Patent Description:
A transistor such as a MOSFET may be used as a switch to power on or off a load from a power source.

The MOSFETs are likely to have failures in use. These failures are often attributed to over voltage, over current, over temperature etc.. In operation, the temperature of the transistor may increase. When a critical temperature is reached, the transistor should be turned off to avoid any damage.

To protect the MOSFET against overheating, it is known to use an intelligent MOSFET including a temperature protection circuitry normally present on a printed circuit board on which the MOSFET is mounted. In an intelligent MOSFET with temperature protection, a temperature sensor is sitting on a die or semiconductor part of the MOSFET. This temperature sensor can measure very fast the temperature. If the temperature sensor is alternatively mounted on the PCB, a fast temperature increase cannot be detected.

However, it is also desired to monitor the reliability of standard MOSFETs and protect them against overheating by quickly detecting any temperature increase. More generally, it is desired to monitor the reliability of a system including a plurality of electrical components. Examples of relevant disclosures in the field include: <CIT> and <CIT>.

The present disclosure concerns a method of monitoring reliability of a system according to claim <NUM>.

The present disclosure concerns a method of monitoring reliability of one or more electrical components ECn of a system <NUM>, with n=<NUM>, <NUM>,.

A particular embodiment of the system <NUM> is illustrated in <FIG> and includes a transistor EC1 having the function of switching on or off a load <NUM> from a power source <NUM>, and an interface connecting the transistor EC<NUM> to the load <NUM>. The transistor EC1 may be a FET, for example a MOSFET. The interface may include an electrical shunt EC2, for example a copper shunt, and an electrical cable EC3. The transistor EC1 may be mounted on a printed circuit board, the copper shunt EC2 may be a copper track of the PCB, <NUM>. The electrical cable EC3 may be external to the printed circuit board <NUM> and connect the shunt EC2 and the load <NUM>.

In operation, the temperature of the electrical components ECn of the system <NUM> may vary over time, for example due to power loss. The present method allows to determine a temperature information of the electrical components ECn of the system <NUM> and monitor the reliability of these electrical components ECn using the determined temperature information. For each electrical component ECn of the system <NUM>, the temperature information is determined by processing input data, that includes electrical characteristics of the electrical component ECn, using a stored thermal model representing heat transfer for the electrical component ECn. The electrical characteristics of the electrical component ECn used as input data to determine the temperature information of said electrical component ECn can comprise a voltage across the electrical component ECn, a current flowing through the electrical component ECn, and/or an electrical resistance value of the electrical component ECn.

The thermal model related to an electrical component ECn having an electrical power consumption Pn represents heat transfer for said electrical component ECn. The heat transfer refers to the heat flow between two given points including a first point of the electrical component ECn, where the temperature is to be estimated, and a second point, where a temperature referred as a reference or ambient temperature Ta is known, for example by measurement. The second point is for example a point of the printed circuit board <NUM> on which a temperature sensor <NUM> is mounted. In another example, the ambient temperature Ta may be the air temperature around the cable EC3.

In an embodiment, the thermal model is a Cauer thermal model, for example a first order Cauer thermal model having a simple structure as represented by an equivalent circuit in <FIG>, including a thermal capacitance Cthn and a thermal resistance Rthn of the electrical component ECn, both connected in parallel between a power supply point, provided with the electrical power Pn, and the ground. The thermal resistance Rthn is a quantification of how difficult it is for heat to be conducted between the two given points. The thermal capacitance Cthn is a quantification of how quickly heat is conducted between the two given points. The thermal modal could be a Cauer model with higher order. In that case, the Cauer model just needs additional calculations after first order is determined.

The electrical power Pn consumed or dissipated by the electrical component ECn can be determined from measurements of a voltage Vn across the electrical component and/or a current In flowing through the electrical component ECn. As well-known by the skilled person, the electrical power Pn dissipated by the electrical component ECn can be expressed by any of the following equations: <MAT> <MAT> <MAT>.

