Method for determining a temperature of an electric machine

Abstract

The invention relates to a method for determining temperatures of an electric machine (100) having a rotor (110) and a stator (120), the method comprising: determining a first thermal computational model which models thermal variables of the stator (120); determining a second thermal computational model which models thermal variables of the rotor (110); determining a heat exchange between the rotor (110) and the stator (120) in the first thermal computational model and in the second thermal computational model, in each case independently of one another; determining a temperature of the stator (120) by means of the first thermal computational model; and determining a temperature of the rotor (110) by means of the second thermal computational model.

Description

[0001] Description

[0002] Method for determining a temperature of an electrical machine

[0003] The present invention relates to a method for determining a temperature of an electrical machine as well as a computing unit and a computer program for carrying out the method.

[0004] Background of the invention

[0005] For the operation of an electrical machine, it can be important to be able to determine the stator temperature as accurately as possible during operation. This allows for monitoring thermally critical stator components, such as stator insulation, and preventing damage. The more precisely the stator temperature can be determined, the closer the stator's thermal limit can be approached during operation, thus utilizing or increasing the performance of the electric machine.

[0006] Accordingly, it can be important to be able to determine the rotor temperature as accurately as possible. Here, too, component temperature limits must not be exceeded to prevent, for example, demagnetization of permanent magnets or damage to a rotor winding.

[0007] For this purpose, for example, a thermal protection model can be calculated online (i.e. during operation) in software on a control unit of the power unit belonging to the electrical machine (so-called inverter).

[0008] Disclosure of the Invention Against this background, a method for determining the temperature of an electrical machine, as well as a computing unit and a computer program for implementing the method, are proposed, having the features of the independent patent claims. Advantageous embodiments are the subject of the dependent claims and the following description.

[0009] The invention utilizes the measure of establishing thermal calculation models for a rotor and a stator of an electrical machine, in which heat transfer from one model to the other does not have to be identical to the heat transfer from the other model to the one model, i.e., energy conservation across both models is not required. Thus, no overall thermal model of the electrical machine, including rotor and stator temperatures, is established; instead, two separate models are used, with the energy balance between rotor and stator deliberately softened (intentionally not maintained). The resulting degree of freedom significantly increases the model accuracy of the rotor and stator temperatures.The seemingly unphysical violation of energy conservation at first glance reflects the effect that heat flows from or into the system of interest, which cannot be represented or can only be inadequately represented by a model with a manageable network size (model size), can nevertheless be (implicitly) allowed.

[0010] In detail, a thermal calculation model of the stator is determined, provided or used as the first thermal calculation model, which models or maps thermal quantities or thermal parameters or thermal elements of the stator. This first thermal calculation model is also referred to below as the stator model. Furthermore, a thermal calculation model of the rotor is determined, provided or used as the second thermal calculation model, which models or maps thermal quantities or thermal parameters or thermal elements of the rotor. This second thermal calculation model is also referred to below as the rotor model. Heat exchange between the rotor and the stator is determined, modeled, considered or taken into account independently of one another in the first thermal calculation model and in the second thermal calculation model.At least one temperature of the stator, hereinafter also referred to as stator temperature, is determined using the first thermal calculation model, and at least one temperature of the rotor, hereinafter also referred to as rotor temperature, is determined using the second thermal calculation model.

[0011] The electric machine can be controlled based on the specific temperatures of the stator and rotor. With precise knowledge of the stator and rotor temperatures, the electric machine can be operated close to the thermal limit temperatures of thermally critical components without exceeding these limit temperatures and without causing danger or damage to the electric machine. The performance of the electric machine can thus be increased.

[0012] Within the scope of the present invention, the stator model and the rotor model are modeled independently of one another with respect to the actual heat exchange between rotor and stator. The heat or energy flow between the stator and rotor is considered independently of one another in the two calculation models and is not linked one-to-one. The heat exchange between stator and rotor determined in the stator model therefore does not necessarily have to correspond to the heat exchange determined in the rotor model. In particular, it is not assumed for the two calculation models that the amount of heat that the stator transfers to the rotor is automatically identical to the amount of heat that the rotor receives from the stator.

[0013] Traditionally, thermal calculation models of electrical machines model all energy flows between individual calculation model elements as accurately as possible, and energy conservation within the calculation model is assumed. For example, in such conventional calculation models, the amount of heat transferred from the stator to the rotor is automatically identical to the amount of heat the rotor receives from the stator. However, such a calculation modeling approach places very high demands on knowledge of all heat flows present in the electrical machine, including external disturbances. As a result, the achievable calculation model accuracy can often be limited in practice, and the calculation models can become very large and thus complex in terms of computational effort and parameter identification.

[0014] The approach proposed here allows for a softening of the energy balance boundary condition through an "open" system model in which the system boundaries can be cut closer to the stator while still appropriately accounting for the rotor influence via a temperature boundary condition. In particular, the method is independent of the type of computational modeling used for the stator and rotor temperature model. For example, both data-based and physics-based computational models can be combined.

[0015] According to one embodiment, the first thermal calculation model and the second thermal calculation model are not coupled or linked to one another via the heat exchange between the rotor and the stator as a boundary condition. Alternatively or additionally, no energy conservation between the first thermal calculation model and the second thermal calculation model with regard to the heat exchange between the rotor and the stator is assumed as a boundary condition. The two calculation models are therefore not physically precisely coordinated with one another, but are considered physically independent of one another. In particular, precise knowledge of all heat flows and external disturbances present in the electrical machine is therefore not assumed. In this way, the temperatures of the rotor and stator can be determined more precisely and with less effort using the independent calculation models than would be the case with a physically precise overall model.

