Battery system with a battery, which is designed to supply a high-voltage network with electric energy, and a measuring device for measuring at least one insulation resistance of the battery

The invention relates to a battery system (100) with a battery (20), which is designed to supply a high voltage network (70) with electric energy, and a measuring device (130) for measuring at least one insulation resistance provided between the battery (20) and a housing of the battery (20). The measuring device (130) is equipped with two measuring paths (140, 150), each of which is paired with one of two high-voltage connections (21, 22) of the battery (20), each of which comprises a series circuit that comprises a first resistor (142, 152) and a relay (145, 155), and each of which is connected between the paired high-voltage connection (21, 22) and a point (25) that has a housing potential. Furthermore, each series circuit has a semiconductor switch (147, 157). The measuring device (130) also has two functional modes in which the relays (145, 155) of the measuring paths (140, 150) are closed. When switched to a passive functional mode of the two functional modes, the measuring device (130) is designed to open each semiconductor switch (147, 157) or to keep the semiconductor switch in an open state. When switched to an active functional mode of the two functional modes, the measuring device (130) is additionally designed to alternately open and close the semiconductor switches (147, 157), to measure a first voltage which drops over the first resistor (142, 152) of each measuring path (140, 150) when the semiconductor switch (147, 157) of the corresponding measuring path (140, 150) is closed, and to determine a corresponding insulation resistance of the battery (20) using each measured first voltage.

BACKGROUND OF THE INVENTION

The present invention relates to a battery system with a battery which is designed to supply a high-voltage network with electrical energy and a measuring device for measuring at least one insulation resistance of the battery, and a corresponding method for measuring at least one insulation resistance of a battery which is designed to supply a high-voltage network with electrical energy. The invention also relates to a vehicle having such a battery system.

FIG. 1shows a battery system10known from the prior art, with a battery20configured as a high-voltage battery or traction battery, and a measuring device30for measuring at least one insulation resistance of the battery20, which is present inside or outside the battery20. The battery20comprises a plurality of series-connected battery cells. In the interests of simpler representation, said plurality of battery cells are not identified by reference numbers. Herein, a first insulation resistance26is the insulation resistance of the battery20which is present between a positive high-voltage terminal21of the battery20and a point25having a potential of a housing of the battery20, hereinafter designated as the housing potential25. Moreover, a second insulation resistance27is the insulation resistance of the battery20which is present between a negative high-voltage terminal22of the battery20and the housing potential25. The positive high-voltage terminal21of the battery20is hereinafter designated as the first high-voltage terminal21of the battery20. The negative high-voltage terminal22of the battery20is hereinafter designated as the second high-voltage terminal21of the battery20. Moreover, a third insulation resistance28is the insulation resistance of the battery20which is present between a connection point, by means of which at least two battery cells in the battery20are interconnected, and the housing potential25.

The measuring device30, arranged in a battery control device (not represented) of the battery system10, comprises a first measuring path40and a second measuring path50, each of which comprises a high-resistance voltage divider41,51and a relay45,55, and are connectable between an assigned high-voltage terminal21,22of the two high-voltage terminals21,22and the housing potential25. Herein, the first high-voltage terminal21is assigned to the first measuring path40. The second high-voltage terminal22is, moreover, assigned to the second measuring path50. Each voltage divider41,51is comprised of a first resistor42,52and a second resistor43,53. Herein, each first resistor42,52is connected to the housing potential25, and each second resistor43,53is connectable, via the corresponding relay45,55, to its assigned high-voltage terminal21,22. In the event of an insulation fault between the battery20and the housing, during the alternating closing of the relays45,55on the measuring paths40,50, a measurable current flux flows through at least one of the voltage dividers41,51, such that a measurable voltage also drops across the first resistor42,52of the at least one voltage divider41,51. Each voltage drop across the first resistor42,52of each voltage divider41,51is measured via a respective measuring input49,59of an evaluation and control unit60of the measuring device30which is assigned to the corresponding measuring path40,50. The measuring input49which is assigned to the first measuring path40is connected, via a further resistor46, to that terminal of the first resistor42on the voltage divider41of the first measuring path40which is not connected to the housing potential25. For the measurement of the voltage drop across the first resistor52on the voltage divider51of the second measuring path50, the measuring device30is equipped with an operational amplifier56which is connected, on the input side, to the first resistor52on the voltage divider51of the second measuring path50and, on the output side, to the measuring input59of the evaluation and control unit60assigned to the second measuring path50. The evaluation and control unit60thus defines the respective voltage drops across the first resistors42,52on the voltage dividers41,51. By the alternating switching-in of the measuring paths40,50, the voltage drop across each of the first resistors42,52is determined and, in consideration of known system variables, the insulation resistances26,27,28of the battery20can be calculated in each case. The evaluation and control unit60is moreover designed to control the relays45,55, i.e. to open and close the latter.

