Four-Quadrant AC Welding Power Supply with Square Wave Control
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Solution Overview
Problem
AC welding power supplies face challenges such as inefficient energy conversion, high electromagnetic interference, and difficulty in maintaining the electric arc due to sinusoidal voltage changes, which limit the rate of current transition and affect process stability and efficiency.
Innovation Solution
A power supply architecture with a primary converter that inverts DC to high frequency AC, an isolating high frequency transformer, and an output converter that can rectify and invert high frequency voltage, enabling faster current transitions and improved efficiency through a four-quadrant converter topology and embedded synchronous rectification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If sinusoidal AC voltage is used for welding, then the power supply can deliver alternating current, but the voltage changes too slowly to ignite arc plasma particles, requiring high voltage surges that produce electromagnetic interference
Solution Approach 1:
The patent uses periodic square wave voltage changes instead of sinusoidal waves, creating regular high-rate voltage transitions at each half-cycle that reliably ignite arc plasma particles without requiring excessive voltage surges, thereby reducing electromagnetic interference while maintaining AC welding functionality
Solution Approach 2:
The patent dynamically adjusts the voltage waveform from sinusoidal to square wave with controlled rise times, enabling the voltage to change rapidly enough to ignite arc particles while maintaining controllability and reducing the need for high voltage surges that generate electromagnetic interference
2Reliability
If a high voltage ignition unit is used to generate voltage surges, then arc ignition is achieved, but copious amounts of electromagnetic interference are produced
Solution Approach 1:
The patent changes the voltage waveform parameters from sinusoidal to square wave with controlled rise times of 1-10 microseconds, achieving reliable arc ignition through controlled rapid voltage changes rather than high voltage surges, thereby reducing electromagnetic interference while maintaining ignition reliability
3Duration of action of moving object
If fast current transition is implemented to sustain arc after ignition, then arc sustainability is improved, but high frequency harmonics increase causing acoustic noise and cable losses
Solution Approach 1:
The patent implements periodic square wave current with controlled rise times that provide sufficient speed to sustain arc plasma particles throughout the entire half-cycle duration, while the regular periodic nature prevents excessive high frequency harmonics, reducing acoustic noise and cable losses compared to uncontrolled fast transitions
4Stress or pressure
If a large series inductor is used to transform voltage, then high voltage is achieved, but the inductor opposes current buildup and affects arc ignition
Solution Approach 1:
The patent uses a controllable power electronics-based voltage source that dynamically adjusts voltage output with controlled rise times, achieving high voltage levels without the current-limiting effect of large series inductors, thereby enabling both high voltage for arc ignition and fast current buildup for arc sustainability
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
This solution enhances the efficiency and stability of AC welding by allowing rapid voltage and current changes, reducing electromagnetic interference, and improving the overall power conversion efficiency, enabling sustained electric arcs during AC welding processes.
Implementation Method 1
a primary converter that inverts DC to high frequency AC
Implementation Method 2
an isolating high frequency transformer
Implementation Method 3
an output converter that can rectify and invert high frequency voltage
Data Source
AI summary
A power supply, including a primary pre-converter, coupled to supplying mains, configured to receive an AC voltage at low frequency and output a high DC voltage, and further configured to receive the high DC voltage and to output the alternating current; a primary converter, disposed on a primary side of the power supply, coupled to the high DC voltage from the primary pre-converter; an isolating transformer to receive the high frequency AC voltage and output a high frequency secondary AC voltage, and to receive a high frequency secondary AC current and to output primary high frequency AC current; and an output converter, on a secondary side of the power supply, wherein the output converter is configured to receive high frequency AC voltage from the isolating transformer and to output a DC voltage of a first or second polarity to an output, and wherein the output converter is configured to receive DC current of a first or second direction from the output and to output a high frequency AC current to the isolating transformer.