[0016] According to one embodiment, the first thermal calculation model has an interface or an input for the temperature of the rotor, and the second thermal calculation model has an interface or an input for the temperature of the stator. In particular, these interfaces are each provided as open interfaces for the heat exchange between the rotor and stator. The interface of the stator model represents, in particular, an external, open coupling to the rotor temperature, and the interface of the rotor model represents, in particular, an external, open coupling to the stator temperature. Via these interfaces, the heat transfer between the rotor and stator can be taken into account individually and independently of one another in the two calculation models. For example, the rotor temperature can be specified externally via the interface of the stator model.For example, the rotor temperature determined using the rotor model can be passed to the stator model via this interface. Conversely, the stator temperature can be specified externally via the rotor model's interface, e.g., as the stator temperature determined using the stator model. The use of these open interfaces, in particular, allows for the possibility of openly or loosely coupling the two calculation models.

[0017] According to one embodiment, operating parameters of the electric machine are determined. Depending on these determined operating parameters, the temperature of the stator is determined using the first thermal calculation model, and the temperature of the rotor is determined using the second thermal calculation model. For example, sensor values ​​can be recorded as such operating parameters during operation of the electric machine. Alternatively or additionally, the operating parameters can be determined depending on sensor values ​​recorded in this way. These operating parameters can, for example, describe one or more operating points of the electric machine, e.g., a first operating point related to the stator and a second operating point related to the rotor.

[0018] According to one embodiment, the thermal variables of the stator in the first thermal calculation model and / or the thermal variables of the rotor in the second thermal calculation model are each modeled as a function of a torque and / or a rotational speed and / or a phase current and / or an intermediate circuit voltage and / or a control frequency and / or a modulation method of the electrical machine. The phase current, the intermediate circuit voltage, the control frequency and the modulation method are in particular electrical operating parameters for controlling an inverter circuit for controlling the electrical machine. The control frequency can in particular be a carrier frequency of an underlying PWM-based control of power semiconductors. The modulation method can in particular be a control method, e.g. a space vector modulation."Space Vector Modulation", SVPWM), sine modulation, sine modulation with third harmonic or triangular offset, flat top, fundamental frequency clocking, etc.

[0019] Alternatively or additionally, according to one embodiment, the thermal variables of the stator and / or the rotor are each modeled as a function of a temperature of a cooling fluid for cooling the stator and / or a volume flow of this cooling fluid for cooling the stator. This cooling fluid can, for example, be circulated through a cooling system for cooling the stator and can be, for example, cooling water or cooling air.

[0020] Alternatively or additionally, according to one embodiment, the thermal variables of the rotor are each modeled as a function of a temperature of a cooling fluid for cooling the rotor and / or a volume flow of this cooling fluid for cooling the rotor. For example, this cooling fluid for cooling the rotor can be passed through a hollow shaft of the rotor as an internal fluid and can be, for example, a cooling oil.

[0021] Alternatively or additionally, according to one embodiment, the thermal variables of the rotor are each modeled as a function of a transmission oil temperature. The transmission can be connected downstream of the electric machine to convert the torque generated by the electric machine.

[0022] According to one embodiment, the first thermal calculation model represents thermal variables of a stator body and thermal variables of a stator winding of the stator in a dependent manner. In the electrical machine, the stator winding is expediently arranged within the stator body, e.g. within slots within the stator body. The stator winding can protrude from the stator body on both axial sides and form a winding overhang there in each case. Thus, with the aid of the stator model, a temperature of the stator body, in particular a maximum temperature within the stator body, and a temperature of the stator winding, in particular a maximum temperature within the stator winding, can be expediently determined. For example, a first hotspot or a first thermal node can be modeled in the stator model, which represents the stator winding and its maximum temperature, and a second hotspot ora second thermal node, which represents the stator body and its maximum temperature. Thermal relationships or interactions between the stator body and the stator winding can be conveniently modeled in the stator model, e.g., as relationships or links between these two nodes.

[0023] According to one embodiment, the first thermal calculation model models a temperature of the stator winding, a thermal power loss of the stator winding, and / or a thermal capacitance of the stator winding as thermal variables, dependent on one another. For example, the first node can map these three variables of the stator winding dependent on one another. Alternatively or additionally, according to one embodiment, the first thermal calculation model models a temperature of the stator body, a thermal power loss of the stator body, and / or a thermal capacitance of the stator body, dependent on one another. For example, the second node can map these three thermal variables of the stator winding dependent on one another.For example, the thermal power loss and the thermal capacitance of the stator winding as well as the thermal power loss and the thermal capacitance of the stator body can each be modeled as a function of a first operating point of the electrical machine related to the stator, wherein this first operating point describes, for example, a combination of current values ​​for one or more of the following operating parameters: the torque, the speed, the phase current, the intermediate circuit voltage, the control frequency, the modulation method, the temperature of the cooling fluid for cooling the stator, the volume flow of the cooling fluid for cooling the stator, a power loss of the stator, the temperature of the rotor. The thermal capacitances of the stator winding and stator body can each assume constant values, for example, or vary depending on the current first operating point.Crucial to the achievable accuracy is the correct determination of the power losses of the stator body and the stator winding. These are conveniently determined in each magazine depending on the current electrical and thermal operating point.

[0024] Alternatively or additionally, according to one embodiment, the first thermal calculation model models a particularly variable thermal resistance between the temperature of the stator winding and the temperature of the stator body. For example, this thermal resistance can link the first node and the second node. This thermal resistance is determined, in particular, as a function dependent on the first operating point.

[0025] Alternatively or additionally, according to one embodiment, the first thermal calculation model models a particularly variable thermal resistance between the rotor and the stator, in particular between the temperature of the rotor and the temperature of the stator body. The temperature of the rotor can, for example, be specified as a boundary condition via the open interface. This thermal resistance can, for example, link the second node point with respect to the stator body and the rotor temperature boundary condition. For example, this thermal resistance is determined as a function dependent on the speed of the electric machine and dependent on the first operating point.

