METHOD AND DEVICE FOR DETECTING A PASSIVE COMPONENT DRIFT IN AN ELECTRICAL POWER CONVERTER

Abstract

The method comprises the steps of: a) recording a nominal resonant frequency (Fn) and a nominal AC resistance (Ran) of a series resonant circuit of the converter and defining a frequency sweep (fmin, fmax) of the circuit by a constant current at variable frequency (Ic) over a bandwidth including the nominal resonant frequency; b) injecting the current into the circuit, recording an effective resonant frequency (Fm) and a minimum voltage (Vcrm) between terminals of the circuit, this effective frequency being equal to a current frequency (f) of the current when the minimum voltage occurs, and determining an effective resistance (Ram) from the effective frequency and the minimum voltage; and c) comparing the nominal and effective frequencies and the nominal and effective resistances and detecting a drift on the basis of at least one recorded comparison deviation (D_F, D_R). Figure 1

Description

Title of the invention: METHOD AND DEVICE FOR DETECTING A PASSIVE COMPONENT DRIFT IN AN ELECTRICAL POWER CONVERTER

[0001] The present invention relates generally to the field of electrical power converters. More particularly, the invention relates to a method and a device for detecting a drift of a passive component in an electrical power converter. The method and the device according to the invention are suitable for being embedded in electrified vehicles, but not exclusively.

[0002] Electrical power converters are essential components for the energy transformation of our societies towards a low-carbon economy. Thus, the transport sector, which is the source of a significant proportion of polluting emissions and greenhouse gas emissions, is experiencing increasing electrification of the various transport systems, and significant technological developments in the field of electrical power conversion.

[0003] Electrical converters of various types are integrated, as essential functional components, in electrified motor vehicles, of hybrid and all-electric types, as well as in electrical charging systems such as electrical charging stations and robots, of the conduction (wired) or electromagnetic induction type. Electrical power supply networks, in particular those dedicated to electric mobility, will in the future integrate a greater number of electrical power converters for their connection to the future intelligent electrical network, known as "smart grid" in English. Optimizing energy performance and the functional availability of equipment requires effective preventive maintenance of electrical power converters.

[0004] Studies, simulations and tests carried out by the inventive entity have highlighted the interest in detecting drifts in the characteristics of the passive components of the resonant circuits, known as "RLCs", which are integrated into the power electronics of the electrical power converters. These drifts affect the conformity of the electrical power converter with one or more expected performances thereof and knowledge of these drifts is useful for detecting failures, or even for anticipating them, for the benefit of effective preventive maintenance, and for better functional management of the converter, for example, by modifying the control strategy towards a degraded mode.

[0005] The aging of capacitors and inductors in "RLC" circuits is often the cause of drifts in their characteristics. A degradation of the Litz wire used in the winding of inductors and transformers can also be the cause of a drift in the resistance in alternating current. This degradation is generally due to vibrations and heating which alter the insulation of the strands forming the Litz wire.

[0006] Generally speaking, to measure the resistance, inductance and capacitance characteristics of passive components in an electrical circuit or network, it is known to use measuring devices such as a network analyzer or a micro-ohmmeter. These known measuring devices are not intended to be installed in vehicles, in particular due to their excessive mass and size. In addition, network analyzers are not suitable for measuring very low resistances. Micro-ohmmeters are accurate and can be used to measure very low resistances, but only in direct current. The resistance in alternating current, the value of which is dependent on the frequency due to the skin effect, cannot be measured with a micro-ohmmeter.

[0007] The present invention aims to provide a new solution for detecting a drift of a passive component in a series resonant circuit of an electrical power converter, which is capable of being integrated into an electrified vehicle for application to an on-board converter of the vehicle.

[0008] According to a first aspect, the invention relates to a method for detecting a passive component drift in a series resonant circuit of an electrical power converter. According to the invention, the method comprises the steps of: a) recording a nominal resonant frequency and a nominal alternating current resistance of the series resonant circuit and defining a frequency sweep of the series resonant circuit by a constant current at variable frequency, the frequency sweep being defined over a predetermined frequency bandwidth including the nominal resonant frequency;(b) injecting the variable-frequency constant current into the series resonant circuit, recording an effective resonant frequency and a minimum voltage appearing between pole terminals of the series resonant circuit, with the effective resonant frequency being equal to a common frequency of the variable-frequency constant current when the minimum voltage occurs, and determining an effective alternating current resistance from the recorded effective resonant frequency and minimum voltage; (c) comparing the nominal and effective resonant frequencies and the nominal and effective alternating current resistances and detecting a passive component drift based on at least one recorded comparison deviation.

