DC-to-DC voltage converter, voltage supply device, and diagnostic method for a DC-to-DC voltage converter

Abstract

A diagnosis method for the switching elements in a bidirectional DC-to-DC voltage converter comprising: charging a capacitor in the bidirectional DC-to-DC voltage converter to a predetermined first test voltage, then specifically actuating the switching elements in the bidirectional DC-to-DC voltage converter, and evaluating the voltage in the charged capacitor of the bidirectional DC-to-DC converter to identify a faulty switching element within the switching elements in the bidirectional DC-to-DC voltage converter.

Claims

1. A diagnostic method for a bidirectional DC-to-DC voltage converter that comprises a first capacitor (C1) and a first full bridge (1) at a first DC voltage terminal (10) and that comprises a second full bridge (2) at a second DC voltage terminal (20), wherein the first full bridge (1) comprises two half bridges (11, 12) each having a first switching element (M1, M2) and a second switching element (M3, M4), comprising the steps of: providing (S1) a first DC voltage at the second DC voltage terminal (20) of the bidirectional DC-to-DC voltage converter; opening (S2) the first switching elements (M1, M2) and the second switching elements (M3, M4) of the first full bridge (1); charging (S3) the first capacitor (C1) to a predetermined first test voltage by driving the second full bridge (2); closing (S4) one of the first switching elements (M1, M2) of the first full bridge (1); detecting (S5) a faulty second switching element (M3, M4) if the electric voltage across the first capacitor (C1) drops by more than a predefined first voltage value within a predetermined first time interval following the closure of the first switching element (M1, M2); opening (S6) the closed first switching element (M1, M2) of the first full bridge (1); closing (S7) one of the second switching elements (M3, M4) of the first full bridge (1); and detecting (S8) a faulty first switching element (M1, M2) if the electric voltage across the first capacitor (C1) drops by more than a predefined second voltage value within a predetermined second time interval following the closure of the second switching element (M3, M4).

2. The diagnostic method as claimed in claim 1, wherein the steps of opening (S6) the closed first switching element (M1, M2), of closing (S7) the second switching element (M3, M4) and of detecting (S8) a faulty first switching element (M1, M2) are performed only if no faulty second switching element (M3, M4) has been detected.

3. The diagnostic method as claimed in claim 1, comprising a step of charging the first capacitor (C1) to a predetermined second test voltage after the closed first switching element (M1, M2) has been opened.

4. The diagnostic method as claimed in claim 3, wherein the predetermined second voltage to which the first capacitor (C1) is charged is determined depending on a maximum forward current, a maximum operating temperature and/or a maximum heat dissipation of the first switching elements (M1, M2) and/or of the second switching elements (M3, M4) in the first full bridge (1).

5. The diagnostic method as claimed in claim 1, wherein the predetermined first voltage to which the first capacitor (C1) is charged is determined depending on a maximum forward current, a maximum operating temperature and/or a maximum heat dissipation of the first switching elements (M1, M2) and/or of the second switching elements (M3, M4) in the first full bridge (1).

6. The diagnostic method as claimed in claim 1, comprising a step of identifying the faulty switching element (M1 . . . M4) if a faulty first switching element (M1, M2) or a faulty second switching element (M3, M4) has been detected.

7. The diagnostic method as claimed in claim 1, wherein the value of the first test voltage to which the first capacitor (C1) is charged is greater than the value of the first DC voltage that is provided at the second DC voltage terminal (20).

8. The diagnostic method as claimed in claim 1, comprising a step of activating the bidirectional DC-to-DC voltage converter if no faulty first switching element (M1, M2) and no faulty second switching element (M3, M4) has been detected.

9. A DC-to-DC voltage converter for a bidirectional DC-to-DC voltage conversion between a first DC voltage terminal (10) and a second DC voltage terminal (20), having: a first capacitor (C1) that is electrically coupled to the first DC voltage terminal (10); a first full bridge (1) that is electrically coupled to the first DC voltage terminal (10) and that comprises two half bridges (11, 12) each having a first switching element (M1, M2) and a second switching element (M3, M4); a second full bridge (2) that is electrically coupled to the second DC voltage terminal (20); and a controller (7) that is designed to open the first switching elements (M1, M2) and the second switching elements (M3, M4) of the first full bridge (1), to charge the first capacitor (C1) by driving the second full bridge (2) at a predetermined first test voltage, to then close one of the first switching elements (M1, M2) in the first full bridge (1) and to detect a faulty second switching element (M3, M4) in the first full bridge (1) if the electric voltage across the first capacitor (C1) drops by more than a predefined first voltage value within a predetermined first time interval following the closure of the first switching element (M1, M2), to then open the closed first switching element (M1, M2) in the first full bridge (1), to close one of the second switching elements (M3, M4) in the first full bridge (1) and detect a faulty first switching element (M1, M2) if the electric voltage across the first capacitor (C1) drops by more than a predefined second voltage value within a predetermined second time interval following the closure of the second switching element (M3, M4).

