Induction Motor Rotor Time Constant Estimation via Q-Axis Voltage
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Solution Overview
Problem
Conventional methods for estimating the rotor time constant of induction motors are inadequate, especially at high speeds and varying load conditions, leading to inconsistent torque generation and performance in hybrid electric vehicles (HEVs) and electric vehicles (EVs), as they rely on d-axis voltage changes which are insufficient for accurate detection.
Innovation Solution
An apparatus that estimates rotor time constant using a combination of q-axis voltage estimation, proportional integral control, and reference tables based on temperature and d-axis current, allowing for accurate compensation and maintaining consistent torque generation across varying conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If d-axis voltage is used for rotor time constant estimation, then the method can be implemented with existing control signals, but the voltage change is too small to accurately detect rotor time constant changes
Solution Approach 1:
The patent introduces q-axis voltage as an intermediary signal to indirectly detect rotor time constant changes. Instead of directly measuring the small d-axis voltage changes, the system uses q-axis voltage which exhibits larger changes in response to rotor time constant variations, thereby improving detection accuracy through a mediator signal
Solution Approach 2:
The patent changes the measurement parameter from d-axis voltage to q-axis voltage. By switching to a different electrical parameter (q-axis voltage instead of d-axis voltage), the system captures larger signal variations that are more sensitive to rotor time constant changes, especially under light load and high speed conditions
2Measurement precision
If d-axis voltage multiplication by speed or d-axis current is attempted to amplify the signal, then the detection sensitivity improves, but the method still fails at high speed operation where d-axis voltage changes remain insufficient
Solution Approach 1:
The patent creates a universal estimation method using q-axis voltage that works across all operating conditions (light load, heavy load, low speed, high speed). Unlike the d-axis voltage method which requires different approaches for different conditions, the q-axis voltage method provides consistent detection performance throughout the entire operating range
Solution Approach 2:
Instead of trying to amplify the weak d-axis voltage signal through multiplication operations, the patent inverts the approach by selecting q-axis voltage from the beginning, which naturally provides sufficient signal magnitude without requiring amplification operations
3Reliability
If conventional estimation methods are used, then the system structure remains simple, but torque generation becomes inconsistent under varying temperature and load conditions
Solution Approach 1:
The patent implements feedback by continuously estimating rotor time constant using q-axis voltage and using this estimation to adjust the flux reference. This closed-loop feedback mechanism compensates for rotor time constant changes due to temperature and load variations, maintaining consistent torque generation
Solution Approach 2:
The patent replaces physical temperature sensors or complex measurement systems with an electrical measurement approach using q-axis voltage. This substitution provides accurate rotor time constant estimation through electrical signals rather than requiring additional mechanical or thermal sensing components
Data Source
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AI summary
An apparatus for estimating rotor time constant of induction motor, the apparatus being such that d-axis and q-axis current commands are received to output q-axis voltage command, to output q-axis voltage estimate, to output a changed value of rotor time constant, which is a difference between the q-axis voltage command and the q-axis voltage estimate, and to add the changed value of the rotor time constant to a rotor time constant, whereby the changed rotor time constant is outputted.