Method for determining the offset of an angular position encoder on the rotor shaft of an electric motor

Abstract

The present invention relates to a method for determining the offset of an angular position encoder on a rotor shaft of an electric motor. In particular, it relates to a method (1) for determining the offset of an angular position encoder (101), wherein the angular position encoder (101) is connected to the rotor of a motor (100), wherein a reference offset of a reference angular position encoder of a reference motor is known under the conditions of a reference speed and a reference current (51, 55) having a reference phase angle (53, 57) and a reference absolute value, and the method comprises the following steps: - applying a current (61, 65) having a reference absolute value; - setting the phase angle (63, 67) of the current to achieve the reference speed; - comparing the phase angle (63, 67) with the reference phase angle (53, 57) and the reference offset; - determining the offset (59, 69) based on the comparison.

Description

Technical Field

[0001] The invention relates to a method for determining the offset of an angular position encoder on a rotor shaft of an electric machine. Background Art

[0002] Electric motors are generally known as electrical machines and are increasingly used to drive vehicles. Electric motors consist of a stator and a rotor.

[0003] The stator comprises a number of slots for guiding the windings. The rotor is located in the stator and is connected to the rotor shaft. In order to control the motor, the exact angular position of the rotor in the stator must be known. The orientation angle can be measured continuously by a device called an angular position encoder. For example, the angular position encoder can be fixed to the stator or the support plate, but must be arranged to be spaced apart from the rotor.

[0004] Document DE 10 2011 087 396 A1 describes a method for mounting an angular position encoder on the rotor shaft of an electric machine. Since the physical position is never absolutely exact, the deviation between the installed position and the desired position must be determined for each electric machine. This manufacturing-induced position deviation is also called offset. In the method known from DE '396, after the angular position encoder has been mounted, the exact position (i.e. the offset) of the angular position encoder relative to the rotor and the angular position encoder fixed to the stator is determined on an electric machine test bench.

[0005] Technical solutions and solutions

[0006] It is an object of the invention to provide a method for determining the offset of an angular position encoder which is simple and time-saving.

[0007] According to the present invention, a method for determining an angular position encoder offset associated with a motor rotor is provided, wherein a reference offset of a reference angular position encoder of a reference motor at a reference speed and a reference current having a reference phase angle and a reference absolute value is known, the method comprising the following steps: applying a current having a reference absolute value, setting a phase angle of the current to achieve the reference speed, comparing the phase angle with the reference phase angle and the reference offset, and determining the offset based on the comparison.

[0008] In a reference motor, the reference current having a reference phase angle and a reference absolute value is determined at a reference speed. In the reference motor, a reference offset of an angular position encoder caused by manufacturing is determined on a motor test bench by known methods. Using the known reference offset, the control system sets a reference current having an optimal reference phase angle. The current components include a q current and a d current, which define a phase angle in the complex plane, and the length of the current pointer represents the reference absolute value of the reference current.

[0009] In the case where the offset is unknown, the phase angle will not be optimal, which will result in an offset from d current to q current.

[0010] For example, in the case of an electric machine used as a synchronous machine, this can lead to increased energy consumption or, in extreme cases, even to a change in the direction of rotation; which is undesirable.

[0011] In contrast, with a reference motor having an angular position encoder with a known reference offset, the reference phase angle is known at a reference rotational speed and a reference current absolute value.

[0012] In a motor with similar electrical properties to the reference motor (that is, for example, the same winding wire type, the same number of stator slots, a similar rotor and the same manufacturing-induced deviations in the mounting position of the angular position encoder), the same phase angle as the reference motor is created in order to achieve the reference speed required for optimal energy utilization.

[0013] The manufacturing-induced deviations that occur when mounting the angular position encoder and the resulting offset of the angular position encoder vary from motor to motor and are therefore not the same compared to a reference motor. Therefore, the offset must be determined individually for each motor.

[0014] Since the optimum reference phase angle with the reference absolute value at the reference speed and the reference offset is known, and since the same optimum phase angle with the reference absolute value and offset at the reference speed is created in similar motors, the difference between the reference phase angle and the phase angle is substantially equal to the angular position encoder offset due to manufacturing-induced variations. In this context, “substantially” means that, for example, the resistance in the coils of different motors has a negligible effect on the phase angle.

[0015] In other words, the phase angle of the motor to be tested will be the same as the reference phase angle of the reference motor if the two angular position encoders have the same offset. The deviation between the reference phase angle and the phase angle corresponds to the deviation of the offset of the motor to be measured relative to the reference offset of the reference motor. Since the reference offset is known, the offset of the motor to be measured can be determined.

