OPTIMIZED STRUCTURE OF A DC VOLTAGE SYSTEM AND METHOD IN THE EVENT OF FAILURE OF THE SUPPLYING NETWORK

Abstract

The invention relates to an electrical DC voltage system which is coupled to at least one AC voltage network (1). A supply circuit (5) is used to convert three-phase AC voltage into DC voltage which supplies a DC voltage system. The latter contains devices (13, 14, 21, 23, 27, 22, 17, 19, 20) each having a decentralized precharge device (7). The invention also relates to a method for operating such an electrical DC voltage system on the basis of a voltage value applied to the busbar (12).

Claims

1.-23. (canceled)

24. An electrical DC voltage system, comprising: a plurality of items of equipment, a busbar switchably connected to a DC side of a supply circuit, with an AC side of the supply circuit connected to an AC voltage network for supplying electrical energy to the DC voltage system, a local pre-charging device, which is integrated into a respective item of equipment or is connected upstream of the respective item of equipment and which is specifically designed for the respective item equipment, connecting each of the respective items of equipment to the busbar in one-to-one correspondence, wherein an item of equipment is a single piece of equipment, a combination of a plurality of pieces of equipment or a sub-system.

25. The electrical DC voltage system of claim 24, wherein the local pre-charging device comprises a circuit arrangement composed of a resistor connected in parallel with two semiconductors, and a switch connected in series with the circuit arrangement.

26. The electrical DC voltage system of claim 24, wherein the AC voltage network is designed as a three-phase AC voltage network.

27. The electrical DC voltage system of claims 24, wherein at least one item of equipment in the DC voltage system comprises the local pre-charging device.

28. The electrical DC voltage system of claim 24, wherein the local pre-charging device is connected upstream of at least one item of equipment present in the DC voltage system.

29. The electrical DC voltage system of claim 24, wherein each item of equipment present in the DC voltage system is connected to the busbar via a single local pre-charging device.

30. The electrical DC voltage system of claim 25, wherein the two semiconductors are connected anti-serially.

31. The electrical DC voltage system of claim 25, wherein the two semiconductors are implemented as controllable bipolar transistors, IGBTs, controllable field effect transistors, or MOSFETs.

32. The electrical DC voltage system of claim 24, wherein the local pre-charging device incorporates or is connected to a supervision unit.

33. The electrical DC voltage system of claim 24, wherein the local pre-charging device incorporates or is connected to a control unit.

34. The electrical DC voltage system of claim 33, wherein, below a defined voltage value, the control unit turns off at least one of the two semiconductors to interrupt current flow through the semiconductors and, above the defined voltage value, renders at least one of the two semiconductors conducting to enable current to flow through the semiconductors.

35. The electrical DC voltage system of claim 24, wherein the supply circuit is switchably connected to the AC voltage network.

36. The electrical DC voltage system of claim 24, wherein the supply circuit comprises a rectifier circuit.

37. The electrical DC voltage system of claim 24, wherein the DC voltage system is part of an industrial plant.

38. A method for operating an electrical DC voltage system having a plurality of items of equipment, wherein each of the respective items of equipment is connected to a busbar via a local pre-charging device in one-to-one correspondence, the method comprising: measuring a voltage value present on the busbar, when the measured voltage value is greater than a first minimum voltage, operating the electrical DC voltage system in a normal mode, wherein a supply circuit supplying electrical energy to the DC voltage system is connected to an AC voltage network and the local pre-charging device is deactivated, and when the measured voltage value falls below the first minimum voltage, disconnecting the supply circuit from the AC voltage network.

39. The method of claim 38, further comprising: when the measured voltage value is less than the first minimum voltage and exceeds a second minimum voltage, supplying electrical energy to the DC voltage system from controllable energy storage devices or energy sources disposed in the DC voltage system.

40. The method of claim 39, further comprising: when the measured voltage value is less than the first minimum voltage and exceeds the second minimum voltage, switching off loads disposed in the electrical DC voltage system.

41. The method of claim 39, further comprising: when the measured voltage value falls below the second minimum voltage, activating the local pre-charging devices disposed in the electrical DC voltage system.

42. The method of claim 38, further comprising: when the measured voltage value is less than a second minimum voltage and greater than a third minimum voltage, deactivating controllable energy storage devices or energy sources disposed in the electrical DC voltage system.

43. The method of claim 38, further comprising: when the measured voltage value is less than a second minimum voltage and exceeds a third minimum voltage, switching off ail loads disposed in the electrical DC voltage system.