The battery20represented inFIG. 1is designed to a supply a high-voltage network70with electrical energy. To this end, the battery20is connectable to the high-voltage network70via two further relays71,72. Via the two further relays71,72, the first high-voltage terminal21of the battery20is directly connectable to a first high-voltage network terminal73on the high-voltage network70, and the second high-voltage terminal22of the battery20is directly connectable to a second high-voltage network terminal74on the high-voltage network70. Between the two high-voltage network terminals73,74on the high-voltage network70, a series-connected arrangement of two capacitors75,76(Y-capacitors) is provided, connected in parallel with an intermediate circuit capacitor77, which forms an intermediate circuit. A connection point, by means of which the two series-connected capacitors75,76are connected, is connected to a housing potential25. The high-voltage network70moreover comprises an inverter78and a motor79. On its input side, the inverter78is connected in parallel with the intermediate circuit capacitor77, and is designed to convert a DC voltage which can be delivered by the battery20into a three-phase AC voltage which is then delivered, on its output side, to the motor79.

According to the prior art, dielectric withstand between a low-voltage network, which is galvanically separated from the high-voltage network70, and the battery20, or between the housing potential25and the battery20, must be metrologically proven, both in-factory and during the conduct of all repairs on the battery20. To this end, in the course of dielectric withstand testing (by a dielectric withstand test) using the battery control device (not represented) which is switched to a test mode, a test voltage is applied between the housing potential25and each high-voltage terminal21,22of the battery20for a specified time. The test criterion to be used for this purpose is a measured current value. The test voltage here is delivered in the form of a DC voltage or an AC voltage.

In order to protect the electronic measuring systems of the measuring device30against damage during dielectric withstand testing, and to prevent any overshoot of a predefined limiting current value by the current value of any measuring current generated in course of insulation resistance measurement, the measuring paths40,50must be configured with a correspondingly high resistance. As the predefined limiting current value cannot be selected to be infinitely small, each measuring path40,50, in a time during which dielectric withstand testing is in progress, and in a time during which no insulation resistance measurement is taking place, is galvanically separated from the battery20, and thus also from the high-voltage network70, wherein the relays (electromechanical switches)44,55are opened.

According to the prior art, the measuring device30, during each insulation resistance measurement, is connected via the relay45on the first measuring path40or via the relay55on the second measuring path50to the battery20. During its service life, each relay45,55undergoes from several tens of thousands up to a hundred thousand switching operations or switching cycles. The low measuring currents which arise during insulation resistance measurements, together with high switching voltages, which comprise voltage values of several hundred volts, are conducive to low-energy corona discharge during switching operations on these relays45,55. In combination with potential gas emissions from the relay housing material, this can lead to unwanted carbonization or film-formation on the switching contacts of the relays45,55. A current-related switching contact transition resistance can occur on the relays45,55, thereby invalidating the measurement.

From document CN 101603986 A, a high-voltage insulation resistance measuring circuit is known, comprising a high-voltage switching unit with a plurality of relays and a voltage measuring unit wherein, in a test mode, various components of the voltage measuring unit deliver a high-voltage signal via the closed relays.

