RELIABLE FAULT DETECTION AND FAULT LOCALIZATION IN A LOAD ZONE OF A DC SYSTEM

Abstract

A load zone of a DC system includes a connection interface for supplying the load zone with electrical energy, an electronic switch arranged between the connection interface and a DC bus, and at least two electrical devices connected in parallel to the DC bus. A voltage sensor measures a voltage across a fuse arranged between the DC bus and a respective electrical device. An evaluation unit identifies a defective device of the at least two electrical devices based on a polarity of the voltage measured by the voltage sensor across the fuse. A DC system with such a load zone and an energy source connected to the connection interface of the load zone, as well as a method for operating such load zone or DC system are also disclosed. A device is identified as being defective when the voltage measured across the fuse exceeds a specified limit value.

Claims

1.-13. (canceled)

14. A load zone, comprising: a connection interface for supplying the load zone with electrical energy; a DC bus; an electronic switch arranged between the connection interface and the DC bus; at least two electrical devices, each electrically connected in parallel to the DC bus; a fuse arranged between the DC bus and a respective one of the at least two electrical devices; a voltage sensor configured to measure a voltage across the fuse; and an evaluation unit configured to identify a defective device of the at least two electrical devices based on a polarity of the voltage measured by the voltage sensor across the fuse.

15. The load zone of claim 14, wherein the connection between the DC bus and a respective one of the at least two electrical devices is constructed without a current transformer.

16. The load zone of claim 14, wherein a peak value of the voltage across the fuse is measured and stored as a stored data value which is reduced, in particular reset, when the voltage measured across the fuse is negative.

17. The load zone of claim 16, further comprising a peak value rectifier arranged between the fuse and the voltage sensor, with the peak value rectifier measuring the peak value of the voltage across the fuse.

18. The load zone of claim 16, wherein a further data value is captured and stored, with the stored data value measuring and storing a positive peak value, and the further data value measuring and storing a negative peak value.

19. A DC system, comprising: at least one energy source; a load zone comprising a connection interface connected to the at least one energy source, with the at least one energy source supplying the load zone with electrical energy; a DC bus; an electronic switch arranged between the connection interface and the DC bus and configured to interrupt the electrical connection between the energy source and the DC bus; at least two electrical devices, each electrically connected in parallel to the DC bus; a fuse arranged between the DC bus and a respective one of the at least two electrical devices; a voltage sensor configured to measure a voltage across the fuse; and an evaluation unit configured to identify a defective device based on a polarity of the voltage measured by the voltage sensor across the fuse of the defective device.

20. A method for fault localization in a load zone of a DC system, comprising: measuring with a voltage sensor a voltage across a fuse of the load zone arranged between a DC bus and a respective one of at least two electrical devices electrically connected in parallel to the DC bus; and identifying a defective device of the at least two electrical devices based on a polarity of the voltage measured by the voltage sensor across the fuse of the defective device.

21. The method of claim 20, wherein the defective device is identified when the voltage measured across the fuse of the defective device exceeds a specified limit value.

22. The method of claim 21, further comprising comparing voltage levels of a voltage drop measured across respective fuses of the at least two electrical devices, and identifying the electrical device of the at least two electrical devices having a highest voltage level as the defective device.

23. The method of claim 22, further comprising when or after a fault occurs in the load zone, measuring and storing as a stored data value a peak value of the voltage drop, and identifying the defective device as a function of the stored data value.

24. The method of claim 23, further comprising identifying the defective device as the device having a highest peak value of all measured voltage drops, as measured across the fuse associated with the defective device.

25. The method of claim 23, wherein the stored data value is reduced, in particular reset, when the voltage drop measured as across the fuse has a negative polarity.

26. The method of claim 23, further comprising: measuring and storing a further data value, with the stored data value measuring a positive peak value, and with the further data value measuring a negative peak value of the voltage drop measured as across the fuse.

27. The method of claim 26, further comprising capturing and storing a time when the stored data value or the further data value occurs, and detecting the defective device depending on the captured and stored time.

28. The method of claim 20, wherein the method is started when a fault is present in the load zone.

Description

[0034] The invention is described and explained in greater detail below with reference to the exemplary embodiments illustrated in the figures, in which:

[0035] FIG. 1 shows a DC system with a load zone, and

[0036] FIG. 2 to FIG. 5 show exemplary embodiments of an advantageous peak value rectifier.

