Induction Machine Magnetizing Curve Determination via Square-Wave Excitation
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Solution Overview
Problem
Existing methods for determining the magnetizing curve of induction machines are either sensitive to sampling errors, computationally demanding, or not suitable for accurate vector control, especially in high-speed operations where optimal magnetizing inductance updating is challenging.
Innovation Solution
A system that applies a square-wave excitation to the induction machine's phases to determine stator and rotor resistances, calculating a magnetizing curve based on these resistances, and using this curve to control the machine's operation, allowing for individualized magnetizing inductance identification and updating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If single-phase sinusoidal excitations at different frequencies are applied to imitate locked rotor and no-load situations, then rotor resistance identification can be achieved, but the solution becomes very sensitive to sampling errors resulting in large rotor resistance identification error
Solution Approach 1:
The patent applies periodic square-wave excitations at two specific frequencies (first frequency and second frequency) to the induction machine. This periodic excitation approach allows for determining rotor resistance by comparing responses at different frequencies while maintaining robustness against sampling errors through the structured periodic nature of the excitation signals.
Solution Approach 2:
The patent changes the excitation frequency parameter by applying square-wave excitations at two distinct frequencies. This parameter variation enables the determination of rotor resistance by analyzing the difference in machine responses at these frequencies, thereby improving identification accuracy while reducing sensitivity to sampling errors.
2Measurement precision
If recursive least squares algorithm is used for magnetizing curve identification, then high precision can be achieved, but computational demands become too high leading to long operation cycle
Solution Approach 1:
The patent extracts only the essential information needed for magnetizing curve identification by using simple square-wave excitations and basic electrical measurements. This extraction approach achieves sufficient accuracy without requiring the full computational power of recursive least squares algorithms, thereby reducing operation cycle time while maintaining acceptable precision.
Solution Approach 2:
The patent uses computationally inexpensive methods (simple resistance measurements and basic calculations) instead of computationally intensive algorithms. This approach sacrifices some computational complexity to achieve faster operation cycles, making the system more suitable for real-time control applications.
3Ease of manufacture
If curve fitting algorithms with explicit functions are used for magnetizing curve identification, then coefficients can be solved from magnetizing inductance estimation values, but the real magnetizing curve relies on no definite function making these methods not the best choice for accurate vector control
Solution Approach 1:
The patent enables the induction machine itself to provide the necessary information for magnetizing curve identification through its natural response to square-wave excitations. By measuring the machine's own electrical characteristics (currents, voltages, resistances) during simple excitation tests, the system self-determines its magnetizing parameters without requiring external curve fitting or assumed mathematical functions.
Data Source
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AI summary
A system for identifying magnetizing inductance and rotor resistance of an induction machine comprises an induction machine comprising a rotor and a stator, a DC voltage bus, and a DC-to-AC voltage inverter coupled to the DC voltage bus and to the induction machine. The system also comprises a controller configured to cause the DCto- AC voltage inverter to apply a square-wave excitation to a plurality of phases of the induction machine, determine a stator resistance of the stator of the induction machine based on the square-wave excitation, and determine a rotor resistance of the rotor of the induction machine based on the square-wave excitation. The controller is also configured to calculate a magnetizing curve for the induction machine based on the stator and rotor resistances and control the induction machine to operate based on the magnetizing curve.