Permanent Magnet Motor Temperature Estimation via Load Disconnection

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Solution Overview

Problem

Existing control methods for permanent magnet motors face challenges in accurately estimating magnet temperature due to ambient temperature and inertia effects, leading to low accuracy and potential irreversible demagnetization.

Innovation Solution

A control device comprising a rotor position detector, magnet temperature estimator, and current compensator that disconnects the motor from the load, estimates magnet temperature based on rotating speed, and adjusts current commands to compensate for temperature changes, thereby controlling the motor independently of ambient temperature and inertia.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If the motor is connected to the load during temperature estimation, then the motor can operate under normal conditions, but the temperature estimation accuracy is reduced due to ambient temperature and inertia effects

Engineering Contradiction:

Improvemagnet temperature estimation accuracyVSAvoidambient temperature and inertia effects

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent extracts the motor from the load by controlling the clutch to disconnect them during the temperature estimation phase. This isolation removes the harmful effects of ambient temperature and inertia from the estimation process, allowing for accurate temperature measurement based solely on rotating speed data, while the motor can remain connected to the load during normal operation phases.

Inventive Principle:

Principle #2Taking out (Extraction)

2Reliability

If compensation current is supplied to maintain torque, then torque stability is improved, but heat generation increases causing magnet temperature to rise

Engineering Contradiction:

Improvetorque stabilityVSAvoidmagnet temperature

Core Design Contradiction:

ReliabilityVSTemperature

Solution Approach 1:

The patent performs preliminary temperature estimation by disconnecting the motor from the load before compensation current is supplied. This allows the control system to know the actual magnet temperature in advance, enabling it to calculate the appropriate compensation current that maintains torque stability while avoiding excessive heat generation that would raise the magnet temperature to dangerous levels.

Inventive Principle:

Principle #10Preliminary action

3Power

If the motor operates at high temperature to maintain performance, then torque output is improved, but irreversible demagnetization occurs

Engineering Contradiction:

Improvetorque outputVSAvoidmagnet integrity

Core Design Contradiction:

PowerVSReliability

Solution Approach 1:

The patent implements a feedback mechanism where the magnet temperature is continuously estimated based on rotating speed measurements. This temperature information feeds back to the control system, which adjusts the compensation current and torque commands to maintain optimal torque output while ensuring the magnet temperature remains below the threshold for irreversible demagnetization, thus protecting magnet integrity.

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

This solution allows for precise temperature estimation and torque control, preventing irreversible demagnetization and improving motor efficiency by disconnecting the motor from the load to isolate temperature effects.

Implementation Method 1

a rotor position detector configured to detect a rotating speed of a rotor of a permanent magnet motor in a state in which the permanent magnet motor is disconnected from a load by a clutch and rotates without power supply

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Implementation Method 2

a magnet temperature estimator configured to estimate a magnet temperature of the permanent magnet motor based on the detected rotating speed

Methodology Applied

Scientific EffectFriction heating: Friction

Implementation Method 3

a magnet temperature estimator configured to estimate a magnet temperature of the permanent magnet motor based on the detected rotating speed

Methodology Applied

Scientific EffectJoule heating: Joule Heating

Implementation Method 4

a current compensator configured to determine a compensation amount for compensating for a current command to the permanent magnet motor based on the estimated magnet temperature

Methodology Applied

Scientific EffectTemperature compensation:

Implementation Method 5

a drive control device configured to control a power converter for driving the permanent magnet motor based on the compensation amount

Methodology Applied

Scientific EffectElectromagnetic conversion: Electromagnetic Induction

Data Source

PatentUS9160272B2Control device and control method for permanent magnet motor

Publication Date: 2015.10.13 MITSUBISHI ELECTRIC MOBILITY CORP

AI summary

A control device for a permanent magnet motor, including: a rotor position detector configured to detect a rotating speed of a rotor of a permanent magnet motor in a state in which the permanent magnet motor is disconnected from a load by a clutch and rotates without power supply; a magnet temperature estimator configured to estimate a magnet temperature of the permanent magnet motor based on the detected rotating speed; a current compensator configured to determine a compensation amount for compensating for a current command to the permanent magnet motor based on the estimated magnet temperature; and a drive control device configured to control a power converter for driving the permanent magnet motor based on the compensation amount.