10. The DC-to-DC voltage converter as claimed in claim 9, having a transformer (3) that is electrically coupled to the first full bridge (1) by way of a primary side and electrically coupled to the second full bridge (2) by way of a secondary side.

11. A voltage supply device for an electric or hybrid vehicle having: a high-voltage on-board system that is designed to provide electrical energy at a first predetermined electric voltage; a low-voltage on-board system that is designed to provide electrical energy at a second predetermined electric voltage; a DC-to-DC voltage converter as claimed in claim 9, wherein the first DC voltage terminal (10) of the DC-to-DC voltage converter is able to be electrically coupled to the high-voltage on-board system, and the second DC voltage terminal (20) of the DC-to-DC voltage converter is electrically coupled to the low-voltage on-board system.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention is explained in more detail below with reference to the exemplary embodiments indicated in the schematic figures of the drawings. In the figures:

(2) FIG. 1: shows a schematic illustration of a DC-to-DC voltage converter according to one embodiment;

(3) FIG. 2: shows a schematic illustration of a voltage timing diagram of the voltage profile during diagnosis of a DC-to-DC voltage converter according to one embodiment; and

(4) FIG. 3: shows a schematic illustration of a flowchart underlying a diagnostic method for a DC-to-DC voltage converter according to one embodiment.

DETAILED DESCRIPTION

(5) FIG. 1 shows a schematic illustration of a DC-to-DC voltage converter according to one embodiment. The DC-to-DC voltage converter is in particular a bidirectional DC-to-DC voltage converter, that is to say the DC-to-DC voltage converter is able to selectively convert an electric voltage in one direction or the other.

(6) The DC-to-DC voltage converter is able to be electrically connected to a first DC voltage system at a first DC voltage terminal 10. This first DC voltage system may be for example a high-voltage on-board system of an electric or hybrid vehicle. In the embodiment illustrated here, the first DC voltage system is for example represented by a first DC voltage source 5 that is connected to the first DC voltage terminal 10 of the DC-to-DC voltage converter via a circuit breaker 4. A first capacitor C1 and a first full bridge 1 are connected to the first DC voltage terminal 10. The first full bridge 1, in the embodiment illustrated here, comprises two half bridges 11 and 12. The first half bridge 11 has an upper switching element M1 and a lower switching element M3. In the same way, the second half bridge 12 has an upper switching element M2 and a lower switching element M4. The upper switching elements M1 and M2 are connected here for example to the positive connection element of the DC voltage terminal 10. The lower switching elements M3 and M4 are accordingly connected to the negative connection element of the first DC voltage terminal 10. The connecting nodes between the upper switching elements M1 and M2 and the lower switching elements M3 and M4 are connected to one side, for example the primary side, of a transformer 3.

(7) The DC-to-DC voltage converter furthermore comprises a second full bridge 2 that is possibly connected to a second DC voltage terminal 20 together with a second capacitor C2. This second DC voltage terminal 20 may be connected to a further DC voltage system, for example a low-voltage on-board system of an electric or hybrid vehicle. This second DC voltage system is represented here by way of example by the second DC voltage source 6. In the same way as for the first full bridge 1, the second full bridge 2 is connected to another side of the transformer 3, for example a secondary side of the transformer 3. The DC-to-DC voltage converter, in particular the switching elements in the first full bridge 1 and the second full bridge 2, is driven by way of a controller 7.

(8) In order to ensure that the switching elements M1 to M4 of the first full bridge 1 are able to ensure a correct electrical disconnection during operation of the DC-to-DC voltage converter, a diagnosis of the switching elements M1 to M4 may be performed. To this end, for example, an electric voltage across the first capacitor C1 may be detected by way of a voltage sensor 71. By charging the first capacitor C1 to a predefined test voltage and then setting predefined switching states in the first full bridge 1, it is possible to reach a conclusion about the functionality of the switching elements M1 to M4 of the first full bridge 1 from the voltage profile across the first capacitor C1.

(9) The process of diagnosing the switching elements M1 to M4 in the first full bridge 1 will be described below.

