Method for generating lost heat in an electric power train for a vehicle, and system

Abstract

The invention relates to a method for generating lost heat in an electric power train (10) for a vehicle and to a system (8), the power train (10) having at least one converter (12) and an electric motor (14). An initial rotor flux axis (72) of the electric motor (14) is determined in a stator-oriented coordinate system (70) by a control device (36), a DC component (76) of a current space vector (68) is introduced into the stator-oriented coordinate system (70) by the control device (36) in such a way that the DC component (76) of the current space vector (68) is oriented parallel and / or antiparallel to the determined initial rotor flux axis (72), pulse-width-modulated control signals (G1, G2) are output at least indirectly to switching devices (18, 20) of the converter (12) by the control device (36) such that that current components corresponding to the DC component (76) of the current space vector (68) are supplied to the electric motor (14), and a power loss caused by the current space vector (68) is dispensed as lost heat to at least one heat transfer circuit (52).

Description

[0001] Method for generating waste heat in an electric powertrain for a vehicle and system

[0002] The invention relates to a method for generating waste heat in an electric drive train for a vehicle and a system.

[0003] Battery-powered electric vehicles generate comparatively little waste heat in their drive units compared to vehicles with combustion engines. Therefore, battery-powered electric vehicles require additional electric heaters or heat pumps to provide the necessary heat output for heating the passenger compartment and / or the battery cooling circuit, for example, during optimized fast charging while taking into account the optimized temperature characteristics. The components required for this result in additional costs, increased maintenance, and added weight, which in turn affects the vehicle's range.

[0004] The object of the invention is to provide the desired heating output at low cost and low weight.

[0005] The problem is solved according to the invention by a method for generating waste heat in an electric powertrain for a vehicle. The powertrain has at least one inverter and one electric motor. The method comprises at least the following steps:

[0006] An initial rotor flux axis of the electric motor is determined by a control device in a stator-oriented coordinate system.

[0007] A common-mode component of a current space vector is impressed into the stator-oriented coordinate system by the control device in such a way that the common-mode component of the current space vector is oriented parallel and / or antiparallel to the determined initial rotor flux axis.

[0008] Pulse-width modulated control signals are output, at least indirectly, to switching devices of the inverter by the control device, so that the electric motor is supplied with current components corresponding to the DC component of the current space vector. Power loss caused by the current space vector is dissipated as waste heat to at least one heat transfer circuit.

[0009] The underlying idea of ​​the invention, in short, is to control the drive motor, at least partially, in a way that generates more waste heat than is necessary for the currently required drive power. To generate this heat loss, a stator-oriented coordinate system is used, i.e., a coordinate system that does not rotate with the rotation of the electric motor's magnetic field. In other words, a non-rotating coordinate system is used. While typical control of the electric motor in known control methods is based on the rotating d / q coordinate system, the stationary coordinate system commonly referred to as "assy" is used instead.

[0010] The initial rotor flux axis can be defined by the rotor position relative to the stator (synchronous motor), by the rotor current in the rotor winding (asynchronous motor), or by the rotor flux generated in the squirrel cage (asynchronous machine). Therefore, if a current space vector is precisely impressed (injected) along the initial rotor flux axis, no torque will be produced by the electric motor, provided the determined initial rotor flux axis exactly matches the actual rotor flux axis.

[0011] By considering the stator-oriented coordinate system and the orientation of the imprinted current space vector relative to the initial rotor flux axis, a (generally possible) misorientation of the imprinted current space vector along the determined initial rotor flux axis relative to the actual rotor flux axis generally leads to the occurrence of a torque. However, the torque depends on the angular difference, which is typically small. Furthermore, the torque acts in the direction of the determined initial rotor flux axis of the electric motor. In other words, the method utilizes a self-centering effect of the stator-oriented coordinate system, so that only negligible torques occur. Nevertheless, the drivetrain can be used to generate waste heat to meet the heating requirements of vehicle components.Since current control methods only consider co-rotating coordinate systems, an injection direction that rotates according to the rotation of the coordinate system itself can be taken into account. However, a deviation between the injection direction at a given time relative to the actual orientation of the rotor flux axis in this coordinate system at that time is not compensated for due to the rotation. This means that in this case, the electric motor continuously generates a torque, thereby placing a constant load on the components coupled to the electric motor. Furthermore, any irregularity in the position signal can also lead to irregularities in the impressed current space vector and thus to irregularities in the torque.This effect can be suppressed by fixing the angle according to which the DC component of the current space vector is impressed, which is made possible by the stator-oriented coordinate system.

[0012] Optionally, the control device includes or is coupled to a pulse width modulator. The pulse width modulator outputs the pulse-width modulated control signals, at least indirectly, to switching devices of the inverter. These control signals are used to deliberately operate the switching devices inefficiently, thus generating the desired power loss. However, the control signals can be adjusted to ensure the orientation of the DC component of the current space vector relative to the initial rotor flux axis is maintained, i.e., a parallel or antiparallel alignment.

