Motor Control Third-Harmonic Correction for Stable PWM Waveforms
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Solution Overview
Problem
Existing motor control devices that superimpose a third harmonic on three-phase voltage command values to improve voltage utilization ratio may generate noise due to abrupt changes in waveforms, particularly when calculating the harmonic as an average between maximum and minimum phase voltage command values.
Innovation Solution
A motor control device that includes a voltage command value calculation unit, a third harmonic calculation unit, an amplitude calculation unit, a third harmonic conversion unit, and a correction unit to calculate and correct the third harmonic, mitigating abrupt changes by subtracting the corrected third harmonic from the three-phase voltage command values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a third harmonic is superimposed on three-phase voltage command values to improve voltage utilization ratio, then voltage utilization ratio is improved, but noise is generated due to abrupt change points in waveforms
Solution Approach 1:
The patent applies preliminary action by calculating the third harmonic in advance based on the voltage command values, then applying a correction coefficient to mitigate abrupt changes before the harmonic is superimposed on the PWM duty ratios. This pre-correction prevents noise generation while maintaining voltage utilization improvement.
Solution Approach 2:
The patent changes the parameter of the third harmonic by introducing a correction coefficient that adjusts the harmonic's amplitude or characteristics. This modification reduces abrupt changes in the waveform while preserving the voltage utilization benefits, thereby suppressing noise generation.
2Productivity
If the average value between maximum and minimum phase voltage command values is used to calculate the third harmonic, then voltage utilization ratio is improved, but abrupt change points occur in waveforms after superimposition
Solution Approach 1:
The correction coefficient is calculated in advance based on the voltage command values and their derivatives, allowing the system to pre-adjust the third harmonic to prevent abrupt waveform changes before they occur during PWM generation.
Solution Approach 2:
The patent uses feedback by calculating the derivative of the voltage command values and using this information to determine the correction coefficient. This feedback mechanism allows the system to adaptively adjust the third harmonic to maintain waveform stability while improving voltage utilization.
Data Source
AI summary
A motor control device includes a third harmonic calculation unit configured to calculate a first third harmonic on a basis of an average value between a voltage command value of a maximum phase with a maximum duty ratio and a voltage command value of a minimum phase with a minimum duty ratio among three-phase voltage command values; an amplitude calculation unit configured to calculate an amplitude of the three-phase voltage command values; a third harmonic conversion unit configured to convert the first third harmonic into a second third harmonic on a basis of the first third harmonic and the amplitude; a correction unit configured to correct the three-phase voltage command values by subtracting the second third harmonic from the three-phase voltage command values.