EV Inverter Relay Circuit for Back-EMF Suppression

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Solution Overview

Problem

Electric vehicles face the challenge of suppressing high back electromotive voltage applied to the electric motor's power line when the system main relay is switched to an open state during operation, potentially leading to damage to power semiconductors and capacitors.

Innovation Solution

An electric vehicle configuration that includes an electric motor, an inverter, a battery, a first switch (system main relay), a second switch, and an electric power converter circuit, where the second switch is normally closed and coupled between the electric motor's power line and the converter circuit, allowing the converter to generate a voltage that drives the first switch to a closed state based on back electromotive voltage, thereby managing and suppressing the high voltage.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the system main relay is switched to an open state during operation, then the electric power line is disconnected for safety, but high back electromotive voltage is applied to the electric motor's power line which may damage power semiconductors and capacitors

Engineering Contradiction:

Improvesafety of electric power line disconnectionVSAvoidback electromotive voltage damage to power semiconductors and capacitors

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

A second switch is introduced as an intermediary component between the inverter and the electric motor. When the system main relay opens, the second switch remains closed to provide an alternative current path, preventing high back electromotive voltage from damaging the inverter's power semiconductors and capacitors while still disconnecting the main power line for safety.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The second switch is prepared in advance to be normally closed and is designed to automatically provide a bypass path when the system main relay opens. This preliminary arrangement ensures that before the back electromotive voltage can cause damage, the protective path is already in place to redirect the current safely.

Inventive Principle:

Principle #10Preliminary action

2Reliability

If the first switch is opened to disconnect power, then safety is improved, but regenerative current has no path to flow which causes high voltage buildup

Engineering Contradiction:

Improvesafety of power disconnectionVSAvoidenergy loss from blocked regenerative current

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

The second switch acts as an intermediary that allows regenerative current to flow through the electric power converter circuit even when the system main relay is open. This mediator component enables energy recovery while maintaining the safety benefits of the disconnected main power line.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The potential harmful effect of blocked regenerative current is converted into a beneficial situation by providing an alternative path through the second switch and electric power converter circuit. The regenerative energy that would otherwise be wasted or cause damage is now safely dissipated or stored, turning a potential problem into a solution.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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 configuration effectively reduces the risk of damage to the inverter and its components by allowing regenerative current to flow to the battery, suppressing the back electromotive voltage within safe limits and preventing adverse effects on the inverter during abnormal conditions.

Implementation Method 1

in a case where the electric power converter circuit receives a back electromotive voltage from the electric motor via the second switch, generate a voltage that drives the first switch to be in a close state, on the basis of the back electromotive voltage

Methodology Applied

Scientific EffectBack electromotive voltage: Electromagnetic Induction

Implementation Method 2

The battery is configured to supply electric power to the inverter

Methodology Applied

Scientific EffectBattery: Battery (electricity)

Implementation Method 3

The inverter is configured to drive the electric motor

Methodology Applied

Scientific EffectElectromagnetic conversion: Electromagnetic Induction

Data Source

PatentUS11916412B2Electric vehicle

Publication Date: 2024.02.27 SUBARU CORP

AI summary

An electric vehicle includes an electric motor, an inverter, a battery, a first switch, an electric power converter circuit, and a second switch. The inverter is configured to drive the electric motor. The battery is configured to supply electric power to the inverter. The first switch is normally open, and configured to open and close an electric power line provided between the battery and the inverter. The second switch is normally closed, and coupled between an electric power line of the electric motor and the electric power converter circuit. The electric power converter circuit is configured to, in a case where the electric power converter circuit receives a back electromotive voltage from the electric motor via the second switch, generate a voltage that drives the first switch to be in a close state, on the basis of the back electromotive voltage.