Converter Module For A Multi-Stage Converter And Method For Operating Said Converter Module

Abstract

A converter module for a multi-stage converter includes an energy storage device connected in parallel with a series circuit of a first and a second semiconductor switching unit. At least one of the semiconductor switching units has a bidirectional switch. A switch-on unit is connected in parallel with the bidirectional switch. With the switch-on unit there can be produced a switch-on voltage for switching on the bidirectional switch from a voltage dropping across the bidirectional switch. There is also disclosed a multi-stage converter having the novel converter module and a method for operating the converter module.

Claims

1-12. (canceled)

13. A converter module for a multi-stage converter, comprising: a series circuit of a first semiconductor switching unit and a second semiconductor switching unit; at least one of said first and second semiconductor switching units having a bidirectional switch; an energy storage device connected in parallel with said series circuit; and a switch-on unit connected in parallel with said bidirectional switch and configured to generate a switch-on voltage for switching on said bidirectional switch from a voltage dropping across said bidirectional switch.

14. The converter module according to claim 13, wherein said switch-on unit is configured to generate the switch-on voltage by way of a voltage division of the voltage dropping across the bidirectional switch.

15. The converter module according to claim 13, wherein said switch-on unit comprises a deactivation switch enabling said switch-on unit to be deactivated.

16. The converter module according to claim 15, wherein said bidirectional switch comprises a first terminal, a second terminal and a control terminal, and said switch-on unit comprises: a first divider branch between said first terminal of said bidirectional switch and a central potential node; a second divider branch between said second terminal of said bidirectional switch and the central potential node; and a control branch between said control terminal of said bidirectional switch and the central potential node; and wherein said first and second divider branches respectively include at least one resistance element which are dimensioned in such a way that the switch-on voltage for switching on said bidirectional switch can be generated by a voltage division of the voltage dropping across said bidirectional switch.

17. The converter module according to claim 16, wherein the deactivation switch is arranged in one of said first or second divider branches.

18. The converter module according to claim 17, wherein said deactivation switch is a semiconductor switch which is passively conductive in a forward direction thereof and which can be switched off.

19. The converter module according to claim 18, wherein said deactivation switch is a junction field effect transistor switch.

20. The converter module according to claim 16, wherein: said bidirectional switch comprises a first controllable semiconductor switch which can be switched on and off, and a second controllable semiconductor switch which can be switched on and off, and wherein said second semiconductor switch is arranged anti-parallel to said first semiconductor switch; said first divider branch is arranged between an emitter terminal of said first semiconductor switch and a central potential node; said second divider branch is arranged between a collector terminal of said first semiconductor switch and the central potential node; and said control branch is arranged between a control terminal of said first semiconductor switch and the central potential node.

21. The converter module according to claim 13, which comprises a first connecting terminal connected to a potential node between said first and second semiconductor switching units, and a second connecting terminal connected to said energy storage device.

22. The converter module according to claim 21, wherein only said semiconductor switching unit arranged between said first and second connecting terminals comprises a bidirectional switch.

23. A multi-stage converter, comprising: a converter branch connected between a DC voltage terminal and an AC voltage terminal; said converter branch including a series circuit of two-pole converter modules, said two-pole converter modules including at least one converter module with a bidirectional switch; a switch-on unit connected in parallel with said bidirectional switch and configured for generating a switch-on voltage for switching on said bidirectional switch from the voltage dropping across said bidirectional switch.

24. A method for operating a converter module of a multi-stage converter having an energy storage device connected in parallel with a series circuit of two semiconductor switching units, wherein at least one of said two semiconductor switching units includes a bidirectional switch, the method comprising: providing a switch-on unit in parallel with the bidirectional switch; and precharging the energy storage device by generating with the switch-on unit a switch-on voltage for switching on the bidirectional switch from a voltage dropping across the bidirectional switch.

Description

[0029] The present invention is to be described in greater detail below, based on FIGS. 1 to 3.

[0030] FIG. 1 shows a schematic representation of an exemplary embodiment of a multi-stage converter according to the present invention, comprising a converter module according to the present invention;

[0031] FIG. 2 shows a schematic representation of an exemplary embodiment of a bidirectional switch;

[0032] FIG. 3 shows a schematic representation of an exemplary embodiment of a switch-on unit.

