Continuous anisotropy testing in sensorless operation of an electric machine to increase reliability

Abstract

Method for continuous anisotropy testing of an electrical machine (2), in particular an electrical synchronous machine, comprising the following steps: a) Provision of an electric machine (2) with a stationary rotor (1), b) Performing a first application to determine the angle w_d_est of a longer semi-axis d of an ellipse using a first injection signal; c) Running a second application to determine the angle w_q_est of a shorter semi-axis q of the ellipse using a second injection signal; d) Determination of the angle difference of the magnitudes of the longer semi-axis d and the shorter semi-axis q according to delta_w=|w_d_est-w_q_est|, e) If the condition is met that the angular difference of the magnitudes of the longer semi-axis d and the shorter semi-axis q lies within a defined interval between and a defined error tolerance value FTW, according to |delta_w-90|≤FTW, energize the electrical machine (2) and terminate the procedure, f) If the condition is met that the difference in the magnitudes of the lengths between the first AC vector and the second AC vector is |delta_w-90|>FTW, issue a warning message and / or shut down the system. g) Repeat steps b) to f).

Description

[0001] The invention relates to a method for continuous anisotropy testing of an electrical machine, such as a permanent magnet synchronous machine (PMSM), i.e., an electrical synchronous machine. The invention further relates to a computer program product, a control unit, and an electrical machine.

[0002] Sensorless operation of an electric motor eliminates the need for a rotor position sensor, which is typically used to determine the current rotor angle. Current sensor signals and measured or estimated phase voltages are used to determine the rotor position and motor speed using a model.

[0003] Below a certain speed threshold, the absolute speed, it is necessary to feed in so-called injection signals, which support the identification of the rotor position and speed in this speed range. Starting with a stationary rotor, the rotor position must be determined using an initialization routine. The injection methods allow the motor to operate in the lower speed range until, for example, a switchover to a model-based sensorless algorithm takes place.

[0004] In other words, in sensorless operation, only the current sensors, which are indispensable for field-oriented control anyway, are used. This control concept, which is particularly widespread in 3-phase permanent magnet synchronous machines, is based on a transformation of the 3-phase alternating quantities into a two-axis coordinate system that rotates synchronously with the rotor flux of the machine. In such a coordinate system, usually referred to as a d / q coordinate system, for example, the three phase currents of the stator winding i_u, i_v, i_w are represented by a 2-dimensional current vector with the components i_q and i_d. With an ideal sinusoidal rotor flux and ideal sinusoidal phase currents, the original alternating quantities i_u, i_v, i_w are mapped to equal quantities i_q, i_d as a result of the rotor flux-synchronous rotating coordinate system.

[0005] In field-oriented current control, the voltage or current values ​​of the phases of the synchronous machine's stator are transformed in a known manner into a two-dimensional coordinate system, whose mutually perpendicular axes are usually denoted by d ("direct") and q ("quadrature"). This coordinate system rotates relative to the synchronous machine's stator and is stationary relative to the synchronous machine's rotor. The transformation itself is called the Park transformation, and the two-dimensional coordinate system to which the transformation is performed is called the Park coordinate system. The Park transformation can be performed via the intermediate step of an equally well-known Clarke transformation, which transforms the voltage or current values ​​of the phases of the synchronous machine's stator into a two-dimensional, orthogonal coordinate system that is stationary relative to the stator.

[0006] In sensorless operation of an electric motor, as mentioned above, the rotor position sensor, which is usually used to determine the current rotor angle, is omitted. Current sensor signals and measured or estimated phase voltages, for example, are used to infer the rotor position and speed of the motor using a model. Below a speed threshold of the absolute speed, it is necessary to feed in so-called injection signals, which support the identification of the rotor position and speed in this speed range. Starting with a stationary rotor, the rotor position must be determined using an initialization routine.

[0007] The initial rotor position can be determined by applying an alternating voltage excitation, a high-frequency oscillation in d- and q-voltage, for a specific number of points on a voltage circular path, where the exciting voltage amplitude results in a resulting current amplitude. Due to the d-q coordinates, an ellipse must be formed in the dq-plane for a circular excitation in the voltage and current. The major axis of the ellipse corresponds to the d-direction. This direction of the major axis thus describes the initial value of the rotor position.

