Method for determining a blocked rotor in an injection-signal-based sensorless operation of a synchronous machine, control unit, synchronous machine and vehicle

Abstract

The invention relates to a method for determining a blocked rotor during injection-signal-based sensorless operation of a synchronous machine, comprising the following steps: Applying a three-phase alternating voltage, which includes an injection signal, to stator windings of the synchronous machine according to an estimated rotation angle φ est ; Detect a three-phase current flowing in the stator windings in response to the application of the alternating voltage; Transform the detected current into a first current vector that corresponds to a first angle φ est +45° in a dq coordinate system, and a second current vector corresponding to a second angle φ est-45° in a dq coordinate system; determining the contributions of the injection signal to the lengths of the first and second current vectors; determining the difference between these contributions as an error signal; and determining the amplitude of the error signal. The method also includes the following steps: comparing the amplitude of the error signal with a predetermined threshold; and determining the blocked rotor if the amplitude of the error signal exceeds the predetermined threshold.

Description

[0001] The present invention relates to a method for determining a locked rotor, i.e., rotor slippage, during injection-signal-based sensorless operation of a synchronous machine, in particular a permanent-magnet synchronous machine. The present invention also relates to a control unit configured and programmed to carry out the method, a synchronous machine having the control unit, and a vehicle having the synchronous machine.

[0002] In sensorless or encoderless operation, i.e., sensorless control / regulation, of a synchronous machine, such as a permanent magnet synchronous machine, a rotation angle sensor for detecting the current rotation angle of a rotor of the synchronous machine is omitted. Instead, currents detected in stator windings and detected or estimated voltages are used to determine the rotation angle and speed of the rotor of the synchronous machine using a model of the synchronous machine. Below a speed threshold of the absolute speed, it is necessary to feed in an injection signal to support the identification of the rotation angle and speed in this speed range. Starting with a stationary rotor, the current rotation angle can be determined using an initialization routine.With this injection method, the synchronous machine can be operated in the lower speed range until a switch to a model-based sensorless algorithm takes place.

[0003] The initial rotation angle can be determined by specifying an injection signal, i.e., a high-frequency oscillation in the d- and q-voltages, for a specific number of points on a voltage circular path, in which the exciting voltage amplitude results in a resulting current amplitude. Due to the dq coordinates, an ellipse must be created in the dq coordinate system for a circular excitation by applying the voltage due to the anisotropy of the synchronous machine in the current. The major axis of the ellipse corresponds to the d-axis or d-direction. This direction of the major axis thus describes the initial value of the rotation angle.

[0004] A longer major axis of an ellipse, which consequently corresponds to the current curve in the dq coordinate system, can be found using an iterative controller approach. By imposing the injection signal on the three-phase AC voltage applied to the stator windings, a three-phase current can be measured in the stator windings. However, the current is then not transformed into the imaginary d-direction, but into an imaginary d+45° direction and an 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, since the current in the q-direction disappears when the real d-axis is found. This makes detection more robust against disturbances, especially in dynamic situations. The amplitudes corresponding to the injection signal are then determined, and the two amplitudes for +45° and -45° are compared.The estimated rotation angle is then corrected so that the two amplitudes for +45° and -45° 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 shorter semi-axis, i.e., the q-axis, is found. This approach not only allows the initial rotation angle to be determined, but also allows the synchronous machine to be operated with the determined rotation angle.

[0005] Furthermore, in a sequential time sequence, the shorter and then the longer semi-axis of the ellipse can be determined first. The two found semi-axes are then set in relation to each other, with the angle between the semi-axes being within a range of 90° ± epsilon°. Epsilon is set to a few degrees. In practice, the longer semi-axis is often used to operate the system sensorless.

[0006] Similarly, the shorter and longer semi-axes of the ellipse can be observed by using two different injection frequencies consecutively to find the angles for the shorter and longer semi-axes.

[0007] The injection-signal-based approach to initializing the rotation angle takes advantage of the anisotropy of the synchronous machine, as described above. The anisotropy of a synchronous machine, especially a permanent-magnet synchronous machine, refers to the differences in inductances in the d- and q-directions, which ultimately leads to the elliptical current curve in the dq coordinate system.

