Initial alignment of position of rotor of electric motor

Abstract

This document discloses a method for an initial alignment of a position of a rotor (12) of an electric motor (10). The method comprises applying (110), to the electric motor (10), a first alignment pulse (101) having a first electrical angle; applying (120), to the electric motor (10) after the first alignment pulse (101), a second alignment pulse (102) having a second electrical angle, the second electrical angle differing from the first electrical angle by a first angle difference; comparing (140) the first amount of movement (A1) to a first angle threshold, the first angle threshold being less than or equal to the first angle difference; applying (150), after the second alignment pulse (102), a third alignment pulse (103) having a third electrical angle, wherein the third electrical angle differs from the second electrical angle by a second angle difference and depends on a result of said comparing (140).

Description

[0001] METHOD FOR INITIAL ALIGNMENT OF POSITION OF ROTOR OF ELECTRIC MOTOR, MOTOR CONTROLLER, MOTION CONTROL ARRANGEMENT, AND ELEVATOR SYSTEM

[0002] FIELD OF THE INVENTION

[0003] The present invention relates in general to control of electric motors. In particular, however, not exclusively, the present invention concerns initial alignment of a position of a rotor of an electric motor and motor controllers and control arrangements therefor, such as in elevator systems.

[0004] BACKGROUND

[0005] Typically, the initial rotor angle must be known when starting to operate an electric motor, such as by using a field-oriented control. If the rotor angle is incorrect, motor torque may be in an opposite direction to the reference torque leading to severe problems, for example, in elevator door drive.

[0006] Absolute encoders and resolvers can be used, but their cost and size are high. An incremental encoder is therefore a preferred solution in many applications. However, because incremental encoders measure only the change in angle, the initial angle must be determined in start-up. A common method for rotor angle detection is forced alignment in which DC voltage is applied to the stator and the rotor should align accordingly.

[0007] There are drawbacks in known methods, for example, if there is a mechanical limit which prevents the rotor movement during alignment or if the initial rotor position is about 180 degrees against the applied voltage vector, resulting in too low torque to move the rotor. There is, thus, a need to develop improved methods and motor controllers for performing initial alignment of the rotor.

[0008] SUMMARY

[0009] An objective of the present invention is to provide a method for an initial alignment of a position of a rotor of an electric motor, a motor controller, a motion control arrangement, and an elevator system. Another objective of the present invention is that the method and the motor controller provide convenient and reliable means to perform initial alignment of the rotor.

[0010] The objectives of the invention are reached by a method for an initial alignment of a position of a rotor of an electric motor, a motor controller, a motion control arrangement, and an elevator system as defined by the respective independent claims.

[0011] According to a first aspect, a method for an initial alignment of a position of a rotor of an electric motor, such as of a permanent magnet synchronous motor, is provided.

[0012] The method comprises applying, to the electric motor, such as to motor winding(s) thereof, a first alignment pulse having a first electrical angle, and applying, to the electric motor after the first alignment pulse, a second alignment pulse having a second electrical angle, the second electrical angle differing from the first electrical angle by a first angle difference, and further determining a first amount of movement of the rotor due to the second alignment pulse. The method also comprises comparing the first amount of movement to a first angle threshold, the first angle threshold being less than or equal to the first angle difference. Furthermore, the method comprises applying, to the electric motor after the second alignment pulse, a third alignment pulse having a third electrical angle.

[0013] The third electrical angle differs from the second electrical angle by a second angle difference and depends on a result of said comparing of the first amount of movement at least as follows: a) if the first amount of movement is more than the first angle threshold, the third electrical angle is between the first electrical angle and the second electrical angle, and b) if the first amount of movement is less than the first angle threshold, the third electrical angle is such that the second electrical angle is between the first electrical angle and the third electrical angle.

[0014] In some embodiments, the method may comprise comparing the first amount of movement to an opposite value of the first angle threshold, if the first amount of movement is less than the first angle threshold.

[0015] In some embodiments, the third electrical angle may depend on the result of said comparing of the first amount of movement in case of b) as follows: bl) if the first amount of movement is less than an opposite value of the first angle threshold, the second angle difference has a first lower value, and b2) if the first amount of movement is higher than the opposite value of the first angle threshold, the second angle difference has a first higher value. Furthermore, the first lower value may be an opposite value of the difference between the third electrical angle the second electrical angle in step a) hereinabove.

[0016] An absolute value of the first lower value may be in the range from 25 to 65 degrees, preferably about 45 degrees in case of bl), and / or an absolute value of the first higher value is in the range from 70 to 200 degrees, preferably about 90 or about 180 degrees in case of b2).

[0017] The method may comprise, with or without bl) and / or b2) above, determining a second amount of movement of the rotor due to the third alignment pulse, and comparing the second amount of movement to a second angle threshold, the second angle threshold being less than or equal to a second angle difference.

