EPS Inverter Bridge Control for Damping Current Suppression

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Solution Overview

Problem

Electric Power Assisted Steering (EPS) systems face issues with damping currents due to back-EMF in faulty inverter bridges, which reduce steering assistance and increase heat generation, requiring additional components like blocking relays that occupy space and are costly.

Innovation Solution

A method to control EPS systems by applying a gate-source voltage to switching elements in affected inverter bridges to prevent current flow, effectively disabling the faulty inverter without the need for additional components, using Gallium Nitride FETs that suppress reverse conduction when subjected to high back-EMF.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If blocking relays or switches are added to prevent damping currents in faulty inverter bridges, then damping currents are suppressed and steering assistance is maintained, but device complexity increases, space is occupied, heat is dissipated, and cost increases

Engineering Contradiction:

Improvesteering assistance maintenanceVSAvoidadditional power components

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent extracts and removes the faulty inverter bridge from the system by detecting its failure state and preventing it from participating in motor drive operations. Instead of adding blocking components, the solution extracts the problematic element (faulty inverter) and isolates it through control logic, allowing the healthy inverter to provide full assistance without opposition from damping currents.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The system uses its own monitoring capabilities to detect inverter bridge failures and automatically reconfigures operation to exclude the faulty bridge. The EPS control system serves itself by identifying the fault condition and implementing the isolation strategy without requiring external blocking components, thereby maintaining reliability while reducing complexity.

Inventive Principle:

Principle #25Self-service

2Reliability

If additional blocking components are installed in each inverter bridge, then damping currents are prevented, but manufacturing cost increases and ease of manufacture decreases

Engineering Contradiction:

Improvefault toleranceVSAvoidassembly complexity

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent makes the inverter bridge system universal by designing it so that each inverter can independently provide full steering assistance when the other is faulty. The control system implements multi-functionality by being able to operate with either inverter alone, eliminating the need for bridge-specific blocking components. This universal design simplifies manufacturing while maintaining fault tolerance.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Object-generated harmful factors

If phase connection is broken to prevent damping currents, then damping is eliminated, but additional blocking switches are required that occupy space and dissipate heat

Engineering Contradiction:

Improvedamping currentsVSAvoidcomponent space

Core Design Contradiction:

Object-generated harmful factorsVSArea of stationary object

Solution Approach 1:

The patent replaces the mechanical/electrical blocking approach (physical switches or relays) with an electronic control solution. Instead of mechanically breaking the phase connection with blocking components, the system uses electronic control to prevent the faulty inverter from generating or responding to damping currents, thereby eliminating the need for physical blocking components and their associated space and heat dissipation issues.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 prevents damping currents and maintains steering assistance while avoiding the need for extra components, reducing heat generation and maintaining performance even in faulty conditions.

Implementation Method 1

preventing current flow in said one or more affected inverters by applying a gate-source voltage to one or more of the switching elements of the affected inverter bridge(s)

Methodology Applied

Scientific EffectGate-source voltage control:

Implementation Method 2

using Gallium Nitride FETs that suppress reverse conduction when subjected to high back-EMF

Methodology Applied

Scientific EffectReverse conduction suppression:

Implementation Method 3

the generation of a back-EMF (also known as regeneration voltage) within the motor 130 can drive damping currents within the faulty inverter bridge

Methodology Applied

Scientific EffectBack-EMF generation: Electromagnetic Induction

Data Source

PatentUS10988165B2Control for electric power steering

Publication Date: 2021.04.27 TRW LIMITED

AI summary

A method of controlling an electric power assisted steering (EPS) system comprising one or more inverter bridges each connected to a multi-phase motor configured to provide power assist to steering of a vehicle, each inverter comprising a plurality of switching elements each associated with a phase of the motor, is provided. The method comprises, preventing current flow in said one or more affected inverters by applying a gate-source voltage to one or more of the switching elements of the affected inverter bridge(s) in response to detecting a predefined event affecting current flow in one or more of the inverter bridges. A control system for an electric power assisted steering apparatus comprising one or more inverter bridges and a control means configured to control the switching elements in accordance with the method is also provided.