ELECTRIC INSULATION MONITORING ARRANGEMENT

Abstract

An electric insulation monitoring arrangement (10) for monitoring electric insulation in an electric system (2), in particular of a vehicle, comprising a first conductor (11) and a second conductor (12), the electric insulation monitoring arrangement comprising: an insulation monitoring device (15) comprising a primary measuring unit (13) configured to monitor a first voltage (V.sub.1) between the first conductor and ground, and a second voltage (V2) between the second conductor and ground, the insulation monitoring device being configured to determine an electric insulation of the electric system based on measurement data from the primary measuring unit, at least one secondary measuring unit (14) configured to monitor the first voltage and the second voltage with respect to ground, wherein the at least one secondary measuring unit is provided separately from the insulation monitoring device.

The insulation monitoring device is configured to use measurement data relating to the first voltage and the second voltage received from the at least one secondary measuring unit to verify the determined electric insulation.

Claims

1. An electric insulation monitoring arrangement for monitoring electric insulation in an electric system comprising a first conductor and a second conductor, the electric insulation monitoring arrangement comprising: an insulation monitoring device comprising a primary measuring unit configured to monitor a first voltage between the first conductor and ground, and a second voltage between the second conductor and ground, the insulation monitoring device being configured to determine an electric insulation of the electric system based on measurement data relating to the first voltage and the second voltage from the primary measuring unit, characterized in that the electric insulation monitoring arrangement further comprises at least one secondary measuring unit configured to monitor the first voltage and the second voltage with respect to ground, wherein the at least one secondary measuring unit is provided separately from the insulation monitoring device, and that the insulation monitoring device is configured to use measurement data relating to the first voltage and the second voltage received from the at least one secondary measuring unit to verify the determined electric insulation.

2. The electric insulation monitoring arrangement according to claim 1, wherein the at least one secondary measuring unit is controlled independently from the insulation monitoring device.

3. The electric insulation monitoring arrangement according to claim 1, wherein the at least one secondary measuring unit is configured to monitor the first voltage and the second voltage at a different position than the primary measuring unit.

4. The electric insulation monitoring arrangement according to claim 1, further comprising a communication interface for communicating measurement data from the at least one secondary measuring unit to the insulation monitoring device.

5. The electric insulation monitoring arrangement according to claim 1, comprising at least two separate secondary measuring units, wherein the insulation monitoring device is configured to use measurement data relating to the first voltage and the second voltage received from both of the at least two secondary measuring units for verifying the determined electric insulation.

6. The electric insulation monitoring arrangement according to claim 1, wherein the insulation monitoring device comprises means for applying an insulation test load or test signal between at least one of the first and second conductors and ground.

7. The electric insulation monitoring arrangement according to claim 1, wherein the insulation monitoring device is configured to determine that an electric insulation fault is present given that at least one insulation fault criterion is fulfilled.

8. The electric insulation monitoring arrangement according to claim 7, wherein the insulation monitoring device is configured to, in response to the determination of the electric insulation fault, generate a signal and/or disconnect a power supply of the electric system.

9. The electric insulation monitoring arrangement according to claim 7, wherein the at least one insulation fault criterion includes a criterion which is considered fulfilled if the first voltage and/or the second voltage as measured by the at least one secondary measuring unit differ/s from the first voltage and/or the second voltage as measured by the primary measuring unit by more than a predetermined threshold value.

10. The electric insulation monitoring arrangement according to claim 7, wherein the at least one insulation fault criterion includes a criterion which is considered fulfilled if measurement data from at least one of the primary measuring unit and the at least one secondary measuring unit indicate a calculated insulation resistance below a predetermined threshold value.

11. A method for monitoring electric insulation in an electric system comprising a first conductor and a second conductor, the method comprising: applying a test load or a test signal between at least one of the first conductor and the second conductor and ground; while applying the test load or test signal, using a primary measuring unit, monitoring a first voltage between the first conductor and ground, and a second voltage between the second conductor and ground, based on measurement data relating to the first voltage and the second voltage from the primary measuring unit, determining an electric insulation of the electric system, verifying the determined electric insulation based on measurement data relating to the first voltage and the second voltage received from at least one secondary measuring unit provided separately from the primary measuring unit.

12. A computer program comprising program code means for causing an insulation monitoring device of to perform the method according to claim 11 when said computer program is run on a control unit of the insulation monitoring device.

13. A computer readable medium carrying a computer program comprising program means for causing the an insulation monitoring device according to to perform the method according to claim 11 when said computer program is run on a control unit of the insulation monitoring device.