[0033] FIG. 1 depicts a multi-stage converter 1 in detail. The multi-stage converter 1 comprises a first phase branch 2 which extends between a first AC voltage terminal 6 and a first DC voltage terminal 8. Furthermore, the multi-stage converter 1 comprises a second phase branch 3 which extends between the first AC voltage terminal 6 and a second DC voltage terminal 9, a third phase branch 4 which extends between a second AC voltage terminal 7 and the first DC voltage terminal 8, and a fourth phase branch 5 which extends between the second AC voltage terminal 7 and the second DC voltage terminal 9. The AC voltage terminals 6, 7 are configured to connect the multi-stage converter 1 to an alternating-current grid, which is not depicted in the figure. The DC voltage terminals 8, 9 are configured to connect the multi-stage converter 1 to a direct-current grid, which is not depicted in the figure. In this case, the DC voltage line to be connected to the DC voltage terminals 8, 9 is made up of two DC voltage conductors, wherein one of the DC voltage conductors may also be provided via a ground connection.

[0034] In the exemplary embodiment depicted in FIG. 1, the alternating-current grid to be connected is two-phase; thus, the multi-stage converter 1 is also configured to be two-phase. Within the scope of the present invention, it is of course also possible to configure the multi-stage converter 1 to have three or more phases, wherein in such a case, the multi-stage converter may be extended to additional phase branches in a manner known to those skilled in the art.

[0035] A series circuit of two-pole converter modules is arranged in the first phase branch 2, wherein only a first converter module 10 is graphically depicted in FIG. 1 for reasons of clarity. The additional converter modules, which are not depicted in the figures, have the same configuration as the first converter module 10. Correspondingly, a series circuit of converter modules is arranged in the second phase branch 3, of which only a second converter module 11 is graphically depicted. In the same manner, the third phase branch 4 comprises a series circuit of converter modules, of which only a third converter module 12 is graphically depicted, and finally, the fourth phase branch 5 likewise comprises a series circuit of converter modules, of which only a fourth converter module 13 is depicted. In the exemplary embodiment depicted in FIG. 1, all converter modules, both the ones which are graphically depicted and the ones which are not graphically depicted, are configured identically.

[0036] Using the example of the first converter module 10, the inner configuration of said converter module will be described below in greater detail. The first converter module 10 comprises an energy storage device in the form of a capacitor 14. A series circuit made of a first semiconductor switching unit 15 and a second semiconductor switching unit 16 is arranged in parallel with the capacitor 14.

[0037] The first semiconductor switching unit 15 comprises a semiconductor switch 17 which can be switched on and off, to which a flyback diode 18 is connected in anti-parallel. The forward direction of the flyback diode 18 is opposite the blockable forward direction of the semiconductor switch 17. The semiconductor switch 17 is, for example, a gate turn-off (GTO) thyristor or an insulated-gate bipolar transistor (IGBT) or an integrated gate-commutated thyristor (IGCT).

[0038] The second semiconductor switching unit 16 comprises a bidirectional switch 19, the configuration of which will be discussed in greater detail in FIG. 2. The bidirectional switch 19 is configured as a two-pole device and comprises a first terminal 26 and a second terminal 27.

[0039] A switch-on unit 20 is arranged in parallel with the second semiconductor switching unit 16, or rather, the bidirectional switch 19. The configuration of the switch-on unit 20 will be described in greater detail in conjunction with the description of FIG. 3.

[0040] The second semiconductor switching unit 16 is connected to a control device 21. The first semiconductor switching unit 15 is also connected to the control device 21, which, however, is not depicted graphically in FIG. 1 for reasons of clarity. The control device 21 is configured to control the semiconductor switches of the first converter module 10, according to a predetermined control algorithm. The control device 21 also assumes control of all remaining semiconductor switches in all converter modules of the multi-stage converter 1.

[0041] In the present exemplary embodiment, the switch-on unit 20 is designed to be controllable. The control device 21 assumes control of the switch-on unit 20, or rather, controllable components of the switch-on unit 20.

[0042] A first connecting terminal 28 of the first converter module 10 is connected to a potential point 281 between the first and second semiconductor switching units 15 and 16. A second connecting terminal 29 is directly connected to a pole of the capacitor 14. Accordingly, the first converter module 10 forms a half-bridge circuit.

[0043] FIG. 2 shows an exemplary embodiment of a bidirectional switch 19 of one of the converter modules 10 to 13 of the multi-stage converter 1 of FIG. 1. A first IGBT 22 is connected in series with a diode 23, wherein the emitter 24 of the IGBT 22 and the cathode 25 of the diode 23 are oriented in the direction of the first terminal 16. The emitter 24 of the first IGBT 22 is connected to the first terminal 26, and the anode 30 of the diode 23 is connected to the second terminal 27. A second IGBT 31 is arranged in parallel with the series circuit made up of the first IGBT 22 and the diode 23. The emitter 32 of the second IGBT 31 is connected to the second terminal 27 of the bidirectional switch 19. The first and second IGBTs 22 and 31 may be controlled, i.e., switched on and off, by means of their control terminals 33 and 34. In an initial state of the bidirectional switch during commissioning of the multi-stage converter 1, the bidirectional switch 19 is generally in a blocked state. In this state, both IGBTs 22, 31 are blocking, so that the connection between the first terminal 26 and the second terminal 27 is not electrically conductive. Generally, such a bidirectional switch may have a breakdown voltage ranging from 1 kV to more than 5 kV.