[0013] Preferably, the control device varies the signal profile of the pulse-width modulated control signals to adjust the proportions of power losses caused in the inverter and / or the electric motor. This allows influence to be exerted on where the power losses originate. For example, the inverter and the electric motor can be coupled with different heat transfer circuits to heat different vehicle components. This increases the variability of the method.

[0014] Preferably, the electric drive train can be coupled with a single heat transfer circuit that jointly provides cooling for the inverter and / or the electric motor. This single heat transfer circuit can, in particular, be a cooling circuit that uses water and / or oil as the cooling medium, hereinafter referred to as the water circuit or oil circuit.

[0015] For example, both the inverter and the electric motor can be water-cooled.

[0016] Alternatively, the inverter can be water-cooled and the electric motor oil-cooled.

[0017] In another alternative, the inverter can be water-cooled and the electric motor can be partly water-cooled and partly oil-cooled.

[0018] For this purpose, the internal oil circuit of the drive train, if present, can be coupled to the existing water circuit by means of a heat exchanger, so that the oil can be heated into the water.

[0019] Particularly preferably, the control signals can be adapted by the control device in such a way as to adjust a modulation method, a switching frequency, a slope of the switching edges of the switching devices, a profile shape of the alternating current generated in the electric motor based on the signal profile, or combinations thereof. The profile shape of the generated alternating current can be, for example, a triangular profile, a rectangular profile, a sawtooth profile, a sinusoidal profile, or a combination thereof. Overall, this results in a multitude of possibilities for influencing the control signals and thus also the power losses in the inverter and / or in the electric motor as required.

[0020] In one embodiment, the control device can inject an additional current space vector and / or an additional current space vector component, which has an additional AC component in addition to the DC component of the current space vector in the stator-oriented coordinate system. This means that the current space vector is superimposed with an additional current space vector / an additional current space vector component. Since the additional AC component is implemented by means of a different control of the inverter's switching devices, this enables a time-averaged symmetrical current supply to the windings of the electric motor (phases of the stator). In other words, the resulting power loss and thus the thermal load can be distributed more evenly over all windings of the electric motor (phases of the stator) on average over time.Due to the more even distribution of power loss across the electric motor windings, the overall average power loss can also be increased, especially compared to an asymmetrical current distribution across the windings. Asymmetrical current distribution could cause derating at a lower overall power loss, as individual components would be overloaded. In other words, the more even distribution, facilitated by the additional alternating current component, allows for the generation of more waste heat per unit of time, which can then be transferred to the heat transfer circuit. This is particularly advantageous when the electric motor is stationary, for example, when the vehicle is parked.

[0021] Typically, the frequency of the alternating component can be chosen to be relatively high, so that the variation in power loss, taking the additional alternating component into account, can be negligible. In this case, the comparatively high-frequency variation in power loss is largely suppressed due to the significantly larger thermal time constants, i.e., due to the thermal inertia of the drivetrain components.

[0022] In general, the additional switching component can also be used, if desired for specific applications, to influence the resulting power loss as needed and depending on the time. In particular, time-varying power losses can also be generated in this way, if this is desired for specific applications.

[0023] Optionally, the additional switching component is oriented parallel or antiparallel to the determined initial rotor flux axis.

[0024] Alternatively, the additional switching component can be oriented orthogonally to the determined initial rotor flux axis.

[0025] Alternatively, several additional components can be injected, for example alternately, oriented on the one hand along the determined initial rotor flow axis and on the other hand orthogonally to it.

[0026] Although the additional alternating component can be oriented orthogonally to the determined initial rotor flux axis, if appropriately chosen, it does not result in a continuous torque output. This is achieved by the additional alternating component having a sufficiently high frequency so that the resulting torque averages out to zero over time. In other words, the additional alternating component can be a so-called mean-value-free alternating signal. The average value is zero over a period. Consequently, no non-negligible forward or reverse torque is generated, thus preventing any stress on the components coupled to the electric motor's rotor. In other words, the additional alternating component is chosen such that, on average, no non-negligible torque is generated over integer multiples of a period of the additional alternating component.

[0027] Preferably, the additional switching component has a frequency selected taking into account at least one of the following factors: the audible or perceptible vibrations in the vehicle, so-called NVH disturbances (noise, vibration, harshness); the range of mechanical resonance frequencies of the powertrain or its components. These resonance frequencies are typically in the range between 0 Hz and 50 Hz; the resonances, in particular of housing components, which, when excited, lead to the acoustic radiation of vibrations in the human hearing range. Such components then act similarly to a loudspeaker. This range particularly concerns the frequency range between 20 Hz and 20 kHz; the power losses caused by the selected frequency.Higher injection frequencies generally lead to higher losses in the electric motor at the same injection amplitude, because frequency-dependent losses increase disproportionately with frequency; a sufficiently high frequency to justify the assumption that the output torque corresponds sufficiently closely to the time average of zero; or.

