Power Conversion Device Suppressing Waveform Distortion
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Solution Overview
Problem
The two-phase modulation scheme in three-phase inverters causes waveform distortion and increases harmonic components in the output voltage, leading to higher zero-phase current due to discontinuous voltage commands.
Innovation Solution
A power conversion device that includes a controller generating a zero-phase voltage command using a two-phase modulation scheme and a third harmonic component of the three-phase voltage commands, which is added to correct each phase voltage command to suppress waveform distortion by comparing them with a carrier wave for switching control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a two-phase modulation scheme is applied to reduce switching loss, then switching loss is reduced, but waveform distortion occurs in the output voltage
Solution Approach 1:
The patent applies parameter changes by adding a third harmonic component to the voltage commands of two phases. This modifies the voltage command parameters to ensure continuity when switching between phases, thereby reducing waveform distortion while maintaining the reduced switching frequency benefit of the two-phase modulation scheme
Solution Approach 2:
The third harmonic component acts as an intermediary element that bridges the discontinuity between voltage commands of different phases. By introducing this intermediate signal, the patent smooths the transitions and eliminates the waveform distortion that would otherwise occur in the two-phase modulation scheme
2Loss of energy
If voltage commands are corrected in two-phase modulation, then switching loss is reduced, but discontinuity occurs in voltage commands causing harmonic components
Solution Approach 1:
The patent changes the parameter of the voltage command by superimposing a third harmonic component. This parameter modification ensures that the voltage commands remain continuous during phase switching, preventing the information loss (discontinuity) that would otherwise occur while maintaining the switching loss reduction benefit
3Device complexity
If two-phase modulation is used to simplify control, then device complexity is reduced, but zero-phase current increases
Solution Approach 1:
By changing the voltage command parameters through third harmonic addition, the patent eliminates the discontinuity that causes zero-phase current. This maintains the simplified control structure of two-phase modulation while removing the harmful zero-phase current effect
Data Source
AI summary
A power conversion device includes: a three-phase inverter including a plurality of switching elements; and a controller configured to PWM-control the three-phase inverter based on three phase voltage commands. The controller generates a zero-phase voltage command using a two-phase modulation scheme and a third harmonic component of the three phase voltage commands. The controller adds the generated zero-phase voltage command to each of the three phase voltage commands to thereby correct each of the three phase voltage commands. The controller compares each of the corrected three phase voltage commands with a carrier wave, to thereby generate a control signal for controlling switching of the plurality of switching elements.