SUMMARY OF THE INVENTION

According to the invention, a battery system is disclosed with a battery which is designed to supply a high-voltage network with electrical energy and a measuring device for measuring at least one insulation resistance which is present between the battery and a housing of the battery. In this case, the measuring device incorporates two measuring paths, each assigned to one high-voltage terminal of two high-voltage terminals of the battery, each comprising a series-connected arrangement of a first resistor and a relay, and each connected between the high-voltage terminal assigned thereto and a point at a housing potential. Each series-connected arrangement moreover comprises a semiconductor switch. The measuring device also has two functional modes, in which the relays on the measuring paths are closed. When switched to the passive functional mode of the two functional modes, the measuring device here is designed to open the respective semiconductor switch, or to maintain the latter in an open state. When switched to an active functional mode of the two functional modes, the measuring device is additionally designed to alternately open and close the semiconductor switches, to respectively measure a first voltage which drops across the first resistor of each measuring path when the semiconductor switch of the corresponding measuring path is closed, and to determine a corresponding insulation resistance of the battery using each measured first voltage.

According to the invention, a method is moreover disclosed for measuring at least one insulation resistance which is present between a battery which is designed to supply a high-voltage network with electrical energy and a housing of the battery, by means of a measuring device. In this case, the measuring device incorporates two measuring paths, each assigned to one high-voltage terminal of two high-voltage terminals of the battery, each comprising a series-connected arrangement of a first resistor and a relay, and each connected between the high-voltage terminal assigned thereto and a point at a housing potential. Each series-connected arrangement moreover comprises a semiconductor switch. The measuring device also has two functional modes, in which the relays are closed. The measuring device is switched from a passive functional mode of the two functional modes, in which the semiconductor switches are respectively opened or are maintained in an open state, to an active functional mode of the two functional modes, in which the semiconductor switches are alternately closed and opened, a first voltage which drops across the first resistor of each measuring path when the semiconductor switch of the corresponding measuring path is closed is respectively measured, and the corresponding insulation resistance is determined using each measured first voltage.

In the invention, the relays arranged in the measuring device according to the invention, in a state in which the measuring device is not supplied with electrical energy by the battery, i.e. a state in which no insulation measurement occurs, are closed. This means that, under normal conditions, the measuring device according to the invention is permanently galvanically connected to the battery or to a high-voltage network which is supplied by the battery. For the continued switchable execution of each measuring path or measuring channel in the measuring device, a cost-effective semiconductor switch is connected in each measuring path, in series with the corresponding relay.

Preferably, the respective semiconductor switches employed in the measuring paths only fulfil such technical requirements as are necessary for the conduction or blocking of the resulting measuring signals associated with the corresponding insulation resistance measurements. It is additionally preferred that the semiconductor switches are not designed in accordance with the technical requirements necessary for the execution of a dielectric withstand test, in which a test voltage in the high-voltage range is applied or is applicable between each of the high-voltage terminals of the battery and the housing.

In a preferred form of embodiment of the invention, the battery system according to the invention has a protective device for the protection of the measuring device. The protective device moreover comprises a control unit, which is designed to detect the presence of a test mode on a battery control device of the battery system, in which a test voltage is applied between at least one high-voltage terminal of the two high-voltage terminals and the housing and/or between at least one high-voltage network terminal of two high-voltage network terminals of the high-voltage network and the housing respectively, at least temporarily. Preferably, the test voltage is equal to a high voltage with a predefined characteristic. It is additionally preferred that the test voltage has a magnitude that rises continuously from a magnitude of 0 V up to a predefined magnitude, wherein the test voltage, immediately after the achievement of the predefined magnitude, is equal to a high voltage with a predefined characteristic. The control unit is moreover designed to open the relays upon the start of the test mode, and to close the relays at the end of the test mode.

Preferably, each high-voltage terminal, via a further relay which is assigned thereto, is directly connectable to a high-voltage network terminal of the two high-voltage network terminals which is assigned thereto.

The control unit is preferably a microcontroller arranged in the battery control device.

It is additionally preferred that the protective device comprises a voltage measuring unit which is designed to measure a second voltage which is present between each high-voltage terminal and the housing and/or between each high-voltage network terminal and the housing respectively and, in the event of a magnitude of each second voltage which is equal to a predefined limiting value, or which exceeds the latter, to transmit a control signal to the control unit. In this case, the control unit is designed, in the presence of each control signal, to detect the start of the test mode and to open the relays.

