Electrical system and method for diagnosing the functionality of power relays in an electrical system

Abstract

An electrical system comprises at least one high-voltage battery, at least one DC link capacitor and at least two power relays, whereby one power relay is arranged between a positive connector of the high-voltage battery and the DC link capacitor, while the other power relay is arranged between a negative connector of the high-voltage battery and the DC link capacitor, whereby the electrical system has a galvanically isolated DC/DC converter that is connected to a voltage source in the electrical system, whereby the DC/DC converter is configured such that it can transmit electric energy to a high-voltage side with the DC link capacitor in order to pre-charge the DC link capacitor, whereby the electrical system has a diagnostic device to test the power relays, whereby the diagnostic device has switchable voltage sensors.

Claims

1. An electrical system comprising: at least one high-voltage battery; at least one DC link capacitor; and two power relays, wherein the two power relays include: a first power relay arranged between a positive connector of the at least one high-voltage battery and the at least one DC link capacitor, and a second power relay arranged between a negative connector of the at least one high-voltage battery and the at least one DC link capacitor; a galvanically isolated DC/DC converter that is connected to a voltage source in the electrical system, whereby the DC/DC converter is configured to transmit electric energy to a high-voltage side with the at least one DC link capacitor in order to pre-charge the at least one DC link capacitor; and a diagnostic device configured to test the two power relays, whereby the diagnostic device has switchable voltage sensors, whereby the switchable voltage sensors include: a first voltage sensor arranged in parallel to the at least one high-voltage battery, a second voltage sensor arranged in parallel to the at least one DC link capacitor, a third voltage sensor arranged in parallel to the first power relay, a fourth voltage sensor arranged in parallel to the second power relay, a fifth voltage sensor arranged between the positive connector of the at least one high-voltage battery and the negative connector of the at least one DC link capacitor, and a sixth voltage sensor arranged between the negative connector of the at least one high-voltage battery and a connector between the first power relay and the positive connector of the at least one DC link capacitor.

2. The electrical system according to claim 1, further comprising a fuse arranged between the first power relay and the positive connector of the at least one DC link capacitor, wherein a connector for the sixth voltage sensor is situated between the first power relay and the fuse.

3. An electrical system, comprising: at least one high-voltage battery; at least one DC link capacitor; two power relays, wherein the two power relays include: a first power relay situated between a positive connector of the at least one high-voltage battery and the at least one DC link capacitor and a second power relay arranged between a negative connector of the at least one high-voltage battery and the at least one DC link capacitor; a galvanically isolated DC/DC converter that is connected to a voltage source in the electrical system, whereby the DC/DC converter is configured to transmit electric energy to a high-voltage side with the at least one DC link capacitor in order to pre-charge the at least one DC link capacitor; and a diagnostic device configured to test the two power relays, whereby the diagnostic device includes a switchable voltage sensor arranged in parallel to the at least one high-voltage battery, at least one switchable source of energy, and a plurality of switches connected to at least one of the two power relays to diagnose the functionality of the two power relays.

4. The electrical system according to claim 3, further comprising: a series circuit which includes a first resistor connected in series to the at least one switchable source of energy, which is configured as a voltage source, a second resistor and a voltage sensor arranged in parallel to the series circuit, wherein the plurality of switches includes: a first switch situated between the positive connector of the at least one high-voltage battery and a positive connector of the switchable voltage source, a second switch situated between the positive connector of the switchable voltage source and the negative connector of the at least one DC link capacitor, a third switch situated between the negative connector of the switchable voltage source and the negative connector of the at least one high-voltage battery, a fourth switch situated between the negative connector of the switchable voltage source and a connecting point between the first power relay and the positive connector of the at least one DC link capacitor, and a fifth switch connected in series to a third resistor parallel to a fuse that is situated between the connecting point for the fourth switch and the positive connector of the at least one DC link capacitor.

5. The electrical system according to claim 3, wherein the switchable source of energy is configured as a current source to which a voltage sensor is arranged in parallel, the plurality of switches including: a first switch situated between the positive connector of the at least one high-voltage battery and a positive connector of the switchable current source, a second switch situated between the positive connector of the switchable current source and a negative connector of the at least one DC link capacitor, a third switch situated between the negative connector of the switchable current source and a negative connector of the at least one high-voltage battery, a fourth switch situated between the negative connector of the switchable current source and a connecting point between the first power relay and a positive connector of the at least one DC link capacitor, a fifth switch that is connected in series to a fourth resistor situated between the connecting point of the fourth switch and the negative connector of the at least one DC link capacitor.

