Method and device for determining a direct current and resistance welding device

• US 20110260711A1
• Filed: 12/01/2009
• Published: 10/27/2011
• Est. Priority Date: 12/09/2008
• Status: Active Grant

• Current Assignee: Fronius International GmbH (G&K Privatstiftung)
• Original Assignee: Fronius International GmbH (G&K Privatstiftung)
• Inventors: Ennsbrunner, Helmut, Badegruber, Thomas
• Granted Patent: US 8,912,786 B2
• Time in Patent Office: Days
• US Class Current: 324/127
• CPC Class Codes: B23K 11/257 the measured parameter being an electrical current
• CPC Class Codes: G01R 15/181 using coils without a magnetic core, e.g. Rogowski coils
• CPC Class Codes: H01F 27/40 Structural association with built-in electric component, e.g. fuse
• CPC Class Codes: H01F 38/085 Welding transformers

Abstract

The invention relates to a method and a device for determining a direct current (i(t)) flowing in a conductor (7) and having an amplitude greater than 500 A, which direct current (i(t)) is composed of a number of time-dependent partial currents (i_i(t)) flowing in individual conductors (8) with switching elements. To create a drift-free measured value, it is provided that at least one Rogowski coil (10) is arranged around at least one of the individual conductors (8) for the induction of a partial voltage (u_i(t)) through the at least one partial current (i_i(t)), wherein the individual conductor (8) is formed by a path of a rectifier (6) on a secondary side of a transformer (5) with central tapping, the at least one integrator (11) is designed for integration of the at least one partial voltage (u_i(t)), and the at least one integrator (11) is connected to an evaluation unit (12) for determining the direct current (i(t)).

Claims

1. Method for determining a direct current (i(t)) flowing in a conductor (7) and having an amplitude greater than 500 A, which direct current (i(t)) is composed of a number of time-dependent partial currents (i_i(t)) flowing in individual conductors (8) having switching elements (9), wherein at least one induced partial voltage (u_i(t)) is created by the partial current (i_i(t)) flowing in at least one individual conductor (8) by arranging at least one Rogowski coil (10) around at least one individual conductor (8), wherein individual conductor (8) is formed by a path of a rectifier (6) on a secondary side of transformer (5) with central tapping, and this induced partial voltage (u_i(t)) is integrated in at least one integrator (11) and the direct current (i(t)) is determined with an evaluation unit (12) connected to the at least one integrator (11).

2. Method according to claim 1, wherein a sum voltage (Σ

u(t)) is formed of at least two partial voltages (u_i(t)) induced in two Rogowski coils (10) wired equally opposed, and this is integrated in an integrator (11).

3. Method according to claim 1, wherein a differential voltage (u_Δ

i(t)) induced in one Rogowski coil (10) is formed by a current difference (Δ

i(t)) formed by at least two partial currents (i_i(t), i_i+1(t)) oriented opposed.

4. Method according to claim 1, wherein each integrator (11) of the evaluation unit (12) is periodically reset during the flowing of direct current (i(t)), when the at least one partial current (i_i(t)) in individual conductor (8) causing the at least one induced partial voltage (u_i(t)) is ≦

zero.

5. Method according to claim 4, wherein each integrator (11) is reset, when the switching element (9) in individual conductor (8) of the at least one partial current (i_i(t)) causing the partial voltage (u_i(t)) to be integrated, is opened.

6. Method according to claim 1, wherein the method is applied in a device for determining a direct current (i(t)) flowing in a conductor (7) and having an amplitude greater than 500 A, which direct current (i(t)) is composed of a number of time-dependent partial currents (i_i(t)) flowing in individual conductors (8) having switching elements (9), wherein at least one Rogowski coil (10) is arranged around at least one individual conductor (8) for the induction of a partial voltage (u_i(t)) by the at least one partial current (i_i(t)), wherein the individual conductor (8) is formed by a path of a rectifier (6) on a secondary side of transformer (5) with central tapping, the at least one integrator (11) is designed for integration of the at least one partial voltage (u_i(t)), and the at least one integrator (11) is connected to an evaluation unit (12) for determining of the direct current (i(t).