[0028] Combinations thereof.

[0029] In one embodiment, the sign of the DC component of the current space vector is varied after an adjustable time interval. This change in sign corresponds to a change in the orientation of the DC component of the current space vector from parallel to antiparallel relative to the initial rotor flux axis, or vice versa. This prevents permanently unbalanced load conditions between individual components of a converter half-bridge, such as the upper and lower switching devices (so-called high-side and low-side switching devices) and diodes. This unbalanced load would otherwise occur, for example, in insulated-gate bipolar transistors (IGBTs).

[0030] Optionally, the control device receives a minimum heat output request from an external vehicle component. Based on this minimum heat output request, the control device adjusts at least one component of the current space indicator such that the resulting power loss is at least equal to the minimum heat output request. This allows the heating requirement for vehicle components to be determined and transmitted to the control device as a minimum heat output request. In particular, this enables the heat loss provided by the resulting power loss to be adjusted situationally and according to demand.

[0031] In one embodiment, the heat transfer circuit can be at least indirectly coupled to vehicle components requiring heating, such as a high-voltage battery or a passenger compartment. By utilizing the waste heat generated during the process, additional heating elements that would otherwise be needed to heat the corresponding vehicle components can be eliminated or reduced in size. If individual components can be omitted, the necessary wiring is also eliminated. This makes the vehicle less complex. Furthermore, the vehicle is lighter, which increases its range for a comparable amount of energy used for propulsion (electric charge and / or fuel).

[0032] Preferably, the control device adjusts at least one component of the current space vector based on the minimum heat output requirement only to the extent that the electrical and thermal load limits of the drive train or its components are maintained, i.e., not exceeded as a result of the process. This ensures that the drive train components are subjected to only gentle stress, thus guaranteeing a long service life.

[0033] According to one aspect, the control device can determine the angle of the initial rotor flux axis in the stator-oriented coordinate system, at least in part, based on the rotor position of the electric motor, either detected by a rotor position sensor or determined without one. This allows the initial rotor flux axis to be determined with high precision, which is particularly advantageous for synchronous motors. In the case of asynchronous machines, any orientation of the applied current space vector can be used, provided the rotor flux has completely dissipated beforehand. If the rotor flux has not completely dissipated, the initial rotor flux axis must be determined and taken into account when applying the current space vector.

[0034] Optionally, the control device takes into account the phase currents of the electric motor when determining the control signals underlying the injected current space vectors. This allows the current for the drive train to be precisely controlled, for example with a feedback control loop, which also increases the precision with regard to the power loss caused by the current space vectors.

[0035] Preferably, the phase currents of the electric motor are measured using phase current sensors in the drive train. Alternatively, the phase currents of the electric motor can also be determined using other approaches. For example, the phase currents can be estimated at a given time based on specific motor parameters, such as:

[0036] Current sensors arranged between low-side switching devices and the DC link (power rail) of the inverter with the low / negative potential, at least one current sensor arranged in the commutation cell formed in the inverter in a negative or positive DC link (high / positive or low / negative potential),

[0037] - a motor model of the electric motor based on the output voltage of the inverter and the rotor position sensor.

[0038] According to a further aspect, the invention also relates to a computer program product comprising instructions that, when the computer program product is executed by a processor, cause the processor to execute at least part of the method described above, in particular the arithmetic and output steps. The advantages achieved by the method described herein are also achieved by the computer program product in a corresponding manner.

[0039] According to an additional aspect, the invention also relates to a computer-readable storage medium comprising instructions that, when the computer program product is executed by a processor, cause the processor to execute at least part of the method described above, in particular the arithmetic and output steps. The advantages achieved by the method described herein are also achieved correspondingly by the computer-readable storage medium.

[0040] According to a further aspect, the problem is also solved according to the invention by a system comprising a drive train for a vehicle with at least one inverter, an electric motor, and a control device coupled to the inverter and the electric motor. The control device is configured to: determine and store an initial angle of a rotor flux axis of the electric motor in a stator-oriented coordinate system of the electric motor, imprint a DC component of a current space vector parallel and / or antiparallel to the direction of the stored initial rotor flux axis, and output pulse-width modulated control signals at least indirectly to switching devices of the inverter, so that the electric motor is supplied with current components corresponding to the DC component of the current space vector.

[0041] The system has at least one heat transfer circuit that can absorb the power loss caused by the current space vector as waste heat.

[0042] The advantages achieved through the process are correspondingly realized by the system. In particular, power loss can be generated on demand. The electrical power loss is dissipated as waste heat via at least one heat transfer circuit to other vehicle components, enabling them to be heated as needed. This is achieved without the electric motor delivering a significant torque. This prevents continuous mechanical stress on the relevant components.