[0037] FIG. 1 shows a DC system 10 comprising a load zone 1 and an energy source 6. The energy source 6 in this case can be embodied as a voltage source, for example. The energy source 6 is connected to connection interfaces 30 of the load zone 1 and supplies electrical energy to the electrical devices 4 of the load zone 1. For this purpose, a DC bus 3 is arranged in the load zone 1 and carries the voltage to the electrical devices 4. The electrical devices 4 are connected to the DC bus 3 in this case via an electrical connection. A fuse 5 is arranged in this electrical connection respectively for each electrical device 4 of the load zone 1, The voltage u.sub.Sx across the fuse 5 is captured by the voltage sensor 7. The captured values of the voltage across the respective fuses 5 are transmitted by the voltage sensors 7 to an evaluation unit 9. If a number n of electrical devices 4 are present in the load zone, this means that in total the number n of fuses 5 and therefore also the number n of voltage sensors 7 are also present. The designation of the voltage u.sub.Sx represents the voltage at the x.sup.th fuse 5, where x then assumes a value between 1 and n. Electrical devices 4 in this exemplary embodiment take the form of inverters 12, each of which has an indirect capacitor 11. Alternatively, electrical devices can also be present as any type of electrical consumer unit and/or energy storage unit.

[0038] If a short circuit occurs in or at one of the electrical devices 4, the indirect capacitors 11 of the remaining electrical devices 4 also feed into this short circuit. Moreover, further energy from the individual inverters 12 can also be fed into this short circuit. For the purpose of separating the load zone 1 from the energy source 6, the load zone 1 has an electronic switch 2 which is arranged between the connection interfaces 30 of the load zone and the DC bus 3, Using this electronic switch 2, the energy supply from the energy source 6 to the electrical devices 4 of the load zone 1 can quickly be interrupted.

[0039] If a fault occurs in a first electrical device 41, e.g. a short circuit, the current from the energy source 6 and the further electrical devices 4 consequently causes the fuse 5 to trip in the corresponding connection between the first electrical device 41 and the DC bus 3. As a result of the tripping of the corresponding fuse 5, the site of the fault at the first electrical device 41 can be localized definitively.

[0040] If however a protection device, which is not described in detail here, of the DC system 10 or of the load zone 1 detects a fault within this load zone 1, the electronic switch 2 can be opened as a reaction to this and already before the fuse 5 has tripped. In this case, no more electrical energy is fed into the short circuit of the first electrical device 41 by the energy source 6 after the opening of the electronic switch 2. Only the remaining electrical devices 4 feed energy, e.g. from the indirect capacitors 11 and/or the inverter 12, into the short circuit of the first electrical device 41. In this case, the corresponding current through the fuse 5 can be so small that the fuse 5 no longer trips but remains conductive. In this case, the defective first electrical device can no longer be detected on the basis of the status of the fuse 5. For this purpose, nowadays a current sensor is usually installed in series with the fuse in order that currents caused by e.g. a short circuit can be detected.

[0041] However, in order to also allow localization of the fault without a current sensor, i.e. omitting a current sensor, the voltage u.sub.Sx dropping across the fuse 5 is measured for the individual fuses 5 of the load zone 1 in each case. The polarity of the measurement by the voltage sensor 7 in this case is such that an electrical energy flowing into the electrical device 4 is captured as a positive voltage. The electrical device 4 with the highest voltage u.sub.Sx measurement is detected as the defective electrical device. It can be assumed that the fault, in particular the short circuit, is present at this device. As a result of using the fuse 5, which is required in any case, as a type of instrument shunt of a current sensor, no additional component is required in the energy path. However, unlike an instrument shunt of a current sensor, the resistance value of the fuse 5 is rather imprecise and subject to considerable variability among the various fuses 5. It is nonetheless possible, even with this significant variability/imprecision in the resistance of the fuses 5 to distinguish an operating current from a current in the event of a fault. Significant demands are generally made on an instrument shunt in order to be able to perform fault detection and fault localization with corresponding precision. It has been shown that these otherwise normal demands on the resistance of the fuse 5 do not have to be satisfied in order to be able reliably to distinguish an operating current from a fault current. This also means that no additional losses are generated in the feed line between the DC system 3 and the electrical device 4, The evaluation unit 9 can identify which of the electrical devices 4 is defective on the basis of the values transferred by the voltage sensors 7.

