Electronic device and method for determining at least one characteristic parameter of an electric machine connected to an electric starter, related power supply chain and computer program

An electronic determination device is configured for determining at least one characteristic parameter of an electric machine with P phases, P≥3, connected to an electric starter and including at least P-1 switching arms, each switching arm being connected to a respective phase of the electric machine. The determination device comprises a control module configured to control respective switching arm(s) to close and the other switching arm(s) to open, so as to generate a current injection on two phases of the electric machine; an acquisition module configured to acquire measurements of respective current(s) and voltage(s) for said two phases, further to the generation of the current injection; and a calculation module configured to calculate at least one characteristic parameter of the electric machine according to the respective current(s) and voltage(s) measurements.

FIELD OF THE INVENTION

The present invention relates to an electronic determination device for determining at least one characteristic parameter of an electric machine connected to an electric starter.

The invention also relates to a power supply chain for an electric machine, the power supply chain comprising an electric starter being adapted to be connected between an alternative power source and the electric machine, and such an electronic determination device for determining at least one characteristic parameter of the electric machine.

The invention also relates to a determination method for determining at least one characteristic parameter of an electric machine connected to an electric starter, the method being implemented by such an electronic determination device.

The invention also relates to a computer program including software instructions which, when executed by a processor, implement such a determination method.

BACKGROUND OF THE INVENTION

This invention concerns the evaluation of characteristic parameter(s) of an electric machine, in particular of an electric motor.

Currently, with a variable speed drive, it's possible to evaluate characteristic parameter(s) of an electric machine, while the variable speed drive can generate any voltage waveforms thanks to pulse width modulation techniques and power electronics switches.

Such characteristic parameter(s) then allow estimating mechanical torque and mechanical speed. For instance, it allows to estimating the losses of the electric machine that are important for the quality and performance of the torque estimation, and then the torque control.

With an electric starter, voltage waveforms are fully constraint to be pieces of mains supply. Currently, there is no full identification of the machine parameter(s) with an electric starter.

Currently with an electric starter, the losses are therefore adjusted approximately by a user.

However, it can be difficult to know what value of the losses shall be entered since it depends on the electric machine. Moreover, this value of the losses is also influenced by the resistance of the cable connected between the electric starter and the electric machine.

SUMMARY OF THE INVENTION

An object of the invention is therefore to provide an electronic determination device and related method for determining at least one characteristic parameter of an electric machine connected to an electric starter, which allow an easier and more precise determination of said characteristic parameter(s).

For this purpose, the subject-matter of the invention is an electronic determination device for determining at least one characteristic parameter of an electric machine connected to an electric starter, the electric machine having P phases, P being an integer greater than or equal to 3, the electric starter being adapted to be connected to an alternative power source and including at least P-1 switching arms, each switching arm being connected to a respective phase of the electric machine,

the determination device comprising:a control module configured to control respective switching arm(s) to close and the other switching arm(s) to open, so as to generate a current injection on two phases of the electric machine;an acquisition module configured to acquire measurements of respective current(s) and voltage(s) for said two phases, further to the generation of the current injection; anda calculation module configured to calculate at least one characteristic parameter of the electric machine according to the respective current(s) and voltage(s) measurements.

The determination device according to the invention therefore allows using the switching arms of the starter in order to generate a current injection in the electric machine at standstill. Indeed, since the control module controls the switching arm(s) of at least one phase to open, the machine is at standstill. The current injection is generated on two other phases of the electric machine. The calculation module then calculates at least one characteristic parameter of the electric machine in a convenient and precise manner according to the respective current(s) and voltage(s) measurements for said two other phases.

According to other advantageous aspects of the invention, the electronic determination device comprises one or several of the following features, taken individually or according to any technically possible combination:each characteristic parameter is chosen from among the group consisting of:a stator resistance of the electric machine;a rotor resistance of the electric machine;a leakage inductance of the electric machine; anda main inductance of the electric machine;the control module is configured, further to the generation of the current injection occurring at an initial time instant, to control at an end time instant the respective previously closed switching arm(s) to open, so as to switch off the current injection;

a duration of the current injection between the initial time instant and the end time instant being preferably a predefined time period;

the predefined time period being preferably greater than five times a rotor time constant;the calculation module is configured to calculate a value of a stator voltage for a stator of the electric machine from the voltages measurements for said two phases, and respectively a value of a stator current for the stator from the currents measurements for said two phases, the calculation module being further configured to calculate the at least one characteristic parameter of the electric machine according to said stator voltage and stator current values;the calculation module is configured to calculate the respective stator voltage and stator current values according to a transformation applied to the respective voltages measurements and currents measurements for said two phases;

the calculation module being preferably configured to calculate the respective stator voltage and stator current values according to the following equations:

where Usrepresents the stator voltage,

U1, and respectively U2, represent the voltage in a first phase, and respectively in a second phase;

