Device and method for restricting fault current in DC voltage system

Abstract

To provide a device with less loss as much as possible during an operation of a DC transmitting / distributing device and with reliability and a method for restricting fault current by using the device.SOLUTION: A device (20) for restricting fault current in a DC voltage circuit (6 to 9), comprising a series connection of current restriction modules (23.1 to 23.2n) in a housing device (24), wherein each current restriction module comprises: a plurality of power semiconductor switches (331 to 33n); and a surge arrestor (34) connected in parallel with the power semiconductors, and further comprises: control devices (26, 37) which perform control to actuate the power semiconductor switches by using different gate-emitter voltages; a power unit (27) for supplying energy to the current restriction modules; a cooling device (28) for cooling the current restriction modules or their power semiconductors; and a measuring instrument (29) for detecting measurement quantities of current and / or voltage, etc. in the device.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a device for limiting fault currents in a DC voltage circuit, comprising a series connection of several current limiting modules, each of which comprises several power semiconductor switches and a surge arrester connected in parallel to the power semiconductors.

[0002] Devices for limiting or suppressing fault currents (often called DC circuit breakers or DC fault isolation devices) are important for the operation of DC voltage-based transmission and distribution systems (point-to-point systems, multi-terminal systems, and meshed systems). In contrast to AC voltage / current, DC voltage systems do not have natural current zero crossings, and therefore specific solutions are required for their application. For DC circuit breakers / DC fault isolation devices, it is particularly important that they have low forward losses. Multiple devices using power electronics can be used to suppress fault currents, and in these cases, in addition to minimizing the forward losses mentioned above, avoiding derating due to the parallel and series connection of multiple semiconductors is also a technical challenge.

[0003] The device mentioned at the outset is known from DE 10 2004 014 142 A1. The known device comprises a power electronic DC circuit breaker with a series connection of semiconductor switching elements and a flywheel path electrically connected in parallel with the series connection of the switches, each of the semiconductor switching elements having a power electronic switch and a surge arrester. This known solution differs from DC circuit breakers with mechanical switches in the operating current path (path through which the operating current flows during normal operation) in that in the known DC circuit breaker, several power semiconductor switches are arranged in the operating current path. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] German Patent Application Publication No. 10 2015 211 339 A1 [Patent Document 2] International Publication No. 2012 / 107010 A1 Brochure Summary of the Invention [Problem to be solved by the invention]

[0005] SUMMARY OF THE INVENTION The object of the invention is to provide a device as mentioned at the beginning which operates with as few losses as possible and is reliable. [Means for solving the problem]

[0006] This problem is solved by a device according to the features of claim 1.

[0007] According to the invention, the device comprises a control device for controlling a plurality of power semiconductor switches, the control device being configured to operate the power semiconductor switches with different gate-emitter voltages, i.e. configured to switch the power semiconductor switches on or off using control signals (for this purpose the control device is connected to the gates of each of the associated power semiconductor switches). The power semiconductor switches are preferably power semiconductor switches that can be switched off, such as IGBTs, IGCTs, MOSFETs, JFETs, and SiC- or GaN-based power semiconductor switches.

[0008] The present invention makes use of the finding that the collector-emitter voltage UCE (and therefore also the forward losses) in a power semiconductor generally depends on the applied gate-emitter voltage UGE (at least for currents up to about 2.5 kA). In particular, the voltage UCE generally decreases as the voltage UGE is increased. The operation of a semiconductor switch with an increased UGE is described, for example, in US Pat. No. 6,449,399.

[0009] However, according to the present invention, not all power semiconductor switches are operated by one (and the same) elevated voltage UGE, but rather the power semiconductor switches are controlled and operated by different gate-emitter voltages in order to increase the reliability of the device.

[0010] Suitably, the gate-emitter voltage lies between 18 V and 35 V for positive voltages or between 0 V and -15 V for negative voltages. When the power semiconductor switch is in the off-state, the collector-emitter voltage UCE can have a value between 1 kV and 10 kV. The forward voltage can have a value up to 10 V, for example. In addition to activating or deactivating all current limiting modules, the control device is particularly configured to activate only some of these modules, for example to throttle the current gently or to limit the current at a maximum value.

[0011] In practice, the control device is configured to operate at least one first power semiconductor switch of a current limiting module with a first gate-emitter voltage corresponding to a nominal gate-emitter voltage and to operate at least one second power semiconductor switch of the same current limiting module with a second gate-emitter voltage having a value higher than the nominal gate-emitter voltage. The control device is particularly configured to operate two power semiconductor switches of one and the same current limiting module with different gate-emitter voltages. For example, the first power semiconductor switch can be operated with a first gate-emitter voltage, which may be the nominal gate-emitter voltage. The nominal gate-emitter voltage is specified, for example, by the manufacturer of the relevant power semiconductor. The second power semiconductor switch can be operated with a higher gate-emitter voltage.

