Low-Voltage Auxiliary Pre-Charging Circuit for Power Converters
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Solution Overview
Problem
Traditional medium voltage power converters require additional bulky resistors and contactors for pre-charging, leading to reduced power density and increased equipment and manufacturing costs.
Innovation Solution
An auxiliary pre-charging device is introduced, which includes a switch, a transformer, a pre-charging resistor, and a rectifier connected in series, allowing pre-charging to start from the low-voltage side, reducing the number of components needed on the medium voltage side.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional pre-charging circuit with bulky resistors and contactors is used on medium voltage side, then pre-charging function is achieved, but device size and manufacturing cost increase
Solution Approach 1:
The patent inverts the traditional pre-charging approach by moving the pre-charging circuit from the medium voltage side to the low voltage side. Instead of pre-charging the medium voltage DC bus before closing the main switch, the invention pre-charges the low voltage DC bus after the main switch is closed, using a transformer to couple the low voltage pre-charging circuit with the medium voltage side. This inversion eliminates the need for bulky medium voltage pre-charging resistors and contactors.
Solution Approach 2:
The patent introduces a transformer as an intermediary device to couple the low voltage pre-charging circuit with the medium voltage DC bus. The transformer enables energy transfer between different voltage levels, allowing the low voltage pre-charging circuit to perform the pre-charging function that traditionally required medium voltage components. This intermediary approach reduces device complexity while maintaining the pre-charging function.
2Reliability
If additional pre-charging components are added to medium voltage converter, then pre-charging capability is provided, but power density decreases
Solution Approach 1:
By inverting the pre-charging location from medium voltage side to low voltage side, the patent eliminates the need for heavy medium voltage pre-charging resistors and contactors. The low voltage pre-charging circuit components are significantly lighter and smaller, thereby improving the overall power density of the medium voltage converter while maintaining the essential pre-charging capability.
3Reliability
If medium voltage pre-charging circuit is used, then pre-charging is achieved, but manufacturing cost increases
Solution Approach 1:
The patent reduces manufacturing cost by inverting the pre-charging circuit to low voltage side, where cheaper components can be used. Low voltage pre-charging resistors, contactors, and switches are significantly less expensive than their medium voltage counterparts. The transformer enables this cost-effective approach while maintaining the pre-charging function.
Solution Approach 2:
The patent employs cheaper low voltage components for the pre-charging circuit instead of expensive medium voltage components. The low voltage pre-charging resistors, contactors, and switches are more economical and easier to manufacture, thereby reducing the overall manufacturing cost of the medium voltage converter while achieving the same pre-charging function.
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 reduces the size and cost of the pre-charging circuit, increases reliability and safety by starting from a low voltage, and allows for the use of smaller, low-power components, thereby enhancing overall system efficiency and reducing manufacturing costs.
Implementation Method 1
an auxiliary pre-charging device including a switch, a transformer, a pre-charging resistor, and a rectifier sequentially connected in series
Implementation Method 2
a rectifier sequentially connected in series, one end of the switch is connected to the medium and high voltage AC power source, and an output end of the rectifier is connected to the low voltage DC bus
Data Source
AI summary
The present invention provides an auxiliary pre-charging device for a power converter. The power converter includes at least one power unit with an input end being connected to a medium and high voltage AC power source, and an output end being connected to a low voltage DC bus, wherein the auxiliary pre-charging device includes a switch, a transformer, a pre-charging resistor, and a rectifier sequentially connected in series, one end of the switch is connected to the medium and high voltage AC power source, and an output end of the rectifier is connected to the low voltage DC bus. The present invention also provides a pre-charging method for a power converter, which uses the aforementioned auxiliary pre-charging device to start pre-charging at the low-voltage output end of the power converter.