METHOD FOR REGULATING AN ELECTRIC THREE-VOLTAGE MACHINE AND THREE-VOLTAGE MACHINE SYSTEM FOR SUCH A METHOD

Description

[0001] The invention relates to a method for controlling an electric three-phase machine, in particular an asynchronous machine, with a rotor, a stator and at least two phases, wherein at least one electrical signal, in particular a voltage signal, is applied to at least one phase, preferably all phases, of the three-phase machine and an electrical signal waveform, in particular a current waveform, in which at least one phase is measured or determined, wherein an intermodulation signal component caused by slotting effects and magnetic saturation effects in the three-phase machine, which is determined from the signal waveform measured or determined in the at least one phase, is used for controlling the three-phase machine, wherein the intermodulation signal component is extracted by eliminating other signal components.

[0002] Furthermore, the invention relates to a three-phase machine system for carrying out such a method.

[0003] Modern control systems for three-phase motors often require knowledge of the rotor's angular position. To obtain this information, sensors such as incremental encoders, absolute encoders, or resolvers can be used, which can be based on a variety of physical principles. However, a disadvantage of all types of encoders is the additional cost. Furthermore, encoders have a limited lifespan, which is often shorter than the planned lifespan of the three-phase motor. A perceived defect in a three-phase drive is frequently due to the failure of such a sensor. Failures and downtime, for example, of defective trains on railway lines, can be associated with considerable effort and high costs and should therefore be avoided whenever possible.

[0004] To avoid the use of such sensors in three-phase machines or drives, so-called sensorless control methods have been developed. These methods determine the angular position of the flux linkage from the electrical parameters within the three-phase machine without the need for a sensor to measure the angle or rotational speed. In these methods, excitation signals are often applied using a frequency converter, and the motor's response signals are measured. The angular position or rotational speed of the rotor can then be determined through appropriate analysis.

[0005] Sensorless control methods utilize the fact that three-phase machines exhibit asymmetries due to their design or caused by electrical or magnetic effects during operation, which can change over time and space. These changes in asymmetries typically cause changes in inductance and can therefore be detected, for example, by a change in the current rise time. WO 99 / 39430 A1 describes a sensorless control method.

[0006] An example of a design-related asymmetry is the rotor of a permanent magnet synchronous machine (PMS), which has permanent magnets at certain locations that have a lower relative permeability than the surrounding iron regions. This increases the magnetic resistance in the permanent magnet region compared to the iron regions. As the PMS rotor rotates, the magnetic resistance varies temporally and spatially along the circumference of the air gap, manifesting as changes in inductance.

[0007] An example of electrical or magnetic asymmetry is local saturation phenomena of the magnetic flux paths in the three-phase machine.

[0008] The weaker the rotor-related asymmetries of a three-phase machine, the more difficult it is to detect a change in the rotor's angle of rotation without sensors. It is particularly difficult to determine the angular position of an asynchronous machine's rotor without sensors (i.e., without sensors of the type described above, such as incremental encoders), because asynchronous machines, especially compared to synchronous machines, exhibit lower asymmetries. In asynchronous machines, a slot signal component contained in the measured current waveforms is typically isolated and evaluated from other signal components, or the saturation signal is used. The slot signal component is caused by the rotor's slotting as it rotates past the stator's slot and the associated change in inductance.Since the inductance changes caused by the rotating slot are relatively small, the slot signal component is generally small and can therefore be difficult to identify and separate from other signal components, depending on the operating state and design of the asynchronous machine. In particular, with increasing load on the asynchronous machine, the slot signal component can be difficult or even impossible to distinguish from other signal components.

[0009] Determining the slot signal component by eliminating the intermodulation signal component and the saturation signal component is known from the prior art, for example, from: Wolbank T.M. et al.: "Comparison of inherent saliency tracking methods for zero speed sensorless control of standard induction machines", ELECTRIC MACHINES AND DRIVES CONFERENCE, 2009. IEMDC , 09. IEEE INTERNATIONAL, IEEE, PISCATAWAY, NJ, USA, 3. Mai 2009 (2009-05-03), Seiten 1258-1263, XP031475932, ISBN: 978-1-4244-4251-5 und Metwaly Mohamed K. et al.: "Slotting Saliency Extraction For Sensorless Torque Control of Standard Induction Machines", IEEE TRANSACTIONS ON ENERGY CONVERSION, IEEE_ SERVICE CENTER, PISCATAWAY, NJ, US, Bd. 33, Nr. 1, 1. März 2018 (2018-03-01 ), Seiten 68-77, XP011677884, ISSN: 0885-8969, DOI: 10.1109 / TEC.2017.2726998.

[0010] In light of these considerations, it is therefore an object of the present invention to mitigate or even completely eliminate the disadvantages of the prior art. In particular, it is an object of the present invention to provide a method of the type mentioned above in which the angular position and / or rotational speed of a rotor of a three-phase machine, especially an asynchronous machine, can be determined in an improved manner and over a wide speed and load range from at least one electrical signal waveform.

[0011] This problem is solved by a method with the features of claim 1. According to the invention, it is provided that in a method of the type mentioned at the outset, a slotting angle is determined from an angle of the intermodulation signal component by comparing the angle of the intermodulation signal component with an angle of a saturation signal component contained in at least one signal waveform according to the calculation rule. θ slot t = ± θ sat t − θ inter t The intermodulation signal component, the intermodulation signal component, and the saturation signal component are combined, with phase angles being defined as the slot angle, inter(t), inter-t angle, saturation signal component, and slot angle. θinter(t) denotes the intermodulation signal component angle, θsat(t) the saturation signal component angle, and slot angle.