44. The method of claim 38, further comprising: connecting the supply circuit when the measured voltage value falls below a third minimum voltage or when a minimum time has elapsed since the measured voltage fell below a second minimum voltage or when all local pre-charging devices have transmitted an acknowledgment signal to a higher-order control unit concerning their activation.

45. The method of claim 44, further comprising: deactivating the local pre-charging devices, when the measured voltage value exceeds the first minimum voltage.

46. The method of claim 38, further comprising: when the measured voltage value falls below a second minimum voltage, switching off all loads disposed in the electrical DC voltage system, and switching on at least one particular load, when the measured voltage value exceeds the second minimum voltage after supplying electrical energy from controllable energy storage devices or from energy sources disposed in the electrical DC voltage system.

Description

[0056] The invention will now be described and explained in greater detail with reference to the exemplary embodiments depicted in the accompanying drawings in which:

[0057] FIG. 1 shows an active supply circuit with pre-charging device according to the prior art,

[0058] FIG. 2 shows an embodiment of a DC voltage system with local pre-charging devices which is connected to a three-phase AC voltage network via a supply circuit,

[0059] FIG. 3 shows a method for operating an electrical DC voltage system, and

[0060] FIG. 4 shows an embodiment of a switching and protection device with pre-charging resistor.

[0061] FIG. 1 shows an embodiment of an active supply circuit with pre-charging device 55, also termed supply circuit, according to the prior art. A DC voltage system is linked to a three-phase AC voltage network 50 via a supply circuit 55. For each phase, the supply circuit 55 has a switch 51 which can bridge a pre-charging resistor 52 for each phase.

[0062] The supply circuit also has chokes 54 which are required for storing energy for increasing the DC voltage. Rectification of a three-phase AC voltage from the three-phase AC voltage network 50 is performed by means of controllable semiconductors 53, particularly IGBTs. However, it is also possible for passive components, particularly diodes, to be used for rectifying a three-phase AC voltage. The supply circuit also incorporates a smoothing capacitor 56. When the DC voltage system is uncharged, current limiting must be ensured when the three-phase AC voltage network 50 is switched on, as any voltage difference between a DC voltage in the DC voltage system and a rectified AC voltage results in an uncontrollable current which damages or destroys sensitive components in the DC voltage system. This current limiting is achieved by the pre-charging device in the supply circuit 55. Initially the pre-charging resistor 52 is used. This serves to limit the current. When the DC voltage system is finally charged and its DC voltage corresponds to the rectified AC voltage, the pre-charging resistor 52 present in the active supply circuit 55 is bridged by means of the switch 51.

[0063] FIG. 2 shows an embodiment of the inventive design of a DC voltage system which is linked to a three-phase AC voltage network 1 by means of a supply circuit 5. Such an arrangement is possible e.g. within an industrial plant.

[0064] The three-phase AC voltage supply 1 is connected to a rectifier circuit via a switch 2 for each phase and a choke 3 for each phase. The rectifier circuit comprises six passive components, particularly diodes, or six controllable semiconductors, particularly IGBTs with antiparallel freewheeling diode 4. A capacitor 6 is connected between the supply circuit 5 and a DC voltage busbar 12. The capacitor 6 is used to smooth the rectified AC voltage. A pre-charging circuit as per FIG. 1 can be provided to pre-charge the capacitor 6.

[0065] The DC voltage busbar 12 is connected to the supply circuit 5 via a switching and protection device 8. The switching and protection device 8 comprises an anti-series connection of two controllable semiconductors, preferably IGBTs with anti-parallel freewheeling diode 10, 11, and a switch 9 connected in series with this arrangement.

[0066] A DC voltage system is connected to the DC voltage busbar 12. According to the invention, different items of equipment are present in the DC voltage system. A first load 13 is connected to the DC voltage busbar 12 via a first local switching and protection device with pre-charging resistor 7 (local pre-charging device). The switching and protection device with pre-charging resistor 7 is described in FIG. 4 and comprises a pre-charging resistor 73. This pre-charging resistor 73 is connected in parallel with an anti-series connection of two controllable semiconductors, preferably IGBTs with anti-parallel freewheeling diode 71, 72. A switch 74 is located in series with this arrangement or in series with the pre-charging resistor 73.

[0067] in particular, a fan, a heater or a lamp can be connected as the first load 13. Connected to the DC voltage busbar 12 via another switching and protection device with pre-charging resistor 7 is a first inverter 14 and a capacitor 15 connected upstream of the first inverter 14. In addition, a sub-system is connected to the busbar 12 by means of a DC voltage busbar 30, wherein this connection can be established via another switching and protection devices with pre-charging device 7. Present in this sub-system are a second and a third load 19 and 20 which are each connected to the sub-system busbar 30 via another switching and protection device with pre-charging resistor 7. Also present in the DC voltage sub-system are a second inverter 22 with upstream capacitor 16 connected via another switching and protection device with pre-charging resistor 7, and a third inverter 17 with upstream capacitor 18 connected via another switching and protection device with pre-charging resistor 7. In particular, motors or robots are connected to the inverters. The DC voltage system also has a capacitive storage device 21 which is connected to the DC voltage busbar 12 via another switching and protection device with pre-charging resistor 7.