[0009] According to a particular characteristic, step c) of the method comprises detecting a drift of a capacitor and / or an inductance of the series resonant circuit on the basis of a comparison difference noted between the nominal resonant frequency and the effective resonant frequency.

[0010] According to another particular characteristic, step c) of the method comprises detecting a drift of a resistive component of the series resonant circuit on the basis of a comparison difference noted between the nominal alternating current resistance and the effective alternating current resistance.

[0011] The invention also relates to an assembly of an electrical power converter and a device for detecting a drift of a passive component in a series resonant circuit of the converter, in which the device comprises means including a voltage-controlled oscillator and arranged for implementing the method briefly described above.

[0012] The invention also relates to another assembly of an electrical power converter and a device for detecting a drift of a passive component in a series resonant circuit of the converter, the assembly comprising a control computer, in which the control computer comprises digital-analog and analog-digital conversion means and a memory storing program instructions for implementing the method briefly described above.

[0013] The invention also relates to an electrified vehicle comprising an assembly as indicated above.

[0014] Other advantages and characteristics of the present invention will appear more clearly on reading the detailed description below of several particular embodiments of the invention, with reference to the accompanying drawings, in which

[0015] [Fig.l] is a flowchart showing steps of the method according to the invention.

[0016] [Fig.2] is a timing diagram showing several signal waveforms used for implementing the method of the invention.

[0017] [Fig. 3] is a block diagram of an assembly formed of an electrical power converter and a first particular embodiment of a device according to the invention.

[0018] [Fig.4] is a block diagram of an assembly formed of an electrical power converter and a second particular embodiment of a device according to the invention.

[0019] As shown in [Fig.l], the method of the invention dedicated to the detection of drifts in the characteristics of the passive components of a series “RLC” type resonant circuit, including an electrical power converter, comprises in particular four major steps S1 to S4. These steps S1 to S4 are implemented by a processing process.

[0020] Step SI is a step prior to the detection of drifts strictly speaking. In this step SI, the processing process stores values ​​of quantities used for detection, namely, a nominal resonant frequency Fn and a nominal alternating current resistance Ran of the resonant circuit, which are determined during the design of the resonant circuit. The resistance Ran is the resistive component of the resonant circuit, knowing that the impedance of this resonant circuit is equal to Ran at the nominal resonant frequency Fn.

[0021] A constant current le, of variable frequency f, used for detection is also defined in step S1. The constant current le is used by the method to perform a frequency sweep of the resonant circuit. A frequency variation range [fmin, fmax] defined by a minimum frequency fmin and a maximum frequency fmax is assigned to the frequency f of the constant current le. The minimum frequency fmin and the maximum frequency fmax are determined so as to frame the nominal resonant frequency Fn. The frequency bandwidth fmax-fmin of the sweep and the position of the frequency Fn in the range are fixed so as to include a drift of the resonant frequency linked to the aforementioned drifts of characteristics of the passive components.

[0022] Step S2 is a measurement step. In this step, the processing process controls the injection of the constant current le into the resonant circuit. The frequency f of the current le is modified according to a frequency sweep ramp, for example from the minimum frequency fmin to the maximum frequency fmax. Depending on the application, the frequency sweep ramp is a ramp with step variation or a continuously variable ramp. Typically, the frequency sweep ramp may be repeated cyclically until measurements estimated to be valid by the processing process are obtained.

[0023] An example of a staircase frequency sweep ramp RP is shown in line A of [Fig.2]. The ramp RP is typically a setpoint voltage applied to a voltage-controlled oscillator to obtain a frequency f varying in steps between fmin and fmax. The frequency variation over time (t) of the constant current le, between fmin and fmax, is shown in line B of [Fig.2]. In this example, the frequency f varies between fmin = 40 kHz and fmax = 45 kHz, in steps of 1 kHz.

[0024] During the frequency sweep carried out, a voltage Ver at the terminals of the resonant circuit is scanned. The frequency f=Fm of the injected current producing a minimum voltage at the terminals of the resonant circuit is recorded, as well as this minimum voltage Vcr=Vcrm. The recorded frequency Fm is the effective resonant frequency of the resonant circuit. In the example of [Fig.2], the minimum voltage Verni occurs for the frequency f = 43 kHz. The effective resonant frequency measured here is therefore Fm = 43 kHz.