[0026] Alternatively or additionally, according to one embodiment, the first thermal calculation model models, dependently from one another, a temperature of the cooling fluid for cooling the stator, in particular as a boundary condition, as well as a particularly variable thermal resistance between the temperature of the stator body and the temperature of this cooling fluid for cooling the stator. This thermal resistance can, for example, link the second node with respect to the stator body and the boundary condition with respect to the cooling fluid temperature. In particular, a first thermal resistance between the temperature of the stator body and the temperature of the cooling fluid can be modeled depending on operating parameters of the electric machine, and a second thermal resistance between the temperature of the stator body and the temperature of the cooling fluid can be modeled depending on operating parameters with respect to the cooling fluid or the entire cooling system for cooling the stator.For example, this first thermal resistance between stator body temperature and cooling fluid temperature can be determined depending on the first operating point and the second thermal resistance between stator body temperature and cooling fluid temperature depending on a volume flow of the cooling fluid for cooling the stator and / or on the temperature of the cooling fluid for cooling the stator.

[0027] According to one embodiment, the part of the stator winding within the slots of the stator body and the part of the stator winding protruding from the stator body in the form of the winding overhangs can be modeled separately in the stator model. For this purpose, the first thermal calculation model can model a temperature, a thermal power loss, and / or a thermal capacitance of the stator winding in a winding slot of the stator as thermal variables dependent on one another. For example, a first node can map these three variables of the winding slot dependent on one another. Furthermore, the first thermal calculation model can model a temperature, a thermal power loss, and / or a thermal capacitance of a winding overhang of the stator as thermal variables dependent on one another. For example, a second node can map these three variables of the winding overhang dependent on one another.In particular, the accuracy of the model can be improved in this way, as stator winding losses can be divided into losses in the winding overhang and losses in the winding slot. The winding overhang losses and the winding losses can then each be fed into a separate node. As explained above, the first thermal calculation model can further model a temperature, a thermal power loss, and a thermal capacitance of the stator body dependent on one another, with a third node representing these three variables. Furthermore, a thermal resistance between the temperature of the stator winding in the winding slot and the temperature of the stator body can be modeled. This thermal resistance can, for example, be determined as a function dependent on the first operating point.Alternatively or additionally, a thermal resistance can be determined between the temperature of the stator winding in the winding slot and the temperature of the winding overhang. This thermal resistance can also be determined, for example, as a function of the first operating point. Furthermore, a thermal resistance can be modeled between the temperature of the stator body and the temperature of the cooling fluid used to cool the stator.

[0028] According to one embodiment, the second thermal calculation model models the temperature of the rotor, a thermal power loss of the rotor, and / or a thermal capacity of the rotor as interdependent thermal variables. For example, the temperature, the thermal power loss, and the thermal capacity of the rotor can be mapped to a node for the rotor.The thermal power loss and the thermal capacity of the rotor can, for example, each be modeled as a function of a second operating point of the electric machine related to the rotor, whereby this second operating point describes a combination of current values ​​for one or more of the following operating parameters: the torque, the speed, the phase current, the intermediate circuit voltage, the control frequency, the modulation method, the temperature of the cooling fluid for cooling the stator, the volume flow of this cooling fluid for cooling the stator, the temperature of the cooling fluid for cooling the rotor, the volume flow of this cooling fluid for cooling the rotor, a power loss of the rotor, the temperature of the stator, the temperature of the transmission oil. The thermal capacity of the rotor can, for example, assume constant values ​​or vary depending on the current second operating point.In particular, the correct determination of rotor power losses is crucial for achieving the achievable accuracy. This is conveniently determined in each magazine depending on the current electrical and thermal operating point.

[0029] Alternatively or additionally, according to one embodiment, the second thermal calculation model models a particularly variable thermal resistance between the rotor and the stator, in particular between the temperature of the rotor and the temperature of the stator. The stator temperature can, for example, be specified as a boundary condition via the open interface. For example, this thermal resistance can be determined as a function of the speed of the electric machine and the second operating point.

[0030] Alternatively or additionally, according to one embodiment, the second thermal calculation model models, dependently on one another, the temperature of the cooling fluid for cooling the stator and a particularly variable thermal resistance between the rotor and the cooling fluid for cooling the electric machine. This thermal resistance can be determined, in particular, as a function of the rotational speed and the second operating point.

[0031] Alternatively or additionally, according to one embodiment, the second thermal calculation model models, dependently on one another, the temperature of the cooling fluid, in particular the internal cooling fluid for cooling the rotor, and a particularly variable thermal resistance between the rotor and the cooling fluid for cooling the rotor. This thermal resistance is determined, for example, as a function of the rotational speed, the temperature and volume flow of the cooling fluid for cooling the rotor, as well as the second operating point.

[0032] Alternatively or additionally, according to one embodiment, the second thermal calculation model models the temperature of the transmission oil and, in particular, a variable thermal resistance between the rotor and the transmission oil as a function of one another. This thermal resistance is determined, for example, as a function of the rotational speed and the second operating point.

[0033] According to one embodiment, the electric machine has a temperature sensor arranged on or in the stator. The first thermal calculation model then models a temperature of the temperature sensor and / or a thermal capacitance of the temperature sensor as thermal variables, dependent on one another. This thermal capacitance of the temperature sensor can be a fixed value or can vary depending on the first operating point explained above. Alternatively or additionally, according to one embodiment, the stator model models a thermal resistance, in particular a variable one, between the temperature of the stator winding, the temperature of the stator body, and the temperature of the temperature sensor. This thermal resistance can be determined, for example, as a function dependent on the rotational speed and the first operating point.

[0034] Alternatively or additionally, according to one embodiment, the stator model models a particularly variable thermal resistance between the temperature of the cooling fluid for cooling the stator and the temperature of the temperature sensor. This thermal resistance can be determined, in particular, as a function of the rotational speed and the first operating point.

[0035] Alternatively or additionally, according to one embodiment, the stator model models a particularly variable thermal resistance between a temperature of an oil, in particular a cooling oil for cooling the electric machine, and the temperature of the temperature sensor, wherein this thermal resistance can be determined in particular as a function depending on the rotational speed, the temperature of the oil and the first operating point.

[0036] Without using such a temperature sensor, for example, a basic version of the stator model can be designed as a pure forward simulation. This sensorless approach allows residual errors to remain, which can be further reduced by extending the basic model with the help of the stator temperature sensor. For example, in the stator model, the individual thermal variables related to the temperature sensor can be connected to the node related to the stator winding. Using the stator temperature sensor, the accuracy of the prediction of the stator hotspot temperature can be increased by evaluating the deviation between the measured sensor temperature and the expected, modeled temperature and, for example, a weighted feedback to the stator model. For example, a Luenberger observer, Kalman filter, and / or PI controller can be used for this purpose.

