Method for controlling the operation of a multi-phase electrical machine

Abstract

The invention relates to a method for controlling the operation of a multiphase electric machine (7), comprising at least two sub-machines (7a, 7b) each with at least three phases (11a-c, 12a-c), wherein a target power loss is determined and a power loss is generated based on the target power loss, characterized in that the power loss is generated in a standstill state by controlling the electric machine (7) such that the rotating fields of the sub-machines (7a, 7b) have a phase shift and the rotating fields rotate with a predefined frequency or frequency profile. The invention further relates to an electric drive arrangement (5), an axle drive (4) with such a drive arrangement (5), and a motor vehicle (1).

Description

[0001] The invention relates to a method for controlling the operation of a multi-phase electrical machine, wherein a target power loss is determined and a power loss is generated based on the target power loss.

[0002] Methods for controlling the operation of electrical machines, specifically those of motor vehicles, in which a target power loss is determined and, based on this, a corresponding power loss is generated in the electrical machine, are generally known from the prior art. Typically, a power loss is deliberately generated to produce heat, which is then used for at least one function of the electrical machine or an associated component, such as an electrical energy storage device, the vehicle's interior, and the like. Specifically, the heat can be generated to selectively regulate the temperature of the electrical machine, the electrical energy storage device, or the vehicle's interior. This is also known by the abbreviation ESR ("Efficiency Shift Request").

[0003] It is known that conditions can arise in which demanding such power dissipation can lead to uneven temperature distribution in the electric machine. In particular, during standstill states of the electric machine, where no rotational motion is generated and must not be generated, the static state of the rotor can lead to uneven temperature distribution when the electric machine is driven uniformly. This uneven temperature distribution does not change over time due to the lack of rotor rotation. This can result in uneven loading and heating of the electric machine and its associated power electronics. For example, in such a standstill state, it is not possible to apply a constant direct current to achieve the required target power dissipation.

[0004] The present invention is based on the objective of proposing a method for controlling the operation of a multiphase electrical machine, thereby ensuring a more even load distribution across the machine. This objective is achieved by a method comprising the features of claim 1. Further advantageous embodiments are described in the dependent claims.

[0005] According to a first aspect of the invention, a method for controlling the operation of a multiphase electric machine, in particular a multiphase electric machine of a motor vehicle, which has at least two sub-machines with at least three phases each, provides that a target power loss is determined and, based on the target power loss, a power loss is generated, wherein the power loss is generated in a standstill state by controlling the electric machine in such a way that the rotating fields of the sub-machines have a phase shift and the rotating fields rotate with a predefined frequency or a predefined frequency profile.

[0006] The electric machine controlled by the process can be a permanent magnet machine (PMM), an asynchronous machine (AMM), or a rotating field machine. An asynchronous machine, also known as an induction machine, is an electric motor in which the rotor does not rotate synchronously with the rotating field of the stator. The rotational speed depends on the load and the frequency of the supplied alternating current. These machines are robust and require little maintenance. A permanent magnet machine uses permanent magnets to generate the magnetic field in the rotor, instead of electromagnetic windings. This eliminates the need for an external excitation voltage, which increases efficiency and reduces the size. A rotating field machine is an electric machine based on the principle of a rotating magnetic field generated by the phase shift of multiphase alternating currents.The rotating magnetic field in the stator induces movement in the rotor, which leads to energy conversion.

[0007] Multiphase electrical machines have at least two sub-machines, each with a three-phase winding containing more than three phases. A sub-machine is defined as the portion of the winding's phases that are connected via a circuit. Each sub-machine has three or more phases and can thus independently generate a rotating magnetic field within the electrical machine.

[0008] The aforementioned power loss is to be generated during the operation of the electric machine, in such a way that the power loss corresponds to a specific target power loss. The method is therefore distinguished from operating methods of the electric machine in that power loss is to be generated intentionally. The power loss is thus not generated unintentionally during the operation of the electric machine, but rather intentionally generated in order to use it for at least one predetermined function, in particular the temperature control of the electric machine, a coolant and / or lubricant, another component of a motor vehicle containing the electric machine, and / or the interior of a motor vehicle.

[0009] The power loss is generated in a standstill state by appropriately controlling the electric machine, whereby, firstly, the rotating fields of the sub-machines of the electric machine have a phase shift, and secondly, these rotating fields rotate at a predefined frequency or frequency profile. The phase shift can be selected symmetrically. For example, the phase shift in an electric machine with two sub-machines, each with three phases, can be 180°. Preferably, the sub-machines have a phase shift with each other, for example, 30°.