[0042] If a fault has already been detected in the load zone 1, e.g. on the basis of an overcurrent, and the electronic switch 2 is already open, the fault can be localized more precisely within the load zone 1 by comparing the voltage levels of the voltage u.sub.Sx dropping across the respective fuses 5 with each other. The electrical device at which the highest voltage u.sub.Sx drops across the fuse 5 in the connection between the electrical device and the DC bus 3 is detected as the defective device. It is alternatively or additionally possible to detect a defective device in that the voltage u.sub.Sx dropping across the fuse 5 exceeds a specifiable limit value. As a result of this transgression of the limit value, it can be assumed that a fault is present in this device and therefore in the load zone 1. The detection of the fault can optionally also be used by the evaluation unit 9 to open the electronic switch 2 as marked by a broken line in FIG. 1.

[0043] It has also proven advantageous to capture and store the individual voltages u.sub.Sx which drop across the respective fuses 5. Furthermore, it has proven advantageous alternatively or additionally to capture and store the peak value of the voltage u.sub.Sx across the fuse 5. In this case, the peak value can be determined and stored e.g. by means of a peak value rectifier 8 (not shown here) or in the data processing entity, i.e. in the evaluation unit 9. In the case of a peak value rectifier 8, the storage can be effected hi that the peak value is continuously present across a capacitor 15. This is described and explained in greater detail below in FIG. 2 to FIG. 5. By virtue of knowing the peak value, localization of the fault by comparing the peak values of the voltages u.sub.Sx is still possible if there is no short-circuit current flow or only a slight short-circuit current flow,

[0044] FIG. 2 shows an exemplary embodiment of a peak value rectifier 8. This allows the peak value of a voltage u.sub.Sx across the fuse 5 to be generated at the rectification capacitor 15, As soon as the voltage u.sub.Sx across the fuse 5 is greater than the voltage at the rectification capacitor 15, the rectification capacitor 15 is charged via the diode 16 until the voltage at the rectification capacitor 15 has also reached the voltage u.sub.Sx across the fuse 5. If the voltage u.sub.Sx across the fuse 5 falls back again, a discharge current of the rectification capacitor 15 is prevented by the diode 16 and the peak value of the voltage u.sub.Sx across the fuse 5 remains at the rectification capacitor 15. This corresponds to a storage of the peak value of the voltage u.sub.Sx across the fuse 5, The voltage sensor 7 can then pick up the stored peak value and transfer it to an evaluation unit 9 (not illustrated here). The determination of the defective electrical device can then take place in the evaluation unit 9.

[0045] The advantage of this peak value rectifier 8 is that data does not have to be continuously captured and/or transmitted. If a fault occurs and/or is detected in the load zone 1, the determination can take place in the evaluation unit 9 because the corresponding peak values are available to the evaluation unit or can be made available by the voltage sensor 7 as a voltage at the rectification capacitor 15, even after the fault has occurred and the electronic switch 2 has opened.

[0046] FIG. 3 shows a further exemplary embodiment of the peak value rectifier 8. For the avoidance of repetition, reference is made to the description for FIG. 2 and the reference signs assigned therein. This exemplary embodiment additionally has a switch 17 which is activated by a polarity capture 20. If the voltage u.sub.Sx across the fuse 5 assumes a negative value, the polarity capture 20 detects this and closes the switch 17. The rectification capacitor 15 is thereby short-circuited and discharged. The voltage at the rectification capacitor assumes the value zero in this case. This means that the peak value that is present and stored at the rectification capacitor is reset. Alternatively, a resistance can be arranged in series with the switch 17. Using this arrangement, the capacitor is then discharged continuously and not suddenly. This corresponds to a reduction of the stored value.

[0047] As soon as the voltage u.sub.Sx across the fuse 5 assumes positive values, the switch 15 opens and the peak value of the voltage u.sub.Sx across the fuse 5, which peak value occurred since the opening of the switch 17, is present at the rectification capacitor again.