[0008] One way to determine the initial rotor position is to move to several points on the circular path, which results in several points on an ellipse. From these points, the angular position of the semi-axes of the ellipse must then be deduced. If many points are selected, the result is more accurate, but it takes a certain amount of time, since each point must be approached and evaluated with a different amplitude in the d and q directions. If fewer points are selected, the process is accelerated, but the result may then be inaccurate under certain circumstances, since the angular position of the semi-axes cannot be determined as accurately from the few points. The measured data during evaluation is subject to a certain amount of noise, which ultimately falsifies the result. With glued-on magnets, the inductances Ld and Lq are more similar to each other than with buried magnets. The ellipse is then less pronounced and more resembles a circle.

[0009] DE 10 2007 003 874 A1 describes a method for the field-oriented operation of a converter-fed, sensorless induction machine with asymmetries. An estimated flux position is continuously corrected using a test signal fed into the induction machine in the direction of a presumed flux axis. At least two alternating signals of different frequencies are provided simultaneously as the test signal.

[0010] EP 2 432 115 A1 also describes a method for continuous anisotropy testing of an electrical machine.

[0011] The object of the invention is therefore to provide an improved - in particular faster and more accurate - method for determining an initial rotor position of a rotor of an electrical machine, in particular a synchronous electrical machine, and thus to test the ongoing anisotropy of the electrical machine. It is furthermore the object of the invention to realize a computer program product for carrying out an improved method for determining an initial rotor position of a rotor of an electrical machine, in particular a synchronous electrical machine. It is also the object of the invention to develop a control unit for carrying out an improved method for determining an initial rotor position of a rotor of an electrical machine, in particular a synchronous electrical machine. Finally, it is also the object of the invention to provide an improved electrical machine.

[0012] It is the object of the present invention to provide an improved charging system, since the known solutions always have certain disadvantages.

[0013] In other words, during sensorless operation, the difference between the inductances Ld and Lq in the system under consideration should be continuously monitored. To do this, the angle of the longer semi-axis of the ellipse is determined using an injection signal, and the angle of the shorter semi-axis of the ellipse is determined using a second injection signal. It is expected that both semi-axes are at right angles to each other. If this is not the case for an extended period of time, minus a tolerance threshold, appropriate conclusions can be drawn, such as shutting down the system.

[0014] This object is achieved by a method for determining an initial rotor position of a rotor of an electrical machine, in particular an electrical synchronous machine, comprising the following steps: a) Provision of an electrical machine with a stationary rotor, b) running through a first application for determining the angle w_d_est of a longer semi-axis d of an ellipse using a first injection signal; c) passing through a second application to determine the angle w_q_est of a shorter semi-axis q of the ellipse using a second injection signal; d) Determination of the angular difference of the magnitudes of the longer semi-axis d and the shorter semi-axis q according to delta_w=|w_d_est-w_q_est|, e) If the condition is met that the angular difference between the magnitudes of the longer semi-axis d and the shorter semi-axis q lies within a defined interval between and a defined error tolerance value FTW, according to |delta_w-90|≤FTW, energising the electrical machine and terminating the process, f) If the condition exists that the difference in the magnitudes of the lengths between the first AC vector and the second AC vector is |delta_w-90|>FTW, issuing a warning message and / or switching off the system, g) Repeat steps b) to f).

[0015] Advantageously, steps b) running through a first application for determining the angle w_d_est of a longer semi-axis d of an ellipse with the aid of a first injection signal and c) running through a second application for determining the angle w_q_est of a shorter semi-axis q of the ellipse with the aid of a second injection signal are carried out in parallel and simultaneously.

[0016] Furthermore, the possible 180° uncertainty should be resolved for motor operation based on the long semi-axis. When resolving the 180° uncertainty, the difference between the angles of the d- and q-axes can reverse its sign. Such a reversal should not occur during operation. If it does occur, it may indicate, for example, that the ellipse is weak.

[0017] The two angles for the detected d- and q-axes should differ by +-90°. If the deviation from +-90° is too large, this should be reported to higher-level software for diagnostic purposes, for example, to shut down the system. Possible trigger thresholds must be determined in tests. The trigger thresholds can be determined in characteristic maps based on the current, iq and id. The trigger thresholds can also be determined based on the temperature.

[0018] During operation, abnormal operating points can be blocked using an adaptive learning algorithm if anomalies occur repeatedly. This could potentially prevent shutdown and increase availability.

