SE2150307A1

SE2150307A1 - A method for monitoring the operation of a vehicle battery circuit with parallel batteries and a battery circuit

Info

Publication number: SE2150307A1
Application number: SE2150307A
Authority: SE
Inventors: Gunnar Ledfelt; Lukas Rydén
Original assignee: Scania Cv Ab
Priority date: 2021-03-18
Filing date: 2021-03-18
Publication date: 2022-09-19
Also published as: DE102022103986A1; SE544761C2

Abstract

A battery circuit (1) for a vehicle (300), said battery circuit (1) comprises a primary battery circuit (101) comprising a primary battery (102); a secondary battery circuit (104) comprising a secondary battery (105), and a generator configured to supply a first demanded voltage to a positive pole of the primary battery, in response of a first voltage demand signal applied to the generator. The battery circuit (1) further comprises a connection circuit (100) comprising an input (107) connected to a positive pole of the primary battery (102), and an output (108) connected to a positive pole of the secondary battery (105), the connection circuit further comprises a first branch (109) which connects the input (107) to the output (108), wherein the first branch (109) comprises a diode (D1). A control circuit (110) is provided, configured to generate a first voltage demand signal and to determine that the generator supplies the first demanded voltage to the positive pole of the primary battery (102), and then to measure the voltage of the input (107), Vin0, and the voltage of the output (108), Vout0, and to generate a second voltage demand signal to increase the generator output, from the first demanded voltage to a second demanded voltage, and to measure the voltage of the input (107), Vin1, and the voltage of the output (108), Vout1, and then to determine the operation status of the battery circuit (1) based on the measured values.

Description

A method for monitoring the operation of a ' Technical field The present disclosure relates to a method for monitoring the operation of a battery circuit for a vehicle, and a battery circuit, and particularly a method for monitoring the operation of the battery circuit by performing a functional test of a diode in a connection circuit of the battery circuit.

Background ln modern vehicles, there is often at least two parallel battery systems. Often these systems comprise a primary battery and a secondary battery connected in parallel for providing redundancy in power supply for critical systems. This is especially important for autonomous vehicles, which have safety systems for monitoring and control of the vehicle, which must be operational for safety reasons. lt is of course important that both the primary battery and the secondary battery are operational and functional.

To increase the safety of autonomous vehicles, the functionality is divided into two control systems. ln order for the vehicle to be considered to have normal function, both systems must be fully functional. Should one of the control systems stop working, the vehicle must be able to maintain its ability to stay safe.

The separation of the vehicle's functionality has required that the current electrical power supply must be extended such that each control system can be supplied separately. The reason is that one fault faults in the power supply must not close down both control systems.

Generally, to achieve the extension and separation of the power supply, a battery circuit is provided that comprises a diode, a fuse and a secondary battery pack, which is disclosed in figure 2. 2 Below some documents in this technical field will be briefly discussed.

WO-2012/104036 discloses a circuit arrangement for a motor vehicle that comprises several rechargeable batteries and lithium ion capacitors connected in parallel. A diode is provided in the arrangement.

DE102009029335 discloses an accumulator for a two-battery electrical system in a vehicle, particularly in a micro hybrid vehicle, that is charged with electric power by a generator when electrical energy supply from the generator is interrupted. A coupling unit is provided that includes a diode coupled in parallel to a DC/DC- converter.

EP0753925 relates to control arrangements for IC-engined vehicle's electrical supplies, provided with separate batteries for starter and other loads, with various battery and alternator switching options.

EP2562910 discloses an electrical system for a vehicle with internal combustion engine, has third electrical energy source which can be selectively connected in parallel with alternator via a second switch.

DE102012014912 relates to a vehicle has a left energy storage device for storing electrical energy and a right energy storage device for storing electrical energy, that are electrically connected to a starter generator (SG) for starting an internal combustion engine, such that the energy storage devices are charged by the starter generator. The right energy storage device is electrically connected to the starter generator through a switch diode arrangement, and a diode is connected in parallel with the switch diode arrangement.