In an embodiment, the measurements of electrical characteristic(s) are sampled or performed at successive times ti, with i=<NUM>, <NUM>, <NUM>,. , every time step dt. For example, the time step dt may be of the order of a few hundred microseconds. A temperature information of the electrical component ECn such as a temperature variation or difference relative to the reference or ambient temperature Ta can be determined using the thermal model. The temperature Ta may be measured by a sensor near the electrical component ECn, for example the temperature sensor <NUM> mounted on the printed circuit board <NUM>. In case the thermal model is the first order Cauer thermal model represented in <FIG>, an incremental temperature variation, or temperature increment, of the electrical component ECn relative to the ambient temperature Ta over the time set dt can be expressed by the following equation: <MAT> where.

Furthermore, a temperature difference of the electrical component ECn relative to the ambient temperature Ta can be estimated by accumulating the successive values of incremental temperature variation and thus calculating a cumulated temperature variation or difference, expressed by the following equation: <MAT> where.

Any other type of thermal modal could be used for modelling heat transfer through the electrical component.

Due to the temperature variation over time of the electrical components of the system <NUM>, some electrical characteristics of the system <NUM> may also vary over time. For example, the electrical resistance value of an electrical component ECn may vary over time due to a temperature variation of this electrical component ECn. Consequently, an electrical current flowing through this electrical component ECn may vary over time. The present method allows to determine and update over time the values of electrical characteristics of the system <NUM> that are temperature dependent, as explained later in more detail.

The method of monitoring reliability of the system <NUM> may be carried out by a monitoring device <NUM>. In an embodiment, the monitoring device <NUM> is mounted on the printed circuit board <NUM>. The monitoring device <NUM> includes an input interface <NUM>, a measurement module <NUM>, a memory system <NUM>, a processing module <NUM>, and a diagnostic module <NUM>. The monitoring device <NUM> may also include a controlling module <NUM> configured to control the transistor EC1.

The monitoring device <NUM> may be implemented with hardware and software. For example, the monitoring device <NUM> may include a processor, not represented in <FIG>, and software or computer programs or applications configured to run on the processor.

The input interface <NUM> is a user interface configured to exchange information between the system <NUM> and a user, and to switch on and off the transistor EC1.

The measurement module <NUM> is configured to measure voltage across the transistor EC1 and across the shunt EC2 and acquire the temperature measured by the temperature sensor <NUM>. The measurement module <NUM> may include one or more amplifier(s) to amplify low measurement values to higher values, and one or more analog to digital converter(s) to convert analog measured values to digital data and transmit the digital data to the memory system <NUM>.

In an embodiment, the memory system <NUM> may include:.

The processing module <NUM> is configured to receive or acquire input data including electrical characteristics of the electrical components ECn of the system <NUM>. The processing module <NUM> is further configured to process said input data using stored thermal models representing heat transfer for the electrical components ECn respectively, to determine a temperature information of the electrical components ECn. The processing module may further be configured to determine temperature-dependent electrical characteristics of the electrical components ECn, such as a resistance and/or a current, using the determined temperature information. The processing module <NUM> may include a processor.

The diagnostic module <NUM> is configured to monitor the reliability of the system <NUM> using the determined temperature information of the electrical components ECn and/or the electrical characteristics of the electrical components ECn determined based on the determined temperature information, as will be described in more detail in the description of the method.

An embodiment of the method of monitoring reliability of one or more electrical components ECn of the system <NUM> is illustrated in <FIG> and will now be described. The method is performed by the monitoring device <NUM>.

Let's consider the electrical component ECn of the system <NUM>. The method may include an iterative process performed at successive times t<NUM>, t<NUM>, t<NUM>,. , or sampling times, for the electrical component ECn. At each iteration of time ti with i≥<NUM>, the iterative process includes:.

The steps S1 and S2 can be performed by the processing module <NUM>.

In the first step S1, the processing module <NUM> receives or acquires input data.

The input data includes electrical characteristics of the electrical component ECn.

The electrical characteristics of the electrical component ECn may include a voltage Vn(ti) across the electrical component ECn, and/or a current In(ti) flowing through the electrical component ECn. The voltage Vn(ti) across the electrical component ECn or the current In(ti) flowing through the electrical component ECn may be obtained by or derived from measurement performed at time ti.

In an embodiment, the voltage Vn(ti), or current In(ti), of the electrical component ECn is measured by the measurement module <NUM> and transmitted to the monitoring device <NUM>.