[0018] The method may comprise, with or without bl) and / or b2) above, applying, to the electric motor after the third alignment pulse, a fourth alignment pulse having a fourth electrical angle, wherein the fourth electrical angle differs from the third electrical angle by a third angle difference.

[0019] The fourth electrical angle may, with or without bl) and / or b2) above, depend on a result of said comparing of the second amount of movement at least as follows: c) if the second amount of movement is more than the second angle threshold, the fourth electrical angle is between the second electrical angle and the third electrical angle. In addition, the fourth electrical angle may further depend on a result of said comparing of the second amount of movement at least as follows: d) if the second amount of movement is less than the second angle threshold, the fourth electrical angle is such that the third electrical angle is between the second electrical angle and the fourth electrical angle.

[0020] In addition, the fourth electrical angle may depend on the result of said comparing of the second amount of movement in case of b), b2), or d) at least as follows: dl) if the second amount of movement is less than an opposite value of the second angle threshold, the third angle difference has a second lower value, and d2) if the second amount of movement is higher than the opposite value of the second angle threshold, the third angle difference has a second higher value.

[0021] An absolute value of the second lower value may be in the range from 25 to 65 degrees, preferably about 45 degrees in case of dl), and / or an absolute value of the second higher value may be in the range from 70 to 110 degrees, preferably about 90 degrees in case of d2). Alternatively, the fourth electrical angle may further depend on a result of said comparing of the second amount of movement in case of b) or b2) at least as follows: el) if the second amount of movement is less than an opposite value of the second angle threshold, the fourth electrical angle is such that the third electrical angle is between the second electrical angle and the fourth electrical angle, and e2) if the second amount of movement is higher than the opposite value of the second angle threshold, the fourth electrical angle is between the second electrical angle and the third electrical angle.

[0022] The third angle difference may be in the range from 25 to 65 degrees, preferably about 45 degrees, in case of el), and / or the third angle difference is in the range from 70 to 110 degrees, preferably about 90 degrees, in case of e2).

[0023] An absolute value of the first angle difference may be in the range from 70 to 110 degrees, preferably from 80 to 100 degrees, or more preferably about 90 degrees.

[0024] The first angle threshold may be at least 70, preferably at least 80, more preferably at least 90, 95, or 98 percent, and optionally up to 99 or 100 percent, of the first angle difference. For example, if the first angle difference is 90 degrees (clockwise or counterclockwise), the first angle threshold may be 81 degrees (90 percent).

[0025] An absolute value of the second angle difference may be in the range from 25 to 65 degrees, preferably about 45 degrees, in case of a).

[0026] An absolute value of the third angle difference may be in the range from 25 to 65 degrees, preferably about 45 degrees, in case of c).

[0027] In various embodiments, one or several or all of the first alignment pulse, the second alignment pulse, the third alignment pulse, and the fourth alignment pulse may comprise a sloped rising edge and / or a sloped falling edge, and a constant amplitude portion therebetween.

[0028] The electric motor may include or may be affected by a mechanical limit for limiting movement of the rotor.

[0029] According to a second aspect, a motor controller comprising a processing unit is provided. The motor controller is configured to perform the method or any embodiment thereof in accordance with the first aspect.

[0030] According to a third aspect, a motion control arrangement is provided. The motion control arrangement comprises an electric motor and the motor controller or any embodiment thereof in accordance with the second aspect, the motor controller being connected to the electric motor.

[0031] According to a fourth aspect, an elevator system is provided. The elevator system comprises an elevator car, and the motion control arrangement or any embodiment thereof in accordance with the third aspect.

[0032] The present invention provides a method for an initial alignment of a position of a rotor of an electric motor, a motor controller, a motion control arrangement, and an elevator system. The present invention provides advantages over known solutions in that it takes into account the mentioned challenges related to the known attempts. The initial alignment in accordance with the present invention is simple and reliable, even if there is a mechanical limit which prevents the rotor movement during alignment.

[0033] Various other advantages will become clear to a skilled person based on the following detailed description.

[0034] The expression "a number of’ may herein refer to any positive integer starting from one (1).

[0035] The expression "a plurality of’ may refer to any positive integer starting from two (2), respectively.

[0036] The terms “first”, “second”, “third”, and “fourth” are herein used to distinguish one element from another element, and not to specially prioritize or order them, if not otherwise explicitly stated.

[0037] The exemplary embodiments of the present invention presented herein are not to be interpreted to pose limitations to the applicability of the appended claims. The verb "to comprise" is used herein as an open limitation that does not exclude the existence of also unrecited features. The features recited in the appended patent claims are mutually freely combinable unless otherwise explicitly stated.

[0038] The novel features which are considered as characteristic of the present invention are set forth in particular in the appended claims. The present invention itself, however, both as to its construction and its method of operation, together with additional objectives and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. BRIEF DESCRIPTION OF FIGURES

[0039] Some embodiments of the invention are illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings.

[0040] Figure 1 shows a flow diagram of a method.

[0041] Figure 2 shows various stages of an initial alignment of a rotor.