(10) During the diagnosis of the switching elements M1 to M4 in the first full bridge 1, the DC-to-DC voltage converter is electrically connected at the second DC voltage terminal 20 to a voltage source 6, for example a low-voltage on-board system of a vehicle. Furthermore, the first DC voltage terminal 10 is decoupled from other electrical consumers. By way of example, the circuit breaker 4 may be opened. To this end, for example, the controller 7 may provide a corresponding drive signal to the circuit breaker 4.

(11) The switching elements M1 to M4 with the half bridges 11 and 12 of the first full bridge 1 are furthermore opened by corresponding driving, for example by way of drive signals from the controller 7.

(12) The second full bridge 2, in particular the switching elements M5 to M8 of the second full bridge 2, is then driven by the controller 7. As a result, an AC voltage is provided on the secondary side of the transformer 3. The AC voltage then induced on the primary side of the transformer 3 is rectified by way of the diodes arranged parallel to the switching elements M1 to M4 of the first full bridge 1 and then charges the first capacitor C1. By virtue of suitable driving of the switching elements M5 to M8 in the second full bridge 2, the first capacitor C1 is thereby able to be charged to a predefined test voltage Up.

(13) After the first capacitor C1 has been charged to the predefined test voltage Up, the driving of the second full bridge 2 is ended.

(14) An upper switching element M1 or M2 in one of the two half bridges 11 or 12 is then closed, whereas the other three switching elements remain open. By way of example, the first switching element M1 may be closed, whereas the switching elements M2 to M4 remain open.

(15) If the lower switching elements M3 and M4 in the half bridges 11 and 12 of the first full bridge 1 are able to ensure sufficient isolation in this switching state, then the first capacitor C1 is not discharged and the electric voltage across the first capacitor C1 will stay kept approximately constant. To this end, the voltage profile across the first capacitor C1 may be detected for example by way of the voltage sensor 71 and provided to the controller 7. If the electric voltage across the first capacitor C1 remains approximately constant during a predefined time interval Δt, that is to say if the electric voltage across the first capacitor C1 drops by less than a predefined threshold value, then it is able to be assumed that the lower switching elements M3 and M4 of the two half bridges 11 and 12 in the first full bridge 1 are able to ensure sufficiently good isolation.

(16) If, on the other hand, the lower switching element M3 in the half bridge 11 is defective, in which half bridge the upper switching element M1 has been closed in a targeted manner, then the electric voltage across the first capacitor C1 will drop very quickly. In this case, this voltage drop is able to be detected by the voltage sensor 71.

(17) If, on the other hand, the upper switching element M1 that has been closed in a targeted manner and the faulty lower switching element M4 are situated in different half bridges 11, 12, then the first capacitor C1 will discharge across the switching element M1 closed in a targeted manner, the primary side of the transformer 3 and the faulty switching element M4. In this case, the first capacitor C1 will also discharge, but more slowly than in the case in which the faulty lower switching element and the upper switching element closed in a targeted manner are situated in the same half bridge. In this case, the voltage across the first capacitor C1 will therefore drop less greatly within a predefined time interval.

(18) It is accordingly able to be established, by evaluating the voltage profile across the first capacitor C1, whether the lower switching elements M3 and M4 ensure sufficient isolation in the open state, or whether one of the two lower switching elements M3 or M4 is not able to ensure sufficient electrical isolation. By comparing the electric voltage across the first capacitor C1 with a first predefined limit value and possibly a second predefined limit value, it is then able to be determined whether one of the two lower switching elements M3 or M4 is faulty. From the level of the voltage drop within the predetermined time interval Δt, it may be possible to draw a conclusion as to which of the two switching elements M3 or M4 is faulty.

(19) If it is established that one of the two lower switching elements M3 or M4 is faulty, then the diagnosis may already be ended at this time. Otherwise, or if the upper switching elements M1 and M3 are additionally also to be checked, a corresponding diagnosis for the two upper switching elements M1 and M2 may then be performed.

(20) To this end, the first capacitor C1 may possibly be recharged. By way of example, the first capacitor C1 may be recharged to the predefined test voltage Up through corresponding driving of the switching elements in the second full bridge 2.

(21) As an alternative, it is also possible, if the electric voltage across the first capacitor C1 still lies above a predefined limit value, to dispense with recharging the first capacitor C1 and to perform the further diagnosis using the remaining residual voltage in the capacitor C1. Independently of whether the first capacitor C1 has or has not been recharged, a lower switching element M3 or M4 is closed, whereas all of the other switching elements are opened, for the diagnosis of the upper switching elements M1 and M2. By way of example, to this end, the lower switching element M3 in the first half bridge 11 may be closed, whereas the upper switching elements M1 and M2 and the other lower switching element M4 remain open.