[0048] The switch 17 can be part of a contactor, said switch 17 being a switching contact of the contactor and the coil of the contactor being part of the polarity capture 20. A diode of the polarity capture 20 ensures that a voltage is applied to the coil of the contactor as soon as the voltage u.sub.Sx across the fuse 5 is negative. This voltage causes the contactor to react whereby the switch 17 is dosed.

[0049] FIG. 4 shows a further exemplary embodiment of the peak value rectifier 8. For the avoidance of repetition, reference is made to the description for FIG. 2 and FIG. 3 and the reference signs assigned therein. This exemplary embodiment likewise has the switch 17 and the polarity capture 20. In this case, the switch 17 is so arranged that the voltage at the rectification capacitor 15 is reduced and not suddenly discharged in the event of a negative voltage u.sub.Sx across the fuse 5. In this case, a resistance 19 is arranged in series with the switch 17. The magnitude of the resistance value of the resistance 19 in this case determines the speed with which the voltage is reduced at the rectification capacitor 15. The reduction of the voltage at the rectification capacitor 15 signifies a reduction in the stored data value of the peak value.

[0050] By resetting or reducing the stored data value for the peak value, it is much easier to detect the defective electrical device. This is because the non-defective electrical devices often release energy when a fault occurs in the load zone and therefore a negative voltage is produced at the fuse. Therefore the defective device, at which a positive voltage is present at least at the instant of the fault, can be identified even more easily and reliably since at least some of the correctly functioning electrical devices have a negative voltage u.sub.Sx at their assigned fuse 5 and thereby reduce the stored data value.

[0051] FIG. 5 shows a further exemplary embodiment of the peak value rectifier 8. For the avoidance of repetition, reference is made to the description for FIG. 2 to FIG. 4 and the reference signs assigned therein. This exemplary embodiment no longer has a switch 17 or a polarity capture 20. In this peak value rectifier 8, a positive peak value is determined and stored with the aid the diode 16 in a similar manner to the exemplary embodiments in FIG. 2 to FIG. 4. In addition to this, a negative peak value is determined with the aid of a further diode 18 and stored as a voltage at the second rectification capacitor 15. The negative peak value is defined as the greatest absolute value of a negative voltage. This positive and negative peak value can be captured in each case by the voltage capture 7 and supplied to the evaluation unit 9. The knowledge of positive and negative peak values can further increase the reliability of determining the defective electrical device, since in addition to a comparison of the data values of different electrical devices, a positive and a negative peak value is also available for each electrical device. In this way, the positive and the negative peak value can be compared with each other as a further criterion for the determination of the defective electrical device.

[0052] In summary, the invention relates to a load zone comprising an electronic switch, a DC bus and at least two electrical devices, the electronic switch being so arranged as to separate the DC bus from an energy source that can be connected to the load zone, the electrical devices being electrically connected to the DC bus in each case. In order to improve the fault detection in the load zone, it is proposed to arrange a fuse between the DC bus and the respective electrical device, a voltage sensor being so arranged as to be able to capture a voltage across the fuse. The invention further relates to a DC system comprising such a load zone and at least one energy source, the energy source being connected to the load zone in such a way that the electrical devices can be supplied with electrical energy from the energy source, the electrical connection between the energy source and the DC bus being interruptible by means of the electronic switch. The invention further relates to a method for operating such a load zone or such a DC system, a defective device of the electrical devices being identified on the basis of the voltage across the fuse.

[0053] In other words, the invention relates to a load zone comprising an electronic switch, a DC bus, a connection interface for supplying the load zone with electrical energy, and at least two electrical devices, the electronic switch being arranged between the connection interface and the DC bus, the electrical devices each being electrically connected in parallel to the DC bus. In order to improve the fault detection and fault localization in the load zone, it is proposed to arrange a fuse between the DC bus and the respective electrical device, a voltage sensor being so arranged as to capture a voltage across the fuse. The invention further relates to a DC system comprising such a load zone and at least one energy source, the energy source being connected to the connection interface of the load zone. The invention further relates to a method for operating such a load zone or such a DC system, a defective device of the electrical devices being identified on the basis of the voltage across the fuse in that the voltage across the fuse exceeds a specifiable limit value.