7. Device for determining a direct current (i(t)) flowing in a conductor (7) and having an amplitude greater than 500 A, which direct current (i(t)) is composed of a number of time-dependent partial currents (i_i(t)) flowing in individual conductors (8) having switching elements (9), wherein at least one Rogowski coil (10) is arranged around at least one individual conductor (8) for the induction of a partial voltage (u_i(t)) by the at least one partial current (i_i(t)), wherein the individual conductor (8) is formed by a path of a rectifier (6) on a secondary side of transformer (5) with central tapping, the at least one integrator (11) is designed for integration of the at least one partial voltage (u_i(t)), and the at least one integrator (11) is connected to an evaluation unit (12) for determining of the direct current (i(t).

9. Device according to claim 7, wherein at least two Rogowski coils (10) are arranged around at least two individual conductors (8) equally opposed, and the Rogowski coils (10) are connected to each other and to the one integrator (11) for taking a mean value free sum voltage (Σ

u(t)) from the partial voltages (u_i(t)) induced in the Rogowski coils (10).

10. Device according to claim 7, wherein one Rogowski coil (10) is arranged around at least two individual conductors (8) running equally opposed, and the Rogowski coil (10) is connected to the one integrator (11) for taking a mean value free differential voltage (u_Δ

i(t)) of a current difference (Δ

i(t)) of the partial currents (i_i(t)).

11. Method according to claim 7, wherein each integrator (11) is periodically reset during the flowing of direct current (i(t)), when the partial current (i_i(t)) flowing in individual conductor (8) causing the at least one induced partial voltage (u_i(t)) is zero.

12. Device according to claim 11, wherein the at least one integrator (11) is respectively connected to at least one switching element (9) of an individual conductor (8) so that the integrator (11) can be reset, when the switching element (9) of the individual conductor (8) is opened.

13. Device according to claim 7, wherein the switching elements (9) are formed by diodes.

14. Device according to claim 7, wherein at least two Rogowski coils (10) are arranged around one individual conductor (8) each.

15. Device according to claim 14, wherein each Rogowski coil (10) is connected to an integrator (11) each.

16. Device according to claim 14, wherein all Rogowski coils (10) are connected to an integrator (11).

17. Device according to claim 7, wherein each Rogowski coil (10) is provided with a shielding plate.

18. Device according to claim 7, wherein the at least one integrator (11) is connected to a memory (14).

19. Device according to claim 7, wherein the device practices a method for determining a direct current (i(t)) flowing in a conductor (7) and having an amplitude greater than 500 A, which direct current (i(t)) is composed of a number of time-dependent partial currents (i_i(t)) flowing in individual conductors (8) having switching elements (9), wherein at least one induced partial voltage (u_i(t)) is created by the partial current (i_i(t)) flowing in at least one individual conductor (8) by arranging at least one Rogowski coil (10) around at least one individual conductor (8), wherein individual conductor (8) is formed by a path of a rectifier (6) on a secondary side of transformer (5) with central tapping, and this induced partial voltage (u_i(t)) is integrated in at least one integrator (11) and the direct current (i(t)) is determined with an evaluation unit (12) connected to the at least one integrator (11).

8. Device (1) for resistance welding having two electrodes (3) which are movable relative to one another and connected to a power source (4) for providing a direct current (i(t)) having an amplitude greater than 500 A for welding, wherein the power source (4) comprises at least one transformer (5) and one rectifier (6) having switching elements (9) for delivering time-dependent partial currents (i_i(t)) flowing in individual conductors (8), and having an apparatus for determining the direct current (i(t)), wherein at least one Rogowski coil (10) is arranged around at least one individual conductor (8) for the induction of a partial voltage (u_i(t)) through the at least one partial current (i_i(t)), wherein the individual conductor (8) is formed by a path of the rectifier (6) on the secondary side of a transformer (5) with central tapping, the at least one integrator (11) is designed for the integration of the at least one partial voltage (u_i(t)), and the at least one integrator (11) is connected to an evaluation unit (12) for determining the direct current (i(t)).