[0042] Figure 3 shows various stages of an initial alignment of a rotor.

[0043] Figure 4 illustrates schematically an electric motor affected by a mechanical limit.

[0044] Figure 5 shows an example an alignment pulse.

[0045] Figure 6 shows a flow diagram of a method.

[0046] Figure 7 shows a flow diagram of a method.

[0047] Figure 8 shows graphs as a function of time related to an initial alignment of a rotor in a first scenario.

[0048] Figure 9 shows graphs as a function of time related to an initial alignment of a rotor in a second scenario.

[0049] Figure 10 shows graphs as a function of time related to an initial alignment of a rotor in a third scenario.

[0050] Figure 11 shows graphs as a function of time related to an initial alignment of a rotor in a fourth scenario.

[0051] Figure 12 shows graphs as a function of time related to an initial alignment of a rotor in a fifth scenario.

[0052] Figure 13 shows graphs as a function of time related to an initial alignment of a rotor in a sixth scenario.

[0053] Figure 14 illustrates schematically a motor controller connected to an electric motor.

[0054] Figure 15 illustrates schematically an elevator system. DETAILED DESCRIPTION OF SOME EMBODIMENTS

[0055] Figure 1 shows a flow diagram of a method. The method is, preferably, for a method for an initial alignment of a position of a rotor of an electric motor, such as of a permanent magnet synchronous motor. The method is started at 100.

[0056] Item or method step 110 refers to applying, to the electric motor, a first alignment pulse having a first electrical angle.

[0057] Item or method step 120 refers to applying, to the electric motor after the first alignment pulse, a second alignment pulse having a second electrical angle, the second electrical angle differing from the first electrical angle by a first angle difference.

[0058] Item or method step 130 refers to determining a first amount of movement of the rotor due to the second alignment pulse.

[0059] Item or method step 140 refers to comparing the first amount of movement to a first angle threshold, the first angle threshold being less than or equal to the first angle difference.

[0060] Item or method step 152 refers to applying, to the electric motor after the second alignment pulse, a third alignment pulse having a third electrical angle, wherein the third electrical angle differs from the second electrical angle by a second angle difference and depends on a result of said comparing of the first amount of movement at least as follows.

[0061] Item or method step 154 refers to: a) if the first amount of movement is more than the first angle threshold, the third electrical angle is between the first electrical angle and the second electrical angle.

[0062] Item or method step 156 refers to: b) if the first amount of movement is less than the first angle threshold, the third electrical angle is such that the second electrical angle is between the first electrical angle and the third electrical angle.

[0063] Items or method steps 152, 154, and 156 may be included in item or method step 150 which is related, in general, to applying, a third alignment pulse having a third electrical angle. In some embodiments, the method may comprise comparing the first amount of movement to an opposite value of the first angle threshold, if the first amount of movement is less than the first angle threshold.

[0064] The method may be ended at 199.

[0065] In some embodiments, the third electrical angle may depend on the result of said comparing of the first amount of movement in case of b) above as follows: bl) if the first amount of movement is less than an opposite value of the first angle threshold, the second angle difference has a first lower value, and b2) if the first amount of movement is higher than the opposite value of the first angle threshold, the second angle difference has a first higher value. Furthermore, the first lower value may be an opposite value of the difference between the third electrical angle the second electrical angle in item or method step 154, in step a), described hereinabove.

[0066] Figure 2 shows various stages of an initial alignment of a rotor 12. In the first portion of the figure from top to bottom, the first alignment pulse 101 having a first electrical angle is applied to the motor 10, such as to windings of stator 14 thereof. As a response to the first alignment pulse 101, the rotor 12 rotates or at least tries to rotate to a position aligned with the first electrical angle. The rotation may be clockwise or counterclockwise. This is marked in the figure by Pl . A0 refers to angle difference or amount of movement between the pre-position (that is, the position prior to applying the first alignment pulse 101) of the rotor 12 and the position in accordance with the first electrical angle. As understood, A0 may indeed be zero or non-zero, depending how closely the first electrical angle happens to or is intended to match the pre-position (which is or may be unknown).

[0067] In the second portion of the figure, the second alignment pulse 102 with a second electrical angle, the second electrical angle differing from the first electrical angle by a first angle difference, is being applied to the motor 10, thus the rotor 12, if not prevented, rotates from position Pl to position P2. The first angle difference may be, for example, is in the range from 70 to 110 degrees, preferably from 80 to 100 degrees, or more preferably about 90 degrees, referring preferably to electrical angles or in some cases mechanical angles.

[0068] When or after the rotation due to the second alignment pulse 102 is finished, a first amount of movement of the rotor 12 due to the second alignment pulse 102 is determined 130. In the process, after the first amount of movement is determined, the first amount of movement is compared 140 to a first angle threshold, the first angle threshold being less than or equal to the first angle difference. The first angle threshold may be at least 70, preferably at least 80, more preferably at least 90, 95, or 98 percent, and optionally up to 99 or 100 percent, of the first angle difference.

