OBC Pre-Charging DC Link Capacitor Surge Currents
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Solution Overview
Problem
On-board chargers (OBCs) for electric vehicles face the challenge of surge electrical currents when initially connected to the mains supply, which can damage internal components and require pre-charging of the DC link capacitor to prevent such surges.
Innovation Solution
The OBC is configured to operate in a pre-charge mode using electrical power from the traction battery to charge the DC link capacitor, with a controller managing the transition to a stable operation mode where the mains supply is used for charging the traction battery, and the Power Factor Correction (PFC) stage is disabled during pre-charging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the DC link capacitor is charged directly from the mains supply when the OBC is first connected, then the capacitor charges quickly, but surge electrical currents occur that can damage internal components and the mains supply
Solution Approach 1:
The patent applies preliminary action by using the traction battery to pre-charge the DC link capacitor before connecting to the mains supply. This preliminary charging action from a low-voltage source prevents the harmful surge current that would occur if direct mains connection were made to an uncharged capacitor, while still enabling subsequent normal operation from the mains supply.
2Reliability
If the PFC stage is used to pre-charge the DC link capacitor from the mains supply, then the capacitor charges to the required voltage, but surge currents are generated that can damage components
Solution Approach 1:
The patent applies inversion by reversing the normal power flow direction. Instead of using the high-voltage mains supply through the PFC stage to charge the DC link capacitor (which causes surge currents), the system uses the low-voltage traction battery to charge the capacitor in reverse. This inverted approach achieves the same voltage regulation function without generating harmful surge currents.
3Object-affected harmful factors
If the OBC waits for the DC link capacitor to be fully charged before connecting to the mains supply, then surge currents are prevented, but charging time is extended
Solution Approach 1:
The patent performs preliminary charging of the DC link capacitor using the traction battery before mains connection is established. This preliminary action ensures the capacitor is pre-charged to prevent surge currents, and the controller is configured to enable mains connection only after the capacitor reaches a predetermined voltage threshold, thus minimizing the time extension while ensuring safety.
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 prevents surge currents and ensures safe and efficient charging by pre-charging the DC link capacitor using the traction battery's energy, thereby protecting the OBC and mains supply, and allows for stable operation once the capacitor reaches the desired voltage.
Implementation Method 1
the DC/DC converter is configured to charge the DC link capacitor using electrical energy from the traction battery
Implementation Method 2
The PFC stage converts AC electrical power from the mains supply into DC electrical power and delivers this DC electrical power to the DC link capacitor and to the DC/DC stage
Implementation Method 3
a DC link capacitor between the PFC stage and the DC/DC converter
Data Source
AI summary
An on-board charger (OBC) for charging a traction battery of an electric vehicle includes a Power Factor Correction (PFC) stage to convert AC power from a mains supply into DC power for use in charging the traction battery, a bi-directional DC/DC converter coupled to the traction battery, a DC link capacitor between the PFC stage and the DC/DC converter, and a controller. The controller is operable to control the PFC stage and the DC/DC converter to operate in (i) a pre-charge mode in which the DC link capacitor is pre-charged using electrical power from the traction battery and (ii) a stable operation mode in which the traction battery is charged using the AC power from the mains supply.