[0010] The frequency at which the rotating magnetic field of each sub-machine rotates can be predefined or preset. Alternatively, the frequency can be variable or adjustable. While the rotating magnetic fields of the sub-machines do generate local tangential forces, these forces cancel each other out, resulting in no torque being produced by the electric machine. A high frequency allows for a short time to establish the target current for generating the desired power loss. A low frequency is advantageous for the acoustic properties of the electric machine.

[0011] In contrast to the previously described method for generating power losses, in which a constant direct current is impressed into an electrical machine to generate the power loss, it is proposed here to provide an electrical machine with a number of sub-machines, where this number is preferably greater than or equal to two and corresponds to an even positive integer. Each sub-machine also has a number of phases, where this number is preferably greater than or equal to three and corresponds to an odd positive integer. In this sense, the electrical machine has an even number of sub-machines, with each sub-machine of the electrical machine having an odd number of phases.

[0012] The target power loss is determined by comparing the generated current with the losses incurred, particularly copper losses, using predefined equations and / or models. Copper losses refer to energy losses caused by the electrical resistance of the copper windings. These losses occur when electric current flows through the windings. Copper losses are often also referred to as winding losses. Determining the target power loss involves defining a current for a specific time point that is required to generate the desired losses or to be applied to the electrical machine, particularly to the respective phase of the sub-machine.

[0013] It is conceivable to determine the actual power loss generated. This can be done by taking into account the current fed into the respective sub-machine at a given time, specifically for monitoring purposes and / or for indirectly determining the target power loss.

[0014] The proposed method allows the power loss to be distributed evenly across all phases of all sub-machines. The electric machine is controlled in such a way that no torque is generated when the vehicle is stationary. A stationary state exists when the vehicle is not moving and no rotary motion is generated by the electric machine or when no torque is transmitted to a rotating drive shaft.

[0015] The method can, in particular, provide that the average power loss generated during an operating period of the electrical machine corresponds to the target power loss. In other words, it is possible that power losses may be generated within several operating periods, each of which may contain several sub-periods, that deviate from the target power loss. However, when considered over the entire operating period, the average power loss for that period corresponds to the target power loss. Since such fluctuations in power loss typically occur over relatively short periods, especially if the entire operating period lasts only a few seconds, this leads, particularly due to the thermal inertia of the electrical machine, to the conclusion that it is sufficient for the average power loss to be considered.The average loss, which is the sum of the power losses occurring over the operating period, corresponds to the target power loss. The high thermal inertia or heat capacity of the individual components of the electrical machine thus smooths the energy input generated by the power losses. The duration of an operating period, also referred to as the period, can be relatively short, particularly in the range of a few seconds or less than a second, or, for example, several hundred milliseconds. The number of operating periods depends primarily on the number of phases in the individual components of the electrical machine. Specifically, the number of operating periods is determined by the number of phases in the individual components of the electrical machine. The individual operating periods can be executed consecutively or alternate in any sequence.The load within the electrical machine, in particular the temperature input into the phases and also into the electronic components of the power electronics, can be homogenized by performing the same or different operating periods.

[0016] Preferably, the power losses generated in different phases are balanced over a number of different operating periods corresponding to the number of phases. If, for example, the respective sub-machine of the electrical machine has three phases, three identical, partially identical, or different operating periods can be provided for this sub-machine, alternating sequentially or in any order. With two sub-machines, each with three phases, a total of six identical, partially identical, or different operating periods can be provided for the electrical machine. In each operating period, one phase carries a higher phase current than the other phases. On average, since the individual operating periods alternate, the power losses generated in the individual operating periods are balanced.symmetrized, so that the thermal load for the individual phases and the associated power electronics is also symmetrized.

[0017] In other words, the current in one phase of a given sub-machine can periodically be higher than the current in the other phases. However, this results in the power loss being adjusted evenly across the sub-machines and throughout the entire operating period, specifically according to the target power loss. Since the phases carrying the maximum current alternate, this does not lead to a one-sided load on the electric machine, the sub-machines, or the power electronics; instead, the load is balanced.

[0018] During the respective operating period, current-controlled operation and / or flux-controlled operation of the respective sub-machine of the electrical machine can be carried out.

[0019] In at least one phase, a target current can be built up and maintained for a defined duration before being reduced again. Maintaining the target current for the defined duration primarily results in energy input into the respective sub-machine of the electric machine due to the current flow. Subsequently, as previously described, the current is reduced again. A predefined current waveform can be set for the current. This waveform can be, for example, sinusoidal, rectangular, or of another shape. In any case, the waveform is chosen such that the load on the phases is essentially uniform or symmetrical when averaged. This ensures that thermal losses are distributed evenly across the three phases.It is also conceivable that, in addition to a fundamental waveform, i.e. a predefined current waveform, further current waveforms, in particular harmonics, can be introduced to influence further operating characteristics, such as the acoustics of the electrical machine.