[0069] The process then continues based on the result of the comparison. A third alignment pulse 103 having a third electrical angle, wherein the third electrical angle differs from the second electrical angle by a second angle difference, is then applied to the motor 10.

[0070] On the bottom left of the figure is shown that, if the first amount of movement is more than the first angle threshold, the third electrical angle is between the first electrical angle and the second electrical angle. This is shown by position P3 being between position Pl and P2. Thus, the rotor 12 is rotated to the opposite direction due to the third alignment pulse 103 compared to the direction rotated due to the second alignment pulse 102.

[0071] After the rotor 12 has finished the rotation due to the third alignment pulse 103 in the case of the bottom left of the figure, the rotor 12 may be concluded to be in the initial position for starting the operation.

[0072] On the bottom right of the figure is shown that, if the first amount of movement is less than the first angle threshold, the third electrical angle is such that the second electrical angle is between the first electrical angle and the third electrical angle. This is shown by position P2 being between position Pl and P3. Thus, the rotor 12 is rotated to the same direction due to the third alignment pulse 103 compared to the direction rotated due to the second alignment pulse 102.

[0073] After the rotor 12 has finished the rotation due to the third alignment pulse 103 in the case of the bottom right of the figure, the rotor 12 may be concluded to be in the initial position for starting the operation. Such concluding may be done, for example, if the first amount of movement is less than the first angle threshold, and if the first amount of movement has a value less than an opposite value of the first angle threshold.

[0074] Alternatively, the process may continue by determining a second amount of movement A2 of the rotor 12 due to the third alignment pulse 103, and comparing the second amount of movement A2 to a second angle threshold, the second angle threshold being less than or equal to a second angle difference. The second angle threshold being less than or equal to the second angle difference. The second angle threshold may be at least 70, preferably at least 80, more preferably at least 90, 95, or 98 percent, and optionally up to 99 or 100 percent, of the second angle difference.

[0075] Figure 3 shows various stages of an initial alignment of a rotor. The process may be up to a certain point, such as to the final step, substantially identical to what is described hereinabove in connection with Fig. 2. However, Fig. 3 shows optional further steps.

[0076] In Fig. 3, the method, preferably, comprises determining, at 160, a second amount of movement A2 of the rotor 12 due to the third alignment pulse 103, and comparing, at 165, the second amount of movement A2 to a second angle threshold, the second angle threshold being less than or equal to a second angle difference.

[0077] An absolute value of the second angle difference is in the range from 25 to 65 degrees, preferably about 45 degrees if the first amount of movement Al is more than the first angle threshold.

[0078] Thereafter, the method may comprise applying (at 170), to the electric motor 10 after the third alignment pulse 103, a fourth alignment pulse 104 having a fourth electrical angle, wherein the fourth electrical angle differs from the third electrical angle by a third angle difference. An absolute value of the third angle difference may be in the range from 25 to 65 degrees, preferably about 45 degrees if the second amount of movement A2 is more than the second angle threshold and the fourth electrical angle is between the second electrical angle and the third electrical angle.

[0079] In various preferable embodiments, the fourth electrical angle may depend on a result of said comparing of the second amount of movement A2 to the to second angle threshold.

[0080] The fourth electrical angle may depend on said result at least as follows: if the second amount of movement A2 is more than the second angle threshold, the fourth electrical angle is between the second electrical angle and the third electrical angle. This is shown in Fig. 3 on the bottom left which shows position P4 being between positions P3 and P2, also showing a third amount of movement A3.

[0081] If the second amount of movement A2 is less than the second angle threshold, the bottom right in Fig. 3 may apply. The fourth electrical angle may be such that the third electrical angle is between the second electrical angle and the fourth electrical angle. This is shown on the bottom right in Fig. 3 by position P4_l and respective third amount of movement A3_l. Thus, the fourth alignment pulse 104 may rotate the rotor 12 even further to the same direction as previous alignment pulses. On the other hand, if the second amount of movement A2 is less than the second angle threshold, the fourth electrical angle may be between the third electrical angle and the second electrical angle. This is shown on the bottom right in Fig. 3 by position P4_2 and respective third amount of movement A3_2.

[0082] In some embodiments, in which the fourth electrical angle is between the third electrical angle and the second electrical angle (P4_2), it may be that the first amount of movement Al is less than the first angle threshold, and the third electrical angle is such that the second electrical angle is between the first electrical angle and the third electrical angle, and furthermore, the difference between the second electrical angle and the third electrical angle (the second angle difference) is more than 90 degrees, more preferable more than 135 degrees, even about 180 degrees. In general, in these cases, the second angle difference is more, or more preferably at least 1.5 times the first angle difference, even at least two times the first angle difference.