[0025] In addition, step S2 uses the minimum voltage measured Verni to determine an effective measured alternating current resistance Ram of the resonant circuit, for the re resonance of the circuit intervening at the measured effective resonant frequency Fm. The resistance Ram is given by the equality Ram = Vcrm / Ic.

[0026] In step S3, the processing process makes a comparison between the nominal resonant frequency Fn and the measured effective resonant frequency Fm so as to detect a possible deviation D_F. The deviation D_F is representative of a drift of a capacitor and / or an inductance of the resonant circuit. The processing process also makes a comparison between the nominal alternating current resistance Ran and the measured effective alternating current resistance Ram so as to detect a possible deviation D_Ra. The deviation D_Ra is representative of a drift of the resistive component of the resonant circuit, typically due to deterioration of the Litz wire of a winding.

[0027] Step S4 is a decision step which uses the deviation information D_F and D_Ra obtained in step S3 to decide whether or not to issue a drift alert AL_D. Different decision methods may be used depending on the application. Thus, for example, a decision to issue a drift alert may be taken on the basis of the amplitude of the deviations D_F and / or D_Ra, by comparing them to predefined thresholds, or on the basis of the number of times the deviations D_F and / or D_Ra are exceeded, compared to the thresholds, over a predefined duration, or on another basis using D_F and / or D_Ra.

[0028] With particular reference to [Fig. 3], a particular application of the invention to an electrical power converter PW_CH is now described. The converter PW_CH is here an on-board electrical charger for an electrified vehicle.

[0029] As visible in [Fig.3], the PW_CH charger comprises an alternating-direct conversion stage called “AC / DC” and a direct-direct conversion stage called “DC / DC”, marked respectively C_AC / DC and C_DC / DC.

[0030] The C_AC / DC conversion stage is connected to a three-phase power supply network and is supplied with electrical energy by three phase wires phi, ph2 and ph3 and a neutral wire N. The C_AC / DC conversion stage is here of the power factor correction type, called “PFC” (for “Power Factor Correction” in English), and comprises a four-branch switching bridge. This bridge comprises four pairs of power electronic switches (M1, M2), (M3, M4), (M5, M6) and (M7, M8), typically “MOSFET” type transistors. The C_AC / DC conversion stage delivers a DC voltage which supplies the C_DC / DC conversion stage.

[0031] The C_DC / DC conversion stage is of the resonant type, with a structure of the so-called “LLC” type. This “LLC” structure comprises in particular a capacitor C, an inductance L1 and a transformer Tr and is substantially equivalent to a series resonant circuit shown in the box EC in [Fig.3]. This series resonant circuit equivalent to an impedance Z formed by the aforementioned components C and L1, as well as an inductance L2, representative of the transformer Tr, and the alternating current resistance Ran representative of the total resistive component of the circuit. The resonant frequency Fn is given by the equality Fn = l / (2.ir.(LC)1 / 2), with L=L1+L2.

[0032] In the C_DC / DC conversion stage, the DC voltage supplied by the C_AC / DC stage is chopped by a two-branch switching bridge which supplies the aforementioned “LLC” structure. This bridge comprises two pairs of power electronic switches (M9, M10) and (Mil, M12), typically “MOSFET” type transistors. A two-branch diode bridge, formed by two pairs of power diodes (D1, D2) and (D3, D4), is supplied by a secondary winding of the transformer Tr to produce a high DC voltage HV+, HV-. This high DC voltage HV+, HV- is intended here for the electrical charging of a high voltage battery pack of the vehicle.

[0033] The charger PW_CH is connected to a device DDE1 according to the invention. The device DDE1 implements the method of the invention for detecting drifts of the passive components of the aforementioned “LLC” structure.

[0034] As visible in [Fig.3], the device DDE1 is connected to two terminals B1, B2, of the “LLC” structure and essentially comprises a voltage-controlled oscillator VCO, a measurement amplifier AM, an envelope detector DE, a measurement circuit CM and a comparison and decision circuit CD.

[0035] The terminals Bl, B2, correspond to the two polar terminals of the aforementioned equivalent series resonant circuit, or in other words, to the two polar terminals of the impedance Z. It will be noted that, in order to carry out the detection of the drifts in accordance with the invention, these terminals Bl, B2, are electrically isolated (disconnected) from the switching bridge by suitable controls on the gates of the transistors M9, M10 and Mil, M12, which place them in a high impedance state.