[0037] According to one embodiment, the temperature sensor can also be modeled by two temperatures in the first thermal calculation model. For this purpose, the first thermal calculation model can model a first temperature of the temperature sensor and / or a second temperature of the temperature sensor and / or a first thermal capacitance of the temperature sensor and / or a second thermal capacitance of the temperature sensor as thermal variables, dependent on one another. In this way, the temperature sensor can be represented by two nodes to improve the model.Alternatively or additionally, according to one embodiment, the stator model models a first thermal resistance between the temperature of the stator winding and the first temperature of the temperature sensor and / or a second thermal resistance between the first temperature of the temperature sensor and the second temperature of the temperature sensor and / or a third thermal resistance between the temperature of the cooling fluid for cooling the stator and the second temperature of the temperature sensor. These three thermal resistances can each be determined, for example, as a function of the rotational speed and the first operating point.

[0038] According to one embodiment, the electric machine has oil cooling. In such an oil-cooled electric machine, also referred to as a wet electric machine, with oil in a rotor-stator gap, the stator and its winding are in direct contact with the oil. The first thermal calculation model then models, as interdependent thermal variables, a temperature of the oil of the oil cooling system and, in particular, a variable thermal resistance between the temperature of the oil of the oil cooling system and the temperature of the stator winding. This additional cooling path of the oil cooling system can be represented in the stator model, for example, by connecting the first node with respect to the stator winding to the oil temperature. The oil temperature can be provided, for example, by an oil temperature sensor or by an oil temperature model.If the stator temperature sensor is also in direct contact with the oil, this can be modeled by additionally connecting the sensor node to the oil temperature. The thermal resistance between the temperatures of the oil and the stator winding depends in particular on the speed and on a third operating point, whereby this third operating point describes in particular a current combination of torque, speed, phase current, DC link voltage, control frequency, modulation method, cooling fluid temperature (for cooling the stator), volume flow of the cooling fluid (for cooling the stator), oil temperature, volume flow of the oil, stator power loss and / or rotor temperature. In this case, too, feedback of the sensor information, e.g., within the framework of an observer approach, as mentioned above, can improve the estimation of the stator hotspot temperature.

[0039] This method is particularly suitable for use in the automotive sector, e.g., in hybrid or electric vehicles. Using this method, the temperature of the electric motor can be precisely determined and used, for example, in engine control.

[0040] A computing unit according to the invention, e.g. a control unit of a motor vehicle, is configured, in particular in terms of programming, to carry out a method according to the invention.

[0041] The implementation of a method according to the invention in the form of a computer program or computer program product with program code for carrying out all method steps is also advantageous, since this entails particularly low costs, in particular if an executing control unit is also used for other tasks and is therefore already present. Finally, a machine-readable storage medium is provided with a computer program stored thereon, as described above. Suitable storage media or data carriers for providing the computer program are, in particular, magnetic, optical, and electrical memories, such as hard disks, flash memories, EEPROMs, DVDs, and others. Downloading a program via computer networks (Internet, intranet, etc.) is also possible. Such a download can be wired or cable-based or wireless (e.g., via a WLAN network, a 3G, 4G, 5G, or 6G connection, etc.).Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

[0042] The invention is illustrated schematically in the drawing using exemplary embodiments and is described below with reference to the drawing.

[0043] Short description of the drawings

[0044] Figure 1 shows schematically an electrical machine which may form the basis of an embodiment of the method according to the invention.

[0045] Figure 2 schematically shows a thermal calculation model which models thermal variables of a stator of an electrical machine, according to an embodiment of the method according to the invention.

[0046] Figure 3 schematically shows thermal calculation models, each modeling thermal variables of a stator of an electrical machine, each according to an embodiment of the method according to the invention.

[0047] Figure 4 schematically shows a thermal calculation model which models thermal variables of a rotor of an electrical machine, according to an embodiment of the method according to the invention.

[0048] Figure 5 shows schematically a temperature-time diagram that can be determined within the scope of an embodiment of the method according to the invention.

[0049] Embodiment(s) of the invention

[0050] Figure 1 shows an electrical machine in a schematic sectional view and is designated by 100. For example, the electrical machine 100 can be used in a vehicle, e.g., in a hybrid or electric vehicle.

[0051] The electric machine 100 has a rotor 110 with a rotor body 112 arranged on a rotor shaft 111, and a stator 120 surrounding the rotor 110. The stator 120 has a stator body 121 in which a stator winding 122 is arranged, in particular in winding slots of the stator body 121. The stator winding 122 projects on both axial sides of the stator body 121 and forms a winding head 123, 124 there. The stator body 121 can be made of iron or an iron alloy, e.g., steel or sheet metal, and can be provided, for example, as a laminated core. The stator winding 122 can, for example, be made of copper or a copper alloy.

[0052] A temperature sensor 130, e.g. a negative temperature coefficient thermistor (NTC thermistor), is arranged on the stator 120, e.g. in the winding head 124 of the stator winding 122.

[0053] A cooling system 140 is provided to transport one or more cooling fluids for cooling the rotor and / or the stator and / or the entire electric machine 100. Such cooling fluids can be, for example, cooling water, cooling air, or cooling oil.

[0054] A control unit 150, e.g. an engine control unit of the vehicle, is provided for controlling the electric machine 100 and can, for example, have an inverter circuit.