US2015239411 discloses a power supply device for vehicle, has electrical storage units that conserve electric power, and control unit controls switches at OFF state, and controls switches in order of another switch and one switch, when starting control unit. ln order to provide the required redundant operation, the battery circuit disclosed in figure 2 must fulfil high functionality demands. Thus, the object of the present invention is to improve the safety when monitoring the operation of a battery circuit including a primary and a secondary battery.

Summary The above-mentioned object is achieved by the present invention according to the independent claims.

Preferred embodiments are set forth in the dependent claims. ln the battery circuit disclosed in figure 2, the diode is a critical component of the redundant system and should therefore be monitored in order to ensure that the diode connecting the primary battery to the secondary battery of a vehicle functions properly. ln that regard, common faults for a diode are that it is short- circuited or has an electrical interruption.

According to a first aspect, the present disclosure relates to a method for monitoring the operation of a battery circuit 1 for a vehicle 300.

The battery circuit 1 comprises: - a primary battery circuit 101 comprising a primary battery 102, and a primary load 103 connected in parallel to the primary battery 102; - a secondary battery circuit 104 comprising a secondary battery 105 with a nominal voltage equal to a nominal voltage of the primary battery 102, and a secondary load 106 connected in parallel to the secondary battery 105; - a generator configured to supply a first demanded voltage to a positive pole of the primary battery, in response of a first voltage demand signal applied to the generator.

The battery circuit 1 further comprises a connection circuit 100 comprising an input 107 connected to a positive pole of the primary battery 102, and an output 108 connected to a positive pole of the secondary battery 105, the connection circuit further comprises: - a first branch 109 which connects the input 107 to the output 108, wherein the first branch 109 comprises a diode (D1) arranged such that electric current may flow from the input 107 to the output 108, and a control circuit 110.

The method comprises: 4 -when the generator supplies said first demanded voltage to the positive pole of the primary battery, -measuring the voltage of the input 107, Vino, and -measuring the voltage of the output 108, Vouio, -increasing the generator output to a second demanded voltage, -measuring the voltage of the input 107, Vim, -measuring the voltage of the output 108, Vom, -determining the operation status of the battery circuit 1 based on the measured values.

According to a second aspect, the present disclosure relates to a battery circuit 1 for a vehicle 300. The battery circuit 1 comprises: - a primary battery circuit 101 comprising a primary battery 102, and a primary load 103 connected in parallel to the primary battery 102; - a secondary battery circuit 104 comprising a secondary battery 105 with a nominal voltage equal to a nominal voltage of the primary battery 102, and a secondary load 106 connected in parallel to the secondary battery 105; - a generator configured to supply a first demanded voltage to a positive pole of the primary battery, in response of a first voltage demand signal applied to the generator.

The battery circuit 1 further comprises a connection circuit 100 comprising an input 107 connected to a positive pole of the primary battery 102, and an output 108 connected to a positive pole of the secondary battery 105, the connection circuit further comprises: - a first branch 109 which connects the input 107 to the output 108, wherein the first branch 109 comprises a diode (D1) arranged such that electric current may flow from the input 107 to the output 108; and - a control circuit 110, comprising an input voltage detector 111 configured to measure the voltage of the input 107, Vin, and an output voltage detector 112 configured to measure the voltage of the output 108, Vom; wherein said control circuit 110 is configured to generate said first voltage demand signal and to determine that the generator supplies said first demanded voltage to the positive pole of the primary battery 102, and then to measure the voltage of the input 107, Vino, and the voltage of the output 108, Vouto.

The control circuit 110 is then configured to generate a second voltage demand signal to increase the generator output, from the first demanded voltage to a second demanded voltage, and to measure the voltage of the input 107, Vim, and the voltage of the output 108, Vom, and then to determine the operation status of the battery circuit 1 based on the measured values.

