Method and device for controlling a stator of an electrical machine having a rotor and a stator, and electrical drive system
Patent Information
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- ROBERT BOSCH GMBH
- Filing Date
- 2024-07-22
- Publication Date
- 2026-06-24
Smart Images
Figure EP2024070682_27022025_PF_FP_ABST
Abstract
Description
[0001] Description
[0002] title
[0003] Method and device for controlling a stator of an electrical machine having a rotor and a stator, and electrical drive system
[0004] The present invention relates to a method and a device for controlling a stator of an electrical machine having a rotor and a stator, a computing unit and a computer program for carrying out the method, and an electrical drive system.
[0005] Background of the invention
[0006] The primary function of a power converter (so-called inverter) in an electric drive, e.g., in a vehicle (traction drive or range extender), is to provide the electric machine with a multi-phase alternating voltage generated from the direct voltage provided by a direct voltage source, such as a battery. This alternating voltage is generated by switching power switches on and off (so-called commutation), for which different modulation methods can be used. A distinction is made between time-synchronous methods and angle-synchronous methods (FFC - Fundamental Frequency Clocking).
[0007] In a time-synchronous process (also called a carrier frequency process), a voltage signal can be modulated using pulse width modulation (PWM), for example. In this case, each power breaker in the converter is switched on and off a maximum of once per PWM period. In an angle-synchronous process, the power breakers are switched on and off once or more per period, depending on the electrical angle of the machine. In a time-synchronous process, the switching pattern is based on a fixed switching or calculation grid, i.e. the carrier frequency. In angle-synchronous processes, the switching pattern is firmly based on the electrical period or its angle. Due to angle-synchronous switching, these processes are only suitable above a certain electrical frequency and are particularly effective at high electrical frequencies.The voltage yield is maximum with the block commutation mode variant (also called block clocking or fundamental frequency clocking and English six-step mode), and subharmonic frequencies are avoided due to synchronicity, and the switching frequency is minimal. However, one problem is the transition from time-synchronous processes to block commutation mode. Block commutation mode has (by definition) a modulation index of m=1 (ratio between the voltage amplitude of the fundamental wave and the voltage amplitude of the fundamental wave in block commutation mode). Time-synchronous processes can achieve a maximum modulation index of approximately m=0.907 without overmodulation due to theoretical and practical limitations (e.g., minimum pulse widths or dead times). This creates a difference of approximately 10%, which must be overcome abruptly during switching.
[0008] DE 10 2019 200 919 A1 describes a solution that ensures that the control gap between time-synchronous methods and block commutation mode can be reduced by using an additional operating mode in which the clocking is angle-synchronous with an adjustable voltage vector length. In principle, any angle-synchronous control method that allows variation of the voltage vector length is possible for this purpose. In particular, triple center pulse clocking, as explained in more detail therein, can be used. This noticeably improves controllability and smooths the transition between system states. When a control threshold and an electrical frequency threshold are reached, the system switches from the time-synchronous modulation or commutation method to the additional operating mode, and from there to block commutation mode.
[0009] Disclosure of the Invention: According to the invention, a method and a device for controlling a stator of an electrical machine having a rotor and a stator, a computing unit and a computer program for implementing the method, and an electrical drive system with the features of the independent patent claims are proposed. Advantageous embodiments are the subject of the dependent claims and the following description.
[0010] The invention can improve the transition or change from a first operating mode using a time-synchronous clocking with a predetermined maximum first voltage vector length, wherein the electrical machine is in a first current operating point, to a second operating mode using an angle-synchronous block clocking (block commutation mode) with a predetermined second voltage vector length, wherein the electrical machine is in a second current operating point, and back, so that a stationary persistence of the system in a third operating mode (between the first and the second operating mode) using an angle-synchronous clocking with an adjustable third voltage vector length is avoided, as can occur under certain circumstances in the DE 102019 200 919 A1 mentioned in the introduction.In this context, the current operating point is understood to be the operating point of the stator current, which can be expressed, for example, as an id / iq operating point. A mechanical operating point is understood to be a pair of torque and speed.
