Controller method and apparatus for welding system
A method, performed in a welding or cutting system including a power supply configured to deliver a current to a welding torch to create an arc on a cut-off workpiece, comprises: sampling the current to produce digitized current values; filtering the digitized current values using a first digital filter to produce filtered digitized current values; sampling a voltage corresponding to the current to produce digitized voltage values; filtering the digitized voltage values using a second digital filter to produce filtered digitized voltage values; and controlling a current level of the current using the filtered digitized current values or the filtered digitized voltage values.
1. A method performed in a welding or cutting system including a welding power supply configured to, responsive to a switching frequency of the welding power supply, deliver a current and a voltage to a welding torch to create an arc on a workpiece, the method comprising:
filtering the current with a first anti-aliasing filter having a first low pass cut-off frequency that is less than or equal to a first sample rate to produce an anti-aliased current;
sampling the current at the first sample rate to produce digitized current values;
filtering the digitized current values using a first digital filter to produce filtered digitized current values;
filtering the voltage with a second anti-aliasing filter having a second low pass cut-off frequency that is less than or equal to a second sample rate;
sampling the voltage at the second sample rate to produce digitized voltage values;
filtering the digitized voltage values using a second digital filter to produce filtered digitized voltage values; and
controlling a current level of the current using the filtered digitized current values or the filtered digitized voltage values.
2. The method of claim 1 , wherein:
the first digital filter has a first low pass frequency response; and
the second digital filter has a second low pass frequency response.
3. The method of claim 2 , wherein:
the first digital filter includes a Finite Impulse Response (FIR) filter or an Infinite Impulse Response (IIR) filter; and
the second digital filter includes an FIR filter or an IIR filter.
4. The method of claim 2 , wherein the first low pass frequency response matches the second low pass frequency response.
5. The method of claim 2 , wherein:
the first low pass frequency response has a first stopband set depending on the switching frequency to attenuate power supply switching noise on the current; and
the second low pass frequency response has a second stopband set depending on the switching frequency to attenuate power supply switching noise on the voltage.
6. The method of claim 1 , wherein:
sampling the voltage includes sampling the voltage concurrently with sampling the current, and the second sample rate matches the first sample rate.
7. The method of claim 1 , wherein:
the filtered digitized voltage values differ from an arc voltage based on an electrical circuit parameter of a weld circuit through which the welding power supply delivers the current to the welding torch; and
controlling includes:
compensating the filtered digitized voltage values based on the filtered digitized current values and a known value of the electrical circuit parameter, to produce compensated voltage values as an estimate of the arc voltage; and
controlling the current level of the current based on the compensated voltage values.
8. The method of claim 7 , wherein sampling the voltage includes sampling the voltage at a voltage sense point, on the welding power supply or the weld circuit, that is spaced-apart from the welding torch, such that the electrical circuit parameter introduces a voltage drop that causes the filtered digitized voltage values to differ from the arc voltage.
9. The method of claim 7 , wherein the electrical circuit parameter includes a resistance of the weld circuit, and compensating includes compensating the filtered digitized voltage values based on the filtered digitized current values and a known value of the resistance, to produce the compensated voltage values.
10. The method of claim 7 , wherein the electrical circuit parameter includes an inductance of the weld circuit, and compensating includes compensating the filtered digitized voltage values based on the filtered digitized current values and a known value of the inductance, to produce the compensated voltage values.
11. The method of claim 7 , further comprising:
calibrating the weld circuit using a calibration current, to determine a value of the electrical circuit parameter.
12. An apparatus for welding or cutting comprising:
a welding power supply configured to, responsive to a switching frequency of the welding power supply, deliver a current and a voltage to a welding torch to create an arc on a workpiece; and
a controller coupled to the welding power supply and including:
a first anti-aliasing filter having a first low pass cut-off frequency that is less than or equal to a first sample rate;
a first digitizer to sample the current at the first sample rate to produce digitized current values;
a first digital filter to filter the digitized current values, to produce filtered digitized current values;
a second anti-aliasing filter having a second low pass cut-off frequency that is less than or equal to a second sample rate;
a second digitizer to sample the voltage at the second sample rate, to produce digitized voltage values; and
a second digital filter to filter the digitized voltage values to produce filtered digitized voltage values,
wherein the controller is configured to control a current level of the current using the filtered digitized current values or the filtered digitized voltage values.
13. The apparatus of claim 12 , wherein:
the first digital filter has a first low pass frequency response; and
the second digital filter has a second low pass frequency response.
14. The apparatus of claim 13 , wherein:
the first digital filter includes a Finite Impulse Response (FIR) filter or an Infinite Impulse Response (IIR) filter; and
the second digital filter includes an FIR filter or an IIR filter.
15. The apparatus of claim 13 , wherein the first low pass frequency response matches the second low pass frequency response.
16. The apparatus of claim 13 , wherein:
the first low pass frequency response has a first stopband set depending on the switching frequency to attenuate power supply switching noise on the current; and
the second low pass frequency response has a second stopband set depending on the switching frequency to attenuate the power supply switching noise on the voltage.
17. The apparatus of claim 12 , wherein:
the second digitizer is configured to sample the voltage concurrently with sampling of the current, and the second sample rate matches the first sample rate.
18. The apparatus of claim 12 , wherein the filtered digitized voltage values differ from an arc voltage based on an electrical circuit parameter of a weld circuit through which the welding power supply is configured to supply the current to the welding torch, and the controller is further configured to perform:
compensating the filtered digitized voltage values based on the filtered digitized current values and a known value of the electrical circuit parameter, to produce compensated voltage values as an estimate of the arc voltage; and
controlling the current level of the current based on the compensated voltage values.
19. An apparatus for welding or cutting comprising:
a welding power supply configured to, responsive to a switching frequency of the welding power supply, deliver a current and a voltage to a welding torch to create an arc on a workpiece; and
a controller coupled to the welding power supply and including:
a first digitizer to sample the current to produce digitized current values;
a first digital filter to filter the digitized current values, to produce filtered digitized current values, wherein the first digital filter has a first stopband set depending on the switching frequency to attenuate power supply switching noise;
a second digitizer to sample the voltage corresponding to the current to produce digitized voltage values; and
a second digital filter to filter the digitized voltage values to produce filtered digitized voltage values, wherein the second digital filter has a second stopband set depending on the switching frequency to attenuate the power supply switching noise,
wherein the controller is configured to control a current level of the current using the filtered digitized current values or the filtered digitized voltage values.