[0055] In order to be able to determine the temperatures of the rotor 110 and the stator 120 precisely and reliably during operation of the electric machine 100, the control unit 150 is configured, in particular in terms of programming, to carry out an embodiment of a method according to the invention. In the course of this, a first thermal calculation model, which models thermal variables of the stator 120, and a second thermal calculation model, which models thermal variables of the rotor 110, are executed independently of one another in the control unit 150. These calculation models can, for example, be determined or created during a manufacturing or configuration process of the electric machine 100 and stored in the control unit 150. During operation of the electric machine 100, the control unit 150 uses the first thermal calculation model or stator model to determine a temperature of the stator 120 and the second thermal calculation model or stator model to determine a temperature of the stator 120.Rotor model a temperature of the rotor 110. Depending on these specific temperatures, the control unit 150 controls the electrical machine 100, for example, in such a way that the machine 100 can be operated close to thermal limit temperatures of thermally critical components of the stator 120 and the rotor 110 without causing danger or damage to the electrical machine 100.

[0056] The determination of the independent stator and rotor models according to an embodiment of the present invention is explained below with reference to Figures 2 to 5.

[0057] In Figure 2, a stator model according to an embodiment of the method according to the invention is shown schematically and designated by 200.

[0058] The stator model 200 has an interface 230 for the temperature 240 of the rotor 110. This interface 230 represents an open interface for the heat exchange between the rotor 110 and the stator 120 and an external, open coupling to the temperature 240 of the rotor 110. This interface allows the heat exchange between the rotor 110 and the stator 120 to be considered independently of the rotor model. For example, the rotor temperature 240 can be specified manually or externally via the interface 230, e.g., as a result of the rotor model.

[0059] In the stator model 200, thermal variables of the stator body 121 and thermal variables of the stator winding 122 are mapped dependently. For example, a first hotspot or a first thermal node 210 is modeled in the stator model 200, which represents the stator winding 122. For example, this first node 210 can represent a temperature Tstator.cu of the stator winding 122, a thermal power loss P v , stator, cu of the stator winding 122 and a thermal capacitance Ccu of the stator winding 122 are dependent on one another.

[0060] Furthermore, a second hotspot or node 220 is modeled in the stator model 200, which represents the stator body 121. For example, this second node 220 can represent a temperature Tstator, Fe of the stator body 121, a thermal power loss P v , stator, Fe of the stator body 121 and a thermal capacitance CF6 of the stator body 121 are dependent on one another.

[0061] For example, the thermal power loss P v , stator, cu and the thermal capacitance Ccu of the stator winding 122 as well as the thermal power loss Pv, stator, Fe and the thermal capacitance CF6 of the stator body 121 are each modeled as a function of a first operating point related to the stator 120. This first operating point describes, for example, a combination of current values ​​for a torque, a speed, a phase current, an intermediate circuit voltage, a control frequency, a modulation method, a temperature of a cooling fluid for cooling the stator 120, a volume flow of this cooling fluid for cooling the stator 120, a power loss of the stator

[0062] 120 and the rotor temperature 110.

[0063] In the stator model 200, a variable thermal resistance 211 is connected between the temperature of the stator winding 122 and the temperature of the stator body

[0064] 121, whereby this thermal resistance 211 connects the first node 210 and the second node 220. This thermal resistance 211 is determined as a function depending on the first operating point, Rc u =h(Grandpa).

[0065] Furthermore, a variable thermal resistance 241 between the rotor 110 and the stator 120 is modeled in the stator model 200, which, for example, links the second node 220 and the rotor temperature 240 as a boundary condition. For example, this thermal resistance 241 is determined as a function dependent on the speed of the electric machine 100 and dependent on the first operating point, RR Ot=f(nEm, Opi). The stator model 200 further models the temperature 250 of the cooling fluid for cooling the stator and a first thermal resistance 251 and a second thermal resistance 252 between the temperature of the stator body 121 and the temperature 250 of the cooling fluid. This cooling fluid can be supplied, for example, using the cooling system. These thermal resistances 251, 251 can link the second node 220 and the temperature 250 of the cooling fluid as a boundary condition. The first thermal resistance 251 can be determined, for example, as a function dependent on the first operating point, RFei=k(Opi). The second thermal resistance 252 can be determined, for example, as a function dependent on the temperature and volume flow of the cooling fluid, RFe2=g(V'cooling fluid, TKÜM- fluid)

[0066] For example, the stator model 200 represents a basic version as a forward simulation in which the temperature sensor 130 installed in the stator 120 is not taken into account. This basic model can be expanded using the stator temperature sensor 130, as explained below with reference to Figures 3a to 3d.

[0067] Figures 3a to 3d each schematically show a stator model according to an embodiment of the method according to the invention, wherein the same reference numerals in Figures 2, 3a, 3b, 3c and 3d denote the same or equivalent elements.

[0068] In Figure 3a, the embodiment of the extended stator model is designated 300. Furthermore, thermal variables relating to temperature sensor 130 are modeled in stator model 300. Stator model 300 has a further node 310, which represents the temperature of temperature sensor 130. Furthermore, a thermal capacitance 312 of temperature sensor 130 is modeled, for example, as a function dependent on the first operating point. Furthermore, stator model 300 models a variable thermal resistance 311 between the temperature of stator winding 122, the temperature of stator body 121, and the temperature of temperature sensor 130. For example, thermal resistance 311 can link nodes 210 and 310 and be determined, for example, as a function dependent on the rotational speed and the first operating point, Rcu,sensor=f(nEm, Opi).

[0069] In the extended stator model 300, a variable thermal resistance 321 is also modeled between the temperature 250 of the cooling fluid for cooling the stator and the temperature 310 of the temperature sensor 130. This thermal resistance 321 can be determined, for example, as a function of the speed and the first operating point, Rcooiant,sensor=f(nEm, Opi).

[0070] Using the stator temperature sensor 130, the accuracy of the stator hotspot temperature prediction can be increased by evaluating the deviation between the measured sensor temperature and the expected, modeled temperature and, for example, providing a weighted feedback to the stator model 300. For example, a Luenberger observer, Kalman filter, and / or PI controller can be used for this purpose.

[0071] The cooling system 140 may further comprise an oil cooling system for cooling the stator 100, wherein the extended stator model may also take into account thermal variables related to this oil cooling system, as explained below with reference to Figure 3b.