[0012] An intermodulation signal component, caused by slotting and magnetic saturation effects in the three-phase machine, is used to control the three-phase machine. This component is derived from the electrical signal waveform measured or determined in at least one phase. In particular, the intermodulation signal component can be used to determine the rotor position, i.e., the angular position of the rotor, which can then be used to control the three-phase machine. Preferably, at least one electrical current waveform is measured or determined and used as the electrical signal waveform. For this reason, the following explanations refer to measured current waveforms. However, measured or determined voltage waveforms can also be used.Determining the signal waveform, particularly the current waveform, in at least one phase of the three-phase machine can be achieved, for example, by measuring currents and / or voltages in a DC link of the inverter, in the inverter's power supply, or in the feed to a machine-side inverter. In particular, phase currents of the three-phase machine can be determined based on a DC link current. Since the method is particularly suitable for use with asynchronous machines or electrical machines with at least partially asynchronous characteristics (e.g., synchronous machines with a damper cage), the following descriptions primarily refer to asynchronous machines. Preferably, the three-phase machine can have two, three, or more than three phases.The three-phase machine is particularly preferably configured as a three-phase three-phase machine, especially as a three-phase asynchronous machine with three phases. The invention is based on the understanding that, as explained in more detail below, a mathematical or physical relationship exists between the intermodulation signal component and the slot signal component, which is representative of the angular position or rotational speed of the rotor. Therefore, a control and position signal for controlling the three-phase machine can be derived from the intermodulation signal component and used. Thus, the slot signal component, which is often difficult to determine, no longer needs to be used directly.Advantageously, the intermodulation signal component in the signal response of the three-phase machine, in response to an excitation signal, is significantly larger than the slotted signal component in most operating states of the three-phase machine and can therefore be more easily identified and separated from other signal components. The intermodulation signal component can be evaluated in the time domain and / or the frequency domain. In particular, the angular position and / or rotational speed of the rotor can subsequently be determined from the intermodulation signal component. For this purpose, a saturation signal component can also be used and combined with the intermodulation signal component (see below). The intermodulation signal component is mainly caused by effects of the slotting of the rotor or stator of the three-phase machine and by effects of magnetic saturation of magnetic flux paths within the three-phase machine.The intermodulation signal component has a different fundamental frequency in most operating states than the slotted signal component and the saturation signal component. The effects described, in turn, cause their own signal components, which are also contained in at least one measured current waveform. The signal components in the current waveform generated by the slots of the rotor and stator of the three-phase machine are called slotted signal components. The fundamental frequency of the slotted signal components generally corresponds essentially to the... N-The signal components in the current waveform caused by temporal and spatial variations in the magnetic saturation of magnetic flux paths within the three-phase machine are called saturation signal components. The fundamental frequency of the saturation signal component typically corresponds essentially to twice the fundamental or operating frequency of the machine. By physically combining these two effects, their signal components are also combined within the three-phase machine, thereby generating the intermodulation signal component. The frequencies of this intermodulation signal component differ from the frequencies of the saturation signal component and the frequencies of the slot signal component in most operating states.The effect of the described intermodulation occurs particularly in asynchronous machines and electrical machines with at least partially asynchronous machine-like characteristics, which is why the method according to the invention is particularly suitable for controlling asynchronous machines. In previous applications known from the prior art, the intermodulation signal component in the machine's response to an excitation signal was considered a disturbance component and eliminated. As already mentioned, the invention is based on the finding that there is a relationship between the intermodulation signal component and the slotted signal component, which is representative of the rotor's angular position and speed, and that the intermodulation signal is therefore also suitable for controlling the three-phase machine. The relationship between the frequencies of the intermodulation, slotted, and saturation signal components is given by... ω inter = ± ω sat − ω slot , where ωinter is the frequency of the intermodulation signal component, ωsat is the frequency of the saturation signal component, and ωslot is the frequency of the slot signal component. The sign of ωsat in equation (1) depends on the design and construction of the three-phase machine. To calculate the slot signal component using the intermodulation signal component, the saturation signal component, preferably its fundamental frequency, can be used. The saturation signal component can be determined from the currents in the phases of the three-phase machine. In addition to the fundamental frequencies, the aforementioned signal components may also contain harmonics, which, however, are neglected for the sake of simplicity and due to their negligible influence.The invention is based on the further finding that the relationship between the intermodulation signal component and the slot signal component can be used to determine the angular position and / or rotational speed of the rotor using the intermodulation signal component, without having to directly derive or use the slot signal component from the current waveform. The intermodulation signal component can therefore advantageously be used in all control methods where knowledge of the rotor's angular position or the angular position of the flux linkage is necessary. In contrast to the invention, the intermodulation signal is typically eliminated as a noise signal in the prior art, and the slot signal component or the saturation signal component is used directly for control.

