Method for determining a temperature of a component of a power inverter

Abstract

The inventions deals with a computer-implemented method for determining a temperature of a first component of a power inverter (6), the inverter (6) being connected to a rotary electrical machine (2), the machine (2) comprising a second component (3), distinct from the first component, wherein alternating current circulates in the second component (3), the method comprising a step of measuring the temperature of the second component by a temperature sensor (4), the method being characterized in that it comprises a step of determining (140) the temperature of the first component of the inverter (6) on the basis of the temperature of the second component (3) measured with the temperature sensor (4).

Description

[0001] Description

[0002] Title of the invention: Method for determining a temperature of a component of a power inverter

[0003] The invention relates to the temperature of power inverters.

[0004] In particular, it relates to a method for determining the initialization temperature of a component of a power inverter in a vehicle when the vehicle is restarted after a parking period.

[0005] To avoid malfunctions and possible damage, the temperatures of the components of an inverter must be known. Given that it is difficult and expensive to place a temperature sensor in each inverter, in particular in a motor vehicle, the temperatures are estimated from thermal models specific to the components and according to the supplied electrical power associated with the components.

[0006] However, when the vehicle has been parked for a while and restarts, the initialization temperature of these components is difficult to know. Some of them, which have a low thermal time constant, quickly cooled down to the temperature of the inverter cooling water. However, components with a high thermal time constant, such as a DC-capacitor, may still exhibit a high temperature upon restart.

[0007] Conventionally, as a typical method for determining the initialization temperature of a component of an inverter which has a high thermal time constant, it is known to obtain the thermal time constant of the component, the parking time of the vehicle, the last known or estimated temperature of the component before parking took place, and to calculate the initialization temperature of the component from these values.

[0008] A disadvantage of this method is that the parking time stored by the system inside the vehicle is usually inaccurate because it is recorded discretely, resulting in an incorrect initialization temperature when the actual parking time does not match one of the possible discrete values. Another disadvantage is that the last known or estimated temperature before parking took place could be lost if the storing of that value has an issue, making the initialization temperature impossible to determine.

[0009] It is an object of the present to improve the determination of the temperature of a component of an inverter.

[0010] In order to achieve this object, there is provided a computer-implemented method for determining a temperature of a first component of a power inverter, the inverter being connected to a rotary electrical machine, the machine comprising a second component, distinct from the first component, wherein alternating current circulates in the second component, the method comprising the steps of:

[0011] - measuring the temperature of the second component by a temperature sensor, - determining the temperature of the first component of the inverter on the basis of the temperature of the second component measured with the temperature sensor.

[0012] Indeed, the temperature of the component is induced by its losses. It appears that for some of the components of a power inverter, the losses are mainly due to the alternating current supplied by the inverter. Therefore, the temperature of the first component of the inverter and the temperature of the second component flowing alternating current are related even if the inverter and the second component are not thermally connected. The temperature of the first component can be calculated without a sensor located inside the inverter and is based on accurate data. In particular, this method does not require estimating a parking time and determining the thermal time constant of the component. It is therefore simpler and more precise. It also does not require storing a last known or estimated temperature before parking took place.

[0013] In a general way, the letter “AC” refers to a part into which an alternating current can circulate through and the letter “DC” refers to a part into which a direct current can circulate through.

[0014] Hereafter follow other optional features taken alone or in combination.

[0015] Preferably, the first component is a DC-link capacitor or a DC-busbar inverter or an AC- interface of the inverter.

[0016] For example, a DC-Busbar inverter is a DC-Busbar arranges to distribute DC current inside the inverter. For example, the DC-busbar is arranged inside the inverter and is connected to a DC-Connector. The DC-connector can directly be connected to the power supply of the vehicle.

[0017] For example, the AC-interface is a burbar or a cable. For example, the AC-lnterface is arranged to distribute AC current inside or outside the inverter. For example, the AC-lnterface is connected to power switches of the inverter.

[0018] Thus, the temperature of the DC-link capacitor of the inverter is determined thanks to the temperature of the machine. Indeed, the losses of the DC-link capacitor are mainly due to alternating current, the same alternating current circulating in the machine.

[0019] Advantageously, the second component is a stator of an electric motor of the rotary electrical machine, the measured temperature being a temperature of the stator of the electric motor.

[0020] Indeed, the stator circulates alternating current. Its temperature, mainly due to loss associated to this alternating current, allows to determine the temperature of the first component of the inverter.