[0036] The VCO oscillator has a current output SC and provides the constant current le at variable frequency. The VCO oscillator receives a setpoint voltage, here for example the staircase frequency sweep ramp RP, to control the variation of the frequency f of the constant current le.

[0037] The injection of the constant current Ie into the “LLC” structure generates the voltage Ver between the terminals B1, B2. The voltage Ver is applied to high impedance inputs of the measurement amplifier AM. The amplifier AM provides an amplified measurement voltage Ver to the envelope detector DE. The envelope detector DE makes it possible to overcome the alternating component of the voltage Ver and delivers envelope information e_Vcr as output.

[0038] The measuring circuit CM receives as input the envelope information e_Vcr, as well as the constant current le and frequency f information. The measuring circuit CM, by exploiting the information e_Vcr, le and f, detects the minimum voltage Verni and the corresponding frequency f, which is equal at that moment to the effective resonant frequency Fm. Knowing the values ​​of the minimum voltage Vcrm and the current le, the measuring circuit CM is able to calculate the effective alternating current resistance Ram. The measuring circuit CM outputs the measured information Fm and Ram to the comparison and decision circuit CD.

[0039] The comparison and decision circuit CD receives the measured information Fm and Ram and, knowing the nominal information Fn and Ran, determines the deviations D_F and D_Ra. From the deviation information D_F and D_Ra, the circuit CD decides whether or not to emit drift alert information AL_D. The drift alert information AL_D concerns a drift of the capacitor and the inductors and / or a drift of the alternating current resistance of the “LLC” structure.

[0040] With particular reference to [Fig. 4], another particular application of the invention is now described to an electrical power converter PW_C having an “LLC” type structure, here designated S_LLC. The structure S_LLC is analogous here to the “LLC” structure described with reference to [Fig. 3] and has an equivalent diagram comprising two inductors L1, L2, a capacitor C and a nominal direct current resistance Ran.

[0041] In this application of the invention, the device DDE2 used for implementing the method of the invention for detecting drifts of the passive components of the S_LLC structure is a digital version of the device DDE1 described above with reference to [Fig.3].

[0042] As visible in [Fig.4], the converter PW_C is connected to an ECU which ensures its control via switching control signals C_SW.

[0043] The ECU calculator comprises a memory MEM in which a control software module CTRL_C and a drift detection module SW_DE are housed.

[0044] The CTRL_C control software module is responsible for controlling, via the C_SW signals, the switching bridges of the PW_C converter. The CTRL_C module typically applies several control strategies depending on the life situation of the PW_C converter.

[0045] The drift detection software module SW_DE is dedicated to the implementation of the method of the invention. The execution of code instructions of the module SW_DE by the ECU computer allows the implementation of the method of the invention to detect drifts of the passive components of the structure S_LLC.

[0046] For the implementation of the DDE2 device in the ECU, the SW_DE module cooperates with an input-output interface port P_OI of the ECU. The input-output interface port P_OI is connected to the two polar terminals B1, B2, of the S_LLC structure. The P_OI port includes a digital-to-analog converter (DAC) and an analog-to-digital converter (ADC).

[0047] The digital-to-analog converter DAC has a current output and provides the constant current at variable frequency under the control of the SW_DE module. The analog-to-digital converter CAN comprises a high-impedance input amplifier which receives the voltage Ver present between the terminals Bl, B2, of the S_LLC structure. The voltage Ver is digitized in the analog-to-digital converter CAN before being provided to the SW_DE module.

[0048] The module SW_DE, in addition to a current generation control function Ic, includes functions (not shown) for envelope detection, measurement, comparison and decision and performs processing similar to that of the device DDE1 to detect drifts of the passive components of the structure S_LLC and emit the drift alert information AL_D.

[0049] Generally speaking, this embodiment DDE2 of the device of the invention has the advantage of being more economical than the embodiment DDE1 of [Fig.3]. However, the bandwidth of the DDE2 device is limited by the performance of the ECU. The DDE1 device with a voltage-controlled oscillator is capable of providing greater bandwidth, when the application requires it.

[0050] The invention provides a simple solution, easy to implement and able to be installed in a vehicle, for early detection of possible failures in electrical power converters. It makes it possible to improve the availability of the converters and to increase the service life of their components. The method of the invention may be implemented in different phases of the life of an electrical power converter, for example, in the factory, at the end of its manufacture, and throughout its life, for example at each power-up, and at other times of life, depending on the applications.

