METHOD FOR CONTROLLING THE LOW-PASS FILTER OF A POWER MODULE, AND COMPUTER PROGRAM BASED ON SUCH A METHOD

Abstract

The invention relates to a method for controlling at least one arm of a power module comprising a low-pass filter, each arm comprising: - high and low sections connecting a positive and negative DC voltage to one phase; - MOSFET transistors connected in parallel to the high and low sections; - a power supply capacitor module disposed between the high and low sections; - at least one low-pass filter; the control method comprising the following steps: - a complete discharge (E0) and (E1) partial recharge of the capacitor module (DCL); - a short-circuiting (E2) of said capacitor module (DCL) by connecting the drain to the source; - a determination (E3) of the operation of said low-pass filter by calculating its capacitance based on the frequency of its inherent inductance. The invention also relates to a program based on such a method. Abstract figure: Fig. 2

Description

Title of the invention: METHOD FOR CONTROLLING A LOW-PASS FILTER OF A POWER MODULE, AND COMPUTER PROGRAM BASED ON SUCH A METHOD

[0001] The invention relates to the field of power modules for electrical devices, in particular for electric vehicle traction systems. The invention relates more particularly to the control of low-pass filters of these power modules.

[0002] The power modules are highly integrated converters. In the context of the invention, it is a three-arm inverter, each arm having a high side and a low side with a number of Mosfet transistors M in parallel.

[0003] For reasons of electromagnetic compatibility, one or more RCS low-pass filters (or "RC snubber" in English) in parallel, illustrated in the electronic system of [Fig.l], are provided between the drain on the high side, and the source on the low side of the arm.

[0004] A high capacity DCL (or “DC link” in English) capacity module is used to provide power.

[0005] In this electronic system, several gate drivers are used to control the gate of the Mosfet M devices and open or close them.

[0006] The high side and the low side are connected to strands denoted HV+ and HV- producing a measurable signal.

[0007] Unfortunately, once the power module is built, it is difficult to measure whether said RCS low-pass filter is working as expected. Indeed, if a conventional RLC meter is connected to the HV+ and HV+ strands, this will measure not only the capacitance of the RCS low-pass filter, but also a parasitic capacitance coming from the Mosfet M device. Thus, such a measurement does not allow one to determine whether the RCS low-pass filter is working.

[0008] The capacitance of the RCS low-pass filter can be measured on the power module before the Mosfet M devices are placed on the printed circuit board (but after the RCS low-pass filters are placed there), but this involves a lot of constraints and manufacturing time of the power module.

[0009] 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 one or more filters faulty low-pass filter in a power module, and more specifically an inverter.

[0010] To achieve this objective, the invention proposes a method for controlling at least one arm of a power module comprising a low-pass filter, each arm comprising: - an upper part connecting a positive direct voltage to a phase; - a lower part connecting a negative direct voltage to the phase; - Mosfet transistors connected in parallel on the upper part; - Mosfet transistors connected in parallel on the lower part; - a capacity module providing power, arranged between the upper part and the lower part; - at least one low-pass filter connected in parallel between the high and low parts on the one hand and the capacity module on the other hand; the control method comprising the following steps: - a step of complete unloading of the capacity module of one of the arms; - a step of partial recharging of said capacity module; - a step of short-circuiting said capacity module by connecting the upper part to the lower part; - a step of determining the operation of said low-pass filter by calculating its capacity on the basis of the formula p~ —1—_where 2X^C)- - F is a resonance frequency of the voltage difference between the high part and the low part; - L is the value of an equivalent inductance inherent in the low-pass filter and the Mosfet transistors of the upper and lower parts; - C is the value of the low-pass filter capacity.

[0011] Advantageously, short-circuiting the DC capacitance module of an arm under test allows the parasitic capacitance of the Mosfet device to be closed and discharged quickly. In addition, a high current appears, which facilitates the selective determination of the capacitance of the low-pass filter.

[0012] Thanks to the invention, it is not necessary to implement a specific printed circuit board to determine whether said low-pass filter is functional.

[0013] Furthermore, the formula makes it possible to determine the capacity of the low-pass filter with precision.