(22) The voltage profile across the first capacitor C1 is then evaluated again for a predetermined time interval. If the voltage drop across the first capacitor C1 in this case remains below a predefined voltage drop, then the upper switching elements M1 and M2 may also be classed as functional. If, on the other hand, the electric voltage across the first capacitor C1 drops below a predefined limit value, then at least one of the two upper switching elements M1 and M2 is faulty. In this case too, based on the level of the voltage drop across the first capacitor C1 during the predetermined time interval, it is possible to conclude as to whether the upper switching element M1, M2, in the same half bridge 11, 12 in which the lower switching element M3, M4 closed in a targeted manner is also situated, is faulty or whether the lower switching element M3, M4 closed in a targeted manner and the faulty upper switching element M1, M2 are situated in different half bridges 11, 12.

(23) FIG. 2 shows a schematic illustration of a voltage time profile during a diagnosis of a DC-to-DC voltage converter according to one embodiment. At the time to, the capacitor C1 is initially charged to the predefined test voltage Up. At the time t1, the voltage across the first capacitor C1 reaches the predefined test voltage Up. The charging of the first capacitor C1 is then ended and the voltage profile across the first capacitor C1 is monitored. If, after a predetermined time interval Δt, at the time t2, the electric voltage across the first capacitor C1 still lies above a predefined first limit value U1, then the switching elements to be checked may be classed as intact. If the electric voltage across the first capacitor C1 lies below the first predefined limit voltage U1, at least one of the switching elements to be checked is faulty. If the electric voltage across the first capacitor C1 in this case possibly drops below a predefined second voltage value U2, then this is an indication that the faulty switching element and the switching element closed in a targeted manner are situated in the same half bridge.

(24) If no faulty switching element has been classed, then the further switching elements may then also be checked. If for example the lower switching elements M3 and M4 were initially checked, then the upper switching elements M1 and M2 may then be checked. To this end, the electric voltage across the first capacitor C1 may possibly be recharged to the test voltage Up. If this is reached at the time t3, then the voltage profile across the first capacitor C1 is monitored again for a predefined time interval Δt. If the voltage is still above the predefined limit voltage U1 at the time t4, then the switching elements checked in this case are also intact. If, on the other hand, the voltage has fallen below the predefined limit voltage U1, then at least one of the switching elements to be checked is faulty. If the voltage across the first capacitor C1 in the process drops below a lower second limit voltage U2, then this is again an indication that the switching element closed in a targeted manner and the faulty switching element are situated in the same half bridge.

(25) FIG. 3 shows a schematic illustration of a flowchart underlying a diagnostic method for a DC-to-DC voltage converter according to one embodiment. The diagnostic method described below here essentially corresponds to the diagnosis as has already been described above.

(26) In step S1, a first DC voltage is first of all provided at the second DC voltage terminal 20 of the DC-to-DC voltage converter and, in step S2, all of the first switching elements M1, M2 and second switching elements M3, M4 in the first full bridge 1 of the DC-to-DC voltage converter are opened. In step S3, the first capacitor C1 is then charged to a predetermined test voltage Up by driving the second full bridge 2. Then, in step S4, one of the first switching elements M1, M2 in the first full bridge 1 is closed. If the electric voltage across the first capacitor C1 drops by more than a predefined first voltage value within a predetermined first time interval Δt following the closure of the first switching element M1, M2, then a faulty second switching element is able to be detected in step S5. In this case, the method may be ended since a faulty switching element has already been detected.

(27) If no faulty second switching element M3, M4 has been detected, or the first switching elements M1, M2 are also to be checked in spite of a faulty second switching element M3, M4, then, in step S6, the closed first switching element M1, M2 of the first full bridge 1 is opened and a second switching element M3 or M4 in the first full bridge 1 is closed. If the electric voltage across the first capacitor C1 then drops by more than a predefined voltage value within a predetermined second time interval following the closure of the second switching element M3 or M4 in step S7, then a faulty first switching element M1, M2 is thereby able to be detected in step S8.

(28) In order to protect the components in the DC-to-DC voltage converter, the electric voltage to which the first capacitor C1 is charged may be limited. In particular, the maximum electric voltage to which the first capacitor C1 is charged may be determined depending on a maximum permissible forward current in the switching elements M1 to M4 in the first full bridge 1, a maximum operating temperature and/or a maximum heat dissipation of the switching elements M1 to M4.

(29) In summary, the present invention relates to diagnosing the switching elements in a bidirectional DC-to-DC voltage converter. By charging a capacitor in the DC-to-DC voltage converter and then driving the switching elements in a targeted manner and evaluating the voltage in the charged capacitor of the DC-to-DC voltage converter, it is possible to identify a faulty switching element.