[0083] Furthermore, the fourth electrical angle may depend on the result of said comparing of the second amount of movement A2 at least as follows: if the second amount of movement is less than an opposite value of the second angle threshold, the third angle difference has a second lower value, and if the second amount of movement is higher than the opposite value of the second angle threshold, the third angle difference has a second higher value. Thus, depending on the case, the magnitude of the angle difference may vary. An absolute value of the second lower value is in the range from 25 to 65 degrees, preferably about 45 degrees, and / or an absolute value of the second higher value is in the range from 70 to 110 degrees, preferably about 90 degrees.

[0084] Furthermore, the fourth electrical angle may further depend on a result of said comparing of the second amount of movement (in case of b) or b2)) at least as follows: el) if the second amount of movement is less than an opposite value of the second angle threshold, the fourth electrical angle is such that the third electrical angle is between the second electrical angle and the fourth electrical angle, and e2) if the second amount of movement is higher than the opposite value of the second angle threshold, the fourth electrical angle is between the second electrical angle and the third electrical angle. The third angle difference is in the range from 25 to 65 degrees, preferably about 45 degrees, in case of el), and / or the third angle difference is in the range from 70 to 110 degrees, preferably about 90 degrees, in case of e2).

[0085] Figure 4 illustrates schematically an electric motor 10 affected by a mechanical limit 30. The mechanical limit 30 limits movement, such as rotation, of the rotor 12. The motor 10 may comprise a stator 14 including a three-phase winding for generating a magnetic field to rotate the rotor 12. In this case the three phases are shown highly schematically as a, b, and c (returning conductors a’, b’, and c’, respectively). Fig. 4 shows a stator coordinate system with a and 0 axes. Fig. 4 also shows a rotor coordinate system with direct (d) and quadrature (q) axes. The motor 10 may have one or several pole-pairs. The number of pole pairs affects the relation between mechanical angles and electrical angles, as is well known.

[0086] The method and process described hereinabove work especially with motors 10 having a mechanical limit 30. It should especially be noted that method step 140 the first amount of movement Al is compared to the first angle threshold value. Therefore, if there is a mechanical limit 30 in the motor 10, and it is in the path of the rotor movement, the rotor 12 is unable to move the expected amount.

[0087] The mechanical limit 30 may limit the movement of the rotor 12 either by affecting the rotor 12 more or less directly, or by affecting another portion of the system in which the motor 10 is set to operate. For example, if the motor 10 operates an elevator door in an elevator system, the mechanical limit 30 may be in the door mechanism, thereby creating a limit for the movement of the rotor 12 via the mechanism.

[0088] Furthermore, in some embodiments, including method step 165, the second amount of movement A2 is compared to a second angle threshold, the second angle threshold being less than or equal to a second angle difference. Thus, in this case too, if the second amount of movement A2 is not as expected, a mechanical limit 30 may be blocking the rotor movement. The method may thus comprise one or two steps of comparing the amount of movement to a threshold value, as described hereinbefore.

[0089] Figure 5 shows an example an alignment pulse. The alignment pulse in Fig. 5 may represent one, two, three, or four of the following: the first alignment pulse, the second alignment pulse, the third alignment pulse, and the fourth alignment pulse. The alignment pulse comprises a sloped rising edge and / or a sloped falling edge, and a constant amplitude portion therebetween. The rising edge and / or falling edge may take, for example, about 100 milliseconds. The total pulse duration (including rising edge, constant portion, falling edge) may be, for example, about 500 milliseconds.

[0090] Figure 6 shows a flow diagram of a method. The steps shown in Fig. 6 are already described hereinbefore and are marked with corresponding reference signs. Fig. 6 further shows an example of the electrical angles, or specifically differences between thereof, which may be utilized to carry out the invention. Considering the scope of the present disclosure, the angles or angle differences are not limited to those in Fig. 6.

[0091] Figure 7 shows a flow diagram of a method. The steps shown in Fig. 7 are already described hereinbefore and are marked with corresponding reference signs. Fig. 7 further shows an example of the electrical angles, or specifically differences between thereof, which may be utilized to carry out the invention. Considering the scope of the present disclosure, the angles (0p) or angle differences are not limited to those in Fig. 7.

[0092] The most significant difference between Figs. 6 and 7 is in step 156 and in the fourth electrical angle with respect to the third electrical angle in the case where the second amount of movement A2 is less than the second angle threshold but higher than the opposite value of the second angle threshold (see the box in the bottom left of Figs. 6 and 7).

[0093] In Fig. 6, in step 156, when the first amount of movement is less than the first angle threshold but higher than the opposite value of the first angle threshold, the electrical angle of the third alignment pulse differs 180 degrees from the electrical angle of the second alignment pulse, whereas in Fig. 7 the difference is 90 degrees.

[0094] Furthermore, in Fig. 6, with said 180-degree-difference, the fourth electrical angle is - 90 degrees, so it is towards the third electrical angle, however, not all the way to the second electrical angle, whereas in Fig. 7, the fourth electrical angle is 90 in the similar case, that is, away from the third electrical angle.

