FR3092434A1 - Power relay diagnostic and take-off process - Google Patents

Abstract

The invention relates to a method for diagnosing and taking off a power relay capable of electrically connecting a power source to an electric load, comprising steps of: - checking (E2) of the state of said power relay after a opening control of said power relay, during which said power relay is diagnosed stuck, - application (E4) of a predefined number (N) of opening and closing commands of said previously diagnosed stuck power relay. Figure for the abstract: Figure 2

Description

Method for diagnosing and taking off a power relay

The present invention relates generally to the field of electrical engineering and relates more specifically to a method for diagnosing and taking off a power relay.

When charging the traction battery of an electric or hybrid vehicle with direct current, power relays are required between the charging station and the traction battery, to secure the start and end of charging. However, when the relays are closed, transient current peaks can reach values of 460A (amperes). This sometimes causes the relays to be welded together. Likewise when the relays open, electric arcs can cause the relays to stick. A temporary current overload during charging can also cause the relays to stick.

When such relay sticking occurs, it is usually detected by the charging system, and safety mechanisms protect the traction battery. However, a new charge of the vehicle is then no longer possible before it goes to after-sales, where a technician will in most cases be able to take off the faulty relay(s) by mechanical action, for example by tapping on it with a screwdriver. However, such a maintenance procedure is costly and very restrictive for the user of the vehicle.

One of the aims of the invention is to remedy at least some of the drawbacks of the prior art by providing a method for diagnosing and taking off a power relay, which does not require the intervention of a technician after -sale in most cases.

To this end, the invention proposes a method for diagnosing and taking off a power relay capable of electrically connecting a power source to an electrical load, comprising steps of:

- verification of the state of said power relay after an opening command of said power relay, during which said power relay is diagnosed as stuck,

- application of a predefined number of opening and closing commands of said power relay previously diagnosed as stuck.

Thanks to the invention, the stuck diagnosed relay is automatically detached when the sticking by welding is light, which avoids the intervention of an after-sales technician. In fact, the inventors have observed that a few successive opening and closing commands of a stuck relay make it possible to locally stress the welding of the incriminated contact, and therefore to detach the relay in most cases. This process works when the sticking of the relay is not very strong, i.e. when the relay can also be peeled off by simply tapping on it with a screwdriver.

According to an advantageous characteristic of the system according to the invention, said application step is followed by a step for determining the state of said power relay, during which said power relay is diagnosed as functional or permanently stuck. This step makes it possible in particular to send an alert to the user, so that he can go to after-sales to change a relay that has been diagnosed as permanently stuck.

According to another advantageous characteristic of the invention, said method comprises a step of comparing a number of times when said method has been previously used to unstick said relay with a threshold, and when said number of times is greater than or equal to said threshold , said applying step is not performed for said relay, and said relay is diagnosed as permanently stuck during said determining step. So when the same relay has been detached via said process said number of times, the user is forced to change the relay by going to after-sales, because the relay concerned is certainly in poor condition and the cause of a future failure.

Preferably, said predefined number is greater than 9 opening and closing commands. The inventors have in fact found that in the case of a light sticking of a relay diagnosed as stuck, ten opening and closing commands were enough to unstick it in 99% of cases.

The invention also relates to a system for charging a traction battery of an electric or hybrid vehicle, comprising

- a traction battery,

- a charging socket,

- a connection box capable of electrically connecting the terminals of said traction battery to the terminals of said charging socket, said connection box comprising two power relays each capable of connecting a different terminal of said traction battery to a corresponding terminal of said charging socket,

- a computer connected to means for controlling said relays, and to means for detecting or measuring the voltage at the terminals of said charging socket or at the terminals of at least one of said relays, said charging system being characterized in that that said computer comprises means for implementing the method for diagnosing and taking off a power relay according to the invention.

The charging system according to the invention has advantages similar to those of the diagnostic and take-off method according to the invention.

Other characteristics and advantages will appear on reading a preferred embodiment described with reference to the figures in which:

represents a charging system according to the invention, in this preferred embodiment,

represents a method for diagnosing and taking off a power relay according to the invention, in this preferred embodiment.