[0011] Specifically, the method comprises controlling the stator of the electric machine in a first operating mode using time-synchronous timing with a predetermined maximum first voltage vector length to provide a mechanical operating point from a torque and a rotational speed, wherein the electric machine is in a first current operating point. 'Controlling a stator' is understood here to mean the application of voltages to the windings or phases of the stator. Furthermore, the method comprises determining a modeled control level of the first operating mode as a function of the torque and the rotational speed; comparing the modeled control level with a control threshold; and comparing the rotational speed with a rotational speed threshold.Furthermore, the method comprises controlling the stator of the electric machine in a second operating mode using an angle-synchronous block clock with a predetermined second voltage vector length to provide the same mechanical operating point, wherein the electric machine is in a second current operating point.
[0012] Finally, the method comprises switching from the first operating mode to the second operating mode when the modeled modulation level reaches or exceeds the modulation threshold and when the rotational speed reaches or exceeds the rotational speed threshold, and / or switching from the second operating mode to the first operating mode when the modeled modulation level falls below the modulation threshold, possibly with a hysteresis discount, or the rotational speed falls below the rotational speed threshold. The modulation threshold can be 1 or substantially 1. The hysteresis discount can serve to avoid frequent switching back and forth.
[0013] This prevents steady-state operation in the third operating mode with increased DC link voltage ripple. Advantageously, the DC link capacitor can be designed smaller, thus saving costs and space, and / or providing more power and expanding the operating range of the angle-synchronous block clocking, which in turn reduces losses and increases efficiency.
[0014] A customer requirement that is usually essential for system design concerns the voltage ripple in the DC link of the converter (DC link voltage ripple). Typically, a maximum permissible voltage ripple is specified for a specific operating range. The voltage ripple depends on the capacitance of the DC link capacitor (high capacitance leads to low voltage ripple), as well as on the modulation method (e.g., higher voltage ripple with medium-pulse triple switching as an example of the third operating mode (see Fig. 4) than with SVPWM (Space Vector Pulse Width Modulation) at the same operating point), and the switching frequency (higher voltage ripple at lower switching frequency with SVPWM). The capacitance of the DC link capacitor is selected during system design so that the voltage ripple requirement is always met.
[0015] In the invention, the suitable selection of the control threshold value as a function of the second target speed ensures that a switch from the first to the second operating mode passes through the third operating mode without remaining there.
[0016] This alternative threshold defines a significantly higher minimum modulation level than in the prior art in order to keep the DC link voltage ripple low when activating angle-synchronous block synchronization at the same electrical frequency. This higher minimum modulation level cannot be achieved by the (modulation-limited) first operating mode (time-synchronous synchronization) before activating the second operating mode (angle-synchronous block synchronization). Therefore, instead of the actually effective modulation level, a modeled modulation level is determined, for example, estimated using a model (see Fig. 7). Switching to the second operating mode only occurs if the thus estimated "unlimited" modulation level exceeds the modulation threshold for the respective target speed.
[0017] The modeled modulation level of the first operating mode is, in particular, greater than the actual modulation level of the first operating mode. The modeled modulation level of the first operating mode is, in particular, greater than m=0.907, whereby this value represents a maximum value for the modulation level of the first operating mode in field weakening.
[0018] This method can prevent the transition to angle-synchronous block clocking from occurring at unfavorable operating points, which, due to an insufficient steady-state modulation level, lead to steady-state operation with medium-pulse triple clocking as an example of the third operating mode, and thus generate an impermissibly large intermediate circuit voltage ripple over a longer period. According to one embodiment, a transition between the control of the stator of the electrical machine in the first operating mode and the control of the stator of the electrical machine in the second operating mode takes place by controlling the stator of the electrical machine in a third operating mode and / or vice versa using angle-synchronous clocking with an adjustable third voltage vector length.Angle-synchronous timing with a variably adjustable voltage vector length can achieve a smooth transition between the maximum voltage vector length during time-synchronous timing in the first operating mode and the voltage vector length during angle-synchronous block timing and / or vice versa. This can improve the operating behavior of the electric drive system during the transition between time-synchronous timing and block timing and / or vice versa.
[0019] According to one embodiment, in the third operating mode, during the transition from the first operating mode to the second operating mode, the adjustable third voltage vector length is continuously changed from the predetermined maximum first voltage vector length for the time-synchronous clocking up to the predetermined second voltage vector length of the angle-synchronous block clocking and / or conversely, during the transition from the second operating mode to the first operating mode, the adjustable third voltage vector length is continuously changed from the predetermined second voltage vector length of the angle-synchronous block clocking up to the predetermined maximum first voltage vector length for the time-synchronous clocking. By continuously adjusting the adjustable third voltage vector length, a continuous transition between the time-synchronous clocking and the angle-synchronous block clocking can be achieved. In particular, jumps can thus be avoided.This has a positive effect on both the mechanical behavior and the acoustic properties.