[0008] For robust and stable operation, the injection-based method for sensorless operation of a synchronous machine requires pronounced anisotropy. With magnets bonded to the rotor, in contrast to buried magnets, the inductances Ld and Lq are more similar to each other, so the anisotropy is consequently smaller. The ellipse is then less pronounced and therefore more circular.

[0009] Smaller synchronous machines, such as those used in pump drives, often have less pronounced anisotropy due to the use of bonded magnets. Particularly during demanding maneuvers, such as sudden jumps in torque or speed, the synchronous machine, which is often designed to the limits of its performance for the application, can, in the worst case, lose synchronization and / or even slip completely in the event of a spontaneous blockage. A sensorless control or regulation algorithm usually has model-based measures for smoothing the determined rotation angle and speed signals through prediction. This can lead to the control algorithm seeing or detecting a rotating rotor, while the rotor is actually stationary or blocked.

[0010] DE 10 2008 042 360 A1 describes a method for determining the angular position of a synchronous machine with a magnetically anisotropic rotor with several iteration stages.

[0011] DE 10 2021 108 229 A1 describes a method for detecting a stalled state of an electric motor operated by commutation electronics. The stalled state is determined by evaluating the EMF compared to a stored threshold value SGRUND. First, the EMF is determined taking into account a temperature-dependent parameter representing the stator resistance R of the motor, followed by a deviation of the determined EMF due to the influence of the actual winding temperature. A correction factor k is then determined to correct the stator resistance parameter in order to determine a corrected EMF. Whether the motor is stalled is then determined by comparing the temperature-dependent corrected EMF with the stored threshold value.

[0012] DE 10 2019 108 725 A1 describes a method for detecting a rotor lock of a sensorless motor. The speed of the electric motor is controlled using field-oriented control, and an estimated value representing the magnetic flux in the electric motor is calculated. A value representing the change in the magnitude of the estimated magnetic flux is also calculated. The calculated value is compared with a threshold value. An error is signaled if the calculated value remains below the threshold value for a certain period of time.

[0013] It is therefore an object of the present invention to provide a suitable measure which makes it possible to determine a blocked rotor, ie a slippage of the rotor, in an injection signal-based sensorless operation of a synchronous machine.

[0014] The object is achieved by the subject matter having the features according to the independent claims. Advantageous embodiments are the subject matter of the dependent claims.

[0015] A method according to the invention for determining a blocked or slipping rotor in an injection signal-based sensorless operation of a synchronous machine, in particular a permanent magnet synchronous machine, comprises the following steps: First, a step is carried out for applying a three-phase alternating voltage, which comprises an injection signal, to stator windings of the synchronous machine according to an estimated rotation angle φ est. That is, a high-frequency injection signal is superimposed on the three-phase alternating voltage. This is followed by a step of detecting a three-phase current flowing in the stator windings in response to the application of the alternating voltage. This is followed by a step of transforming the detected current into a first current vector corresponding to a first angle φ. est +45° in a dq coordinate system, and a second current vector corresponding to a second angle φ est-45° in a dq coordinate system. Accordingly, the recorded currents are not transformed onto the d- or q-axis, but rather onto directions deviating by ±45° from the d-axis. This is followed by a step for determining a portion of the length of the first current vector caused by the injection signal and a step for determining a portion of the length of the second current vector caused by the injection signal. Accordingly, it is determined which length portion of the first and second current vectors is generated by the superimposed injection signal. Once these length portions have been determined, a step follows for determining a difference between the portion of the length of the first current vector and the portion of the length of the second current vector as an error signal. This means that the error signal corresponds to the difference between the length portions of the two current vectors determined above.A further step is then performed to determine the amplitude of the error signal. This is followed by a step to compare the amplitude of the error signal with a predetermined threshold, and a step to determine whether the rotor is locked if the amplitude of the error signal exceeds the predetermined threshold.