[0013] It is particularly advantageous to apply electrical signals, especially voltage signals, to all phases of the three-phase machine and to determine, specifically measure, evaluate, and use the resulting current profile of each phase to determine the intermodulation signal component. The applied electrical signals can include excitation signals. The machine's response to these excitation signals allows conclusions to be drawn about its operating state, enabling the determination of the intermodulation signal component. Various types and forms of excitation signals can be used. For example, the excitation signals can be voltage signals that are (already) applied to generate the rotating magnetic field in the air gap. These excitation signals can also result from switching operations of the power semiconductors in a converter, such as pulse-width modulation (PWM) or similar methods.The inverter generates the rotating magnetic field in the air gap through switching operations. Therefore, the excitation signals can be integrated into the rotating field excitation process. For example, the carrier frequency of the PWM or its harmonics can also be considered and used as an excitation signal. Thus, parts of the switching sequence are used to operate the three-phase machine, and its current waveforms are determined and evaluated. However, the excitation signals can also be independent of the switching sequence used to generate the rotating field of the three-phase machine. These signals can be inserted between and / or superimposed on the switching sequences used to generate the rotating field in the air gap. Square wave pulses are preferred as excitation signals because they can be easily generated using an inverter. However, the excitation signals can also be, for example, sinusoidal, transient, pulsating, and / or rotating.The excitation signals can themselves be PWM-modulated. The only important thing is that a machine response to an excitation signal (e.g., a current waveform) can be determined, allowing conclusions to be drawn about the changing asymmetries of the three-phase machine mentioned earlier. Preferably, when applying excitation signals that are not part of the switching sequence for operating the three-phase machine, i.e., do not serve to generate the rotating field, the frequency of the excitation signals is selected such that they have no or only a minimal influence on the generated rotating field, or on the torque, in the air gap.

[0014] In a preferred embodiment, the angular position and / or rotational speed of the rotor are determined from the intermodulation signal component, and this angular position and / or rotational speed is used to control the three-phase machine. For example, the rotational speed can be determined using formula (1). Therefore, a saturation signal component, in particular its angle or a representative angle, can also be used to determine the angular position and / or rotational speed. In one embodiment, the angular position of the rotor can be calculated by integrating the angular velocity ωslot. The angular position can be used, in particular, to represent the physical, especially electrical, quantities required for control in a control method.

[0015] Preferably, the intermodulation signal component is determined from at least one current waveform, in particular from its change over time. The corresponding change over time can also be determined by a mathematical equation after combining several current waveforms from different strands.

[0016] In a further embodiment, it is provided that current waveforms, particularly their temporal changes, are determined in at least two, and preferably three, phases of the three-phase machine, and that these current waveforms, preferably their temporal changes, are combined into a single signal using a mathematical equation, particularly an equation for calculating a space vector, and the intermodulation signal component is determined from this combined signal. Preferably, the measured current waveforms represent discrete time signals. However, the measured current waveforms can also be continuous-time signals. Voltage waveforms can also be used instead of current waveforms.

[0017] When determining the internal states of the three-phase machine, it is due to the electrical relationship u t = L di t dt It is advantageous if the temporal changes of the current waveforms are linked by the mathematical equation or if a temporal change of the linked signal is determined after the linkage, since the asymmetries that allow an evaluation of the angular position or rotational speed of the rotor can be detected, in particular, by changes in inductance, and the inductance L is related to the voltage u(t) via the temporal change of the current di(t) / dt. If the applied electrical signal is an essentially sinusoidal voltage signal, the measured current values, in particular amplitudes or RMS values, can also be used and linked essentially directly, since the relationship according to equation (2) can be derived from complex AC circuit analysis. U t = jωLI t In simplified terms, U represents voltage, j the imaginary unit, ω an angular velocity / frequency, L an inductance, and I a current. An equation for linking the current waveforms, particularly their time variation, could be, for example, an equation for calculating a space vector, such as... ϑ saliency = i U t + i V t e j 2 π 3 + i W t e j 4 π 3 or ϑ saliency = di U t dt + di V t dt e j 2 π 3 + di W t dt e j 4 π 3 The following are used, where i U,V,W (t) represents a current waveform (or di U,V,W (t) / dt its first time derivative) in one phase U, V, W of the three-phase machine, j the imaginary unit, e Euler's number, and π the mathematical constant. The resulting signal ϑ Saliency is, in this case, a complex vector, equivalent to a space vector. A space vector maps physical quantities, especially quantities of a multiphase system, into the complex plane with real and imaginary parts. The intermodulation signal can subsequently be determined from the resulting signal.

[0018] The intermodulation signal component is extracted by eliminating other signal components. Preferably, the intermodulation signal component is extracted by eliminating saturation signal components due to magnetic saturation effects and / or slotted signal components due to slotting effects in the three-phase machine, particularly from the compounded signal. In other words, the intermodulation signal component is isolated. Further signal components can also be eliminated. The elimination of signal components other than the intermodulation signal component can be achieved, for example, by filtering. Elimination can also be achieved by subtracting the unwanted signal components. For example, the unwanted signal components can be estimated in terms of frequency, amplitude, and phase and subtracted from the current waveform or the compounded current signal.This can be done, for example, by prior identification of the machine and by using a cost function, as explained in "Identification and Compensation of High-order Harmonic Distortions in Saliency Based Sensorless Control of Induction Machines" by W. Fahrner, MA Vogelsberger and T. Wolbank or in "Induction Machine Design Methodology for Self-Sensing: Balancing Saliencies and Power Conversion Properties." by Brown, Ian Paterson and Robert D. Lorenz.

[0019] According to the invention, it is provided that slot information, namely a slot angle, is determined from an angle of the intermodulation signal component by comparing the angle of the intermodulation signal component with an angle of a saturation signal component contained in the current waveform according to the calculation rule. θ slot t = − θ inter t ± θ sat t The intermodulation signal component is combined. θ slot (t) corresponds to the calculated slot angle, θ inter (t) to the angle of the intermodulation signal component, and θ sat (t) to the angle of the saturation signal component. The slot angle θ slot (t) determined in this way essentially corresponds to the angle of the slot signal component. In other words, the slot angle θ slot (t) is determined or calculated by combining the angle θ inter (t) of the intermodulation signal component and the angle θ sat (t) of the saturation signal component. The angles θ slot (t), θ inter (t), and θ sat (t) are phase angles, specifically phase angles of the fundamental frequencies of the individual effects. The angle θ sat (t) of the saturation signal component can be determined from twice the angle of the stator current, whereby a load-dependent offset value can be provided for correction. The offset value can be determined, for example, using a cost function from measurements on the three-phase machine.

