Motor Controller Fault Handling for Electric Power Steering

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Solution Overview

Problem

Conventional electric power steering devices with polyphase motors face challenges in distinguishing between bridging-type and open-type faults, leading to torque pulsations, increased component count, and system complexity, which complicates downsizing and cost reduction.

Innovation Solution

A motor controller with fault determination means that distinguishes between open-type and bridging-type faults, allowing for targeted control to stop current supply to faulty systems, thereby suppressing torque pulsations and reducing the number of components needed.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If power relays are added to stop current supply in case of fault, then reliability is improved, but device complexity and component count increase

Engineering Contradiction:

Improvefault handling capabilityVSAvoidcontrol system complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent replaces mechanical power relays with electronic control of switching elements in the inverter. The control unit directly controls the switching elements to stop current supply to faulty phases, eliminating the need for separate power relay mechanisms while maintaining fault handling capability.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The control unit is given multiple functions: it not only controls normal motor operation but also performs fault detection and fault response by controlling switching elements. This multi-functionality eliminates the need for separate dedicated fault isolation components.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Reliability

If multiple power relays are provided for each inverter, then reliability is improved, but manufacturing cost increases

Engineering Contradiction:

Improvefault isolation capabilityVSAvoidmanufacturing cost

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent eliminates mechanical power relays by using electronic switching control. The control unit manages current supply to each phase through the switching elements, providing fault isolation capability without requiring additional power relay components, thereby reducing manufacturing cost.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Reliability

If fault detection and differentiation system is added, then reliability is improved, but device complexity increases

Engineering Contradiction:

Improvefault detection accuracyVSAvoidcontrol system complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The control unit performs multiple functions including normal motor control, fault detection, fault type differentiation, and fault response. By consolidating these functions in a single control unit, the patent avoids adding separate complex subsystems while maintaining high reliability through accurate fault detection and differentiation.

Inventive Principle:

Principle #6Universality (Multi-functionality)

4Device complexity

If conventional fault handling is used without fault differentiation, then device complexity is reduced, but torque pulsation occurs

Engineering Contradiction:

Improvecontrol system simplicityVSAvoidtorque pulsation

Core Design Contradiction:

Device complexityVSObject-generated harmful factors

Solution Approach 1:

The patent uses electronic control of switching elements to precisely manage current supply to faulty phases. This electronic approach allows for smooth current interruption without the mechanical abruptness that causes torque pulsation, while maintaining simple control system architecture.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The control unit dynamically adjusts switching element control based on detected fault conditions. By dynamically managing current supply to faulty phases rather than using fixed mechanical relay configurations, the system suppresses torque pulsation while maintaining operational simplicity.

Inventive Principle:

Principle #15Dynamics

Data Source

PatentUS8981704B2Motor controller and electric power steering device using the same

Publication Date: 2015.03.17 MITSUBISHI ELECTRIC CORP

AI summary

Provided are a motor controller for suppressing a torque pulsation with a simple configuration and obtaining a sufficient output torque in the case of an open-type fault occurring in any one of windings of a motor and inverters, and an electric power steering device using the motor controller. In the motor controller for controlling a current supplied from and a voltage applied from a power source with respect to the motor including winding sets of a plurality of systems, when a fault determination unit (31) determines the occurrence of the open-type fault, the supply of the currents to the windings of one of the systems in which the fault has occurred is stopped by control performed on switching elements included in the inverter of the faulty system, whereas the supply of the currents to the windings of the normal system in which the fault has not occurred is continued.