DSP based plasma cutting system

• US 6,365,868 B1
• Filed: 02/29/2000
• Issued: 04/02/2002
• Est. Priority Date: 02/29/2000
• Status: Expired due to Term

• Current Assignee: Hypertherm Incorporated
• Original Assignee: Hypertherm Incorporated
• Inventors: Borowy, Dennis M., Ren, Tianting
• Primary Examiner(s): PASCHALL, MARK H
• Application Number:
  US09/515,139
• Time in Patent Office: 763 Days
• Field of Search: 219/121.39, 219/121.49, 219/121.44, 219/121.54, 219/121.57, 219/130.1
• US Class Current: 219/121.54
• CPC Class Codes: B23K 10/006 Control circuits therefor circuits for plasma torches H05H1/36

Abstract

This invention relates to methods and apparatus for controlling a power supply of a plasma arc system. According to the method, any AC input voltage within a range of input voltages is provided into the input stage and a rectified output voltage is thereby generated. The rectified output voltage is provided into the power factor corrected boost stage and a DC signal is thereby generated. The DC signal is provided into an auxiliary power supply and a regulated power signal is thereby generated. The regulated power signal is provided into a digital signal processor module and an output control signal is thereby generated. The output control signal is provided into the inverter stage and a plasma arc current is thereby generated.

Claims

1. A method of controlling a power supply of a plasma arc system, the power supply including an input stage, a power factor corrected boost stage and an inverter stage, the method comprising:

(a) providing into the input stage any AC input voltage within a range of input voltages and thereby generating a rectified output voltage;

(b) providing into the power factor corrected boost stage the rectified output voltage and thereby generating a DC signal;

(c) providing into an auxiliary power supply the DC signal and thereby generating a regulated power signal;

(d) providing into a digital signal processor module the regulated power signal and thereby generating an output control signal; and

(e) providing into the inverter stage the output control signal and thereby generating a plasma arc current.

2. The method of claim 1 wherein step (d) comprises generating the output control signal based on an average duty cycle of the inverter stage.

3. The method of claim 1 further comprising (f) providing into the digital signal processor module at least one of (i) a start signal generated in response to a user input and (ii) a current command signal generated in response to a user input and (iii) a current feedback signal generated in response to current flow through a plasma torch electrode.

4. The method of claim 3 wherein step (e) comprises providing the output control signal to the inverter stage based on the regulated power signal and at least one of (i) the start signal, (ii) the current command signal and (iii) the current feedback signal.

5. The method of claim 1 further comprising (f) providing into the digital signal processor module a rectified voltage signal generated in response to the rectified output voltage of the input stage.

6. The method of claim 5 further comprising (g) limiting one of (i) a plasma arc voltage and (ii) the plasma arc current based on the rectified voltage signal.

7. The method of claim 1 further comprising:

(f) providing into the digital signal processor module a transfer signal generated in response to current flow through a work piece; and

(g) providing from the digital signal processor module to a nozzle in a plasma torch electrode a pilot arc control signal.

8. The method of claim 7 wherein step (e) comprises providing the output control signal to the inverter stage based on the transfer signal.

9. The method of claim 7 further comprising (h) inhibiting current flow through the nozzle in the plasma torch electrode in response to the pilot arc control signal.

10. The method of claim 1 further comprising providing a relay control signal from the digital signal processor module to a relay that opens or closes a substantially short circuit in parallel with an inrush current limiting resistor provided in the power supply.

11. The method of claim 10 wherein the step of providing the relay control signal is based on at least one of (i) the regulated power signal and (ii) the rectified output voltage.

12. The method of claim 1 further comprising (f) providing to the power factor corrected boost stage from the digital signal processor module a second output control signal.

13. The method of claim 12 wherein the second output control signal is based on the frequency of the switching of the inverter stage.

14. The method of claim 1 further comprising providing into the digital signal processor module a safety status signal generated in response to the removal of a retaining cap of a plasma torch electrode.

15. The method of claim 14 further comprising (g) latching the state of the safety status signal when the safety status signal changes from a first value to a second value.

16. The method of claim 14 further comprising inhibiting the flow of the plasma arc current in response to the safety status signal.

17. The method of claim 1 further comprising (f) using a harmonic injection algorithm to modify a power factor of the power supply.

18. The method of claim 1 wherein step (c) comprises:

(c1) providing the DC signal to a transformer provided inside the auxiliary power supply;

(c2) providing from the transformer the regulated power control signal; and

(c3) switching the DC signal through the transformer in response to a value of the regulated power signal.

