Method for field-oriented control of a synchronous machine, control unit and electric drive train

Abstract

The invention relates to a method for the field-oriented control / regulation of a synchronous machine of a vehicle, in which an additional leakage current is impressed in stator windings of the synchronous machine for heating at least one further component of the vehicle with the resulting lost heat. When the vehicle and thus the synchronous machine are stationary, a first operating point (1) at which the leakage current is impressed is changed by 90° clockwise in a d-current / q-current diagram to a second operating point (2) after a predetermined period has elapsed. The invention also relates to a control unit designed and programmed to carry out the method, and to an electric drive train having the control unit.

Description

[0001] The present invention relates to a method for the field-oriented control / regulation of a synchronous machine, in particular a permanent magnet synchronous machine, of a vehicle, in which an additional leakage current is injected into the stator windings of the synchronous machine to heat at least one other component of the vehicle with the resulting waste heat. The invention further relates to a control unit configured and programmed to carry out the method, as well as to an electric drive train comprising the control unit.

[0002] Electric vehicles are becoming increasingly popular on the market. In addition to one or more synchronous motors for propulsion, an electric vehicle has a battery as its energy source. In the event that the battery is cold, for example, during a start, especially in winter, the battery's power output or consumption is limited. This limitation is particularly important during charging, as only a battery operating at the optimal temperature range can be charged with high power and thus in a short time.

[0003] To achieve optimization, synchronous machines with improved oil cooling, known as groove cooling, were developed so that the dissipated waste heat can be used to heat the battery. This allows the battery to operate at a more favorable operating point.

[0004] To quickly bring a cold synchronous machine, and thus a cold battery, to a favorable operating point, US 2018 / 0 083 509 A1 and US 10 183 580 B2, for example, teach the generation of additional waste heat in a synchronous machine. Compared to an auxiliary electric heater, such as one provided in the battery, existing hardware can be utilized to improve overall efficiency. Eliminating the additional hardware can result in both a cost and weight advantage.

[0005] The methods described in the cited publications generate significantly higher losses in the synchronous machine by selecting a different setpoint current, without noticeably affecting the torque of the electric motor. The application of constant auxiliary currents (DCI - direct current injection) is the simplest method and can be used efficiently in a rotating synchronous machine. Setting constant auxiliary currents has been successfully used for decades in field weakening to enable the synchronous machine to operate at a higher speed range in special situations. This is called a special situation because the application of the auxiliary current sets an operating point with lower efficiency.

[0006] For the warm-up phase, there are so-called high-frequency methods that additionally impress high-frequency currents. This can lead to intentional torque modulations. With an appropriate choice of excitation, which does not depart from the constant torque hyperbola, torque modulations can be largely avoided. Such methods are known, for example, from DE 10 2021 003 611 A1, DE 10 2021 003 612 A1, and DE 10 2021 003 621 A1. These high-frequency methods are capable of generating iron losses and eddy current losses even at low speeds, making them a complement or alternative to the injection of constant additional currents.

[0007] The application of constant or high-frequency auxiliary currents is very efficient, but when the synchronous machine is at a standstill, depending on the current rotor position, it leads to an uneven current load and thus to different heating of the individual stator windings of the synchronous machine. This can lead to the failure of more heavily loaded stator windings if the power is not significantly reduced (up to 50%) compared to rotating operation. Nevertheless, even with a reduced current load, uneven aging of the stator windings can occur, which can cause the synchronous machine to behave asymmetrically during normal operation, resulting in noise and / or noticeable torque fluctuations. In addition, the paths of the individual phases in a power electronics unit that controls the synchronous machine are also heated unevenly, which can also lead to premature aging of individual paths.

[0008] The object of the present invention is therefore to eliminate or at least mitigate these disadvantages. In particular, failure and / or uneven aging of more heavily loaded stator windings when applying an additional current to generate additional losses in a synchronous machine is to be avoided.

[0009] This object is achieved by the subject matter having the features according to the independent claims. Advantageous embodiments are the subject matter of the dependent claims.

[0010] Disclosed is a method for the field-oriented control / regulation of a synchronous machine, in particular a permanent magnet synchronous machine, of a vehicle, in which an additional leakage current is impressed into the stator windings of the synchronous machine to heat at least one other component of the vehicle with the resulting waste heat. When the vehicle, and thus the synchronous machine, is stationary, a first operating point at which the leakage current is impressed is changed by 90° clockwise in a d-current / q-current diagram after a predetermined period has elapsed to a second operating point. It should be noted that the torque provided by the synchronous machine is intercepted by a parking brake or park lock during standstill.This leads to uniform heating of the stator windings and also to uniform heating of the respective paths in a power electronics unit that controls the synchronous machine. With a uniform load, higher power, up to twice the power, can be impressed.

