor closes.
Solution Approach 2:
The patent uses an intermediary approach by introducing auxiliary contactors and pre-charge circuits as intermediate elements between the incoming DC source and the main DC bus. These intermediaries facilitate controlled voltage equalization through diode-based pre-charge paths before the main parallel connection is established, mediating the transition to avoid harmful current spikes.
2Object-affected harmful factors
If the voltage of the incoming DC source is lowered temporarily, then current spike is avoided during parallel connection, but additional control complexity and connection time are required
Solution Approach 1:
The patent extracts the voltage equalization function from the main parallel connection process by separating it into a distinct pre-charge phase. The auxiliary contactors and pre-charge circuits are used temporarily only for voltage matching, then disconnected before the main contactor closes. This extraction simplifies the main connection operation while handling the complexity in a controlled, time-limited manner.
Solution Approach 2:
The patent applies self-service by using the incoming DC source itself to charge its own capacitors through the pre-charge circuit and diodes. The system automatically equalizes voltages without requiring external intervention or complex control systems, as the diode-based pre-charge path naturally directs current flow to balance capacitor voltages before parallel connection.
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 method effectively reduces or eliminates current spikes during the parallel connection of high voltage DC sources, extending the life of contactors and ensuring stable power distribution to the DC bus.
Implementation Method 1
using a pair of diodes and an auxiliary contactor to make the parallel connection, ensuring equal capacitor voltages and avoiding current spikes by natural commutation
Data Source
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AI summary
To join two sources in parallel, the second source output is lowered and then raised until two diodes providing an auxiliary path are passing current. This can reduce current spikes. Alternatively, the diodes can reversed, the voltage raised, and the lowered until diose are passing current.