In the invention, the measuring device according to the invention, during each dielectric withstand test in which a critical test voltage is applied, is galvanically separated from the battery or from the high-voltage network which is to be supplied with electrical energy by the battery. To this end, galvanic separation of the measuring device according to the invention from the battery or from the aforementioned high-voltage network is executed immediately prior to the application of the critical test voltage. By this approach, the technical requirements which are to be fulfilled by the relays or electromagnetic switches which are incorporated in the measuring device in the course of their service life are significantly reduced. It is highly advantageous here that cyclical switching, to be executed under load, of the relays incorporated in the measuring device is omitted, and that the number of purely mechanical switching operations to be executed on these relays under dry load conditions is reduced to a minimum. Moreover, the risk of an occurrence of corona discharge, and of unwanted film formation on the switching contacts of said relays, is eliminated.

In another preferred form of embodiment of the invention, each semiconductor switch is arranged between the point which is at the housing potential and the relay on the corresponding measuring path and/or is designed for the switching of a voltage, the magnitude of which does not exceed a further predefined limiting value. Preferably, each first resistor is directly connected to the point which is at the housing potential. Preferably, each series-connected arrangement comprises a second resistor which, specifically, is directly connected to the high-voltage terminal which is assigned to the measuring path which incorporates the corresponding series-connected arrangement.

A further aspect of the invention relates to a vehicle having a battery system according to the invention.

DETAILED DESCRIPTION

FIG. 2shows a battery system100according to a first form of embodiment of the invention. The battery system100comprises a battery20for the supply of a high-voltage network70with electrical energy. The battery20delivers a battery voltage VB. Additionally, the battery20is connectable via two further relays71,72to the high-voltage network70.

The battery system100represented inFIG. 2is distinguished from the battery system10represented inFIG. 1by the design of a measuring device130which is incorporated in the battery system100for the measurement of at least one insulation resistance (not represented) which is present between the battery20and a housing of the battery20. The battery20, the at least one insulation resistance and the two further relays71,72of the battery system100according to the first form of embodiment, together with the associated high-voltage network70, are each configured in an equivalent manner to the corresponding components represented inFIG. 1. In the interests of simpler representation, the at least one insulation resistance is not shown inFIG. 2, and the high-voltage network70is represented in a simplified manner, wherein a series-connected arrangement of two capacitors (Y-capacitors), which is present between two high-voltage network terminals73,74of the high-voltage network70, is not represented.

The measuring device130comprises a first measuring path140and a second measuring path150, which are connected respectively between a point25having a potential of the housing of the battery20, also designated here as the housing potential25, and a high-voltage terminal21,22of two high-voltage terminals21,22of the battery20which is assigned thereto. Herein, a first high-voltage terminal21of the two high-voltage terminals21,22of the battery20is assigned to the first measuring path140. Additionally, a second high-voltage terminal22of the two high-voltage network terminals21,22of the battery20is assigned to the second measuring path150.

Each measuring path140,150has a corresponding series-connected arrangement, respectively comprising a first resistor142,152, a second resistor143,153, a relay145,155and a semiconductor switch147,157. Herein, the first resistor142on each measuring path140,150is directly connected to the housing potential25and to the corresponding semiconductor switch147,157. Moreover, the second resistor143,153on each measuring path140,150is directly connected to the high-voltage terminal21,22of the battery20which is assigned thereto, and to the relay145,155on the corresponding measuring path140,150. Consequently, the semiconductor switch147,157on each measuring path140,150is arranged between the first resistor142,152and the relay145,155of the corresponding measuring path140,150.

