Method for estimating in operation the temperature of the rotor of a permanent-magnet synchronous electric machine

Abstract

The invention provides a method for estimating the operating temperature (of the rotor of a permanent-magnet synchronous electric machine consisting in E3) in a phase of use during which no torque is requested: E31) determining an internal control voltage and measuring the speed of rotation of the rotor; E32) calculating a corrected value of the internal control voltage equal to the quotient of said voltage and a correction factor (expressing a ratio between an induced voltage measured at the end of manufacture and an induced voltage of a reference machine); and E33) estimating a value of the operating temperature of the rotor that is obtained, using a model, for the measured speed of rotation and the corrected value of the internal control voltage.

Description

[0001] Description

[0002] Method for estimating the rotor temperature of a permanent magnet synchronous electric machine during operation

[0003] Technical field of the invention

[0004] [1]The invention relates to a method for estimating the temperature of the rotor of a permanent magnet synchronous electric machine, also called a PMSM (Permanent Magnet Synchronous Machine).

[0005] [2]The invention relates, for example, to the temperature of the rotor of a permanent magnet synchronous electric motor belonging to the propulsion system of an electric or hybrid propulsion vehicle.

[0006] Technical background of the invention

[0007] [3]During operation or use, the rotor temperature is important for the protection of the components of the electrical machine. The rotor temperature is particularly necessary to apply the correct parameters to the machine (currents, voltages) and to protect the permanent magnets from overheating.

[0008] [4]But the temperature cannot be determined directly using existing technologies, because no temperature sensor can be installed in the rotor to provide an instantaneous measured value of this temperature.

[0009] [5]Since the rotor is a moving part, direct temperature measurement is only possible in the laboratory (e.g. by telemetry or infrared measurements).

[0010] [6]For serial applications, it is necessary to use temperature modeling (e.g. using Tau models, neural networks, etc.).

[0011] [7]Tau models require extensive setup work to cover all the conditions under which the electrical machine will be used: electrical power, motor speed (due to internal fans used for cooling), inverter coolant temperature (due to conduction effects between the inverter and the motor), ambient temperature, airflow / air direction around the machine.

[0012] [8]A neural network must also be trained under these different usage conditions, with the additional critical risk of providing inaccurate values ​​if the machine is used and operates in an area that has not been trained.

[0013] [9]Another possibility is to use the property of permanent magnet synchronous electric machines (PMSM) to generate a back-EMF (Back Electromotive Force) under certain conditions. Such a solution is described in document CN103888041 A, but the non-linear relationship between flux and temperature makes measurements on "multiple" samples, at multiple temperatures, necessary.

[0010] These two possibilities are only valid for a given configuration and must be re-parameterized in the event of modifications to the hardware design or changes in the environment of the electric machine.

[0014] Summary of the invention

[0015]

[0011] The invention proposes a method for estimating the operating temperature of the rotor of a given permanent magnet synchronous electric machine, a method comprising the following step and sub-steps:

[0016] - E3) in operation of said specific electrical machine, in a phase of use during which no torque is required:

[0017] — E31) determine an internal control voltage and measure the rotor rotation speed;

[0018] — E32) calculate a corrected value of said internal control voltage which is equal to the quotient of said voltage by a correction factor reflecting a ratio between:

[0019] * an induced voltage measured at the end of manufacture on said electrical machine determined for a known temperature and rotor rotation speed,

[0020] * and an induced voltage of a reference electrical machine under the same temperature and rotor rotation speed conditions;

[0021] — E33) estimate a value of the operating temperature of the rotor of said determined electrical machine which is obtained by using a model, linking the reference induced voltage, the reference rotation speed and the reference temperature of the rotor of a reference electrical machine, for said measured rotation speed and said corrected value of said internal control voltage.

[0022]

[0012] According to other characteristics of the process:

[0023] - it also includes the following steps:

[0024] - E0) for a reference electrical machine, develop a model linking the reference induced voltage, the reference rotation speed and the reference rotor temperature;

[0025] - E1) for said determined electrical machine, measure at the end of manufacture and store an induced voltage, a temperature and a rotation speed of the rotor;

[0026] - E2) for said determined electrical machine, calculate and store said correction factor equal to the quotient of said induced voltage at the end of manufacture by an estimated value of the reference induced voltage which is obtained by using said model for the rotation speed and said rotor temperature measured at the end of manufacture;

[0027] - in a reference frame of axes d and q linked to the rotor, the currents Id, of phase d, and Iq, of phase q are measured, from which the said internal control voltage is determined;

[0028] - said induced voltage, said temperature and said rotor rotation speed measured are stored in a memory integrated into said determined electrical machine or into equipment of this machine;

[0029] - said correction factor is stored in a memory integrated into said specific electrical machine or into equipment of this machine.;

[0030] - the phase of use during which no torque is required from the determined permanent magnet synchronous electric machine, is a phase of torque control at a set value equal to zero Nm.

