SAFETY CIRCUIT FOR A POWER SYSTEM OF A VEHICLE AND METHOD FOR CONTROLLING THE SAFETY CIRCUIT

Abstract

A safety circuit (100) for a power system (102) of a vehicle (300), the safety circuit comprising: a hazardous voltage interlock loop (HVIL) circuit (104) configured to disconnect a high-voltage energy source (106) from a high-voltage system (108), the HVIL-circuit comprising a contactor (110) and a HVIL control unit (111); a current meter (112) arranged to measure a current; a fuse (114); a switching circuit (116) controlling the contactor of the HVIL-circuit; and a safety circuit control unit (118) connected to the current meter and to the switching circuit for controlling the contactor, wherein the safety circuit control unit is configured to: if the HVIL control unit provides a control signal to the switching circuit to open the contactor, and if the current measurement exceeds a first threshold current value, control the switching circuit to delay the opening of the contactor by a controllable time period.

Claims

1. A safety circuit for a power system of a vehicle, the safety circuit comprising: a hazardous voltage interlock loop circuit configured to disconnect a high-voltage energy source from a high-voltage system, the HVIL-circuit comprising a contactor arranged between the high-voltage energy source and the high-voltage system, and a HVIL control unit; a current meter arranged to measure a current between the high-voltage energy source and the high-voltage system; a fuse arranged between the high-voltage energy source and the high-voltage system; a switching circuit arranged to control the contactor of the HVIL-circuit; and a safety circuit control unit connected to the current meter to receive a current measurement of a current running through the contactor and to the switching circuit for controlling the contactor, wherein the safety circuit control unit is configured to: if the HVIL control unit provides a control signal to the switching circuit to open the contactor, and if the current measurement exceeds a first threshold current value, control the switching circuit to delay the opening of the contactor by a controllable time period.

2. The safety circuit according to claim 1, wherein the controllable time period is based on an amplitude of the measured current.

3. The safety circuit according to claim 1, wherein the fuse is configured to break an electric path between high-voltage energy source and the high-voltage system if the current through the contactor is higher than a safe disconnection current for the contactor.

4. The safety circuit according to claim 3, wherein the contactor is configured to have safe disconnection current of at least 2000A.

5. The safety circuit according to claim 1, wherein the controllable time period is based on properties of the fuse.

6. The safety circuit according to claim 1, wherein the controllable time period is longer than a time required for the fuse to break at the measured current.

7. The safety circuit according to claim 1, wherein the controllable time period is inversely proportional to the measured current.

8. The safety circuit according to claim 1, wherein the switching circuit is a bi-stable circuit.

9. The safety circuit according to claim 1, wherein the switching circuit is a flip-flop circuit.

10. A power system for a vehicle comprising: a high-voltage energy source; a high-voltage system; and a safety circuit according to claim 1.

11. A vehicle comprising a power system according to claim 10.

12. Method for controlling a safety circuit for a power system of a vehicle, the safety circuit comprising a hazardous voltage interlock loop circuit configured to disconnect a high-voltage energy source from a high-voltage system, the HVIL-circuit comprising a contactor arranged between the high-voltage energy source and the high-voltage system, and a HVIL control unit; a current meter arranged between the high-voltage energy source and the high-voltage system; a fuse arranged between the high-voltage energy source and the high-voltage system; a switching circuit arranged to control the contactor of the HVIL-circuit; and a safety circuit control unit, the method comprising: by the current meter, measuring a current between the high-voltage energy source and the high-voltage system; detecting that the HVIL control unit provides a control signal to the switching circuit to open the contactor; comparing the measured current with a current threshold value; and if the measured current exceeds the threshold value, controlling the switching circuit to delay the opening of the contactor by a controllable time period.

13. The method according to claim 12, wherein the controllable time period is based on an amplitude of the current and on the properties of the fuse such that if the measured current is higher than a safe disconnection current of the contactor, the time period is controlled to be longer than a time required for the fuse to break.

14. The method according to claim 12, further comprising controlling the switching circuit to set the contactor to a stable open position after the controllable time period.

15. A control unit for controlling a safety circuit for a power system of a vehicle, the control unit being configured to perform the steps of the method according to claim 12.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] With reference to the appended drawings, below follows a more detailed description of embodiments of the invention cited as examples.

[0023] In the drawings:

[0024] FIG. 1 is a schematic illustration of safety circuit in a power system according to an embodiment of the invention;

[0025] FIG. 2 is a flow-chart outlining a method of controlling a safety circuit in a power system according to an embodiment of the invention, and

[0026] FIG. 3 is a vehicle comprising a power system according to an embodiment of the invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE INVENTION

[0027] In the present detailed description, various embodiments of a safety circuit for a power system according to the present invention are mainly discussed with reference to a power system in a truck. It should however be noted that this by no means limits the scope of the present invention since the described invention is equally applicable in other types of vehicles such as cars, buses and construction vehicles. The described safety circuit may also be used in marine applications such as boats and ships, and in other applications comprising a high-voltage power source and a high-voltage system.

[0028] FIG. 1 schematically illustrates a circuit schematic of a safety circuit 100 and a power system 102 of a vehicle 300. The safety circuit comprises a hazardous voltage interlock loop HVIL circuit 104 configured to disconnect a high-voltage energy source 106 from a 10 high-voltage system 108. The high-voltage energy source 106 is here illustrated as a battery and the high-voltage system 108 may be an electrical propulsion system of the vehicle.

