METHOD FOR DETECTING AN OPEN MOSFET TRANSISTOR IN A POWER MODULE OF A MOTOR VEHICLE, AND COMPUTER PROGRAM BASED ON SUCH A METHOD

Abstract

The invention relates to a method for detecting an open Mosfet transistor in a power module conducting a three-phase current, comprising:- a DC connector module (DCL);- a plurality of Mosfet type transistors (M1 - M6), connected together in parallel,the method comprising:- a step of charging the DC connector module (DCL);- a pulse step by short-circuiting the three phases,- a step of comparing the voltage (VUV, VVW, VUW) between two phases (U, V, W) and a reference value of a reference power module,- a conclusion step in which if a difference is greater than a threshold, then a Mosfet transistor is open between the measured phases, and if the difference is less than said threshold, then all Mosfet transistors are closed. The invention also relates to a program based on such a method. Abstract figure: Fig. 1

Description

Title of the invention: METHOD FOR DETECTING AN OPEN MOSFET TRANSISTOR IN A POWER MODULE OF A MOTOR VEHICLE, AND COMPUTER PROGRAM BASED ON SUCH A METHOD

[0001] The invention relates to the field of power modules for electric vehicle traction systems. In particular, the invention relates to the detection of defective Mosfet devices in these power modules. The invention is more particularly oriented towards the detection of open Mosfet devices because the forced open state is one of the failure modes of Mosfet devices.

[0002] The power module is widely used for high power inverter applications. It consists of a three half-bridge topology which is required to conduct a three-phase current. A half-bridge is composed of a low-side and a high-side. Each of the sides may have one or more transistor chips (Mosfet / Sic Mosfet / IGBT / Gan type) in parallel. This invention is provided on a power module with at least two Mosfets in parallel.

[0003] Due to high current and high power flowing in the power module, a high temperature may occur inside the power module. The highest temperature is located in the center of the chips. It is called the junction temperature. For safety reasons, this temperature must be monitored by means of thermal sensors.

[0004] When overheating of the chips, and therefore an increase in the junction temperature, is detected inside the power module, the latter is switched off by a control unit.

[0005] To monitor the temperature, a thermal sensor is placed directly on the power module's circuit board, as close as possible to the chips.

[0006] However, due to the thermal inertia of the power module for a few seconds, it may be difficult to detect in time overheating of a junction which has a faster inertia.

[0007] This is all the more true for a power module with Mosfet transistors in parallel, when of all the Mosfet transistors in operation, only one is open.

[0008] To control this, a drain-source voltage (or VDS) monitoring strategy for "drain-source voltage" in English) has been implemented in the prior art. It gives a direct relationship between voltage, current and drain resistance. If the drain-source voltage is too high, it means that an overcurrent occurs inside the chips, or that a MOSFET transistor is open.

[0009] However, in the case of a large number of Mosfet transistors in parallel, it is difficult to detect whether a single Mosfet transistor is open based on monitoring the drain-source voltage, mainly due to the variation of the drain resistance between the chips.

[0010] It is commonly known for example that the variation in drain resistance between chips can be up to +30% and for example the change from 6 Mosfet in parallel to 5 Mosfet in parallel in the event of a fault, increases the drain resistance by 20%.

[0011] Since the drain resistance variation in the case of an open Mosfet transistor is less than the possible drain resistance variation due to distribution (over a million pieces), we cannot know if the increase in drain resistance is due to a defective Mosfet transistor or only to a tolerance problem.

[0012] An objective of the present invention is to remedy the defects of the prior art, and in particular to propose a solution making it possible to detect an open Mosfet transistor with a high number of Mosfet transistors in parallel.