[0095] Figure 8 shows graphs as a function of time related to an initial alignment of a rotor 12 in a first scenario. At 810, there are shown three consecutive alignment pulses. At 820, there is shown a rotational speed of rotor 12. At 830, there are shown real 831 and estimated 832 electrical angles. At 840, shows a distance between the current position of the rotor 12 and the position of the mechanical limit 30 in electrical angles.

[0096] The spacing of the horizontal axis in Figs. 8-13 may be, for example, in the range of 0.1 to 1.5 seconds, preferably about 0.5 seconds.

[0097] In Fig. 8, during the first alignment pulse 101, such as a voltage pulse, the rotor 12 moves to the pre-position. The second alignment pulse 102 rotates the rotor 90 degrees forward. The alignment procedure could be stopped here because the rotor has rotated the same angle as the angle difference between last two voltage pulses. However, the third alignment pulse is applied 45 degrees backwards with respect to the last movement to verify that the rotor is aligned correctly. Finally, for example, a field-oriented control or the like control method for the normal operation may be started since the initial alignment has been performed. In this case, the mechanical limit 30 was not reached.

[0098] Figure 9 shows graphs as a function of time related to an initial alignment of a rotor 12 in a second scenario. At 910, there are shown four consecutive alignment pulses. At 920, there is shown a rotational speed of rotor 12. At 930, there are shown real 931 and estimated 932 electrical angles. At 940, shows a distance between the current position of the rotor 12 and the position of the mechanical limit 30 in electrical angles.

[0099] In Fig. 9, the rotor 12 “hits” the mechanical limit 30 during the first alignment pulse and is prevented from moving further to the pre-position. During the second alignment pulse, the rotor 12 is aligned correctly to position 90 degrees but it does not rotate enough. During the third alignment pulse, the rotor 12 aligns correctly, and it rotates more than the angle threshold (81 degrees in this case). The fourth alignment pulse is applied and moves the rotor 12 backwards 45 degrees with respect to the last movement and the rotor 12 aligns correctly. Finally, for example, a field-oriented control or the like control method for the normal operation may be started since the initial alignment has been performed.

[0100] Figure 10 shows graphs as a function of time related to an initial alignment of a rotor 12 in a third scenario. At 1010, there are shown four consecutive alignment pulses. At 1020, there is shown a rotational speed of rotor 12. At 1030, there are shown real 1031 and estimated 1032 electrical angles. At 1040, shows a distance between the current position of the rotor 12 and the position of the mechanical limit 30 in electrical angles.

[0101] In Fig. 10, the rotor 12 is on the mechanical limit 30 during the first and second alignment pulses, and thus doesn’t move due to said alignment pulses. During the third alignment pulse, the rotor 12 is aligned correctly but it does not rotate enough. The fourth alignment pulse moves the rotor 12 even more away from the mechanical limit and the rotor aligns correctly. Finally, for example, a field-oriented control or the like control method for the normal operation may be started since the initial alignment has been performed.

[0102] Figure 11 shows graphs as a function of time related to an initial alignment of a rotor 12 in a fourth scenario. At 1110, there are shown four consecutive alignment pulses. At 1120, there is shown a rotational speed of rotor 12. At 1130, there are shown real 1131 and estimated 1132 electrical angles. At 1140, shows a distance between the current position of the rotor 12 and the position of the mechanical limit 30 in electrical angles. In Fig. 11, during the first alignment pulse, the rotor 12 moves to the pre-position, being 0-degree position. During the second alignment pulse, the rotor 12 “hits” the mechanical limit 12 and it is, thus, not aligned correctly. During the third alignment pulse, the rotor 12 stays on the mechanical limit 30. The fourth pulse moves the rotor 12 away from the limit 30 and the rotor 12 is aligned correctly. Finally, for example, a field-oriented control or the like control method for the normal operation may be started since the initial alignment has been performed.

[0103] Figure 12 shows graphs as a function of time related to an initial alignment of a rotor in a fifth scenario. At 1210, there are shown four consecutive alignment pulses. At 1220, there is shown a rotational speed of rotor 12. At 1230, there are shown real 1231 and estimated 1232 electrical angles. At 1240, shows a distance between the current position of the rotor 12 and the position of the mechanical limit 30 in electrical angles.

[0104] In Fig. 12, during the first alignment pulse, the rotor 12 moves to the pre-position, being 0-degree position. During the second and third alignment pulses, the rotor 12 hits and stays on the mechanical limit 30 and it is not aligned correctly. During fourth alignment pulse, the rotor 12 moves away from the limit 30 and the rotor 12 is aligned correctly. Finally, for example, a field-oriented control or the like control method for the normal operation may be started since the initial alignment has been performed.

[0105] Figure 13 shows graphs as a function of time related to an initial alignment of a rotor in a sixth scenario. At 1310, there are shown three consecutive alignment pulses. At 1320, there is shown a rotational speed of rotor 12. At 1330, there are shown real 1331 and estimated 1332 electrical angles. At 1340, shows a distance between the current position of the rotor 12 and the position of the mechanical limit 30 in electrical angles.