[0011] The specified duration can be selected so that it can be set by the current controller with sufficient quality and no phase of the motor or the power electronics heats up excessively.

[0012] The first operating point can be set up to a maximum permissible current and / or a maximum permissible voltage in the d-current / q-current diagram. This allows for greater power loss and thus faster heating of the synchronous machine and thus of the other components.

[0013] Furthermore, the first operating point in the d-current / q-current diagram can be switched to the second operating point along a torque hyperbola. This way, the synchronous motor provides a constant torque, eliminating any disturbing noise and preventing the parking brake from being subjected to dynamic stress.

[0014] In addition, after the specified duration has elapsed, the operating points can be repeatedly switched between until the vehicle, and thus the synchronous motor, is moved again. Consequently, a repeated switch between the first operating point and the second operating point occurs. The specified duration can also be selected so that it can be set by the current controller with sufficient quality and no phase of the motor or power electronics overheats excessively.

[0015] Furthermore, a map or look-up table can be extrapolated to determine the operating points in the direction of negative d-currents and positive q-currents. Consequently, the operating points can also be changed for higher torque values.

[0016] The map or look-up table used to determine the operating points can be extrapolated toward positive d-currents and positive q-currents. Consequently, the operating points can also be changed for higher torque values.

[0017] The at least one further component can be a battery and / or a fluid circuit of the vehicle. Consequently, the battery can be heated quickly for faster charging. Furthermore, a fluid circuit can be heated more quickly, for example, to warm a vehicle interior more quickly.

[0018] Also disclosed is a control unit configured and programmed to execute the method according to the preceding aspects. The control unit has inputs for receiving analog or digital measured values. The measured values ​​are subsequently processed according to the method described above, which is implemented as program code. The control unit then controls a power electronics unit that drives the synchronous machine accordingly.

[0019] An electric drive train comprises the power electronics unit and the synchronous machine, in particular the permanent magnet synchronous machine. Furthermore, the electric drive train comprises the control unit for causing the power electronics unit to control the synchronous machine according to the method according to the above aspects.

[0020] The present invention is described in detail below with reference to the figures. They show: Fig. 1 a d-current / q-current diagram in which an exemplary characteristic map for determining operating points of a synchronous machine, torque hyperbolas, a magnetic flux and an MTPA characteristic are plotted; Fig. 2 a d-current / q-current diagram in which an exemplary first operating point and a second exemplary operating point as well as operating points along a torque hyperbola are plotted.

[0021] The present invention will be described below using preferred embodiments with reference to the figures. However, the description of the embodiments should not be considered exhaustive.

[0022] Fig. Figure 1 shows a d-current / q-current diagram, illustrating an example characteristic map for determining operating points of a synchronous machine. Torque hyperbolas along which constant torque is present, as well as an MTPA characteristic curve, are also plotted. Furthermore, magnetic flux values ​​are shown. It should be noted that the characteristic map can also be stored in the form of a look-up table.

[0023] It can be seen that a specific torque can be achieved through a variety of different combinations of d-current and q-current. In normal operation, a combination of d-current and q-current is set along an MTPA (maximum torque per ampere) characteristic curve to achieve efficient operation of the synchronous machine. There are also approaches to selecting the combination of d-current and q-current according to an MTPL (maximum torque per loss) characteristic curve. These two characteristic curves are closely related, so the procedure is described below using only the MTPA characteristic curve.

[0024] To generate additional losses in the synchronous machine, a combination of d-current and q-current is selected that is as far away from the MTPA characteristic as possible. It is advisable to go up to the two current limits of the d-current and q-current at the ends of the torque hyperbolas within the maximum permissible current and / or the maximum permissible voltage for the power electronics unit or the synchronous machine.

[0025] In Fig. 2 shows an example of a first operating point 1 which is shifted to a lower edge of a characteristic map in the d-current / q-current diagram in order to cause additional losses in the synchronous machine.

[0026] It has been recognized that setting such an operating point when the synchronous machine, i.e., the electric vehicle, is at a standstill leads to uneven loading of the synchronous machine's stator windings. Furthermore, the paths of the individual phases in a power electronics unit that controls the synchronous machine are also unevenly loaded. At high currents, this can even cause damage. Even setting lower currents can lead to uneven aging of the stator windings and the paths in the power electronics unit.