[0072] In Figure 3b, the embodiment of the extended stator model is designated 300'. As shown in Figure 3b, the temperature 340 of the oil is specified as a boundary condition. A variable thermal resistance 341 is modeled between the temperature 340 of the oil and the temperature 210 of the stator winding 122. The cooling path of the oil cooling can be represented in the stator model 300, for example, by connecting it to the first node 210. The thermal resistance 341 between the oil temperature 340 and the temperature of the stator winding 210 can, for example, be determined as a function of the speed and of another operating point, Rcuöi=f(nEm, Opa). This another operating point describes, for example,a current combination of torque, speed, phase current, intermediate circuit voltage, control frequency, modulation method, cooling fluid temperature (for cooling the stator 120), volume flow of the cooling fluid for cooling the stator 120, oil temperature, volume flow of the oil, stator power loss and rotor temperature.

[0073] Furthermore, the stator model 300' has a variable thermal resistance 331 between the temperature 340 of the oil and the temperature 310 of the temperature sensor 130, e.g., as a function depending on the rotational speed, the temperature of the oil and the first operating point, Röi,sensor=f(nEm, TÖI, Opi).

[0074] To improve the model of the stator temperature sensor 130, the number of nodes in the sensor submodel can be increased, as explained below with reference to Figure 3c.

[0075] In Figure 3c, the embodiment of the extended stator model is designated 300". In the stator model 300", instead of the node 310 of the model 300 or 300', a first node 350 and a second node 350 are provided, which each represent the temperature of the temperature sensor 130. The first node 350 can, for example, represent a first temperature Ts e - nsori of the temperature sensor 130, and the second node 350 can, for example, represent a second temperature Tsensor2 of the temperature sensor 130. Furthermore, a first thermal capacitance 351 of the first node 350 and a second thermal capacitance 352 of the second node 360 ​​are modeled in the stator model 300".

[0076] Furthermore, the stator model 300" models a first variable thermal resistance 353 between the temperature of the stator winding 122 and the first temperature Tsensori of the temperature sensor 130. For example, this first thermal resistance 353 can link the nodes 210 and 350 and can be determined, for example, as a function depending on the speed and the first operating point, Rcu,sensori = f(nEm,Opi). A second variable thermal resistance 354 is modeled between the first temperature Tsensori and the second temperature Tsensor2 of the temperature sensor 130 and connects the nodes 350 and 360. This second variable thermal resistance 354 can be determined depending on the speed and the first operating point, Rsensorl ,Sensor2 = f(n Em ,Grandpa).

[0077] A third variable thermal resistance 355 is modeled between the temperature 250 of the cooling fluid for cooling the stator and the second temperature Tsensor2 of the temperature sensor 130. This third variable thermal resistance 355 can, for example, be determined as a function depending on the speed and the first operating point, Rcoolant,Sensor2 = f(n Em ,Grandpa).

[0078] The accuracy of models 200, 300, 300', and 300" can be further improved, for example, by separately considering the part of the stator winding 122 within the slots of the stator body 120 and the part of the stator winding 122 extending beyond the stator body 120, i.e., the winding heads 123, 124. This allows, for example, a change in the distribution of the winding losses. For example, stator winding losses can be divided into losses in a winding head and losses in a slot. The winding head losses Pv, stator, cu, wickeikopf can be fed into node 210. The slot losses in the slot P v , stator, cu. winding slot can be fed into node 220. Knowing the respective node temperatures 210 and 220, the individual temperature-dependent electrical resistances in the winding head 123, 124 and in the slot can be determined and updated. The stator iron losses P v, stator, Fe can additionally be fed into node 220 as explained above.

[0079] However, to improve model accuracy, it is also conceivable to add another node and model the stator winding 122 using two nodes, whereby the winding losses in the winding overhang 123, 124 and the losses in the slot can then be better distributed between the nodes, as will be explained below with reference to Figure 3d. In Figure 3d, the embodiment of the extended stator model is designated 300''. In this stator model with 300'', in comparison to models 200, 300, 300' and 300", the node 210 with respect to the stator winding 122 is replaced by two nodes 370 and 380, wherein the node 370 represents the stator winding 122 in a winding slot of the stator 120 and wherein the node 380 represents a winding overhang 123, 124.

[0080] Node 370 represents the temperature Tstator.cu.winding slot, the thermal power loss Pv, stator, Cu, winding slot, and the thermal capacitance Ccu.winding slot of the stator winding 122 in the winding slot, dependent on one another. Node 380 represents the temperature Tstator.cu.winding head, the thermal power loss Pv, stator, cu, winding head, and the thermal capacitance Ccu.winding head of the winding head 123, 124, dependent on one another. The losses in the winding head P v , stator, cu.wickeikopt and in the slot P v , stator, cu.wickiungsnut can thus be directly distributed to the nodes 370 and 380. The stator iron losses P v , stator, Fe are fed into node 220 as explained above.

[0081] In the stator model 300'", a variable thermal resistance 371 is further modeled between the node 220 with respect to the stator body 121 and the node 370 with respect to the winding slot. This thermal resistance 371 can be determined as a function depending on the first operating point, RK™- ten220,370= f(0 P i).

[0082] Another variable thermal resistance 372 is provided between the node 370 relative to the winding slot and the node 380 relative to the winding head. This thermal resistance 372 can also be determined as a function of the first operating point, Ri <noten37o,38o=f(Opi) .

[0083] As shown in Figure 3d, a direct connection may also be provided between node 380 and resistor 353. This is to be understood in particular in such a way that the connection of the sensor path, symbolized by nodes 350 and 360, can be carried out optionally via node 370 or node 380, in particular depending on the installation location of the sensor and depending on whether a 2-node model, symbolized by nodes 220 and 370, or a 3-node model, symbolized by nodes 220, 370, and 380, is to be used to map the stator hotspot temperature.

[0084] It is understood that replacing the node 210 with respect to the stator winding 122 by the two nodes 370 and 380 with respect to the winding slot and the winding head, as explained here with respect to the model 300", can also be applied in a corresponding manner to the stator models 200, 300 and 300'.

[0085] In Figure 4, a rotor model according to an embodiment of the method according to the invention is shown schematically and designated by 400.