According to a preferred embodiment of the invention represented in FIG. 1 , a charging system according to the invention comprises a traction battery BATT, a charging socket CV, a connection box BOX and a computer CAL. The charging system is on board an electric or hybrid vehicle and comprises software means for implementing the method according to the invention.

The BATT traction battery is connected by its two electrical terminals to the corresponding terminals of the CV charging socket integrated into the vehicle, via the BOX connection box which includes two power relays REL1 and REL2. The power relay REL1 connects the positive terminal of the battery BATT to one terminal of the charging socket CV, and the power relay REL2 connects the negative terminal of the battery BATT to the other terminal of the charging socket CV. The relays REL1 and REL2 are, in this embodiment, relays supporting a voltage of 400V (volts) and a current of 200A.

It should be noted that in this application, the term “traction battery” refers to a battery of power accumulators large enough to ensure the traction or propulsion of an electric or hybrid vehicle. The voltage Vbatt of the BATT traction battery thus reaches 400V when fully charged.

In this embodiment of the invention, the CV charging socket is used to charge the traction battery BATT with high power direct current. To do this, a BC charging station is connected to the vehicle, supplying a power of the order of 50 kW in direct current to the vehicle, via a DC charging cord comprising a “Combo” type CCo connector. The CCo connector is plugged into the CV charging socket, which initiates a DC charge of the BATT battery.

This load is supervised on the vehicle side by the computer CAL, which comprises means for controlling the relays REL1 and REL2, and means for receiving measurements or results of voltage detection carried out by a voltage detector V connected to the terminals of the CV charging socket upstream of relays REL1 and REL2. This detector returns an all or nothing state following a threshold of 60V. If the voltage at the terminals of the charging socket CV is greater than 60V, then the detector sends the "voltage present" status back to the computer CAL, otherwise the "no voltage" status. The computer CAL also comprises means of communication with a battery computer, integrated into the battery BATT, and battery relay control means located downstream of the connection unit BOX. The computer CAL also optionally comprises means of communication with the charging terminal BC.

With reference to FIG. 2 , a power relay diagnostic and take-off method according to the invention is represented in the form of an algorithm comprising steps E1 to E5. It is implemented, in this embodiment of the invention, in the computer CAL, just after the end of a fast charge by direct current of the traction battery BATT. The relays at the charging terminal BC are therefore open.

Step E1 is the opening control of the relays REL1 and REL2 by the computer CAL.

The next step E2 is a step for checking the state of the power relays REL1 and REL2 by the computer CAL. For this, the computer CAL dynamically receives the state or the measurement Vmes of the voltage determined by the voltage detector V, at the terminals of the charging socket CV upstream of the relays REL1 and REL2.

In this step E2, if the state or the measurement Vmes returned by the voltage detector V indicate the presence of voltage, then the two relays REL1 and REL2 are stuck. They are therefore diagnosed as stuck by the computer. If, on the contrary, the state or the measurement Vmes returned by the voltage detector V indicate the absence of voltage, then in this step E2 the computer CAL commands the closing of the relay REL1.

If after this command to close relay REL1, the state or the measurement Vmes reported by the voltage detector V indicate the presence of voltage, then the computer CAL diagnoses relay REL2 as being stuck and relay REL1 as being operational. If, on the contrary, the state or the measurement Vmes reported by the voltage detector V indicate the absence of voltage, then, still in this step E2, the computer CAL commands the opening of the relay REL1 and the closing of the relay REL2.

If, after this command to open relay REL1 and to close relay REL2, the state or measurement Vmes returned by voltage detector V indicate the presence of voltage, then computer CAL diagnoses relay REL1 as being stuck and the relay REL2 as functional. If, on the contrary, the state or the measurement Vmes returned by the voltage detector V indicate the absence of voltage, then, still in this step E2, the computer CAL diagnoses the two relays REL1 and REL2 as being functional.

It is assumed, in this example of use of the invention, that relay REL1 is diagnosed as stuck at the end of step E2, relay REL2 being diagnosed as functional.