6. The electrical system according to claim 3, wherein the switchable source of energy is the at least one high-voltage battery, the electrical system further comprising: the plurality of switches including: a first switch and a second switch arranged in parallel to the first power relay, a third switch and a fourth switch arranged in parallel to the second power relay, a fifth switch connected in series with a second resistor, wherein the fifth switch and the second resistor are arranged in parallel to the first power relay at the positive connector of the at least one high-voltage battery, a sixth switch connected in series with a third resistor, wherein the sixth switch and the third resistor are arranged in parallel to the second power relay at the negative connector of the at least one high-voltage battery, a seventh switch that is connected in series to a fourth resistor; a voltage sensor connected in parallel with a first resistor, wherein the voltage sensor and first resistor are arranged between a first center tap between the first and second switches and between a second center tap between the third and fourth switches, wherein the seventh switch and the fourth resistor are arranged between the first center tap and a positive connector of the at least one DC link capacitor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be explained in greater detail below making reference to preferred embodiments. The following is shown in the figures:

(2) FIG. 1: an electrical system in a first embodiment,

(3) FIG. 2: an electrical system in a second embodiment,

(4) FIG. 3: an electrical system in a third embodiment; and

(5) FIG. 4: an electrical system in a fourth embodiment.

DETAILED DESCRIPTION OF THE INVENTION

(6) FIG. 1 shows an electrical system 100 in a first embodiment. The electrical system 100 comprises a high-voltage source of energy 50 and a traction network 60 having a DC link capacitor 2. Moreover, the electrical system 100 comprises a galvanically isolated DC/DC converter 70 to pre-charge the DC link capacitor 2 and it also comprises a diagnostic device 80. The diagnostic device 80 comprises a control unit 81 as well as six switchable voltage sensors S.sub.Bat, S.sub.ZK, S1-S4.

(7) The high-voltage source of energy 50 comprises a high-voltage battery 1 consisting of a plurality of battery cells that have a positive pole or positive connector 5 and a negative pole or negative connector 6. At the positive pole 5, there is a power relay 7 that is situated between the positive pole 5 and a positive pole or connector 3 of the DC link capacitor 2, whereby in addition, a fuse 9 is connected in series. Accordingly, a second power relay 8 is arranged between the negative pole 6 of the high-voltage battery 2 and a negative connector 4 of the DC link capacitor 2. In this context, a switchable voltage sensor S.sub.Bat is arranged in parallel to the high-voltage battery 1 and it comprises a switch 11 and a voltage sensor 10. Another switchable voltage sensor S.sub.ZK is arranged in parallel to the DC link capacitor 2 and it comprises a switch 13 as well as a voltage sensor 12. The switchable voltage sensor S1 with a switch 15 and a voltage sensor 14 is arranged in parallel to the first power relay 7. The switchable voltage sensor S2 with a switch 17 and a voltage sensor 16 is arranged in parallel to the second power relay 8. Another switchable voltage sensor S3 with a switch 19 and a voltage sensor 18 is arranged between the positive pole 5 and the negative connector 4. Finally, a switchable voltage sensor S4 with a switch 21 and with a voltage sensor 20 is arranged between the negative pole 6 and a connector between the first relay 7 and the fuse 9.

(8) In order to ensure functional safety when the traction network 60 is connected to or disconnected from the high-voltage source 50, it is necessary to first plausibilize not only the states of the power relays 7, 8 but also those of the switchable sensors S.sub.Bat, S.sub.ZK, S1-S4 and of the fuse 9.

(9) In a first initial step, the switch 11 is closed, whereby the voltage sensor 10 would then have to measure the voltage U.sub.Bat of the high-voltage battery 1. This voltage, which is being detected anyway, can be plausibilized using the detected individual voltages of the battery cells. If the deviation of U.sub.Bat relative to the sum of the individual voltages of the battery cells is smaller than a threshold value (for example, 10 V), then the switchable voltage sensor S.sub.Bat is operating properly.

