Magnet Flux Estimation for IPMSM Demagnetization Detection

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Solution Overview

Problem

In interior permanent magnet synchronous motors (IPMSM), the variation of permanent magnet flux with temperature leads to fluctuations in generated torque, and irreversible demagnetization can occur, making it difficult to detect demagnetization states, especially when the motor is stationary, and existing methods require significant time and current to detect magnet flux.

Innovation Solution

A magnet flux estimation device that includes a magnetic pole position detector, an inductance-equivalent value determination module, and a magnet flux estimator, which calculates the magnet flux amount based on d-axis inductance, allowing for rapid estimation without motor rotation and enabling detection of abnormal demagnetization states.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If the motor rotates to detect magnet flux using voltage-speed proportionality, then the demagnetize state can be detected, but the motor cannot be detected in the halt state and requires motor rotation

Engineering Contradiction:

Improvemagnet flux detection accuracyVSAvoiddetection availability

Core Design Contradiction:

Measurement precisionVSEase of operation

Solution Approach 1:

The patent replaces the mechanical rotation requirement with an electrical measurement method. By applying a voltage command to the motor and measuring the resulting current, the system can calculate magnet flux without requiring the motor to rotate mechanically. This substitutes a mechanical system (motor rotation) with an electrical measurement system.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The motor itself serves as the measurement device. By utilizing the motor's own electrical characteristics (voltage-current relationship) and control system, the patent enables the motor to self-diagnose its magnet flux state without requiring external testing equipment or rotation mechanisms.

Inventive Principle:

Principle #25Self-service

2Reliability

If positive/negative bias current is applied to detect demagnetize state through magnetic saturation, then the demagnetize state can be detected, but a long detection time is required and the magnet flux amount cannot be estimated

Engineering Contradiction:

Improvedemagnetize detection accuracyVSAvoiddetection time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The patent changes the measurement parameter from detecting magnetic saturation (binary state) to measuring the voltage-current relationship characteristics (continuous parameter). By analyzing the slope or impedance derived from voltage and current measurements, the system can both detect demagnetize states and estimate the actual magnet flux amount, providing more information in a single measurement.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

Instead of applying sufficient bias current to reach magnetic saturation (excessive action requiring large current and time), the patent uses partial action by measuring the voltage-current relationship at normal operating current levels. This allows detection and estimation without requiring the motor to be driven into saturation, reducing both current requirements and detection time.

Inventive Principle:

Principle #16Partial or excessive action

3Measurement precision

If the motor rotates at sufficient speed to detect magnet flux, then the demagnetize state can be detected, but the detection cannot be performed in the halt state or low speed operation

Engineering Contradiction:

Improvemagnet flux detection accuracyVSAvoidmotor rotational speed

Core Design Contradiction:

Measurement precisionVSSpeed

Solution Approach 1:

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

Enables precise and rapid estimation of magnet flux and detection of demagnetization without rotating the motor, improving torque precision and reducing detection time and current requirements.

Implementation Method 1

an inductance-equivalent value determination module that determines an inductance-equivalent value of a d-axis

Methodology Applied

Scientific EffectElectrical Inductance: Inductor

Implementation Method 2

a magnet flux amount estimator that calculates an estimation value of a magnet flux amount of the permanent magnet, based on the inductance-equivalent value

Methodology Applied

Scientific EffectMagnetic Flux: Magnetic Field

Data Source

PatentEP2770625B1Magnet flux amount estimation device, abnormal demagnetize determination device, synchronous motor driving device, and electric motor car

Publication Date: 2019.12.18 KK TOSHIBA

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AI summary

According to one embodiment, a magnet flux amount estimation device includes a magnetic pole position detector (8) configured to detect a magnetic pole position of a permanent magnet synchronous motor (7) including a permanent magnet within a rotor; an inductance-equivalent value determination module (10) configured to determine an inductance-equivalent value of a d-axis corresponding to a determined magnetic pole direction; and a magnet flux amount estimator (11) configured to calculate an estimation value of a magnet flux amount of the permanent magnet, based on the inductance-equivalent value.