[0016] Consequently, the locked rotor is determined based on the error signal. The error signal arises because the ellipse rotates around the dq coordinate system, which is stationary with the rotor, and the actual, i.e., the fixed or stationary, rotation angle of the rotor no longer matches the estimated, i.e., the rotating, rotation angle. The error signal oscillates at twice the estimated speed, since the actual rotation angle and the estimated rotation angle overlap twice per revolution of the ellipse.

[0017] Since the two current vectors are directed to the two angles φ est+45° and φ est By transforming the ellipse to -45°, a pronounced error signal can be obtained even with a less pronounced ellipse, i.e., with less pronounced anisotropy in the synchronous machine. By setting the threshold to a predetermined value, a permissible angular deviation between the actual rotation angle and the estimated rotation angle can also be specified.

[0018] It is conceivable that a locked rotor can be determined if the threshold is exceeded by the amplitude of the error signal a predetermined number of times. Consequently, the rotor-fixed dq coordinate system was traversed by the ellipse half the number of times. Consequently, a locked rotor can be reliably determined.

[0019] Preferably, the components of the lengths of the two current vectors caused by the injection signal can be determined using a bandpass filter. Consequently, the high-frequency components generated by the injection signal can be reliably determined.

[0020] The amplitude of the error signal can advantageously be determined using a PLL (phase-locked loop) filter. As already mentioned, the error signal oscillates at twice the estimated speed, so a PLL approach is well suited for filtering the amplitude from the error signal.

[0021] The synchronous machine can be designed to drive a pump. As mentioned above, synchronous machines for driving pumps are often designed with limited power, so that rotor slippage can occur during sharp torque and / or speed changes. The method according to the invention is therefore particularly suitable for such synchronous machines.

[0022] Furthermore, the synchronous machine can be a permanent magnet synchronous machine, in which magnets are glued to the rotor. In this type of synchronous machine, the anisotropy is less pronounced due to the glued magnets. By transforming the current vectors to the two angles φ est +45° and φ est -45° a pronounced error signal can still be determined and consequently a reliable determination of the blocked rotor can be made.

[0023] Preferably, a binary determination signal can be set to 1 to indicate a locked rotor. The binary determination signal indicates whether or not the locked rotor is present. A value of 0 indicates that the rotor is rotating. A value of 1 indicates that the rotor is locked or slipping. The determination signal can also be output to initiate corresponding control processing. The determination signal is reset to 0 when the amplitude of the error signal falls below the threshold again.

[0024] Advantageously, a reinitialization of the rotation angle can be performed when a locked rotor is detected. The detection signal can advantageously be used to determine the locked rotor detection. Consequently, the reinitialization can be implemented in a synchronous machine controller as an interrupt routine triggered by the detection signal being set to 1.

[0025] The present invention also relates to a control unit configured and programmed to execute the method according to one of the above aspects. The control unit is accordingly configured to obtain the measured values ​​required for executing the method and to output control commands to the synchronous machine. Consequently, the control unit can achieve the aforementioned advantages.

[0026] The present invention also relates to a synchronous machine having a stator and a rotor rotatable relative to the stator. The synchronous machine further comprises the control unit according to the above aspect. In particular, the synchronous machine is a permanent magnet synchronous machine. The synchronous machine can be used to drive a pump. Furthermore, magnets can be glued to the rotor of the synchronous machine. Since the synchronous machine has the control unit according to the invention, which is designed and programmed to carry out the method according to the invention, the above-mentioned advantages can be achieved.

[0027] A vehicle according to the invention comprises the synchronous machine according to the above aspect. The synchronous machine can be used in the vehicle to drive a pump. The magnets can be glued to the rotor of the synchronous machine. By implementing the control unit according to the invention, ie, the method according to the invention, reliable detection of rotor slippage can be achieved.

[0028] The present invention is described in detail below with reference to the figures. They show: Fig. 1 Time diagrams showing simulated courses of measured values ​​when applying the method according to the invention; and Fig. 2 Time diagrams showing measured values ​​when applying the method according to the invention.

[0029] An embodiment of the present invention will be described below with reference to the figures.