[0043] Optionally, the control device is configured to inject an additional current space vector / component, which has at least one alternating component in addition to the constant component of the impressed current space vector. The alternating component can be oriented orthogonally to the direction of the initial rotor flux axis. This provides an additional variation option to adjust the resulting power loss as required and / or to subject the drive train components to a uniform thermal load over time.

[0044] The heat transfer circuit is preferred as a cooling system for the

[0045] Components of the drive train are designed, particularly for the inverter and / or the electric motor. This allows power losses, which are converted into waste heat by the inverter and / or the electric motor, to be dissipated from the drive train via the cooling system. The generated waste heat is then transferred from the drive train components to heat a cooling medium in the heat transfer circuit.

[0046] Optionally, multiple heat transfer circuits can be provided, designed as separate cooling systems with different cooling media circuits. For example, the cooling requirements for the inverter may differ from those for the electric motor. Different heat transfer circuits allow the cooling requirements of the various components of the drive train to be met.

[0047] The heat transfer circuit can be coupled to different vehicle components to provide heat to these components, such as a passenger compartment or a high-voltage storage system. Naturally, multiple heat transfer circuits can also be coupled separately to one or more different vehicle components.

[0048] In one embodiment, the control device can be coupled to at least one device for determining the rotor position. For this purpose, the device can include a rotor position sensor. Alternatively, the device can be designed to estimate the rotor position of the electric motor without a position sensor. In this case, the device can be integrated as part of the control device itself. Knowing the rotor position, the control device can then determine the initial rotor flux axis.

[0049] Preferably, the control device is coupled with phase current sensors configured to detect phase currents supplied by the inverter to the electric motor and transmit them to the control device. This allows the adjustment of the current space indicators, based on control signals output by the control device to the inverter's switching devices, to influence power loss. The vehicle can be a land vehicle, rail vehicle, aircraft, or watercraft. It can be a hybrid vehicle, comprising both an internal combustion engine and an electric motor, or it can be a fully electric vehicle.

[0050] The invention, as well as further advantageous embodiments and developments thereof, are described and explained in more detail below with reference to the examples shown in the drawings. The drawings show:

[0051] Fig. 1 shows a drive train of a system according to the invention,

[0052] Fig. 2 shows a heat transfer circuit of the system according to the invention,

[0053] Fig. 3 shows a method according to the invention for generating waste heat in an electric drive train for a vehicle,

[0054] Fig. 4 shows a schematic representation of the actual rotor flux axis and a possible directional deviation of the current space vector in the stator-oriented coordinate system, and

[0055] Fig. 5 shows a schematic representation of a DC component and an AC component of the current space vector in the stator-oriented coordinate system.

[0056] All features mentioned below with reference to the exemplary embodiments and / or the accompanying figures can be combined alone or in any subcombination with features of the invention, including features of preferred embodiments.

[0057] Fig. 1 shows a drive train 10 of a system 8 according to the invention for a vehicle. The drive train 10 comprises at least one inverter 12 and an electric motor 14. The inverter 12 is configured to provide current signals for the electric motor 14 so that the electric motor 14 can output torque to a component of the vehicle, for example for propulsion.

[0058] In the embodiment shown, the converter 12 comprises a B6 bridge with three half-bridges 16. The following functionality is illustrated only with respect to one half-bridge 16, but is to be applied accordingly to all half-bridges 16 of the B6 bridge.

[0059] Each half-bridge 16 comprises a first switching device 18, for example a transistor, which acts as a high-side power switch, and a second switching device 20, for example also a transistor, which acts as a low-side power switch.

[0060] The transistors can be metal-oxide-semiconductor field-effect transistors (MOSFETs), insulated-gate bipolar transistors (IGBTs), or SiC or gallium nitride field-effect transistors (SiC or GaN FETs).

[0061] Between the first switching device 18 and the second switching device 20, each half-bridge 16 includes a central node 22 to output an alternating current signal, in this case L2, to the electric motor 14.

[0062] Three corresponding AC signals, L1, L2 and L3 (phase currents), are applied to the electric motor 14 via the three half-bridges 16. However, other topologies are also possible, which then require corresponding modifications to the converter 12, for example a six-phase electric motor 14.

[0063] The respective half-bridges 16 are coupled to a busbar structure 24 of the inverter 12. The inverter 12 is coupled to a DC voltage source 26, for example, a high-voltage storage device. The DC voltage source 26 comprises terminals 28 and 30, between which a high voltage (HV) is provided, for example, with a voltage amplitude of 100 V or more, in particular 400 V or 800 V.

