Precharge Converter for UPS DC Link Inrush Current Control
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Solution Overview
Problem
Conventional uninterruptible power supplies (UPS) face challenges in efficient and economical power-up due to large inrush currents and the need for bulky, expensive components during precharging, especially in AC power absent environments.
Innovation Solution
The implementation of a precharge converter with a DC power supply and a control unit that powers the DC link via two output connectors connected to a common reference point, allowing for efficient and simultaneous power provisioning, eliminating the need for bulky resistors and enabling startup in AC power absent conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a boost rectifier is used to boost DC voltage above peak AC input voltage, then the DC link voltage can be increased, but undesirably large inrush currents are produced when the rectifier is coupled to an AC source
Solution Approach 1:
The precharge converter is activated before the main rectifier to pre-charge the DC link capacitors to a voltage close to or above the utility peak voltage. This preliminary action ensures that when the main rectifier is subsequently connected, the voltage difference is minimized, thereby preventing large inrush currents while still achieving the required DC link voltage level.
2Reliability
If conventional precharge techniques using power resistors are used, then the DC link can be precharged, but the precharge time is long and the components are bulky and expensive
Solution Approach 1:
The precharge converter is designed as a multi-functional unit that can operate in different modes: it can pre-charge the DC link from the AC utility, and it can also function as a dedicated power supply for startup in AC-absent environments. This universal design eliminates the need for separate precharge resistors and control devices, reducing component count and system complexity while maintaining reliable precharge capability.
Solution Approach 2:
The precharge converter uses its own internal DC-DC conversion capability to generate the required output voltage without relying on external bulky resistors or complex control circuits. The converter serves itself by using its controlled switching and rectification functions to regulate the precharge current, thereby simplifying the overall precharge system.
3Reliability
If a dedicated power supply is used for startup in AC power absent environment, then reliable power-up is enabled, but the system complexity increases
Solution Approach 1:
The precharge converter is designed to perform multiple functions: it serves as the precharge device during normal AC-powered operation, and it simultaneously functions as the dedicated startup power supply when the AC utility is absent. By integrating both functions into a single converter unit, the system achieves reliable startup capability without increasing overall system complexity.
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 solution enables a quick and economical startup of the UPS system, reducing assembly complexity and avoiding common mode voltages, while ensuring reliable operation even during blackouts.
Implementation Method 1
a converter circuit for receiving DC power from the power connectors and providing DC power to the first and second output connector
Data Source
AI summary
An uninterruptable power supply system is disclosed with a precharge converter for connecting to a DC link of the uninterruptable power supply system to a DC power supply, whereby the DC link comprises a first and a second DC bus line, which are both coupled to a common reference point, whereby the common reference point can be an AC power supply neutral of the uninterruptable power supply system, comprising power connectors for connecting to the DC power supply, a first and second output connector for connecting to the first and the second DC bus line, respectively, a converter circuit for receiving DC power from the power connectors and providing DC power to the first and second output connector, and a control unit for controlling operation of the converter circuit.