[0030] First, the determination of an error signal, which is used to determine a locked rotor, will be described. First, a three-phase alternating voltage is applied to the stator of a synchronous machine, in particular a permanent-magnet synchronous machine. The three-phase alternating voltage is calculated based on an estimated rotation angle φ. est , which is estimated by a sensorless or encoderless control algorithm. The three-phase AC voltage includes an injection signal, which is a high-frequency signal superimposed on the three-phase AC voltage. Consequently, a three-phase current is generated in the stator windings, which includes a component caused by the injection signal.

[0031] The three-phase current is measured and converted into a first current vector corresponding to a first angle φ est+45° in a dq coordinate system, and a second current vector corresponding to a second angle φ est -45° in a dq-coordinate system. It is assumed that the dq-coordinate system with the estimated rotation angle φ est rotates.

[0032] Subsequently, a portion of the length of the first current vector caused by the injection signal and a portion of the length of the second current vector caused by the injection signal are determined using a bandpass filter. From this, a difference between the portion of the length of the first current vector and the portion of the length of the second current vector is determined as an error signal. The amplitude of the error signal is then determined using a PLL (phase-lock loop) filter.

[0033] When the rotor is locked or slipping, the elliptical current curve, which is present due to anisotropy in the synchronous machine, rotates around the rotor-fixed dq coordinate system at the estimated speed. Due to the rotation, the two components of the current vector lengths differ, resulting in the error signal. Since two superpositions of the ellipse with the rotor-fixed dq coordinate system occur per revolution, the error signal oscillates at twice the value of the estimated speed. This phenomenon will be illustrated below using simulated and measured time diagrams.

[0034] In Fig. 1 shows time diagrams showing simulated courses of measured values ​​when applying the method according to the invention.

[0035] The uppermost diagram shows the curve of a measured rotation angle (reference numeral 1) and the curve of a rotation angle estimated by a sensorless control algorithm (reference numeral 2) in a range from 0 to 2π. It can be seen that the curves are split in two. At the beginning, the rotor slips, as a result of which the estimated rotation angle 2 no longer corresponds to the actual rotation angle 1. The rotation angle 2 estimated by the sensorless algorithm continues to rotate at a constant speed. However, the rotor cannot follow a rotating field that is generated by applying the three-phase alternating voltage with the estimated rotation angle to the stator windings. Due to the constant jumping of the rotating field across the rotor, it performs a sinusoidal movement, since with each jump, the rotor is briefly accelerated and then decelerated again.After a reinitialization and a short transient response, the estimated rotation angle 2 and the actual rotation angle 1 match again from about 0.58 s.

[0036] The second diagram shows a curve for an actual speed (reference symbol 3) and a curve for an estimated speed (reference symbol 4). The estimated speed 4 continues to assume a constant speed of 200 rpm. However, due to the rotating field being skipped across the rotor, the actual speed 3 oscillates sinusoidally around zero speed before reinitialization occurs and it can accelerate to a higher speed of 300 rpm.

[0037] The third diagram shows the error signal (reference numeral 5), which clearly oscillates sinusoidally around a value of zero. The frequency of error signal 5 is twice as high as the estimated speed 4 and the sine wave at the actual speed 3, since two solutions exist per revolution of the locked rotor. Thus, error signal 5 can also be described as a second-order oscillation.

[0038] The third diagram also shows the amplitude of the error signal (reference numeral 6). A suitable method for determining the amplitude 6 of the error signal is a PLL filter, which derives the second-order amplitude 6 from the error signal 5. The third diagram shows that the error signal 5, and consequently the amplitude 6, return to a value of zero shortly after reinitialization. Consequently, a rotation of the rotor corresponds to a rotation of the ellipse.

[0039] The bottom diagram shows the curve of a binary determination signal (reference number 7). It can be seen that the determination signal 7 is already set to 1 at the beginning due to the amplitude of the error signal exceeding a threshold value (not shown). At approximately 0.55 s, a reinitialization then occurs by reducing the estimated rotational speed 2 (see second diagram). The rotor can thus be caught again and then accelerated to a desired speed. After a short settling time, the actual rotation angle 1 and the estimated rotation angle 2 agree again (see first diagram). Consequently, the actual rotational speed 3 and the estimated rotational speed 4 also agree again. Since the amplitude 6 of the error signal is then below the threshold value, the determination signal 7 is set back to 0.