[0064] Additionally, the inverter 12 includes a DC link capacitor 34, which serves as a coupling element between the DC voltage source 26 and the electric motor 14. The DC link capacitor 34 ensures that fluctuations in the coupling of the DC voltage source 26 with the AC side of the inverter 12, which is implemented by the switching devices 18, 20 taking into account the coupling with the electric motor 14, can be dampened. The current amplitude and / or voltage amplitude can be made more uniform by means of the DC link capacitor 34, for example, under varying load conditions. Depending on the switching state of the power switches 18, 20 in the inverter 12, different output voltages can be generated. In particular, the desired output voltage is achieved on average over a modulation period by a suitable combination of these switching states.To control the switching states of the switching devices 18, 20, the drive train 10 includes or is coupled to a control device 36. The control device 36 includes at least one computing unit, for example a processor 38, a field-programmable gate array (FPGA), or a digital signal processor (DSP).

[0065] The control device 36 is configured to provide corresponding control signals G1 and G2 for the switching devices 18 and 20, so that the switching positions of the switching devices 18 and 20 are influenced based on these control signals. The control signals G1 and G2 depend on a modulation signal determined by the processor 38. For example, the control device 36 has a pulse width modulator 40 to generate the underlying modulation signal.

[0066] The control signals G1 and G2 are output to gate driver circuits 44, which are coupled to the gate electrodes of the switching devices 18 and 20. Based on the control signals G1 and G2, the gate driver circuits 44 generate corresponding gate voltage signals to influence the switching states of the switching devices 18 and 20.

[0067] The control signals G1 and G2 can be influenced, in particular, based on the modulation signal of the pulse width modulator. This allows the switching frequency of the switching devices 18 and 20 between different switching states and the profile shape of the AC signals L1, L2, and L3 (phase currents) output by the inverter to be influenced. The slew rate of the switching edges can be adjusted by means of additional control signals via the gate driver circuits 44.

[0068] The control device 36 is generally coupled to other components of the drive train 10, for example, to the electric motor 14, the DC voltage source 26, or corresponding sensors. According to this embodiment, the drive train 10 includes phase current sensors 42 arranged between the center nodes 22 and the electric motor 14. The phase current sensors 42 are configured to detect the phase currents (AC signals) output by the inverter 12 and transmit them to the control device 36.

[0069] In addition, the drive train 10 according to this embodiment includes a rotor position sensor 46, which is configured to detect a rotor position of the electric motor 14 and transmit it to the control device 36.

[0070] Alternatively, the rotor position can also be estimated without a position sensor. For this purpose, the control device 36 can include a corresponding estimation algorithm.

[0071] Based on the received sensor data, the control device 36 can output corresponding control signals G1 and G2, for example, depending on the rotor position, i.e., the position of the rotor relative to the stator of the electric motor 14, using a current control loop. This applies corresponding current signals to the windings of the electric motor 14. The precise control of the electric motor 14, and thus the characteristics of the control signals G1 and G2, generally depend on a torque request 48, which the control device 36 receives from a higher-level component of the vehicle. The torque request 48 specifies the output torque to be provided by the electric motor 14.

[0072] For example, the torque requirement 48 can depend on the pedal position of a pedal in the vehicle.

[0073] Furthermore, the control device 36 is coupled with a storage device 50 in which a history of operating parameters and / or state parameters of the drive train 10, in particular of the converter 12, the electric motor 14, the rotor position sensor 46 and / or the phase current sensors 42, can be stored.

[0074] Fig. 2 shows an exemplary heat transfer circuit 52 of the system 8 according to the invention. In general, the system 8 can have several heat transfer circuits 52. The switching operations of the switching devices 18, 20 result in switching losses in the switching devices 18, 20 in the inverter 12. Due to the way in which the output voltage is generated by means of pulse-width modulated signals, additional current fluctuations, so-called current ripple, are generated, which cause additional losses in the electric motor 14 compared to pure sinusoidal current operation. Likewise, line losses (ohmic losses) in the inverter 12 and the electric motor 14 lead to electrical power losses in the drive train 10. The electrical power loss leads to heating of at least the inverter 12 and the electric motor 14. The electrical power loss is thus converted into waste heat.

[0075] In order to reduce the thermal stress on the components of the drive train 10 and at the same time increase the power density, typically at least the inverter 12 and the electric motor 14 are cooled by means of the heat transfer circuit 52, in particular in the form of a cooling system.

[0076] For this purpose, the heat transfer circuit 52, according to the embodiments of system 8 shown here, has three sub-circuits 54A, 54B, 54C, in each of which a cooling medium 56 circulates. The waste heat generated in the inverter 12 and the electric motor 14 is used to heat the cooling medium 56 in the first sub-circuit 54A.

[0077] According to this embodiment, the heat transfer circuit 52 has a heat exchanger 58 that thermally couples the sub-circuits 54A, 54B, 54C. In this way, heat can be dissipated from the inverter 12 and the electric motor 14 via sub-circuit 54A and transferred to the other sub-circuits 54B, 54C.

