EVSE DC Bus Pre-Charge Circuit for Inrush Current Control
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Solution Overview
Problem
Current electric vehicle charging systems experience high inrush currents due to unbalanced Y capacitance between the electric vehicle supply equipment and the vehicle, which can damage contactors on the DC+ and DC− lines without pre-charge circuits on all three connections (DC+ line, DC− line, and PE line).
Innovation Solution
Incorporating a first and second pre-charge circuit in parallel to the contactors of the DC+ and DC− lines, respectively, along with pre-charge resistors and relays, and optionally a pre-charge resistor matrix, to pre-charge both lines simultaneously, preventing or limiting high inrush currents by charging the output near the vehicle's battery voltage and filtering direct current with X capacitors, while monitoring isolation with resistors and disconnecting if necessary.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a pre-charge circuit is provided only on one of the DC+ line or DC− line, then the device complexity is reduced, but high inrush current occurs on the line without pre-charge circuit due to Y capacitance and unbalance
Solution Approach 1:
The pre-charge function is segmented and applied independently to each DC line (DC+ and DC−) through separate pre-charge circuits. Each pre-charge circuit includes its own resistor and contactor, allowing independent pre-charging of each line to eliminate the harmful inrush current effect on any single line.
Solution Approach 2:
Different parts of the system (DC+ line and DC− line) are treated with different local qualities by providing dedicated pre-charge circuits to each line. This ensures that each line receives appropriate pre-charge treatment according to its specific electrical characteristics and Y capacitance values, preventing localized inrush current problems.
2Object-affected harmful factors
If pre-charge circuits are provided on both DC+ line and DC− line, then high inrush currents are prevented on both lines, but the device complexity increases
Solution Approach 1:
The pre-charge system is divided into two independent segments (one for DC+ line, one for DC− line), each with its own contactor and resistor. This segmentation allows the system to address inrush current on both lines simultaneously while maintaining modular architecture that simplifies control and troubleshooting.
Solution Approach 2:
The pre-charge circuits perform preliminary action by charging the Y capacitance on each DC line before the main contactors close. This preliminary charging action prevents the harmful inrush current from occurring when the main power connection is established, protecting the contactors and other sensitive components.
3Ease of operation
If contactors are used to selectively allow current flow, then the charging process is controlled and safe, but the contactors may get damaged by high inrush current
Solution Approach 1:
The pre-charge contactors close before the main contactors, performing a preliminary action to charge the Y capacitance on each DC line. This preliminary charging prevents high inrush current from flowing through the main contactors when they close, thereby protecting the main contactors from damage and improving their reliability and durability.
Solution Approach 2:
The pre-charge contactors and resistors act as intermediaries between the power source and the main contactors. They provide a controlled path for initial charging current, preventing direct high inrush current from reaching the main contactors, thus protecting them while still enabling controlled charging operation.
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
Effectively prevents or limits high inrush currents on both DC+ and DC− lines, protecting the contactors and ensuring safe charging by pre-charging all relevant lines, thus enhancing the reliability and safety of the electric vehicle charging process.
Implementation Method 1
a pre-charge circuit, having a pre-charge resistor, is provided in parallel to the contactor of one of the DC+ line or the DC− line
Implementation Method 2
each of the DC+ line and the DC− line is provided with a contactor configured for selectively allowing a current flow from the power module to the output
Data Source
AI summary
Described herein is an electric vehicle charging arrangement for charging an electric vehicle, including an electric vehicle supply equipment (EVSE). The EVSE includes a power module configured for providing electrical energy to charge the electric vehicle, an output configured for connecting the power module to the electric vehicle for charging the electric vehicle, and a direct current (DC) bus having a DC+ line and a DC− line and provided between and connected to the power module and the output and configured for transporting electric energy from the power module to the output. Each of the DC+ the DC− lines is provided with a contactor configured for selectively allowing a current flow from the power module to the output. A first pre-charge circuit is provided in parallel to the contactor of the DC+ line, and a second pre-charge circuit is provided in parallel to the contactor of the DC− line.