14. A vehicle comprising an electric system and at least one electric insulation monitoring arrangement for monitoring electric insulation in the electric system according to any claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] With reference to the appended drawings, below follows a more detailed description of embodiments of the invention cited as examples.

[0036] In the drawings:

[0037] FIG. 1 schematically shows a vehicle in which an electric insulation monitoring arrangement according to the invention may be provided,

[0038] FIG. 2 schematically shows an example embodiment of an electric insulation monitoring arrangement according to the invention;

[0039] FIG. 3 is a diagram illustrating a voltage measurement, and

[0040] FIG. 4 is a flow-chart illustrating a method according to an embodiment of the invention.

[0041] The drawings are schematic and not necessarily drawn to scale.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE INVENTION

[0042] In the present detailed description, embodiments of the method according to the present invention are mainly described with reference to an all-electric bus, comprising a propulsion system in the form of battery powered electric motors. However, it should be noted that various embodiments of the described invention are equally applicable for a wide range of hybrid and electric vehicles. The invention is also applicable in electric systems in e.g. construction equipment, vessels, etc.

[0043] FIG. 1 shows a simplified perspective view of an all-electric vehicle in the form of a bus 1. The bus 1 comprises an electric system 2, which herein comprises an electric drive unit 3 for propulsion of the bus. Of course, other loads may be provided in addition to or instead of the electric drive unit 3, for example auxiliary systems requiring electric power, and/or an on-board charger, and/or a power take-off. The electric drive unit 3 may comprise a traction motor, power electronics, and controls associated therewith (not shown).

[0044] The bus 1 further carries an electric energy storage system (ESS) 4 comprising a plurality of battery modules 5, wherein each battery module 2 may in turn comprise a plurality of battery cells (not shown). The battery cells may be connected in series to provide an output DC voltage having a desired voltage level. Suitably, the battery cells are of lithium-ion type, but other types may also be used. The number of battery cells per battery module 5 may be in the range of 50 to 500 cells. It is to be noted that the ESS 4 may also include a plurality of battery packs, each comprising one or more battery modules 5. An ESS control unit 6 is provided for controlling operation of the ESS 4.

[0045] FIG. 2 schematically shows an electric system 2 of a vehicle, such as the electric system 2 of the bus 1 illustrated in FIG. 1. The electric system 2 comprises a first conductor 11 in the form of a positive DC line, and a second conductor 12 in the form of a negative DC line. An insulation monitoring arrangement 10 according to an embodiment of the invention is connected to the electric system 2 and configured for monitoring the electric insulation resistance of the electric system 2, i.e. between each of the conductors 11, 12 and a ground reference. In this case, a chassis of the vehicle 1 serves as the ground reference.

[0046] The electric insulation monitoring arrangement 10 comprises an insulation monitoring device 15 for monitoring the electric insulation resistance between the first conductor 11 and ground, and between the second conductor 12 and ground, respectively. For this purpose, the insulation monitoring device 15 comprises a primary measuring unit 13 configured to monitor a first voltage V.sub.1 between the first conductor 11 and ground by continuously or periodically measuring a set of voltage values V.sub.1-1, and a second voltage V.sub.2 between the second conductor 12 and ground by continuously or periodically measuring a set of voltage values V.sub.2-1. The insulation monitoring device 15 further comprises a control unit 16 configured to control the voltage measurements performed by the primary measuring unit 13. The control unit 16 is further configured to determine the electric insulation resistance of the electric system 2 based on the measurement data V.sub.1-11,V.sub.2-1 10 relating to the first voltage V.sub.1 and the second voltage V.sub.2, respectively, received from the primary measuring unit 13.

[0047] The electric insulation monitoring arrangement 10 further comprises a secondary measuring unit 14, provided separately from the insulation monitoring device 15 and consequently also separately from the primary measuring unit 13. For example, but not necessarily, the secondary measuring unit 14 and the insulation monitoring device 15 may be located in separate metal housings, such as aluminium housings. The secondary measuring unit 14 is configured to monitor the first voltage V.sub.1 and the second voltage V.sub.2 by, over time, measuring a set of voltage values V.sub.1-2 between the first conductor 11 and ground, and a set of voltage values V.sub.2-2 between the second conductor 12 and ground, respectively.