[0013] To achieve this objective, the invention proposes a method for detecting an open field effect transistor in a power module conducting a current over three phases, each phase comprising a high side and a low side, the power module comprising: - a DC connector module providing power; - a plurality of Mosfet type field effect transistors, connected together in parallel, the detection method comprising the following steps: - a DC connector module charging step; - a pulse step in which the three phases are short-circuited on the high and low sides so as to generate a current pulse, - a comparison step in which the voltage measurement between two of said phases is compared with a reference value corresponding to a power module in which all the transistors are functional, - a conclusion step in which if a difference between the voltage measurement and the reference value is greater than a predetermined threshold, then it is concluded that a Mosfet transistor is open between the measured phases, and if the difference between the voltage measurement and the reference value is less than said threshold, then we conclude that all the Mosfet transistors are closed.

[0014] In particular, the impulse step and the comparison step are concomitant.

[0015] Advantageously, the invention makes it possible to detect an opening of a Mosfet transistor independently of the strong variation of the drain resistance. The detection is made for an open Mosfet transistor with a much higher number of Mosfet transistors in comparison with the monitoring of the voltage or the drain resistance.

[0016] According to a variant, the comparison step comprises a comparison of all the phases two by two, and the conclusion step comprises a determination of the phase comprising the open Mosfet transistor.

[0017] This makes it possible to strengthen the detection and to find on which phase there is an open transistor.

[0018] According to a variant, the detection method comprises detecting a variation in parasitic inductance of the power module.

[0019] This makes it possible to simplify the detection of defective Mosfet transistors.

[0020] According to a variant, the charging step (El) is stopped at a low voltage between 3V and 50V, preferably between 5V and 40V.

[0021] The voltage is chosen so as to limit the short-circuit current so as not to damage the Mosfet transistors.

[0022] According to a variant, the detection method further comprises a side determination step in which the sign of said difference is determined to conclude whether the open Mosfet transistor is on the high side or the low side.

[0023] This determines whether the Mosfet transistor is on the high side or the low side.

[0024] According to a variant, the reference value is 0V, and, in the conclusion step, if the voltage measurement is 0V, then we conclude that a Mosfet transistor is open between the measured phases, and if the voltage measurement is greater than 0V, then we conclude that all Mosfet transistors are closed.

[0025] This makes detection easier.

[0026] The invention further relates to a computer program comprising program code instructions for executing the steps of the detection method according to the invention, when said program operates on a computer.

[0027] The invention will be further detailed by the non-limiting description of variants, and on the basis of the appended figures, in which: - [Fig.l] schematically illustrates an electrical architecture of an assembly of Mosfet transistors in a power module suitable for implementing the invention; and - [Fig.2] schematically illustrates a graphical representation of the voltage and intensity as a function of time during the implementation of the detection method according to the invention.

[0028] The invention relates to a method for detecting an open field effect transistor in a power module of a motor vehicle. This type of power module conducts a current on three phases U, V, W illustrated in [Fig.l].

[0029] The power module includes a DC connector module DCL providing power.

[0030] The power module further comprises a plurality of field effect transistors of the Mosfet type M1, M2, M3, M4, M5, M6. These transistors are connected together in parallel as illustrated in [Fig.l].

[0031] The aim of this invention is to rely not on detecting an increase in drain voltage or resistance in the case of an open Mosfet transistor, but on detecting the variation in parasitic inductance of the power module.

[0032] The detection strategy takes place during the charging phase of the DC-LINK (or "DC-LINK" in English) DC connector module. We can speak of a charging step E1 illustrated in [Fig.2]. At the beginning, the DC-LINK DC connector module is charged by the charger from 0 to 400V or 800V. The idea is to stop charging at a low voltage, for example between 5V and 40V.

[0033] Then, the second step is to short-circuit all three phases on the high side and the low side at the same time. The consequence is a high current pulse. This can be referred to as an E2 pulse step. This pulse can be safely limited by the amount of voltage previously charged inside the DCL DC connector module.

[0034] At the very beginning of the current pulse, the current is really small and has a high slope. Therefore, at the beginning, the voltage drop due to the drain resistance is small and the voltage drop due to the parasitic inductance is high.

