N-Phase Power Conversion Control for Harmonic and Torque Suppression
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Solution Overview
Problem
Conventional power conversion devices experience increased neutral point potential and harmonic components near the maximum modulation factor, leading to noise and torque unevenness when driving motors.
Innovation Solution
A power conversion device that converts DC power into n-phase AC power, where n is an odd number of 3 or more, outputs an n-phase voltage based on a modulation factor, using a waveform obtained by subtracting a common offset wave from sinusoidal waveforms, suppressing high-order harmonics and reducing noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If conventional PWM control is used near maximum modulation factor, then output voltage amplitude is maximized, but neutral point potential increases and harmonic components increase causing noise and torque unevenness
Solution Approach 1:
The patent applies parameter changes by modifying the voltage command values based on the modulation factor. When the modulation factor exceeds the first threshold, the system changes the voltage command values to have different amplitudes in different phases, which suppresses the neutral point potential and reduces high-order harmonics while maintaining high output voltage amplitude.
Solution Approach 2:
The patent implements dynamics by dynamically adjusting the voltage command values according to the modulation factor. The control unit continuously monitors the modulation factor and switches between different voltage command value strategies (equal amplitude vs. different amplitude) based on whether the modulation factor exceeds the threshold, enabling adaptive suppression of harmonics and noise during high-power operation.
2Device complexity
If voltage command values have equal amplitude in all phases, then control is simple, but neutral point potential increases causing torque unevenness
Solution Approach 1:
The patent changes the parameter of voltage command value amplitudes from equal to unequal when the modulation factor exceeds the threshold. This parameter change suppresses the neutral point potential and reduces torque unevenness, while the control unit manages the complexity by implementing a clear threshold-based switching strategy.
Solution Approach 2:
The patent segments the control strategy into two distinct modes: one for low modulation factors (equal amplitude voltage commands) and another for high modulation factors (different amplitude voltage commands). This segmentation allows the system to maintain simplicity when possible and apply complexity only when necessary to suppress torque unevenness and neutral point potential.
Data Source
AI summary
A power conversion device converts DC power into n-phase AC power. A first voltage and a second voltage lower than the first voltage are applied to the power conversion device, and the power conversion device outputs an n-phase output voltage based on a modulation factor. n is the number of phases of the AC output, and is an odd number of 3 or more. At a low modulation factor equal to or less than a first modulation factor, the output voltage becomes a sinusoidal output. At the second modulation factor larger than the first modulation factor, the output voltage is switched every electrical angle π/n between the phase in which the output voltage is fixed to the maximum voltage and the phase in which the output voltage is fixed to the minimum voltage.