According to the first and second aspects of the disclosure, the voltage across the diode is measured, the generator voltage is increased to ensure that the primary side voltage is dominant, and then the voltage across the diode is measured again. Based upon these measured voltage values across the diode it is determined that the diode works as intended, and thus it is determined the operation status of the battery circuit.

By applying the solution according the present invention, including measuring voltages across the diode as described above, no physical components need to be added to perform the monitoring of the operation status of the battery circuit, which is advantageous.

Brief description of the drawinqs Figure 1 is a schematic illustration of a part of a vehicle where a battery circuit according to the invention is arranged.

Figure 2 is a schematic illustration of a block diagram of the battery circuit according to the invention.

Figure 3 is a schematic flow diagram of the method according to the present invenﬁon.

Figure 4 is a schematic flow diagram of embodiments of the method according to the present invention.

Figure 5 is a schematic block diagram illustrating a computer-readable storage medium according to the present invention.

Detailed description The method, the battery circuit, the computer-readable storage medium, and the vehicle will now be described in detail with references to the appended figures.

Throughout the figures the same, or similar, items have the same reference signs.

Moreover, the items and the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.

With references to the block diagram of figure 2, and the flow diagram of figure 3, the method for monitoring the operation of a battery circuit 1 for a vehicle 300 will now be described in detail.

The battery circuit 1 comprises a primary battery circuit 101 comprising a primary battery 102, and a primary load 103 connected in parallel to the primary battery 102, and a secondary battery circuit 104 comprising a secondary battery 105 with a nominal voltage equal to a nominal voltage of the primary battery 102, and a secondary load 106 connected in parallel to the secondary battery 105.

The primary battery circuit and the secondary battery circuit are connected in parallel for providing redundancy in power supply for critical systems of the vehicle.

The battery circuit further comprises a generator 120 configured to supply a first demanded voltage to a positive pole of the primary battery 102, in response of a first voltage demand signal 121 applied to the generator 120.

As defined in this application, the nominal voltage of the battery is determined in accordance with IEC Standard 60050-482:2004.

The battery circuit 1 further comprises a connection circuit 100 comprising an input 107 connected to a positive pole of the primary battery 102, and an output 108 connected to a positive pole of the secondary battery 105. 7 The connection circuit 100 also comprises a first branch 109, which connects the input 107 to the output 108, wherein the first branch 109 comprises a diode (D1) arranged such that electric current may flow from the input 107 to the output 108. ln addition, the connection 100 circuit comprises a control circuit 110. ln figure 3 a flow diagram of the method is illustrated; the method comprises: -determining that the generator supplies the first demanded voltage to the positive pole of the primary battery and when the generator supplies the first demanded voltage to the positive pole of the primary battery: -measuring the voltage of the input 107, Vino, and -measuring the voltage of the output 108, Vouio, -increasing the generator output to a second demanded voltage, -measuring the voltage of the input 107, Vim, -measuring the voltage of the output 108, Vom, -determining the operation status of the battery circuit 1 based on the measured values.

Thereby is achieved that the operation status of the battery circuit is determined without adding further components.

More in detail, the method is based upon known functionality of a fully functioning battery circuit. The step of determining that the generator supplies the first demanded voltage is necessary in order to have a known input voltage at the positive pole of the primary battery. When that is determined, the voltage over the diode D1 is measured at input 107 and output 108. Thereafter the generator output is increased to a known second demanded voltage, and the voltage over the diode is measured again. The second demanded voltage is related to the first demanded voltage such that the measured values at the input and output before and after generator output voltage increase, unambiguously indicates the operation status of the battery circuit, as there exist known relationships between the measured values for a fully functioning battery circuit.

The first branch 109 shown in figure 2 further comprises a fuse F1 arranged to protect the diode D1 against over current. The fuse F1 of the first branch 109 also protects the primary battery circuit 101 in case of a short-circuit in the secondary battery circuit 104.

The diode D1 is a diode with low forward voltage drop and of high current type, such as for example a Schottky power diode.

