Bidirectional DC-DC Converter Pre-Charge Control for EV Battery
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Solution Overview
Problem
Conventional pre-charge relays used in electric vehicle charging systems are prone to durability issues due to continuous on/off operation and require significant space, especially for 3-phase inputs, and they do not effectively prevent inrush currents during slow charging with commercial AC power.
Innovation Solution
A battery charging apparatus and method that employs a bidirectional DC-DC converter and a controller to initially charge a link capacitor using electrical power discharged from the battery, eliminating the need for a pre-charge relay by controlling PWM signals to manage the charging current and voltage, thereby preventing inrush currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a pre-charge relay is used to charge the link capacitor before battery charging, then inrush current is reduced, but the relay suffers from durability deterioration due to continuous on/off operation and requires large space
Solution Approach 1:
The patent removes the pre-charge relay from the system entirely and replaces it with a controlled switching mechanism using the second switching part (S21-S24) and controller. The controller selectively turns on specific switching elements based on the link capacitor voltage level, eliminating the mechanical relay and its associated durability issues while maintaining the inrush current protection function.
Solution Approach 2:
The patent replaces the mechanical pre-charge relay with an electronic switching system composed of semiconductor switching elements (S21-S24) controlled by a controller. This substitution eliminates the mechanical on/off operations that caused relay durability deterioration while achieving the same electrical function of controlling inrush current to the link capacitor.
2Object-affected harmful factors
If a pre-charge relay is used for initial charging, then the link capacitor is charged before battery charging, but the circuit design becomes complex and space is increased
Solution Approach 1:
The patent makes the second switching part (S21-S24) and controller serve multiple functions: they control power flow to the battery during normal charging operation and simultaneously control charging of the link capacitor when needed. This multi-functionality eliminates the need for a separate pre-charge relay circuit, reducing overall circuit complexity and component count.
Solution Approach 2:
The patent combines the pre-charge function and the main power conversion function into a single integrated switching circuit (the second switching part with S21-S24). Instead of having separate circuits for pre-charging and main charging, the same switching elements and control logic handle both functions based on operational conditions, simplifying the overall circuit design.
3Object-affected harmful factors
If three or more pre-charge relays are used for 3-phase input, then adequate charging coverage is achieved, but the device size and complexity increase significantly
Solution Approach 1:
The patent enables the second switching part to handle multiple phases and multiple functions (pre-charge and main power conversion) using the same set of switching elements S21-S24. The controller intelligently configures the switching elements to provide adequate coverage for 3-phase inputs without requiring multiple separate relay components, thereby reducing device space while maintaining comprehensive inrush current protection.
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 simplifies the circuit design, enhances durability by eliminating the need for a pre-charge relay, and effectively prevents inrush currents during slow charging, reducing the risk of damage to other components.
Implementation Method 1
a rectifier part for rectifying an AC power applied from a commercial AC power source to a DC power
Implementation Method 2
a link capacitor connected in parallel to the rectifier part to smooth the rectified DC power
Implementation Method 3
a first switching part configured to convert a DC power applied from the PFC circuit part to an AC power
Implementation Method 4
a transformer configured to boost or reduce a voltage of the AC power converted at the first switching part
Implementation Method 5
a second switching part configured to rectify an AC power applied from the transformer to a DC power to charge the battery for a vehicle
Data Source
AI summary
An apparatus, for charging a battery for a vehicle, includes a PFC circuit comprising a rectifier for rectifying an AC power to a DC power, and a link capacitor for smoothing the rectified DC power, a bidirectional DC-DC converter including a first switch for converting the DC power of the PFC circuit to an AC power, a transformer for boosting or reducing a voltage of the AC power converted at the first switch, and a second switch for rectifying an AC power from the transformer to a DC power, and a controller configured to control a phase of a PWM signal applied to the second switch such that the link capacitor is charged by an electrical power from the battery, when a voltage of the link capacitor is below a predetermined voltage prior to entering a battery charging mode.