Method for determining an offset of an angular position encoder on a rotor shaft of an electric machine

Abstract

A method for determining an offset of an angular position encoder is associated with a rotor of an electric machine, wherein a reference offset of a reference angular position encoder of a reference electric machine is known at a reference rotational speed and a reference current with a reference phase angle and a reference absolute value. The method includes the steps of applying a current having the reference absolute value; setting a phase angle of the current to achieve the reference rotational speed; comparing the phase angle with the reference phase angle and the reference offset; and determining the offset on the basis of this comparison.

Claims

1. A method for determining an offset of an angular position encoder, which is associated with a rotor of an electric machine, wherein a reference offset of a reference angular position encoder of a reference electric machine is known at a reference rotational speed and at a reference current with a reference phase angle and a reference absolute value, said method comprising the following steps: applying a current having the reference absolute value; setting a phase angle of the current to achieve the reference rotational speed; comparing the phase angle with the reference phase angle and the reference offset; and determining the offset on a basis of this comparison, wherein the offset is determined at two different reference rotational speeds and a mean value is formed.

2. The method according to claim 1, wherein the reference rotational speeds have the same absolute value, but are in different rotation directions.

3. The method according to claim 1, wherein applying the current as an end-of-line test in a case of series production.

4. A method for determining an offset of an angular position encoder, which is associated with a rotor of an electric machine, wherein a reference offset of a reference angular position encoder of a reference electric machine is known at a reference rotational speed and at a reference current with a reference phase angle and a reference absolute value, said method comprising the following steps: applying a current having the reference absolute value; setting a phase angle of the current to achieve the reference rotational speed; comparing the phase angle with the reference phase angle and the reference offset; and determining the offset on a basis of this comparison, wherein the reference rotational speed lies in a range between one third and two thirds of a nominal motor rotational speed.

Description

DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows an arrangement of an electric machine with an inverter and a controller.

(2) FIG. 2 shows a flow diagram of the invention.

(3) FIG. 3 shows a pointer diagram with an applied current in the complex plane.

(4) FIG. 4 shows a vehicle with an electric machine and an angular position encoder.

(5) FIG. 1 schematically shows an electric machine 21, in particular an electric motor. The electric machine 21 is connected to an inverter 19 via three phases 27, which inverter supplies the electric machine 21 with alternating current from a direct current source—for example battery—(not shown).

(6) A pulse width modulator 17 switches the switch elements in the inverter 19 in order to supply the electric machine with an alternating voltage from a direct voltage source. A current controller 15 defines to the pulse width modulator 17 what duty cycle of the inverter 19 should be set for inverting the current. The current controller 15 receives a response 23 from the inverter 19 regarding the current of the three phases 27 actually fed into the electric machine.

(7) The current controller 15 receives, from a current specifier 13 in the rotational speed controller 29, the specifications for the current to be applied with current value and phase angle, that is to say values for q current 9 and d current 7. The adaptive rotational speed controller 11 for this purpose specifies to the current specifier 13 a phase angle 5 necessary for this purpose that the electric machine 21 should achieve. The adaptive rotational speed controller 11 in turn receives a response 25 from the electric machine 21 regarding the rotational speed actually present at the electric machine 21 and may correct the rotational speed as appropriate by means of an intervention on the part of the current specifier.

(8) Since the rotational speed controller 29 with its components is necessary only for the determination of the offset, it is possible to dispense with this during operation of the electric machine once the offset has been determined, for example in a vehicle.

(9) By means of the structure shown in FIG. 1, the offset with a known reference offset of the reference machine may be determined on structurally identical electric series machines.

(10) FIG. 2 shows the course of the method 1 for determining the offset of the angular position encoder. In a first step 31 the reference offset of a reference machine is determined using a method known from the prior art.

(11) In a second step 33, the reference machine is accelerated to a reference rotational speed in accordance with a structure shown in FIG. 1, and the reference phase angle is measured in a third step 35. The values thus obtained are then used subsequently when determining the offset of the electric machine or the machine to be measured. The reference absolute values are determined in an exemplary manner for the reference motor.

(12) Hereinafter, the offset of a machine to be measured is determined in accordance with the structure of FIG. 1, wherein the machine to be measured is connected instead of the reference motor. For example, the motor inclusive of the inverter may also be changed in comparison to the reference machine. In a fourth step 37 the machine to be measured is accelerated to the reference rotational speed, and the phase angle is measured in a fifth step 39.

(13) In a sixth step 41 the set phase angle is compared with the reference phase angle. The deviation corresponds to the difference between the offset of the electric machine to be measured and the reference offset of the reference machine. Since this reference offset is known, it is now possible to determine the offset of the electric machine to be measured.

(14) As seventh step 43, a checking of the determined offset is optionally possible. The determined offset is set as the offset of the machine to be measured. The phase angle present after acceleration to the reference rotational speed is now substantially identical to the reference phase angle, regardless of the different offsets of the two machines.

(15) For the use as series test it is necessary to perform steps four to six and optionally seven in any produced motor in order to determine the offset of the angular position encoder. Alternatively, steps four to six and optionally seven may be performed with any produced motor and inverter combination.

(16) FIG. 3 shows an example of a current pointer graph in the complex plane. The d current Id 7 is plotted on the abscissa, and the q current Iq 9 is plotted on the ordinate.

(17) The solid arrow 51 represents the vector of a reference current of the reference electric machine.

(18) In the case of the reference electric machine, the reference current 51 is applied at a predefined reference rotational speed. The reference phase angle 53 present in this case is the argument of the vector 51. Since, in the case of this reference machine, the angle of the angular position encoder is correct due to the known reference offset, the reference current ensures optimal operation of the reference machine.

(19) A further reference current vector 55 (shown by the dotted line) may optionally be applied at a second reference rotational speed, for example a negative rotational speed. The resultant second argument 57 of this second reference current vector 55 may additionally be used as a second reference phase angle 57 for more accurate determination of the offset.

(20) In an electric machine to be measured, with unknown offset of the angular position encoder, a current 61 is applied at the predefined reference rotational speed. The phase angle 63 present in this case is the argument of the current presented as a short-dash vector 61. Since, in this machine to be measured, the angle of the angular position encoder is inaccurate due to the unknown offset, the current does not ensure optimal operation of the machine to be measured.

(21) Optionally, a further current vector 65 (showed by long dashes) may be applied at the second reference rotational speed, for example a negative rotational speed. The resultant second argument 67 of this second current vector 65 may additionally be used as second phase angle 67 for more accurate determination of the offset.

(22) The difference between the reference phase angle 53 of the reference machine and the phase angle 63 of the machine to be measured at the same reference rotational speed gives the deviation of the offset of the machine to be measured from the reference offset. Since the reference offset of the reference machine is known, the offset may be determined for example as the sum of reference offset and the difference 59 of the phase angle 63 and reference phase angle 53 at the reference rotational speed.

(23) The same calculation may be performed optionally for the second reference rotational speed. A second offset 69 is thus determined from the sum of the reference offset and the difference 69 of the second phase angle 67 and second reference phase angle 57 at the second reference rotational speed. The offset may optionally be corrected by the second offset.

(24) The uniform length of all vectors shows that the absolute values of all currents are identical.

(25) FIG. 4 is a schematic sketch of an exemplary embodiment of a vehicle 103, for example a hybrid vehicle or an electric vehicle, comprising an electric machine 100, in particular an electric motor for driving the vehicle, with an angular position encoder 101, the offset of which is determined by means of the method according to the invention.