[0086] Rotor model 400 is determined independently of stator model 200 or 300. In rotor model 400, heat exchange between rotor 110 and stator 120 is considered independently of the heat exchange in stator model 200 or 300. Stator models 200, 300, and rotor model 400 are not linked via the heat exchange between rotor 110 and stator 120. Energy conservation between stator model 200, 300, and rotor model 400 with respect to the heat exchange between rotor 110 and stator 120 is not assumed.

[0087] Corresponding to the stator model 200 or 300, the rotor model 400 has an interface 420 for the temperature 430 of the stator 120. This interface 420 represents an open interface for the heat exchange between the rotor 110 and the stator 120 and an external, open coupling to the temperature 430 of the stator 120. The heat exchange between the rotor 110 and the stator 120 can be taken into account via this interface 420 in the rotor model 400 independently of the stator model 200, 300. For example, the stator temperature 430 can be specified manually or externally via the interface 420, e.g., as a result of the stator model 200, 300.

[0088] In the rotor model 400, the temperature 410 of the rotor 110, a thermal capacity 411 of the rotor 110, and a thermal power loss 412 of the rotor 110 are modeled. For example, this temperature TRotor, this thermal capacity ÜRotor, and this thermal power loss P v, rotor of the rotor 110 can be mapped in a node point or hotspot for the rotor 110. The thermal power loss 412 and the thermal capacitance 411 of the rotor 110 can, for example, each be modeled as a function of a second operating point related to the rotor 110, wherein this second operating point describes a combination of current values ​​for the torque, the speed, the phase current, the intermediate circuit voltage, the control frequency, the modulation method, a temperature of the cooling fluid for cooling the stator 100, a volume flow of this cooling fluid for cooling the stator 100, a temperature of the cooling fluid for cooling the rotor 110, a volume flow of this cooling fluid for cooling the rotor 110, a power loss of the rotor 110, the temperature of the stator 120 and the temperature of the transmission oil.

[0089] The rotor model 420 further comprises a variable thermal resistance 431 between the rotor 110 and the stator 120 or between the temperature 410 of the rotor 110 and the temperature 430 of the stator 120, wherein this thermal resistance 431 can be determined depending on the rotational speed of the electric machine 100 and on the second operating point, Rstator(nEm, Op2).

[0090] Furthermore, the temperature 450 of the cooling fluid for cooling the stator 100, the temperature 460 of the rotor-internal cooling fluid for cooling the rotor 110 and a temperature 470 of the transmission oil are modeled as boundary conditions in the rotor model 420, as well as a variable thermal resistance 451 between the temperature 410 of the rotor 110 and the temperature 450 of the cooling fluid for cooling the stator 100, a variable thermal resistance 461 between the temperature 410 of the rotor 110 and the temperature 460 of the cooling fluid for cooling the rotor 110 and a variable thermal resistance 471 between the temperature 410 of the rotor 110 and the temperature 470 of the transmission oil.

[0091] The thermal resistance 451 with respect to the temperature 450 of the cooling fluid can be determined depending on the speed and the second operating point, R eMachinecooiant(nEm, OP2). The thermal resistance 461 with respect to the temperature 460 of the rotor-internal cooling fluid can be determined depending on the speed, the temperature and the volume flow of the rotor-internal cooling fluid as well as the second operating point, RR O torintemaicooiang(nEm, TR O t o - rintemaicooiant, OP2). The thermal resistance 471 with respect to the temperature 470 of the transmission oil can be determined depending on the speed and the second operating point, RoilGearbox (n E m, OP2).

[0092] By using the two separate, independent calculation models for the stator 120 and the rotor 110 with deliberate softening or intentional non-compliance with the energy balance between rotor 110 and stator 120, the temperatures of the stator 120 and the rotor 110 can be modeled and determined more precisely than would be the case with an overall thermal model of the electrical machine 100 in which the heat exchange between rotor and stator is physically correctly represented, as explained below with reference to Figure 5.

[0093] Figure 5 shows schematically a diagram 500 of a temperature plotted against time.

[0094] Curve 510 represents the time course of the maximum stator temperature or stator hotspot temperature that was actually measured on a test bench during operation of the electric machine 100.

[0095] Curve 520 represents the corresponding stator temperature determined using the stator model 200 according to an embodiment of the invention, which was executed on the controller 150 during operation of the electric machine 100.

[0096] Curve 530 represents the time course of the temperature of the cooling fluid for cooling the stator 120.

[0097] As can be seen in Figure 5, the stator temperature can be reproduced relatively accurately using the stator model 200.

Claims

Claims 1 . A method for determining temperatures of an electrical machine (100) having a rotor (110) and a stator (120), comprising: determining a first thermal calculation model (200, 300, 300', 300", 300"') which models thermal variables of the stator (120); Determining a second thermal calculation model (400) which models thermal variables of the rotor (110); Determining a heat exchange between the rotor (110) and the stator (120) in the first thermal calculation model (200, 300, 300', 300", 300'") and in the second thermal calculation model (400) independently of one another; Determining a temperature of the stator (120) using the first thermal calculation model (200, 300, 300', 300", 300'"); and Determining a temperature of the rotor (110) using the second thermal calculation model.

2. The method according to claim 1, wherein no energy conservation is assumed between the first thermal calculation model (200, 300, 300', 300", 300'") and the second thermal calculation model (400) with respect to the heat exchange between the rotor (110) and the stator (120).

3. The method according to claim 1 or 2, wherein the first thermal calculation model (200, 300, 300', 300", 300'") has an interface (230) for the temperature (240) of the rotor (110) and wherein the second thermal calculation model (400) has an interface (430) for the temperature (420) of the stator (120).

4. The method according to any one of the preceding claims, further comprising: determining operating parameters of the electric machine (100); Determining the temperature of the stator (120) using the first thermal calculation model (200, 300, 300', 300", 300"') depending on the determined operating parameters; and Determining the temperature of the rotor (110) using the second thermal calculation model (400) depending on the determined operating parameters.

