Active Line Filter for Resistance Welding Harmonic Reduction
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Solution Overview
Problem
Resistance welding converters that generate two-phase pulse-width-modulated alternating current from rectified AC line current using power semiconductors cause high harmonic currents in multiphase power grids, leading to increased losses and inefficiencies.
Innovation Solution
An active line filter is used to adjust the AC line current to a sinusoidal waveform before generating the pulse-width-modulated current for the welding transformer, measuring line voltage and current to detect deviations and automatically feed in or feedback current to maintain sinusoidal waveforms, reducing harmonic currents and power grid losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a B6-input bridge is used to generate two-phase pulse-width-modulated alternating current from rectified AC line current, then the welding converter can operate with the required current waveform, but extremely high harmonic currents are caused in the power grid
Solution Approach 1:
An active line filter is introduced as an intermediary component between the power grid and the welding converter. This filter contains harmonic current components generated by the welding converter, preventing them from propagating into the power grid. The filter acts as a mediator that allows the welding converter to operate with pulse-width-modulated current while maintaining clean sinusoidal current in the power grid.
Solution Approach 2:
The active line filter extracts harmful harmonic current components from the total current waveform. By separating and filtering out the harmonic components (particularly the fifth harmonic that can reach 80%), the system maintains the required pulse-width-modulated current for welding operation while removing the harmful effects from the power grid connection.
2Power
If high harmonic currents flow in the power grid, then the welding converter can deliver required power, but power grid effective phase current and losses increase
Solution Approach 1:
The active line filter serves as a mediator that decouples the welding converter's power delivery function from the power grid's current quality. It allows full power delivery to the welding transformer while preventing energy losses in the power grid feed line by eliminating harmonic current components that would otherwise cause increased I²R losses.
3Device complexity
If the AC line current is not sinusoidally adjusted, then the welding converter operates simpler, but harmonic currents cause increased losses and inefficiencies
Solution Approach 1:
The active line filter acts as an intermediary that handles the complexity of sinusoidal current adjustment separately from the welding converter. The filter automatically detects deviations from sinusoidal waveform and compensates by feeding in or feedback current, allowing the welding converter to maintain its simpler pulse-width-modulation operation while achieving clean sinusoidal current at the power grid connection point.
4Object-generated harmful factors
If active line filter is used to maintain sinusoidal waveform, then harmonic currents are reduced, but the system requires measuring apparatus and control arrangements
Solution Approach 1:
The active line filter is designed to automatically detect and correct its own performance. The measuring apparatus continuously monitors the line current waveform, automatically detects deviations from sinusoidal shape, and the control system self-adjusts by feeding in or feedback current as needed. This self-service capability reduces the need for external complex control arrangements while effectively eliminating harmonic currents.
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 significantly reduces harmonic currents and power grid losses by ensuring a nearly sinusoidal waveform, decreasing the instantaneous current required by the resistance welding converter and allowing for efficient power factor correction to 1.
Implementation Method 1
The line filter preferably measures the line voltage and/or the line current automatically via a measuring apparatus for measuring the line voltage and/or the line current
Implementation Method 2
the line filter preferably automatically feeds in line current via a feed-in arrangement, and if necessary, also automatically feeds current back into the power grid again via a return feed arrangement
Implementation Method 3
which rectifies the AC line current. A two-phase pulse-width-modulated alternating current is in turn generated from the rectified AC line current using power semiconductors
Implementation Method 4
A two-phase pulse-width-modulated alternating current is in turn generated from the rectified AC line current using power semiconductors
Implementation Method 5
which generated current can be supplied to the primary side of a welding transformer
Data Source
AI summary
The disclosure describes a system that uses an active filter connected to phases of a three-phase power grid in parallel with a resistance welding apparatus in order to bring an input current of a welding converter closer to a sinusoidal shape.