[0020] In one embodiment, the mechanical angular position of the rotor can be calculated by dividing the slot angle by the number of slots in the rotor. Preferably, the number of slots corresponds to the total number of slots in the rotor.

[0021] During tests with the method according to the invention, it was found that the angle of the intermodulation signal component can deviate depending on the rotational speed and / or the load of the three-phase machine, such that the rotor's angular position determined from the intermodulation signal component may differ from the actual angular position. For this reason, it can be advantageous, for example, to correct the angle of the intermodulation signal component as a function of the load, in particular the torque, and / or the rotational speed of the three-phase machine using an intermodulation correction value. The intermodulation correction value can be determined before applying the method, for example, by measurements on the machine or calculations, and stored, for example, in a table or modeled by a mathematical function.

[0022] Furthermore, the tests revealed that the angle of the saturation signal component can also deviate depending on the rotational speed and / or the load of the three-phase machine. Therefore, it can be implemented to correct the angle of the saturation signal component as a function of the load, particularly the torque, and / or the rotational speed of the three-phase machine using a saturation correction value. The saturation correction value can be determined before applying the method, for example, by measurements on the machine or calculations, and stored in a table or modeled using a mathematical function.

[0023] In one embodiment, the electrical signal applied to the three-phase machine may be an excitation signal that is essentially independent of the fundamental frequency of the rotating magnetic field of the three-phase machine, the fundamental frequency of which is preferably at least five times, and more preferably at least ten times, the fundamental frequency of the voltages in the phases (U, V, W) used to generate the rotating magnetic field of the three-phase machine. Preferably, the excitation signal is a voltage signal. In another embodiment, the fundamental frequency of the excitation signal is at least twice the operating slip frequency of an asynchronous machine.The excitation signal can also be generated from a sequence of essentially rectangular voltage pulses (step functions), which can be formed both by individual switching operations of the inverter and as a pulsed combination of several individual pulses with time-step and / or different duty cycles (duty levels).

[0024] In one embodiment, the electrical excitation signal is a current signal, and the response of the three-phase machine, in particular the voltage at the three-phase machine, is evaluated to determine the intermodulation signal component.

[0025] The problem stated above is also solved by a three-phase machine system according to claim 12. The three-phase machine system comprises: a three-phase machine, in particular an asynchronous machine, with a rotor, a stator and at least two phases; a power section, in particular an inverter, which is electrically connected to the three-phase machine, wherein the power section is configured to apply excitation signals, in particular voltage signals or current signals, to at least one phase, preferably all phases, of the three-phase machine; at least one measuring device, which is configured to measure or determine a time course of the response of the machine, in particular a current course or a voltage course, in which at least one phase or in an intermediate circuit of the inverter or in the power supply for the inverter or in the feed of a machine-side inverter; a control unit, which is configured toto control the three-phase machine on the basis of an intermodulation signal component caused by slotting and magnetic saturation effects in the three-phase machine, which intermodulation signal component is contained in the at least one measured current waveform, in particular in its change over time, wherein the control unit is further configured to extract the intermodulation signal component by eliminating other signal components and to determine a slotting angle from an angle of the intermodulation signal component by comparing the angle of the intermodulation signal component with an angle of a saturation signal component contained in the at least one signal waveform according to the calculation formula , θ slot t = ± θ sat t − θ inter t is combined, where the slotting angle θ slot (t), the angle θ inter (t) of the intermodulation signal component and the angle θ sat (t) of the saturation signal component are phase angles.

[0026] The three-phase machine system is configured to perform the procedure described above. For the advantages, technical effects, and other features, reference is made to the procedure described above. The power section can generate excitation signals through switching operations. For this purpose, the power section can have a plurality of electrical switches, for example, semiconductor switches. The measuring device can have at least one current or voltage sensor. Preferably, the current waveforms in all phases of the three-phase machine can be determined using the measuring device. For this purpose, a current sensor can be provided in each phase of the three-phase machine. In the case of m phases, a current sensor can also be provided in each of the m-1 phases, and the current of the m-th phase can be calculated based on Kirchhoff's current law.

[0027] The phase currents of the three-phase machine can also be determined or calculated by measuring in the intermediate circuit of the converter, in the power supply of the converter or in the feed to the machine-side converter.

[0028] The control unit can be, for example, a standalone unit or a component of another unit, in particular a microprocessor. The control unit can be integrated into the inverter. The phases of the three-phase machine form coils or are connected to coils that can generate a magnetic flux in the air gap between the rotor and stator of the three-phase machine.

[0029] The invention will be described below with reference to the figures, to which it is not limited. Fig. 1 schematically shows a three-phase machine system with a converter and a three-phase machine; Fig. 2 shows a cross-section of an asynchronous machine; Fig. 3A schematically shows an example excitation signal; Fig. 3B schematically shows current waveforms as a result of the excitation signal according to Fig. 3A (with different rotor positions); Fig. 4A shows a linked signal in the time domain, which was generated from a combination of current waveforms of all phases of the three-phase machine; Fig. 4B shows the linked signal from Fig. 4A in the frequency range; Fig. 5 shows a real component of the linked signal; Fig. 6 shows a real component of an intermodulation signal component; Fig. 7A-D show different signal waveforms of the three-phase machine under different operating conditions of the three-phase machine; Fig. 8A-C Each shows progressions of correction values; Fig. 9 shows a block diagram as an example of how to implement the invention; and Fig. 10A-C represent excitation signals and the resulting current profiles.

