Motor Control Circuit Delay Compensation for Harmonic Reduction
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Solution Overview
Problem
In the control of triphase electric motors, existing field-oriented control (FOC) techniques face accuracy issues due to voltage harmonics generated by inverters, which introduce higher order current harmonics, and the use of low-pass filters to reduce noise introduces time delays that complicate precise current measurement.
Innovation Solution
A control circuit that includes a measuring device, analog-to-digital converters, and a measure control circuit to generate a timing signal that compensates for delays introduced by the measuring device, allowing current measurements at specific instants to minimize the contribution of higher order harmonics, thereby reducing control errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If low-pass filters are used to reduce noise in current measurements, then measurement reliability is improved, but time delay is introduced causing measurement precision to deteriorate
Solution Approach 1:
The system pre-calculates the time delay introduced by the low-pass filter based on the PWM frequency and filter characteristics. This preliminary determination of delay allows the control system to compensate for the timing error by adjusting the measurement timing accordingly, thus maintaining measurement precision while still using the filter for noise reduction.
2Ease of operation
If current measurements are taken at arbitrary instants, then ease of operation is improved, but control accuracy deteriorates due to higher order current harmonics contribution
Solution Approach 1:
The system implements periodic measurement of phase currents at specifically timed instants within each PWM cycle. By synchronizing measurements to occur at predetermined times (such as when voltage switches state), the system eliminates higher order current harmonics contribution while maintaining operational simplicity through automated periodic sampling.
3Productivity
If inverter is used to drive motor with PWM, then productivity is improved, but measurement precision deteriorates due to voltage harmonics generating higher order current harmonics
Solution Approach 1:
The system uses feedback from the measured phase currents to continuously monitor and detect the time delay introduced by measurement circuits. This feedback mechanism allows the control system to dynamically adjust measurement timing or apply compensation algorithms, thereby maintaining high measurement precision despite the presence of PWM-generated voltage harmonics and higher order current harmonics.
Data Source
AI summary
A control circuit controls an electric motor and includes: a measuring device configured to measure a first phase current of the motor and provide a corresponding first analog signal; an analog-to-digital converter structured to convert the first analog signal into a first digital signal; a conversion module for generating a first converted digital signal representative of the first digital signal expressed in a rotating reference system; a node structured to compare the first converted digital signal into a first reference signal and generate a first error signal; and a measure control circuit structured to provide a timing signal of the analog-to-digital converter depending on the first error signal and a time delay introduced by the measuring device.