(10) A total of seven mesh equations is available for purposes of diagnosing the other switchable voltage sensors S1-S4, S.sub.ZK as well as the fuse 9. Thus, the functionality of all of the elements can be unambiguously tested. Starting from the initial state in which the sensor S.sub.Bat was plausibilized and its switch 11 is closed and all of the other switches are open, all of the remaining elements are tested, either one at a time or at the same time. 1.sup.st mesh: switches 17 and 19 are closed. Mesh loop via S.sub.Bat (10), S3 (18) and S2 (16). The sum of the voltages should be zero or should be below a threshold value (for instance, 3×5 V=15 V with a measuring tolerance of ±2.5 V of the individual sensors). 2.sup.nd mesh: switches 15 and 21 are closed. Mesh loop via S.sub.Bat (10), S1 (14) and S4 (20). The sum of the voltages should be zero or should be below a threshold value (for instance, 3×5 V=15 V with a measuring tolerance of ±2.5 V of the individual sensors). 3.sup.rd mesh: switches 13, 15 and 17 are closed. Mesh loop via S.sub.Bat (10), S1 (14), FI (9), S.sub.ZK (12) and S2 (16). The sum of the voltages should be zero or should be below a threshold value (for instance, 4×5 V=20 V with a measuring tolerance of ±2.5 V of the individual sensors). 4.sup.th mesh: switches 13, 15 and 19 are closed. Mesh loop via S3 (18), S1 (14), FI (9) and S.sub.ZK (12). The sum of the voltages should be zero or should be below a threshold value (for instance, 3×5 V=15 V with a measuring tolerance of ±2.5 V of the individual sensors). 5.sup.th mesh: switches 13, 17 and 21 are closed. Mesh loops via S4 (20), FI (9), S.sub.ZK (12) and S2 (16). The sum of the voltages should be zero or should be below a threshold value (for instance, 3×5 V=15 V with a measuring tolerance of ±2.5 V of the individual sensors). 6.sup.th mesh: switches 13, 19 and 21 are closed. Mesh loops via S.sub.Bat (10), S3 (18), S.sub.ZK (12) FI (9) and S4 (20). The sum of the voltages should be zero or should be below a threshold value (for instance, 4×5 V=20 V with a measuring tolerance of ±2.5 V of the individual sensors). 7.sup.th mesh: switches 15, 17, 19 and 21 are closed. Mesh loops via S1 (14), S4 (20), S2 (16) and S3 (18). The sum of the voltages should be zero or should be below a threshold value (for instance, 4×5 V=20 V with a measuring tolerance of ±2.5 V of the individual sensors).

(11) Once all of the switchable voltage sensors have been plausibilized, the two power relays 7, 8 can be diagnosed. If one of these two relays is stuck, then the parallel-connected voltage sensor 14 or 16 measures a voltage below a prescribed threshold value (of, for example, 5 V).

(12) The advantage of this circuit is that it is very fast since the DC link capacitor 2 does not have to be charged or charge-reversed. Here, the switches 11, 13, 15, 17, 19, 21 can be configured as discrete semiconductor switches or as relays.

(13) FIG. 2 depicts an alternative embodiment of an electrical system 100, whereby the same elements as in FIG. 1 are designated by the same reference numerals. The circuit, in turn, has a switchable voltage sensor S.sub.Bat as well as five switches SW.sub.2a, SW.sub.2b, SW.sub.3a, SW.sub.3b, SW.sub.4, it has a potential-free switchable voltage source U.sub.q with a switch SW.sub.1 and it also a potential-free voltage sensor S. A resistor R1 is connected in series to the switch SW.sub.1 of the switchable voltage source U.sub.q. Another resistor R2 is connected in parallel to the series circuit comprising the switch SW.sub.1, the voltage source U.sub.q and the resistor R1. The first switch SW.sub.2a is situated between the positive pole 5 of the high-voltage battery 1 and the positive connector of the voltage source U.sub.q. The second switch SW.sub.2b is situated between the positive connector of the voltage source U.sub.q and the negative connector 4 of the DC link capacitor. The third switch SW.sub.3a is situated between the resistor R1 of the voltage source U.sub.q and the negative pole 6 of the high-voltage battery 1. The fourth switch SW.sub.3b is situated between the resistor R1 of the voltage source U.sub.q and a connector 25 between the first power relay 7 and the fuse 9. The fifth switch SW.sub.4 is connected in series to a resistor R3 in parallel to the fuse 9.