[0019] This offers numerous advantages. Previously known methods require different inductances in the d- and q-direction, as only then is the ellipse pronounced. The method according to the invention means that the ellipse can always be reliably detected, even when it is weak. This creates the option of continuously determining the ratio of the inductances in the system during operation from the control unit connected later in operation, and thus evaluating the inductances. System-specific influences on the current measurement and the motor parameters are thus taken into account. The motor parameters that initially ensured that the ellipse was accurately detected can change during operation, e.g. due to demagnetization or aging of the components, so that the previous detection during commissioning does not appear sufficient under all circumstances.Although these influences cannot be reduced with the method according to the invention, the safer and reproducible anisotropy test of the electrical machine helps to operate it for as long as possible.

[0020] Advantageous embodiments are claimed in the subclaims and are explained in more detail below.

[0021] Advantageously, the first application for determining the angle of the longer semi-axis d according to step b) of the method comprises the following steps: I) Providing a starting value d_est, which represents a first angle of the rotor position, II) Generation of a three-phase alternating voltage excitation in the electrical machine by specifying an alternating voltage in the d_est direction, III) Conversion of the three-phase current response to the AC excitation of the electrical machine for the first modified value d_est-45° into a first AC component i_[d_est-45°], IV) Conversion of the three-phase current response to the alternating voltage excitation of the electrical machine for the second modified value d_est+45° into a second alternating current component i_[d_est+45°], V) Calculation of the length of a first alternating current vector having d and q components for the first alternating current component i_[d_est-45°], VI) Calculation of the length of a second alternating current vector having d and q components for the second alternating current component i_[d_est+45°], VII) Determination of the difference in the magnitudes of the lengths between the first alternating current vector and the second alternating current vector according to delta_i=|i_d_est+45°|-|i_d_est-45°|, VIII) If the condition is met that the difference in the magnitudes of the lengths between the first alternating current vector and the second alternating current vector lies within a defined interval between and a defined error tolerance value FTW, according to |delta_i| <FTW, Bereitstellung des initialen Rotorwinkels zur Bestromung der elektrischen Maschine und Beendigung des Verfahrens, IX) If the condition is met that the difference in the magnitudes of the lengths between the first alternating current vector and the second alternating current vector is |delta_i|>FTW, X) In the case that |i_d_est+45°|>|i_d_est-45°|, adjustment of the starting value d_est in such a way that the angle representing the rotor position is rotated clockwise by a predetermined amount and XI) In case |i_d_est+45°|<|i_d_est-45°|, adjusting the starting value d_est in such a way that the angle representing the rotor position is rotated counterclockwise by a predetermined amount, repeating steps III) - XI).

[0022] In other words, by imposing the injection signal on the voltage, a current can be measured. However, this current is not transformed into the imaginary d-direction, but rather into the imaginary d-45° direction and imaginary d+45° direction. This allows significantly larger current amplitudes to be achieved compared to an evaluation of the currents in the d and q directions, where the current in the q direction disappears when the real d-axis is found. This makes detection more robust against interference, especially in dynamic situations. The amplitude of the injection signal is then determined using bandpass filtering, and the two values ​​for +-45° are compared. The assumed angle is then corrected so that the two amplitudes in the +45° and -45° directions are equal. The sign of the correction is chosen so that the longer semi-axis, i.e., the d-axis, is found.If the sign is reversed during the correction, the algorithm finds the shorter semi-axis, i.e., the q-axis. This approach not only allows the initial angle to be determined, but also allows the electric motor to be driven by it.

[0023] This provides the advantage that the initial rotor position can be determined particularly quickly and reliably using an iterative method without a physical rotor position sensor. Furthermore, the method according to the invention can also prevent the electric machine from rotating in the wrong direction, even briefly, during motor operation.

[0024] Advantageously, the first iteration of the iterative solution algorithm is performed with a randomly chosen starting value d_est for the angle. The three-phase current response to an AC voltage excitation of the system in the presumed d-direction is then converted into dq currents using known methods.

[0025] Preferably, the second application for determining the angle of the shorter semi-axis q according to step c) of the method comprises the same steps I) - XII) of the first application, wherein a sign rotation is present in the angle correction.