A Schottky diode is a semiconductor diode formed by the junction of a semiconductor with a metal. lt has a low forward voltage drop and a very fast switching action. When sufficient forward voltage is applied, a current flows in the fon/vard direction. A silicon p-n diode has a typical fon/vard voltage of 600-700 mV, while the Schottky's forward voltage is 150-450 mV. This lower forward voltage requirement allows higher switching speeds and better system efficiency.

As illustrated in figure 2, the control circuit 110 also comprises a primary output 114 configured to control the connection of the controllable primary load 103 to said primary battery 102, a secondary output 115 configured to control the connection of the controllable secondary load 106 to said secondary battery 105, a battery status output 116, which is configured to output a battery status signal indicative of the status of the primary battery, and/or the secondary battery.

The primary load 103 comprises any of an electric system for lighting and an electric system cooling/heating of a vehicle, which vehicle is provided with a further electric battery pack for propulsion of the vehicle. As an alternative, the primary load 103 comprises any of a compressor or a starter motor of a vehicle, which vehicle comprises a combustion engine for the propulsion thereof. The secondary battery 105 may be a battery used to supply the secondary load 106 with electric power. The secondary load 106 may be a system for autonomous control of the vehicle. Other primary and secondary loads are also conceivable within the scope of the present invention.

The normal voltages of the first and second batteries vary in dependence of many different reasons, e.g. the condition of the batteries, the present outtake from the 9 batteries, the temperature, etc. Therefore, the voltages over the batteries are not known, but may be fluctuating in an unpredictable way. That is a reason why it is difficult to ascertain that the diode of the connection circuit is functioning according to set requirements. The disclosed method and battery system according to the present invention solves this problem in that the diode's function is accurately determined.

According to one embodiment, the method step of determining the operation status of the battery circuit 1 comprises preforming a short-circuit test.

The short-circuit test comprises caiculating: Vino - Vouto = Vto, Vin1 - Vouu = Vu, and Vu - Vto = Vtesu, wherein if Vtesu is 0, then the diode is short-circuited, else, the diode is not short-circuited.

This is i||ustrated in the upper part of the ﬂow diagram in figure 4.

First, a measurement is made at the first demanded voltage and a measurement value Vu over the diode is calculated. ln a normally functioning diode Vto should be 0, as the first demanded voltage is chosen to be lower than the diode's forward voltage. Then, the generator output is increased to the second demanded voltage, being higher than the diode's forward voltage, and a measurement value Vu is calculated. ln a normally functioning diode Vu should not be 0, but instead have the value of the forward voltage of the diode. lf the diode is short-circuited, no voltage drop will exist over the diode, i.e. Vu would be 0.

The difference Vtesu between Vu and Vto is then calculated, and if Vtesu is 0 the diode is short-circuited and an alarm will be generated.

An important aspect of this embodiment is to make two measurements, one prior and one after generator voltage increase. The reason is that if only one measurement is performed, the diode could erroneously be considered short- circuited if both the first and second batteries had the same voltage.

According to another embodiment, the method step of determining the operation status of the battery circuit 1 comprises preforming an electrical interruption test. The electrical interruption test comprises calculating: Voun - Vouto = Vtestz, wherein if Vtestz is 0, then the diode is electrically interrupted, else, the diode is not electrically interrupted.

This is illustrated in the lower part of the flow diagram in figure 4.

The output voltage Vouto is measured at the first demanded voltage, the generator output is increased to the second demanded voltage, being higher than the diode's forward voltage, and the output voltage is measured. These steps are illustrated in the upper part of the flow diagram.

The difference Vtestz between Vom and Vouto is then calculated. The diode works as required if Vouto is 0 and Vom has the value of the forward voltage of the diode. lf the diode is electrically interrupted the output voltages would be the same at both measurements, as no electrical connection exists between input 107 and output 108. lf it is determined that Vtesiz is 0 the diode is electrically interrupted and an alarm will be generated.