[0040] In Fig.2 shows time diagrams showing measured values ​​when applying the method according to the invention.

[0041] The bottom diagram shows the actual rotation angle (reference numeral 10), and it is clearly visible that the rotor stalls twice. During this time, the rotation angle estimated by the sensorless algorithm (reference numeral 11) continues to assume the rotor is rotating due to internal model-based predictions.

[0042] The error signal (reference numeral 8) is shown in the top diagram. The calculated amplitude of the error signal (reference numeral 9) is shown in the second diagram. It is clearly visible that the second-order amplitude increases steeply when the rotor is blocked. Depending on the selected threshold (not shown), the determination signal can indicate rotor blockage after a short time.

[0043] By applying the method according to the invention, a blockage or slippage of a rotor can be reliably determined. Appropriate countermeasures, such as reinitializing the rotation angle, can then be implemented.

[0044] The present invention can also be implemented in a control unit. The control unit is then configured and programmed to execute the method according to the invention. The control unit is accordingly configured to obtain the measured values ​​required for executing the method and to output control commands to the synchronous machine.

[0045] The control unit can be used to operate a synchronous machine comprising a stator and a rotor that can rotate relative to the stator. In particular, the synchronous machine can be a permanent magnet synchronous machine. The synchronous machine can be used to drive a pump. Magnets can also be bonded to the rotor of the synchronous machine.

[0046] The synchronous motor can be used in a vehicle. The synchronous motor can be used to drive a pump, and the magnets can be glued to the rotor of the synchronous motor. List of reference symbols 1 actual rotation angle 2 estimated rotation angle 3 actual speed 4 estimated speed 5 Error signal 6 Amplitude of the error signal 7 Determination signal 8 Error signal 9 Amplitude of the error signal 10 actual speed 11 estimated speed

Claims

[1] Method for determining a blocked rotor in an injection signal-based sensorless operation of a synchronous machine, in particular a permanent magnet synchronous machine, comprising the following steps: Applying a three-phase alternating voltage comprising an injection signal to the stator windings of the synchronous machine corresponding to an estimated rotation angle φ est , Detecting a three-phase current flowing in the stator windings in response to the application of the alternating voltage, Transforming the detected current into a first current vector corresponding to a first angle φ est +45° in a dq coordinate system, and a second current vector corresponding to a second angle φ est -45° in a dq coordinate system, Determining a portion of a length of the first current vector caused by the injection signal, Determining a portion of a length of the second current vector caused by the injection signal, Determining a difference between the proportion of the length of the first current vector and the proportion of the length of the second current vector as an error signal, and Determining an amplitude of the error signal, characterized by that the procedure comprises the following steps: Comparing the amplitude of the error signal with a predetermined threshold, and Determine the locked rotor when the amplitude of the error signal exceeds the specified threshold. [2] Method according to claim 1, wherein the components of the lengths of the two current vectors caused by the injection signal are determined by means of a bandpass filter. [3] A method according to any one of claims 1 or 2, wherein the amplitude of the error signal is determined using a PLL filter. [4] A method according to any one of claims 1 to 3, wherein a binary determination signal is set to 1 to indicate a locked rotor. [5] Method according to one of claims 1 to 4, wherein a reinitialization of the rotation angle is performed when a locked rotor is determined. [6] Control unit designed and programmed to carry out the method according to one of claims 1 to 5. [7] Permanent magnet synchronous machine having a stator and a rotor rotatable relative to the stator, characterized by that the permanent magnet synchronous machine is operated by the control unit according to claim 6. [8] Permanent magnet synchronous machine according to claim 7, characterized by that it is designed to drive a pump. [9] Permanent magnet synchronous machine according to claim 7 or 8, characterized by that magnets are glued to the rotor. [10] A vehicle comprising a synchronous machine according to any one of claims 7 to 9.

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