[0026] Preferably, the frequency of the first injection signal and the frequency of the second injection signal are selected to be different. The frequency of the second injection signal must be selected to be significantly different from the first injection signal. It should be noted that the bandpass filtering of both injection signals should not show any interference. The frequency should also not be selected too low. Values ​​for a pump actuator of f1 = 4 kHz for the longer semi-axis and f2 = 3.2 kHz for the shorter semi-axis would be conceivable.

[0027] The object of the invention can also be achieved by a computer program product stored on a machine-readable carrier, or computer data signal embodied by an electromagnetic wave, with program code suitable for carrying out the method according to the aspects explained above.

[0028] Furthermore, the object of the invention can also be achieved by a control unit for controlling and energizing an electrical machine, in particular a synchronous electrical machine, comprising a processor and a memory containing computer program code, wherein the memory and the computer program code are configured, with the processor, to cause the control unit to carry out a method for continuously testing an anisotropy of an electrical machine. According to a further particularly preferred embodiment of the invention, it can be provided that the control unit does not have a connection for a rotor position sensor for detecting the rotor position of the rotor, so that the control unit or the electrical machine controlled by it can manage without a physical rotor position sensor.

[0029] Finally, the object of the invention can also be achieved by an electrical machine, in particular a synchronous electrical machine, comprising a stator and a rotor rotatable relative to the stator, as well as a control unit for controlling and energizing the electrical machine, characterized in that the control unit is a control unit according to the features presented above. In a likewise preferred embodiment of the invention, it can also be provided that the electrical machine does not have a rotor position sensor for detecting the rotor position of the rotor. It can also be advantageous to further develop the invention such that the electrical machine is configured for use in an electrically operated or hybrid drive train of a motor vehicle or else in a drive train of a pump or compressor of a production plant.

[0030] The invention is explained in more detail below with the aid of a drawing. It shows: Fig. 1 different positions of the d-axis in a d / q coordinate system, Fig. 2 different positions of the q-axis in a d / q-coordinate system, Fig. 3 electrical machine in a schematic representation, Fig. 4 motor vehicles, each with a hybrid and a fully electric drive train, in a schematic representation.

[0031] The figures are merely schematic and serve only to clarify the invention. The same elements are designated by the same reference numerals.

[0032] Based on the Fig. 1 and Fig. 2, the procedure for continuous anisotropy testing is explained in more detail below. Fig. 1 shown first application and in Fig. The second application shown in Figure 2 runs synchronously and should actually be superimposed in a single diagram. For reasons of clarity, an overlay has been omitted.

[0033] First, an electrical machine 2 with a stationary rotor 1 is provided, as shown by way of example in the Fig. 3. By means of the control unit 3, a three-phase alternating voltage excitation is then generated in the electrical machine 2, which is shown in the Fig. 3 is also indicated by the three parallel dashed lines between the control unit 3 and the energized stator 7.

[0034] First, the first and second applications of the procedure are performed in parallel. For simplicity, the steps of the first application are presented first.

[0035] First, a random starting value d_est is provided, which represents a first rotor position angle. Based on this starting value d_est, the AC voltage excitation is applied in the d_est direction. The three-phase current is measured and transformed into the d_est-45° direction, and the modified value d_est-45° is calculated. A second modified value d_est+45°, which corresponds to the starting value d_est plus 45°, is calculated analogously.

[0036] Subsequently, the three-phase current response to the alternating voltage excitation of the electrical machine 2 for the first modified value d_est-45° is converted into a first alternating current component i_[d_est-45°], and the three-phase current response to the alternating voltage excitation of the electrical machine for the second modified value d_est+45° is converted into a second alternating current component i_[d_est+45°].

[0037] These two alternating current components are shown in Figures a) -c) of the Fig. 1. Now, the length of a first alternating current vector comprising d and q components for the first alternating current component i_[d_est-45°] is calculated, as well as the length of a second alternating current vector comprising d and q components for the second alternating current component i_[d_est+45°].

[0038] In the Fig. Figure 1 schematically shows corresponding ellipses in the real dq-plane. The "estimated" d-axis (d_est) is shown and does not coincide with the direction of the d-axis of the dq-plane. The alternating current components i_(d_est+45°) and i_(d_est-45°) are shown, matching the estimated direction of the d-axis.

[0039] Then the difference in the magnitudes of the lengths between the first alternating current vector and the second alternating current vector is determined according to delta_i=|i_d_est+45°|-|i_d_est-45°|.