The measuring device130has an active functional mode and a passive functional mode. During the active functional mode, the relays145,155on the measuring paths140,150remain closed, and the measuring paths140,150are alternately switched by means of the semiconductor switches147,157. Each measuring path140,150can be switched individually, wherein the semiconductor switch147,157of the measuring path140,150to be switched is closed, and the semiconductor switch157,147of the other measuring path150,140is opened, or is maintained in an open state. Each first voltage drop across the first resistor142,152on each switched-in measuring path140,150here is measured via a respective measuring input149,159, which is assigned to the corresponding measuring path140,150, of an evaluation unit160, which is preferably arranged in the measuring device130. By means of each measured first voltage, the evaluation unit160determines a corresponding insulation resistance (not represented) of the battery20. For the measurement of the first voltage drop across the first resistor152on the second measuring path150, the measuring device130is provided with an operational amplifier158which, on its input side, is connected to one terminal of the first resistor152on the second measuring path150which is not connected to the housing potential25and, on its output side, is connected to the measuring input159of the evaluation unit160which is assigned to the second measuring path150. The semiconductor switches147,157are designed respectively for the switching of a positive or negative voltage of a maximum voltage magnitude VH, i.e. for the switching of a voltage between −VH and +VH and, accordingly, only fulfil such technical requirements as are necessary for the conduction or blocking of measuring signals arising during corresponding insulation resistance measurements.

During the passive functional mode of the measuring device130, in which no insulation resistance measurement occurs, the relays145,155on the measuring paths140,150continue to remain closed, and the measuring paths140,150are electrically isolated from the battery20by means of the semiconductor switches147,157, in which the semiconductor switches145,157are respectively opened or maintained in an open state.

In the first form of embodiment of the invention, the measuring device130is preferably located in a battery control device131of the battery system100.

The battery system100moreover comprises a protective device for the protection of the measuring device130, having a control unit170which, in the first form of embodiment of the invention, is a central microcontroller170of the battery control device131, which can also comprise the evaluation unit160. In this case, the electromechanical relays145,155on the measuring paths140,150are directly controlled by means of the central microcontroller170.

If the battery control device131is in a test mode in which, for the execution of a dielectric withstand test, a positive or negative test voltage ±VT in the high-voltage range is applied between at least one high-voltage terminal21,22of the two high-voltage terminals21,22of the battery20and the housing potential25, the relays145,155on the measuring paths140,150are opened by means of the microcontroller170. The relays145,155remain open over an entire test period. During the test mode or throughout the entire test period, the measuring device130to be protected is thus securely galvanically separated from the battery20or from the high-voltage network70. The open contacts of the relays145,155block the externally applied test voltage ±VT. The microcontroller170is moreover connected to a vehicle interface171which, via a bus system interface172, is connected to a dielectric withstand test device173for the execution of dielectric withstand tests.

FIG. 3shows a battery system200according to a second form of embodiment of the invention. The battery system200comprises a battery20for the supply of a high-voltage network70with electrical energy. The battery20delivers a battery voltage VB. The battery20is connectable via two further relays71,72to the high-voltage network70. Via the two further relays71,72, a first high-voltage terminal21of the battery20is directly connectable to a first high-voltage network terminal73on the high-voltage network70, and a second high-voltage terminal22of the battery20is directly connectable to a second high-voltage network terminal74on the high-voltage network70. The battery system200moreover comprises a measuring device130, which is designed for the measurement of at least one insulation resistance (not represented) which is present between the battery20and a housing of the battery20. The battery20, the at least one insulation resistance and the further relays71,72of the battery system200according to the second form of embodiment of the invention, together with the associated high-voltage network70, are each configured in an equivalent manner to the corresponding components represented inFIG. 1. Moreover, the measuring device130of the battery system200according to the second form of embodiment of the invention is configured in an equivalent manner to the measuring device130of the battery system100according to the first form of embodiment of the invention. In the interests of simpler representation, the at least one insulation resistance is not shown inFIG. 3, and the high-voltage network70is represented in a simplified manner, wherein a series-connected arrangement of two capacitors (Y-capacitors), which is present between the two high-voltage network terminals73,74of the high-voltage network70, is not represented. For the same reason, in the measuring device130represented inFIG. 3, only two measuring paths140,150of the measuring device130and two relays145,155on the two measuring paths140,150are provided with reference numbers. Here again, a first measuring path140of the two measuring paths140,150is assigned to the first high-voltage terminal21of the battery20. Here again, moreover, a second measuring path150of the two measuring paths140,150is assigned to the second high-voltage terminal22of the battery20.