Isrepresents the stator current, and

I1, and respectively I2, represent the current in a first phase, and respectively in a second phase;the calculation module is configured to calculate a total resistance of the electric machine from the stator voltage and stator current at a time instant corresponding to a maximum of the stator current further to the generation of the current injection, the total resistance being equal to the sum of a stator resistance and a rotor resistance of the electric machine;

the calculation module being preferably configured to calculate the total resistance according to the following equation:

where Rtotrepresents the total resistance,

Isrepresents the stator current, and

t0represents the time instant corresponding to a maximum of the stator current;the calculation module is configured to calculate a leakage inductance of the electric machine from the stator voltage and a time derivative of the stator current further to the generation of the current injection;

the calculation module being preferably configured to calculate the leakage inductance according to the following equation:

where Lf represents the leakage inductance,

Usrepresents the stator voltage, and

Isrepresents the stator current;the calculation module is configured to calculate a stator resistance of the electric machine from an integral of the stator voltage and an integral of the stator current over the duration of the current injection;

the calculation module being preferably configured to calculate the stator resistance according to the following equation:

where Rsrepresents the stator resistance,

tinitrepresents the initial time instant of the measurement during current injection,

tendrepresents the end time instant of said measurement, and

T represents the duration of said measurement;the calculation module is configured to calculate a main inductance of the electric machine from a leakage inductance of the electric machine, the stator current and an integral of a stator flux over the duration of the current injection;

the calculation module being preferably configured to calculate the main inductance according to the following equation:

where L represents the main inductance,

Lf represents the leakage inductance,

Isrepresents the stator current, and

φsrepresents the integral of the stator flux over duration of the current injection;

φsbeing preferably defined according to the following equation:
φs=∫tinittend=tinit+T(Us−RsIs)dt

tinitrepresents the initial time instant of the current injection,

tendrepresents the end time instant of the current injection, and

T represents the duration of the current injection;P is equal to 3;the determination device is configured to determine a respective characteristic parameter of the electric machine in at least two successive sequences, and

wherein, during each sequence, the control module is configured to control respective switching arm(s) to close and the other switching arm to open, so as to generate a current injection on two phases of the electric machine; the acquisition module being configured to acquire measurements of respective current(s) and voltage(s) for said two phases, further to the generation of the current injection; and the calculation module being configured to calculate the characteristic parameter of the electric machine according to the respective current(s) and voltage(s) measurements for the respective sequence, and

wherein the open switching arm varies from one sequence to the other, so that each one of at least two switching arms is opened once during the successive sequences;the determination device further comprises a diagnostic module configured to compare the at least two values determined for a respective characteristic parameter over the successive sequences and to generate an alarm signal in the event of a deviation between these at least two determined values exceeding a predefined threshold.

The subject-matter of the invention is also a power supply chain for an electric machine, the electric machine having P phases, P being an integer greater than or equal to 3, the power supply chain comprising:an electric starter being adapted to be connected between an alternative power source and the electric machine, the electric starter including at least P-1 switching arms, each switching arm being adapted to be connected to a respective phase of the electric machine,an electronic determination device for determining at least one characteristic parameter of the electric machine, the electronic determination device being as defined above.

The subject-matter of the invention is also a method for determining at least one characteristic parameter of an electric machine connected to an electric starter, the electric machine having P phases, P being an integer greater than or equal to 3, the electric starter being adapted to be connected to an alternative power source and including at least P-1 switching arms, each switching arm being connected to a respective phase of the electric machine,

the method being implemented by an electronic determination device and comprising the following steps:control respective switching arm(s) to close and the other switching arm(s) to open, so as to generate a current injection on two phases of the electric machine;acquire measurements of respective current(s) and voltage(s) for said two phases, further to the generation of the current injection; andcalculate at least one characteristic parameter of the electric machine according to the respective current(s) and voltage(s) measurements.