[0051] The electrical power converters associated with devices of the invention can be integrated into a large number of equipment and systems, and in particular into electrified vehicles, of hybrid and all-electric types, as well as electric charging terminals and robots for these vehicles.

[0052] The invention is not limited to the particular embodiments which have been described here by way of example. In general, those skilled in the art, depending on the applications of the invention, will be able to make various modifications and variants falling within the scope of protection of the invention.

Claims

Claims

1. Method for detecting a passive component drift in a series resonant circuit of an electrical power converter, characterized in that it comprises the steps of: a) recording a nominal resonant frequency (Fn) and a nominal alternating current resistance (Ran) of said series resonant circuit (S_LLC) and defining a frequency sweep (RP, fmin, fmax) of said series resonant circuit (S_LLC) by a constant current at variable frequency (le, f), said frequency sweep (RP, fmin, fmax) being defined over a predetermined frequency bandwidth including said nominal resonant frequency (Fn);b) injecting said variable frequency constant current (Ie, f) into said series resonant circuit (S_LLC), recording an effective resonant frequency (Fm) and a minimum voltage (Vcrm) occurring between pole terminals (Bl, B2) of said series resonant circuit (S_LLC), with said effective resonant frequency (Fm) being equal to a current frequency (f) of said variable frequency constant current (Ie, f) when said minimum voltage (Vcrm) occurs, and determining an effective alternating current resistance (Ram) from said recorded effective resonant frequency (Fm) and minimum voltage (Vcrm); c) comparing said nominal and effective resonant frequencies (Fn, Fm) and said nominal and effective alternating current resistances (Ran, Ram) and detecting a passive component drift based on at least one recorded comparison deviation (D_F, D_R).;

2. Method according to claim 1, characterized in that step c) comprises detecting a drift of a capacitor and / or an inductance of said series resonant circuit (S_LLC) on the basis of a comparison deviation noted (D_F) between said nominal resonant frequency (Fn) and said effective resonant frequency (Fm).

3. Method according to claim 1 or 2, characterized in that step c) comprises detecting a drift of a resistive component of said series resonant circuit (S_LLC) on the basis of a comparison deviation recorded (D_R) between said nominal alternating current resistance (Ran) and said effective alternating current resistance (Ram).

4. Assembly of an electrical power converter (PW_CH) and a device (DDE1, DDE2) for detecting a drift of a passive component in a series resonant circuit of said converter (PW_CH), characterized in that said device (DDE1, DDE2) comprises means recording a nominal resonant frequency (Fn) and a nominal alternating current resistance (Ran) of said series resonant circuit (S_LLC) and defining a frequency sweep (RP, fmin, fmax) of said series resonant circuit (S_LLC) by a constant current at variable frequency (le, f), said frequency sweep (RP, fmin, fmax) being defined over a predetermined frequency bandwidth including said nominal resonant frequency (Fn), means for injecting said constant current at variable frequency (le, f) into said series resonant circuit (S_LLC), measuring an effective resonant frequency (Fm) and a minimum voltage (Vcrm) appearing between polar terminals (Bl, B2) of said series resonant circuit (S_LLC), with said effective resonant frequency (Fm) being equal to a current frequency (f) of said constant current at variable frequency (le, f) when said minimum voltage occurs (Vcrm),and determining an effective alternating current resistance (Ram) from said measured effective resonant frequency (Fm) and minimum voltage (Vcrm), and means for comparing said nominal and effective resonant frequencies (Fn, Fm) and said nominal and effective alternating current resistances (Ran, Ram) and detecting a passive component drift on the basis of at least one recorded comparison deviation (D_F, D_R).,

5. Assembly according to claim 4, characterized in that said means for injecting said constant current at variable frequency (Ie, f) comprise means including a voltage-controlled oscillator (VCO).

6. Assembly according to claim 4, wherein said device (DDE2) is integrated in a control computer (ECU) of said assembly, characterized in that said control computer (ECU) comprises digital-analog (CNA) and analog-digital (CAN) conversion means and a memory (MEM) storing program instructions (SW_DE) for implementing the method according to any one of claims 1 to 3 when these program instructions are executed by a processor of said control computer (ECU).

7. Electrified vehicle, characterized in that it comprises an assembly (PW_CH, DDE1; PW_C, DDE2) according to any one of claims 4 to 6.

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