[0078] According to this embodiment, the second sub-circuit 54B is coupled at least to the DC voltage source 26, here a high-voltage storage device. The third sub-circuit 54C is coupled at least to the passenger compartment 60. This allows the different temperature requirements of the DC voltage source 26 and the passenger compartment 60 to be taken into account. Of course, shared sub-circuits 54 can also be coupled to the DC voltage source 26 and the passenger compartment 60.

[0079] A vehicle thermal control unit 62 regulates the flow of the cooling medium 56 in the sub-circuits 54B and 54C. The vehicle thermal control unit 62 can, in particular, determine the heating requirement for the DC voltage source 26 and the passenger compartment 60. Subsequently, the vehicle thermal control unit 62 can output a minimum heat output requirement 64 to the control device 36, which, according to this embodiment, also performs the powertrain thermal control. The control device 36 can then determine control signals G1 and G2 depending on the minimum heat output requirement 64. The control device 36 measures the control signals G1 and G2 such that the power loss caused during the operation of the powertrain 10 is sufficient to meet the minimum heat output requirement 64. Optionally, the control device 36 can take boundary conditions into account, for example, the load limits of the components of the powertrain 10.

[0080] The heat exchanger 58 ensures media separation of the sub-circuits 54A, 54B, 54C with regard to the cooling medium 56. Naturally, different cooling media can be used in the different sub-circuits 54A, 54B, 54C.

[0081] In an alternative embodiment, the heat exchanger 58 can also be omitted. In this case, the heat transfer circuit 52 can be configured such that the vehicle component to be heated is directly coupled to the inverter 12 and / or the electric motor 14. For example, a valve can be provided in the heat transfer circuit 52 instead of the heat exchanger 58. This avoids the heat transfer losses of the heat exchanger 58.

[0082] Overall, the heat transfer circuit 52 can be configured in various ways. For example, the coupling of sub-circuits 54 or components of the heat transfer circuit 52 can include: series and / or parallel couplings, valves for controlling volume flows in sub-sections of the heat transfer circuit 52 or for coupling sub-circuits 54, or

[0083] Heat exchanger 58 for coupling sub-circuits 54.

[0084] Fig. 3 shows a method according to the invention for generating waste heat in an electric powertrain 10 for a vehicle. Optional steps are shown with dashed lines.

[0085] In optional step S2, the control device 36 receives the rotor position of the electric motor 14 from a rotor position sensor 46 or determines it without a position sensor. For determining the rotor position without a position sensor, the control device 36 can have a corresponding estimation algorithm. In particular, if the electric motor 14 is a synchronous motor, the initial rotor flux axis is directly determined by the rotor position.

[0086] In the subsequent step S4, the control device 36 determines the initial rotor flux axis of the electric motor 14 in a stator-oriented coordinate system. The stator-oriented coordinate system is a coordinate system that does not rotate with the magnetic field within the electric motor 14 during operation of the drive train 10.

[0087] The determined initial rotor flux axis of the electric motor 14 is preferably stored by the control device 36, for example in the storage device 50.

[0088] In the subsequent optional step S6, the control device 36 receives a minimum heat output request 64, for example from the vehicle heat control 62.

[0089] Following the optional step S6, the procedure includes step S8, in which the control device 36 injects (injects) a DC component of the current space vector into the stator-oriented coordinate system such that the DC component of the current space vector is oriented parallel or antiparallel to the determined initial rotor flux axis. For this purpose, the control device 36 can, for example, take into account the stored value of the initial rotor flux axis. Due to the orientation of the DC component of the current space vector, assuming it overlaps with the rotor flux axis, no torque is produced by the electric motor 14.

[0090] The procedure can be further developed by the subsequent optional step S10, in which the control device 36 imprints an alternating component of an additional current space vector in the stator-oriented coordinate system. The alternating component is oriented orthogonally, parallel, or antiparallel to the initial rotor flux axis.

[0091] Both the DC and AC components of the current space vector lead to the generation of power loss, without necessarily producing a non-negligible torque from the electric motor 14.

[0092] The constant component and the optional alternating component can be determined by the control device 36 in such a way that the imprinting of the current space vector causes an electrical power loss that corresponds to the minimum heat power requirement 64 from the optional step S6.

[0093] According to the following step S12, the control device 36 determines the control signals G1 and G2 and outputs them to the inverter 12, specifically to its gate driver circuits 44. The control device 36 can utilize current control, which may, for example, include a feedback control loop. For this purpose, the control device 36 can consider the AC signals L1, L2, and L3 (phase currents) detected by the phase current sensors 42 and output by the inverter 12 to the electric motor 14. The control signals G1 and G2 are then shaped as required by the pulse width modulator 40.

[0094] Steps S8 to S12 can be further developed in various ways using one or more of the optional steps S14 to S18.

