Detecting a bad contact of a charging cable

Abstract

A method for detecting a bad contact of a charging cable comprises: measuring a cooling fluid temperature of a cooling fluid flowing through the charging cable; measuring a connector base temperature of a connector base of the charging cable, which connector base carries an electrical contact element of the charging cable; estimating a contact temperature of the electrical contact element by determining the contact temperature from a difference of the connector base temperature and the cooling fluid temperature; and deciding presence of a bad contact, when the estimated contact temperature is higher than a threshold temperature.

Claims

1. A method for detecting a bad contact of a charging cable, the method comprising: measuring a cooling fluid temperature of a cooling fluid flowing through the charging cable; measuring a connector base temperature of a connector base of the charging cable, which connector base carries an electrical contact element of the charging cable; estimating a contact temperature of the electrical contact element from the connector base temperature and the cooling fluid temperature, wherein the estimated contact temperature increases, when the difference of the connector base temperature and the cooling fluid temperature increases; and deciding presence of a bad contact, when the estimated contact temperature is higher than a threshold temperature.

2. The method of claim 1, wherein the estimated contact temperature is equal to the cooling fluid temperature, when the connector base temperature and the cooling fluid temperature are equal.

3. The method of claim 2, wherein the estimated contact temperature is the cooling fluid temperature plus the difference of the connector base temperature and the cooling fluid temperature multiplied by a constant factor.

4. The method of claim 2, wherein the connector base comprises a cavity through which cooling fluid is guided.

5. The method of claim 2, wherein the connector base temperature is measured with a temperature sensor attached to an inside of the connector base.

6. The method of claim 2, wherein the connector base temperature is measured with a temperature sensor attached to an outside of the connector base.

7. The method of claim 1, wherein the estimated contact temperature is the cooling fluid temperature plus the difference of the connector base temperature and the cooling fluid temperature multiplied by a constant factor.

8. The method of claim 1, wherein the connector base comprises a cavity through which cooling fluid is guided.

9. The method of claim 1, wherein the connector base temperature is measured with a temperature sensor attached to an inside of the connector base.

10. The method of claim 1, wherein the connector base temperature is measured with a temperature sensor attached to an outside of the connector base.

11. The method of claim 1, wherein the connector base is cooled with cooling fluid; wherein the cooling fluid temperature is measured with a temperature sensor arranged in a cooling fluid flow returning from the connector base; or wherein the cooling fluid temperature is measured with a temperature sensor arranged in a cooling fluid flow flowing towards the connector base.

12. The method of claim 1, wherein the cooling fluid is pumped from a tank through a hose in the charging cable between the tank and the electrical contact.

13. The method of claim 12, wherein the cooling fluid temperature is measured with a temperature sensor in the tank.

14. The method of claim 1, wherein the cooling fluid is a cooling oil.

15. A method for charging an electrical device, the method comprising: charging the electrical device via a charging cable by generating a current in the charging cable; detecting a bad contact of the charging cable with at least the following steps: measuring a cooling fluid temperature of a cooling fluid flowing through the charging cable; measuring a connector base temperature of a connector base of the charging cable, which connector base carries an electrical contact element of the charging cable; estimating a contact temperature of the electrical contact element from the connector base temperature and the cooling fluid temperature, wherein the estimated contact temperature increases, when the difference of the connector base temperature and the cooling fluid temperature increases; deciding presence of a bad contact, when the estimated contact temperature is higher than a threshold temperature; and interrupting the current, when a bad contact has been detected.

16. A controller for a charging station comprising: a memory structured to store a set of instructions; and a processor structured to execute the set of instructions stored by the memory effective to: receive a cooling fluid temperature of a cooling fluid flowing through the charging cable, receive a connector base temperature of a connector base of the charging cable, which connector base carries an electrical contact element of the charging cable, estimate a contact temperature of the electrical contact element from the connector base temperature and the cooling fluid temperature, wherein the estimated contact temperature increases, when the difference of the connector base temperature and the cooling fluid temperature increases, and decide presence of a bad contact, when the estimated contact temperature is higher than a threshold temperature.