[0030] The method according to the invention will now be explained in more detail using an application to an asynchronous machine.

[0031] Fig. 1 Figure 1 schematically shows a three-phase machine system 1 with a three-phase machine 3 configured as an asynchronous machine 2 connected to a converter 4, which has a plurality of (not shown) electronic switches, for example, semiconductor switches. The converter 4 is configured to output voltages with predefined frequencies, amplitudes, and (zero) phase angles at an output 6 by means of appropriate switching operations. The output 6 of the converter 4 is connected to the phases U, V, W of the asynchronous machine 2. The voltages generated by the converter 4 induce a voltage in an air gap of the asynchronous machine 2 between rotor 21 and stator 20 (see Figure 2). Fig. 2 ) generates a rotating field that induces voltages in the rotor 21 of the asynchronous machine 2 and sets it in rotation by the resulting rotor currents.

[0032] The asynchronous machine 2 is in Fig. 1 The asynchronous machine 2 is shown schematically as a circuit diagram. It has three phases U, V, W, each with a phase resistance RU, RV, RW and a phase inductance LU, LU, LW. The voltages EU, EV, EW denote the voltages induced in the stator 20 of the asynchronous machine 2 (back EMF). The currents IU, IV, IW flowing in the phases U, V, W can be measured or determined using current sensors 7a and / or 7b, and a measuring device 8a or 8b, respectively. Phase currents can also be determined using the current sensors 7b, for example, based on a current flowing into the inverter 4. It is possible to provide a current sensor 7a in each phase U, V, W. The current sensors 7a and 7b can be integrated into the inverter 4 or be independent components.Using the current measuring sensors 7a and / or 7b, the time-dependent current profiles i U (t), i V (t), i W (t) of the currents IU , IV , IW in the strands U, V, W can be determined.

[0033] Fig. 2 Figure 1 schematically shows a cross-section of an asynchronous machine 2 without windings, with a stator 20, a rotor 21 and a slot 23, each on rotor 21 and stator 20. For illustration, an angular position θ mech (t) of the rotor 21 is shown.

[0034] As mentioned above, the asynchronous machine 2 exhibits asymmetries that can change over time and space, thereby allowing conclusions to be drawn about the angular position θmech(t) and / or the rotational speed of the rotor 21. One example of such an asymmetry is the slotting 23 of the rotor 21 and / or stator 20. Another example of an asymmetry is the saturation of the magnetic flux paths in the asynchronous machine 2. Both asymmetries cause temporal and spatial changes in inductance during the operation of the asynchronous machine 2, which can be determined by evaluating the current waveforms iU(t), iV(t), iW(t).In a highly simplified model to illustrate an asymmetry, it can be assumed, for example, that the three strand inductances LU , LV , LW in the strands U, V, W each have a mean value L 0 and, depending on a mechanical angular position θ mech (t) of the rotor 21, deviate sinusoidally (with an amplitude LM ) from this mean value L 0: . L U θ mech t = L U , 0 + L U , M sin θ mech t L V θ mech t = L V , 0 + L V , M sin θ mech t + 2 π 3 L W θ mech t = L W , 0 + L W , M sin θ mech t + 4 π 3

[0035] Changing the angular position θmech(t) of the rotor 21 therefore also changes the inductances LU, LV, LW. These changing inductance components can thus also be referred to as modulated inductances. The changes in the inductances LU, LV, LW can be caused, for example, by the slots 23 of the rotor 21 or stator 20 and / or the magnetic saturation of magnetic iron paths in the three-phase machine 3.

[0036] Determining the angular position θ mech (t) of the rotor 21 in asynchronous machines 2 has so far been a major challenge, since asynchronous machines 2, especially compared to most synchronous machines, have significantly smaller asymmetries and therefore significantly smaller inductance fluctuations during operation.

[0037] To determine inductance changes, electrical signals, preferably voltage signals UU(t), UV(t), UW(t), are applied to the phases U, V, W of the asynchronous machine 2, and the resulting current waveforms iU(t), iV(t), iW(t) are measured using the current sensors 7. The voltages or voltage pulses applied by the inverter 4 to operate the asynchronous machine 2 can be used as voltage signals UU(t), UV(t), UW(t). The electrical signals can include excitation signals 9 to determine the operating state of the three-phase machine 3. The excitation signals 9 can be essentially independent of the generation of a rotating magnetic field by the three-phase machine 3. Excitation signals 9 can be used that are applied between or superimposed on the voltage (pulses) generated by the inverter 4 to generate the rotating magnetic field.Voltage waveforms with a higher frequency than that used to generate the fundamental wave of the rotating field can also be used.

[0038] In Fig. 10A bis Fig. 10C The application of an exemplary excitation signal 9 and the resulting current waveforms iU(t), iV(t), iW(t) in the phases U, V, W of a three-phase machine 3 are illustrated. Any ohmic resistances can be neglected here. Figuren 10A-C Two switch positions of the inverter 4 are shown, with which a rectangular excitation signal 9 with a positive voltage +U and a negative voltage -U (amplitude V DC) can be generated. Such an excitation signal 9, which is shown in the upper part of the diagram, Fig. 10A The time t is displayed and switched on, as shown in Fig. 10B The corresponding current increases di U / dt, di V / dt, di W / dt are shown in the current waveforms i U (t), i V (t), i W (t). In Fig. 10B The current waveforms iU(t), iV(t), iW(t) and current rise times diU / dt, diV / dt, diW / dt of each phase U, V, W are shown. Electrical equivalent circuits of the asynchronous machine 2 with applied voltages +U and -U of the excitation signal 9 are shown in the lower two sub-figures. Fig. 10A shown. When the excitation signal 9 is switched on, the following is displayed (with the electrical counting arrow in the direction of travel towards). Fig. 1 Initially, with a positive voltage +U, there is a positive current increase di U / dt in phase U (and thus a positive voltage drop across the phase inductance LU) and a negative current increase di V / dt and di W / dt in phases V and W respectively (and thus a negative voltage drop across the phase inductances LV and LW). With a negative voltage -U of the excitation signal 9, the situation is reversed.

