Mobility Power Converter Precharge Without Resistor-Relay Hardware
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Solution Overview
Problem
Conventional power conversion systems for electrically driven mobility devices require additional resistors and relays for initial charging to prevent DC link capacitor damage from sudden current inflows, which increase weight, size, and cost.
Innovation Solution
A power conversion system that uses a first energy storage device, a second energy storage device with lower voltage, a relay, a bidirectional first DC converter, and an optional second DC converter to charge the DC link capacitor to a preset voltage before switching the relay on, eliminating the need for a resistor and relay for initial charging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a resistor and relay for initial charging are added to prevent DC link capacitor damage, then the reliability of the capacitor is improved, but the device complexity, weight, and cost increase
Solution Approach 1:
The patent applies preliminary action by charging the DC link capacitor to a preset voltage (e.g., 300V) before the main relay is turned on. The controller performs this pre-charging operation in advance, so when the relay closes, the voltage difference is minimized and abrupt current inflow is prevented. This eliminates the need for additional protection components like resistors and relays for initial charging.
Solution Approach 2:
The system uses its own existing DC converter to perform the pre-charging function, rather than requiring separate protection components. The DC converter, which is already part of the system, is utilized to charge the capacitor before relay operation, making the system self-sufficient for protection without adding external components.
2Reliability
If a resistor and relay for initial charging are added to prevent abrupt current inflow, then the DC link capacitor is protected from damage, but the weight and size of the system increase
Solution Approach 1:
The controller performs pre-charging of the DC link capacitor before the main relay is activated. By charging the capacitor to a preset voltage in advance, the voltage differential at relay closure is reduced, preventing harmful inrush current. This eliminates the need for physical protection components that would add weight.
3Reliability
If a resistor and relay for initial charging are added to prevent sudden current inflow, then the DC link capacitor is protected, but the manufacturing cost increases
Solution Approach 1:
The system performs pre-charging of the DC link capacitor through controller operation before relay closure. This preliminary action prevents abrupt current inflow and capacitor damage without requiring additional hardware components, thereby reducing manufacturing costs.
Solution Approach 2:
The existing DC converter within the system is utilized to perform the pre-charging function, eliminating the need for separate protection components. This self-service approach reduces component count and manufacturing 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 reduces system size, weight, and cost by eliminating the resistor and relay, while ensuring the DC link capacitor is charged safely without damage, and improves efficiency across varying load conditions through selective DC converter operation.
Implementation Method 1
a first DC converter provided between the DC link capacitor and the second energy storage device and capable of bidirectional voltage conversion
Implementation Method 2
charge the DC link capacitor to a preset voltage or higher, and then to switch the relay to the on state
Data Source
AI summary
A power conversion system for electrically driven mobility device includes a first energy storage device and a second energy storage device having a voltage output lower than a voltage of the first energy storage device, a relay having one terminal connected to the first energy storage device, a DC link capacitor connected to the other terminal of the relay, a first DC converter provided between the DC link capacitor and the second energy storage device and capable of bidirectional voltage conversion, and a controller configured to control the first DC converter to convert a level of the voltage of the second energy storage device and to apply the voltage having the converted level to the capacitor before switching of the relay from an off state to an on state to charge the DC link capacitor to a preset voltage or higher, and then to switch the relay to the on state.