Thus, if the voltages are the same prior and after increasing the generator output there must be an electrical interruption of the diode, or, as an alternative, the fuse F1 of the first branch 109 has tripped.

According to a further embodiment, if the result of the operation status of the battery circuit 1 is that the battery circuit 1 does not work as required, the method comprises generating an alarm that the battery circuit 1 is malfunctioning enabling the vehicle 300 to take any necessary action in response thereto.

The necessary action may be stop the vehicle in a safe manner. The alarm generated by the control circuit 110 may be applied to a vehicle controller (not shown) that enters into a safety mode of operation. Particularly, if the vehicle is an autonomous vehicle, and an alarm is generated indicative of a battery error the drive train of the vehicle may be disabled, or a safety mode of operation is ll enabled. This way the vehicle is prevented from driving with a malfunctioning battery circuit, battery redundancy is assured since both the primary, and secondary batteries must be operational in order for the vehicle to have full functionality. ln a further embodiment, the method comprises generating, by the control circuit, a second voltage demand signal and applying the signal to the generator to increase the generator output from the first demanded voltage to the second demanded voltage. The difference between the second demanded voltage and the first demanded voltage corresponds to a predetermined voltage value that is chosen in dependence of a nominal value of a forward direction of the diode, such that it is higher than the nominal value of the forward direction of the diode and not exceeds the demanded generator voltage by more than a set percentage, e.g. 3-5%. The set percentage is chosen such that the voltage increase is clearly higher than the nominal value of a forward direction of the diode, but without using too much energy. One exemplary voltage increase may be 1 Volt.

As discussed above, a normal voltage drop in the forward direction for e.g. a Schottky diode is between 0.15-0.46 V. ln still another embodiment, the method comprises keeping the increased generator voltage at the second demanded voltage during a measurement interval in the range of 0.5 - 2.5 seconds, preferably approximately 1 second. The maximal duration of the interval length is chosen to have as little impact of the overall operation of the battery circuit as possible, and the minimal duration is chosen such that the measurements may be performed in a reliable way.

Figure 2 is a schematic illustration of the battery circuit according to the present invenﬁon.

The battery circuit 1 is adapted to be used in a vehicle 300, e.g. of the kind that is shown in figure 1. 12 The battery circuit 1 comprises a primary battery circuit 101 comprising a primary battery 102, and a primary load 103 connected in parallel to the primary battery 102, and a secondary battery circuit 104 comprising a secondary battery 105 with a nominal voltage equal to a nominal voltage of the primary battery 102, and a secondary load 106 connected in parallel to the secondary battery 105. The battery circuit 1 also comprises a generator 120 configured to supply a first demanded voltage to a positive pole of the primary battery, in response of a first voltage demand signal 121 applied to the generator.

Herein, by generator is meant both a traditional electro-mechanical generator, and a DC/DC converter, i.e. any arrangement capable of performing generator functionality and thus submitting a generator output.

Thus, the generator is configured to generate a requested voltage that is typically 28.3 V in normal conditions, 27.3 V in warm conditions, and 29.3 V in cold conditions.

The battery circuit 1 further comprises a connection circuit 100 comprising an input 107 connected to a positive pole of the primary battery 102, and an output 108 connected to a positive pole of the secondary battery 105.

The connection circuit 100 further comprises a first branch 109, which connects the input 107 to the output 108, wherein the first branch 109 comprises a diode (D1) arranged such that electric current may flow from the input 107 to the output 108. ln addition the connection circuit 100 comprises a control circuit 110, comprising an input voltage detector 111 configured to measure the voltage of the input 107, Vin, and an output voltage detector 112 configured to measure the voltage of the output 108, Voui.

The control circuit 110 is configured to generate the first voltage demand signal 121 and to determine that the generator supplies the first demanded voltage to 13 the positive pole of the primary battery 102, and then to measure the voltage of the input 107, Vino, and the voltage of the output 108, Vouto.