[0021] Preferably, the temperature of the second component being a first measured temperature, the method further comprises the steps of :

[0022] - measuring, by another temperature sensor, a second measured temperature of a cooling water of the inverter, and - determining the temperature of the first component of the inverter on the basis on the first

[0023] 75 and second measured temperatures.

[0024] Thus in this example, the temperature of the component of the inverter also depends on the temperature of the cooling water of the inverter.

[0025] Advantageously, the temperature of the first component of the inverter is determined according to the following formula :

[0026] ^inverter- component ~ Twater T * ((^distinct-component ~ Twater) wherein Tinverter-component is the determined temperature of the first component of the inverter, Tdistinct-component is the first measured temperature of the second component, Twateris the second measured temperature of the cooling water, and k is a predetermined value.

[0027] The predetermined value k depends on the specific arrangement and can be calculated or

[0028] 85 deduced by experiment.

[0029] The invention also has as its object a method for determining the initialization temperature of a component of a power inverter, comprising, when the inverter is initialized after sleeping, a step of determining the initialization temperature of the component according to the preceding described method.

[0030] 90 Thus the here-above described method allows to determine the initialization temperature of a component of a power inverter, in particular after a parking took place, without storing the parking time and the a temperature before parking took place. The initialization temperature of the component of the inverter is simpler and more precise as it is based on the temperature of a component of the machine.

[0031] 95 Preferably, the initialization temperature being a first initialization temperature, the method comprises the following steps of:

[0032] - determining the thermal time constant of the component of the inverter;

[0033] - determining the last known temperature of the component;

[0034] - determining a time of sleep of the inverter; 00 - when the inverter is initialized after sleeping, determining a second initialization temperature of the component of the inverter based on the thermal time constant, on the last known temperature of the component and on the time of sleep of the inverter;

[0035] -performing a plausibility check of the first, respectively second, initialization temperature, based on the second, respectively first, initialization temperature. 05 Thus in this example, the temperature of the component of the inverter is determined by the here-above described first method, and also by a conventional second method. The result of the first or second method is thus checked thanks to the respectively second or first method, and it can be corrected.

[0036] The invention also has as its object a computer program comprising instructions which,10 when the program is executed by a computer, cause the computer to implement the steps of the here-above described method for determining a temperature or of the here-above described method for determining the initialization temperature.

[0037] The invention also has as its object a computer-readable storage medium comprising instructions which, when executed by a computer, cause the computer to implement the steps15 of the here-above described method for determining a temperature or of the here-above described method for determining the initialization temperature.

[0038] The invention also has as its object a system comprising:

[0039] - a power inverter, the power inverter comprising a first component,

[0040] - a rotary electrical machine connected to the inverter and comprising a second component20 distinct from the first component, wherein the second component is able to flow alternating current ;

[0041] - a temperature sensor to measure a temperature of the second component, characterized in that the system further comprises computer means configured to command the steps of : 25 - by the sensor, measuring a first temperature of the second component (3) ;

[0042] - determining the temperature of the first component of the inverter based on the first temperature.

[0043] Brief description of the figures 30 The invention will be better understood on reading the following description, which is given only by way of example and is made with reference to the attached drawings in which :

[0044] [Fig. 1] is a schematic view of a vehicle comprising a system according to the invention;

[0045] [Fig. 2] is a schematic view of the system comprising an inverter according to the invention; and 35 [Fig. 3] is a diagram of a method according to the invention.

[0046] Detailed description

[0047] Figure 1 illustrates a motor vehicle 1 comprising a rotary electrical machine 2. The rotary electrical machine 2 is in this example an electrical motor powering the vehicle 1 . Alternatively,40 any type of rotary electrical machine could be considered in the invention, for example an electric motor to power a braking system of vehicle 1 .

[0048] Rotary electrical machine 2 comprises a stator 3 and a rotor, which are not illustrated in details. The stator 3 comprises a temperature sensor 4, in order to measure the temperature of the stator 3. 45 Vehicle 1 also comprises a battery 5 to power the rotary electrical machine 2.

[0049] Vehicle 1 also comprises an inverter 6, connected between battery 5 and rotary electrical machine 2, in order to transform the direct current from battery 5 to alternating current to power machine 2 and to transform the alternating current from machine 2 to direct current to charge the battery 5.