[0048] The measurements performed by the secondary measuring unit 14 are controlled independently from those performed by the primary measuring unit 13, such as by a separate control unit (not shown). Measurement data V.sub.1-2,V.sub.2-2 relating to the first voltage V.sub.1 and the second voltage V.sub.2, respectively, as measured by the secondary measuring unit 14 are however communicated to the insulation monitoring device 15, such as to the control unit 16 thereof. The insulation monitoring device 15 is configured to use the measurement data V.sub.1-2,V.sub.2-2 received from the secondary measuring unit 14 to verify the determined electric insulation resistance, which was determined based on the measurement data V.sub.1-1,V.sub.2-1 from the primary measuring unit 13.

[0049] Means for applying an insulation test load or test signal between each one of the first and the second conductors 11, 12 and ground, most commonly sequentially but in some cases simultaneously, are included in the insulation monitoring device 15. The insulation monitoring device 15 may thus be used both for controlling the test loading of the electric system 10 and for controlling the measurements made by the primary measuring unit 13.

[0050] Typically, an initial test voltage V.sub.initial is applied between one of the conductors 11, 12 and ground, and the voltage response is measured over time by means of the primary measuring unit 13. This is illustrated in FIG. 3, in which the voltage V.sub.1 between the first conductor 11 and ground is monitored as a function of time. Independently from the measurement by the primary measuring unit 13, measurements are performed by the secondary measuring unit 14 and communicated to the insulation monitoring device 15. If a predetermined insulation fault criterion is fulfilled, e.g. if one of the measuring units 13, 14 measure a voltage drop V.sub.drop that corresponds to a calculated insulation resistance below a predetermined threshold value, corresponding to a safe electric insulation level, the insulation monitoring device 15 may determine that there is an insulation fault between the loaded conductor and ground. In response thereto, it may generate a signal for providing a warning and/or for cutting the power to the electric system 2.

[0051] A plurality of insulation fault criteria may be defined, wherein it is determined that an insulation fault exists if at least one of those criteria are fulfilled. Another exemplary insulation fault criterion may be considered fulfilled if the first voltage V.sub.1 and/or the second voltage V.sub.2, as measured by the secondary measuring unit 14, differ/s from the first voltage V.sub.1 and/or the second voltage V.sub.2, as measured by the primary measuring unit 13, respectively, by more than a predetermined threshold value.

[0052] A method for monitoring electric insulation in an electric system 2 comprising a first conductor 11 and a second conductor 12, such as the electric system 2 shown in FIG. 2, is illustrated in the flow chart of FIG. 4. The method comprises the following steps:

[0053] S1: Applying a test load or test signal between at least one of the first conductor 11 and the second conductor 12 and ground, such as a chassis of a vehicle 1 in which the electric system 2 is located. The test load or signal may be applied with a certain time interval. It may e.g. be a current pulse of a predetermined duration.

[0054] S2: While applying the test load or test signal, using the primary measuring unit 13, monitoring a first voltage between the first conductor 11 and ground, and a second voltage between the second conductor 12 and ground. Measurement data V.sub.1-1, V.sub.2-1 relating to the first and the second voltage, respectively, are thus obtained using the primary measuring unit 13. This may be carried out continuously or with a certain time interval while the test load is being applied.

[0055] S3: Based on measurement data relating to the first voltage and the second voltage from the primary measuring unit 13, determining an electric insulation of the electric system 2.

[0056] S4: Verifying the determined electric insulation based on measurement data V.sub.1-2, V.sub.2-2 relating to the first voltage and the second voltage, respectively, received from at least one secondary measuring unit 14 provided separately from the primary measuring unit 13.

[0057] The method may further comprise steps of determining that an electric insulation fault is present given that at least one insulation fault criterion is fulfilled, such as described above, and taking at least one action in response thereto, such as generating a signal and/or disconnecting a power supply of the electric system 2.

[0058] The method may be carried out in the control unit 16 of the insulation monitoring arrangement 10 shown in FIG. 2.

[0059] The control unit 16 may include a microprocessor, a microcontroller, a programmable digital signal processor or another programmable device. Thus, the control unit 16 comprises electronic circuits and connections (not shown) as well as processing circuitry (not shown) such that the control unit 16 can communicate with e.g. different parts of the bus 1 or with different control units of the bus 1 and/or of the electric system 2. The control unit 16 may comprise modules in either hardware or software, or partially in hardware or software, and communicate using known transmission buses such a CAN-bus and/or wireless communication capabilities. The processing circuitry may be a general purpose processor or a specific processor. The control unit 16 comprises a non-transitory memory for storing computer program code and data. Thus, the skilled person realizes that the control unit 16 may be embodied by many different constructions.

[0060] It is to be understood that the present invention is not limited to the embodiments described above and illustrated in the drawings; rather, the skilled person will recognize that many changes and modifications may be made within the scope of the appended claims.