[0020] According to one embodiment, the third operating mode comprises center-pulse triple clocking. With center-pulse triple clocking, two further switching operations are present, starting from a block clocking. The two additional switching operations can, for example, occur symmetrically to the center of the block. In this way, an individual block of a block clocking is divided into two symmetrical sub-blocks, wherein the total length of the two sub-blocks is shorter than the block length of a block during block clocking. In this way, angle-synchronous clocking with a reduced voltage vector length can be achieved. The third operating mode can also comprise other suitable modulation methods, such as triple-edge pulse clocking.
[0021] According to one embodiment, the pulse width of the center pulse of the center pulse triple clocking is adjusted using the adjustable third voltage vector length. By varying the pulse width of the center pulse, the third voltage vector length can be adjusted. In particular, the voltage vector length can be reduced compared to the maximum achievable voltage vector length with block clocking alone.
[0022] According to one embodiment, a transition from the third operating mode to the second operating mode occurs when the pulse width of the center pulse of the center pulse triple clocking falls below a predetermined minimum pulse width, and / or a transition from the second operating mode to the third operating mode occurs when the pulse width of the center pulse of the center pulse triple clocking exceeds the predetermined minimum pulse width. The minimum pulse width defines the time during which a switching element of the power converter is switched on and off, or vice versa, must not be undercut. The minimum pulse width can be predetermined, for example, based on the component properties, in particular the properties of the switching elements, in a power converter. Furthermore, dead times or other characteristic parameters can also be taken into account when specifying the minimum pulse width.
[0023] In one embodiment, the modeled modulation level is determined as a function of the first current operating point on the MTPC characteristic curve (i.e., the shortest current vector length for the given torque base speed range) and / or as a function of the electrical stator resistance. In some embodiments, voltage or flux limits for the current operating point consisting of speed (electrical frequency) and torque are ignored. The modeled modulation can be calculated from the required flux on the MTPC characteristic curve using electrical frequency and DC link voltage. Instead of a model, an observer can also be used to determine the modeled modulation level.
[0024] The invention offers particular advantages in control methods with time-synchronous clocking in the first operating mode, which do not achieve a sufficient level of control for a smooth or smooth transition to block clocking. A control method for the first operating mode that can be advantageously used within the scope of the invention is a method using pulse width modulation or higher-order time-synchronous methods, such as OPP (Optimal Pulse Pattern) or synchronous PWM.
[0025] The invention can be used in a permanent magnet synchronous machine (PSM) or electrically excited synchronous machine (ESM) as an electrical machine, but can also be advantageously applied to other types of machines that require commutation of the stator current, such as asynchronous machines (ASM), etc.
[0026] A computing unit according to the invention, e.g. a control unit of a device for controlling a stator of an electrical machine, is configured, in particular in terms of programming, to carry out a method according to the invention.
[0027] The implementation of a method according to the invention in the form of a computer program or computer program product with program code for carrying out all method steps is also advantageous, as this entails particularly low costs, in particular if an executing control unit is also used for other tasks and is therefore already present. Finally, a machine-readable storage medium is provided with a computer program stored thereon, as described above. Suitable storage media or data carriers for providing the computer program are, in particular, magnetic, optical, and electrical memories, such as hard disks, flash memories, EEPROMs, DVDs, and others. Downloading a program via computer networks (Internet, intranet, etc.) is also possible. Such a download can be wired or cable-based or wireless (e.g., via a WLAN network, a 3G, 4G, 5G, or 6G connection, etc.).
[0028] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.
[0029] The invention is illustrated schematically in the drawing using exemplary embodiments and is described below with reference to the drawing.
[0030] Short description of the drawings
[0031] Figure 1 shows a schematic representation of a block diagram of an electric drive system according to an embodiment;
[0032] Figure 2 shows a schematic representation of a time-synchronous clocking system;
[0033] Figure 3 shows a schematic representation of an angle-synchronous block clock;
[0034] Figure 4 shows a schematic representation of an angle-synchronous clocking for an adjustable voltage vector length;
[0035] Figure 5 shows in three views a) to c) different relationships between the operating mode, the level of modulation and the electrical frequency.
