Welding or cutting power supply using phase shift double forward converter circuit (PSDF)
A technique for dynamically adjusting an output voltage for a welding or cutting operation is provided. The technique allows for varying output voltage at the welding or cutting torch by manipulating the duty cycles of two forward converter circuits. The present disclosure provides methods and systems for increasing synchronized duty cycles in a pair of forward converter circuits in response to increasing output voltage demand then changing a phase shift between the duty cycles in response to further increases in output voltage demand. The present disclosure provides a controller designed to receive input signals and generate output pulse width modulation signals that control the duty cycle width and phase shift of the outputs of the forward converter circuits in response to these signals. Methods of accommodating for the time needed for the transformer core to reset via leading edge or lagging edge compensation are provided.
1. A method of dynamically adjusting an output voltage for a welding or cutting operation, comprising:
detecting an increase in a voltage requirement present at a load;
increasing in phase duty cycles in a pair of forward converter circuits until the in phase duty cycles reach an upper limit as the voltage requirement present at the load increases to increase the voltage output of the pair of forward converter circuits to accommodate the increase in the voltage requirement present at the load; and
changing, as the voltage requirement further increases, a phase shift between the duty cycle of a first forward converter circuit of the pair of forward converter circuits and the duty cycle of a second forward converter circuit of the pair of forward converter circuits upon reaching the upper limit to further increase the voltage output of the pair of forward converter circuits to accommodate the further increase in the voltage requirement present at the load.
2. The method of claim 1 , wherein the upper limit for each of the duty cycles is based on time required for a transformer core in each of the respective forward converter circuits to reset.
3. The method of claim 1 , wherein changing the phase shift comprises delaying a leading edge of a pulse in a switching period to reduce the duty cycle of either the first forward converter circuit or the second forward converter circuit.
4. The method of claim 1 , wherein changing the phase shift comprises initiating an early lagging edge of a pulse in a switching period to reduce the duty cycle of either the first forward converter circuit or the second forward converter circuit.
5. The method of claim 1 , wherein changing the phase shift comprises skipping a pulse in a switching period of either the first forward converter circuit or the second forward converter circuit.
6. The method of claim 1 , wherein changing the phase shift comprises increasing the duty cycles of the pair of forward converter circuits to a maximum limit, shifting outputs of the pair of forward converter circuits fully out of phase, and reducing pulse widths in the switching period for each of the forward converter circuits.
7. The method of claim 1 , comprising preventing saturation of a transformer in one of the pair of forward converter circuits by monitoring voltage and/or current in the transformer and disabling initiation of a new pulse when the voltage and/or current indicates that the transformer has not been reset.
8. The method of claim 1 , comprising flowing current through the pair of forward converter circuits in parallel or in series.