DC Link Precharge Control for EV Charging In-Rush Current
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Solution Overview
Problem
In-rush current during battery charging can damage charging circuitry in electric vehicles, necessitating a solution to mitigate this high initial current.
Innovation Solution
A system with a DC link and a bidirectional DC-DC converter is used to precharge the DC link to the same voltage as the vehicle's traction battery, utilizing switching parameters like frequency and phase shift to control the charging process, reducing in-rush current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high voltage DC power is directly applied to the battery during fast charging, then charging speed is improved, but in-rush current increases causing damage to charging circuitry
Solution Approach 1:
The patent applies preliminary action by pre-charging the DC link capacitor before main charging operation begins. The controller activates the bidirectional DC-DC converter in advance to charge the DC link to a threshold voltage, ensuring the capacitor is ready to accept power without causing in-rush current when the charging process starts. This preparatory step eliminates the harmful in-rush current while maintaining fast charging capability.
Solution Approach 2:
The patent utilizes parameter changes by dynamically adjusting the switching frequency and phase shift of the bidirectional DC-DC converter during the pre-charging process. The controller modifies these switching parameters to control the charging rate of the DC link, ensuring it reaches the threshold voltage safely before main charging begins, thus preventing in-rush current while enabling fast charging.
2Object-affected harmful factors
If a DC link capacitor is pre-charged before battery charging, then in-rush current is reduced, but additional circuitry and control complexity are required
Solution Approach 1:
The patent applies universality by designing the bidirectional DC-DC converter to serve multiple functions: it acts as a pre-charging circuit to charge the DC link capacitor, and simultaneously serves as the main power conversion circuit for battery charging. This multi-functionality eliminates the need for separate pre-charging circuitry, reducing overall system complexity while still preventing in-rush current.
Solution Approach 2:
The patent implements self-service by using the bidirectional DC-DC converter to automatically pre-charge the DC link capacitor without requiring external assistance or additional dedicated components. The controller manages the entire pre-charging process using the existing converter circuitry, making the system self-sufficient and avoiding added complexity from external pre-charging devices.
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 solution effectively reduces in-rush current, preventing damage to charging circuitry by gradually charging the DC link, ensuring safe and efficient battery charging.
Implementation Method 1
A bidirectional DC-DC converter, electrically connected between the DC link and a DC power source, is configured to convert DC power from a first voltage to a second voltage
Data Source
AI summary
A system includes a direct current (DC) link configured to receive DC power from a first converter that converts alternating current power into DC power. A bidirectional DC-DC converter, electrically connected between the DC link and a DC power source, is configured to convert DC power from a first voltage to a second voltage. The bidirectional DC-DC converter includes multiple switches. A controller is configured to control a switching parameter of the plurality of switches to charge the DC link to a threshold voltage from the DC power source before the first converter provides power to the DC power source. The switching parameter is at least one of a switching frequency and a phase shift. Controlling the switching parameter includes initially setting the switching parameter to a first value and, in response to determining that a set of criteria has been met, adjusting the switching parameter to a second value.