Method and device for controlling a stator of an electrical machine and electrical drive system

Abstract

The invention relates to a method for controlling a stator of an electrical machine (30) having a rotor and the stator, comprising controlling (401) the stator of the electrical machine (30) using time-synchronous clocking with a carrier frequency (311), determining the carrier frequency (311) as a function of a rotational speed and / or a torque (331) of the electrical machine (30) in accordance with a first determination rule (330) if the controlling (401) of the stator does not occur in a field weakening range, and determining the carrier frequency (311) as a function of a rotational speed and / or a torque (331) of the electrical machine (30) in accordance with a second determination rule (340) if the controlling (401) of the stator occurs in a field weakening range, wherein the second determination rule (340) results in a higher carrier frequency than the first determination rule (330).The invention further relates to a corresponding control device and an electric drive system.

Description

[0001] The present invention relates to a method and a device for controlling a stator of an electrical machine having a rotor and the stator, a computing unit and a computer program for carrying out the method, and an electrical drive system. Background of the invention

[0002] 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 various modulation methods can be used. A distinction is made between time-synchronous methods, also known as asynchronous switching methods, asynchronous PWM or carrier frequency methods, and angle-synchronous methods (FFC - Fundamental Frequency Clocking).

[0003] In an asynchronous switching process, for example, a voltage signal can be modulated using pulse width modulation (PWM). The switching pattern is based on a fixed switching or calculation grid, i.e. the carrier frequency. Each power switch of the converter is switched on and off a maximum of once per PWM period. If, in a specific control situation, switching occurs too quickly or too frequently, or if the system-specific minimum pulse duration is not met, it can be planned not to switch at all during such a period. Thus, in some processes, periods can occur in which the actual switching frequency / switching frequency is lower than the carrier frequency. The current switching frequency in each case results from the specific sequence of switching operations and the intervals between them.DE 10 2008 040 144 A1 shows an example method with switching frequencies that are lower than the carrier frequency. A so-called flat-top method or discontinuous PWM method (DPWM) is also a method with a switching frequency that is lower than the carrier frequency.

[0004] The voltage yield is maximized with block commutation or block operation, and subharmonic frequencies are avoided through synchronism, and the switching frequency is minimal. However, a problem is the transition from asynchronous switching to block operation. Block operation has (by definition) a modulation index or duty cycle of one (ratio m or r between the voltage amplitude of the fundamental wave and the voltage amplitude of the fundamental wave in block operation). Asynchronous switching processes can achieve a maximum duty cycle of approximately r=0.907 without overmodulation due to theoretical and practical limitations (e.g., minimum pulse widths or dead times). Disclosure of the invention

[0005] According to the invention, a method and a device for controlling a stator of an electrical machine having a rotor and the stator, a computing unit and a computer program for implementing the method, and an electric 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.

[0006] The invention utilizes the measure of separately considering certain operating points, particularly with regard to the carrier frequency, when controlling (i.e., when energizing) a stator. At such operating points, a different (second) determination rule (e.g., characteristic map) is used to determine the carrier frequency. Such operating points occur particularly during field weakening, which is dependent on the intermediate circuit voltage, torque, and speed. Field weakening can be determined when a high modulation level is reached, particularly when the modulation level exceeds a modulation threshold. The modulation threshold can, for example, be approximately m=0.907, with m=1 as the maximum in block operation.

[0007] Specifically, the method comprises controlling the stator of the electric machine using an asynchronous switching method with a carrier frequency, determining the carrier frequency as a function of a rotational speed and / or a torque of the electric machine according to a first determination rule if the stator is not controlled in a field-weakening range, and determining the carrier frequency as a function of a rotational speed and / or a torque of the electric machine according to a second determination rule if the stator is controlled in a field-weakening range. In particular, the second determination rule results in a higher carrier frequency than the first determination rule.

[0008] In the field weakening range, some control methods switch discontinuously, meaning the switching frequency is reduced compared to the carrier frequency. In this case, the carrier frequency can be increased to optimize the performance (e.g., lower DC-link voltage ripple) by increasing the switching frequency.

