Inverter PWM Modulation Factor Control for Harmonic Reduction
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Solution Overview
Problem
Conventional power conversion devices for AC motors experience higher vibrations and noise due to harmonics in the inverter output voltage, as the modulation factor is not optimized to reduce specific harmonic orders, which can coincide with the resonance frequency of the apparatus.
Innovation Solution
A power conversion device with a converter, inverter, capacitor, and control unit that adjusts the capacitor voltage and fixes the PWM modulation factor to reduce specific harmonics in the inverter output voltage, allowing operation at variable voltages and frequencies while minimizing harmonic components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the modulation factor is fixed and DC voltage is varied to control inverter output voltage in higher frequency regions, then the inverter output voltage can be controlled, but harmonics of predetermined order cannot be reduced causing higher vibrations and noises
Solution Approach 1:
The patent applies dynamics by making the modulation factor adjustable rather than fixed. The control unit dynamically changes the modulation factor based on the operating frequency range to achieve both voltage control and harmonic reduction. In higher frequency regions, the modulation factor is specifically set to values that reduce predetermined order harmonics while maintaining the required output voltage through DC voltage variation.
Solution Approach 2:
The patent changes the modulation factor parameter to specific values that reduce harmonics of predetermined order. By selecting particular modulation factor values in higher frequency regions, the invention transforms the voltage control approach into one that simultaneously addresses harmonic reduction, thereby reducing vibrations and noises caused by resonance.
2Power
If the modulation factor is varied to control inverter output voltage in lower frequency regions with fixed DC voltage, then the inverter output voltage can be controlled, but harmonics are not optimized causing potential resonance issues
Solution Approach 1:
The control unit dynamically adjusts the modulation factor based on the operating frequency range. In lower frequency regions, the modulation factor is varied to control output voltage while transitioning to fixed modulation factor with DC voltage variation in higher frequency regions, optimizing harmonic performance across the entire operating range.
Solution Approach 2:
The patent implements periodic action by using different control strategies for different frequency regions. The control unit periodically switches between modulation factor variation (lower frequencies) and DC voltage variation with fixed modulation factor (higher frequencies), ensuring optimal performance and harmonic reduction across the complete operating spectrum.
Data Source
AI summary
A power conversion device includes a converter-inverter controller for controlling a converter and an inverter. The power conversion device further includes a DC capacitor connected between the converter and the inverter and a DC capacitor voltage detector for detecting a DC capacitor voltage Efc between the connection ends of the DC capacitor. The converter-inverter controller provides variable control on the DC capacitor voltage Efc to the converter on the basis of the motor frequency of an AC motor, the DC capacitor voltage Efc, and a pulse mode. Within a predetermined range of motor frequencies, the converter-inverter controller fixes the PWM modulation factor of the inverter to a value m0 and provides operation control to the inverter, where the value m0 being to reduce a harmonic of a predetermined order included in the output voltage from the inverter.