The battery system200moreover comprises a protective device for the protection of the measuring device130which, in the second form of embodiment of the invention, has a monitoring circuit230for the control of the two relays145,155on the two measuring paths140,150of the measuring device130. As soon as at least one second voltage is applicable to the measuring device130via the further relays71,72, i.e. as soon as a second voltage is respectively applicable via the further relays71,72between at least one high-voltage terminal21,22of the two high-voltage terminals21,22of the battery20and the housing potential25, which second voltage lies outside a provided measuring range of the measuring device130and, consequently, has a magnitude which exceeds a maximum magnitude, the two relays140,150on the measuring paths140,150are automatically opened by the monitoring circuit230. To this end, in the conduct of a dielectric withstand test, via the further relays71,72, a test voltage ±VT1, which is applicable between at least one high-voltage terminal21,22of the two high-voltage terminals21,22of the battery20and the housing potential25and defined by a ramp function, is varied until a desired high voltage is achieved, such that the measuring device130, even in consideration of a respective time lag on the two relays145,155of the two measuring paths140,150, can be promptly galvanically separated from the battery20or from the high-voltage network70by means of the monitoring circuit230. To this end, the monitoring circuit230is configured for the detection of test voltages ±VT1, applicable in either direction of polarity, and for the comparison thereof with a predefined threshold value.

The monitoring circuit230comprises a voltage measuring unit231. The voltage measuring unit231comprises a first voltage measurement input (not represented) and a first voltage measuring circuit240which is assigned thereto. Additionally, the voltage measuring unit231comprises a second voltage measurement input (not represented) and a second voltage measuring circuit250which is assigned thereto. The first measuring path140on the measuring device130and the first high-voltage network terminal73of the high-voltage network70are assigned to the first voltage measurement input and the first voltage measuring circuit240. Additionally, the second measuring path150on the measuring device130and the second high-voltage network terminal74of the high-voltage network70are assigned to the second voltage measurement input and the second voltage measuring circuit250.

By means of each voltage measuring circuit240,250, the second voltage applicable via the two further relays71,72on the associated measuring path140,150, i.e. the second voltage between the associated high-voltage network terminal73,74on the high-voltage network70and the housing potential25, is detected. Each second voltage thus detected is compared with a predefined threshold value by means of a comparator245,255on the voltage measuring unit231which is assigned to the corresponding voltage measuring circuit240,250. Each voltage measuring circuit240,250comprises a resistive voltage divider241,251with two resistors, which is connected between the high-voltage network terminal73,74of the high-voltage network70which is assigned to the corresponding voltage measuring circuit240,250and the housing potential25, and an operational amplifier242,252. In the interests of simpler representation, the resistors of the two voltage dividers241,251on the two voltage measuring circuits240,250are not provided with reference numbers. The operational amplifier242,252of each voltage measuring circuit240,250is connected, on its input side, to a connection point by means of which the two resistors of the voltage divider241,251, arranged in the corresponding voltage measuring circuit240,250and, on its output side, to the comparator245,255which is assigned to the corresponding voltage measuring circuit240,250. Both comparators245,255of the voltage measuring unit231are connected respectively, on the input side, to the operational amplifier242,252arranged in the associated voltage measuring circuit240,250and, on the output side, via an OR function232on the voltage measuring unit231, to a control unit233on the monitoring circuit230.

If one of the two comparators245,255of the voltage measuring unit231detects the presence of the corresponding second voltage applicable to the measuring device140via the two further relays71,72which lies outside the provided measuring range of the measuring device130and, consequently, has a magnitude which exceeds the maximum magnitude, the two relays145,155on the measuring device130are opened by means of the control unit233and, in consequence, the measuring paths140,150are securely separated from the battery20or from the high-voltage network70. By means of an appropriate latch functionality, the relays145,155remain open until such time as notification is delivered to a central microcontroller of a battery control device on the battery system200of the termination of the dielectric withstand test or the termination of a corresponding test mode on the battery control device such that, in consequence, no further test voltage ±VT1is present between at least one high-voltage network terminal73,74of the two high-voltage network terminals73,74on the high-voltage network70and the housing potential25.

In addition to the preceding written disclosure, for the further disclosure of the invention, reference shall hereby also be made to the representation inFIGS. 2 and 3.