[0009] The invention thus achieves a reduction in DC-link voltage ripple and harmonic losses in the electric machine. Controllability is improved by the larger number of control loops (measuring, processing, and adjusting). Voltage adjustment, especially at high speeds, is achieved with higher resolution, making the modulated voltage more precise. The use of two different determination rules allows them to be implemented specifically for the specific application, reducing the resolution and memory and runtime consumption compared to a single determination rule that covers everything.

[0010] The actual switching frequency is highly dependent on the operating point and partly time-dependent. Mapping the speed, voltage, and torque in a single calculation rule is complex and requires a large number of sampling points for good resolution.

[0011] In embodiments of the invention, limit values ​​or limitations can also be included in the control, for example to ensure that the limits of the power converter (in particular load) are adhered to and the power loss is not increased compared to continuous voltage modulation methods, such as with SVPWM (space vector PWM), and that the computing capacities of the executing computing unit (e.g. microcontroller) are not exceeded.

[0012] Compared to a closed-loop control, a control system has the advantage that it always works the same, even with slightly different systems, the function is simpler in structure and the safeguarding of the function is easier.

[0013] A higher carrier frequency reduces the DC-link voltage ripple, which is always an optimization goal for inverters. This is because the DC-link voltage ripple interferes with other devices on the DC link and causes losses, for example, in the DC-link capacitor. Depending on the definition of the corner point, the invention can even reduce the maximum DC-link voltage ripple at the corner point. This is the case if the first switching operations are already suspended at the corner point by the modulation method. The corner point and its DC-link voltage ripple are relevant to the design of the capacitor selection. A smaller ripple at the corner point enables a smaller and thus more cost-effective capacitor or power.

[0014] The higher carrier frequency reduces the harmonic losses of the machine. These are inversely proportional to the carrier frequency or the actual switching frequency. Lower losses improve efficiency and increase continuous power. Continuous power is particularly relevant for design at the highest speeds.

[0015] The higher carrier frequency improves the control cycles and thus the controllability of the operating point. More control cycles lead to more stable control in dynamic, noisy, or unfavorable operating points. Noisy or unfavorable operating points are often found in the field weakening region with severe overmodulation and small integer switching frequencies (<25) (ratio of carrier frequency to electrical frequency). A higher carrier frequency would increase the switching frequency. More stable control increases efficiency and torque quality.

[0016] The higher carrier frequency makes the modulated voltage more precise. A smaller switching frequency makes the voltage less precise. A higher carrier frequency increases the switching frequency, thus modulating the set voltage more effectively.

[0017] The invention can be advantageously applied to a permanent magnet synchronous machine (PSM) or electrically excited synchronous machine (ESM) as an electrical machine, but also to other types of machines that require commutation of the stator current, such as asynchronous machines (ASM), etc.

[0018] 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.

[0019] The implementation of a method according to the invention in the form of a computer program or computer program product with program code for carrying out all method steps is also advantageous, since this entails particularly low costs, in particular if an executing control unit is also used for other tasks and is therefore already present. Finally, a machine-readable storage medium is provided with a computer program stored thereon, as described above. Suitable storage media or data carriers for providing the computer program are, in particular, magnetic, optical and electrical memories, such as hard disks, flash memories, EEPROMs, DVDs, and others. Downloading a program via computer networks (Internet, intranet, etc.) is also possible. Such a download can be wired or cable-based or wireless (e.g. via a WLAN network, a 3G, 4G, 5G or 6G connection, etc.).

[0020] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

[0021] The invention is illustrated schematically in the drawing using exemplary embodiments and is described below with reference to the drawing. Short description of the drawings Fig. 1 shows a schematic representation of a block diagram of an electric drive system according to an embodiment; Fig. 2 shows a schematic representation of an asynchronous switching process and a resulting curve A of the fundamental voltage wave; Fig. 3 shows a schematic representation of a control circuit structure as may form the basis of a method for controlling a stator of an electrical machine according to one embodiment. Fig. 4 shows a schematic representation of a flow chart as may form the basis of a method for controlling a stator of an electrical machine according to one embodiment. Embodiment(s) of the invention

[0022] Fig. 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, which can be fed by a power converter 11, and a rotor. 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 five- or six-phase electric machine 30 or an electric machine 30 with any other number of phases.

