AC Motor Control via Envelope Extraction for Sensorless Positioning
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Solution Overview
Problem
Existing AC motor control methods face challenges in accurately estimating motor position and speed, especially at zero speed, due to noise in high-frequency test signals and low responsiveness caused by filtering processes.
Innovation Solution
An AC motor control apparatus incorporating a voltage controller, square-wave voltage generator, current detector, coordinate transformation sections, and envelope extractor, which uses time-averaged command voltage vectors and square-wave voltage commands to control voltage amplitudes and phases, and extracts envelopes from motor currents to estimate magnetic-pole position and speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If high-frequency test signals are applied to estimate motor position and speed, then estimation can be performed over a range from zero speed to high speed, but noise occurs in the frequency band of the test signals and responsiveness becomes low due to filtering
Solution Approach 1:
The patent applies periodic square-wave voltage commands to the motor at specific time intervals. By using periodic excitation signals with defined periods (Ts1, Ts2), the system can estimate position and speed through the motor's response to these periodic inputs, enabling operation from zero speed to high speed while maintaining estimation accuracy through synchronized detection
Solution Approach 2:
The patent extracts envelope signals from the motor currents that result from applying square-wave voltage commands. By extracting only the envelope components (which contain position and speed information) rather than processing the entire high-frequency signal spectrum, the system avoids noise contamination while maintaining responsiveness in position and speed estimation
2Measurement precision
If filters are used to extract currents or voltages at test signal frequencies, then position and speed can be estimated, but responsiveness becomes low and noise is introduced
Solution Approach 1:
The patent replaces traditional filtering methods with envelope extraction and coordinate transformation techniques. Instead of using filters that process the entire frequency spectrum and introduce delay, the system transforms motor currents into rotating coordinate systems and extracts envelope signals, achieving accurate position and speed estimation without the responsiveness loss and noise introduction associated with conventional filtering
Solution Approach 2:
The patent introduces intermediate processing steps including coordinate transformation to rotating reference frames and envelope extraction as mediators between the raw motor currents and the final position/speed estimates. These intermediary transformations isolate the useful information (envelope signals containing position and speed) from the noisy high-frequency components without requiring broad-spectrum filtering
3Measurement precision
If square-wave voltage commands are applied and envelope extraction is performed, then accurate position and speed estimation is achieved without delay, but the system complexity increases
Solution Approach 1:
The patent segments the control process into distinct functional modules: square-wave voltage generation, coordinate transformation sections, envelope extraction units, and position/speed computation blocks. This segmentation allows each module to perform a specific function efficiently, making the overall complex system manageable and implementable through modular design while achieving accurate and responsive estimation
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 solution enables accurate and responsive estimation of magnetic-pole position and speed without delay, even at zero speed, improving torque, speed, and position control performance without the need for position or speed sensors.
Implementation Method 1
The coordinate transformation section is configured to perform coordinate transformation to transform detected values of the motor currents into two-phase currents in a coordinate system at rest
Implementation Method 2
The envelope extractor is configured to take, as inputs, the two-phase currents, configured to extract two-phase currents as waveforms having amplitudes that periodically change from the input two-phase currents, and configured to extract envelopes connecting vertices of the amplitudes of the waveforms
Implementation Method 3
a method in which the position and speed of a motor are estimated using inductance characteristics (a magnetic saliency) that depend on a magnetic-pole position of the motor
Data Source
AI summary
An alternating-current motor control apparatus includes a voltage controller configured to output a command voltage vector so that the command voltage vector is time-averaged for time periods, a square-wave voltage generator configured to control, every time period, amplitudes and phases of voltages to be applied to an alternating-current motor, a current detector configured to detect motor currents at a timing synchronized with periods 1/N-th of the time periods, where N is equal to or larger than one, a coordinate transformation section configured to perform coordinate transformation to transform the motor currents into two-phase currents, an envelope extractor configured to extract two-phase currents as waveforms having amplitudes that periodically change from the two-phase currents, and extract envelopes of the waveforms, and a magnetic-pole-position computing section configured to compute a magnetic-pole position using the envelopes.