[0016] Thus, the offsets of a large number of motors can be determined without accurately measuring the angular position encoder offset of each individual motor on a motor test bench.

[0017] Therefore, series motor manufacturing can become more economical and faster.

[0018] Preferably, the offset can be determined at two different reference rotational speeds and a mean value can be formed therefrom.

[0019] This enables a more precise determination of the offset since a smaller degree of error in the individual measurements is taken into account.

[0020] A further improvement in the determination of the offset can be achieved by forming a mean value or a weighted mean value from the values ​​at a reference speed.

[0021] In another preferred embodiment of the invention, the reference rotational speeds can have the same absolute value, but can have different directions of rotation.

[0022] In the case of completely opposite rotational speeds, a phase angle in the completely opposite direction needs to be assumed. Here, the offset can be seen particularly clearly.

[0023] Preferably, the reference speed may also be between one third and two thirds of the nominal motor speed.

[0024] In the operating range, the amplitude of the flowing current is large enough and the losses due to load and heating are small enough to enable the optimum phase angle to be measured.

[0025] In a further embodiment of the invention, the method can be carried out as a terminal test in the case of series production.

[0026] In this case, the starting point can be any motor in the series to be tested. The following motor must always be controlled to a predefined reference speed. The offset of the angular position encoder relative to the deviation phase angle is thus determined.

[0027] According to the invention, the electric machine is equipped with an angular position encoder having an offset determined according to one of the preferred methods.

[0028] Preferably, the motor is connectable to an inverter.

[0029] The specific offset of the angular position encoder of the electric machine is essentially independent of the connected inverter, because the manufacturing-induced offset of the angular position encoder is always larger than the signal transit time-induced offset of the inverter.

[0030] Even if the inverter changes between the determination of the reference phase angle of the reference motor and the offset of the motor angular position encoder, it has almost no effect on the determination of the phase angle and the offset of the angular position encoder.

[0031] According to the invention, a vehicle is provided which has an electrical machine, in particular an electric motor, which has an angular position encoder, the offset of which is determined according to one of the preferred methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Diagram showing the arrangement of the motor with the inverter and controller.

[0033] Figure 2 A flow chart of the present invention is shown.

[0034] Figure 3Pointer plot showing the applied current in the complex plane.

[0035] Figure 4 A vehicle is shown with a motor and an angular position encoder. DETAILED DESCRIPTION

[0036] Figure 1 A motor 21 , in particular an electric motor, is schematically shown. The motor 21 is connected to an inverter 19 via a three-phase line 27 , and the inverter supplies the motor 21 with alternating current from a direct current source (eg a battery, not shown).

[0037] The pulse width modulator 17 switches the switching elements in the inverter 19 so that the AC voltage is supplied to the motor from the direct voltage source. The current controller 15 defines the duty cycle of the inverter 19 to be set to achieve current inversion to the pulse width modulator 17. The current controller 15 receives a response 23 from the inverter 19 regarding the current actually fed to the three-phase line 27 of the motor.

[0038] The current controller 15 receives an indication of the current to be applied with the current value and the phase angle, i.e. the values ​​for the q-current 9 and the d-current 7, from the current indicator 13 in the speed controller 29. The adaptive speed controller 11 for this purpose indicates to the current indicator 13 the phase angle 5 required for this purpose which the motor 21 should achieve. The adaptive speed controller 11 in turn receives a response 25 from the motor 21 about the speed actually present in the motor 21 and can correct the speed as appropriate by intervening in this part of the current indicator.

[0039] Since the speed controller 29 and its components are only required for determining the offset, they can be omitted during operation of the electric machine (for example in a vehicle) after the offset has been determined.

[0040] pass Figure 1 The structure shown in , can determine the offset of a known reference offset of a reference motor on a substantially identical series of motors.

[0041] Figure 2 The process of method 1 for determining an angular position encoder is shown. In a first step 31 , a reference offset of a reference motor is determined using methods known from the prior art.

[0042] In a second step 33, according to Figure 1 The structure shown in FIG. 1 accelerates the reference motor to a reference speed and measures the reference phase angle in a third step 35. The value obtained thereby is then used in determining the offset of the motor or the motor to be measured. The reference absolute value of the reference motor speed is determined in an exemplary manner.