The control circuit 110 is then configured to generate a second voltage demand signal 122 to increase the generator output, from the first demanded voltage to a second demanded voltage, and to measure the voltage of the input 107, Vim, and the voltage of the output 108, Voun.

Finally, the control circuit 110 is configured to determine the operation status of the battery circuit 1 based on the measured values.

Thereby is achieved that the operation status of the battery circuit is determined without adding further components, which is advantageous as the described determination of the operation status of the battery circuit may easily be applied in a presently used battery circuit. Further advantages are discussed in connection with claim 1. ln the following, some embodiments of the battery circuit are listed. These have the same technical features and advantages as for the corresponding method described above. Consequently, these technical features and advantages are not repeated or explained anew in order to avoid unnecessary repetition. ln one embodiment, the control circuit is configured to determine the operation status of the battery circuit 1 by preforming a short-circuit test.

The short-circuit test comprises to calculate: Vino - Vouto = Vto, Vim - Vouu = Vu, and Vu - Vto = Vtesn, wherein if Vtesn is 0, then the diode is short-circuited, else, the diode is not short-circuited. 14 ln one embodiment, the control circuit is configured to determine the operation status of the battery circuit 1 by preforming an electrical interruption test.

The electrical interruption test comprises to calculate: Voun - Vouto = Vtestz, wherein if Vtestz is 0, then the diode is electrically interrupted, else, the diode is not electrically interrupted.

According to a further embodiment, if the result of the operation status of the battery circuit 1 is that the battery circuit 1 does not work as required, the control circuit is configured to generate an alarm that the battery circuit 1 is malfunctioning enabling the vehicle 300 to take any necessary action in response thereto.

Various necessary actions have been discussed above in connection with the description of the method. ln a still further embodiment, the difference between the second demanded voltage and the first demanded voltage corresponds to a predetermined voltage value that is chosen in dependence of a nominal value of a forward direction of the diode, such that it is higher than the nominal value of the fon/vard direction of the diode and not exceeds the demanded generator voltage by more than a set percentage.

The generator output is increased by a predetermined voltage, e.g. 1 V. The predetermined voltage value is chosen in dependence of the nominal value of forward direction of the diode, such that it is higher than the nominal value without exceeding the normal voltage of the generator by more than a set percentage, e.g. 3-5%.

The control circuit is preferably configured to keep the increased generator voltage at the second demanded voltage during a measurement interval in the range of 0.5 - 2.5 seconds, preferably approximately 1 second.

The present invention further relates to a computer-readable storage medium 450 storing computer program instructions which, when executed by a processor 420, cause the processor 420 to perform a method as described in detail above. Figure 5 shows an exemplary implementation of the control circuit 110 using programmable signal processing hardware 400. The signal processing apparatus 400 shown in figure 5 comprises an input/output section 410 for receiving and transmitting signals to the control circuit 110 as indicated in figure 2. The signal processing apparatus 400 further comprises a processor 420, a working memory 430 and an instruction store 440 storing computer-readable instructions which, when executed by the processor 420, cause the processor 420 to perform processing operations herein described. The instruction store 440 may comprise a ROM which is preloaded with computer readable instructions. Alternatively, instruction store 440 may comprise a RAM or similar type of memory, and the computer readable instructions can be input thereto from a computer program product, such as a computer readable storage medium 450 such as a CD-ROM, etc. or a computer readable signal 460 carrying the computer readable instructions.

The present invention also relates to a vehicle 300 comprising a battery circuit 1 as described in detail above, and in particular an autonomous vehicle.

The battery circuit 1, as disclosed hereinabove, may be connected to a vehicle controller (not shown). The vehicle controller may be a distributed system arranged in the vehicle 300 disclosed hereinabove, or a processing device configured to control the operation of the vehicle. The vehicle controller is connected to a battery status output 116 for receiving a battery status signal, wherein the vehicle controller may further be configured to prevent actuation of a drive train of the vehicle 300 when receiving a battery status signal, which indicates a battery error. ln one exemplary implementation in a vehicle, e.g. an autonomous vehicle, may be in accordance with the following scenario A-E. 16 A. The voltage detectors 111, 112 are provided in the control circuit 110 that coordinates several functions realized by different control units of the vehicle (e.g. an engine control unit, a brake system control unit, and a steering servo control unit) where the function specific control units are power supplied by either the primary or the secondary battery circuit.