(14) The starting point is once again the initial state (only the sensor S.sub.Bat is connected and plausibilized). Owing to the closing of the switches SW.sub.2a and SW.sub.3a, the voltage source U.sub.q is still uncoupled from the rest of the circuit and the sensor S is now connected directly to the high-voltage battery 1. In this manner, the sensor S likewise measures the total high-volt voltage. If the voltage difference between the two sensors S.sub.Bat, S is smaller than a defined threshold value (e.g. 10 V), the functionality of the sensor S and of the switches SW.sub.2a as well as SW.sub.3a is ensured. In addition, through a sequential opening/closing, the switches SW.sub.2a and SW.sub.3a can be diagnosed in terms of their opening/closing. If one of the switches remains permanently open, the value can never fall below the threshold value (e.g. 10 V). However, if one of the two switches is permanently closed, the above-mentioned condition is always fulfilled if one of the appertaining switches is assumed to have been opened. In both cases, an error in the measuring system is detected. Since this resistor R2 is arranged in parallel to the sensor S, the entire source voltage at this resistor drops. In order to limit the losses occurring in R2, said resistor R2 should preferably have a magnitude of at least 1 Mohm.

(15) As the next step, SW.sub.2a and SW.sub.3a are opened again and SW.sub.1 is closed. In this manner, the voltage source U.sub.q applies a voltage drop over the two resistors R1 and R2. Corresponding to the voltage divider ratio, a voltage is set at the resistor R2 that can be measured with the sensor S if the voltage source U.sub.q and the switch SW.sub.1 are functioning correctly.

(16) In addition to the switch SW.sub.1, the switches SW.sub.2b and SW.sub.3b are closed sequentially. As a result, the positive connector of the voltage source is present at the negative pole and the negative connector having the resistor R1 is present at the positive pole of the DC link capacitor 2.

(17) If the switches are functioning properly, the DC link capacitor is charge-reversed. If the capacitor had previously been charge-free, then the magnitude of the DC link voltage rises from zero in the direction of |U.sub.q*R2/(R1+R2)|. The voltage at the sensor S likewise drops from U.sub.q*R2/(R1+R2) to zero at the point in time when both switches are connected and this voltage rises like the voltage at the DC link once again in the direction of the original value of U.sub.q*R2/(R1+R2). The dimensioning of the value for the voltage source and for the resistor R1 depends decisively on the magnitude of the DC link capacitance and on the measuring tolerance of the sensor S. The voltage source U.sub.q should deliver a voltage that is greater than the measuring tolerance of the sensor S by a factor of at least three. So that the DC link voltage can be quickly charged to a measurable voltage value, the resistor R1, as the current limiter, must not be selected too large. For example, at a DC link capacitance of 500 μF and a resistance R1 of 100 ohm, a voltage source of 12 V requires about 27 ms to charge to 5 V and about 90 ms to charge to 10 V. In this context, the aim is for the duration of the diagnosis to be kept as short as possible. During this time, in addition to the plausibilization of the fuse 9 and of the switch SW.sub.4, the switch itself can be closed and opened again. When the switch is being closed, owing to the additional resistor R3, the DC link capacitor is charged more slowly than is the case if the current flows through the fuse in the opened state. In order the readily recognize the difference, R3 should be at least twice as large as R1.

(18) The power relays 7, 8 can be tested once the plausibilization of all of the sensors and auxiliary switches has been successfully completed. This procedure also takes into consideration the insulation resistance R.sub.iso,P, R.sub.iso,N, which consists of a partial resistance between the one connecting point of the appertaining power relay 7, 8 and the housing of the voltage source U.sub.q and also consists of a partial resistance between the housing and the other connecting point of the same power relay 7, 8. For this purpose, the switches SW.sub.1, SW.sub.2a and SW.sub.3b are closed and all of the others are opened. In the case of the open, positive power relay 7 and an insulation fault where R.sub.iso,P is considerably smaller than, for instance, 10 Mohm, the sensor S measures a voltage of U.sub.q*(R2∥R.sub.iso,P)/(R1+(R2∥R.sub.iso,P)) since now, a non-negligible insulation resistance is present in parallel to the resistance R2, as a result of which the voltage divider has been changed. If, in contrast, no insulation fault is present at the positive power relay 7, the sensor S continues to measure a voltage of U.sub.q*R2/(R1+R2). If the power relay 7 is stuck, the sensor S is short-circuited via it, and this is detected as a fault. Analogously, in order to plausibilize the negative power relay 8, exclusively the switches SW.sub.1, SW.sub.2b and SW.sub.3a are closed. Here, too, the sensor S has to be able to measure a voltage of U.sub.q*R2/(R1+R2) in the fault-free case.