In another embodiment, the current In(ti) flowing through the electrical component ECn is estimated by first performing the iterative process including the steps S1 and S2 for another electrical component ECn' of the system <NUM>, based on a temperature information of ECn'. For example, the current flowing through the transistor EC1 and the cable EC3 can be first estimated through the shunt EC2, based on a temperature information of the shunt EC2 determined by performing the iterative process S1-S2 for the shunt EC2, as described later in more detail.

The input data may further include a value of an electrical resistance Rn(ti) of the electrical component ECn. In case this electrical resistance is temperature dependent, the value of the electrical resistance Rn(ti) used as input data at each iteration of the process can correspond to the value of the electrical resistance Rn(ti-<NUM>) determined at the previous iteration of the process, as explained later in more detail.

The input data may further include an ambient temperature Ta near the electrical component ECn. This ambient temperature Ta may be measured at each time ti by a sensor near the electrical component ECn, such as the temperature sensor <NUM> mounted on the printed circuit board <NUM>, and transmitted to the monitoring device <NUM> in the step S1, via the measurement module <NUM>. In another embodiment, if there is no sensor to measure the ambient temperature Ta, this ambient temperature Ta may be set to a maximal ambient temperature that can be expected, prestored in the nonvolatile memory of the memory system <NUM>. In that case, the processing module <NUM> retrieves from memory the ambient temperature Ta in the step S1.

The input data may further include prestored constant values of thermal and/or electrical parameters of the electrical component ECn, such as the thermal resistance Rth and thermal capacitance Cth of the material responsible for heat transfer for the electrical component ECn, a temperature coefficient αn of the electrical component ECn, and a reference electrical resistance value of the electrical component ECn at room temperature, for example <NUM>. The temperature coefficient αn of the electrical component ECn represents a temperature dependency of the electrical resistance of the electrical component ECn. These constant values may be prestored in the non-volatile memory of the memory system <NUM> and retrieved from memory by the processing module <NUM> in the step S1, when needed.

In a step S2, the processing module <NUM> processes the input data using the stored thermal model representing heat transfer for the electrical component ECn to determine a temperature information of the electrical component ECn. The temperature information may include an estimated variation or difference of temperature between a temperature of the electrical component ECn and the ambient temperature Ta, and/or an estimated temperature of the electrical component ECn. The processing step S2 may comprise at least part of the steps S20 to S27 described below.

The step S2 may comprise a step S20 of evaluating the electrical power Pn(ti) dissipated by the electrical component ECn during the current time step dt, by processing the input data acquired at the step S1, based on one of the equations (<NUM>) to (<NUM>).

Then, in a step S21, the processing module <NUM> may compute the value ΔTn,i(ti) of incremental temperature variation of the electrical component ECn relative to the ambient temperature Ta over the current time step dt, between times ti and ti+<NUM>, based on the thermal model, for example with the equation (<NUM>).

The step S2 may further comprise a step S22 of determining the value dTn,i of cumulated or global temperature variation of the electrical component ECn relative to the ambient temperature Ta between the initial time t<NUM> and the current time ti, based on the equation (<NUM>). The iterative step S22 allows to accumulate successive values of incremental temperature variation of the electrical component ECn relative to the ambient temperature Ta.

The step S2 may also comprise a step S23 of estimating the temperature of the electrical component ECn based on the ambient temperature Ta and the temperature difference dTn,i based on the following equation: <MAT> where.

In case the electrical component ECn has an electrical resistance that is temperature dependent, the processing step S2 further includes a step S24 of estimating an electrical resistance value of the electrical component ECn at time ti, based on a predetermined reference electrical resistance value Rref,n of the electrical component ECn, a predetermined temperature coefficient αn of the electrical component ECn, the ambient temperature Ta and the value dTn,i of temperature difference of the electrical component ECn determined at the step S22. The reference electrical resistance value Rref,n may be the electrical resistance value of the electrical component ECn at room temperature, for example <NUM>. The temperature coefficient αn is a predetermined constant parameter of the electrical component ECn. The parameters Rref,n and αn are pre-stored in the memory system <NUM>. In the step S24, the electrical resistance value of the electrical component ECn at time ti may be evaluated based on the following equation: <MAT> where.

The electrical resistance value Rn(ti) of the electrical component ECn determined at the iteration of time ti can be used at the next iteration of time ti+<NUM> to estimate the power dissipated by the component ECn based on the equation (<NUM>) or (<NUM>).

