Vehicle Charging Circuit With Fail-Safe Capacitor Discharge Switching

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Solution Overview

Problem

Electric vehicles with high-voltage rechargeable batteries and energy storage units like capacitors pose safety risks due to dangerous contact voltages, especially during charging and potential rear-end collisions, as existing technologies fail to effectively prevent permanent voltage supply and overheating in fault conditions.

Innovation Solution

A vehicle charging circuit equipped with a rectifier device, intermediate circuit capacitor, and precharge/discharge circuit featuring a changeover switch that connects the capacitor pole to either the rectifier or discharge resistor, preventing permanent current flow and overheating by disconnecting the rectifier from the discharge resistor in actuation failures, thus ensuring safe disconnection and preventing overheating.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the rectifier device is permanently connected to the discharge resistor, then the discharge function is always available, but the discharge resistor overheats and fails due to permanent current flow

Engineering Contradiction:

Improvedischarge function availabilityVSAvoiddischarge resistor temperature

Core Design Contradiction:

ReliabilityVSTemperature

Solution Approach 1:

The patent implements a dynamic connection system using a changeover switch that alternates the connection state between the rectifier device and discharge resistor. The switch transitions between connected and disconnected states based on operational requirements, enabling the discharge resistor to be thermally managed through periodic disconnection while maintaining discharge functionality when needed.

Inventive Principle:

Principle #15Dynamics

2Object-affected harmful factors

If the changeover switch connects the intermediate circuit capacitor to the discharge resistor in the actuation-free state, then dangerous contact voltages are prevented, but the rectifier cannot permanently supply voltage to the discharge resistor in fault conditions

Engineering Contradiction:

Improvedangerous contact voltageVSAvoidprotection against permanent voltage supply

Core Design Contradiction:

Object-affected harmful factorsVSReliability

Solution Approach 1:

The patent inverts the conventional switch default state by designing the changeover switch to connect to the discharge resistor in the actuation-free (default) state rather than to the rectifier. This inversion ensures that any failure to actuate the switch results in a safe state where the discharge resistor is connected and can dissipate dangerous contact voltages, while the controlled connection to the rectifier requires active switching action.

Inventive Principle:

Principle #13The other way round (Inversion)

3Temperature

If the changeover switch design prevents rectifier connection to discharge resistor, then overheating is avoided, but the circuit complexity increases

Engineering Contradiction:

Improvedischarge resistor temperature controlVSAvoidchangeover switch circuit complexity

Core Design Contradiction:

TemperatureVSDevice complexity

Solution Approach 1:

The patent combines multiple functions into a single changeover switch device that simultaneously achieves: (1) prevention of permanent rectifier-to-discharge-resistor connection, (2) controlled precharging capability, (3) discharge function activation, and (4) safe default state configuration. This merging reduces overall system complexity compared to using separate switches for each function while maintaining all required safety and operational features.

Inventive Principle:

Principle #5Merging (Combining)

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 prevents dangerous contact voltages and overheating, ensuring safe operation by preventing permanent current flow and allowing for controlled discharging and precharging, thereby enhancing safety during charging and potential collision scenarios.

Implementation Method 1

at least one intermediate circuit capacitor

Methodology Applied

Scientific EffectCapacitance: Capacitance

Implementation Method 2

at least one discharge resistor

Methodology Applied

Scientific EffectJoule heating: Joule Heating

Data Source

PatentUS20240025259A1Vehicle charging circuit with rectifier device, link capacitor and precharging/discharge circuit

Publication Date: 2024.01.25 SCHAEFFLER TECHNOLOGIES AG & CO KG

AI summary

A vehicle charging circuit is equipped with a rectifier device, at least one intermediate circuit capacitor and at least one precharge/discharge circuit. The rectifier device is connected to the intermediate circuit capacitor via the precharge/discharge circuit. The precharge/discharge circuit has at least one first changeover switch that is configured, in a first position, to connect a first pole of the intermediate circuit capacitor to a first potential of the rectifier device. In a second position, the changeover switch connects the first pole of the intermediate circuit capacitor to the second pole of the intermediate circuit capacitor via a discharge resistor. The changeover switch is configured to adopt the second switching position in the actuation-free state.