[0036] Figure 6 shows a block diagram for determining a modeled control level of the first operating mode; Figure 7 shows a schematic representation of a flowchart underlying a method for controlling a stator of an electrical machine according to one embodiment.
[0037] Figure 8 shows an example transition from PWM clocking to angle-synchronous block clocking
[0038] Embodiment(s) of the invention
[0039] Figure 1 shows a schematic representation of a block diagram of an electric drive system 1 with a device 10 for controlling a stator of an electric machine 30. The electric drive system 1 comprises, for example, an electric machine 30 with the stator and a rotor, which can be fed by a power converter 11. For this purpose, the power converter 11 can be fed, for example, by a DC voltage source such as a battery 20 or the like. The example of a three-phase electric machine 30 shown here serves only to improve understanding and does not represent a limitation of the present invention. Furthermore, any electric machines 30 with a number of electrical phases other than three are of course also possible. For example, it can also be a six-phase electric machine 30 or an electric machine 30 with any other number of phases.
[0040] To control the stator of the electric machine 30, the power converter 11 can convert the DC voltage provided by the battery 20 into a suitable AC voltage. In the case of a three-phase electric machine 30, the power converter 11 can, for example, convert the DC voltage into a three-phase AC voltage. In particular, the amplitude of the AC voltage and / or the value of the output current from the power converter 11 to the stator windings (phases) of the electric machine 30 can be adjusted based on a predetermined setpoint S.
[0041] For example, the power converter 11 can be a power converter with multiple half-bridges. In particular, the power converter 11 can comprise at least one half-bridge with two switching elements for each phase of the electrical machine 30. For example, the power converter 11 for a three-phase electrical machine 30 can have a B6 topology. The switching elements of the power converter 11 can be controlled by the control device 12 using suitable control signals using the setpoint S. In this case, the control device 12 can, for example, provide a control signal for each switching element of the power converter 11 in order to open or close the corresponding switching element. The following description describes, in particular, the control signal for one switching element of the switching elements of a power converter 11. The control signals of the remaining switching elements are formed in the same way.The control of an upper switching element of a half-bridge is complementary to the control of the corresponding lower switching element. In addition, dead times or similar factors may also need to be taken into account.
[0042] Figure 2 shows a schematic representation of a control signal of a time-synchronous clock for controlling a switching element in a power converter 11 for controlling the electrical machine 30. For better understanding, only a few pulses are shown for one period of the output signal. As can be seen in Fig. 2, the switching element in the power converter 11 is controlled on the basis of a fixed time grid with the period T. Within each time grid, the corresponding switching element is switched on and off once. By varying the ratio between the on-time and off-time, the voltage level of the output signal can be adjusted accordingly. For example, the period T of a clock can be 100 ps, so that the clock frequency of the signal is 10 kHz. Furthermore, any other period T or clock frequencies are of course also possible. As shown in Fig.As can be further seen in Figure 2, a corresponding voltage level of the output signal A results depending on the duty cycle of a pulse.
[0043] Figure 3 shows a schematic representation of a control signal for controlling a switching element in the power converter 11 for angle-synchronous block clocking. As can be seen, the corresponding switching element is switched on for half a period T of the output signal and switched off for another half a period. The period T varies depending on the frequency of the output signal A. Beyond this, however, the amplitude of the output signal A cannot be influenced with angle-synchronous block clocking.
[0044] Figure 4 shows a schematic representation of a control signal for a semiconductor switching element of a power converter 11 for a medium-pulse triple clocking as an example of angle-synchronous clocking with adjustable voltage vector length. Here, too, the period T depends on the frequency of the output signal A. The medium-pulse triple clocking differs from the block clocking described in Fig. 3 in that two further switching operations are provided for each half-wave of the output signal A. In this case, an on- and an off-operation are provided symmetrically to the middle of half a period. As a result of these additional on- and off-operations, a medium pulse M with a pulse width t_M is generated at the middle of a block in the range of voltage vector lengths TT / 4 and 3TT / 4.This center pulse M results in the amplitude of the output signal A with a center pulse triple clocking being lower than the amplitude of an output signal A', as would be the case with angle-synchronous block clocking. For clarity, the output signal A according to the center pulse triple clocking is shown as a solid line, and the output signal A' of an angle-synchronous block clocking is shown as a dashed line. By varying the pulse width t_M of the center pulse M, the voltage vector length can be varied.