17. A charging station comprising: a charging cable with a plug comprising electrical contact elements; a cooling system for cooling the charging cable by generating a flow of cooling fluid through the charging cable and the plug; a first temperature sensor for measuring a cooling fluid temperature of the cooling fluid; a second temperature sensor for measuring a connector base temperature of a connector base arranged in the plug; and a controller comprising: a memory structured to store a set of instructions; and a processor structured to execute the set of instructions stored by the memory effective to: receive the cooling fluid temperature of the cooling fluid flowing through the charging cable, receive the connector base temperature of the connector base of the charging cable, which connector base carries an electrical contact element of the charging cable, estimate a contact temperature of the electrical contact element from the connector base temperature and the cooling fluid temperature, wherein the estimated contact temperature increases, when the difference of the connector base temperature and the cooling fluid temperature increases, and decide presence of a bad contact, when the estimated contact temperature is higher than a threshold temperature.

18. The charging station of claim 17, wherein the cooling system comprises pipes in the charging cable for transporting the cooling fluid; wherein the cooling system comprises a pump for pumping cooling fluid through the charging cable; wherein the cooling system comprises a tank for storing cooling fluid.

19. The charging station of claim 18, wherein the charging station and the charging cable are adapted for charging an electric vehicle.

20. The charging station of claim 17, wherein the charging station and the charging cable are adapted for charging an electric vehicle.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The subject-matter of the invention will be explained in more detail in the following text with reference to exemplary embodiments which are illustrated in the attached drawings.

(2) FIG. 1 schematically shows a charging station according to an embodiment of the invention.

(3) FIG. 2 schematically shows a connector at an end of a charging cable for a charging station according to an embodiment of the invention.

(4) FIG. 3 shows a flow diagram with a method detecting a bad contact of a charging cable and for charging an electrical device according to an embodiment of the invention.

(5) FIG. 4 shows a diagram with temperatures over time during a first charging session.

(6) FIG. 5 shows a diagram with temperatures over time during a second charging session.

(7) FIG. 6 shows a diagram with temperatures over time during a third charging session.

(8) The reference symbols used in the drawings, and their meanings, are listed in summary form in the list of reference symbols. In principle, identical parts are provided with the same reference symbols in the figures.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

(9) FIG. 1 shows a charging station 10, which comprises a base unit 12 and a charging cable 14. The base unit 12 may be installed in a service station, in which electric vehicles may be charged.

(10) The base unit 12 may comprise an inverter 16, which may be connected to an electrical grid 18 and/or which may be adapted for converting an AC current from the electrical grid into a DC current to be supplied to the charging cable 14 and via the charging cable 14 to an electric vehicle. The inverter 16 may be controlled by a controller 20, which also may measure a charging current supplied to the charging cable 14 and/or which may control the charging based on the measured current.

(11) In the base unit 12, also components of a cooling loop or cooling system 22 may be accommodated. The cooling loop 22 comprises a tank 24, pump 26 and a heat exchanger 28 with optionally a fan 30.

(12) The tank 24 may be connected with pipes 32 returning from the charging cable and/or may be used for storing cooling fluid, which may be a liquid, such as cooling oil. In the tank 24, a temperature sensor 34 may be arranged that is adapted for measuring a temperature T.sub.f of the cooling fluid. The sensor signal from the sensor 34 may be received and evaluated by the controller 20.

(13) The pump 26 and its speed may be controlled by the controller 20, which may control the speed of the pump 26 based on the measured cooling fluid temperature. When active, the pump 26 pumps cooling fluid through the cooling loop 22 and in particular from the tank 24 to the heat exchanger 28 and from there towards the charging cable 14. When having passed through the charging cable 14 and being heated inside the charging cable 14, the cooling fluid returns into the tank 24.

(14) The fan 30 is used for cooling the heat exchanger 28 and the cooling liquid passing through it. Also the fan 30 and its speed may be controlled by the controller 20, for example based on the measured cooling fluid temperature.

(15) The heat exchanger 28 may be connected with pipes 37 conducting the cooling fluid to the charging cable 14.

(16) It is possible that the components of the cooling loop 22 are arranged in another order. For example, the pump 26 may pump the cooling fluid into the charging cable 14, than the cooling fluid may come back to the base unit 12, may passes through the heat exchanger 28 and the tank 24 before coming back to the pump 26.

(17) The base unit 12 may have a housing 35, in which the components 16, 20, 24, 26, 28, 30, 32, 34 are accommodated.

