DC-AC Converter Current Correction for Zero-Crossing Distortion
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing DC-AC converters face challenges in reducing distortions in output currents, which can lead to a reduction in power factor, due to the inability to effectively correct reactor currents near zero crossings of the AC power source voltage.
Innovation Solution
A DC-AC converter apparatus with a current detector and current corrector that sets a harmonic component for the frequency component of the AC power source voltage, superimposing a current correction value on the commanded current to minimize discrepancies at zero crossings, thereby reducing distortions in output currents using peak current mode control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If peak current mode control is used to control reactor current to sinusoidal commanded current, then the converter operation is simplified and efficient, but current distortions increase near zero crossings where supply voltage is zero
Solution Approach 1:
The patent applies preliminary action by calculating and applying current correction values before the zero-crossing events occur. The correction values are computed based on predicted reactor current discrepancies at upcoming zero crossings, and these corrections are superimposed on the commanded current in advance. This proactive approach prevents the distortions from occurring rather than reacting to them after the fact, thereby maintaining both efficient peak current mode operation and low distortion output currents.
2Object-generated harmful factors
If current correction values are increased to reduce output current distortions, then output current quality improves, but power factor of AC power decreases
Solution Approach 1:
The patent applies local quality by making the current correction values spatially and temporally localized to specific regions around zero crossings. Instead of applying uniform correction across the entire AC cycle, the correction values are computed and applied only in the local time regions where zero crossings occur and distortions are problematic. This localized approach corrects distortions where needed while leaving the rest of the current waveform unchanged, thereby maintaining high power factor overall.
Solution Approach 2:
The patent applies partial action by using only the minimum necessary current correction values required to reduce distortions, rather than excessive correction that would improve current quality but harm power factor. The correction values are precisely calculated based on the actual predicted discrepancies at zero crossings, applying just enough correction to achieve the desired distortion reduction without over-correcting and degrading the power factor.
3Loss of energy
If commanded current is not corrected near zero crossings, then power factor is maintained, but output current distortions increase
Solution Approach 1:
The patent applies feedback by using the detected supply voltage waveform and predicted reactor current behavior to dynamically adjust the current correction values. The system continuously monitors the supply voltage, identifies upcoming zero crossings, and computes appropriate correction values based on the predicted current discrepancies. This closed-loop feedback mechanism ensures that corrections are applied precisely when and where needed to reduce distortions without compromising power factor.
Data Source
AI summary
In an apparatus for controlling a DC-AC converter including a reactor and a plurality of drive switches and configured to convert DC power supplied via input terminals into AC power and supply the AC power to an AC power source connected to output terminals. In the apparatus, a current corrector is configured to set a current correction value including a harmonic component for a frequency component of a supply voltage of the AC power source that has minima at zero crossings where the supply voltage is zero and superimpose the current correction value on a sinusoidal commanded current generated based on the supply voltage of the AC power source, thereby generating a commanded current after correction. A current controller is configured to operate the drive switches using peak current mode control to control the reactor current to the commanded current after correction.