[0039] Due to differing phase inductances LU, LV, LW resulting from asymmetries in the three-phase machine 3, an additional deviation in the current rise times di U / dt, di V / dt, di W / dt occurs. This additional deviation is the Fig. 10B not shown, it is in Fig.3B recognizable.

[0040] In one embodiment, rectangular excitation signals 9, such as those in Fig. 3A shown, applied to the strands U, V, W of the asynchronous machine 2. In Fig. 3A The excitation signal 9 is shown in normalized form. As a result of such an excitation signal 9, which can be applied, for example, between the voltage pulses used to generate the rotating field in the asynchronous machine 2, a current increase occurs in the phases U, V, W due to the relationship illustrated in equation (2): di U / dt, di V / dt, di W / dt. Any ohmic resistances can usually be neglected here.

[0041] In Fig. 3B Three different current rises diU / dt of the phase current IU in phase U at different times, and thus at different phase inductances LU, are shown as an example due to the asymmetries of the three-phase machine 3 (see equations 6A-6C). Analogous representations also apply to the other phases V and W. The representations in the figures have been simplified and are intended to schematically illustrate the principle of inductance determination. The change in the current waveforms iU(t), iV(t), iW(t) over time allows conclusions to be drawn about the change in the inductances LU, LV, LW.

[0042] The current increases diU / dt, diV / dt, diW / dt in the strands U, V, and W, preferably determined at regular intervals, can subsequently be combined into a single signal ϑSaliency by a mathematical equation. However, particularly in the case of sinusoidal excitation signals 9, the current values, i.e., the amplitudes, or RMS values, or instantaneous values, of the currents IU, IV, and IW can also be used and combined. Preferably, a mathematical equation for calculating a space vector is used to combine the current waveforms, for example... ϑ saliency = di U t dt + di V t dt e j 2 π 3 + di W t dt e j 4 π 3 .

[0043] The associated signal ϑ Saliency can also be called the "saliency signal" (from the English "saliency", "prominence"). When the signal ϑ Saliency is calculated as a space vector, ϑ Saliency represents a tensor.

[0044] Fig. 4A The graph shows the trace of the tensor ϑ Saliency, where both the abscissa and the ordinate represent an amplitude in amperes per second. The abscissa represents the real part and the ordinate the imaginary part of the signal ϑ Saliency.

[0045] Fig. 4B This represents in Fig. 4A The signal ϑ saliency is represented in the frequency domain, with the abscissa representing the harmonics N of the signal. As in Fig. 4B As can be seen, ϑ Saliency comprises three distinct signal components. A first distinctive signal component is formed by a slot signal component ϑ slot, which is attributable to the slot 23 of the rotor 21 or the stator 20 of the three-phase machine 3. A second distinctive signal component is formed by a saturation signal component ϑ sat, which is attributable to the saturation of magnetic flux paths in the three-phase machine 3. A third distinctive signal component is formed by an intermodulation signal component ϑ inter, which is attributable to a physical combination of the slot signal component ϑ slot and the saturation signal component ϑ sat. The slot signal component ϑ slot, the saturation signal component ϑ sat, and the intermodulation signal component ϑ inter each have different fundamental frequencies.

[0046] In the prior art, sensorless control using slot information has so far eliminated the intermodulation signal component ϑinter and the saturation signal component ϑsat as interference signals, and used the slot signal component ϑslot to determine the angular position and / or rotational speed of the rotor. However, as in Fig. 4B As can be seen, in this case the slot signal component ϑ slot is relatively small compared to other signal components. Therefore, especially under higher loads on the three-phase machine 3, it can be difficult to identify and extract the slot signal component ϑ slot. Fig. 4B The slot signal component ϑ slot already possesses approximately the same magnitude as higher harmonics of the saturation signal component ϑ sat .

[0047] According to the invention, it is therefore provided that the slot signal component ϑ slot is not used directly for controlling the three-phase machine 3, but rather the intermodulation signal component ϑ inter and its indirectly contained slot or rotor angle information are used for controlling the three-phase electric machine 2. The method according to the invention can be implemented in a control unit 12 (see Fig. 1 The intermodulation signal component ϑinter represents a dominant signal component in the signal ϑsaliency over a large speed range and can therefore be easily identified. The invention is based on the finding that there is a relationship between the fundamental frequency of the intermodulation signal component ϑinter and the fundamental frequency of the slot signal component ϑslot, which allows conclusions to be drawn about the angular position and / or speed of the rotor 21. This relationship can be described by equation (1). ω inter = ± ω sat − ω slot , are described where ωinter is the fundamental frequency of the intermodulation signal component ϑinter, ωsat is the fundamental frequency of the saturation signal component ϑsat, and ωslot is the fundamental frequency of the slot signal component ϑslot. The sign of ωsat depends on the design and construction of the three-phase machine 3.

