Inverter LC Filter DC Voltage Pulsation Control
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Solution Overview
Problem
Inverters with LC filters in the DC link part face challenges in suppressing distortions in the input current due to pulsations at the resonance frequency, making it difficult to separate higher harmonic frequencies from the power pulsation component, leading to low-order distortions.
Innovation Solution
An inverter design that includes a diode bridge, an inverter section, an LC filter, a voltage detecting section to monitor the cross-terminal voltage of the inductance element, and a control section that adjusts the transfer characteristic of the I/O voltage to resemble a first-order lag system, allowing for effective suppression of vibrations and distortions in the input current without interfering with the resonance frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If an LC filter is installed in the DC link part to suppress carrier current components, then the inverter achieves compact size and cost reduction, but the DC voltage pulsates at the resonance frequency of the LC filter due to load fluctuations and output frequency fluctuations
Solution Approach 1:
The patent implements a feedback mechanism where the DC voltage is detected and fed back to the inverter control section. The control section generates a compensation value based on the detected DC voltage and adds it to the voltage command, thereby suppressing DC voltage pulsations and maintaining stability despite the compact LC filter design.
2Stability of the object's composition
If vibration suppression is implemented by detecting DC voltage vibrations with an HPF and suppressing them in the current control system, then DC voltage vibrations are suppressed, but higher harmonic frequency of power pulsation component and resonance frequency of filter become close, making it difficult to separate them, causing low-order distortions in input current
Solution Approach 1:
The patent introduces a new intermediary detection point - the cross-terminal voltage of the inductance element - which serves as a mediator between the DC voltage and the control system. This allows vibration suppression without directly manipulating the current control system, thereby avoiding the distortion problem while still achieving DC voltage stabilization.
3Manufacturing precision
If the inverter controls the I/O voltage transfer characteristic to resemble a first-order lag system based on cross-terminal voltage of the inductance element, then vibrations and distortions in input current are suppressed, but the control system complexity increases
Solution Approach 1:
The patent changes the control parameter from direct current control to voltage-based control using the cross-terminal voltage of the inductance element. By controlling the I/O voltage transfer characteristic to resemble a first-order lag system, the patent achieves distortion suppression while managing control system complexity through parameter optimization.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively suppresses vibrations and distortions in the input current, stabilizes the control system, and enables direct control of the AC load current and DC load current, achieving a high-speed response and stable operation.
Implementation Method 1
the DC voltage sometimes pulsates at the resonance frequency of the LC filter
Implementation Method 2
a diode bridge that rectifies an inputted three-phase AC voltage into a DC voltage
Data Source
Figure 1
Figure 2A~2B
Figure 3
AI summary
The inverter comprises a diode bridge (21) that rectifies an inputted three-phase AC voltage into a DC voltage, an inverter section (22) that converts the DC voltage converted by the diode bridge (21) into an AC voltage and outputs the resulting voltage, an LC filter that has an inductor Ldc connected between one output terminal of the diode bridge (21) and one input terminal of the inverter section and a capacitor Cdc connected across the input terminals of the inverter section, a voltage detecting section (24) that detects cross terminal voltage of the inductor Ldc, and a control section (100) that controls the inverter section (22). The control section (100) controls the inverter section (22) so that the transfer characteristic of the I/O voltage of the inverter section (22) becomes a characteristic of the first-order lag system on the basis of the cross terminal voltage of the inductor Ldc detected by the voltage detecting section (24).