[0035] For example, if the first phase U on the low side has one defective Mosfet transistor out of 6 Mosfet in parallel, in this case the parasitic equivalent inductance can increase by about 20% inside the low side (in a general case, the value can increase or decrease more or less depending on other criteria). Therefore, the distribution of the inductance between the low side and the high side of this phase changes. This implies that the voltage in the middle of the low side and the high side (phase voltage) changes compared to a normally operating phase: T / __ indtictaficeLS ¢1 / OR y U phase ~ phaserj , r^+PhaseU- , V DCL ii liîduc.tath.eHS - Vuphase is the voltage of the Mosfet transistors; - PhaseUincluctafU.eLS is the low side inductance; - PhaseU iTldlKtajlceHS is the high-side inductance; and - dcl is the voltage of the DC connector module DCL.

[0036] By monitoring the voltage between the phases, we can know if we have a open Mosfet transistor. If the voltage between two phases is close to zero, then there is no open Mosfet transistor inside the two phases, if the voltage is not zero (threshold to be defined according to tolerance), we know that at least one phase has an open Mosfet transistor.

[0037] By measuring the three voltages between the phases (UV, VW, UW), by elimination we can know which phase is not working. In addition, with the sign of the voltage between the phases, it is possible to know if it is the high side or the low side that has an open Mosfet transistor.

[0038] Thus, it is easier to detect an open Mosfet base from a parasitic inductance because the distribution of parasitic inductance between the phases is much lower: for example 1% variation of inductance against 30% for the drain resistance. The variation of parasitic inductance depends mainly on the geometry of the power module whose tolerance on the dimensions is known.

[0039] The invention makes it possible to detect an opening of a Mosfet transistor independently of the strong variation of the drain resistance. The detection is made for an open Mosfet transistor with a much higher number of Mosfet transistors in parallel, in comparison with the monitoring of the voltage or the drain resistance.

[0040] The invention makes it possible to know exactly which phase the open Mosfet transistor is in, and whether it is on the high side or the low side.

Claims

Claims

1. A method of detecting an open field effect transistor in a power module conducting current over three phases (U, V, W), each phase comprising a high side and a low side, the power module comprising: - a DC connector module (DCL) providing power; - a plurality of Mosfet type field effect transistors (Ml, M2, M3, M4, M5, M6), connected together in parallel, the detection method comprising the following steps: - a step of charging (El) the DC connector module (DCL);- a pulse step (E2) in which the three phases are short-circuited on the high sides and the low sides so as to generate a current pulse, - a comparison step (E3) in which a voltage measurement between two of said phases is compared with a reference value corresponding to a power module all of whose transistors are functional, - a conclusion step (E4) in which if a difference between the voltage measurement and the reference value is greater than a predetermined threshold, then it is concluded that a Mosfet transistor is open between the measured phases, and if the difference between the voltage measurement and the reference value is less than said threshold, then it is concluded that all the Mosfet transistors are closed.;

2. Detection method according to claim 1, characterized in that the comparison step (E3) comprises a comparison of all the phases two by two, and the conclusion step comprises a determination of the phase comprising the open Mosfet transistor.

3. Detection method according to any one of claims 1 to 2, characterized in that it comprises a detection of a variation in parasitic inductance of the power module.

4. Detection method according to any one of claims 1 to 3, characterized in that the charging step (El) is stopped at a low voltage between 3V and 50V, preferably between 5V and 40V.

5. Detection method according to any one of claims 1 to 4, characterized in that it further comprises a side determination step in which the sign of said difference is determined for conclude whether the open Mosfet transistor is on the high side or the low side.

6. Detection method according to any one of claims 1 to 5, characterized in that the reference value is OV, and in the conclusion step (E4), if the voltage measurement is OV, then it is concluded that a Mosfet transistor is open between the measured phases, and if the voltage measurement is greater than OV, then it is concluded that all the Mosfet transistors are closed.

7. A computer program comprising program code instructions for carrying out the steps of the detection method according to any one of claims 1 to 6, when said program is running on a computer.

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