[0050] The inverter 6 also comprises a computer unit 7 connected to the temperature sensor 3 and to rotary electrical machine 2. Unit 7 comprises computer means to control machine 2 and to perform a method 100 described later.

[0051] In unit 7, the conventional computer means comprise a processor unit 8 and a computer- readable storage medium 9 comprising instructions which, when executed by the processor unit 8, cause the unit to implement the steps of method 100. Indeed, this medium 9 includes a computer program 10 comprising instructions which, when program 10 is executed by a computer or computer means such as the processor unit 8, cause the computer to implement the steps of method 100.

[0052] The inverter 6 also comprises a cooling water circuit 11 . This circuit enables to cool inverter 6, by going through or around components of inverter 6 in a manner known by a skilled person. No details will be described about the arrangement of the circuit 11 .

[0053] The inverter 6 also comprises a second temperature sensor 12 arranged in a manner to measure the temperature of the cooling water circulating in the circuit 11 .

[0054] Figure 2 illustrates components of inverter 6. Inverter 6 comprises a DC-connector 13 connected to battery 5 in an unillustrated manner. The direct current circulating in the DC- connector is called IDO.

[0055] Inverter 6 comprises a DC-Busbar 14 connected to DC-Connector 13 and circulating direct current IDO.

[0056] Inverter 6 also comprises a DC-link Capacitor 15 connected to DC-Busbar 14. Alternating current circulates in DC- link Capacitor 15. The value of the root means square (rms) current, called leap, rms and circulating in DC- link Capacitor 15, is provided by the following formula: wherein M stands for the Modulation Index and Phi stands for the angle between AC-voltage and AC-current. IAC, rms is the root means square current of alternating current IAC circulating in the stator 3 of rotary electrical machine 2.

[0057] Inverter 6 also comprises a DC-Busbar inverter 16, connected to the DC-link capacitor 15 and in which circulates a current whose root means square current called linv,rms is provided by the following formula :

[0058] >

[0059] Inverter 6 also comprises power switches 17 connected to DC-Busbar inverter 16, including insulated-gate bipolar transistors (IGBT) or MOSFETs, circulating alternating current IAC whose root means square current is kc / ms. This current is the alternating current to be provided to machine 2.

[0060] Inverter 6 also comprises an AC-lnterface 18 connected to power switches 17 and circulating alternating current IAC to be provided to the rotary electrical machine 2. The AC- interface may be a bur bar or a AC-cable.

[0061] An example of method 100, for determining the initialization temperature of a DC- link capacitor 15 of power inverter 6, is now described in reference to Figure 3. Finding this initialization temperature is necessary to control in an appropriate manner the electrical current transmitted to rotary electrical machine 2. Indeed, thermal models of inverter-components are calculated in order to ensure thermal inverter-protection. Thus, the power switches 17 are controlled by unit 7 based on a temperature criteria, which has consequences on electrical machine 2. A wrong initialization temperature could for example generate an inadequate torque (too strong or too weak) by machine 2.

[0062] Method 100 is implemented by computer unit 7 after a parking time of vehicle 1. During parking time, rotary electrical machine 2 was off, inverter 6 was in sleep mode.

[0063] At step 110, vehicle 1 is restarted. Rotary electrical machine 2 is on, inverter 5 is on. Initialization temperature needs to be determined.

[0064] At step 120, unit 7 measures temperature Tdistinct -component of stator 3 of machine 2, by first temperature sensor 4 positioned on stator 3.

[0065] At step 130, unit 7 measures, by second temperature sensor 12, temperature Twaterof cooling water 11 of inverter 6.

[0066] At step 140, unit 7 determines Tnverter-component of DC-link capacitor 15 by the following formula:

[0067] T'inverter-component ~ ^water T k * (T^i^ inct~component T'water) ■ k is a coefficient determined by a skilled person thanks to experiment or design data, as k is arrangement-specific.

[0068] This formula comes from the fact that, based on the formulas mentioned above in respect with the electrical current circulating in the components of inverter 5, the losses of the stator 3 as well as the losses of DC- link capacitor 15 are mainly due to alternating current IAC- These losses are responsible for the temperature of these components. As a consequence, although DC-link capacitor 15 and stator 3 are not thermally connected, their respective temperatures are related.