[0023] 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.

[0024] 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.

[0025] Fig. Figure 2 shows a schematic representation of a control signal of an asynchronous switching method for controlling a switching element in a power converter 11 for controlling the electrical machine 30 and a resulting output signal A of the fundamental voltage wave. For better understanding, only a few pulses are shown for one period of the output signal. As in Fig. As can be seen in Figure 2, the switching element in the power converter 11 is controlled based on a fixed time frame (time-synchronous) with the period T, which is the inverse of the carrier frequency. Within each time frame, the corresponding switching element is switched on and off at most once. By varying the ratio between the on-time and off-time, the voltage level of the output signal A can be adjusted accordingly. For example, the period T of a clock pulse can be 100 µs, so that the clock frequency or carrier 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.

[0026] In Fig. 3 schematically shows a control circuit structure 300 according to an embodiment of the invention, which will be described below together with Fig. 4, in which a block diagram of an associated flow chart is shown.

[0027] The control circuit structure 300 can be implemented in one embodiment of a method according to the invention for controlling a stator of an electrical machine with a rotor and the stator, in particular in an executive control device 12.

[0028] In the embodiment shown, the control circuit structure 300 comprises a first determination rule 330 and a second determination rule 340, each of which receives input data 331. A carrier frequency 311 is obtained from the output side of the determination rules, which is supplied to a control path 330, ie, the drive system 1.

[0029] The first determination rule 330 and the second determination rule 340 serve or are configured to determine a carrier frequency 332 or 342 as an output variable from the input data 331. For this purpose, the first determination rule 330 and the second determination rule 340 can include, for example, a characteristic curve and / or a characteristic diagram and / or a functional relationship and / or a mathematical model and / or a machine learning model, etc. The input data 331 includes, for example, the voltage provided by the DC voltage source 20 and / or a rotational speed and / or a torque of the electric machine 30 and / or other input variables.

[0030] The carrier frequencies 332 and 342 are fed to a switching element or selection element 320, which, depending on a selection signal 321, makes a selection between the carrier frequencies 332 and 342 and outputs the carrier frequency 311. The selection signal 321 is generated by a field weakening detection element 322, which, depending on input data 323, determines whether the stator is being driven in a field weakening range. In particular, the field weakening detection element 322 can determine a current control level based on the input data 323 and compare it with a control level threshold value.

[0031] The input data 323 can be different: The modulation itself or DC link voltage and voltage vector length or a voltage reserve and / or other input variables.

[0032] For example, the carrier frequency 311 can be limited in a limiting element 350 to a maximum carrier frequency value 352 and / or to a minimum carrier frequency value 353. The limiting element 350 serves to prevent carrier frequencies from being too high or too low. This is advantageous, for example, when the carrier frequency is coupled with the calculation of the current / torque control loop or other limitations to prevent overloading the computing time of the executing computing unit. The maximum carrier frequency value 352 can, for example, be hardware-dependent.

[0033] The system 330 is operated with the carrier frequency 354 and the selected modulation method and the operating point may result in a reduced number of switching operations.

[0034] In one embodiment of the invention as in Fig.4, in a step 401 the stator of the electric machine 30 is controlled using a time-synchronous clocking with a carrier frequency 311 or 354.

[0035] In a block 402 the carrier frequency to be used is determined.

[0036] In step 403, a current modulation level is determined. The modulation level is calculated from the quotient of the voltage vector length to the intermediate circuit voltage times a constant factor.

[0037] In a step 404, the current modulation level is compared with a modulation level threshold value.

[0038] If the duty cycle exceeds the duty cycle threshold, it is determined that the stator is being driven in a field weakening range and the process branches to step 405.

[0039] If the duty cycle does not exceed the duty cycle threshold, it is determined that the stator is not being driven in a field weakening range and the process branches to step 406.

[0040] In step 405, the carrier frequency 311 is determined as a function of a rotational speed and / or a torque and / or other states of the electric machine 30 in accordance with the second determination rule 340.