[0027] For this reason, after a specified period of time, which can be selected so that the current controller can set it with sufficient quality and no phase of the motor or power electronics overheats, the first operating point 1 switches to a second operating point 2, which is rotated 90° clockwise relative to the first operating point 1. After the specified period has elapsed, the system then switches back to the first operating point. This switching process is repeated until the electric vehicle, and thus the synchronous motor, is moved again.

[0028] It can be mathematically demonstrated that alternating the operating points, which are rotated by 90° in alpha / beta coordinates, results in a uniform load for all phases. There is only one ideal torque, with two operating points located at the edge of the characteristic map and thus within the current limit range.

[0029] The power of a phase depends on the angle theta and a current amplitude of the I_alpha_beta operating point: P(theta, l_amp)=R*(l_amp*cos(theta))2

[0030] Alternating the two operating points offset by 90° results in: P_90_deg(theta, l_amp)=R*0.5*l_amp2*[cos(theta)2+cos(theta+pi / 2)2]=R*0.5*l_amp2*[cos(theta)2+(-sin(theta))2]=R*0.5*l_amp2

[0031] The power of a phase is therefore only dependent on the current amplitude and is half the power with continuous current supply.

[0032] By regularly switching between two operating points offset by 90°, it is possible to load all phases evenly. In extreme cases, the current amplitude can be increased by a factor of square root, or the maximum power can be doubled, without exceeding the maximum phase load.

[0033] Preferably, operating points 1 and 2, as in Fig. 2, are selected so that they lie on the same torque hyperbola, and the operating points 1 and 2 alternate along this torque hyperbola. This ensures that the motor delivers a constant torque, preventing any disturbing noise and exposing a parking brake to no dynamic load.

[0034] In Fig.1 also shows that the choice of torque also influences the possible uniform heating of the stator windings. This is because, for example, for higher torques, there are no longer any values ​​in the characteristic map for negative d-currents and positive q-currents. This means that the second operating point 2 cannot be set. For lower torques, however, the desired 90° phase difference can in most cases already be set using the existing characteristic map. In cases of high torques, the characteristic map or a look-up table can be expanded by extrapolation towards negative d-currents and positive q-currents. Alternatively or additionally, extrapolation towards positive d-currents and positive q-currents can also be performed.

[0035] The method described above can be implemented in a control unit in the form of program code. The control unit can have inputs for receiving measured values ​​and outputs for outputting control signals to the power electronics unit to control the synchronous machine accordingly. The control unit can therefore be used in an electric drive train comprising the power electronics unit and the synchronous machine. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] US 2018 / 0 083 509 A1

[0004] US 10 183 580 B2

[0004] DE 10 2021 003 611 A1

[0006] DE 10 2021 003 612 A1

[0006] DE 10 2021 003 621 A1

[0006]

Claims

[1] Method for the field-oriented control / regulation of a permanent magnet synchronous machine of a vehicle, in which an additional leakage current is impressed in stator windings of the synchronous machine for heating at least one further component of the vehicle with a resulting loss heat, characterized by that when the vehicle and thus the permanent synchronous machine are at a standstill, a first operating point (1) at which the loss current is impressed is changed in a d-current / q-current diagram by 90° clockwise to a second operating point (2) after a predetermined period has elapsed. [2] Method according to claim 1, characterized by that the first operating point is set up to a maximum permissible current and / or a maximum permissible voltage in the d-current / q-current diagram. [3] Method according to claim 1 or 2, characterized bythat the first operating point (1) in the d-current / q-current diagram is changed to the second operating point (2) along a torque hyperbola. [4] Method according to one of claims 1 to 3, characterized by that the operating points (1, 2) are repeatedly switched between after the specified period has elapsed until the vehicle and thus the permanent synchronous machine is moved again. [5] Method according to one of claims 1 to 4, characterized by that a map or a look-up table for determining the operating points (1, 2) is extrapolated in the direction of negative d-currents and positive q-currents. [6] Method according to one of claims 1 to 5, characterized by that the characteristic map or the look-up table for determining the operating points (1, 2) is extrapolated in the direction of positive d-currents and positive q-currents. [7] Method according to one of claims 1 to 6, characterized bythat the at least one further component is a battery and / or a fluid circuit of the vehicle. [8] Control unit designed and programmed to carry out the method according to one of claims 1 to 7. [9] Electric drive train with power electronics unit and permanent magnet synchronous machine, characterized by a control unit according to claim 8.

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