[0014] Preferably, the Mosfet transistor drain at the high part and the Mosfet transistor source at the low part comprise gate control devices, characterized in that the step of short-circuiting the capacitance module is implemented by simultaneously actuating the gate control devices of the upper part and the lower part.

[0015] This makes it possible to simplify the implementation of the short circuit of the DC capacitance module within the framework of the invention.

[0016] Preferably, the step of partially recharging the capacity module is carried out until it reaches a voltage of between 5 V and 50 V, preferably 20 V.

[0017] This allows for sufficient charge to determine the capacity of the low-pass filter while limiting parasitic capacitances.

[0018] Preferably, said arm comprises several low-pass filters in parallel, characterized in that the determined capacity is divided by the number of low-pass filters.

[0019] This allows the number of non-functional low-pass filters to be determined.

[0020] Preferably, the power module comprises three arms each equipped with said drains, sources and Mosfet transistors, and low-pass filters, characterized in that the method is implemented successively on each of said arms.

[0021] This makes it possible to determine whether said low-pass filter of each arm is functional.

[0022] The invention further relates to a computer program comprising program code instructions for executing the steps of the control method according to the invention, when said program operates on a computer.

[0023] 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 arm of a power module suitable for implementing the invention; and - [Fig.2] schematically illustrates the voltage V and the current I at the terminals of components of the architecture of [Fig.l], during the implementation of the invention.

[0024] The invention relates to a method for controlling a low-pass filter of a power module of the type comprising 3 arms. The power module may be an inverter of an electric vehicle traction machine.

[0025] Each arm includes: - a drain equipped with Mosfet M transistors arranged in parallel at a high stage (HV+ strand or the high part); - a source equipped with Mosfet M transistors arranged in parallel at a low stage (HV strand - the lower part); - several RCS low-pass filters in parallel between the drain of Mosfet transistors at the high stage and the source of Mosfet transistors M at the low stage; and - a capacity module (DCL) providing power, placed between the drain and the source.

[0026] The DC_LINK type capacity is used to stabilize the DC voltage network at the terminals of the inverter and provide the power necessary for the operation of the inverter.

[0027] The control method comprises a step of complete E0 discharge of the capacity module (DCL) of one of the arms, down to 0V.

[0028] Then, power is allocated to the system, in particular on one of the arms at a time, by charging the DCL capacity module to a certain voltage, preferably of low value, for example at 20V out of the possible 400 to 800V. Thus, the control method further comprises a step of partial recharging E1 of said DCL capacity module.

[0029] In a second step E2, the capacitance module is short-circuited by closing all the Mosfet M transistors of the high stage and the low stage of the arm under test. At this time, a parasitic capacitance inherent in the Mosfet M transistors being forced to a zero voltage, they are quickly discharged and a high current appears. Thus, the control method further comprises a step E2 of short-circuiting said DCL capacitance module by connecting the high stage to the low stage.

[0030] In a third step E3, only the capacitance of the low-pass filter is still charged. A resonance effect of the RCS low-pass filter voltage is observed between the HV+ and HV- strands for several microseconds. This depends only on the capacitance of the low-pass filter (but not on the parasitic capacitance of the Mosfet device M since it is discharged), on the parasitic inductances of the DCL capacitance module and on the DC bus bar. Thus, the control method further comprises a step E3 of determining the operation of said RCS low-pass filter by calculating its capacitance on the basis of the formula / 7- —L—where - F is a resonance frequency of the voltage difference between the high stage and the low stage; - L is the value of an equivalent inductance inherent in the components of the low-pass filter and the Mosfet transistors of the high stage and the low stage; - C is the value of the RCS low-pass filter capacitance.

[0031] Since the equivalent inductance can be known precisely, for example by performing a finite element simulation on a digital model of the circuit comprising the RCS low-pass filters, the high-stage Mosfet transistors and the low-stage Mosfet transistors, it is possible to precisely calculate the capacitance of the low-pass filter on the basis of the measured frequency.