[0043] In the following, according to Figure 1The offset of the motor to be measured is determined by a structure of, wherein the motor to be measured is connected instead of the reference motor. For example, the electric motor including the inverter can also be changed compared to the reference motor. In a fourth step 37, the motor to be measured is accelerated to the reference speed and in a fifth step 39 the phase angle is measured.

[0044] In a sixth step 41, the set phase angle is compared with a reference phase angle. The deviation corresponds to the difference between the offset of the motor to be measured and the reference offset of the reference motor. Since the reference offset is known, the offset of the motor to be measured can now be determined.

[0045] In a seventh step 43, the determined offset can be optionally verified. The determined offset is set as the offset of the motor to be measured. The phase angle present after acceleration to the reference speed is now substantially the same as the reference phase angle, regardless of the different offsets of the two motors.

[0046] For series testing, steps 4 to 6 and optionally step 7 must be performed in any production motor to determine the offset of the angular position encoder. Alternatively, steps 4 to 6 and optionally step 7 can be performed using any production motor and inverter combination.

[0047] Figure 3 An example of a current pointer diagram in the complex plane is shown. The d current Id 7 is shown as the abscissa and the q current Iq 9 is shown as the ordinate.

[0048] The solid arrow 51 represents the reference current vector of the reference motor.

[0049] In the case of a reference motor, a reference current 51 is applied at a predetermined reference speed. The reference phase angle 53 present in this case is the phase angle of the vector. Since the angle of the angular position encoder is correct in the case of this reference motor (because the reference offset is known), the reference current ensures optimal operation of the reference motor.

[0050] Another reference current vector 55 (shown as a dotted line) may optionally be applied at a second reference speed, such as at negative speeds. Additionally, the resulting second argument 57 of the second reference current vector 55 may be used as a second reference phase angle 57 to more accurately determine the offset.

[0051] In a motor to be measured with an unknown angular position encoder offset, a current 61 is applied at a predetermined reference speed. The phase angle 63 present in this case is the current phase angle, which is represented by the short transverse vector 61. Since the angle of the angular position encoder in this motor to be measured is inaccurate (because the offset is unknown), the current does not ensure optimal operation of the motor to be measured.

[0052] Optionally, another current vector 65 (shown as a long horizontal line) may be applied at a second reference speed, such as at a negative speed. In addition, the resulting second argument 67 of the second current vector 65 may be used as a second phase angle 67 to more accurately determine the offset.

[0053] The difference between the reference phase angle 53 of the reference motor and the phase angle 63 of the motor to be measured at the same reference speed provides the deviation of the offset of the motor to be measured relative to the reference offset. Since the reference offset of the reference motor is known, the offset can be determined, for example, as the sum of the reference offset and the difference 59 between the phase angle 63 and the reference phase angle 53 at the reference speed.

[0054] Optionally, the same calculation can be performed for the second reference speed. Thus, the second offset 69 is determined from the sum of the reference offset and the difference 69 between the second phase angle 67 and the second reference phase angle 57 at the second reference speed. Optionally, the offset can be corrected by the second offset.

[0055] The uniform length of all vectors indicates that the absolute values ​​of all currents are the same.

[0056] Figure 4 is a schematic diagram of an exemplary embodiment of a vehicle 103 , such as a hybrid vehicle or an electric vehicle, comprising an electric machine 100 , in particular for driving the vehicle, having an angular position encoder 101 , the offset of which is determined by the method according to the invention.

Claims

1. A method (1) for determining an offset of an angular position encoder (101) connected to the rotor of an electric motor (100), wherein a reference offset of a reference angular position encoder of a reference electric motor is known at a reference speed and a reference current (51, 55) having a reference phase angle (53, 57) and a reference absolute value, the method comprising the following steps: - applying a current (61, 65) having a reference absolute value; - setting the phase angle (63, 67) of the current to achieve the reference speed; - comparing the phase angle (63, 67) with the reference phase angle (53, 57) to determine a deviation, and comparing the deviation with the reference offset; - Based on the comparison, an offset (59, 69) is determined. 2 . The method ( 1 ) as claimed in claim 1 , wherein the offset is determined at two different reference rotational speeds and a mean value is formed. 3 . The method ( 1 ) according to claim 2 , wherein the reference rotational speeds have the same absolute value, but different directions of rotation.

4. The method (1) according to any of the preceding claims, wherein the reference speed is between one third and two thirds of the nominal motor speed. 5 . The method ( 1 ) according to claim 1 , wherein the method can be carried out as an end-of-line test during series production.

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