[0012] In particular, at least one current limiting module comprises at least two power semiconductor switches arranged in series. In particular, each current limiting module can comprise two power semiconductor switches connected in series. The series-connected power semiconductor switches are operated with different gate-emitter voltages (a first power semiconductor switch in the series connection is operated with a first gate-emitter voltage and a second power semiconductor switch in the series connection is operated with a second gate-emitter voltage different from the first gate-emitter voltage, for example higher than the first gate-emitter voltage) so that the same voltage is applied to each of the power semiconductor switches during operation of the device, thereby equalizing the load on the power semiconductors and thus improving the reliability of the device.

[0013] It is then possible to influence the voltage sharing with respect to this gate-emitter voltage (for example, based on active overvoltage limiting by manipulating the turn-off voltage in the range from -15V to slightly positive voltages), which advantageously allows series connections to be made without derating the voltage utilization of the semiconductors.

[0014] Preferably, at least one current limiting module comprises at least two power semiconductor switches arranged in anti-series with respect to one another. In particular, each current limiting module may comprise (at least) two power semiconductor switches connected in anti-series. Anti-series connection in this case is understood to mean an arrangement of several power semiconductor switches arranged in series with one another but in opposite forward or reverse directions. This provides a bidirectional switch-off function for the device.

[0015] According to one embodiment of the present invention, at least one current limiting module comprises at least two power semiconductor switches connected in parallel with each other. In particular, each current limiting module may comprise (at least) two power semiconductor switches connected in parallel. Basically, the parallel connection increases the current carrying capacity of the device. Advantageously, asymmetries in the mechanical structure (parasitic resistances and parasitic inductances) can be compensated for by (e.g., slight) adjustment of the gate-emitter voltage. In particular, the parallel-connected power semiconductor switches are operated with different gate-emitter voltages (a first parallel-connected power semiconductor switch is operated with a first gate-emitter voltage, and a second parallel-connected power semiconductor switch is operated with a second gate-emitter voltage different from the first gate-emitter voltage) so that the same current flows through the parallel-connected power semiconductors, thereby equalizing the load on the power semiconductors and thus further increasing the reliability of the device.

[0016] According to a particularly preferred embodiment of the present invention, at least one current limiting module comprises at least four power semiconductor switches, each arranged in a parallel circuit of two power semiconductor switches arranged anti-series with respect to one another. This embodiment allows combining the above-mentioned advantages of anti-series and parallel connections of power semiconductor switches. Of course, the current limiting module may comprise more than two power semiconductors arranged in parallel. A series connection of more power semiconductor switches is also conceivable. It is advantageous if some or all of the current limiting modules are configured with multiple power semiconductor switches in series, anti-series, and / or parallel. Multiple parallel connections are possible to allow scalability in terms of the nominal current and the maximum permissible fault current, if desired.

[0017] Preferably, at least one current limiting module, and particularly preferably all current limiting modules, are provided with a bypass switch for bypassing the current limiting module in the event of a fault. The bypass switch is preferably a high-speed (typically mechanical) closing element, which is connected in parallel to the power semiconductor switch of the current limiting module. One or more bypass switches can be used to bypass individual faulty current limiting modules, thereby ensuring reliable operation of the entire device.

[0018] Preferably, at least one current limiting module comprises a parallel resistor connected in parallel to the surge arrester. Advantageously, all current limiting modules each comprise such a parallel resistor. The parallel resistors within the current limiting modules provide symmetrical voltage sharing within the entire device when the device is deactivated (=switched off).

[0019] The device may further comprise a power supply for supplying energy to the current limiting module, the power supply being electrically isolated from the current limiting module, for example the power supply may be a central auxiliary energy supply (device power supply) that supplies energy to the current limiting module in a galvanically isolated manner (e.g. by laser transmission).

[0020] The power semiconductor switches can be heat dissipated in an appropriate manner by means of an active cooling system, which can be achieved, for example, by water cooling.

[0021] The device preferably comprises a series connection of three or more current limiting modules. The power semiconductor switches may or may not optionally have integrated (anti-parallel) diodes (as separate components). The power semiconductor switches may furthermore optionally have a normally-off or normally-on characteristic (also known as semiconductor depletion or enhancement). The desired system behavior (safe state OFF) is adjusted via a control unit (module control unit) internal to the current limiting module. The module control unit is generally configured to operate the power semiconductors, monitor the module status, and communicate with a higher-level closed-loop or open-loop control system. The module control unit is supplied with auxiliary energy from a module power supply. A surge arrester is connected in parallel to the anti-series connection of the power semiconductors in the current limiting module, and DC current is commutated to the surge arrester as soon as the power semiconductor switch is opened (disconnected). In this manner, the DC current flowing through the current limiting module is suppressed (energy absorption) by a high impedance and reduced to a low residual current (eg, <10A).