[0029] The HVIL-circuit in turn comprises a contactor 110 arranged between the high-voltage 15 energy source 106 and the high-voltage system 108, and a HVIL control unit 111. In principle, the HVIL-circuit is configured to detect an electrical fault in the power system and to subsequently shut down the system. A typical HVIL circuit consist of a current source, a physical output pin, a return signal pin, here provided by the HVIL control unit 111, and a measurement device and control unit 111 that can detect if the loop is closed. When a current source is used, the monitoring device will know what current to expect from a closed loop, hence a very high degree of reliability can be obtained and a deviation in the current provided by the current source can be detected, resulting in that the contactor 110 is opened. The use of a HVIL-circuit in high-voltage vehicle systems is known to the skilled person and will therefore not be described in further detail herein.

[0030] The safety circuit 100 further comprises a current meter 112 arranged to measure a current between the high-voltage energy source 106 and the high-voltage system 108, a fuse 114 arranged between the high-voltage energy source 106 and the high-voltage system 108, a switching circuit 116 arranged to control the contactor 110 of the HVIL-30 circuit; and a safety circuit control unit 118 connected to the current meter 112 to receive a current measurement of a current running through the contactor and to the switching circuit 116 for controlling the contactor 110. The current measurement is here received from the current meter 112. A current meter 112 is commonly present in a power system for a vehicle in order to monitor a current to or from a battery. The current meter 112 is advantageously capable of measuring the high currents which may occur during electrical faults.

[0031] Each of the safety circuit control unit 118 and the HVIL control unit 111 may include a microprocessor, microcontroller, programmable digital signal processor or another programmable device. The control unit may also, or instead, include an application specific integrated circuit, a programmable gate array or programmable array logic, a programmable logic device, or a digital signal processor. Where the control unit includes a programmable device such as the microprocessor, microcontroller or programmable 10 digital signal processor mentioned above, the processor may further include computer executable code that controls operation of the programmable device.

[0032] The safety circuit control unit 118 is configured to detect if the HVIL control unit 111 provides a control signal to the switching circuit 116 to open the contactor 110, and if the current measurement exceeds a first threshold current value, to control the switching circuit 116 to delay the opening of the contactor 110 by a controllable time period. The HVIL-control circuit 111 is thereby blocked from controlling the switching circuit 116 and is consequently blocked from controlling the contactor 110. The safety circuit control unit 118 will allow the contactor to be opened after the controllable time period has passed.

[0033] The controllable time period may be set to take on a limited number of fixed and predetermined values where the value to select is based on the measured current for a given configuration of fuse and contactor.

[0034] In a practical example, a nominal rating of the fuse may be 150A, meaning that 150A can flow uninterrupted though the fuse for thousands of hours. To provide robustness to the fuse a certain margin to the current can be designed. A typical performance of a 150A fuse may be:

TABLE-US-00001 Fuse current Trip (pre-arc opening) time  200 A More than 1 h  300 A 10 s  600 A 500 ms 1000 A 200 ms 2000 A 60 ms 3000 A 30 ms 5000 A Less than 10 ms

[0035] An example contactor can safely open at 1000A but may experience problems with opening and/or arcing at 2000A, and will fail at 5000A.

[0036] In the above example, when the current is lower than 1000A the circuit may be opened by the contactor after typically 20-30 ms of continuous fault situation, and when the current is higher than 1000A the fuse will break the current after a worst-case time of 200 ms.

[0037] The above described design makes it possible to have safe interruption of all possible fault currents but still allowing a fast HVIL reaction of less than for instance 30 ms, except in the unlikely situation of HVIL being opened at the same time as having over-current in the power circuit.

[0038] The design also means that once the circuit is opened by the HVIL-circuit the vehicle is electrically safe and the power system such as a traction voltage system will not go live until the HVIL loop is closed again.

[0039] In FIG. 1, the switching circuit 116 and contactor 110 are illustrated as separate units for clarity. It should be understood that the described functionality of the switching circuit and contactor may also be provided by a single unit. Moreover, fuse may be configured to break with a few milliseconds for a so called “hard short” giving rise to a current far above a nominal current. For a “soft short” giving rise to a current which is lower but still above a normal operating current, the fuse trigger time may be in the range of several seconds.

[0040] The described safety circuit thus allows a delayed circuit shut-down at soft short but a fast triggering when arc protection is needed in case of a hard short.

[0041] The described delay in opening the contactor 110 can also be used if a fault in HVIL circuit is suspected, i.e. if a signal to open the contactor 110 is provided by the HVIL control unit 111 without an elevated current having been detected. The signal may for example be the result of a fault in the logic or other components of the HVIL-circuit. A delay may allow the operator of the vehicle to stop the vehicle in a secure manner or to take the vehicle to a workshop.

[0042] FIG. 2 is a flow chart outlining the general steps of a method for controlling a safety circuit 100 according to an embodiment of the invention. The method is performed in a safety circuit 100 for a power system 102 of a vehicle according to any of the above described embodiments or examples.

[0043] The method comprises: by the current meter 112, measuring 200 a current between the high-voltage (HV) energy source 106 and the high-voltage system 108; detecting 202, by the safety circuit control unit 118, that the HVIL control unit 111 provides a control signal to the switching circuit 116 to open the contactor 110; comparing 204 the measured current with a current threshold value; and if the measured current exceeds the threshold value, controlling 206 the switching circuit 116 to delay the opening of the contactor by a controllable time period. Further features and effects of the method are similar to the ones described above in relation to the functionality of the safety circuit 100.

[0044] FIG. 3 is a vehicle 300 comprising a safety circuit 100 for a power system according to any of the aforementioned embodiments and examples.

[0045] 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.