In an embodiment, the processing step S2 may further comprise a step S25 of estimating a value of the electrical current In(ti) flowing through the electrical component ECn, for example based on the voltage value Vn(ti) across the electrical component ECn received in the step S1 and the electrical resistance value Rn(ti) of the electrical component ECn estimated at the step S24, based on the equation: <MAT>.

In an optional step S27, the current flowing through the electrical component ECn can be averaged over a time window or cycle including N iterations of the process, and having a length N*dt (in other words, over N successive time steps dt). For example, an average value of the current In(ti) may be determined periodically or cyclically, every N iterations of the process, here at time tN, t2N, t3N,. , each cycle including N consecutive iterations of the step S25. During each cycle, the current In(ti) can be summed up until the N iterations of the step S25 of the cycle have been executed, in other words over N successive iterations. At the end of each cycle of N consecutive iterations, in a step S26, the sum of the N successive current values estimated in the step S25 over said N iterations is divided by N to determine the averaged current <MAT>. The average current at time ti for i=N, 2N, 3N,. can be expressed by the following equation: <MAT>.

In this way, the average current is updated every N measurements, or every N iterations of the process.

Averaging allows to reduce noise. The current value may be more accurate with averaging.

If N is a power of <NUM>, namely N=<NUM>q, dividing the sum of N successive current values can be easily done by shifting q bits in a bit register storing the sum in binary form.

The estimated value of the electrical current In or <MAT> flowing through the electrical component ECn can be used as input data in the steps S1 and S2 for another electrical component having the same electrical current flowing through it.

The output data of the processing step S2 performed for the electrical component ECn may include at least part of the following values :.

The above list of output data is not exhaustive. Other values of thermal or electrical characteristics of the electrical component ECn could be derived from one of the above listed output values and provided at the output of the processing step S2.

The output of the processing step S2 at time ti may be used as input data for the processing step S2 performed at time ti+<NUM>.

The method further includes a step S3 of monitoring the reliability of the electrical component ECn based on the output data of the processing step S2. The step S3 can be performed by the diagnostic module <NUM>. One or more pieces of the output data of the processing step S2 may be compared to threshold values prestored for example in the non-volatile memory of the memory system <NUM> to detect an abnormality in the system <NUM>. The detected abnormalities may include for example:.

In case an abnormality in the system <NUM> is detected in the step S3, a step of turning off the system <NUM>, or at least one electrical component of the system <NUM>, and/or triggering an alert may be performed, in a step S4.

The iterative process including the steps S1 and S2 is performed at successive times ti, every time step dt, and for each electrical component ECn of the system <NUM> that is monitored.

As an illustrative example, the process performed for each of the electrical components of the system in <FIG>, including the transistor EC1, the shunt EC2, and the cable EC3, will now be described. It includes, for each component EC1, EC2 or EC3, the steps of the method previously described and illustrated in <FIG>. The method steps will be denoted with the suffix _EC1, or _EC2, or _EC3, corresponding to the component for which the method is implemented.

In an embodiment, the process is first performed for the shunt EC2 to estimate the current flowing through the transistor EC1, the shunt EC2 and the cable EC3. The estimated current is then used as an input data in the process performed for the transistor EC1 and the cable EC3.

The shunt EC2 is mounted on the printed circuit board <NUM>. It is a kind of track, for example made of copper. The shunt EC2 is a device used to measure an electrical current I<NUM> that flows through the shunt EC2. <FIG> schematically illustrates a model for the shunt EC2 including a copper outer layer L1, where the temperature is detected with the sensor <NUM>, a copper inner layer L3, through which a current I<NUM> flows, and an insulation layer L2, called "pre-preg", interposed between the outer layer L1 and the inner layer L3.

The iterative process includes the following steps S1_EC2 and S2_EC2 executed for the shunt EC2.

In the acquisition step S1_EC2, at each iteration of time ti, the processing module <NUM> acquires the following values:.

In the processing step S2_EC2, at each time ti, the processing module <NUM> processes the input data using the thermal model. The processing includes the steps S20_EC2 to S27_EC2 described below.

In the step S20_EC2, the processing module <NUM> estimates an electrical power dissipated by the shunt EC2 based on the measured value of the voltage V<NUM>(ti) across the shunt EC2 and the value of the electrical resistance of the shunt EC2 estimated at the previous iteration of time ti-<NUM>, using the following equation: <MAT>.