[0068] An energy source in the form of a photovoltaic system 23 is also available in the DC voltage system. The photovoltaic system 23 is connected to a capacitor 24 via a DC/DC controller 25. This can likewise be connected to the DC voltage busbar 12 via a switching and protection device with pre-charging resistor 7.

[0069] Chemical storage devices preferably in the form of batteries are also possible in this DC voltage system. The battery 27 can be connected via a capacitor 26 and a switching and protection device with pre-charging resistor 7 to a DC/DC controller 29 which can in turn be connected to the DC voltage busbar 12 via a capacitor 28 and a switching and protection device with pre-charging resistor 7.

[0070] The capacitive storage unit 21, the photovoltaic system 23 and the battery 27 enable a defined DC voltage to be maintained in the DC voltage system and also enable a DC voltage to be increased in the DC voltage system, as already explained. Such devices are therefore indispensable for maintaining the DC voltage in the DC voltage system in the event of a fault when a supplying voltage drops or when the three-phase AC voltage network 1 fails.

[0071] In an alternative embodiment (not shown) of the DC voltage system, a local pre-charging device (7) is only connected upstream of loads (13, 19, 20) or rather incorporated therein, but not upstream of the energy storage devices and sources (21, 23, 27).

[0072] FIG. 3 shows a method for operating an electrical DC voltage system which is linked by means of a supply circuit to at least one AC voltage network for supplying electrical energy to the DC voltage system, wherein the electrical DC voltage system, which comprises items of equipment which are each connected to a busbar via at least one local pre-charging device, is operated as a function of a voltage value present on the busbar.

[0073] The method for operating an electrical DC voltage system is preferably employed when the DC voltage system is in normal mode (explained below) and failure of a supplying AC voltage network occurs.

[0074] Normal mode is achieved as follows by connecting the DC voltage system to an AC voltage system: the DC voltage system is connected to a three-phase AC voltage network via a supply circuit and therefore powered up by means of a pre-charging process. All the local pre-charging devices in the DC voltage system are active during this pre-charging process. In the respective local pre-charging device the switch is closed and a control unit turns off at least one IGBT so that a charging current flows via the resistor. As a result, all the capacitors in the DC voltage system are charged. As soon as the difference between a voltage present in the DC voltage system and the voltage on a capacitor in the DC voltage system falls below a defined value, the pre-charging process for said capacitor is terminated and the associated local pre-charging device is deactivated. When all the local pre-charging devices are deactivated, the DC voltage system goes into normal mode.

[0075] In method step S1, the DC voltage system is in normal mode. The supply circuit is connected to the AC voltage network, the local pre-charging devices are deactivated. Pre-charging is no longer in operation. As long as the DC voltage in the DC voltage system, also referred to as UDC, is greater than or equal to a minimum value Umin1denoted by UDC>Umin1 in the figurethe DC voltage system remains in normal mode and therefore in method step S1.

[0076] However, when the DC voltage falls below the minimum value Umin1 an event which is triggered in particular by failure of the three-phase AC voltage supply, UDC<Umin1 applies and the supply circuit is disconnected from the AC voltage supply in method step S2.

[0077] Controllable energy storage devices and sources, particularly capacitive storage devices, batteries or photovoltaic systems, present in the DC voltage system, are then caused by the control unit to supply electrical energy to the DC voltage system. In addition, less critical loads, particularly fans, present in the electrical DC voltage system are switched off or limited in order to reduce power consumption.

[0078] As a result of these measures, it is possible that the DC voltage in the DC voltage system will return above the minimum value Umin1. This is denoted by UDC>Umin1 in the figure.

[0079] When the DC voltage does not exceed the minimum value Umin1 and does not fall below a minimum value Umin2indicated by Umin2<UDC<Umin1the status remains at method step S2. Method step S2 is also characterized in that the supply circuit is not connected even when the AC voltage supply is restored.

[0080] When the DC voltage reduces still further and fails below the minimum value Umin2denoted by UDC<Umin2in method step S3 all the local pre-charging devices are activated and all the equipment in the DC voltage system is switched off, The controllable energy storage devices and/or sources are deactivated and no longer supply energy.

