Sensorless AC Motor Control With Phase Imbalance Correction

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Solution Overview

Problem

Manufacturing variations in AC rotary machines lead to inductance imbalances among phases, reducing the accuracy of magnetic pole position detection and subsequent positioning control without using a position sensor.

Innovation Solution

An AC rotary machine control device that includes a control system to generate fundamental and high-frequency voltage commands, detects currents, calculates magnetic pole positions by extracting high-frequency currents, and adjusts imbalances among these currents using filters to improve position estimation accuracy.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If high-frequency voltage commands are applied to detect magnetic pole position without position sensors, then positioning control can be achieved without additional sensors, but manufacturing variations cause inductance imbalances that reduce detection accuracy

Engineering Contradiction:

Improvesensorless control implementationVSAvoidmagnetic pole position detection accuracy

Core Design Contradiction:

Ease of manufactureVSMeasurement precision

Solution Approach 1:

The patent applies gain correction to the high-frequency current components extracted from each phase. By adjusting the gain parameters for each phase based on detected imbalances, the system compensates for manufacturing variations in inductance values. This parameter adjustment restores the sinusoidal characteristics of the inductance variation and improves magnetic pole position detection accuracy while maintaining sensorless operation

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The system detects the actual high-frequency current components from each phase, compares them against expected values, and uses this feedback to calculate and apply correction gains. This closed-loop feedback mechanism continuously compensates for inductance imbalances caused by manufacturing variations, maintaining accurate position detection without requiring position sensors

Inventive Principle:

Principle #23Feedback

2Ease of manufacture

If manufacturing variations are present in the rotary machine, then production cost and ease of manufacture are improved, but inductance imbalances occur that reduce position estimation accuracy

Engineering Contradiction:

Improvemanufacturing toleranceVSAvoidposition estimation accuracy

Core Design Contradiction:

Ease of manufactureVSMeasurement precision

Solution Approach 1:

The patent converts the harmful effect of manufacturing variations into a beneficial correction process. By detecting the actual inductance imbalances through high-frequency current measurement and applying appropriate gain corrections, the system transforms the manufacturing defects into identifiable parameters that can be compensated. This approach allows standard manufacturing tolerances to be maintained while achieving accurate position estimation through active correction

Inventive Principle:

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

Data Source

PatentUS11799405B2Control device for AC rotary machine and control method for AC rotary machine

Publication Date: 2023.10.24 MITSUBISHI ELECTRIC CORP

AI summary

In sensorless control for a rotary machine, when variations in inductances for U, V, W phases due to manufacturing error are great, imbalance occurs among detected currents for the respective phases. Thus, estimation error of a magnetic pole position of a rotor increases, so that positioning accuracy is reduced. Correction filters for imparting gains in accordance with rotary machine constants for the respective phases are provided to control means or magnetic pole position calculation means, thereby correcting the imbalance occurring among the detected currents for the respective phases.