[0040] If the condition is met that the difference in the magnitudes of the lengths between the first alternating current vector and the second alternating current vector is |delta_i|>FTW, which is shown in figures a) and b) of the Fig. As can be seen in Figure 1, a distinction is made between two further alternatives.

[0041] For the first case, where |i_d_est+45°|>|i_d_est-45°|, the starting value d_est is adjusted in such a way that the angle representing the rotor position is rotated clockwise by a predetermined amount, which is shown in figures a) and b).

[0042] Based on figures a) and b) in the Fig. 1 clearly shows that the lengths of the alternating current components are different. Therefore, the "estimated" d-axis (d_est) must be rotated clockwise by a certain amount. This new "estimated" d-direction is then the new starting value for the next iteration. In Figure b) the Fig. 1 shows one of the next iterations. For the second case, where |i_d_est+45°]<]i_d_est-45°], the starting value d_est is adjusted in such a way that the angle representing the rotor position is rotated counterclockwise by a predetermined amount, which is not included in the Fig. 1 is shown.

[0043] These iterations are carried out until the condition is met that the difference in the magnitudes of the lengths between the first alternating current vector and the second alternating current vector lies within a defined interval between 0 and a defined error tolerance value FTW, according to |delta_i| <FTW.

[0044] In other words, the process is repeated until the projections of the alternating current components, and thus the lengths of the absolute values ​​of the alternating current components, are equal. From the angle of the "estimated" d-axis, the initial angle of the rotor position can then be easily determined. This is shown in the Fig. ) the Fig. 1. Then, on this basis, the initial rotor angle is provided to energize the electric machine and terminate the process.

[0045] At the same time, the second application is performed, the steps of which are identical to the sequence of the first application. However, the difference remains that there is a sign reversal in the angle correction of the second application, as well as a significant difference between the frequency of the first injection signal and the frequency of the second injection signal.

[0046] The description of figures a) - c) of the Fig. 2 correspond to the descriptions of figures a) - c) of the Fig. 1, but taking into account the differences mentioned above.

[0047] After the first and second application are completed, the amount of the angular difference between the longer semi-axis d and the shorter semi-axis q is determined according to delta_w=|w_d_est-w_q_est|.

[0048] When evaluating the angle difference, a distinction is made between two cases: 1st case: If the condition is met that the angular difference between the magnitudes of the longer semi-axis d and the shorter semi-axis q lies within a defined interval between and a defined error tolerance value FTW, according to |delta_w-90|≤FTW, the electrical machine is energized and the process is terminated. 2. If the condition exists that the difference in the magnitudes of the lengths between the first AC vector and the second AC vector is |delta_w-90|>FTW, issue a warning message and / or shut down the system.

[0049] The procedure is then repeated at a predefined interval during operation of the electrical machine 2, so that a continuous anisotropy test is carried out during operation.

[0050] As in the Fig. 3, the control unit 3 for controlling and energizing the electrical machine 2 comprises a processor 4 and a memory 5 containing a computer program code, wherein the memory 5 and the computer program code are configured, with the processor 4, to cause the control unit 3 to carry out the above method.

[0051] Unlike in the Fig. 3, the control unit 3 preferably has no connection for a rotor position sensor 6 for detecting the rotor position of the rotor 1 and can be controlled without a sensor. Fig. The electrical machine 2 shown in Figure 2 has a stator 7 which can be energized and a rotor 1 which can be rotated relative to the stator 7, as well as the control unit 3 for controlling and energizing the electrical machine 2 or the stator 7.

[0052] The electric machine 2 is configured in particular for use in an electrically operable or hybrid drive train 8 of a motor vehicle 9, as is also the case in the Fig. 4 is outlined.