[0095] In accordance with optional step S14, the control device 36 takes into account the electrical and thermal load limits of the components of the drive train 10. This means that the minimum heat output requirement 64, based on specific signal profiles of the control signals G1, G2, is only met by the resulting power loss to the extent that the electrical and thermal load limits of the inverter 12 and the electric motor 14 or their components are not exceeded.

[0096] If the resulting power loss is insufficient to fully meet the minimum heat output requirements 64, it will at least be met as best as possible while adhering to the load limits.

[0097] According to optional step S16, the control device 36 can, in particular, adapt a modulation method underlying the control signals G1, G2 and / or a signal profile of the control signals G1, G2. The control device 36 can adjust the control signals G1, G2 such that the operation of the drive train 10 causes a power loss that corresponds to the minimum heat output requirement 64 received by the control device 36. Naturally, the signal profile can also be dynamically adjusted if the system parameters of the drive train 10 or the minimum heat output requirements 64 vary.

[0098] The signal profile of the control signal G1, G2 can be changed, in particular with regard to the switching frequency at which the switching states of the switching device 18, 20 vary.

[0099] Additional control signals allow the gate control to vary the steepness of the switching edges of a switching device 18, 20.

[0100] Alternatively or additionally, the signal profile of the control signals G1, G2 can also be varied in such a way that the AC signals L1, L2, L3 (phase currents) provided by the inverter 12 have specific signal shapes, for example a sinusoidal shape, a triangular shape, a sawtooth profile, a rectangular shape or combinations thereof.

[0101] The control device 36 can also adjust the signal profiles of the control signals G1 and G2 to influence the proportions of power losses caused in the inverter 12 and / or the electric motor 14. For example, the inverter 12 and the electric motor 14 can be coupled with separate heat transfer circuits 52. In this case, the control device 36 adjusts the signal profiles of the control signals G1 and G2 to set the required power losses.

[0102] The respective control signals G1 and G2 switch the switching devices 18 and 20 in the inverter 12 according to specific switching states. Using the optional step S18, the sign of the DC components of the injected current space vectors can be varied by the control device 36 after an adjustable time interval. This leads to changed switching states of the switching devices 18 and 20, thus preventing continuous load conditions. This allows the load to be distributed more evenly across the different components of the drive train 10.

[0103] The optional steps S14, S16, and S18 allow the operating parameters of the drive train 10 to be adapted to the situation in order to ensure variable profiles of the power loss and thus the heat dissipation. This enables the control device 36 to provide dynamic control of the power loss, in particular, to meet varying minimum heat output requirements 64. Furthermore, a homogeneous load distribution across all components of the drive train 10 can be ensured over time.

[0104] Following step S12, the method includes step S20, in which at least the power loss caused by the DC component of the current space vector is dissipated as waste heat to at least one heat transfer circuit 52. This allows the cooling medium 56 of the heat transfer circuit 52 to be heated by means of the power loss and subsequently used to heat other vehicle components, for example the DC voltage source 26 or the passenger compartment 60.

[0105] Starting from step S20, the procedure has a feedback loop back to step S6. This allows, for example, adjustments to be made to accommodate variations in the minimum heat output requirement 64. Fig. 4 shows a schematic representation of the actual rotor flux axis 66 and a possible directional deviation of the current space vector 68 in the stator-oriented coordinate system 70.

[0106] In the stator-oriented coordinate system 70, the orientation of the actual rotor flux axis 66 is defined by the angle of the rotor flux axis Yrotorfluxaxis. The angle yrotorfluxaxis depends on the operating state of the electric motor 14. In synchronous machines, the angle yrotorfluxaxis depends in particular on the rotor position relative to the stator. In asynchronous machines, the angle yrotorfluxaxis depends on the orientation of the flux induced by the rotor current, which is applied to the rotor winding. The mutually orthogonally oriented currents l a , Iß represent the stator-oriented coordinate system 70.

[0107] The control device 36 now determines the initial rotor flux axis 72, for example based on sensor data from the rotor position sensor 46 or an estimation algorithm. This can generally lead to the determined initial rotor flux axis 72 deviating from the actual rotor flux axis 66. For example, the angle Ycontrol device determined or received by the control device 36 may differ from the angle Yrotor flux axis of the actual rotor flux axis 66.

[0108] If a DC component of the current space vector 68 is now applied along the initial rotor flux axis 72 determined by the control device 36 according to the stator-oriented coordinate system 70, a small torque is produced by the electric motor 14. However, the direction of action of the resulting torque 74 is oriented from the actual rotor flux axis 66 towards the determined initial rotor flux axis 72. This means that a self-centering effect can be utilized in the control system within the stator-oriented coordinate system 70.

