EV Back-EMF Control for Faulted Permanent Magnet Motors

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Existing vehicle systems fail to effectively manage excessive back electromotive force (EMF) generated by failed permanent magnet motors, leading to potential damage to battery and power converter systems in electric vehicles.

Innovation Solution

A vehicle control system that includes a vehicle controller to limit drive current and implement mechanical braking, short circuits, or activate auxiliary power sources to manage back EMF, thereby preventing damage and ensuring safe operation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the vehicle operates with a failed permanent magnet motor in fault mode, then the vehicle can continue to provide service to the driver, but excessive back electromotive force voltage may damage the battery or power converter

Engineering Contradiction:

Improvevehicle service availabilityVSAvoidback electromotive force damage risk

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The controller proactively limits drive current to the healthy motor before excessive back EMF can damage the battery or power converter. By monitoring the voltage difference between back EMF and battery discharge voltage, the system applies preventive current limiting when the difference falls below a threshold, thereby counteracting the harmful effect before it occurs.

Inventive Principle:

Principle #9Preliminary anti-action

Solution Approach 2:

The system converts the potentially harmful back EMF voltage into useful regenerative energy by directing it to charge the battery. When the voltage difference is within acceptable limits, the controller allows the faulty motor to operate in regenerative mode, transforming what would be destructive voltage into beneficial energy recovery that extends vehicle operation.

Inventive Principle:

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

2Reliability

If the vehicle controller limits drive current to prevent back EMF damage, then battery and power converter protection is improved, but vehicle propulsion capability is reduced

Engineering Contradiction:

Improvepower system protectionVSAvoidvehicle propulsion power

Core Design Contradiction:

ReliabilityVSPower

Solution Approach 1:

The controller applies partial current limiting rather than complete shutdown. By limiting drive current only when the voltage difference falls below the threshold, the system maintains sufficient propulsion power for normal operation while preventing damage during critical conditions. This partial action allows the vehicle to continue functioning with reduced but adequate power.

Inventive Principle:

Principle #16Partial or excessive action

Solution Approach 2:

The current limit threshold is dynamically determined based on real-time conditions including vehicle speed, battery charge level, and motor parameters. This dynamic adjustment allows the system to maximize propulsion power when conditions permit while automatically reducing current when back EMF becomes hazardous, thereby balancing protection and performance.

Inventive Principle:

Principle #15Dynamics

3Reliability

If mechanical braking is applied to reduce vehicle speed and limit back EMF, then voltage management is improved, but braking distance and driver control are affected

Engineering Contradiction:

Improvevoltage managementVSAvoiddriver control

Core Design Contradiction:

ReliabilityVSEase of operation

Solution Approach 1:

The controller continuously monitors the voltage difference between back EMF and battery discharge voltage, and only applies mechanical braking when this difference falls below the threshold. This feedback-based approach ensures braking is applied only when necessary for voltage management, maintaining normal driver control during safe operating conditions while preventing damage during critical voltage excursions.

Inventive Principle:

Principle #23Feedback

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 system effectively mitigates the risk of damage from excessive back EMF by controlling voltage levels and reducing vehicle speed, enhancing safety and availability of electric vehicles.

Implementation Method 1

Electric motors are used in electric vehicles (EV) to convert electrical energy from the battery into mechanical energy to turn the wheels

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Implementation Method 2

a second electric motor operative to generate a back electromotive force voltage in a fault mode

Methodology Applied

Scientific EffectBack electromotive force: Electromagnetic Induction

Data Source

PatentUS12454200B2Back electromotive force management for electric vehicles

Publication Date: 2025.10.28 GM GLOBAL TECHNOLOGY OPERATIONS LLC

AI summary

An electric vehicle battery control system including a first electric motor configured to propel a vehicle in a drive mode in response to a drive current, a second electric motor operative to generate a back electromotive force voltage in a fault mode, a battery, having an open circuit battery discharge voltage, for generating the drive current for coupling to the first electric motor, and a vehicle controller for limiting the drive current in response to a difference between the back electromotive force voltage and the open circuit battery discharge voltage being less than a threshold voltage difference.