[0045] In real operation, it is not possible to choose an arbitrarily short time for the time between a switch-on process and a subsequent switch-off process, or between a switch-off process and a subsequent switch-on process. Rather, predetermined framework conditions must be observed. Therefore, the pulse width t_M of the center pulse M cannot be chosen to be arbitrarily short. If, for example, the voltage vector is to be increased within the scope of the control of an electrical machine 30, the pulse width t_M of the center pulse M is increasingly shortened with time-synchronous clocking. If the pulse width t_M of the center pulse M reaches the minimum adjustable pulse width, an immediate transition to angle-synchronous block clocking without a center pulse M takes place, as previously described in connection with Fig. 3.
[0046] For the operation of the electric drive system with the electric machine 30, it is possible to switch between the control methods described above depending on the operating state. Particularly when the electric machine 30 is at a standstill or at low speeds, the control is preferably based on time-synchronous clocking in accordance with the pulse-width-modulated clocking described in connection with Fig. 2. Time-synchronous clocking based on the PWM method generally only allows modulation up to a modulation depth of approximately 0.907. If necessary, the modulation depth can be increased somewhat further by using overmodulation. However, such overmodulation is also associated with disadvantages, so that it may not be desired.
[0047] Angle-synchronous block clocking, as described in connection with Fig. 3, on the other hand, has a modulation depth of 1. Accordingly, this angle-synchronous block clocking is also associated with a fixed voltage vector. In a direct transition from time-synchronous pulse-width-modulated clocking to angle-synchronous block clocking, the difference in the modulation depth from the maximum of the PWM clocking to the block clocking must therefore be overcome abruptly. To avoid such a jump, angle-synchronous clocking with a variable voltage vector length can be implemented during the transition, as described as an example in connection with Fig. 4.
[0048] Figure 5 shows, in a view a), a relationship between a control level r and an electrical frequency f for an exemplary electrical machine. A straight line 601 indicates the control level for maximum torque, and a straight line 602 indicates the control level for zero torque. The achievable range during operation is located in between. A maximum control level 1 for angle-synchronous block clocking is shown with a dashed horizontal line, and a maximum control level for time-synchronous clocking is shown with a dotted horizontal line (this value is exemplary and can be flexibly selected depending on the desired overmodulation; it can be 0.907, for example). In between is a control range 603 that is inaccessible with time-synchronous clocking without overmodulation and can instead be achieved with overmodulation or angle-synchronous clocking with a reduced voltage vector length.
[0049] In a view b), a quadrant of operating points defined by torque M and speed or electrical frequency f is shown, with an operating limit designated by 610. A range limit given by the maximum control level ro=0.9O7 for time-synchronous clocking without field weakening is designated by 611, and a range limit given by the control level n=1 for angle-synchronous block clocking is designated by 612. A frequency limit between time-synchronous clocking and angle-synchronous clocking is designated by fo. Operating points that lie in a range 620 with f < fo or r < ro are accessible with time-synchronous clocking. The range 620 is therefore limited by a frequency limit 621 and a control level limit 622. Operating points that lie in a range 630 with f > fo and ro < r < n are accessible with angle-synchronous clocking with a reduced voltage vector length.Operating points that lie in a range 640 with f > fo and r = 1 are accessible with angle-synchronous block timing.
[0050] In view c), a quadrant of operating points defined by torque M and speed or electrical frequency f is shown, with the range boundary 611 and range 630 being omitted. Instead, within the scope of embodiments of the invention, the electrical machine is also operated in range 630. View a) with time-synchronous clocking, ie, this now belongs to range 620, with a modeled modulation level being determined, as illustrated, for example, in Fig. 6.
[0051] Although only one quadrant of operating points is shown in Figure 5, the invention can be applied accordingly in all four quadrants.
[0052] An exemplary embodiment of a method according to the invention will now be described with reference to Figures 5 to 8, wherein Figure 6 shows a schematic representation of a flow chart underlying a method for controlling a stator of an electrical machine according to one embodiment.
[0053] In a step S1, the stator of the electric machine 30 is controlled in a first operating mode using time-synchronous timing with a predetermined maximum first voltage vector length to provide a first target torque and a first target speed. This can, in particular, involve motor operation of the electric machine at low speed, e.g., slow cruising operation of a vehicle having the electric machine 30. In particular, an operating point characterized by the first target torque and the first target speed lies in the range 620 in Figure 5c), which results in a first operating mode using time-synchronous timing.