[0022] Within the device, a variable number n of current limiting modules are connected in series (n>2) to allow adjustment to different nominal voltages and redundancy. The device further comprises a control device (device control unit) that activates the current limiting modules (including gate drivers with controllably increased gate-emitter voltages) and monitors their status. In addition to activating or deactivating all current limiting modules, the device control unit can activate only a portion of the current limiting modules, for example to throttle the current gently or to limit the current to a maximum value.

[0023] The invention can be advantageously used in a DC voltage system comprising several power converters connected to one another by means of DC voltage connections, and at least one device according to the invention can be used to limit a fault current in one of the DC voltage circuits. In the event of a fault in the DC voltage system, the device or devices can be used to isolate the fault, to characterize the fault and to allow the part of the DC voltage system not affected by the fault to continue operating.

[0024] The invention further relates to a method for limiting a fault current in a DC voltage connection using an arrangement comprising a series connection of several current limiting modules, each current limiting module having several power semiconductor switches and a surge arrester connected in parallel to the power semiconductors, as well as a control device for controlling the power semiconductor switches, in which the power semiconductor switches are operated with different gate-emitter voltages.

[0025] The advantages of the method according to the invention correspond in particular to those already explained in connection with the device according to the invention.

[0026] The invention will now be described in detail with reference to the exemplary embodiment shown in FIGS. [Brief explanation of the drawings]

[0027] [Figure 1] FIG. 1 shows in a schematic diagram an exemplary embodiment of a DC voltage system according to the invention. [Figure 2] FIG. 2 shows a schematic diagram of an embodiment of a device according to the invention for limiting fault currents. [Figure 3] FIG. 3 shows a schematic diagram of an example current limiting module. DETAILED DESCRIPTION OF THE INVENTION

[0028] FIG. 1 shows a DC voltage system 1. The DC voltage system 1 comprises four power converters 2-5, each of which is arranged between an AC voltage system and a DC voltage system 1. The power converters 2-5 are connected to each other using DC voltage circuits 6-9. The DC voltage circuits 6-9 may be unipolar or, for example, bipolar. The DC voltage circuits 6-9 are linked to each other at DC voltage nodes 10-13. In the spatial vicinity of two DC voltage nodes 10 and 12, first, second, third and fourth devices 14-17 are arranged, which can be used to limit fault currents in the associated DC voltage circuits 6-9. The configuration of these devices is explained in more detail in the following FIGS. 2 and 3.

[0029] Figure 2 shows a device 20 for limiting a fault current in a DC voltage circuit, also called a fault isolation device, such as one of the DC voltage circuits 6-9 of Figure 1. The device 20 comprises a first terminal 21, a second terminal 22 and a series connection of current limiting modules 23.1 to 23.2n, the construction of which is subsequently described in more detail in Figure 3.

[0030] The current limiting modules 23.1 to 23.2n are arranged in a housing device 24, which is insulated from ground potential by means of an isolator 25. The device 20 further comprises a control device 26 for controlling the current limiting modules 23.1 to 23.2n or their power semiconductor switches, a power supply device 27 for supplying energy to the current limiting modules 23.1 to 23.2n, a cooling device 28 for cooling the current limiting modules 23.1 to 23.2n or their power semiconductors, and a measuring device 29 for detecting measured quantities, such as current and / or voltage, in the device 20.

[0031] 3 illustrates a current limiting module 30, which may be, for example, one of the current limiting modules 23.1 to 23.2n. The current limiting module 30 has a first module terminal 31 and a second module terminal 32. The current limiting module 20 includes power semiconductor switches 331 to 33n, which are connected in anti-series and in parallel with each other. A freewheeling diode F is connected in anti-parallel to each of the power semiconductor switches 331 to 33n.

[0032] A surge arrester 34 is connected in parallel to the power semiconductors 331 to 33n in the current limiting module 30, and when the power semiconductor switch is opened (turned off), a DC current (fault current) is commutated to the surge arrester 34. In this way, the DC current flowing through the current limiting module 30 is suppressed (energy absorption) by high impedance and reduced to a small residual current (for example, <10 A).

[0033] The number of current limiting modules in the device according to the invention is determined so that the device as a whole can remain operational and fulfill its function even if some current limiting modules fail (redundancy). Correspondingly, high-speed mechanical closing elements or bypass switches 35 are connected in parallel to the power semiconductor switches 331 to 33n of the current limiting modules 30, which allow bypassing individual failed current limiting modules and thus ensuring reliable operation of the device as a whole.