The next step E3 is the comparison, by the computer CAL, between the number of times Comp where the method has been used to take off the relay REL1, and a threshold. If this number of times Comp is less than this threshold, then the next step is step E4, in which the computer tries to take off relay REL1, otherwise the next step is step E5, in which the computer diagnoses relay REL1 as permanently stuck. This threshold is determined experimentally, it corresponds to a number of take-offs of the same relay by the process after which a new take-off attempt would make the contact of this relay too degraded. In particular, the contact resistance of the relay after takeoff using the method must remain below the value guaranteed by the manufacturer, which is 0.75mΩ (micro Ohms) in this embodiment of the invention. In this embodiment of the invention, this threshold is set at three. In a more secure variant it is for example fixed to two or in a less secure variant it is for example fixed to four. It is further assumed, in this example of use of the invention, that the relay has not been unstuck more than twice, and the next step is therefore step E4.

Step E4 is the application of a predefined number N of opening and closing commands for relay REL1. This number N is equal to 10 in this embodiment of the invention. As a variant, it may be equal to a number greater than 5. It is set experimentally and must correspond to a number of switchings after which the relay diagnosed as stuck has a good chance of being unstuck. The opening and closing commands are applied successively alternately. For example in this step E4, the computer CAL begins with a closing command of the relay REL1, then with an opening command, and so on until ten closing and opening commands have been carried out. The step following step E4 is step E5.

Step E5 is the determination of the state of relay REL1. For this, the computer CAL receives the state or the voltage measurement Vmes across the terminals of the CV socket determined by the voltage detector V, the relay REL1 being controlled open and the relay REL2 being controlled closed.

If the state or the measurement Vmes returned by the voltage detector V indicate the presence of voltage, then the computer CAL diagnoses the relay REL1 as permanently stuck. It then sends an alert to a device to alert the user of the need to go to after-sales to have the relay replaced. This feedback can be done via a man-machine interface such as a screen on the dashboard. The device is for example a display device on the dashboard, or a communication device able to send an audible or visual message to the user, for example on his mobile phone. As a variant, the alert is raised directly with an after-sales service, for example if the vehicle is an autonomous vehicle.

If, on the contrary, the state or the voltage measurement Vmes returned by the voltage detector V indicate the absence of voltage in this step E5, then the computer CAL diagnoses the relay REL1 as being operational. In this case, it increments the Comp value by the number of times the method according to the invention has been used to take it off.

Although in this embodiment of the invention, the diagnostic and take-off method is implemented in the computer CAL, other embodiments are possible, in which for example the diagnostic and take-off method is implemented works in a distributed way in several computers. Moreover, the order of the steps and their execution as described in this preferred embodiment are not fixed. Indeed, as a variant, step E3 is not carried out, the process being able in this variant to be repeated indefinitely for the same relay. In another variant, step E3 includes a step of incrementing the counter Comp, which is then not performed in step E5. During step E2, the state of relay REL1 is for example, as a variant, checked before that of relay REL2. Moreover, the method can be used not only just after the end of a battery charge, but also after any other command to open the relay to be diagnosed. The voltage measurements or detections can also be made in places other than at the terminals of the charging socket. The use of the method is also not limited to the relays of a direct current charging system of an electric vehicle.

Claims (1)

System for charging a traction battery (BATT) of an electric or hybrid vehicle, comprising
- a traction battery (BATT),
- a charging socket (CV),
- a connection box (BOX) capable of electrically connecting the terminals of said traction battery (BATT) to the terminals of said charging socket (CV), said connection box (BOX) comprising two power relays (REL1, REL2) each capable of connecting a different terminal of said traction battery (BATT) to a corresponding terminal of said charging socket (CV),
- a computer (CAL) connected to means for controlling said relays (REL1, REL2), and to means for detecting or measuring (V) the voltage at the terminals of said charging socket (CV) or at the terminals of at least one of said relays (REL1, REL2),
said charging system being characterized in that said computer (CAL) comprises means for:
- check the state of one of said power relays (REL1, REL2) after an opening command of said power relay (REL1), during which said power relay (REL1) is diagnosed stuck,
- apply a predefined number (N) of opening and closing commands of said power relay (REL1) previously diagnosed as stuck.