The subject-matter of the invention is also a computer program including software instructions which, when executed by a processor, implement a method as defined above.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

InFIG. 1, a power supply chain10for an electric machine12comprises an electric starter14connected between an alternative power source16and the electric machine12, and an electronic determination device20for determining at least one characteristic parameter, such as a stator resistance Rs, an equivalent rotor resistance Rreq, a leakage inductance Lf, or a main inductance L of the electric machine12.

The electric machine12has P phases22, P being an integer greater than or equal to 3. The electric machine12is a motor or a generator.

In the example ofFIG. 1, the electric machine12is a three-phase machine, and P is equal to 3, the three phases22being respectively denoted U, V, W.

The electric starter14includes at least P-1 switching arms24, each switching arm24being adapted to be connected to a respective phase22of the electric machine12. Each switching arm24is switchable between a closed position in which the current flows through said arm and an open position in which no current flows through said arm. Each switching arm24includes at least one switch26. Preferably, each switching arm24includes two switches26connected in anti-parallel, as represented inFIG. 1. In this example, each switching arm24consists of two switches26connected in anti-parallel. Each switch26is a controllable switch, for example a thyristor as shown inFIG. 1, or a transistor.

When a respective switch26is a thyristor, the skilled person will understand that the expression “to open” related to the switching arm(s)24including such a switch26should be understood as “to be kept open”. Indeed, a thyristor can be controlled to be closed, but opens itself according to forward current condition, going back to zero.

In the example ofFIG. 1, the electric starter14includes P switching arms24, namely a switching arm24for each respective phase22of the electric machine12.

The alternative power source16is known per se, with also P phases.

The determination device20is configured for determining the at least one characteristic parameter Rs, Rreq, Lf, L of the electric machine12. Each characteristic parameter is preferably chosen from among the group consisting of: a stator resistance Rsof the electric machine12; a rotor resistance Rreqof the electric machine12; a leakage inductance Lf of the electric machine12; and a main inductance L of the electric machine12.

The determination device20comprises a control module30for controlling the switching arms24of the electric starter14, so as to generate a current injection32on two phases22of the electric machine12, as shown inFIG. 2and explained in further detail hereinafter.

The determination device20further comprises an acquisition module34for acquiring measurements of respective currents I1, I2and voltages U1, U2for said two phases, further to the generation of the current injection32.

The determination device20also comprises a calculation module36for calculating the at least one characteristic parameter Rs, Rreq, Lf, L of the electric machine12according to the respective currents I1, I2and voltages U1, U2measurements.

As an optional aspect, the determination device20is configured for determining a respective characteristic parameter Rs, Rreq, Lf, L of the electric machine12in at least two successive sequences. According to this optional aspect, the control module30is configured to control the switching arms24of the electric starter14, so as to generate a current injection32on two phases22of the electric machine12, in particular to control respective switching arm(s)24to close and another switching arm24to open; the acquisition module34being configured to acquire measurements of respective current(s) and voltage(s) for said two phases22, further to the generation of the current injection32; and the calculation module36being configured to calculate the characteristic parameter Rs, Rreq, Lf, L of the electric machine12according to the respective current(s) and voltage(s) measurements for the respective sequence. Further, the open switching arm24varies from one sequence to the other, preferably so that each one of at least two switching arms24is opened once during the successive sequences.

According to this optional aspect, the determination device20further comprises a diagnostic module38for comparing the at least two values determined for a respective characteristic parameter Rs, Rreq, Lf, L over the successive sequences and for generating an alarm signal in the event of a deviation between these at least two determined values exceeding a predefined threshold.

In the example ofFIG. 1, the electronic determination device20includes a processing unit40formed for example of a memory42and of a processor44coupled to the memory42.

In the example ofFIG. 1, the control module30, the acquisition module34and the calculation module36, as well as in optional aspect the diagnostic module38, are for example each realized, i.e. implemented, as a software executable by the processor44. The memory42of the processing unit40is adapted to store a control software for controlling the switching arms24of the electric starter14, so as to generate a current injection32on two phases22of the electric machine12; an acquisition software for acquiring measurements of respective currents I1, I2and voltages U1, U2for said two phases, further to the generation of the current injection32; and a calculation software for calculating the at least one characteristic parameter Rs, Rreq, Lf, L of the electric machine12according to the respective currents I1, I2and voltages U1, U2measurements; as well as in optional aspect, a diagnostic software for comparing the at least two values determined for a respective characteristic parameter Rs, Rreq, Lf, L over the successive sequences and for generating an alarm signal in the event of a deviation between these at least two determined values exceeding a predefined threshold. The processor44of the processing unit40is then configured to execute the control software, the acquisition software, and the calculation software, as well as in optional aspect the diagnostic software.

