Rotor Position Detection Using Low-Frequency Admittance
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Solution Overview
Problem
Existing methods for determining the rotor position of electrically excited synchronous machines at standstill or low speeds are imprecise due to low induced voltages and interference from disturbance variables, especially in medium-voltage converters with long modulation periods, leading to uncontrolled machine movement and measurement errors.
Innovation Solution
A method involving impressing voltage test signals at multiple space vector angles with a fundamental frequency, determining Fourier coefficients of the resulting excitation and stator currents, and using indicator variables to accurately determine the rotor position, while minimizing harmonic components and optimizing voltage pulse directions for medium-voltage converters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If induced voltage curves are used to determine rotor position at low speeds, then the method is simple to implement, but measurement precision deteriorates due to low induced voltages and disturbance variables
Solution Approach 1:
The patent changes the frequency parameter of the test signals to a specific range (1-10 Hz) where the electrical machine exhibits maximum admittance difference between d and q axes. This frequency optimization enables precise rotor position detection at standstill and low speeds by exploiting the machine's inherent frequency-dependent characteristics, resolving the contradiction between implementation simplicity and measurement precision.
2Loss of information
If high-frequency voltage pulses are impressed to determine rotor position, then rotor position information can be obtained, but damper windings prevent accurate evaluation of saturation state
Solution Approach 1:
The patent changes the frequency parameter from high-frequency to low-frequency range (1-10 Hz), which allows the test signals to penetrate through the damper windings effectively. At these lower frequencies, the damper windings do not impede the evaluation of saturation state, enabling accurate rotor position determination while overcoming the limitation imposed by damper windings.
3Device complexity
If voltage test signals are impressed in arbitrary directions based on previous measurements, then the evaluation process is simplified, but measurement precision deteriorates in medium-voltage converters with long modulation periods
Solution Approach 1:
The patent applies preliminary action by pre-defining specific space vector directions for voltage test signals before actual measurement. This predetermined approach ensures that test signals are applied in optimal directions that maximize the admittance difference effect, thereby improving measurement precision in medium-voltage converters with long modulation periods while maintaining evaluation simplicity.
4Productivity
If the electrical machine is accelerated quickly to high speed, then the system responds faster, but rotor position control is lost at standstill and low speeds
Solution Approach 1:
The patent applies preliminary action by determining the initial rotor position at standstill using low-frequency test signals before acceleration begins. This preliminary position determination ensures reliable rotor position knowledge is established before the machine accelerates to high speed, allowing for controlled acceleration and maintaining reliability throughout the speed transition.
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 approach provides a more reliable and robust determination of the rotor position, reducing measurement errors and ensuring controlled operation even at low speeds, particularly in medium-voltage converters with long modulation periods.
Implementation Method 1
Impressing voltage test signals into the stator winding (31) with an excitation current flowing through the excitation winding (32) of the rotor (33)
Implementation Method 2
determining the respective resulting values of an excitation current indicator variable as Fourier coefficients of the excitation current resulting from the voltage test signal with respect to the fundamental frequency of the voltage test signal
Data Source
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AI summary
The invention relates to a method for determining the rotor position of an electrically excited electric machine (3), comprising the following steps: - applying voltage test signals at several space vector angles with a fundamental frequency that lies in a frequency range in which an admittance difference exists, particularly when the space vector angles are offset by 90°; - determining the respective resulting values of an excitation current indicator quantity as Fourier coefficients of the excitation current resulting from the voltage test signal with respect to the fundamental frequency of the voltage test signal at the corresponding space vector angles; and - determining the rotor position based on the course of the excitation current indicator quantity.- Determining the respective resulting values of a stator current indicator quantity as Fourier coefficients of the stator current resulting from the voltage test signal with respect to the fundamental frequency of the voltage test signal at the corresponding space vector angles; and - Determining the rotor position based on the course of the stator current indicator quantity.