(18) The charging cable 14 may comprise a flexible cable and a plug 36, which may be connected by a person to the electric vehicle to be charged.

(19) The plug 36 comprises several connectors 38, such as three or four connectors 38, each of which is provided for connecting one phase of the charging current and/or for protective reasons with a corresponding electrical contact of the electric vehicle.

(20) For each connector 38, the charging cable 14 may have a line 40, which comprises two hoses or pipes and one or more electrical conductors for conducting a charging current and optionally measurement signals. The lines 40 of the charging cable may be accommodated in a flexible common cover 42, such as a plastics hose.

(21) A connector 38 is shown in FIG. 2 in more detail. The connector 38 comprises a connector base 44, which may be housed in the plug 36 and a contact element 46, which may protrude from the plug 36. The contact element 46 may comprise an opening 48, in which a pin of the electric vehicle may be plugged. It also is possible that the contact element 46 is formed like a pin. The contact element 46 is directly attached to the base 44. Both the contact element and the base 44 may be made of metal, such as copper.

(22) The connector base 44 comprises a cavity 50 for cooling fluid and an inlet 52 and an outlet 54 to the cavity. Both the inlet 52 and the outlet 54 are connected to a hose or pipe 56. One of the hoses 26 is may be connected to the tank 24 or the pump 26. The other one of the hoses may be connected to the heat exchanger 28. The hoses 56 and the cavity 50 may be seen as further parts of the cooling loop 22.

(23) Through one of the hoses 56 a wire and/or conductor 58 is guided, which connects the connector base 44 to the inverter 16. In such a way, current may be conducted from the inverter 16 through the respective hose 56 to the connector base 44 and therefrom to the electrical contact 46.

(24) The connector 38 furthermore comprises a temperature sensor 60, 60′, which measures a connector base temperature T.sub.b. One possibility is that the temperature sensor 60 is attached to an outside of the connector base 44. In this case, the signal wire 62 connecting the sensor 60 to the controller 20 may run outside of the base 44 and through the charging cable 14 to the base unit 12 of the charging station 10.

(25) Another possibility is that the temperature sensor 60′ is attached to an inside of the base 44, i.e. to the inside of the cavity 50. In this case, the signal wire 62 connecting the sensor 60 to the controller 20 may run through the cavity and/or through one of the hoses 56 through the charging cable 14 to the base unit 12 of the charging station 10. It may be that the signal wire runs to one of the hoses 56 and that the charging wire 58 runs through the other hose 56.

(26) During a normal operation, the resistance between the electric contact element 46 and a corresponding electric contact element of the electric vehicle (such as a pin) is very small. However, when there is dirt on the electrical contact elements, corrosion or a mechanical misalignment, the resistance may become much higher. This may be called a bad contact between the two contact elements. In the case of a bad contact, the electrical contact elements start to heat up more than during normal operation. Although the contact element 46 is cooled, the temperature of the mechanical connected components may rise to values, where damage may take place. This is prevented with the method as described above and below, which estimates a contact temperature T.sub.c of the contact element 46.

(27) FIG. 3 shows a method that may be performed by the controller 20 and that may prevent an overheating of the contact element 46.

(28) In step S10, the plug 36 is plugged into an electrical device, such as an electric vehicle, which is detected by the controller 20 and the controller 20 starts to charge the electrical device via a charging cable 14 by generating a current in the charging cable 14.

(29) In the following steps S12 to S16, the controller 20 detects whether there is a bad contact of the charging cable 14 or not.

(30) In step S12, a cooling fluid temperature T.sub.f of a cooling fluid flowing through the charging cable 14 is measured with a temperature sensor 34. The cooling fluid temperature T.sub.f may be measured with a temperature sensor 34 arranged in the tank 24.

(31) Furthermore, in step S12, a connector base temperature T.sub.b of the connector base 44 of the charging cable14 is measured with a further temperature sensor 60, 60′. The connector base temperature T.sub.b may be measured with a temperature sensor 60′ attached to an inside of the connector base 44 or with a temperature sensor 60 attached to an outside of the connector base 44.

(32) In step S14, a contact temperature T.sub.c of the electrical contact element 46 is estimated from the connector base temperature T.sub.b and the cooling fluid temperature T.sub.f. Both measurement signals from the sensors 34, 60, 60′ are received in the controller 20 and are processed there.