[0031]

[0013] The invention also proposes a calculator characterized in that it comprises at least one memory for storing the correction factor and is configured to implement an estimation according to the method according to the invention.

[0032]

[0014] The invention also proposes a belt-driven electric starter generator system, in particular for a powertrain assembly of a motor vehicle, comprising a determined permanent magnet synchronous electric motor comprising a rotor whose temperature, in use, is intended to be estimated according to the method according to the invention, characterized in that it comprises at least one memory unit for storing said induced voltage, said temperature and said measured rotor rotation speed, and / or storing the correction factor.

[0033] Detailed description of the invention

[0034]

[0015] In the following description, identical, similar or analogous elements will be designated by the same numerical or alphanumeric references.

[0035]

[0016] A specific electrical machine M will be called a synchronous electrical machine (or PMSM - Permanent Magnet Synchronous Machine) comprising a rotor Rot with permanent magnets whose operating (or use) temperature "T" is to be estimated when it is powered and when no torque is required.

[0036]

[0017] We call "œ" the speed or rotational regime of the rotor Rot of the machine M and "U" its induced voltage (or "BEMF - Back Electro Magnetic Force" or "FCEM - Counter Electromotive Force").

[0037]

[0018] The electrical machine M is for example a permanent magnet synchronous motor which is an alternating current (AC) synchronous motor, whose EMC waveform is sinusoidal and whose field excitation is provided by permanent magnets.

[0038]

[0019] The power density of such an MSAP motor is higher than that of induction motors with the same nominal values, because there is no rotor power dedicated to the production of magnetic field.

[0039]

[0020] Such an MSAP motor can provide torque at zero speed (œ=0), and it requires a digitally controlled inverter for its operation.

[0040]

[0021] The control of such an MSAP motor is characterized by smooth rotation throughout the motor speed range, zero-speed torque control, and rapid acceleration / deceleration.

[0022] To achieve such control, such MSAP motors use vector control techniques. Vector control techniques are generally referred to as Field-Oriented Control (FOC).

[0041]

[0023] The vector control algorithm decomposes a stator current into a magnetic field generating component and a torque generating component; both components can be controlled separately after the vector decomposition.

[0042]

[0024] As a non-limiting example, such an MSAP motor may belong to a device or system called “BSG” (Belt-Driven Starter Generator, also called belt-driven starter generator) forming an integral part of a propulsion system of a hybrid electric vehicle (HEV) or an electric vehicle (EV).

[0043]

[0025] A BSG system can provide functions such as stop-start, freewheeling and electrical backup. The BSG system can, for example, consist of an MSAP motor with an integrated converter and inverter. It can be air-cooled or liquid-cooled.

[0044]

[0026] One of the characteristics of permanent magnet synchronous machines is to generate an induced voltage (BEMF) when they rotate without being controlled (freewheel mode, with all the "MOSFETS" (Metal-Oxide-Semiconductor Field-Effect Transistors or metal-oxide-semiconductor field-effect transistors) open).

[0045]

[0027] If the BSG system is not connected to a storage battery, this induced voltage (BEMF) can be measured externally (AC voltage (Alternating Current) between the inverter and the motor, or DC voltage (Direct Current) on the DC side of the inverter).

[0046]

[0028] But in use, on board a vehicle, it is not possible to measure the induced voltage (BEMF) because the inverter is always connected to the battery. In addition, it is generally not possible to operate the inverter in freewheel mode, which is considered a safe state. The electric motor is generally used for torque control.

[0047]

[0029] In order to determine the temperature of the rotor Rot, it appeared possible to replace the measurement of the induced voltage (BEMF), by an internal control voltage Uq determined for example from phase current measurements, and to replace the freewheeling periods of the electrical machine by torque control periods with a zero torque set point.

[0048]

[0030] For such a set point, the value of the current " / " on the d and q axes is assimilated to zero, the voltage Uq then being proportional to the flux psi of the rotor Rot, this flux itself being proportional to the temperature of the magnets.

[0031] The temperature of the permanent magnets corresponds to the temperature of the rotor. The induced voltage of the permanent magnets can be determined from an internal control voltage in alternating current AC.

