Rotating Machine Inverter Control for Accurate Two-Phase Current Detection

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Existing control devices for rotating machines, particularly those using inverters with shunt resistors, face challenges in accurately detecting currents, leading to reduced torque accuracy, increased vibration, and noise due to incorrect current detection.

Innovation Solution

A control device for rotating machines that includes an inverter, a current detector, and a controller. The controller generates torque and weakened field current command values to restrict the modulation rate of the inverter, ensuring the current detector can accurately detect at least two phases of the rotating machine current.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If weakened field control is implemented to expand operational range, then speed and torque features are improved, but current detection accuracy deteriorates

Engineering Contradiction:

Improveoperational rangeVSAvoidcurrent detection accuracy

Core Design Contradiction:

Adaptability or versatilityVSMeasurement precision

Solution Approach 1:

The patent changes the modulation rate parameter to resolve the contradiction. By restricting the modulation rate to a first threshold value or less during weakened field control, the patent ensures that at least two phases of the rotating machine current can be detected by the current detector, thereby maintaining current detection accuracy while expanding the operational range through weakened field control

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent dynamically adjusts the modulation rate based on the detection mode. When operating in a mode where current detection is required (such as during weakened field control), the modulation rate is restricted to ensure detectability. This dynamic parameter adjustment allows the system to maintain both expanded operational range and accurate current detection

Inventive Principle:

Principle #15Dynamics

2Speed

If modulation rate is increased to improve control performance, then response speed is improved, but current detection capability deteriorates

Engineering Contradiction:

Improveresponse speedVSAvoidcurrent detection capability

Core Design Contradiction:

SpeedVSMeasurement precision

Solution Approach 1:

The patent applies parameter changes by setting the modulation rate to a first threshold value or less when current detection is required. This parameter restriction ensures that the inverter's output frequency and voltage maintain a relationship that allows the current detector to accurately detect at least two phases of the rotating machine current, preventing detection failure while still maintaining adequate response speed

Inventive Principle:

Principle #35Parameter changes

3Adaptability or versatility

If conventional weakened field control is used without modulation rate restriction, then operational range is expanded, but torque accuracy deteriorates

Engineering Contradiction:

Improveoperational rangeVSAvoidtorque accuracy

Core Design Contradiction:

Adaptability or versatilityVSManufacturing precision

Solution Approach 1:

The patent changes the modulation rate parameter to a first threshold value or less during weakened field control. This parameter restriction ensures accurate current detection, which is essential for calculating accurate torque values. By maintaining current detection accuracy while implementing weakened field control, the patent preserves torque accuracy across the expanded operational range

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent uses feedback from the current detector to maintain torque accuracy. By ensuring that at least two phases of current can be detected through modulation rate restriction, the system obtains accurate feedback information needed to calculate precise torque values, thereby maintaining torque accuracy even when operating in the expanded range through weakened field control

Inventive Principle:

Principle #23Feedback

Data Source

PatentUS20250132710A1Control device of rotating machine, and electric power steering device

Publication Date: 2025.04.24 MITSUBISHI ELECTRIC CORP

AI summary

A rotating machine control device includes: an inverter that applies a voltage; a current detector provided in the inverter detecting current that flows through, and a controller outputting a voltage command value to the inverter based on a control command, wherein the controller has: a torque current command value generator calculating a torque current command value based thereon; a weakened field current command value generator for calculating a weakened field current command value, and a voltage command value calculator calculating voltage command value based on current command values of the torque and the weakened field, and the weakened field current command value generator outputs a first weakened field current command value as the weakened field current command value, wherein the first weakened field current command value restricts a modulation rate of the inverter to a first threshold value so the current detector is capable of detecting at least two phases.