(33) The contact temperature T.sub.c may be determined with the following formula:
T.sub.c=T.sub.f+c.Math.(T.sub.b−T.sub.f)

(34) A difference of the connector base temperature T.sub.b and the cooling fluid temperature T.sub.f is determined, this difference is multiplied with a constant factor c and the cooling fluid temperature T.sub.f is added to the result. Also higher order terms in the difference T.sub.b−T.sub.f may be present.

(35) The estimated contact temperature T.sub.c may be determined from a function that depends on the difference of the connector base temperature T.sub.b and the cooling fluid temperature T.sub.f.

(36) In step S16, the controller 20 decides, whether there is a bad contact present or not. The controller 20 compares the contact temperature T.sub.c with a threshold temperature T.sub.t. When the contact temperature T.sub.c is higher than the threshold temperature T.sub.t, it is assumed that there is a bad contact.

(37) In step S18, when a bad contact is detected, the controller 20 interrupts the charging current. Otherwise, charging is continued.

(38) FIG. 4 to FIG. 6 show diagrams with measured and estimated contact temperatures that were measured and estimated during different charging sessions. All diagrams show the time t on the x-axis and the temperature Ton the y-axis.

(39) All charging sessions start with 2 minutes just pumping the cooling fluid around, continue with up to 10 minutes of charging at constant current of 450 A, and after that end with 5 minutes cooling down. All charging sessions were performed at 20° C. ambient temperature.

(40) FIG. 4 shows a calibration charging session, that was used to determine constant factor c for a specific design of the connector 38. In the charging session of FIG. 4, the pin, which was plugged into the contact element 46, was a steel pin, which has a higher resistance than a usual used copper pin.

(41) With the measurements of the charging session of FIG. 3, the constant factor was determined to be c=3.9 for the temperature sensor 60 at the outside and c=2.4 for the temperature sensor 60′ at the inside.

(42) The curve 64 shows the measured contact temperature, the curve T.sub.c, 60 the estimated contact temperature determined from the measurements of the sensor 60 and the curve T.sub.c, 60′ the estimated contact temperature determined from the signal of the sensor 60′. It can be seen that the curves are nearly equal.

(43) It may be beneficial to determine the constant factor c with a steel pin or contact with higher resistance as during a normal, good contact, since then, as will be shown below, the resulting formula may overpredict the estimated contact temperature, which will ensure that no calamities are missed. It will however be accurate enough so that it may prevent from having false positives. During normal operation, the method may overpredict the temperature of the contact element, but this predicted value may be far below the threshold limit, thus it is unlikely to have false positives.

(44) FIG. 5 shows a charging session with a good contact. As can be seen, the estimated contact temperatures T.sub.c based on the measurements from the sensor 60 or the sensor 60′ and the corresponding constant factor c as determined in the charging session shown in FIG. 4, are higher than the directly measured contact temperature 64. The method seems to overpredict, but not by more than about 10° C., and only when there is no problem to be detected. It also can be seen that the speed of detection also does not suffer due to the fact that the sensor 60 is further away from the contact element as the sensor 60′.

(45) FIG. 6 shows a charging session with a bad contact. The estimated contact temperatures T.sub.c based on the measurements from the sensor 60 or the sensor 60′ raise a bit higher as the directly measured contact temperature 64. When the threshold temperature T.sub.t is reached, the charging is stopped and the contact element 46 cools down due to the continuing cooling liquid flow.

(46) While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art and practising the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. A single processor or controller or other unit may fulfil the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

LIST OF REFERENCE SYMBOLS

(47) 10 charging station 12 base unit 14 charging cable 16 inverter 18 electrical grid 20 controller 22 cooling loop/cooling system 24 tank 26 pump 28 heat exchanger 30 fan 32 pipes 34 temperature sensor 35 housing 36 plug 37 pipes 38 connector 40 line 42 cover 44 connector base 46 electrical contact element 48 opening 50 cavity 52 inlet 54 outlet 56 hose 58 charging wire 60 temperature sensor 60′ temperature sensor 62 signal wire 64 measure contact temperature T.sub.f cooling fluid temperature T.sub.b connector base temperature T.sub.c contact temperature T.sub.t threshold temperature