B. The coordinating control circuit 110 is power supplied by both battery circuits in order to function even if there is an error in one of the battery circuits. When a test of operation of the battery circuit is made, the control circuit will generate voltage demand signals 121, 122 to demand the engine control unit, which is connected to a voltage regulator, to change the generator voltage in order to perform the method described herein.

C. The coordinating control circuit 110 measures voltage values of the voltage detectors 111, 112 prior and after change of the generator voltage.

D. The coordinating control circuit 110 determines the operating status of the battery circuit.

E. lf the diode does not function as required the coordinating control circuit 110 generates an alarm indicating that the battery circuit 1 is malfunctioning enabling the vehicle 300 to take any necessary action in response thereto. This necessary action may be to generate a request to all function specific control units to stop the vehicle such that the vehicle by movement, braking and steering can reach a suitable position to stop.

The present invention is not limited to the above-described preferred embodiments. Various alternatives, modifications and equivalents may be used. Therefore, the above embodiments should not be taken as limiting the scope of the invention, which is defined by the appending claims.

Claims

1. A method for monitoring the operation of a battery circuit (1) for a vehicle (300), said battery circuit (1) comprises: - a primary battery circuit (101) comprising a primary battery (102), and a primary load (103) connected in parallel to the primary battery (102); - a secondary battery circuit (104) comprising a secondary battery (105) with a nomina| voltage equal to a nomina| voltage of the primary battery (102), and a secondary load (106) connected in parallel to the secondary battery (105); - a generator configured to supply a first demanded voltage to a positive pole of the primary battery, in response of a first voltage demand signal applied to the generator, c h a r a c t e r i z e d i n that the battery circuit (1 ) further comprises a connection circuit (100) comprising an input (107) connected to a positive pole of the primary battery (102), and an output (108) connected to a positive pole of the secondary battery (105), the connection circuit further comprises: - a first branch (109) which connects the input (107) to the output (108), wherein the first branch (109) comprises a diode (D1) arranged such that electric current may flow from the input (107) to the output (108), and a control circuit (110), wherein the method comprises: -when the generator supplies said first demanded voltage to the positive pole of the primary battery, -measuring the voltage of the input (107), Vmo, and -measuring the voltage of the output (108), Vouto, -increasing the generator output to a second demanded voltage, -measuring the voltage of the input (107), Vim, -measuring the voltage of the output (108), Voun, -determining the operation status of the battery circuit (1) based on the measured values.

2. The method according to claim 1, wherein determining the operation status of the battery circuit (1) comprises preforming a short-circuit test, wherein the short-circuit test comprises calculating:Vino - Vouto = Vto, Vim - Voun = Vu, and Vu - Vio = Viesn, wherein if Viesn is 0, then the diode is short-circuited, else, the diode is not short-circuited.

3. The method according to claim 1 or 2, wherein determining the operation status of the battery circuit (1) comprises preforming an electrical interruption test comprises calculating: Voun - Vouto = Viestz, wherein if Viesiz is 0, then the diode is electrically interrupted, else, the diode is not electrically interrupted.

4. The method according to any of claims 1-3, wherein if the result of the operation status of the battery circuit (1) is that the battery circuit (1) does not work as required, the method comprises generating an alarm that the battery circuit (1) is malfunctioning enabling the vehicle (300) to take any necessary action in response thereto.

5. The method according to any of claims 1-4, comprising, generating, by the control circuit, a second voltage demand signal and applying the signal to the generator to increase the generator output from the first demanded voltage to the second demanded voltage, wherein the difference between the second demanded voltage and the first demanded voltage corresponds to a predetermined voltage value that is chosen in dependence of a nominal value of a forward direction of the diode, such that it is higher than the nominal value of the forward direction of the diode and not exceeds the demanded generator voltage by more than a set percentage.