As a variant not shown, the control module30, the acquisition module34and the calculation module36, as well as in optional aspect the diagnostic module38, are each in the form of a programmable logic component, such as a Field Programmable Gate Array or FPGA, or in the form of a dedicated integrated circuit, such as an Application Specific integrated Circuit or ASIC.

When the electronic determination device20is in the form of one or more software programs, i.e. in the form of a computer program, it is also capable of being recorded on a computer-readable medium, not shown. The computer-readable medium is, for example, a medium capable of storing electronic instructions and being coupled to a bus of a computer system. For example, the readable medium is an optical disk, a magneto-optical disk, a ROM memory, a RAM memory, any type of non-volatile memory (for example EPROM, EEPROM, FLASH, NVRAM), a magnetic card or an optical card. A computer program with software instructions is then stored on the readable medium.

The control module30is configured to control respective switching arm(s)24to close and the other switching arm(s)24to open, so as to generate the current injection32on two phases22of the electric machine12.

The skilled person will understand that when the control module30controls switching arm(s)24to close, it means that said switching arm(s)24are switched to their closed position; and respectively when the control module30controls switching arm(s)24to open, it means that said switching arm(s)24are switched to their open position.

When the electric starter14includes P switching arms24, namely a switching arm24for each respective phase22of the electric machine12, the control module30is configured to control two respective switching arms24to close and the other switching arm(s)24to open, so as to generate the current injection32on said two phases22. In other words, when the electric starter14includes P switching arms24, the control module30is configured to control two respective switching arms24to close and (P-2) switching arm(s)24to open, so as to generate said current injection32. In the example ofFIGS. 1 and 2, where P is in particular equal to 3, the control module30is therefore configured to control two respective switching arms24to close and the other switching arm24to open, so as to generate said current injection32.

In the example ofFIG. 2, the control module30is configured to control the switching arms24for phases U, V to close and the other switching arm24for phase W to open, so as to generate the current injection32on phases U, V. InFIG. 2, a first current curve50, and respectively a second current curve52, represent a current of the electric machine12, hereinafter called machine current, and respectively the machine current in phase V, while a third current curve54represents the machine current in phase W, said third current curve54being null since the switching arm24for phase W remains open in this example. In thisFIG. 2, a first voltage curve60, and respectively a second voltage curve62, represent a voltage of the electric machine12, hereinafter called machine voltage, in phase U, and respectively the machine voltage in phase V, while a third voltage curve64represents the machine voltage in phase W.

In addition, the control module30is configured, further to the generation of the current injection32occurring at an initial time instant tinit, to control at an end time instant tendthe respective previously closed switching arms24to open, so as to switch off the current injection32.

A duration of the current injection32between the initial time instant tinitand the end time instant tendis preferably a predefined time period T, shown inFIG. 2. The predefined time period T is preferably greater than five times a rotor time constant Tr. This ratio between the predefined time period T and the rotor time constant Tr allows to have the stabilization of a flux of the electric machine12, in particular for the calculation of the stator resistance Rs.

In optional addition, to avoid a knowledge on a power of the electric machine12, the duration time is chosen according to the power of the electric starter14or else is fixed, with no dependency on the power of the electric machine12or of the electric starter14. In this latter case, predefined time period T is for example equal to 10 seconds, which covers all the power range of the electric machine12.

Further to the generation of the current injection32at the initial time instant tinitand during said current injection, i.e. before the end time instant tend, the acquisition module34is configured to acquire measurements of respective current(s) and voltage(s) for said two phases22where the current injection32is present. For example, the acquisition module34is configured to acquire measurements of a first current I1and a first voltage U1in a first phase22, and respectively of a second current I2and a second voltage U2in a second phase22, where the current injection32is present.

The calculation module36is configured to calculate the at least one characteristic parameter Rs, Rreq, Lf, L of the electric machine12according to said respective current(s) I1, I2and voltage(s) U1, U2measurements.