[0106] In Fig. 13, rotor is initially on the mechanical limit 30. During the first alignment pulse, it moves away from the limit 30 to the pre-position. During the second alignment pulse, the rotor moves 90 degrees forward. The third alignment pulse is applied to move the rotor 12 backwards 45 degrees with respect to the last movement and the rotor 12 aligns correctly. Finally, for example, a field-oriented control or the like control method for the normal operation may be started since the initial alignment has been performed.

[0107] The normal operation, that is performed after the initial alignment, can clearly be seen in Figs. 8-13, at 830, 930, 1030, 1130, 1230, and 1330 when the electrical angle starts to oscillate (the rotor 12 is rotating full cycles). Figure 14 illustrates schematically a motor controller 20 connected to an electric motor 10, thereby forming a motion control arrangement. The motor controller 20 comprises a processing unit 22, and preferably a memory 24 (may be comprised in the processing unit 22). The motor controller 20 is, preferably, configured to perform the method, or any embodiment thereof, as described hereinabove. The motor controller 20 may be or comprise an electrical converter, such as a frequency converter or an inverter. An output of the motor controller 20 is connectable or connected to the electric motor 10, preferably to winding(s) of stator 14 thereof. On the other hand, the motor controller 20 may also be connected to a further control unit, such as of a system or device which comprises the motor 10 and the motor controller 20. Thus, the motor controller 20 may receive commands or data from the further control unit.

[0108] Figure 15 illustrates schematically an elevator system 200. The elevator system 200 may comprise a motor controller 20, such as including an electric converter (a frequency converter and / or an inverter), in connection with an electric motor 10. As can be seen, the electric motor 10 may be a hoisting motor or a motor of an elevator door 280.

[0109] The elevator system 200 may thus comprise an elevator, or “hoisting”, motor, such as a permanent magnet electric motor, for moving an elevator car 201 comprised in the elevator system 200. The elevator motor may be arranged to rotate a traction sheave 208. The elevator car 201 may be mechanically coupled to the electric motor 202, preferably, by a hoisting rope 206, for example, extending via the traction sheave 208.

[0110] The elevator car 201 may be moved in and / or along an elevator shaft 242. The elevator car 201 may be moved in a normal operation mode to serve landings 240 or landing floors 240 in accordance with elevator calls. Also shown are the elevator doors 280 and the landing floor doors.

[0111] The hoisting rope 206 may comprise, for example, steel or carbon fibers. The term ‘hoisting rope’ does not limit the form of the rope anyhow. For example, the hoisting rope 206 may be implemented as a rope or a belt. The elevator system 200 may also comprise a counterweight 234 in connection with the elevator car 201, such as via the hoisting rope 206.

[0112] The elevator system 200 may comprise an elevator control unit 290, which can be said further control unit, for controlling the operation of the elevator system 200, such as various devices thereof. The elevator control unit 290 may be a separate device or may be comprised in the other components of the elevator system 200 such as in or as a part of the motor controller. In various embodiments, the elevator control unit 290 comprises the motor controller. The elevator control unit 290 may be in connection with a brake controller 300 to control the operation thereof.

[0113] In some embodiments, the elevator control unit 290 may comprise the motor controller 20, however, in other embodiments, they may be separate entities, in which case the elevator control unit 290 may be in communication connection with the motor controller 20, such as providing input signal / data thereto and / or therefrom.

[0114] There may be also a main electrical power supply 225 such as a three-phase or singlephase electrical power grid, an electrical connection 230 between the power supply 225 and the motor controller 20, another electrical connection 235 between the motor controller 20 and the electric motor 10.

[0115] It is also noted herein that while the above describes example embodiments, these should not be viewed in a limiting sense. Rather, there are several variations and modifications, which may be made without departing from the scope of the present disclosure as defined in the appended claims.

[0116] The previously presented considerations concerning the various embodiments of the device may be flexibly applied to the embodiments of the method, and vice versa, as being appreciated by a skilled person.

[0117] Some advantageous embodiments according to the invention have been described above. The invention is not limited to the embodiments described above, but the inventive idea can be applied in numerous ways within the scope of the claims. The features recited in dependent claims are mutually freely combinable unless otherwise explicitly stated.

Claims

CLAIMS1. A method for an initial alignment of a position of a rotor (12) of an electric motor (10), such as of a permanent magnet synchronous motor, the method comprising: applying (110), to the electric motor (10), a first alignment pulse (101) having a first electrical angle; applying (120), to the electric motor (10) after the first alignment pulse (101), a second alignment pulse (102) having a second electrical angle, the second electrical angle differing from the first electrical angle by a first angle difference; determining (130) a first amount of movement (Al) of the rotor (12) due to the second alignment pulse (102); comparing (140) the first amount of movement (Al) to a first angle threshold, the first angle threshold being less than or equal to the first angle difference; applying (150), to the electric motor (10) after the second alignment pulse (102), a third alignment pulse (103) having a third electrical angle, wherein the third electrical angle differs from the second electrical angle by a second angle difference and depends on a result of said comparing (140) of the first amount of movement (Al) at least as follows: a) if the first amount of movement (Al) is more than the first angle threshold, the third electrical angle is between the first electrical angle and the second electrical angle, and b) if the first amount of movement (Al) is less than the first angle threshold, the third electrical angle is such that the second electrical angle is between the first electrical angle and the third electrical angle.

