Method for controlling a battery-powered welding device, and battery-powered welding device

Abstract

A method controls a battery-powered welding device and a battery-powered welding device includes a battery having a battery voltage and a battery current and a welding controller containing a boost converter having at least a switch and a buck converter having at least one switch for controlling a welding current and a welding voltage supplied to a welding torch. A switch for bypassing the booster converter is connected to a switch controller designed to close the switch if the intermediate circuit voltage between the boost converter and the buck converter is less than or equal to the battery voltage and to open the switch if the boost converter is activated.

Claims

1. A method for controlling a battery-powered welding device comprising: providing a battery, the battery providing a battery voltage and a battery current; supplying a welding current and a welding voltage to a welding torch; providing a welding controller containing a boost converter having a first switch and a buck converter having a second switch, the boost converter being connected to the buck converter via an intermediate circuit connection; controlling by the welding controller the battery voltage and the battery current to give the welding current and the welding voltage supplied to the welding torch; bypassing the boost converter using a bypass comprising a third switch controlled by a switch controller when an intermediate circuit voltage between the boost converter and the buck converter is less than or equal to the battery voltage, the bypass feeding into the intermediate circuit connection; and opening the third switch for bypassing the boost converter when the boost converter is activated; wherein the third switch for bypassing the boost converter is opened when the welding current is less than the maximum current through the boost converter and the buck converter is deactivated; wherein the first switch of the boost converter and the second switch of the buck converter are operated at the same clock frequency; and wherein the intermediate circuit voltage is measured only during part of each period duration of the clock frequency and evaluated during the remainder of each period duration.

2. The method according to claim 1, wherein the boost converter is deactivated when the welding voltage is less than the battery voltage minus a predetermined voltage.

3. The method according to claim 1, wherein the boost converter is regulated via a regulation device by comparing the intermediate circuit voltage to a desired welding voltage and comparing this comparison value and the current through the boost converter by a comparator and supplying it to the regulation device.

4. The method according to claim 1, wherein the boost converter is operated as a voltage regulator.

5. The method according to claim 1, wherein the buck converter is operated as a current regulator.

6. The method according to claim 1, wherein only the buck converter is activated during normal welding operation.

7. The method according to claim 1, wherein both the boost converter and the buck converter are activated if the desired welding current is less than the maximum current through the boost converter.

8. The method according to claim 1, wherein the battery receives unused power back from the buck converter.

9. A battery-powered welding device comprising a battery having a battery voltage and a battery current, a welding controller containing a boost converter having a first switch and a buck converter having a second switch for controlling the battery voltage and the battery current to give a welding current and a welding voltage supplied to a welding torch, an intermediate circuit connection connecting the boost converter to the buck converter, a switch controller, and a bypass comprising a third switch for bypassing the boost converter, the third switch being connected to the switch controller, the bypass feeding into the intermediate circuit connection, wherein the switch controller is designed to close the third switch when the intermediate circuit voltage between the boost converter and the buck converter is less than or equal to the battery voltage and to open the third switch when the boost converter is activated, wherein the switch controller is designed to open the third switch for bypassing the boost converter when the welding current is less than the maximum current through the boost converter and the buck converter is deactivated, wherein the first switch of the boost converter and the second switch of the buck converter are designed to operate at the same clock frequency, and wherein the intermediate circuit voltage is measured only during part of each period duration of the clock frequency and evaluated during the remainder of each period duration.

10. The battery-powered welding device according to claim 9, further comprising a regulation device for the boost converter, the regulation device being configured to deactivate the boost converter when the welding voltage is less than the battery voltage minus a predetermined voltage.

11. The battery-powered welding device according claim 10, further comprising a comparator for comparing a comparison value of the intermediate circuit voltage to a desired welding voltage and the current through the boost converter, the comparator being connected to the regulation device for regulating the boost converter.

12. The battery-powered welding device according to claim 9, wherein the battery has a battery voltage less than or equal to 60 V.

13. The battery-powered welding device according to claim 9, further comprising a capacitor arranged in the intermediate circuit connection between the boost converter and the buck converter.

14. The battery-powered welding device according to claim 9, wherein the third switch for bypassing the boost converter is a field-effect transistor.

15. The battery-powered welding device according to claim 9, wherein the battery is a lithium iron phosphate battery.

16. The battery-powered welding device according to claim 9, wherein the buck converter is usable as a loading circuit for loading the battery when operated in the opposite direction.

Description

(1) The present invention will be discussed in more detail by means of the attached drawings. In the drawings:

(2) FIG. 1 shows a block diagram of a battery-powered welding device according to the present invention;

(3) FIG. 2 shows an expanded block diagram of a welding controller for a battery-powered welding device of the present type;

(4) FIG. 3 shows a block diagram of an embodiment of a regulation of a boost converter;

(5) FIG. 4 shows a block diagram of an embodiment of a regulation of the buck converter;

(6) FIG. 5 shows a time diagram for illustrating the manner for determining the intermediate circuit voltage as an input parameter for controlling the switch for bypassing the boost converter; and

(7) FIG. 6 shows a diagram for visualising the various operation states of the battery-powered welding device having the combination of a boost converter and a buck converter.

