Rotary Machine Inductance Measurement via Constant DC Voltage
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Solution Overview
Problem
Existing methods for measuring the inductance of rotary machines require high-performance A/D converters or microcomputers for fast sampling, cause vibration and noise due to prolonged current flow, and cannot accurately measure magnetic saturation characteristics.
Innovation Solution
A control device with a voltage instruction generation section, voltage application section, and current detection section that applies constant DC voltages and calculates inductance from selected voltage instructions and current measurements, reducing the need for high-speed sampling and minimizing current flow duration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If fast sampling is performed to accurately measure current changes during inductance measurement, then measurement precision is improved, but device complexity increases due to need for high-performance A/D converters and microcomputers
Solution Approach 1:
The patent changes the measurement approach from fast transient sampling to steady-state comparison. By applying different constant DC voltages and measuring steady-state currents, the system avoids the need for high-speed sampling while achieving accurate inductance measurement through the relationship L = V/(di/dt) where di/dt is calculated from steady-state current values.
2Measurement precision
If AC current is continuously applied to measure magnetic saturation characteristics, then measurement accuracy is improved, but vibration and noise increase
Solution Approach 1:
Instead of continuous AC current application, the patent uses periodic application of constant DC voltages at different levels. By sequentially applying DC voltages and measuring steady-state currents, the system obtains magnetic saturation characteristics without continuous electromagnetic excitation that causes vibration and noise.
3Measurement precision
If current is flown for extended period to obtain accurate inductance measurement, then measurement precision is improved, but productivity decreases due to longer measurement time
Solution Approach 1:
The patent applies constant DC voltages in advance to establish steady-state currents before measurement. By pre-establishing the current conditions and then quickly switching between different voltage levels to compare steady-state currents, the system achieves accurate inductance measurement without requiring extended measurement periods.
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 allows for accurate measurement of inductance without high-performance A/D converters, suppresses vibration and noise, and enables the measurement of magnetic saturation characteristics, improving rotary machine controllability.
Implementation Method 1
voltage for causing DC excitation is applied to an induction electric motor, the induction electric motor is maintained in a stopped state, a signal for slightly changing secondary magnetic flux due to the DC excitation
Implementation Method 2
a d-axis current step instruction having a predetermined height is given to the control device, voltage corresponding to voltage drop due to a primary resistance of an electric motor is subtracted from a d-axis voltage instruction value
Data Source
AI summary
A control device for rotary machine includes: a voltage instruction generation section for generating a voltage instruction; a voltage application section for applying voltage to a rotary machine based on the voltage instruction; a current detection section for detecting rotary machine current of the rotary machine; and an inductance calculation section for calculating an inductance of the rotary machine from the voltage instruction and the rotary machine current. The voltage instruction generation section generates voltage instructions of constant DC voltages. The voltage application section applies voltages to the rotary machine based on the voltage instructions. The inductance calculation section calculates the inductance from a voltage instruction for measurement arbitrarily selected from the voltage instructions, and the rotary machine currents detected by the current detection section before and after application of the voltage instruction for measurement.