The calculation module36is for example configured to calculate a value of a stator voltage Usfor a stator of the electric machine12from the voltages measurements U1, U2for said two phases22, and respectively a value of a stator current Isfor the stator from the currents measurements I1, I2for said two phases22, the calculation module36being further configured to calculate the at least one characteristic parameter Rs, Rreq, Lf, L of the electric machine12according to said stator voltage Usand stator current Isvalues.

According to this example, the calculation module36is typically configured to calculate the respective stator voltage Usand stator current Isvalues according to a transformation applied to the respective voltages measurements U1, U2and currents measurements I1, I2for said two phases22. The applied transformation is for example a Clark's transformation.

According to this example, the calculation module36is preferably configured to calculate the respective stator voltage Usand stator current Isvalues via the following equations:

where Usrepresents the stator voltage,

U1, and respectively U2, represent the voltage in a first phase22, and respectively in a second phase22;

Isrepresents the stator current, and

I1, and respectively I2, represent the current in a first phase22, and respectively in a second phase22.

The calculation module36is alternatively configured to calculate the respective stator voltage Usand stator current Isvalues via the following equations:

where Us, U1, U2, Is, I1and I2represent the same variables as the ones aforementioned for equations (1) and (2).

When the calculated characteristic parameter of the electric machine12is the stator resistance Rs, the calculation module36is for example configured to calculate said stator resistance Rsfrom an integral of the stator voltage Us, such as the one defined by equation (1), and an integral of the stator current Is, such as the one defined by equation (2), over the duration of the current injection32.

According to this example, the calculation module36is preferably configured to calculate the stator resistance Rsvia the following equation:

where Rsrepresents the stator resistance;

tinitrepresents the initial time instant of the measurement during current injection32; alternatively, the initial time instant is equal to 0, i.e. the beginning of the sequence;

tendrepresents the end time instant of said measurement, alternatively, the end time is at the end of the full sequence; and

T represents the duration of said measurement.

Alternatively, the calculation module36is configured to calculate a ratio between a filtering of the stator voltage Usand a filtering of the stator current Is.

Since the stator voltage Usand the stator current Isare typically vectors, there are different variants to calculate the stator resistance Rsof the electric machine12.

According to a first variant, the stator resistance Rsis calculated on each direction of a representative frame, such as a dq frame, known per se.

According to a second variant, the stator resistance Rsis calculated based on the module of the vectors, i.e. via the following equation:

where Rsdrepresents the stator resistance Rson the d axis of the dq frame, and

Rsqrepresents the stator resistance Rson the q axis of said dq frame.

When the calculated characteristic parameter of the electric machine12is the rotor resistance Rreq, the calculation module36is further configured to calculate a total resistance Rtotof the electric machine12from the stator voltage Usand stator current Isat a time instant to corresponding to a maximum of the stator current Isfurther to the generation of the current injection32, the total resistance Rtotbeing equal to the sum of the stator resistance Rsand the rotor resistance Rreq.

According to this example, the calculation module36is preferably configured to calculate the total resistance Rtotvia the following equation:

where Rtotrepresents the total resistance,

Isrepresents the stator current, and

t0represents the time instant corresponding to a maximum of the stator current.

Alternatively, the calculation module36is configured to calculate a function of respective averages of the stator voltage Usand the stator current Is when arm is closed, i.e. while the current is non zero.

The calculation module36is then configured to determine a value of the rotor resistance Rreqfrom the previously calculated values of the stator resistance Rsand the total resistance Rtot, by subtracting the value of the stator resistance Rsfrom the value of the total resistance Rtot.

The time instant t0corresponding to the maximum of the stator current Isis typically around 5 ms after the start of the injection, i.e. around 5 ms after the initial time instant tinit.

As for the stator resistance Rs, the calculation of the total resistance Rtotis for example done on each direction of the representative frame, such as the dq frame, according to a first variant; or based on the module of the vectors, according to a second variant.

According to said first variant, the value of total resistance Rtotis for example the mean of both stator resistance Rsand rotor resistance Rreq. Further, it may allow to detect a problem on the electric machine12if there is an important difference between both resistances Rsand Rreq.

According to said second variant, the total resistance Rtotis calculated based on the module of the vectors, i.e. via the following equation:

In addition, there are also several alternatives to acquire the currents I1, I2and voltages U1, U2at the time instant t0corresponding to the maximum of the stator current Is. According to a first alternative, at each sampling period, the currents I1, I2and voltages U1, U2are acquired only if the new value of the current is higher than the previously acquired one. If there is no update during a given time period, for example 10 ms, the last acquired values correspond to the maximum of current and the equivalent voltage. According to a second alternative, the currents I1, I2and voltages U1, U2are acquired at each sampling time from the initial time instant tinitand this acquisition is stopped when a respective current I1, I2becomes null. The maximum of current is then obtained by post treatment of the acquired data.

