Induction Motor Speed Estimation Using m-t Axes
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Solution Overview
Problem
Existing speed sensorless vector control methods for induction motors face challenges in maintaining accurate speed control and preventing torque shortages due to changes in primary resistance values caused by coil temperature, leading to deteriorated control characteristics.
Innovation Solution
A power conversion device and method that utilizes a speed estimation calculation unit to convert command and detection values using a primary current direction and a 90-degree delayed direction as a rotating coordinate system, calculating speed estimation values on m-t axes to reduce sensitivity to primary resistance changes, thereby improving accuracy and stability of speed control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If speed sensorless vector control is implemented using a disturbance observer to estimate speed, then speed control can be achieved without a speed sensor, but torque shortage occurs in low speed range due to sensitivity to primary resistance changes
Solution Approach 1:
The patent changes the coordinate system parameters from the conventional d-q axes to m-t axes, where the m-axis aligns with the primary current direction and the t-axis is 90 degrees delayed. This parameter change in the coordinate system transformation reduces sensitivity to primary resistance variations, thereby preventing torque shortage in low speed range while maintaining sensorless operation capability
2Ease of manufacture
If conventional d-q axes coordinate system is used for speed estimation, then standard vector control can be implemented, but estimation error increases when primary resistance value changes with coil temperature
Solution Approach 1:
The patent transforms the coordinate system parameters from conventional d-q axes to m-t axes, redefining the transformation matrix to align the m-axis with the primary current direction. This parameter change makes the speed estimation less sensitive to primary resistance variations caused by temperature changes, thereby improving estimation accuracy while maintaining ease of implementation
3Measurement precision
If primary resistance value is used in speed estimation formula, then speed can be calculated from back electromotive force, but estimation error occurs when resistance value changes with temperature
Solution Approach 1:
The patent changes the coordinate system parameters to m-t axes, which reduces the sensitivity of the speed estimation formula to primary resistance value changes. By transforming the voltage and current equations into the m-t coordinate system, the estimation becomes less dependent on accurate primary resistance values, thereby maintaining accuracy across temperature variations
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
The method achieves highly accurate speed control characteristics with reduced torque shortages and low sensitivity to primary resistance variations, especially in low-speed ranges, by using the m-t axes coordinate system for speed estimation and control.
Implementation Method 1
induction motor speed estimation method and power conversion device using the induction motor speed estimation method
Data Source
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AI summary
The present invention relates to the speed sensorless vector control of an induction motor and the purpose thereof is to provide a speed estimation method capable of preventing torque shortage caused by the coil temperature inside the induction motor and obtaining highly accurate speed control characteristics and to provide a power conversion device using the speed estimation method. In order to achieve the above purpose, a power conversion device for driving an induction motor by speed sensorless vector control has: a coordinate conversion unit for converting a command value or a detection value to control axes using a primary current direction and a direction delayed by 90 degrees from the primary current direction as a rotating coordinate system; and a speed estimation calculation unit for calculating the speed estimation value of the induction motor on the basis of the command value or the detection value converted by the coordinate conversion unit. The power conversion device controls an output frequency value on the basis of the speed estimation value.