5. The method according to one of the preceding claims, wherein the thermal variables of the stator (120) in the first thermal calculation model (200, 300, 300', 300", 300'") and / or the thermal variables of the rotor (110) in the second thermal calculation model (400) are each modeled as a function of one or more of the following operating parameters: a torque of the electric machine (100); a rotational speed of the electric machine (100); a phase current of the electric machine (100); an intermediate circuit voltage of the electric machine (100); a control frequency of the electric machine (100); a modulation method of the electric machine (100); a temperature of a cooling fluid for cooling the stator (120); a volume flow of the cooling fluid for cooling the stator (120); a temperature of a cooling fluid for cooling the rotor (110); a volume flow of this cooling fluid for cooling the rotor (110); a temperature of a transmission oil.

6. Method according to one of the preceding claims, wherein the first thermal calculation model (200, 300) maps thermal variables of a stator body (121) and thermal variables of a stator winding (122) of the stator (120) dependently from one another.

7. Method according to one of the preceding claims, wherein the first thermal calculation model (200, 300, 300', 300") models one or more of the following thermal variables dependently on one another: a temperature (210) of a stator winding (122) of the stator (120); a thermal power loss (210) of the stator winding (122); a thermal capacitance (210) of the stator winding (122); a temperature (220) of a stator body (121) of the stator (120); a thermal power loss (220) of the stator body (121); a thermal capacitance (220) of the stator body (121); a thermal resistance (211) between the temperature (210) of the stator winding (122) and the temperature (220) of the stator body (121); a thermal resistance (241) between the rotor (110) and the stator (120); a temperature (250) of a cooling fluid for cooling the stator (120) and a thermal resistance (251, 252) between the temperature (220) of the stator body (121) and the temperature (250) of the cooling fluid for cooling the stator (120).

8. The method according to one of claims 1 to 6, wherein the first thermal calculation model (300') models one or more of the following thermal variables dependent on one another: a temperature (370) of the stator winding (122) in a winding slot of the stator (120); a thermal power loss (370) of the stator winding (122) in the winding slot of the stator (120); a thermal capacitance (370) of the stator winding (122) in the winding slot of the stator (120); a temperature (380) of a winding overhang (123, 124) of the stator (120); a thermal power loss (380) of the winding overhang (123, 124) of the stator (120); a thermal capacitance (380) of the winding overhang (123, 124) of the stator (120); a temperature (220) of a stator body (121) of the stator (120); a thermal power loss (220) of the stator body (121); a thermal capacity (220) of the stator body (121);a thermal resistance (371) between the temperature (370) of the stator winding (122) in the winding slot of the stator (120) and the temperature (220) of the stator body (121); a thermal resistance (372) between the temperature (370) of the stator winding (122) in the winding slot of the stator (120) and the temperature (380) of the winding overhang (123, 124) of the stator (120); a thermal resistance (241) between the rotor (110) and the stator (120); a temperature (250) of a cooling fluid for cooling the stator (120); and a thermal resistance (251, 252) between the temperature (220) of the stator body (121) and the temperature (250) of the cooling fluid for cooling the stator (120).

9. The method according to one of the preceding claims, wherein the second thermal calculation model (400) models one or more of the following thermal variables dependent on one another: the temperature (410) of the rotor (110); a thermal power loss (412) of the rotor (110); a thermal capacity (411) of the rotor (110); a thermal resistance (431) between the rotor (110) and the stator (120); a temperature (450) of a cooling fluid for cooling the stator (100); a thermal resistance (451) between the rotor (110) and the cooling fluid for cooling the stator (100); a temperature (460) of a cooling fluid for cooling the rotor (110); a thermal resistance (461) between the rotor (110) and the cooling fluid for cooling the rotor (110); a temperature (470) of a transmission oil; a thermal resistance (471) between the rotor (110) and the transmission oil.

10. The method according to any one of the preceding claims, wherein the electric machine (100) has a temperature sensor (130) arranged on or in the stator (120), wherein the first thermal calculation model (300, 300') models one or more of the following thermal variables dependent on one another: a temperature (310) of the temperature sensor (130); a thermal capacitance (312) of the temperature sensor (130); a thermal resistance (311) between the temperature of the stator winding (122), the temperature of the stator body (121), and the temperature (310) of the temperature sensor (130); a temperature (250) of a cooling fluid for cooling the stator (120); a thermal resistance (321) between the temperature (250) of the cooling fluid for cooling the stator (120) and the temperature (310) of the temperature sensor (130); a temperature (340) of an oil; a thermal resistance (331) between the temperature (340) of the oil and the temperature (310) of the temperature sensor (130).

11. The method according to one of claims 1 to 9, wherein the electric machine (100) has a temperature sensor (130) arranged on or in the stator (120), wherein the first thermal calculation model (300", 300"') models one or more of the following thermal variables dependent on one another: a first temperature (350) of the temperature sensor (130); a second temperature (360) of the temperature sensor (130); a first thermal capacitance (351) of the temperature sensor (130); a second thermal capacitance (352) of the temperature sensor (130); a first thermal resistance (353) between the temperature of the stator winding (122) and the first temperature (350) of the temperature sensor (130); a second thermal resistance (354) between the first temperature (350) of the temperature sensor (130) and the second temperature (360) of the temperature sensor (130); a temperature (250) of a cooling fluid for cooling the stator (120);a third thermal resistance (355) between the temperature (250) of the cooling fluid for cooling the stator (120) and the second temperature (360) of the temperature sensor (130); 12. Method according to one of the preceding claims, wherein the electric machine (100) has an oil cooling system, wherein the first thermal Calculation model (300') models one or more of the following thermal variables dependent on one another: a temperature (340) of an oil of the oil cooling system; a thermal resistance (341) between the temperature (340) of the oil of the oil cooling system and the temperature (210) of the stator winding (122).

13. A computing unit (150) which is designed to carry out all the process steps of a To carry out the method according to one of the preceding claims.

14. A computer program which causes a computing unit (150) to carry out all method steps of a method according to one of claims 1 to 12 when it is executed on the computing unit (150).

15. A machine-readable storage medium having stored thereon a computer program according to claim 14.

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