[0041] In step 406, the carrier frequency 311 is determined as a function of the rotational speed and / or the torque and / or other states of the electric machine 30 in accordance with the first determination rule 330.

[0042] The carrier frequency 311 determined in this way is used for driving in step 401.

[0043] It is advantageous if the modulation method is one that does not reduce the drive by increasing the carrier frequency, since otherwise an increase in the carrier frequency would also increase the field weakening current due to the lower voltage. A method without drive reduction is No-Zero-Pointer (NZP), as described, for example, in WO 2023 / 198336 A1.

[0044] However, the invention can also be operated with control methods that influence the modulation depending on the carrier frequency, as is known, for example, from DE 10 2008 040 144 A1 cited above. However, a possible change in the field weakening current must then be taken into account.

[0045] Although only two different determination rules are described in the figure, it should be noted that more than two determination rules can be used, which can be selected depending on different input variables such as modulation level, voltage, speed, torque, operating mode, etc. 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] DE 10 2008 040 144 A1 [0003, 0044] WO 2023 / 198336 A1

[0043]

Claims

[1] Method for controlling a stator of an electrical machine (30) having a rotor and the stator, comprising: Controlling (401) the stator of the electrical machine (30) using an asynchronous switching method with a carrier frequency (311); Determining (406) the carrier frequency (311) as a function of a rotational speed and / or a torque (331) of the electrical machine (30) in accordance with a first determination rule (330) if the control (401) of the stator does not take place in a field weakening range; Determining (405) the carrier frequency (311) as a function of a rotational speed and / or a torque (331) of the electrical machine (30) in accordance with a second determination rule (340) when the control (401) of the stator takes place in a field weakening range, wherein the second determination rule (340) results in a higher carrier frequency than the first determination rule (330). [2] The method of claim 1, further comprising: Determining whether the control (401) of the stator takes place in a field weakening range, depending on a control level that describes a ratio of a voltage applied to the stator to a maximum voltage that can be applied to the stator. [3] The method of claim 2, further comprising: Determining that the driving (401) of the stator takes place in a field weakening range when the modulation level exceeds a modulation level threshold value. [4] The method of claim 2 or 3, further comprising: Determining that the driving (401) of the stator does not occur in a field weakening range if the duty cycle does not exceed the duty cycle threshold value. [5] Method according to one of claims 2 to 4, further comprising: Determining (403) the degree of modulation as a function of the voltage provided by a DC voltage source (20) to the electrical machine (30) and a voltage vector length. [6] Method according to one of the preceding claims, further comprising: Limiting (350) the carrier frequency (311) to a maximum (352) and / or minimum (353) carrier frequency value. [7] Method according to one of the preceding claims, wherein the determination of the carrier frequency (311) as a function of a rotational speed and / or a torque (331) of the electrical machine (30) in accordance with the first determination rule (330), if the control (401) of the stator does not take place in a field weakening range, comprises: Determining the carrier frequency (311) as a function of a rotational speed and / or a torque (331) of the electrical machine (30) in accordance with several different first determination rules. [8] Method according to one of the preceding claims, wherein the determination of the carrier frequency (311) as a function of a rotational speed and / or a torque (331) of the electrical machine (30) in accordance with the second determination rule (340) when the control (401) of the stator takes place in a field weakening range comprises: Determining the carrier frequency (311) as a function of a rotational speed and / or a torque (331) of the electrical machine (30) in accordance with a plurality of different second determination rules. [9] Computing unit (12) which is designed to carry out all method steps of a method according to one of the preceding claims. [10] 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) comprising 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 8, which is electrically coupled to the power converter (11) and provides the control signals for the power converter (11). [11] Electric drive system (1), with: a device (10) for controlling a stator of an electrical machine (30) according to claim 9, and an electrical machine (30) with the stator and a rotor, which is electrically coupled to the power converter (11) of the device (10) for controlling the stator of the electrical machine (30). [12] Computer program which causes a computing unit (12) to carry out all method steps of a method according to one of claims 1 to 7 when it is executed on the computing unit. [13] A machine-readable storage medium having stored thereon a computer program according to claim 11.

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