2. The method of claim 1, wherein the third electrical angle depends on the result of said comparing (140) of the first amount of movement (Al) in case of b) as follows: bl) if the first amount of movement is less than an opposite value of the first angle threshold, the second angle difference has a first lower value, and b2) if the first amount of movement is higher than the opposite value of the first angle threshold, the second angle difference has a first higher value.

3. The method of claim 1 or 2, comprising determining (160) a second amount of movement (A2) of the rotor (12) due to the third alignment pulse (103), and comparing (165) the second amount of movement (A2) to a second angle threshold, the second angle threshold being less than or equal to a second angle difference.

4. The method of claim 3, comprising applying (170), to the electric motor (10) after the third alignment pulse (103), a fourth alignment pulse (104) having a fourth electrical angle, wherein the fourth electrical angle differs from the third electrical angle by a third angle difference.

5. The method of claim 4, wherein the fourth electrical angle depends on a result of said comparing (165) of the second amount of movement (A2) at least as follows: c) if the second amount of movement (A2) is more than the second angle threshold, the fourth electrical angle is between the second electrical angle and the third electrical angle.

6. The method of claim 5, wherein the fourth electrical angle further depends on a result of said comparing (165) of the second amount of movement (A2) at least as follows: d) if the second amount of movement (A2) is less than the second angle threshold, the fourth electrical angle is such that the third electrical angle is between the second electrical angle and the fourth electrical angle.

7. The method of claim 6, wherein the fourth electrical angle depends on the result of said comparing (165) of the second amount of movement (A2) in case of b), b2), or d) at least as follows: dl) if the second amount of movement (A2) is less than an opposite value of the second angle threshold, the third angle difference has a second lower value, and d2) if the second amount of movement (A2) is higher than the opposite value of the second angle threshold, the third angle difference has a second higher value.

8. The method of claim 5, wherein the fourth electrical angle further depends on a result of said comparing (165) of the second amount of movement (A2) in case of b) or b2) at least as follows: el) if the second amount of movement (A2) is less than an opposite value of the second angle threshold, the fourth electrical angle is such that the third electrical angle is between the second electrical angle and the fourth electrical angle, and e2) if the second amount of movement (A2) is higher than the opposite value of the second angle threshold, the fourth electrical angle is between the second electrical angle and the third electrical angle.

9. The method of any of claims 1-8, wherein an absolute value of the first angle difference is in the range from 70 to 110 degrees, preferably from 80 to 100 degrees, or more preferably about 90 degrees.

10. The method of any of claims 1-9, wherein the first angle threshold is at least 70, preferably at least 80, more preferably at least 90, 95, or 98 percent, and optionally up to 99 or 100 percent, of the first angle difference.

11. The method of any of claims 1-10, wherein an absolute value of the second angle difference is in the range from 25 to 65 degrees, preferably about 45 degrees, in case of a).

12. The method of claim 5, wherein an absolute value of the third angle difference is in the range from 25 to 65 degrees, preferably about 45 degrees, in case of c).

13. The method of any of claims 2-12, wherein an absolute value of the first lower value is in the range from 25 to 65 degrees, preferably about 45 degrees in case of bl), and / or an absolute value of the first higher value is in the range from 70 to 200 degrees, preferably about 90 or about 180 degrees in case of b2).

14. The method of claim 7, wherein an absolute value of the second lower value is in the range from 25 to 65 degrees, preferably about 45 degrees in case of dl), and / oran absolute value of the second higher value is in the range from 70 to 110 degrees, preferably about 90 degrees in case of d2).

15. The method of claim 8, wherein the third angle difference is in the range from 25 to 65 degrees, preferably about 45 degrees, in case of el), and / or the third angle difference is in the range from 70 to 110 degrees, preferably about 90 degrees, in case of e2).

16. The method of any of claims 1-15, wherein one or several or all of the first alignment pulse (101), the second alignment pulse (102), the third alignment pulse (103), and the fourth alignment pulse (104) comprises a sloped rising edge and / or a sloped falling edge, and a constant amplitude portion therebetween.

17. The method of any of claims 1-16, wherein the electric motor (10) includes or is affected by a mechanical limit (30) for limiting movement of the rotor (12).

18. A motor controller (20) comprising a processing unit (22), configured to perform the method of any of claims 1-17.

19. A motion control arrangement comprising an electric motor (10), and the motor controller (20) of claim 18 connected to the electric motor (10).

20. An elevator system (200) comprising an elevator car (201), and the motion control arrangement of claim 19.

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