(8) FIG. 1 shows a block diagram of a battery-powered welding device 1 having a battery 2, which may be formed, for example, by a lithium iron phosphate battery having a particularly high power density. If desired, the battery 2 may also be designed replaceable. The battery 2 supplies a battery voltage U.sub.in and a battery current I.sub.in. In a welding controller 3, the battery voltage U.sub.in provided by the battery 2 and the battery current I.sub.in are controlled to a respective welding current I.sub.out supplied to a welding torch 11 and a welding voltage U.sub.out supplied to the welding torch 11. The outputs of the welding controller 3 are connected to the welding torch 11 and the workpiece 17 to be welded. The desired welding current I.sub.set and the desired welding voltage U.sub.set are set, for example, via an input device 16 and transferred to the control device 15. The control device 15 supplies the respective control signals for the components contained in the welding controller, the boost converter 4 having at least one switch 5 and the buck converter 6 having at least one switch 7. Furthermore, the control device 15 may be connected to a display 13 for displaying the most important operating parameters or the like. If required, the battery voltage U.sub.in supplied by the battery 2 is changed to a respectively higher value U.sub.out by the boost converter 4; during normal welding operation, only the buck converter 6 is usually active, changing the battery voltage U.sub.in to a respectively lower value of the welding voltage U.sub.out. In order to reduce the losses during normal welding operation, when only the buck converter 6 of the welding controller 3 is active, a switch 8 for bypassing the boost converter 4 is provided. The turn-on condition for the switch 8 is met when the intermediate circuit voltage U.sub.zw between the boost converter 4 and the buck converter 6 is less than or equal to the battery voltage U.sub.in. The turn-off condition for the switch 8 is met when the boost converter 4 is activated by the control device 15. This means that if the battery voltage U.sub.in is sufficient for welding operation and the boost converter 4 is not needed, it is bypassed by the switch controller 9 via the switch 8. As a consequence, only the conduction losses of the switch 8 need to be considered during normal welding operation. When choosing an appropriate switch 8, however, in particular a MOSFET, these losses are particularly low. For the basic condition for controlling the switch 8, measuring the intermediate circuit voltage U.sub.zw and the battery voltage U.sub.in is required. In addition, the output voltage U.sub.out may also be considered in the switch controller 9. Typically, the required parameters are digitised by means of analogue-to-digital converters and processed by means of a microprocessor contained in the switch controller 9. A capacitor 12 is usually provided between the boost converter 4 and the buck converter 6.

(9) According to a further turn-off condition of the switch 8 for bypassing the boost converter 4, the welding current I.sub.out is compared to the maximum current I.sub.b,max through the boost converter 4, and the switch 8 is opened if the welding current I.sub.out is less than the maximum current I.sub.b,max through the boost converter 4 and the buck converter 6 is deactivated.

(10) The boost converter 4 is deactivated if the welding voltage U.sub.out is less than the battery voltage U.sub.in minus a predetermined voltage, for example 2 V. In this case, the welding voltage U.sub.out and/or the arc voltage is less than the battery voltage U.sub.in minus the predetermined voltage value, so only the buck converter operates.

(11) The switches 5 and 7 of the boost converter 4 and the buck converter 6, respectively, are preferably formed by MOSFETs and are operated at the same switching frequency of preferably 40 to 50 kHz. The boost converter 4 is operated in a voltage-regulated manner whereas the buck converter 6 is operated in a current-regulated manner.

(12) If the buck converter 6 is used in the opposite direction, as a boost converter 4, the battery 2 may be loaded via the connections for the welding torch 11 and the workpiece 17.

(13) FIG. 2 shows a detailed block diagram of the welding controller 3 of the battery-powered welding device 1, wherein the control device 15 has the respective input parameters

(14) U.sub.in battery voltage

(15) I.sub.b current through the boost converter 4

(16) U.sub.zw intermediate circuit voltage

(17) U.sub.out welding voltage

(18) I.sub.out welding current

(19) U.sub.set set and/or desired welding voltage

(20) I.sub.set set and/or desired welding current

(21) The corresponding data is obtained by hardware for regulating the boost converter 4 in order to be able to reach the speed required for a high-dynamics regulation.

(22) FIG. 3 shows a block diagram of an embodiment of a regulation of the boost converter 4, wherein the intermediate circuit voltage U.sub.zw and the set desired welding voltage U.sub.set are compared in a control circuit 18 and converted into an analogue comparison value in a digital-to-analogue converter. In a comparator 10, this regulation output and the current I.sub.b flowing through the boost converter 4 are compared and supplied to the regulation 14 of the boost converter 4. The intermediate circuit voltage U.sub.zw and the current I.sub.b through the boost converter 4 may be filtered by appropriate filter circuits 20, 21.

(23) FIG. 4 shows a block diagram of an embodiment of a regulation of the buck converter 6, wherein the input parameters of the welding current I.sub.out and the desired set welding current I.sub.set are supplied to a controller 22, which is preferably formed by a PID controller. An additionally generated signal responsible for the maximum permissible welding current I.sub.out is supplied to a digital-to-analogue converter 23 and then analogously compared to the welding current I.sub.out in a comparator 24 and supplied to the regulation 14. Filters 25, 26 can be used here as well.

(24) FIG. 5 shows a time diagram of the intermediate circuit voltage U.sub.zw over time, wherein the intermediate circuit voltage U.sub.zw is measured only in part of the period of the clock frequency f.sub.t. In the example illustrated, the intermediate circuit voltage U.sub.zw is measured four times per period T.sub.t, and the mean value is determined. This mean value of the intermediate circuit voltage U.sub.zw is used to decide, after comparing it to the battery voltage U.sub.in, whether the switch 8 for bypassing the boost converter 4 is connected through or not. The remainder of the period duration T.sub.t, during which the intermediate circuit voltage U.sub.zw is not measured, remains for evaluation. In this way, a fast regulation and scanning, which has proven important for a welding process having optimal welding quality, may be performed.

(25) Finally, FIG. 6 shows a diagram of the welding voltage U.sub.out in relation to the welding current I.sub.out, wherein both the boost converter 4 and the buck converter 6 operate in the hatched area. In area II, only the buck converter 6 operates. This represents the normal welding state. The envelope according to FIG. 6 shows the maximum values and/or maximum power statically and/or dynamically.