EV Capacitor Active Discharge Circuit With Battery Disconnect Check

Solution Overview

Problem

Existing active discharge systems in electric vehicles risk damaging resistors when performing discharge while the battery is still connected to the capacitor, leading to high power losses, increased costs, and reduced availability due to overheating and long cool-down times.

Innovation Solution

The method involves using an auxiliary circuit to determine a voltage drop across the capacitor, confirming the battery's disconnection before engaging the active discharge circuit, thereby reducing the need for high-power resistors and minimizing the risk of damage by ensuring the high voltage switch is open before discharge.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If high power resistors are used in the active discharge circuit to prevent damage when the battery is connected, then the reliability is improved, but the cost and space requirements increase significantly

Engineering Contradiction:

Improveactive discharge circuit reliabilityVSAvoidresistor space

Core Design Contradiction:

ReliabilityVSArea of stationary object

Solution Approach 1:

The auxiliary circuit performs a preliminary voltage drop test before activating the active discharge circuit. By closing the auxiliary switch and measuring the resulting voltage drop, the system determines whether the battery is disconnected from the capacitor. This preliminary action allows the use of lower power resistors in the active discharge circuit, reducing space and cost while maintaining reliability through conditional activation.

Inventive Principle:

Principle #10Preliminary action

2Reliability

If high power resistors are used in the active discharge circuit, then the reliability is improved, but the power losses increase

Engineering Contradiction:

Improveactive discharge circuit reliabilityVSAvoidpower loss

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

The auxiliary circuit performs a preliminary voltage drop test before activating the active discharge circuit. By closing the auxiliary switch and measuring the resulting voltage drop, the system determines whether the battery is disconnected from the capacitor. This preliminary action allows the use of lower power resistors in the active discharge circuit, reducing space and cost while maintaining reliability through conditional activation.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system changes the operational parameters of the discharge resistor based on the battery connection status. When the battery is confirmed disconnected (via auxiliary circuit voltage drop), the active discharge circuit uses a lower power rating resistor. This parameter change reduces power losses while maintaining sufficient discharge capability for the isolated capacitor.

Inventive Principle:

Principle #35Parameter changes

3Ease of manufacture

If software protection strategies are used to limit power dissipated by active discharge resistors, then the cost is reduced, but the cool down time becomes unacceptably long

Engineering Contradiction:

ImprovecostVSAvoidcool down time

Core Design Contradiction:

Ease of manufactureVSLoss of time

Solution Approach 1:

The auxiliary circuit performs a preliminary voltage drop test before activating the active discharge circuit. By closing the auxiliary switch and measuring the resulting voltage drop, the system determines whether the battery is disconnected from the capacitor. This preliminary action allows the use of lower power resistors in the active discharge circuit, reducing space and cost while maintaining reliability through conditional activation.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The auxiliary circuit uses a low-power, inexpensive switch and measurement mechanism to detect battery disconnection status. This cheap preliminary detection mechanism enables the main active discharge resistor to be smaller and cheaper, eliminating the need for expensive high-power resistors while avoiding long cool-down times through accurate conditional activation.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

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 reduces the power rating and cost of resistors, minimizes space requirements, and enhances the reliability and speed of active discharge, avoiding overheating issues and improving system availability.

Implementation Method 1

determining a voltage drop of the capacitor, based on closing the auxiliary switch

Methodology Applied

Scientific EffectVoltage drop: Ohm's Law

Implementation Method 2

The active discharge circuit may include a resistor to discharge the stored charge

Methodology Applied

Scientific EffectJoule heating: Joule Heating

Data Source

PatentUS20240146094A1Methods and systems for performing active discharge using an active discharge circuit and an auxiliary circuit

Publication Date: 2024.05.02 DELPHI INT OPERATIONS LUXEMBOURG SARL

AI summary

A method may include receiving a discharge request to perform discharge of a capacitor of an electric vehicle; closing a first switch a first circuit provided in parallel with a second circuit of the electric vehicle; determining a voltage drop of the capacitor, based on closing the first switch; and closing a second switch of the second circuit to perform the discharge of the capacitor, based on the determining the voltage drop of the capacitor indicating that a battery of the electric vehicle is disconnected from the capacitor.