[0034] By means of the parallel resistor 36, an even (symmetrical) voltage distribution within the current limiting module 30 can be achieved when the power semiconductor switches 331 to 33n are in the cut-off state.

[0035] The current limiting module 30 further comprises a module control device 37, which is connected to the gates of the power semiconductor switches 331 to 33n and to a control device center (numbered 26 in FIG. 2 ), which together with all module control devices forms a control device for operating the power semiconductor switches. The module control device 37 comprises, in particular, corresponding gate drivers with a controllably increased gate-emitter voltage. The module control device 37 is configured for operating the power semiconductors, for monitoring the module status, and for communicating with a higher-level control device.

[0036] A modular energy supply module 38 is provided for supplying the module control devices with energy and for this purpose is electrically isolated and connected (for example by means of optical fibres) to the central power supply.

[0037] During operation, the first power semiconductor switch 331 is operated with a nominal gate-emitter voltage (e.g., according to the manufacturer's data sheet or corresponding specifications), whereas the second power semiconductor switch 332 is operated with a gate-emitter voltage that is higher than the nominal gate-emitter voltage. The determination of these gate-emitter voltages to be used can be determined once during commissioning or dynamically and repeatedly during operation.

Claims

1. A device (20) for limiting fault currents in a DC voltage circuit, comprising a series connection of current limiting modules (23.1 to 23.2n), each current limiting module (23) comprising a plurality of power semiconductor switches (331 to 33n) and a surge arrester (34) connected in parallel to the power semiconductors (331 to 33n), a control device (26) for controlling the power semiconductor switches (331-33n), the control device (26) being configured to operate the power semiconductor switches (331-33n) with different gate-emitter voltages.

2. 2. The device (20) according to claim 1, wherein the control device (26) is configured to operate at least one first power semiconductor switch (331-33n) of a current limiting module (23.1-23.2n) with a first gate-emitter voltage corresponding to a nominal gate-emitter voltage, and to operate at least one second power semiconductor switch (331-33n) of the same current limiting module (23.1-23.2n) with a second gate-emitter voltage having a value higher than the nominal gate-emitter voltage.

3. 3. The device (20) according to claim 1 or 2, wherein at least one current limiting module (23.1 to 23.2n) comprises at least two power semiconductor switches (331 to 33n) arranged in series connection.

4. 4. The device (20) according to claim 1, wherein at least one current limiting module (23.1 to 23.2n) comprises at least two power semiconductor switches (331 to 33n) arranged in anti-series with respect to one another.

5. 5. The device (20) according to claim 1, wherein at least one current limiting module (23.1 to 23.2n) comprises at least two power semiconductor switches (331 to 33n) arranged in parallel connection with one another.

6. 6. The device (20) according to claim 1, wherein at least one current limiting module (23.1 to 23.2n) comprises at least four power semiconductor switches (331 to 33n), each of which is arranged in parallel with two power semiconductor switches (331 to 33n) arranged anti-series to one another.

7. 7. The apparatus (20) according to any one of claims 1 to 6, wherein at least one current limiting module (23.1-23.2n) comprises a bypass switch (35) for bypassing said current limiting module (23.1-23.2n) in the event of a fault.

8. The device (20) according to any one of claims 1 to 7, wherein at least one current limiting module (23.1 to 23.2n) comprises a parallel resistor (36) in parallel connection with the surge arrester.

9. 9. The apparatus (20) according to any one of claims 1 to 8, wherein the apparatus comprises a power supply (27) for supplying energy to the current limiting modules (23.1 to 23.2n), the power supply (27) being electrically isolated from the current limiting modules (23.1 to 23.2n).

10. The device (20) according to any one of claims 1 to 9, wherein the power semiconductor switches (331-33n) are heat dissipating means of active cooling.

11. 11. A DC voltage system (1) comprising a plurality of power converters (2-5) connected to one another by means of a plurality of DC voltage circuits (6-9) and at least one device (14-17) according to any one of claims 1 to 10, by means of which a fault current in one of the DC voltage circuits (6-9) can be limited.

12. A method for limiting fault currents in a DC voltage circuit (6-9), comprising: - a series connection of current limiting modules (23.1 to 23.2n), each current limiting module (23.1 to 23.2n) having a plurality of power semiconductor switches (331 to 33n) and a surge arrester (36) connected in parallel to said power semiconductors (331 to 33n), and - a control device (26, 37) for controlling the power semiconductor switches (331 to 33n), Using the device, The method, wherein the power semiconductor switches (331 to 33n) are operated with different gate-emitter voltages.

Images