[0044] An overvoltage protection unit 35 is arranged in parallel with the first IGBT 22. Overvoltages across the first IGBT 22 may be limited by means of the overvoltage protection unit 35. The overvoltage protection unit 35 may, for example, comprise one or a plurality of resistors and/or surge arresters.

[0045] FIG. 3 depicts the switch-on unit 20 of the first converter module 10 from FIG. 1. The switch-on unit 20 is explained here in conjunction with the bidirectional switch 19 of FIG. 2. However, a corresponding configuration of the switch-on unit 20 may also be used in conjunction with bidirectional switches having a different configuration.

[0046] The switch-on unit 20 has the configuration of a voltage divider. It comprises a first divider branch 36, which extends between the first terminal 26 of the bidirectional switch 19 and a central potential point 37. A first divider resistor 38 is arranged in the first divider branch 36. The switch-on unit 20 furthermore comprises a second divider branch 39, which extends between the second terminal 27 of the bidirectional switch 19 and the central potential point 37. A second divider resistor 40 is arranged in the second divider branch 39. Alternatively, the second divider branch 39 may also be routed via the diode 23 to the second terminal 27.

[0047] The central potential point 37 is furthermore connected to the control device 21 via an additional resistor 41. In addition, the switch-on unit 20 comprises a control branch 42 which connects the control terminal 33 of the first IGBT 22 to the central potential point 37 and thus also to the control device 21.

[0048] The switch-on unit 20 comprises a deactivation switch 43 which is arranged in the second divider branch 39 in series with the second divider resistor 40. The deactivation switch 43 is a JFET and is conductive in its initial state. The deactivation switch is designed for 3 kV in the present exemplary embodiment. A control terminal 44 of the deactivation switch 43 is also connected to the control device 21.

[0049] The functionality of the switch-on unit 20 is to be explained in greater detail below in conjunction with the previously described configuration of the converter module of the multi-stage converter 1 of FIG. 1.

[0050] In the initial situation, the multi-stage converter 1 is connected to an alternating-current grid. Accordingly, an alternating current is applied to the AC voltage terminals 6, 7. The capacitors 14 of the converter modules are to be charged from the alternating-current grid. In the present initial state, the bidirectional switch 19 is blocked in its reverse direction. In this case, the reverse direction corresponds to the forward direction of the flyback diodes 18.

[0051] During a first time span, the electrical potential at the first AC voltage terminal 6 is higher than the electrical potential at the second AC voltage terminal 7.

[0052] In this case, the current (technical current direction) in the first converter module 10 flows in the forward direction of the diode 23 in the bidirectional switch 19. Due to the voltage difference between the second terminal 27 of the bidirectional switch 19 and the control terminal 33 of the IGBT 22 in the bidirectional switch 19, the IGBT 22 is turned on. The current can flow though the bidirectional switch 19 of the first converter module 10, said bidirectional switch now being conductive in the reverse direction.

[0053] In the second converter module 11, the current flows via the flyback diode 18 of the second converter module 11 and charges the capacitor 14 of the second converter module 11.

[0054] In the third converter module 12, the current flows correspondingly via the flyback diode 18 of the third converter module 12 and charges the capacitor 14 of the third converter module 12.

[0055] In the fourth converter module 13, the current flows in the forward direction of the diode 23 in the bidirectional switch 19 of the fourth converter module 13. Due to the voltage difference between the second terminal 27 of the bidirectional switch 19 and the control terminal 33 of the IGBT 22 in the bidirectional switch 19, the IGBT 22 is turned on. The current can flow through the bidirectional switch 19 of the fourth converter module 13, which is conductive in the reverse direction.

[0056] With this polarity at the terminals 6 and 7, the capacitors 14 of the converter modules in the second and third phase branches 3 and 4 are accordingly charged.

[0057] Due to the AC voltage present at the AC voltage terminals 6, 7, the electrical potential at the first AC voltage terminal 6 is lower than the electrical potential at the second AC voltage terminal 7 during a second period of time.

[0058] In the case of a reversed polarity at the AC voltage terminals 6 and 7, the current direction is correspondingly reversed. Correspondingly, in the case of the reversed polarity of the current, the capacitors 14 in the first and fourth phase branches 2 and 5 are charged.

[0059] If all capacitors 14 of all converter modules are charged, the power supply of the control device 21 is also provided. In this case, the control device 21 may deactivate the switch-on unit 20 by means of a suitable control of the deactivation switch 43.