[0109] Even if a small torque is initially generated by the electric motor 14, the deviation with respect to the actual rotor flux axis 66 is quickly compensated for within the control system due to the self-centering effect, as the actual rotor flux axis 66 aligns with the determined initial rotor flux axis 72. After this initial alignment, the actual rotor flux axis 66 subsequently coincides with the determined initial rotor flux axis 72.

[0110] Fig. 5 shows a schematic representation of a DC component 76 and an AC component 78 of the additional current space vector 80 in the stator-oriented coordinate system 70. Here it is assumed that the determined initial rotor flux axis 72 coincides with the actual rotor flux axis 66.

[0111] The DC component 76 of the current space vector 68 is injected along the initial rotor flux axis 72, i.e., parallel or antiparallel to the direction of the initial rotor flux axis 72. The DC component 76 is therefore also oriented parallel or antiparallel to the direction of the current space vector 68.

[0112] The sign change explained with regard to the optional step S18 corresponds in the stator-oriented coordinate system 70 to a rotation of the DC component 76 by 180°.

[0113] Due to its varying direction, the alternating component 78 can be injected orthogonally to the direction of the initial rotor flux axis 72. Since the frequency of the alternating component 78 is selected accordingly, it does not produce any torque on average over time. This prevents the electric motor 14 from outputting any torque, even if an alternating component 78 is injected in addition to the constant component 72.

Claims

Patent claims 1. Method for generating waste heat in an electric powertrain (10) for a vehicle, wherein the powertrain (10) comprises at least one inverter (12) and one electric motor (14) and wherein the method comprises at least the following steps: Determining an initial rotor flux axis (72) of the electric motor (14) in a stator-oriented coordinate system (70) by a control device (36), Imprinting a DC component (76) of the current space vector (68) in the stator-oriented coordinate system (70) by the control device (36) such that the DC component (76) of the current space vector (68) is oriented parallel and / or antiparallel to the determined initial rotor flux axis (72), Output of pulse-width modulated control signals (G1, G2) at least indirectly to switching devices (18, 20) of the converter (12) by the control device (36), so that the electric motor (14) is supplied with current components corresponding to the DC component (76) of the current space vector (68), and Dissipation of power loss caused by the current space pointer (68) as waste heat to at least one heat transfer circuit (52).

2. Method according to claim 1, characterized in that a signal profile of the pulse-width modulated control signals (G1, G2) is determined by the The control device (36) is varied to adjust proportions of the power loss caused in the inverter (12) and / or the electric motor (14).

3. Method according to claim 1 or 2, characterized in that an additional current space vector (80) is injected by the control device (36), which has an additional alternating component (78) in addition to the direct component (76) of the current space vector (68) in the stator-oriented coordinate system (70).

4. Method according to claim 3, characterized in that the additional switching component (78) is oriented parallel or antiparallel to the determined initial rotor flow axis (72), and / or that the additional switching component (78) is oriented orthogonally to the determined initial rotor flow axis (72).

5. Method according to one of the preceding claims, characterized in that a sign of the common component (76) of the current space vector (68, 80) is varied after an adjustable time interval.

6. Method according to one of the preceding claims, characterized in that the control device (36) receives a minimum heat power requirement (64) from an external component of the vehicle and adjusts at least one component of the current space pointer (68) based on the minimum heat power requirement (64) such that the power loss caused is at least equal to the minimum heat power requirement (64).

7. Method according to claim 6, characterized in that the control device (36) adjusts the at least one component of the current space indicator (68) based on the minimum heat power requirement (64) only to the extent that electrical and thermal load limits of the drive train (10) are observed.

8. Method according to one of the preceding claims, characterized in that the control device (36) determines an angle of the initial rotor flux axis (72) in the stator-oriented coordinate system (70) at least also based on a rotor position of the electric motor (14) detected by means of a rotor position sensor (46) or determined without a position sensor.

9. System (8) comprising a drive train (10) for a vehicle with at least one inverter (12), an electric motor (14) and a control device (36) coupled to the inverter (12) and the electric motor (14), wherein the control device (36) is configured to: determine and store an initial angle of a rotor flux axis (72) of the electric motor (14) in a stator-oriented coordinate system (70) of the electric motor (14), - to imprint a common component (76) of the current space vector (68) parallel and / or antiparallel to the direction of the stored initial rotor flux axis (72), and - to output pulse-width modulated control signals (G1, G2) at least indirectly to switching devices (18, 20) of the inverter (12), so that the electric motor (14) is supplied with current components corresponding to the DC component (76) of the current space vector (68), and wherein the system (8) has at least one heat transfer circuit (52) which can absorb the power loss caused by the current space vector (68) as waste heat.

10. System (8) according to claim 9, characterized in that the control device (36) is configured to inject one or more additional current space vector components having an alternating component (78) in addition to the impressed direct component (76), wherein the alternating component (78) is oriented orthogonally to the direction of the direct component (76) of the current space vector (68).

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