[0081] When the DC voltage does not exceed the minimum value Umin2 and does not fall below a minimum value Umin3denoted by Umin3<UDC<Umin2the status remains at method step S3. Also in method step S3, the supply circuit is not connected when the AC voltage network is restored.

[0082] By the local pre-charging devices first being activated and ail the loads only being switched off subsequently, the DC voltage across the equipment decreases further so that a minimum value Umin3 is fallen below.

[0083] With the minimum value Umin3 being fallen below, denoted by UDC<Umin3, a state is reached in which all the local pre-charging devices are safely activated.

[0084] Then in a method step S4 the supply circuit is connected and restoration of the three-phase AC voltage network is awaited. This state is maintained as long as UDC<Umin1 applies. The controllable energy storage devices and/or sources no longer supply energy.

[0085] As an alternative to falling below the minimum value Umin3 as an indicator that all the local pre-charging devices are activated, an activation acknowledgment from the local pre-charging devices can take place or a minimum time tmin since falling below the minimum voltage Umin2 required at the most by the local pre-charging devices for activation can be allowed to elapse. For these alternatives, it is irrelevant whether initially the local pre-charging devices are activated or the equipment is switched off.

[0086] When the three-phase AC voltage network is restored and UDC>Umin1 obtains, the pre-charging process recommences in method step S5 as already described above for connection of the DC voltage system. The start of the pre-charging process can be linked to enabling by a control unit.

[0087] When the pre-charging process is complete, denoted by Vf in the figure, the DC voltage system is returned to normal mode in method step S1. When the pre-charging process is not complete, denoted by Vnf, the status remains at method step S5.

[0088] In an alternative embodiment, in the event of a DC voltage in the DC voltage system falling below a minimum value Umin2denoted in the figure by UDC<Umin2 in the dashed branch, in method step S31 the DC voltage setpoint for controllable energy storage devices and/or sources present in the DC voltage system is increased to a peak value of the network voltage at an upper tolerance limit. All the loads present in the DC voltage system are switched off.

[0089] The energy storage devices and sources increase the DC voltage by supplying electrical energy. As long as UDC<Umin2 applies, the status remains at method step S31.

[0090] In this method step 31, the local pre-charging devices continue to be activated and the supply circuit can be connected when the AC voltage network is restored. The pre-charging process for the transition to normal mode can be started.

[0091] When the minimum value Umin2 is exceededdenoted by UDC>Umin2the local pre-charging devices particularly of critical items of equipment, preferably motors or robots, are deactivated in method step S32 and the critical items of equipment are connected, whereby, as long as UDC>Umin2 applies, the latter move to a defined position or complete at least part of this movement before consumption of electrical energy causes the DC voltage in the DC voltage system to return below the value Umin2denoted by UDC<Umin2 in the figure.

[0092] In addition, in step 32 the supply circuit is not connected when the AC voltage supply is restored. When the defined position is reached and UDC<Umin2 also applies, denoted by UDC<Umin2 & SZ, the DC voltage system goes to S3.

[0093] The action from method step S31 is repeated. The energy storage devices and sources increase the DC voltage by again supplying electrical energy so that, when the value Umin2 is exceededdenoted by UDC>Umin2in method step S32 robots or motors can execute the remainder of their movement to a defined position. In an embodiment not shown in the figure, when the DC voltage in the DC voltage system exceeds the voltage Umin1 in the states S31 or S32, the supply circuit can be connected on restoration of the AC voltage network. The DC voltage system can transition to the S1 state when pre-charging is complete.

[0094] In the method described, it can happen that the DC voltage system remains continuously in S32, as the DC voltage remains between the values Umin1 and Umin2 and the energy storage devices and/or sources exactly cover the energy requirement of the critical loads, particularly motors and robots. In this case it is provided that, when the AC voltage supply is restored, the supply circuit is not connected and non-critical loads are not put into operation. In order to avoid this state, in an embodiment not shown in the figure the energy storage devices and/or sources are deactivated as soon as critical loads have reached their defined position. The voltage in the DC voltage system therefore goes below the value Umin2 and the DC voltage system transitions to S31 where it waits for the AC voltage supply to be restored.

[0095] FIG. 4 shows an embodiment of a local switching and protection device with pre-charging resistor 7 (local pre-charging device). This comprises a pre-charging resistor 73. Said pre-charging resistor 73 is connected in parallel with an anti-series connection of two controllable semiconductors, preferably IGBTs with anti-parallel freewheeling diode 71, 72. A switch 74 is connected in series with this arrangement or in series with the pre-charging resistor 73. The switching and protection device with pre-charging device 7 in FIG. 4 is incorporated in the equipment shown in FIG. 2 or connected upstream thereof.