(19) This yields the following diagnosis sequence by way of an example when the vehicle is started up, before the traction network is connected: 1. All of the switches (except for 11) are initially open. 2. Close switch SW.sub.2a, then close switch SW.sub.3a and subsequently open SW.sub.2a (plausibilize SW.sub.2a, SW.sub.3a and sensor S). 3. Open switch SW.sub.3a and concurrently close switch SW.sub.1 (plausibilize voltage source U.sub.q). 4. Close switch SW.sub.2b, then close switch SW.sub.3b (plausibilize SW.sub.2b and SW.sub.3b). 5. If applicable, close switch SW.sub.4 (plausibilize fuse and SW.sub.4). 6. Open switch SW.sub.2b and concurrently close switch SW.sub.2a (plausibilize power relay 7). 7. Open switch SW.sub.2a and concurrently close switch SW.sub.2b, then open switch SW.sub.3b and concurrently close switch SW.sub.3a (plausibilize power relay 8). 8. All of the switches (except for 11) are opened once again.

(20) Moreover, this circuit also has the advantage that, using the sensor S, the voltage of the DC link capacitor during the pre-charging can be detected and used to regulate the DC/DC converter.

(21) FIG. 3 shows a third embodiment of an electrical system 100 which largely corresponds to the circuit shown in FIG. 2. The difference lies in the fact that the voltage source U.sub.q and the resistors R1, R2 are replaced by a switchable current source I.sub.q. Moreover, the fifth switch SW.sub.4 having a resistor R3 is replaced by a switch SW.sub.5 having a resistor R4, situated between the connecting point 25 and the negative connector 4 of the DC link capacitor 2.

(22) However, the mode of operation and the procedure are similar. The plausibilization of the switches SW.sub.2b and SW.sub.3b is carried out by means of the connectable resistor R4. In contrast, during the brief charging of the DC link capacitor 2 by the current source I.sub.q, the fuse 9 is tested after the SW.sub.2b and SW.sub.3b have been closed. If one of the two power relays 7, 8 is stuck, the current source would be short-circuited by it and the sensor S would detect this fault.

(23) The underlying idea of the two above-mentioned circuits is the possibility to diagnose the power relays 7, 8 by a suitable connection of an active source to these two power relays in order to detect their state.

(24) FIG. 4 shows another alternative embodiment, whereby, unlike FIG. 2 and FIG. 3, the high-voltage battery 1 is the switchable source of energy, whereby, however, a larger number of switches and resistors is needed.

(25) The following diagnosis sequence can be implemented with this circuit: 1. Establish the initial state (only the sensor S.sub.Bat is connected and has already been plausibilized). 2. Close switch SW.sub.1a and switch SW.sub.2a one after the other and open them again (plausibilize SW.sub.1a, SW.sub.2a and sensor S). 3. Close switch SW.sub.1a, open switch SW.sub.2a, then close switch SW.sub.2b and shortly thereafter likewise close SW.sub.4 (plausibilize SW.sub.2b, SW.sub.4 and power relay 8). If the power relay 8 is stuck, the battery voltage is present at the sensor S immediately after the switch SW.sub.2b has been closed. In contrast, if the power relay 8 is open but an insulation fault is present, the resistors R5 and R.sub.iso,N form a voltage divider via the source. Since the insulation resistance is not known, the switch SW.sub.4 connects a defined resistance in order to bring about a voltage change at the sensor S, thereby recognizing the fault. If the power relay 8 is open and no insulation fault is present, the sensor S can only detect a defined voltage value of U.sub.Bat R5/(R5+R7) once the switches SW.sub.2b, SW.sub.4 are being closed.

(26) 4. The switches SW.sub.1a, SW.sub.2b and SW.sub.4 are opened, then switch SW.sub.2a, SW.sub.1b and subsequently switch SW.sub.3 are closed (plausibilize SW.sub.2a, SW.sub.3 and power relay 7). 5. Open switch SW.sub.1b and then close switch SW.sub.6 (plausibilize SW.sub.6 and fuse).

(27) In order to minimize losses, the resistances should have high values (e.g. 1 Mohm). Since all of the switches connect and disconnect the source of energy, they have to be dimensioned for the voltage that is present at the source.