[0048] To determine the rotor's angular position, which can be used to control the three-phase machine 2, the intermodulation signal component ϑinter is separated from other signal components, i.e., essentially isolated, for example by filtering or estimating the unwanted signal components and subtracting them. An angle θinter(t) is determined from the signal ϑinter, in particular from its fundamental frequency. This angle can be a phase angle that changes over time. This can be achieved, for example, using a PLL (phase-locked loop). Furthermore, an angle, in particular a phase angle, θsat(t) of the saturation signal component ϑsat, in particular from its fundamental frequency, is determined. The two angles θsat(t) and θinter(t) are combined using the equation θ slot t = − θ inter t ± θ sat t , to obtain a calculated angle θ slot (t) of a slot angle. In this disclosure, θ denotes angles, while ϑ represents signals or signal components. The slot angle θ slot (t) determined by equation (5) is essentially a calculated angle of the slot signal component ϑ slot. By dividing the slot angle θ slot (t) by the number N of slots of the rotor, a mechanical angular position θ mech (t) of the rotor 21 can be determined from θ slot (t). θ mech (t) can subsequently be used, for example, in the control of the three-phase machine 3. For example, electrical quantities can be represented in a rotor-related coordinate system using θ mech (t), or the angular position (angular position control) and / or the rotational speed (speed control) of the rotor can be controlled.

[0049] Fig. 5 shows a time course of the real component of the linked current signal ϑ Saliency in seconds. This signal contains the slot signal component ϑ slot, the saturation signal component ϑ sat, and the intermodulation signal component ϑ inter.

[0050] Fig. 6 The graph shows the time course of the real part of the intermodulation signal component ϑinter, in seconds, where the slot signal component ϑslot and the saturation signal component ϑsat have been eliminated. However, the signal shown still contains its own harmonics and harmonics of other signal components.

[0051] Fig. 7A-D The graphs show signal waveforms at different operating states of the asynchronous machine 2 at different times. On the abscissa of the Figuren 7A-D is the case with all figures Fig. 7A-D Time t is plotted in seconds. Fig. 7A The real part 10 and the imaginary part 11 of the intermodulation signal component ϑ inter are shown. Fig. 7B The mechanical rotational speed ω mech of rotor 21 is shown in revolutions per minute (rpm) over time. Fig. 7C The figure shows the torque generated by the three-phase machine 3 relative to a rated torque over time. Fig. 7D Figure 1 shows an angular deviation θdev between the mechanical angular position θmech(t) of the rotor determined using the method according to the invention and a mechanical angular position determined using a rotary encoder, expressed in degrees. Fig. 7D It is evident that, with the aid of the method according to the invention, mechanical angular positions θ mech (t) of the rotor can be determined which have a deviation from the actual (measured) mechanical angular position of less than 1°.

[0052] Tests have shown that the accuracy of the inventive method can be further increased by taking into account the dependencies of the angle θinter(t) of the intermodulation signal component ϑinter and the angle θsat(t) of the saturation signal component ϑsat on the rotational speed and / or load of the three-phase machine 3. It has been found that the angle θinter(t) of the intermodulation signal component ϑinter and the angle θsat(t) of the saturation signal component ϑsat can exhibit deviations depending on the load, in particular the torque M of the three-phase machine 3. Therefore, in one embodiment, it can be provided that the angle θinter(t) of the intermodulation signal component ϑinter is corrected as a function of the load of the three-phase machine 3, in particular the torque M, using an intermodulation correction value θinter_corr.The dependence of θ inter_corr on the torque M (in % relative to the rated torque) of the three-phase machine 3 is in . Fig. 8A depicted.

[0053] Furthermore, it can also be provided that the angle θ sat (t) of the saturation signal component ϑ sat is corrected as a function of the load and the speed of the three-phase machine 3, in particular the torque M, using a saturation correction value θ sat_corr. The dependence of θ sat_corr on the torque M (in % relative to the rated torque) of the three-phase machine 3 is shown in Fig. 8B depicted.

[0054] The angle θ inter of the intermodulation signal component ϑ inter can also have a dependence on the rotational speed of the three-phase machine 3 (see Fig. 8C ). This dependency can also be taken into account using the intermodulation correction value θ inter_corr, in addition to or as an alternative to the torque dependency.

[0055] Fig. 9Figure 1 schematically shows a possible implementation of the method according to the invention. In the illustrated embodiment, the input variables used are the intermodulation signal component ϑin-ter, an electrical angle θele(t), a torque M, and a mechanical angular velocity ωmech. θele(t) represents the angle of the fundamental waveform of the stator current and can be determined from the measured phase currents IU, IV, IW, for example, as a space vector. ωmech can be determined from the intermodulation signal component ϑinter. By multiplying the electrical angle θele(t), preferably by a factor of 2, the angle θsat(t) of the saturation signal component ϑsat can be obtained, which can be corrected using a previously determined saturation correction value θsat_corr.Using a phase-locked loop (PLL) signal processing unit, the angle θinter(t) of the intermodulation signal component ϑinter can be obtained from the intermodulation signal component ϑinter and corrected using an intermodulation correction value θinter_corr. By combining the two angles θinter(t) and θsat(t), particularly with the aid of equation (5), a slot angle θslot(t) can be calculated. The slot angle θslot(t) is calculated in an unwrapped block to form a continuous angular profile (unwrapped phase) and then divided by the number of slots N of the rotor to obtain a mechanical angular position θmech(t) of the rotor. The mechanical angular position can then be converted back in a WRAP block so that θ mech (t) is represented in an angular interval, in particular between [-180°;180°] or [0°;360°] (English "wrapped phase").θ mech (t) can then be used to control the three-phase machine 3.

