DC-AC Inverter Voltage Correction for Transformer Saturation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing conversion systems fail to effectively reduce direct or low-frequency components of alternating current output when disturbing loads, such as arc furnaces, are connected to the AC network, leading to current fluctuations and transformer saturation due to inadequate precision in current sensors and noisy reference signals.
Innovation Solution
The system incorporates a voltage inverter with two DC voltage sources connected in series between its input terminals, a midpoint, and a correction device that measures voltage components at frequencies below 10 Hz to calculate and inject corrective signals, reducing DC or low-frequency components in the output current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If current sensors and reference signals are used to measure and correct DC components in conventional conversion systems, then the system can reduce magnetization effects, but the measurement precision becomes insufficient when disturbing loads are connected, leading to failure in reducing DC components
Solution Approach 1:
The patent introduces voltage as an intermediary measurement parameter instead of directly measuring current. By measuring the voltage at the inverter output terminals and detecting its fundamental frequency component, the system indirectly obtains information about DC current components with higher precision. This intermediary approach avoids the limitations of direct current measurement under disturbing load conditions.
Solution Approach 2:
The patent replaces the conventional current-based measurement and correction mechanism with a voltage-based measurement and correction mechanism. Instead of using current sensors to detect DC components and injecting corrective current signals, the system measures output voltage, extracts its fundamental component, and injects corrective voltage signals to achieve the same correction effect with superior precision under disturbing loads.
2Device complexity
If conventional correction methods are used with noisy reference signals, then the system structure remains simple, but the correction effectiveness deteriorates when disturbing loads are connected to the network
Solution Approach 1:
The patent extracts and isolates the fundamental frequency component of the output voltage from the complex voltage waveform containing harmonics and noise. By using a fundamental component extraction circuit, the system separates the useful fundamental component from disturbing harmonics and noise, enabling accurate DC component detection even when disturbing loads are connected, without significantly increasing system complexity.
3Ease of operation
If direct current components are not reduced in the inverter output, then the control system operates simply, but transformer saturation occurs due to circulation of direct currents
Solution Approach 1:
The patent implements a feedback control mechanism where the output voltage is continuously measured, its fundamental component is extracted, and the difference between the measured fundamental component and a reference fundamental component is used to generate corrective signals. This feedback loop automatically adjusts the inverter output to eliminate DC current components, preventing transformer saturation while maintaining simple operation through automated control.
Data Source
Figure 1
Figure 2
Figure 3
AI summary
The system (100) has a voltage converter (18) converting an input direct current (DC) into an alternating output current, where the converter includes two input terminals (26A, 26B), output terminals (28U, 28V, 28W) and a switching arm (30). A correction device (98) comprises a measuring element for measuring a part of voltage with frequencies preferably less than or equal to 1 Hz supplied by the inverter. The correction device is provided with a calculating element for calculating correction signals (Vuc, Vvc, Vwc) depending on the measured voltage part. An independent claim is also included for a method for controlling a conversion system.