Inverter Offset Current Generation for Harmonic Distortion Reduction
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Solution Overview
Problem
Inverter devices face damage from returning electric current due to shutdown, leading to increased total harmonic distortion of the current when operated in boundary conduction mode, which existing methods fail to effectively mitigate.
Innovation Solution
An inverter device with a detection unit and control unit that generates an offset current to be superposed with the AC current, adjusting the PWM signal's duty cycle based on the current harmonic component to reduce total harmonic distortion, where the offset current's RMS value and frequency match those of the harmonic component.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the inverter operates in boundary conduction mode and stops operation near zero crossing point to prevent damage from returning current, then the reliability of the inverter is improved, but the total harmonic distortion of the current increases
Solution Approach 1:
The control unit proactively generates an offset current in advance to counteract the current harmonic components that would otherwise be generated by the boundary conduction mode operation. This preliminary anti-action prevents the harmful harmonic distortion before it occurs, while maintaining the protective shutdown function near zero crossing points
Solution Approach 2:
An offset current is introduced as an intermediary element to mediate between the boundary conduction mode operation and the grid current. This offset current acts as a compensating force that cancels out the harmful harmonic components, allowing the inverter to operate in BCM without generating excessive harmonic distortion
Data Source
AI summary
The invention is directed to an inverter device and a power converting method thereof. A control unit adjusts a pulse width modulation (PWM) signal serving to control power conversion of an inverter circuit according to a current harmonic component detected by a detection unit to generate an offset current to be superposed to an AC current output by the inverter circuit.