[0054] If the speed of the electric machine is to be increased, e.g. in order to increase the driving speed of the vehicle having the electric machine, this is usually linked to an increase in the stator current, whereby the electric machine is then in a certain mechanical operating point consisting of a torque and a speed and in a first current operating point.
[0055] In a step S2, an unlimited modeled degree of control of the first operating mode is determined as a function of the torque and the speed, for example as shown in Figure 7, which shows a block diagram for determining a modeled degree of control of the first operating mode as a function of a current torque and a current speed.
[0056] The current torque M, 501 , together with other optional inputs 502 such as the rotor temperature, etc., is fed to a calculation function 510, which is designed, for example, as a characteristic map and outputs a magnetic flux ^PMTPC, 511 , on the MTPC characteristic curve (Maximum Torque per Current) (total flux that prevails at this torque and current operating point on the MTPC characteristic curve). The flux ^MTPC, 511 , is multiplied at 512 by the electrical frequency or angular frequency oo e i, 513, is multiplied to obtain the voltage ui , 514, from flux and speed, which corresponds to a total stator voltage without resistance (length of the voltage vector) prevailing at this current operating point.
[0057] At 516, an electrical resistance 518 of the stator is multiplied by a phase current 517 to calculate an electrical voltage drop across the stator. This voltage is added to the voltage ui , 514, to obtain the modeled voltage 519 along the MTPC characteristic curve, which is normalized at 521 to the maximum voltage (maximum voltage at block clocking (r=1)) 520 to obtain the modeled duty cycle 522.
[0058] In step S3, the modeled modulation level is compared with a modulation threshold, in particular r=1, and the speed is compared with a speed threshold. A suitable speed threshold can be obtained, for example, through ripple simulation; the machine must rotate fast enough to meet the DC link ripple requirements.
[0059] If the modeled modulation level reaches or exceeds the modulation threshold, branch "1," and the speed reaches or exceeds the speed threshold, the operating mode changes from the first operating mode to the second operating mode in step S4. In step S4, the stator of the electric machine 30 is controlled in the second operating mode using the angle-synchronous block clocking with a predetermined second voltage vector length to provide the mechanical operating point from the torque and the speed, wherein the electric machine is in a second current operating point that differs from the first current operating point.
[0060] In embodiments, switching from the first operating mode to the second operating mode takes place via the third operating mode, as explained above. In this case, for example, time-synchronous PWM clocking can initially take place to control the electric machine 30. Such time-synchronous PWM clocking can take place, for example, up to a predetermined maximum voltage vector length. If, starting from PWM clocking, it is intended to transition to angle-synchronous clocking, angle-synchronous clocking with a variable voltage vector length is initially carried out, for example a center pulse triple clocking, as described in connection with Fig. 4. In principle, however, other control methods for angle-synchronous clocking with variable voltage vector length are also possible. The voltage vector length can be varied by varying the pulse width t_M of the center pulse M.Subsequently, the voltage vector length can be continuously adjusted and, in particular, increased during angle-synchronous clocking. If the voltage vector length reaches the upper limit, the system switches to angle-synchronous block clocking without a center pulse. This can occur, in particular, if the pulse width t_M of the center pulse M falls below a previously specified minimum pulse width.
[0061] However, if the modeled modulation level does not reach the modulation threshold value in step S3, branch "0", the stator of the electric machine 30 continues to be controlled in the first operating mode, step S1.
[0062] The change or switching in the opposite direction from the second operating mode to the first operating mode takes place analogously when the modeled modulation level falls below the modulation threshold value or the speed falls below the speed threshold value, wherein a hysteresis of the modulation threshold value and / or the speed threshold value is expediently provided in order to avoid frequent switching back and forth.
[0063] An exemplary transition from PWM clocking to angle-synchronous block clocking is schematically visualized in Figure 8.
[0064] View a) shows the aforementioned MTPC characteristic curve 710 and an equal-torque characteristic curve 720 (iso-M line, iso-torque line) in an id / iq diagram of the stator current. View b) shows the MTPC line 710 in an id / ^M diagram, and view c) shows the MTPC line 710 in an id / M diagram.
[0065] In a base speed range (i.e. as long as the required voltage can be provided by means of the voltage modulation method used (first operating mode)), the optimal current operating point 731 is set, which results from the intersection point of the MTPC characteristic curve 710 with the iso-torque curve 720.
[0066] If the speed is now increased in the first operating mode with a constant desired torque, the current operating point remains at 731 as long as the required voltage can be set in the first operating mode.
