Induction Machine Rotor Time Constant Estimation via Sine-Wave Injection
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Solution Overview
Problem
Existing methods for estimating the rotor time constant of an induction machine are prone to errors due to uncertainties in stray inductance calculations, particularly caused by eddy currents and saturation effects.
Innovation Solution
A method involving the injection of a sine-wave current during DC magnetization, where the rotor time constant is calculated based on the induced voltage component, eliminating the need for accurate stray inductance measurements by using only stator and rotor resistance estimates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If current injection method is used to estimate rotor time constant, then estimation can be performed, but accuracy deteriorates due to uncertainties in stray inductance calculations caused by eddy currents and saturation effects
Solution Approach 1:
The invention extracts and eliminates the problematic stray inductance parameter from the estimation process. By using a test signal injection method during DC magnetization, the solution directly measures the rotor time constant through the relationship between injected current and induced voltage, bypassing the need to calculate stray inductance separately. This extraction of the essential measurement from the problematic calculation path resolves the accuracy-reliability contradiction.
Solution Approach 2:
The invention introduces a test signal (sine-wave current during DC magnetization) as an intermediary to facilitate the measurement. This test signal acts as a mediator that enables direct observation of the rotor time constant through the induced voltage response, avoiding the need to rely on uncertain stray inductance calculations. The intermediary test signal transforms the measurement problem into a direct observation problem.
2Measurement precision
If multiple parameters including stray inductance are measured to calculate rotor time constant, then comprehensive data is obtained, but measurement complexity increases and uncertainty propagates
Solution Approach 1:
The invention extracts only the essential measurement needed for rotor time constant estimation. Instead of measuring multiple parameters (stator resistance, rotor resistance, stray inductance, main inductance), the method directly injects a test signal and measures the induced voltage to obtain the rotor time constant in one step. This extraction principle reduces measurement complexity while maintaining or improving accuracy.
Solution Approach 2:
The invention inverts the traditional measurement approach. Rather than measuring multiple parameters and calculating the rotor time constant through complex formulas involving stray inductance, the method directly measures the rotor time constant by observing the induced voltage response to a known test current injection. This inversion simplifies the measurement system while improving reliability.
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
This method provides a simple and accurate estimation of the rotor time constant, allowing for precise calculation of the main inductance, with improved accuracy and reduced uncertainty compared to previous methods.
Implementation Method 1
a sine-wave current is injected into the stator. The induced voltage is measured in the direction of the injected current
Data Source
AI summary
A method for estimating the rotor time constant (τr) of an induction machine when the stator resistance (Rs) and rotor resistance (Rr) of the induction machine are known. The method comprises the steps of feeding a DC current to the stator of the induction machine, injecting a sine-wave current component into the stator of the induction machine, the current having an amplitude (isc) and an angular frequency (ωc), measuring the voltage component (uscd) of the stator voltage of the induction machine in the same direction and with the same angular frequency as the injected current, and calculating the rotor time constant using equationτr=1ωcuscd-Rsisc(Rs+RR)isc-uscd.