[0049]

[0032] The alternating voltage is regulated in the coordinate system "dq", which is another representation of the three-phase system UVW which are for example the three letters used to represent the windings.

[0050]

[0033] The formulas generally valid for the alternating voltage in the coordinate system dq according to the two orthogonal axes d and q angularly linked to the rotor are the following:

[0051] [Formula 1]

[0052] [Formula 2]

[0053] [Formula 3]

[0054] [Formula 4]

[0055]

[0034] Formulas in which:

[0056] L is the inductance, 4 is the flux, u is the voltage, i the current, ÙJ is the speed

[0057]

[0035] In the absence of current on the d and q axes, the voltage Uq is proportional to the flux 4 of the rotor, which is itself proportional to the temperature of the magnets.

[0036] The problem with this method is that the voltage is not very sensitive to the temperature and, when we take into account the unit-by-unit (machine-by-machine) deviations, we see that this introduces a very significant error in the temperature value.

[0058]

[0037] For example, by comparing the temperature which would be estimated from a “nominal” electrical machine and that of a “maximum” machine, the difference in values ​​can reach 30°C for a temperature T of 100°C.

[0059]

[0038] The estimation principle according to the invention aims to compensate for these differences between the different units or machines manufactured in series, in particular:

[0060] - using the value of the induced voltage (BEMF) and the value of the temperature and the associated rotation speed - at the end of the production line (eol = End Of Line) and for each unit or machine manufactured - which are measured and are stored completely, for example in an integrated memory of the BSG system;

[0061] - and, for each unit or machine manufactured, by developing a corrective factor to take into account the dispersion effect in the mass production of electric units or motors.

[0062]

[0039] Thus the invention proposes a method for estimating the operating temperature Tfct of the rotor of a given permanent magnet synchronous electric machine M, which is characterized by a step E3) comprising a first sub-step E31) - carried out in operation of the machine M during a phase of use during which no torque is requested from the machine M - during which an internal control voltage Uqfct is determined and the rotation speed cofct of the rotor is measured.

[0063]

[0040] To determine this internal control voltage Uqfct, in the d and q axis reference frame linked to the rotor, the currents Id, of phase "d", and Iq, of phase "q", are measured, from which, for example using software for controlling the torque of the machine, the internal control voltage Uqfct is obtained.

[0064]

[0041] For example, in the case where the determined machine M is a motor belonging to a BSG system forming an integral part of a propulsion system of an electric or hybrid electric vehicle, this is the software for controlling the torque supplied by the motor when it is supplied with current.

[0065]

[0042] The phase of use during which no torque is requested from the electric machine M, is a phase of controlling the torque at a setpoint value Ccons equal to zero Nm.

[0066]

[0043] Without departing from the scope of the invention, this setpoint value Ccons may be a reduced value of the torque, close to zero Nm, corresponding to a minimum torque value intended to compensate for the losses linked to the rolling resistance of the rotating machine, taking into account the fact that the higher the rotation speed, the greater these losses.

[0044] During a second sub-step E32), a corrected value Umcor of the internal control voltage Uqfct obtained at the end of the first sub-step E31) is calculated according to the formula:

[0067] Umcor = Uqfct / Fcor

[0068] In this quotient, Fcor is a correction factor reflecting a ratio between:

[0069] - an induced voltage Ueol measured on said machine M at the end of manufacturing, for example at the end of the manufacturing line, for a known temperature Teol and rotor rotation speed coeol;

[0070] - and an estimated value Uzéro of the reference induced voltage of a reference electrical machine Mref for the same conditions of Teol temperature and coeol rotor rotation speed.

[0071]

[0045] The estimated value Uzéro of the reference induced voltage is for example obtained by using a suitable model - linking the reference induced voltage Uref) the reference rotation speed coref and the reference temperature Tref of the rotor of a reference electrical machine Mref - for the rotation speed coeol) and said temperature Teol) of the rotor measured at the end of manufacturing.

[0072]

[0046] During a third sub-step E33), the value Tfct of the operating temperature of the rotor of said determined electrical machine (M) is estimated using said model for said measured rotation speed cofct and said corrected value Umcor of said internal control voltage Uqfct.

[0073]

[0047] Thus, in operation, an estimated value Tfct of the rotor of the electric machine is obtained.

[0074]

[0048] The model mentioned above can be developed, for example by mathematical modeling of the reference machine Mref or by mapping, during a prior step E0).

[0075]

[0049] We thus develop a model linking the reference induced voltage Uref, the reference rotation speed coref and the reference temperature Tref of the rotor.