[0069] Unit 7 has now determined the initialization temperature of DC-link capacitor 15 and can now control inverter 6 based on this temperature. Furthermore, evolution of the temperature, thanks to any thermal model, may then be determined by unit 7 on the basis of this initialization temperature, in order to ensure thermal protection of DC-link capacitor 15 without having abnormal consequences on the torque generated by machine 2. Following steps are additional and optional steps to check and potentially modify the initialization temperature that has been found.

[0070] At step 150, unit 7 determines the thermal time constant Tconstant of DC-link capacitor 15 of the inverter 6. This value is in particular stored in a memory of unit 7, as this constant value is determined or known during conception of the inverter 6.

[0071] At step 160, unit 7 determines the last known temperature Tbeforesieep of DC-link capacitor 15. In particular, the last known temperature is the temperature determined by unit 7 using a thermal model, before the inverter goes to mode sleep when the vehicle parks.

[0072] At step 170, unit 7 determined the temperature T water, beforesleep of the cooling water 1 1 at the time when vehicle 1 parks, just before the inverter goes to mode sleep.

[0073] At step 180, unit 7 determines a time of sleep Tpark of inverter 6, meaning a period between the time at which inverter 6 switches to sleep mode, when the vehicle parks, and the time at which inverter 6 has to be initialized again after sleeping, when vehicle 1 restarts.

[0074] At step 190, unit 7 determines a second initialization temperature T inverter-com ponent-2 of DC-link capacitor 15 based on the following formula:

[0075] To improve the safety, at step 200, unit 6 performs, in this example, a plausibility check of the first initialization temperature T inverter-component, based on the second initialization temperature T inverter-component-2.

[0076] A plausibility check is any method known by a skilled person that enables to check whether a result value is legit based on another reference value. Such a check can lead to change the first value that has been found, based on the second value. For example, If a certain threshold of the plausibility check is exceeded, the initialization is considered not trustworthy. As a consequence, the initialization could take place with e.g. a worst case temperature to ensure thermal protection.

[0077] Steps 160 to 100 could be performed before steps 120 to 150. In that case the plausibility checks is then performed on second initialization temperature T inverter-component-2 based on the first initialization temperature T inverter-component-

[0078] The invention is not limited to the embodiments shown and other embodiments will be apparent to those skilled in the art.

[0079] First of all, the invention is not limited to a method for determining an initialization temperature. Indeed, the relation between the temperature of DC-link capacitor 15 of the inverter 6 and the temperature of stator 3 of the electrical rotary machine 2 is not limited to an initialization after sleep mode, it is thus possible to determine the temperature of DC-link capacitor at any time. Moreover, instead of the temperature of the DC-link capacitor 15, it is possible to determine, with the same formula and an adapted coefficient k value, the temperature of DC-busbar inverter 16 and AC-interface 18. Indeed, based on the formulas described above in reference to these components, the main losses of these components are also due to alternating current IAC. Therefore, the invention is not limited to calculate the temperature of DC-link capacitor 15, it can be implemented to determine the temperature of other components of inverter 6.

[0080] Furthermore, if AC-interface 18 was considered as part of the rotary electrical machine 2 and if temperature sensor 4 was positioned on AC-interface 18 instead of stator 3, the same method would allow to determine the temperature of DC-link capacitor 15 or DC-busbar inverter 16 based on the temperature measured on AC-interface 18, with an adapted k value. Therefore, the invention is not restricted by measuring the temperature of a stator, it can be implemented to measure the temperature of another component of rotary electrical machine 2 in order to determine the temperature of a component of inverter 6.

[0081] Thus, more generally, the invention provides a computer-implemented method 100 for determining a temperature of a first component 15 of a power inverter 6, the inverter being connected to a rotary electrical machine 2, the machine comprising a second component 3, distinct from the first component 15, wherein alternating current circulates in the second component 3, the method 100 comprising a step 120 of measuring the temperature of the second component 3 by a temperature sensor 4, the method 100 comprising a step 140 of determining the temperature of the first component 15 of the inverter 6 on the basis of the temperature of the second component 3 measured with the temperature sensor 4.