At an initial time t<NUM>, the value of the electrical resistance of the shunt EC2 may be set to the reference resistance value Rref,<NUM> of the shunt EC2 at room temperature.

In the step S21_EC2, the processing module <NUM> estimates a value ΔT<NUM>,i of incremental temperature variation of the shunt EC2 relative to the ambient temperature Ta over the current time step dt, between times ti and ti+<NUM>, based on the thermal model, using the following equation derived from the equation (<NUM>): <MAT>.

In the step S22_EC2, the processing module <NUM> determines a value dT<NUM>,i of temperature difference of the shunt EC2 relative to the ambient temperature Ta. For that purpose, the processing module <NUM> computes the cumulated temperature variation between the initial time t<NUM> and the current time ti, by adding ΔT<NUM>,i to the value of temperature difference dT<NUM>,i-<NUM> of the shunt EC2 relative to the ambient temperature Ta determined at the previous iteration of time ti-<NUM>, based on the equation (<NUM>).

In the step S23_EC2, the processing module <NUM> may estimate the temperature of the shunt EC2 based on the ambient temperature Ta(ti), that is the temperature on the printed circuit board <NUM> measured by the sensor <NUM>, and the value of temperature difference dT<NUM>,i based on the following equation derived from the equation (<NUM>): <MAT>.

In the step S24_EC2, the processing module <NUM> estimates the value of the electrical resistance of the shunt EC2 at time ti, based on the following equation: <MAT> α<NUM> = <NUM> if the shunt resistance is not temperature dependent.

In the step S25_EC2, the processing module <NUM> estimates the electrical current I<NUM>(ti) flowing through the shunt EC2 based on the voltage value V<NUM>(ti) measured across the shunt EC2 and the electrical resistance value R<NUM>(ti) of the shunt EC2 estimated at the step S24, based on the equation: <MAT>.

Optionally, in the step S27_EC2, the current flowing through the shunt EC2 may be averaged every N iterations of the process. For that purpose, the current I<NUM>(ti) can be summed up until the N iterations of the step S25_EC2 have been executed during each cycle of N consecutive iterations. At the end of each cycle of N iterations, at i=N, 2N, 3N,. , the sum of the N successive current values I<NUM>(ti) is then divided by N to determine the average current <MAT>. The average current at time tN, t2N, t3N,. , can be expressed by the following equation: <MAT>.

Optionally, a step S3 of monitoring the output of the processing step S2 may be performed for the shunt EC2. For example, the diagnostic module <NUM> may compare the temperature difference dT<NUM>,i, and/or the temperature T<NUM>(ti), and/or the current I<NUM>(ti), and/or the averaged current <MAT>, to respective thresholds, so as to detect an abnormality in the system <NUM>. When an abnormality is detected, the transistor EC1 may be turned off and/or an alert may be triggered.

In an embodiment, the diagnostic module <NUM> may include an analog comparator <NUM> configured to quickly detect that the current I<NUM> flowing through the shunt EC2 exceeds a maximal value of current, prestored in the non-volatile memory of the memory system <NUM>, and denoted as Idsmax. The maximal current Idsmax may be the maximal drain-source current allowed through the transistor EC1. For example, the analog comparator may be a voltage comparator configured to receive in input a maximal analog voltage V<NUM>max(ti) through the shunt EC2 and the measured voltage through the shunt EC2, at each time ti. The maximal analog voltage V<NUM>max(ti) can be determined by computing V<NUM>max(ti) = Idsmax * R<NUM>(ti) by the processing module <NUM> and converting the computed digital value into an analog value by a digital to analog converter DAC <NUM>. The output of the comparator <NUM> is connected to the controlling module <NUM>. In case the current I<NUM> exceeds the maximal value of current Idsmax, the comparator <NUM> transmits to the controlling module <NUM> a signal indicative of a peak of current that is too high. In an embodiment, upon receiving this signal, the controlling module <NUM> turns off the transistor EC1.