Claims

1. Method for controlling an electric rotary current machine (3), in particular an induction machine (2), with a rotor (21), a stator (20) and at least two phase windings (U,V,W), wherein at least one electrical signal, in particular a voltage signal (UU,V,W(t)), is applied to at least one phase winding (U,V,W), preferably all phase windings (U,V,W), of the rotary current machine (3) and an electrical signal waveform, in particular a current waveform (iU,V,W(t)) in the at least one phase winding (U,V,W), is measured or determined, whereby an intermodulation signal induced in the rotary current machine by slotting effecs and magnetic saturation effects which is measured or determined from the at least one phase winding (U,V,W) is used to control the rotary current machine (1), whereby the intermodulation signal component (ϑinter) is extracted by elimination of other signal components, characterized in that a slotting angle (θslot(t)) is determined from an angle (θinter(t)) of the intermodulation signal component (ϑinter) by combining the angle (θinter(t)) of the intermodulation signal component (ϑinter) with an angle (θsat(t)) of a saturation signal component (ϑsat) contained in at least one signal waveform, using the calculation rule θ slot t = ± θ sat t − θ inter t , whereby the slotting angle (θslot(t)), the angle (θinter(t)) and the angle (θsat(t)) of the saturation signal component (ϑsat) represent phase angles.

2. Method according to Claim 1, characterized in that a mechanical angular position (θmech(t)) and / or a rotation speed of the rotor is determined from the intermodulation signal component (ϑinter) and the angular position (θmech(t)) and / or the rotation speed is used to control the rotary current machine (3).

3. Method according to Claim 1 or 2, characterized in that the intermodulation signal component (ϑinter) is determined from a rate of change of the at least one signal waveform, in particular the current waveform (iU,V,W(t)).

4. Method according to any one of Claims 1 to 3, characterized in that in at least two phase windings (U,V,W), in particular in three phase windings (U,V,W), of the rotary current machine (3), current waveforms (iU,V,W(t)), in particular their rates of change (diU,V,W(t) / dt), are determined and the current waveforms (iU,V,W,(t)), in particular their rates of change (diU,V,W(t) / dt), are combined by means of a mathematical equation to form a combined signal (ϑSaliency) and the intermodulation signal component (ϑinter) is determined from the combined signal (ϑSaliency).

5. Method according to Claim 4, characterized in that the mathematical equation is an equation for calculating a tensor, in particular a space vector.

6. Method according to any one of Claims 1 to 5, characterized in that the intermodulation signal component (ϑinter) is extracted by elimination of saturation signal components (ϑsat) due to magnetic saturation effects in the rotary current machine (3) and / or slot signal components (ϑslot) due to slotting effects.

7. Method according to Claims 1 to 6, characterized in that a mechanical angular position (θmech(t)) of the rotor is determined by dividing the slotting angle (θslot(t)) by the number of slots of the rotor.

8. Method according to Claims 1 to 7, characterized in that the angle (θinter(t)) of the intermodulation signal component (ϑinter) is corrected by means of an intermodulation correction value (θinter_corr) as a function of the rotation speed of the rotor (21) and / or the load on the rotary current machine (3), in particular the torque (M).

9. Method according to any one of Claims 1 to 8, characterized in that the angle (θsat(t)) of the saturation signal component (ϑsat) is corrected by means of a saturation correction value (θsat_corr) as a function of the rotation speed of the rotor and / or the loading on the rotary current machine (3), in particular the torque (M).

10. Method according to any one of Claims 1 to 9, characterized in that the electrical signal comprises an excitation signal (9), which is essentially independent of the generation of a fundamental wave of the rotary current machine (3) and the fundamental frequency of which is preferably at least five times as great, even more preferably at least ten times as great, as the temporal frequency of the fundamental wave of the voltages in a phase winding (U,V,W) for generating the fundamental wave of the rotary current machine (3).

11. Method according to any one of Claims 1 to 10, characterized in that the electrical signal is a current signal and the response of the rotary current machine (3) to the current signal is evaluated to determine the intermodulation signal component (ϑinter) .

12. Rotary current machine system (1), comprising: - a rotary current machine (3), in particular an induction machine (2), having a rotor, a stator and at least two phase windings (U,V,W); - a converter (4) which is electrically connected to the rotary current machine (3), wherein the converter (4) is configured to apply electrical signals, in particular voltage signals (UU,V,W), to at least one phase winding (U,V,W), preferably all phase windings (U,V,W), of the rotary current machine (3); - at least one measuring device (8a, 8b) which is configured to measure or determine at least one electrical signal waveform, in particular a current waveform (iU,V,W(t)) in the at least one phase winding (U,V,W), - a control unit (12) that is configured to control the rotary current machine (3) on the basis of an intermodulation signal component (ϑinter) caused by slotting effects and magnetic saturation effects in the rotary current machine (3), which intermodulation signal component (ϑinter) is contained in the at least one measured signal waveform, the control unit (12) further being configured to extract the intermodulation signal component (ϑinter) by elimination of other signal components, characterized in that the control unit (12) is configured to determine from an angle (θinter(t)) of the intermodulation signal component (ϑinter) a slotting angle (θslot(t)) by combining the angle (θinter(t)) of the intermodulation signal component (ϑinter) with an angle (θsat(t)) of a saturation signal component (ϑsat) contained in at least one signal waveform, using the calculation rule θ slot t = ± θ sat t − θ inter t , whereby the slotting angle (θslot(t)), the angle (θinter(t)) and the angle (θsat(t)) of the saturation signal component (ϑsat) represent phase angles.

13. Rotary current machine system (1) according to Claim 12, characterized in that the control unit (12) is integrated into the converter (4).