Split DC-Link Passive Balancing for UPS Pre-Charge Stability
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Solution Overview
Problem
In UPS devices with a split DC-link, voltage balancing is challenging, especially in 3-wire distributions where the midpoint is floating, leading to unbalanced voltages and currents during pre-charging, and existing pre-charge circuits lack resistance against failures.
Innovation Solution
A converter design incorporating a DC split link with parallel resistors to the capacitors, which are engaged during the pre-charge phase to balance voltages, and a controller to manage the switchable contacts for resistor engagement and disengagement, ensuring secure passive balancing without active control delays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an AC pre-charge circuit with switches, current limiting resistors and diodes is used, then pre-charging of DC capacitances is achieved, but voltage and current unbalance occurs and resistance against failures is lacking
Solution Approach 1:
The patent extracts the active control elements (switches, diodes) from the pre-charge circuit and replaces them with passive resistive balancing networks. This removes the complexity and failure points associated with active components while maintaining the pre-charge function through purely passive voltage division and balancing resistors.
Solution Approach 2:
The balancing resistors are configured to automatically balance the DC link voltages without requiring external control signals or active management. The passive resistive network self-regulates the voltage distribution across the DC capacitances during pre-charge, eliminating the need for complex control circuits.
2Reliability
If active balancing control is used, then voltage balancing is achieved, but control delays and instability during power outages or shutdowns occur
Solution Approach 1:
The patent replaces the electronic active control system with a passive resistive balancing network. This substitution eliminates control delays inherent in active systems and provides immediate, automatic voltage balancing that remains stable even during power outages or shutdown conditions when active control may fail.
Solution Approach 2:
The balancing resistors act as intermediary elements that passively mediate the voltage distribution across the DC link. Instead of relying on active control loops that may be unstable during transients, the resistive network provides a stable, predictable voltage division that automatically adapts to changing conditions including power outages.
3Adaptability or versatility
If a split DC-link with floating midpoint is used, then system flexibility is improved, but voltage balancing becomes challenging during pre-charging
Solution Approach 1:
The patent introduces balancing resistors that create equipotential conditions across the floating midpoint of the split DC-link. By providing symmetric resistive paths from each DC capacitance to the midpoint, the system automatically establishes balanced voltage distribution without requiring complex control mechanisms, thus maintaining system flexibility while simplifying voltage balancing.
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 stable and secure voltage balancing during pre-charging and supports active balancing, preventing unbalances and ensuring reliable operation even when active balancing is not stable, such as during power outages or shutdowns.
Implementation Method 1
a first resistor arranged in parallel to the first DC capacitance; and a second resistor arranged in parallel to the second DC capacitance. The first and the second resistors are configured to be engaged at least during a pre-charge phase of the converter
Data Source
AI summary
A converter includes a DC split link with a positive line, a floating midpoint, and a negative DC line, a first DC capacitance arranged between the positive line and the floating midpoint, a second DC capacitance arranged between the negative line and the floating midpoint, a first resistor arranged in parallel to the first DC capacitance, a second resistor is arranged in parallel to the second DC capacitance. The first and the second resistors are configured to be engaged during a pre-charge phase of the converter.