6. The method according to any of claims 1-5, comprising keeping the increased generator voltage at said second demanded voltage during a measurement interval in the range of 0.5 - 2.5 seconds, preferably approximately1 second.

7. A battery circuit (1 ) for a vehicle (300), said battery circuit (1) comprises: - a primary battery circuit (101) comprising a primary battery (102), and a primary load (103) connected in parallel to the primary battery (102); - a secondary battery circuit (104) comprising a secondary battery (105) with a nomina| voltage equal to a nomina| voltage of the primary battery (102), and a secondary load (106) connected in parallel to the secondary battery (105); - a generator configured to supply a first demanded voltage to a positive pole of the primary battery, in response of a first voltage demand signal applied to the generator, c h a r a c t e r i z e d i n that the battery circuit (1 ) further comprises a connection circuit (100) comprising an input (107) connected to a positive pole of the primary battery (102), and an output (108) connected to a positive pole of the secondary battery (105), the connection circuit further comprises: - a first branch (109) which connects the input (107) to the output (108), wherein the first branch (109) comprises a diode (D1) arranged such that electric current may flow from the input (107) to the output (108); and - a control circuit (110), comprising an input voltage detector (111) configured to measure the voltage of the input (107), Vin, and an output voltage detector (112) configured to measure the voltage of the output (108), Vom; wherein said control circuit (110) is configured to generate said first voltage demand signal and to determine that the generator supplies said first demanded voltage to the positive pole of the primary battery (102), and then to measure the voltage of the input (107), Vino, and the voltage of the output (108), Vouio, the control circuit (110) is then configured to generate a second voltage demand signal to increase the generator output, from the first demanded voltage to a second demanded voltage, and to measure the voltage of the input (107), Vim, and the voltage of the output (108), Vom, and then to determine the operation status of the battery circuit (1) based on the measured values.

8. The battery circuit (1) according to claim 7, wherein the control circuit is configured to determine the operation status of the battery circuit (1) by preforming a short-circuit test, comprising to calculate: Vino - Vouto = Vto, Vim - Vouu = Vu, and Vu - Vto = Vtesn, wherein if Vtesn is 0, then the diode is short-circuited, else, the diode is not short-circuited.

9. The battery circuit (1) according to claim 7 or 8, wherein the control circuit is configured to determine the operation status of the battery circuit (1) by preforming an electrical interruption test, comprising to calculate: Voun - Vouto = Vtestz, wherein if Vtestz is 0, then the diode is electrically interrupted, else, the diode is not electrically interrupted.

10. The battery circuit (1) according to any of claims 7-9, wherein if the result of the operation status of the battery circuit (1) is that the battery circuit (1) does not work as required, the control circuit is configured to generate an alarm that the battery circuit (1) is malfunctioning enabling the vehicle (300) to take any necessary action in response thereto.

11. The battery circuit (1) according to any of claims 7-10, wherein the difference between the second demanded voltage and the first demanded voltage corresponds to a predetermined voltage value that is chosen in dependence of a nominal value of a forward direction of the diode, such that it is higher than the nominal value of the forward direction of the diode and not exceeds the demanded generator voltage by more than a set percentage.

12. The battery circuit (1) according to any of claims 7-11, wherein the control circuit is configured to keep the increased generator voltage at said second demanded voltage during a measurement interval in the range of 0.5 - 2.seconds, preferably approximately 1 second.

13. A computer-readable storage medium (450) storing computer program instructions which, when executed by a processor (420), cause the processor (420) to perform a method according to any of c|aims 1-

14. A vehicle (300) comprising a battery circuit (1) according to any of c|aims 7-12.

15. A vehicle (300) comprising a battery circuit (1) according to c|aim 14, wherein the vehicle is an autonomous vehicle.