When the calculated characteristic parameter of the electric machine12is the leakage inductance Lf, the calculation module36is configured to calculate said leakage inductance Lf from the stator voltage Usand a time derivative of the stator current Isfurther to the generation of the current injection32.

According to this example, the calculation module36is preferably configured to calculate the leakage inductance Lf via the following equation:

where Lf represents the leakage inductance,

Usrepresents the stator voltage, and

As for the stator resistance Rsand the total resistance Rtot, the calculation of the leakage inductance Lf is for example done on each direction of the representative frame, such as the dq frame; or based on the module of the vectors.

In addition, there are also several alternatives to compute the time derivative of the stator current Is. According to a first alternative, the calculation module36is configured to calculate the leakage inductance Lf via the following equation:

with ΔT the time between two acquisition time instants;

which leads typically to the following equation:

with t2−t1=ΔT,

t1being chosen nearest after the initial time instant tinit.

According to a second alternative, the currents I1, I2and voltages U1, U2are acquired at each sampling time from the initial time instant tinit, and the time derivative of the stator current Isis then obtained by post treatment of the acquired data.

When the calculated characteristic parameter of the electric machine12is the main inductance L, the calculation module36is configured to calculate said main inductance L from the leakage inductance Lf, the stator current Isand an integral φsof a stator flux Ψsover the duration of the current injection32.

According to this example, the calculation module36is preferably configured to calculate the main inductance L via the following equation:

where L represents the main inductance,

Lf represents the leakage inductance,

Isrepresents the stator current, and

φsrepresents the integral of the stator flux over duration of the current injection32;

φsbeing preferably defined via the following equation:
φs=∫tinittend=tinit+T(Us−RsIs)dt(13)

tinitrepresents the initial time instant of the current injection32,

tendrepresents the end time instant of the current injection32, and

T represents the duration of the current injection32.

As for the stator resistance Rs, the total resistance Rtotand the leakage inductance Lf, the calculation of the main inductance L is for example done on each direction of the representative frame, such as the dq frame; or based on the module of the vectors.

In addition, there are also several alternatives to compute the integral of equation (13), among which the one wherein the currents I1, I2and voltages U1, U2are acquired at each sampling time from the initial time instant tinit, and said integral is then obtained by post treatment of the acquired data.

The calculation module36is therefore configured to calculate the four aforementioned characteristic parameters Rs, Rreq, Lf, L of the electric machine12during the injection of current, further to the control, by the control module30, of the respective switching arm(s)24to close and the other switching arm(s)24to open.

According to the optional aspect, in the example ofFIG. 1, the determination device20is preferably configured for determining a respective characteristic parameter Rs, Rreq, Lf, L of the electric machine12in three successive sequences. Therefore, the open switching arm24varies from one sequence to the other, preferably so that each one of the three switching arms24is opened once during the three successive sequences.

Accordingly, in the example ofFIG. 1, the diagnostic module38is configured for comparing the at least two values, preferably the three values, determined for a respective characteristic parameter Rs, Rreq, Lf, L over the successive sequences and for generating an alarm signal in the event of a deviation between these determined values exceeding a predefined threshold.

The operation of the power supply chain10, in particular the determination device20, according to the first embodiment will now be explained in view ofFIG. 3representing a flowchart of a method, according to the first embodiment, for determining the at least one characteristic parameter Rs, Rreq, Lf, L of the electric machine12.

In initial step100, the electronic determination device20controls, via its control module30, respective switching arm(s)24to close and the other switching arm(s)24to open, so as to generate the current injection32on two phases22of the electric machine12. In particular, when the electric starter14includes P switching arms24, the control module30controls two respective switching arms24to close and (P-2) switching arm(s)24to open, so as to generate said current injection32. In the example ofFIGS. 1 and 2, with P equal to 3, the control module30therefore controls two respective switching arms24to close and the other switching arm24to open, for generating said current injection32.