The transistor EC1 is mounted on the printed circuit board <NUM>. The transistor EC1 is a device used to switch on or off the load <NUM>. <FIG> schematically illustrates a model for the transistor EC1 including: a first layer D representing a die or semiconductor part of the transistor EC1, that receives the electrical power P<NUM>, a second layer M representing a metal material conducting heat, a third layer PCB representing the printed circuit board <NUM>, where the ambient temperature is detected with the sensor <NUM>. For example, the transistor EC1 is a MOSFET. The MOSFET has three terminals: drain, gate and source. The electrical power P<NUM> supplied to the MOSFET can be expressed by the following equation: <MAT> where.

In the acquisition step S1_EC1, at each iteration of time ti, the processing module <NUM> acquires the following values:.

Since the transistor EC1 and the shunt EC2 are connected in series, the current I<NUM> through the shunt EC2 corresponds to the drain source current Ids(ti) flowing through the transistor EC1. In other words: <MAT> <MAT>.

In the processing step S2_EC1, at each time ti, the processing module <NUM> processes the input data using the thermal model. The processing includes the steps S20_EC1 to S27_EC1 described below.

In the step S20_EC1, the processing module <NUM> estimates an electrical power P<NUM>(ti) dissipated by the transistor EC1 based on the measured value of the drain source voltage Vds(ti) across the transistor EC1 and the value of the current I<NUM>(ti) or <MAT> through the shunt EC2, corresponding to the drain source current Ids estimated at the iteration of time ti, using the following equation: <MAT>.

In the step S21_EC1, the processing module <NUM> estimates a value ΔT<NUM>,i of incremental temperature variation of the transistor EC1 relative to the ambient temperature Ta over the current time step dt, between times ti and ti+<NUM>, based on the thermal model, using the following equation derived from the equation (<NUM>): <MAT>.

In the step S22_EC1, the processing module <NUM> may estimate a value dT<NUM>,i of temperature difference of the transistor EC1 relative to the ambient temperature Ta. For that purpose, the processing module <NUM> may compute the cumulated temperature variation between the initial time t<NUM> and the current time ti, by adding ΔT<NUM>,i to the value of temperature difference dT<NUM>,i-<NUM> of the transistor EC1 relative to the ambient temperature Ta determined at the previous iteration of time ti-<NUM>, based on the equation (<NUM>).

In the step S23_EC1, the processing module <NUM> may estimate the temperature of the transistor EC1 based on the ambient temperature Ta(ti) measured by the sensor <NUM> and the value of temperature difference dT<NUM>,i with the following equation derived from the equation (<NUM>): <MAT>.

In the step S24_EC1, the processing module <NUM> estimates the value of the electrical drain source resistance Rds of the transistor EC1 at time ti, based on the following equation: <MAT>.

At each iteration of time ti, a monitoring step S3_EC1 may then be performed to monitor the reliability of the transistor EC1 based on the output of the processing step S2. For example, the diagnostic module <NUM> may perform at least one of the following monitoring actions :.

If the temperature T<NUM>(ti) of the transistor EC1 is above T<NUM>max, or the temperature difference dT<NUM>,i is above dT<NUM>max, or the transistor resistance value Rds(ti) is above Rdsmax, the diagnostic module <NUM> generates control signal for turning off the transistor EC1 and/or generating an alert signal.

With the present disclosure, the temperature of the transistor EC1 can be monitored, and if it is too high, the transistor EC1 may be turned off. The transient temperature, that is the difference or variation between the die temperature of the transistor EC1 and the temperature measured on the printed circuit board PCB <NUM>, can also be monitored. If the transient temperature is too high, the transistor EC1 may also be turned off. Indeed, an important transient temperature is likely to produce stress on the transistor EC1. The drain source resistance Rds of the transistor EC1 can also be monitored, when the transistor EC1 is fully conducting. If the resistance Rds is too high, the transistor EC1 may be turned off too.

Alternatively, the diagnostic module <NUM> generates an alert signal warning that the transistor EC1 may have an abnormality and may not be reliable.

The cable EC3 connects the shunt EC2 on the printed circuit board <NUM> and the load <NUM> that is external to the printed circuit board <NUM>. The cable EC3 is external to the printed circuit board <NUM>. <FIG> schematically illustrates an example of model for the cable EC3: it includes a core cable CC in copper surrounded by an insulation layer or sleeve S. In operation, the core cable CC is provided with a certain electrical power and, due to power loss, heat is transferred from the core cable CC to the external surface of the cable EC2 where the temperature is equal to an ambient temperature Ta in the external environment surrounding the cable EC3.