[0076]

[0050] During a measurement step E1), for each electrical machine produced or manufactured, for example at the end of the production line, its induced voltage Ueol, its temperature Teol and its rotor rotation speed coeol Rot are measured.

[0077]

[0051] Preferably, these three values ​​Ueol, Teol and coeol are memorized by storing them in a memory integrated into this specific electrical machine or integrated into electronic equipment of this machine, and for example integrated into a BSG system as mentioned previously.

[0078]

[0052] During a step E2) for each electrical machine produced or manufactured, for example at the end of the manufacturing line, a correction factor Fcor is calculated and then stored, which is equal to the quotient Ueol / Uzéro of the voltage Ueol induced at the end of the manufacturing line by an estimated value Uzéro of the reference induced voltage which is obtained - using the model (for example developed during the prior step EO)) - for the rotation speed coeol and the temperature Teol of the rotor measured at the end of the manufacturing line.

[0079]

[0053] Similarly, preferably, the correction factor Fcor is memorized by storing it in a memory integrated into the determined electrical machine or into electronic equipment of this machine, and for example integrated into a BSG system as mentioned previously.

Claims

Claims

1. Method for estimating the operating temperature (Tfct) of the rotor of a determined permanent magnet synchronous electric machine (M), method comprising the following step and sub-steps: - E3) in operation of said determined electrical machine (M), in a phase of use during which no torque is required: — E31) determine an internal control voltage (Uqfct) and measure the rotation speed (cofct) of the rotor; — E32) calculate a corrected value (Umcor) of said internal control voltage (Uqfct) which is equal to ((Umcor) = (Uqfct) / Fcor) the quotient of said voltage (Uqfct) by a correction factor (Fcor) translating a ratio between: * an induced voltage (Ueol) measured at the end of manufacture on said determined electrical machine (M) for a known temperature and rotor rotation speed, * and an induced voltage of a reference electrical machine (Mref) under the same temperature and rotor rotation speed conditions; — E33) estimating a value (Tfct) of the operating temperature of the rotor of said determined electrical machine (M) which is obtained by using a model, linking the reference induced voltage (Uref), the reference rotation speed (coref) and the reference temperature (Tref) of the rotor of a reference electrical machine (Mref), for said measured rotation speed (cofct) and said corrected value (Umcor) of said internal control voltage (Uqfct).

2. Method according to claim 1, characterized in that it further comprises the following steps: - E0) for a reference electrical machine (Mref), develop a model linking the reference induced voltage (Uref), the reference rotation speed (coref) and the reference temperature (Tref) of the rotor; - E1) for said determined electrical machine (M), measure at the end of manufacture and store an induced voltage (Ueol), a temperature (Teol) and a rotation speed (coeol) of the rotor; - E2) for said determined electrical machine (M), calculate and memorize said correction factor (Fcor) ((Fcor) = (Ueol) / (Uzéro)) equal to the quotient of said voltage (Ueol) induced at the end of manufacturing by an estimated value (Uzéro) of the reference induced voltage which is obtained by using said model for the rotation speed (coeol) and said temperature (Teol) of the rotor measured at the end of manufacturing.

3. Estimation method according to one of claims 1 or 2, characterized in that, in a reference frame of axes d and q linked to the rotor, the currents Id, of phase d, and Iq, of phase q are measured, from which said internal control voltage (Uqfct) is determined.

4. Estimation method according to claim 2, characterized in that said induced voltage (Ueol), said temperature (Teol) and said rotation speed (coeol) of the rotor measured are stored in a memory integrated into said determined electrical machine (M) or into equipment of this machine.

5. Estimation method according to any one of claims 1 or 2, characterized in that said correction factor (Fcor) is stored in a memory integrated into said determined electrical machine or into equipment of this machine.

6. Estimation method according to any one of the preceding claims, characterized in that the phase of use during which no torque is requested from the determined permanent magnet synchronous electric machine (M), is a phase of controlling the torque at a set value equal to zero Nm.

7. Calculator characterized in that it comprises at least one memory for storing said correction factor (Fcor) and is configured to implement an estimation according to the method according to any one of the preceding claims.

8. Belt-driven electric starter generator system (BSG) comprising a determined permanent magnet synchronous electric motor (M) comprising a rotor whose temperature, in use, is intended to be estimated according to the method according to any one of claims 1 to 6, characterized in that it comprises at least one memory unit for storing said measured induced voltage (Ueol), said temperature (Teol) and said rotor rotation speed (coeol), and / or storing the correction factor (Fcor).

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