Further to the generation of the current injection32at the initial time instant tinitand during said current injection, i.e. before the end time instant tend, the electronic determination device20acquires, in step110and via its acquisition module34, measurements of respective current(s) and voltage(s) for said two phases22where the current injection32is present. In particular, the acquisition module34acquires measurements of the first current I1and the first voltage U1in the first phase22, and respectively of the second current I2and the second voltage U2in the second phase22.

In addition, further to the generation of the current injection32occurring at an initial time instant tinit, the control module30controls at the end time instant tendthe respective previously closed switching arms24to open, so as to switch off the current injection32.

Then, during next step120, the electronic determination device20calculates, via its calculation module36, the at least one characteristic parameter Rs, Rreq, Lf, L of the electric machine12according to said respective current(s) I1, I2and voltage(s) U1, U2measurements.

The calculation module36for example calculates a value of the stator voltage Usfrom the voltages measurements U1, U2for said two phases22, and respectively a value of the stator current Isfrom the currents measurements I1, I2for said two phases22, and then calculates the at least one characteristic parameter Rs, Rreq, Lf, L according to said stator voltage Usand stator current Isvalues. The respective stator voltage Usand stator current Isvalues are typically calculated according to a respective transformation, such as the Clark's transformation, applied to the respective voltages measurements U1, U2and currents measurements I1, I2for said two phases22, for example according to equations (1) and (2), or to equations (3) and (4).

Further, when the calculated characteristic parameter of the electric machine12is the stator resistance Rs, the calculation module36for example calculates said stator resistance Rsfrom the integral of the stator voltage Usand the integral of the stator current Isover the duration of the current injection32, typically according to aforementioned equation (5) or (6).

When the calculated characteristic parameter of the electric machine12is the rotor resistance Rreq, the calculation module36further calculates the total resistance Rtotfrom the stator voltage Usand stator current Isat the time instant t0corresponding to the maximum of the stator current Isfurther to the generation of the current injection32, typically according to aforementioned equation (7) or (8).

When the calculated characteristic parameter of the electric machine12is the leakage inductance Lf, the calculation module36for example calculates said leakage inductance Lf from the stator voltage Usand the time derivative of the stator current Isfurther to the generation of the current injection32, typically according to aforementioned equation (9), (10) or (11).

When the calculated characteristic parameter of the electric machine12is the main inductance L, the calculation module36for example calculates said main inductance L from the leakage inductance Lf, the stator current Isand the integral φsof the stator flux Ψsover the duration of the current injection32, typically according to aforementioned equations (12) and (13).

In the example ofFIG. 1, during the initial control step100, the switching arms24for phases U and V are for example controlled to close and the one for phase W controlled to open, so that the current injection32is generated on phases U, V and the acquisition step110, the calculation step120are then carried out for these two phases U, V.

Then, during next step130, also called first repetition step130, the electronic determination device20repeats, respectively via its control module30, its acquisition module34and its calculation module36, the control step100, the acquisition step110and the calculation step120for another phase22being open.

For example, during the first repetition step130, the switching arms24for phases U and W are controlled to close and the one for phase V controlled to open, so that the current injection32is generated on phases U, W and the first repetition step130is further carried out for these two phases U, W.

Then, during next step140, also called second repetition step140, the electronic determination device20repeats, respectively via its control module30, its acquisition module34and its calculation module36, the control step100, the acquisition step110and the calculation step120for yet another phase22being open.

For example, during the second repetition step140, the switching arms24for phases V and W are controlled to close and the one for phase U controlled to open, so that the current injection32is generated on phases V, W and the first repetition step130is further carried out for these two phases V, W.

Lastly, during next step150, the electronic determination device20monitors, via its diagnostic module38, the electric machine12according to the at least one calculated characteristic parameter Rs, Rreq, Lf, L of the electric machine12. In particular, and according to the optional aspect, the diagnostic module38compares the at least two values determined for a respective characteristic parameter Rs, Rreq, Lf, L over the successive sequences and generates the alarm signal in the event of a deviation between these at least two determined values exceeding the predefined threshold.

The skilled person will observe that the electronic determination device20carries out a given sequence only once for the determination of the at least one characteristic parameter Rs, Rreq, Lf, L; or else carries out two or three respective sequences successively by changing the open arm of the electric starter14from one sequence to the other, thereby allowing the diagnostic of the electric machine12.