[0067] As the speed continues to increase and the voltage limit is reached, the current operating point shifts to the left along the iso-torque line 720 toward 732 (=first current operating point). The stator current required to provide the same desired torque increases.
[0068] By comparing the modeled modulation level on the MTPC and the modulation threshold, the switch to block operation is triggered and more voltage is available again; the current operating point jumps to the second current operating point 733 = 731 , whereby the resulting current vector becomes shorter compared to the first current operating point 732.
Claims
Claims 1 . A method for controlling a stator of an electrical machine (30) having a rotor and a stator, comprising: Controlling (S1) the stator of the electrical machine (30) in a first operating mode (620) using a time-synchronous clocking with a predetermined maximum first voltage vector length to provide a mechanical operating point from a torque and a rotational speed, wherein the electrical machine is in a first current operating point (731); Determining (S2) a modeled degree of control of the first operating mode as a function of the torque and the rotational speed; comparing (S3) the modeled degree of control with a control threshold value (612) and comparing (S3) the rotational speed with a rotational speed threshold value; Controlling (S4) the stator of the electric machine (30) in a second operating mode (640) using an angle-synchronous block clock with a predetermined second voltage vector length to provide the mechanical operating point from the torque and the speed, wherein the electric machine is in a second current operating point (732); Switching from the first operating mode to the second operating mode when the modeled modulation level reaches or exceeds the modulation threshold (611) and when the rotational speed reaches or exceeds the rotational speed threshold, and / or switching from the second operating mode to the first operating mode when the modeled modulation level falls below the modulation threshold (611) or the rotational speed falls below the rotational speed threshold.
2. The method according to claim 1, wherein a transition from the actuation (S1) of the stator of the electric machine (30) in the first operating mode (620) into the actuation (S4) of the stator of the electrical machine (30) in the second operating mode (640) and / or conversely by means of actuation of the stator of the electrical machine (30) in a third operating mode using an angle-synchronous clocking with an adjustable third voltage vector length.
3. The method according to claim 2, wherein in the third operating mode, during the transition from the first operating mode to the second operating mode, the adjustable third voltage vector length is continuously changed from the predetermined maximum first voltage vector length to the predetermined second voltage vector length and / or vice versa.
4. Method according to one of the preceding claims, wherein the third operating mode comprises a center pulse triple clocking or triple edge pulse clocking.
5. The method according to claim 4, wherein a pulse width (t_M) of a center pulse of the center pulse triple clocking is set using the adjustable third voltage vector length.
6. The method according to claim 4 or 5, wherein a transition from the third operating mode to the second operating mode (640) occurs when the pulse width (t_M) of the center pulse falls below a predetermined minimum pulse width, and / or wherein a transition from the second operating mode to the third operating mode (640) occurs when the pulse width (t_M) of the center pulse exceeds a predetermined minimum pulse width.
7. Method according to one of the preceding claims, wherein the time-synchronous clocking comprises a pulse width modulation or a time-synchronous higher-order method.
8. The method according to any one of the preceding claims, wherein determining (S2) the modeled degree of control of the first operating mode (620) as a function of the torque and the speed comprises: Determining (S2) the modeled degree of modulation as a function of the first current operating point (733) on an MTPC characteristic curve (710) and / or as a function of an electrical resistance of the stator of the electrical machine (30).
9. Method according to one of the preceding claims, wherein the modeled modulation level of the first operating mode is greater than the actual modulation level of the first operating mode.
10. A computing unit (12) configured to carry out all method steps of a method according to one of the preceding claims.
11. A device (10) for controlling a stator of an electrical machine (30), comprising: a power converter (11) designed to be coupled to an electrical machine (30) having the stator and a rotor and to provide an electrical voltage for controlling the stator of the electrical machine (30); and a computing unit (12) according to claim 10, which is electrically coupled to the power converter (11) and provides the control signals for the power converter (11).
12. An electric drive system (1), comprising: a device (10) for controlling a stator of an electric machine (30) according to claim 11, and an electric machine (30) with the stator and a rotor, which is electrically coupled to the power converter (11) of the device (10) for controlling the rotor of the electric machine (30).
13. A computer program which causes a computing unit (12) to carry out all method steps of a method according to one of claims 1 to 9 when it is executed on the computing unit.
14. A machine-readable storage medium having a computer program according to claim 13 stored thereon.