[0032] This capacitance value is equal to the capacitance of a filter multiplied by the number of functioning RCS low-pass filters. Thus, it is possible to detect any faulty RCS low-pass filter.

[0033] To improve accuracy, it is best to test all three arms one after the other, applying the DCL capacitance module voltage to only one of the three arms at a time.

[0034] In particular, the drain of Mosfet transistors M in the high stage, and the source of Mosfet transistors M in the low stage comprise gate control devices. The gate control device makes it possible to control the gate of said Mosfet device M in opening and closing. The gate control devices are arranged in two sets, one being connected to the high stage, making it possible to implement a high control CH; the other being connected to the low stage, making it possible to implement a low control CL. The two simultaneous controls make it possible to short-circuit the capacitor module DCL. More particularly, the short-circuiting step E2 of the capacitor module DCL is implemented by simultaneously actuating the gate control devices of the high stage CH and of the low stage CL.

[0035] [Fig.2] shows the evolution as a function of time in seconds of the voltage V and the current I at the terminals of the various components during the charging of the DCL capacitance module, then during and after the short circuit. The graphs represent from top to bottom, the voltage of the DCL capacitance module, the voltage of the control system of the high stage CH, of that of the low stage CL, the current at the high stage and at the low stage, and the voltage difference between the high stage and the low stage.

[0036] In use, if all the RCS low-pass filters are functional, then the resonant frequency is at its maximum (see the dotted high-frequency sine curve in [Fig.2]). If some of said RCS low-pass filters are functional, then the resonant frequency is lower than previously (see the solid low-frequency sine curve in [Fig.2]). If none of said filters are functional, then a very low resonant frequency is observed (or no frequency as is the case on the horizontal line at the bottom right of [Fig.2]).

[0037] Thus, based on the oscillation frequency of the voltage across the high and low stages, it is possible to detect the number of functional RCS low-pass filters.

Claims

Claims

1. Method for controlling at least one arm of a power module comprising a low-pass filter (RCS), each arm comprising: - an upper part connecting a positive DC voltage to a phase; - a lower part connecting a negative DC voltage to the phase; - Mosfet transistors (M) connected in parallel on the upper part; - Mosfet transistors (M) connected in parallel on the lower part; - a capacity module (DCL) providing power, arranged between the upper part and the lower part; - at least one low-pass filter (RCS) connected in parallel between the upper and lower parts on the one hand and the capacity module on the other hand; the control method comprising the following steps: - a step of completely discharging (EO) the capacity module (DCL) of one of the arms; - a step of partially recharging (El) said capacity module (DCL);- a step of short-circuiting (E2) said capacitance module (DCL) by connecting the upper part to the lower part; - a step of determining (E3) the operation of said low-pass filter (RCS) by calculating its capacitance on the basis of the formula F =—L—where 2.^LCy - F is a resonant frequency of the voltage difference between the upper part and the lower part; - L is the value of an equivalent inductance inherent in the low-pass filter (RCS) and in the Mosfet transistors of the upper part and the lower part; - C is the value of the capacitance of the low-pass filter (RCS).;

2. Control method according to claim 1 in which the drain of Mosfet transistors (M) at the high part and the source of Mosfet transistors (M) at the low part comprise gate control devices, characterized in that the short-circuiting step (E2) of the capacitance module (DCL) is implemented by simultaneously actuating the gate control devices (CH, CL) of the upper part and the lower part.

3. Control method according to any one of claims 1 to 2, characterized in that the step of partial recharging (El) of the capacity module (DCL) is carried out until it reaches a voltage of between 5 V and 50 V, preferably 20 V.

4. Control method according to any one of claims 1 to 3, wherein said arm comprises several low-pass filters (RCS) in parallel, characterized in that the determined capacity is divided by the number of low-pass filters (RCS).

5. Control method according to any one of claims 1 to 4, in which the power module comprises three arms each equipped with said drains, sources and Mosfet transistors (M), and low-pass filters (RCS), characterized in that the method is implemented successively on each of said arms.

6. A computer program comprising program code instructions for carrying out the steps of the control method according to any one of claims 1 to 5, when said program is running on a computer.

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