19. The method of claim 1 further comprising (f) generating a rectified voltage from the output of the inverter stage of the power supply, the output of the inverter stage capable of producing the plasma arc current.

20. The method of claim 1 further comprising (f) damping the generated rectified output voltage of the input stage.

21. The method of claim 1 further comprising (f) filtering the AC input voltage prior to the step of providing the AC input voltage to the input stage.

22. A system for controlling a power supply of a plasma arc system, the system comprising:

an input stage including a circuit for receiving any AC input voltage within a range of input voltages and generating a rectified output voltage;

a power factor corrected boost stage electrically connected to the input stage, the power factor corrected boost stage including a circuit for receiving the rectified output voltage and generating a DC signal;

an inverter stage electrically connected to the power factor corrected boost stage, the inverter stage including a circuit for receiving the DC signal and generating an AC signal capable of providing a current to a plasma torch electrode;

an auxiliary power supply electrically connected to the power factor corrected boost stage, the auxiliary power supply including a circuit for receiving the DC signal and generating a regulated power signal;

a digital signal processor module in communication with the auxiliary power supply and the inverter stage, the digital signal processor module including a circuit for receiving the regulated power signal and providing an output control signal to the inverter stage for generating a plasma arc current.

23. The system of claim 22 wherein the digital signal processor module is in electrical communication with at least one of a first switch, a second switch, a current sensor, and an input of the power factor corrected boost stage, the first switch providing a start signal in response to a user input, the second switch providing a current command signal in response to a user input, the current sensor providing a current feedback signal in response to current flow through the plasma torch electrode, and the input of the power factor corrected boost stage providing a rectified voltage signal in response to the rectified output voltage of the input stage, and wherein the digital signal processor module is configured to provide the output control signal based on the regulated power signal and at least one of the start signal and the current command signal and the current feedback signal and the rectified voltage signal.

24. The system of claim 22 further comprising:

a pilot arc control switch in electrical communication with the digital signal processor module and a nozzle of the plasma torch electrode, the pilot arc control switch including a circuit for inducing and inhibiting current flow through the nozzle in response to a pilot arc control signal generated by the digital signal processor module.

25. The system of claim 22 further comprising:

a relay in electrical communication with the digital signal processor module, the output of the input stage and the input of the power factor corrected boost stage, the relay opening or closing a substantially short circuit in parallel with an inrush current limiting resistor provided in the power supply in response to a relay control signal generated by the digital signal processor module.

26. The system of claim 22 wherein the digital signal processor module is in electrical communication with the power factor corrected boost stage and is configured to provide a second output control signal to the power factor corrected boost stage.

27. The system of claim 22 wherein the digital signal processor module is in electrical communication with a third switch, the third switch providing a safety status signal in response to the removal of a retaining cap of a plasma torch electrode.

28. The auxiliary power supply of claim 22 wherein the circuit of the auxiliary power supply includes a flyback topology.

29. The system of claim 22 further comprising:

a second rectifier stage electrically connected to the inverter stage and a plasma torch electrode, the second rectifier stage including a circuit for generating a rectified voltage from the output of the inverter stage.

30. The system of claim 22 further comprising:

a damping stage electrically connected to the input stage and the power factor corrected boost stage, the damping stage including a circuit for damping the rectified output voltage of the input stage.

31. The system of claim 22 further comprising:

a filtering stage electrically connected to the input stage, the filtering stage including a circuit for filtering the AC input voltage prior to the input stage receiving the AC input voltage.

32. The system of claim 22 further comprising:

an on-board programming module in electrical communication with the digital signal processor module and an external storage device, the on-board programming module including a circuit for transferring a computer program contained in the storage device to the digital signal processor module.

33. The system of claim 22 wherein the digital signal processor module further comprises:

an input conditioning circuit configured to receive an input signal from an source external to the digital signal processor module and condition the input signal to a level acceptable to a digital signal processor;

an output conditioning circuit configured to receive an output signal from the digital signal processor and condition the output signal to a level acceptable to a circuit external to the digital signal processor module receiving the conditioned output signal; and

a digital signal processor device communication with the first conditioning circuit and the second conditioning circuit, the digital signal processor device configured to receive the input signal and generate the output signal.

34. The system of claim 22 wherein the digital signal processor device is configured to generate the positive switch command signal and the negative switch command signal as a matched set with the same value at the same time frame of the signal generation.