[0020] In this application, "flux" refers to magnetic flux. This means, in particular, that flux-controlled operation concerns the operation of the electric machine in which the electric machine, or the respective sub-machine, is controlled with respect to the realized magnetic flux. Accordingly, the flux of the electric machine can be reduced to zero, especially before the start of the next operating period. Advantageously, flux-controlled operation of the respective sub-machine makes it possible to reduce the flux of that sub-machine to zero in a targeted manner. For example, once the defined holding time has elapsed, the flux in the respective sub-machine can be reduced to zero as quickly as possible before the next operating period. This means that the magnetic flux is reduced before the change of operating period.

[0021] In addition to the method described in the first aspect of the invention, the invention relates in a second aspect to an electric drive arrangement comprising an electric machine and a control device configured to execute the method described above. The control device preferably includes a processing unit for calculating the rotating magnetic field and power electronics that are connected to the electric machine for signal transmission. The power electronics have a number of phases corresponding to that of the electric machine. For example, in the case of two sub-machines, each with three phases, the power electronics are thus configured as six-phase. The power electronics and the processing unit can also be separate units that are connected to each other for signal transmission.

[0022] In one embodiment, the electric machine comprises exactly two sub-machines, a first sub-machine and a second sub-machine each having three phases. The electric machine can, for example, have a 30° phase shift. Such an electric machine is to be understood as an asymmetric six-phase machine.

[0023] Furthermore, according to a third aspect, the invention relates to an axle drive comprising an electrical drive arrangement described above in the second aspect of the invention. In a fourth aspect, the invention relates to a motor vehicle comprising an axle drive described above in the third aspect of the invention and / or an electrical drive arrangement described above in the second aspect of the invention.

[0024] The above definitions and explanations regarding technical effects, advantages and advantageous embodiments of the method according to the first aspect of the invention also apply mutatis mutandis to the electric drive arrangement according to the second aspect of the invention, to the axle drive according to the third aspect of the invention and to the motor vehicle according to the fourth aspect of the invention, and vice versa.

[0025] A preferred embodiment of the invention is explained in more detail below with reference to the figures. Here, it shows Fig. 1 a highly schematic top view of a motor vehicle according to the invention, comprising an axle drive according to the invention with an electrical drive arrangement according to the invention, Fig. 2 a representation of a phase current profile over a rotating field angle of an electric machine of the drive arrangement according to the invention Fig. 1 with two sub-machines and Fig. 3 a representation of a torque curve of the two sub-machines of the electric machine of the drive arrangement according to the invention Fig. 1 in relation to a rotation field angle.

[0026] Fig. Figure 1 shows a highly schematic top view of a motor vehicle 1 according to the invention, comprising a first axle 2 designed as a rear axle and a second axle 3 designed as a steerable front axle, wherein the first axle 2 comprises an axle drive 4 according to the invention with an electric drive arrangement 5 according to the invention, which is provided for driving two wheels 6 of the first axle 2.

[0027] The electric drive arrangement 5 comprises an electric machine 7 and a control unit 8, comprising a computing unit 9 and power electronics 10, wherein the control unit 8 is configured to execute a method according to the invention for controlling the operation of the electric machine 7. The electric machine 7 here has two sub-machines 7a, 7b, each sub-machine 7a, 7b being three-phase. The power electronics 10 is correspondingly six-phase. The sub-machines 7a, 7b can be controlled by the control unit 8 such that a rotating magnetic field can be generated in the stator of the electric machine 7 (not shown here). The rotating magnetic fields of the sub-machines 7a, 7b rotate at a freely selectable, predefined frequency. The rotating magnetic fields of the sub-machines 7a, 7b have a phase shift, for example, of 180°.In normal operation of the electric machine 7, the drive power is divided between the two wheels 6 via a gear stage 13 and a differential 14 and transmitted in a known manner.

[0028] According to a method according to the invention for controlling the operation of the electric machine 7, which can be configured here as a permanent magnet machine, a target power loss is determined in a first method step in a standstill state of the electric machine 7 that differs from normal operation, i.e., when no rotary motion is transmitted to the gear stage 13. This is done in the control unit 8, in particular in the processing unit 9. The target power loss can, for example, be requested by at least one function. The function can, for example, be used for temperature control of a component of the motor vehicle, such as the electric machine 7, an electrical energy storage device (not shown here), the interior of the motor vehicle 1, or the like.After determining the target power losses, in a second process step the electric machine 7 is controlled based on the target power loss to adjust the power loss in the standstill state. This is also done by means of the control unit 8, in particular the power electronics 10.

