Arc Voltage Sensing in Switch Mode Power Supply
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Solution Overview
Problem
In modern welding systems with switch mode power supplies, the variable inductance of external welding cables leads to an undesirable lag between actual arc voltage and sensed arc voltage, resulting in sub-optimal power supply control due to the presence of inductance in the external circuit, making it challenging to accurately measure and control the arc voltage without voltage sensing cables.
Innovation Solution
A method is developed to determine the arc voltage by sensing internal and output voltages during both active power delivery and freewheeling stages of the switch mode power supply, using the internal inductor's predetermined inductance and output current, eliminating the need for voltage sensing cables by calculating the arc voltage based on these measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If voltage sensing cables are used to measure arc voltage, then the measurement can be obtained, but the variable inductance of external welding cables causes an undesirable lag between actual arc voltage and sensed arc voltage
Solution Approach 1:
The patent extracts the voltage sensing function from the external cable circuit and relocates it to the internal circuit of the switch mode power supply. By measuring voltages at internal nodes (Vsw, Vgs, Vds) before the external cables, the system eliminates the harmful inductance of external cables from the sensing path, thereby removing the source of measurement lag while preserving accurate arc voltage detection capability
Solution Approach 2:
The patent introduces computational processing as an intermediary between internal voltage measurements and arc voltage determination. By using a controller to process multiple internal voltage signals (Vsw, Vgs, Vds) and calculate the arc voltage based on known circuit parameters, the system indirectly determines arc voltage without direct external sensing, thus avoiding external cable inductance effects
2Loss of time
If the inductance of external welding cables is reduced, then the sensing lag is reduced, but the cables may still have variable inductance due to varying lengths, cable extenders, and proximity to ferromagnetic materials
Solution Approach 1:
The patent removes the voltage sensing function from the external cable system entirely and relocates it to the internal power supply circuitry. This extraction makes the measurement system independent of external cable characteristics, allowing cables to be configured freely (different lengths, extenders, positions near ferromagnetic materials) without affecting sensing performance
Solution Approach 2:
The system uses its own internal voltage measurements and known internal circuit parameters to determine arc voltage, making the sensing system self-sufficient and independent of external cable properties. The controller calculates arc voltage using internal signals and predetermined inductance values, eliminating reliance on external cable characteristics
3Device complexity
If voltage sensing cables are eliminated, then the complexity of the system is reduced, but accurate arc voltage measurement becomes challenging without direct sensing at the arc
Solution Approach 1:
The patent creates an electrical model/copy of the arc voltage based on internal power supply measurements. By measuring internal voltages (Vsw, Vgs, Vds) and using known circuit parameters (inductance values, switching frequencies), the controller computes a representation of arc voltage that accurately reflects actual arc conditions without requiring physical sensors at the arc location
Solution Approach 2:
The patent replaces the mechanical/electrical sensing system (voltage sensing cables physically connected to the arc) with a computational/electrical modeling system. Instead of directly measuring arc voltage through external cables, the system uses mathematical relationships and internal electrical measurements to determine arc voltage, substituting direct physical sensing with indirect computational determination
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 approach allows for accurate measurement and control of arc voltage, reducing the delay in sensing and improving power supply control, achieving more precise welding operations without the inconvenience of external voltage sensing cables, and providing a more reliable method for determining arc voltage in high-frequency applications.
Implementation Method 1
Since a switch mode power supply operates at ultra-acoustic frequencies (e.g., 20 kHz, 50 kHz, 100 kHz), the required inductance of the output inductor is relatively small
Implementation Method 2
an internal inductor (L1) having a predetermined, in general, current dependent inductance
Data Source
AI summary
A method for determining a value of arc voltage in a welding system, the welding system including a switch mode power supply and a controller that controls operation of the switch mode power supply, the method including, during an active power delivery stage of the switch mode power supply sensing a first internal voltage (V20) within the switch mode power supply prior to an internal inductor and a first output voltage (V21) of the switch mode power supply; during a freewheeling stage of the switch mode power supply sensing a second internal voltage (VF) within the switch mode power supply prior to the internal inductor and a second output voltage (V22) of the switch mode power supply; and determining the value of arc voltage based on the first internal voltage, the first output voltage, the second internal voltage, and the second output voltage.