[0053] The invention is not limited to the embodiments illustrated in the figures. The above description is therefore not to be considered restrictive, but rather explanatory. The following claims are to be understood in such a way that a stated feature is present in at least one embodiment of the invention. This does not exclude the presence of further features. Where the claims and the above description define 'first' and 'second' features, this designation serves to distinguish between two similar features without establishing a priority. List of reference symbols 1 rotor 2 electric machine 3 Control unit 4 processors 5 storage 6 Rotor position sensor 7 Stator 8 Drivetrain 9 Motor vehicle

Claims

[1] Method for the continuous anisotropy testing of an electrical machine (2), in particular a synchronous electrical machine, comprising the following steps: a) providing an electrical machine (2) with a stationary rotor (1), b) running through a first application for determining the angle w_d_est of a longer semi-axis d of an ellipse using a first injection signal; c) passing through a second application to determine the angle w_q_est of a shorter semi-axis q of the ellipse using a second injection signal; d) Determination of the angular difference of the magnitudes of the longer semi-axis d and the shorter semi-axis q according to delta_w=|w_d_est-w_q_est|, e) If the condition is met that the angular difference between the magnitudes of the longer semi-axis d and the shorter semi-axis q lies within a defined interval between and a defined error tolerance value FTW, according to |delta_w-90|≤FTW, energising the electrical machine (2) and terminating the method, f) If the condition exists that the difference in the magnitudes of the lengths between the first AC vector and the second AC vector is |delta_w-90|>FTW, issuing a warning message and / or switching off the system, g) Repeat steps b) to f). [2] Method according to claim 1, characterized by that the first application for determining the angle of the longer semi-axis d according to step b) of the method comprises the following steps: I) Providing a starting value d_est, which represents a first angle of the rotor position, II) Generation of a three-phase alternating voltage excitation in the electrical machine (2) by specifying an alternating voltage in the d_est direction, III) Conversion of the three-phase current response to the AC excitation of the electrical machine (2) for the first modified value d_est-45° into a first AC component i_[d_est-45°], IV) Conversion of the three-phase current response to the AC excitation of the electrical machine (2) for the second modified value d_est+45° into a second AC component i_[d_est+45°], V) Calculation of the length of a first alternating current vector having d and q components for the first alternating current component i_[d_est-45°], VI) Calculation of the length of a second alternating current vector having d and q components for the second alternating current component i_[d_est+45°], VII) Determination of the difference in the magnitudes of the lengths between the first alternating current vector and the second alternating current vector according to delta_i=|i_d_est+45°|-|i_d_est-45°|, VIII) If the condition is met that the difference in the magnitudes of the lengths between the first alternating current vector and the second alternating current vector lies within a defined interval between and a defined error tolerance value FTW, according to |delta_i|≤ FTW, provision of the initial rotor angle for energizing the electric machine (2) and termination of the method, IX) If the condition is met that the difference in the magnitudes of the lengths between the first alternating current vector and the second alternating current vector is |delta_i|> FTW, X) In the case that |i_d_est+45°|>|i_d_est-45°|, adjustment of the starting value d_est in such a way that the angle representing the rotor position is rotated clockwise by a predetermined amount and XI) In case |i_d_est+45°|<|i_d_est-45°|, adjusting the starting value d_est in such a way that the angle representing the rotor position is rotated counterclockwise by a predetermined amount, repeating steps III) - XI). [3] Method according to claim 2, characterized by that the starting value d_est is chosen randomly when the procedure is run for the first time. [4] Method according to claim 2 or 3, characterized by that the second application for determining the angle of the shorter semi-axis q according to step c) of the method comprises the same steps I) - XII), with a sign rotation in the angle correction. [5] Method according to one of claims 1 to 4, characterized by that the frequency of the first injection signal and the frequency of the second injection signal are chosen differently. [6] Computer program product stored on a machine-readable carrier, or computer data signal embodied by an electromagnetic wave, with program code suitable for carrying out the method according to claims 1-5. [7] Control unit (3) for controlling and energizing an electrical machine (2), in particular an electrical synchronous machine, comprising a processor (4) and a memory (5) containing a computer program code, wherein the memory and the computer program code are configured, with the processor (4), to cause the control unit (3) to carry out a method according to claims 1-5. [8] Control unit (3) according to claim 7, characterized by that the control unit (3) has no connection for a rotor position sensor (6) for detecting the rotor position of a rotor (1). [9] Electrical machine (2), in particular an electrical synchronous machine, comprising a stator (7) and a rotor (1) rotatable relative to the stator (7) and a control unit (3) for controlling and energising the electrical machine (2), characterized by that the control unit (3) is a control unit (3) according to claim 7. [10] Electrical machine (2) according to claim 9, characterized by that the electric machine (2) does not have a rotor position sensor (6) for detecting the rotor position of the rotor (1).

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