DC Link Capacitor Partial Pre-Charge for EV Fault Detection
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Solution Overview
Problem
In high voltage DC power systems for electric vehicles and hybrid electric vehicles, the pre-charge process for high voltage DC link capacitors can be inadequate, leading to potential failures and damage when contactors close, as existing methods do not effectively detect operational defects before engaging the high voltage energy source.
Innovation Solution
A system and method for partial pre-charging of the high voltage system to a low voltage state, allowing thorough checks for operational defects before engaging the high voltage energy source. This involves a DC/DC converter configured in boost mode, a controller, and circuits that limit current flow to charge the DC link capacitor to a partial pre-charge state, enabling fault detection and reducing the risk of damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If full high voltage pre-charge is performed before closing contactors, then contactor life is maximized and damage is avoided, but the system cannot detect operational defects before high voltage engagement
Solution Approach 1:
The pre-charge process is divided into two distinct stages: a first pre-charge stage that charges the DC link capacitor to a first voltage level (e.g., 400V) for fault detection, and a second pre-charge stage that charges to the full second voltage level (e.g., 800V) for contactor protection. This segmentation allows each stage to serve its specific function without compromising the other.
Solution Approach 2:
The system performs a preliminary fault detection check at the lower first voltage level before engaging the full high voltage system. This preliminary action identifies potential defects early, preventing damage to expensive components while maintaining contactor protection through the subsequent full pre-charge stage.
2Reliability
If the system is checked for operational defects before engaging high voltage energy source, then reliability is improved, but additional time is required for the pre-charge process
Solution Approach 1:
The pre-charge process is divided into two distinct stages: a first pre-charge stage that charges the DC link capacitor to a first voltage level (e.g., 400V) for fault detection, and a second pre-charge stage that charges to the full second voltage level (e.g., 800V) for contactor protection. This segmentation allows each stage to serve its specific function without compromising the other.
Solution Approach 2:
The system implements periodic fault detection during the first pre-charge stage, systematically checking various components and subsystems at scheduled intervals. This periodic approach ensures thorough verification while maintaining a structured timeline that prevents excessive delays before full system engagement.
3Productivity
If full high voltage is applied immediately without partial pre-charge, then system startup is faster, but operational defects cannot be detected and component damage risk increases
Solution Approach 1:
The pre-charge process is divided into two distinct stages: a first pre-charge stage that charges the DC link capacitor to a first voltage level (e.g., 400V) for fault detection, and a second pre-charge stage that charges to the full second voltage level (e.g., 800V) for contactor protection. This segmentation allows each stage to serve its specific function without compromising the other.
Solution Approach 2:
The system applies a partial voltage (first voltage level) during the initial pre-charge stage, which is sufficient for fault detection purposes but less than the full operating voltage. This partial action enables safety verification without requiring complete system voltage, thereby reducing risk while maintaining startup efficiency.
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 partial pre-charge method allows for thorough fault detection in the high voltage system and loads, reducing the risk of damage and extending the lifespan of contactors and other components by ensuring the system is operational before full high voltage engagement.
Implementation Method 1
a DC/DC converter connected between the DC link capacitor and the low voltage power source. In one embodiment, the DC/DC converter is configured in a boost mode to boost the voltage of the low voltage power source.
Implementation Method 2
a second circuit configured to limit current flowing to the DC link capacitor from the high voltage power source to charge the DC link capacitor to a partial pre-charge state based on the limited current flow. In one embodiment, the second circuit comprises a pair of contactors for controlling the supply of current to charge the high voltage DC link capacitor and a resistor network and a contactor connected in parallel
Data Source
AI summary
A system for partially pre-charging an electrical power system having a high voltage power source, a DC link device with a DC Link capacitor, a low voltage power source and a DC/DC converter. In one embodiment a partial pre-charge of the DC Link capacitor can be achieved in three ways: first, through a DC/DC converter boosting from the low voltage power source, second, through a first circuit provided to charge the DC link capacitor to a partial pre-charge state using the voltage directly from the low voltage power source, and third, through a second circuit provided to limit current flowing to the DC link capacitor from the high voltage power source to charge the DC Link capacitor only to a partial pre-charge level. A controller selectively operates the first circuit, the second circuit, or the DC/DC converter for charging the DC link capacitor to the partial pre-charge state