[0029] A specific current waveform can be impressed upon the sub-machines 7a, 7b of the electrical machine 7, which is chosen such that the phases 11a, 11b, 11c, 12a, 12b, 12c are loaded symmetrically. Fig. Figure 2 shows a phase current waveform of the respective phase 11a, 11b, 11c, 12a, 12b, 12c versus the rotation angle of the sub-machines 7a, 7b. The phase current of the respective phase 11a, 11b, 11c, 12a, 12b, 12c is plotted on the ordinate 15, while the rotation angle is plotted on the abscissa 16. Fig. 2 shows that the current waveforms of the three phases 11a, 11b, 11c of the first sub-machine 7a and of the three phases 12a, 12b, 12c of the second sub-machine 7b are sinusoidal.

[0030] In Fig. Figure 3 shows a torque plotted on the ordinate 15, while the rotation angle is plotted on the abscissa 16. With Fig. Figure 3 further illustrates that the 180° phase shift of phases 11a, 11b, 11c, 12a, 12b, 12c of sub-machines 7a, 7b causes a mutual cancellation of torques generated by the rotating fields from locally acting tangential forces. This is illustrated by the opposing torque curves 17, 18 of sub-machines 7a, 7b. Since the sums cancel each other out, no rotary drive of a rotor or drive shaft of the electric machine 7 (not shown here) occurs. Instead, when the electric machine 7 is at rest, only power losses are generated to produce heat, which is intended to be used for at least one function of the electric machine 7, the drive arrangement 5, or the axle drive 4, for example, an electrical energy storage device, the interior of the motor vehicle 1, and the like.The generated heat can be used in particular to selectively control the temperature of the electric machine 7, the aforementioned electrical energy storage device or the interior of the motor vehicle 1.

[0031] The control unit 8 controls the electric machine 7, in particular the sub-machines 7a, 7b, such that losses are distributed evenly across all phases 11a, 11b, 11c, 12a, 12b, 12c. Furthermore, no torque is generated and transmitted to a drive shaft. In addition, the current applied to phases 11a, 11b, 11c, 12a, 12b, 12c is controlled so that the resulting losses correspond to the target power loss. The target value can be predefined or set by the system. The target value can vary, for example, depending on the ambient temperature or the operating temperature of the electric machine 7.

[0032] The individual Fig. 1, Fig. 2 to Fig.The three described advantages, details and features can be combined, interchanged and transferred to one another as desired.

[0033] The method can also be used for electrical machines 7 that have a topology different from the variant described above. In any case, the electrical machine 7 has an even number of sub-machines 7a, 7b, each sub-machine 7a, 7b having an odd number of phases 11a-c, 12a-c, in any case greater than three, and in any case, two or more sub-machines 7a, 7b with three or more phases 11a-c, 12a-c are provided. Reference sign 1 motor vehicle 2 first axis 3 second axis 4-axle drive 5 electric drive arrangement 6 wheels 7 electric machine 7a first sub-machine 7b second submachine 8 Control unit 9 Calculation unit 10 Power Electronics 11a first phase of the first sub-machine 11b second phase of the first sub-machine 11c third phase of the first sub-machine 12a first phase of the second sub-machine 12b second phase of the second sub-machine 12c third phase of the second sub-machine 13th gear stage 14 Differential 15 Abscissa 16 ordinates 17 Torque curve of the first sub-machine 18 Torque curve of the second sub-machine

Claims

[1] Method for controlling the operation of a multiphase electrical machine (7), comprising at least two sub-machines (7a, 7b) each with at least three phases (11a-c, 12a-c), wherein a target power loss is determined and a power loss is generated based on the target power loss, characterized by , that the power loss in a standstill state is generated by controlling the electrical machine (7) in such a way that the rotating fields of the sub-machines (7a, 7b) have a phase shift and the rotating fields rotate with a predefined frequency or a predefined frequency profile. [2] Method according to claim 1, wherein the sub-machines (7a, 7b) have a phase shift relative to each other. [3] Electric drive arrangement (5) comprising an electric machine (7) and a control device (8) configured to perform the method according to one of the preceding claims. [4] Electric drive arrangement (5) according to claim 3, wherein the electric machine (7) has an even number of sub-machines (7a, 7b), and wherein each sub-machine (7a, 7b) of the electric machine (7) has an odd number of phases (11a-c, 12a-c). [5] Electric drive arrangement (5) according to claim 4, wherein the electric machine (7) has exactly two sub-machines (7a, 7b), and wherein the first sub-machine (7a) and the second sub-machine (7b) each have three phases (11a-c, 12a-c). [6] Axle drive (4) comprising an electrical drive arrangement (5) according to any one of claims 3 to 5. [7] Motor vehicle (1) comprising an axle drive (4) according to claim 6 and / or an electric drive arrangement (5) according to any one of claims 3 to 5.

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