Furthermore, the electronic determination device20carries out a given sequence or successive sequences on a regular basis, for example:at each startup of the electric machine12, which allows typically the initialization of a thermal state of the electric machine12for purpose of protection, and the identification of the machine resistances for better torque control;at each stop of the electric machine12, for example to estimate a current thermal state of the electric machine12, and allow or block the next machine start during a given time;on demand, to compare the results and see a potential deviation in the evolution of the different machine resistances. In addition, if—further to the aforementioned comparison—an imbalance is detected between phases22of the electric machine12, then it is recorded.

This determination of the at least one characteristic parameter Rs, Rreq, Lf, L of the electric machine12allows several advantages. Based on the calculated stator resistance Rs, the torque estimation is improved for a better torque control of the electric machine12. Further, the calculated stator resistance Rsand inductance L allow a better estimation of a mechanical speed of the electric machine12. Another benefit is the estimation of the machine thermal state based on the calculated stator resistance Rsand the calculated rotor resistance Rreq. Based on this data, the protection of the electric machine12is improved and the electric starter14can authorize or not a next start of the electric machine12or begin a temporization before the next start of the electric machine12.

FIGS. 4 and 5illustrate a second embodiment, for which elements similar to the first embodiment described above are identified by identical references.

According to the second embodiment, the electric starter14includes only P-1 switching arms24, namely a switching arm24for P-1 phases22of the electric machine12while the remaining phase22of the electric machine12is directly and permanently, i.e. continuously, connected to the alternative power source16, in particular to its corresponding phase.

According to this second embodiment, the control module30is configured to control one respective switching arm24to close and the other switching arm(s)24to open, so as to generate the current injection32on two phases22, namely on the phase for which the switching arm24is controlled to close and on the phase which is permanently connected to the alternative power source16. In other words, according to this second embodiment, the control module30is configured to control a single respective switching arm24to close and (P-2) switching arm(s)24to open, so as to generate said current injection32. In the example ofFIG. 4, where P is in particular equal to 3, the control module30is therefore configured to control a respective switching arm24to close and the other switching arm24to open, so as to generate said current injection32.

In addition, the control module30is configured, further to the generation of the current injection32occurring at an initial time instant tinit, to control at an end time instant tendthe respective previously closed switching arm24to open, so as to switch off the current injection32.

According to the optional aspect, in the example ofFIG. 4, the determination device20is configured for determining a respective characteristic parameter Rs, Rreq, Lf, L of the electric machine12in two successive sequences. Therefore, the open switching arm24varies from one sequence to the other, preferably so that each one of the two switching arms24is opened once during the two successive sequences.

Accordingly, in the example ofFIG. 4, the diagnostic module38is configured for comparing the two values determined for a respective characteristic parameter Rs, Rreq, Lf, L over the two successive sequences and for generating an alarm signal in the event of a deviation between these two determined values exceeding a predefined threshold.

The operation of the power supply chain10, in particular the determination device20, according to the second embodiment will now be explained in view ofFIG. 5representing a flowchart of a method, according to the second embodiment, for determining the at least one characteristic parameter Rs, Rreq, Lf, L of the electric machine12.

According to the second embodiment, in initial step100, the electronic determination device20controls, via its control module30, one respective switching arm24to close and the other switching arm(s)24, i.e. P-2 switching arm(s)24, to open, so as to generate the current injection32on two phases22of the electric machine12. In the example ofFIG. 4, with P equal to 3, the control module30therefore controls one respective switching arm24to close and the other switching arm24to open, for generating said current injection32.

According to the second embodiment, the acquisition step110, the calculation step120, the first repetition step130and the monitoring step150are similar to the acquisition step110, the calculation step120, the first repetition step130and the monitoring step150of the first embodiment, described above, and are therefore not described again.

The skilled person will observe that the second repetition step140is not carried out according to the second embodiment, since there is one phase for which the electric starter14is not open due to the permanent connection of the electric machine12to the alternative power source16for said phase. In the example ofFIG. 4, said phase for which the electric starter14is not open is the phase U.

In other words, in the example ofFIG. 4, during the initial control step100, the switching arm24for phase V is for example controlled to close and the switching arm24for phase W controlled to open, so that the current injection32is generated on phases U, V and the acquisition step110, the calculation step120are then carried out for these two phases U, V.

Then, during the first repetition step130, the switching arm24for phase W is controlled to close and the switching arm24for phase V controlled to open, so that the current injection32is generated on phases U, W and the first repetition step130is further carried out for these two phases U, W.

The advantages of the second embodiment are similar to those of the first embodiment, described above, and are therefore not described again.