[0082] The invention also provides a system comprising:

[0083] - a power inverter 6, the power inverter comprising a first component 15, 16 or 18 ;

[0084] - a rotary electrical machine 2 connected to inverter 6 and comprising second component 3 distinct from the first component 15, 16, or 18, wherein the second component 3 is able to flow alternating current ;

[0085] - a temperature sensor 4 to measure a temperature of the second component 3,

[0086] - computer means 7, 8 and 9 configured to command the steps of :

[0087] - by the sensor 4, measuring a first temperature of the second component 3 ;

[0088] - determining the temperature of the first component 15, 16, or 18 of the inverter based on the first temperature. Nomenclature

[0089] 1 : vehicle

[0090] 2: rotary electrical machine

[0091] 3: stator of machine 2

[0092] 4 temperature sensor

[0093] 5: battery

[0094] 6 inverter

[0095] 7: computer unit

[0096] 8: processing unit

[0097] 9: computer storage medium

[0098] 10: computer program

[0099] 11 : cooling water circuit

[0100] 12: temperature sensor

[0101] 13: DC-connector

[0102] 14: DC-busbar

[0103] 15: DC-capacitor

[0104] 16: DC-busbar inverter

[0105] 17: Power switches

[0106] 18: AC- Interface

Claims

Claims[Revendication 1] Computer-implemented method (100) for determining a temperature of a first component (15, 16, 18) of a power inverter (6), the inverter (6) being connected to a rotary electrical machine (2), the machine (2) comprising a second component (3), distinct from the first component (15, 16, 18), wherein alternating current circulates in the second component (3), the method (100) comprising a step (120) of measuring the temperature of the second component by a temperature sensor (4), the method (100) being characterized in that it comprises a step of determining (140) the temperature of the first component (15, 16, 18) of the inverter (6) on the basis of the temperature of the second component (3) measured with the temperature sensor (4).[Revendication 2] Method (100) according to the preceding claim, wherein the first component is a DC-link capacitor (15) or a DC-busbar inverter (16) or an AC-interface (18) of the inverter (6).[Revendication 3] Method (100) according to any one of the preceding claims, wherein the second component (3) is a stator of an electric motor of the rotary electrical machine (2), the measured temperature being a temperature of the stator (3) of the machine.[Revendication 4] Method (100) according to any one of the preceding claims, wherein the temperature of the second component (3) being a first measured temperature, the method further comprises the steps of :- measuring (130), by another temperature sensor (12), a second measured temperature of a cooling water of the inverter (6), and- determining (140) the temperature of the first component of the inverter (6) on the basis on the first and second measured temperatures.[Revendication 5] Method (100) according to the preceding claim, wherein the temperature of the first component of the inverter (6) is determined according to the following formula :^inverter-component ~ ^water + k * (Tdistinct-component ~ ^water)wherein Tinverter-comPonent is the determined temperature of the first component (15, 16, 18) of the inverter (6), Tdistinct-component is the first measured temperature of the second component (3), Twater is the second measured temperature of the cooling water, and k is a predetermined value.[Revendication 6] Method (100) for determining the initialization temperature of a component (15, 16, 18) of a power inverter (6), comprising, when the inverter (6) is initialized after sleeping, a step (140) of determining the initialization temperature of the component (15, 16, 18) according to any one of the preceding claims.[Revendication 7] Method (100) according to claim 6, wherein, the initialization temperature determined according to claim 6 being a first initialization temperature, the method comprises the following steps of :- determining (150) the thermal time constant of the component of the inverter;- determining (160) the last known temperature of the component;- determining (180) a time of sleep of the inverter;- when the inverter is initialized after sleeping, determining (190) a second initialization temperature of the component of the inverter based on the thermal time constant, on the last known temperature of the component and on the time of sleep of the inverter;-performing (200) a plausibility check of the first, respectively second, initialization temperature, based on the second, respectively first, initialization temperature.[Revendication 8] A computer program (10) comprising instructions which, when the program is executed by a computer, cause the computer to implement the steps of the method (100) of any one of the preceding claims.[Revendication 9] A computer-readable storage medium (9) comprising instructions which, when executed by a computer, cause the computer to implement the steps of the method (100) according to any of claims 1 to 7.[Revendication 10] System comprising :- a power inverter (6), the power inverter comprising a first component (15, 16, 18),- a rotary electrical machine (2) connected to the inverter (6) and comprising a second component (3) distinct from the first component (15, 16, 18), wherein the second component (3) is able to flow alternating current ;- a temperature sensor (4) to measure a temperature of the second component (3), characterized in that the inverter further comprises computer means (7, 8, 9) configured to command the steps of :- by the sensor (4), measuring a first temperature of the second component (3) ;- determining the temperature of the first component (15, 16, 18) of the inverter based on the first temperature.

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