In an embodiment, the ambient temperature Ta around the cable EC3 is not measured. In the process of monitoring the cable EC3, it is assumed that the ambient temperature Ta is equal to a maximal ambience temperature Ta_max that is expected in the environment surrounding the cable EC3. For example, let's consider that the system <NUM> is implemented in a vehicle. A maximal temperature in the vehicle can be predetermined. In an illustrative and non-limitative example, the expected maximal ambient temperature in the vehicle is equal to <NUM>° (e.g., Ta_max=<NUM>).

The iterative process including the steps S1 and S2 executed for the cable EC3 are described below.

In the acquisition step S1_EC3, at each iteration of time ti, the processing module <NUM> acquires the following values:.

Since the transistor EC1, the shunt EC2, the cable EC3 and the load <NUM> are connected in series, the current I<NUM> through the shunt EC2 corresponds to the current flowing through the cable EC3.

In the processing step S2_EC3, at each time ti, the processing module <NUM> processes the input data using the thermal model. The processing includes the steps S20_EC3 to S27_EC3 described below.

In the step S20_EC3, the processing module <NUM> estimates an electrical power dissipated by the cable EC3 based on the value of the current I<NUM>(ti), or <MAT>, measured or estimated through the shunt EC2 and the value of the electrical resistance of the cable EC3 estimated at the previous iteration of time ti-<NUM>, using one of the following equations: <MAT> or <MAT>.

At the initial time t<NUM>, the value of the electrical resistance of the cable EC3 may be set to the reference resistance value Rref,<NUM> of the cable EC3 at room temperature.

In the step S21_EC3, the processing module <NUM> estimates a value ΔT<NUM>,i of incremental temperature variation of the cable EC3 relative to the ambient temperature Ta over the current time step dt, between times ti and ti+<NUM>, based on the thermal model, using the following equation derived from the equation (<NUM>): <MAT>.

In the step S22_EC3, the processing module <NUM> may estimate a value dT<NUM>,i of temperature difference of the cable EC3 relative to the ambient temperature Ta between the initial time t<NUM> and the current time ti. For that purpose, the processing module <NUM> may compute the cumulated temperature variation by adding ΔT<NUM>,i to the value of the temperature difference dT<NUM>,i-<NUM> of the cable EC3 relative to the ambient temperature Ta determined at the previous iteration of time ti-<NUM>, based on the equation (<NUM>).

In the step S24_EC3, the processing module <NUM> estimates the value of the electrical resistance of the cable EC3 at time ti, based on the following equation: <MAT>.

A step S3_EC3 of monitoring the reliability of the cable EC3 based on the output of the processing step S2_EC3 may be performed for the cable EC3. For example, the diagnostic module <NUM> may compare the temperature difference dT<NUM>,i to a predetermined maximal temperature increase of the cable EC3, so as to detect an abnormality in the system <NUM>.

The monitoring device <NUM> and the system <NUM> can be included in a vehicle.

The present disclosure also concerns a computer program comprising instructions which, when the program is executed by a processor, cause the processor to carry out the steps of the method previously described.

Claim 1:
A method of monitoring reliability of a system (<NUM>) including a plurality of electrical components (EC1, EC2, ...), comprising the steps, performed for each of the plurality of electrical components (EC1, EC2, ...), of receiving (S1) input data including at least one of a voltage across the electrical component, a current through the electrical component and an electrical resistance value of the electrical component;
processing (S2) the input data using a stored thermal model representing heat transfer for said electrical component , the heat transfer referring to heat flow between a first point of the electrical component, where temperature is to be estimated, and a second point at a known reference temperature (Ta), to determine a temperature difference of said electrical component relative to the reference temperature (Ta);
wherein
the processing step (S2_EC2) is first performed for a first electrical component (EC2) of the plurality of electrical components (EC1, EC2, ...) and further includes estimating an electrical current value based on said determined temperature difference of said first electrical component (EC2), and then the processing step (S2_EC1) is performed for a second electrical component (EC1) of the plurality of electrical components (EC1, EC2, ... ) using the estimated electrical current value as input data;
and
monitoring (S3) the reliability of the system (<NUM>) based on output data of the processing steps (S2_EC2, S2_EC1).