# US 9,438,157 B2 · Method for operating a multiphase electric machine and corresponding multiphase electric machine

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- Number: US 9,438,157 B2
- Document ID: US9438157B2
- Status: Granted
- Kind: B2
- Application number: 14/778,817
- Filed: 2014-03-14
- Published: 2016-02-11
- Granted: 2016-09-06
- Earliest claimed: 2013-03-22
- Assignees: Audi AG
- Applicants: Audi AG
- Inventors: Martin Adam; Marcel Kuhn
- Web page: https://patentgrep.com/patent/US9438157B2

## CPC

- H02P 21/18: Estimation of position or speed
- H02P 6/14: Electronic commutators
- H02P 6/16: Circuit arrangements for detecting position
- H02P 6/182: using back-emf in windings
- H02P 21/22: Current control, e.g. using a current control loop
- H02P: CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS

## Abstract

In a method for operating a multiphase electrical machine, which includes a rotor and a rotary encoder operatively connected to the rotor, an actual rotational angle of the rotor is determined from a measured rotational angle determined by means of the rotary encoder and a rotational angle offset. To determine the rotational angle offset the rotor is brought to a specific rotational speed and then an active short circuit of the electrical machine is initiated, wherein an actual current vector is determined, using a dq-transformation, from the current intensities of the currents flowing in at least two of the phases of the electrical machine and the measured rotational angle determined by means of the rotary encoder, and wherein the rotational angle offset is calculated from the actual current vector and a reference current vector.

## Claims

### Claim 1

A method for operating a multiphase electric machine, having a rotor and a rotary encoder operatively connected with the rotor, comprising:
bringing the rotor to a defined rotational speed;
measuring a measured rotation angle of the rotor with the rotary encoder,
inducing an active short circuit of the electric machine;
measuring current strengths of currents that flow in at least two phases of the electric machine in the induced active short circuit;
determining an actual current vector from the current strengths and the measured rotation angle by using a dq-transformation;
calculating a rotation angle offset from the actual current vector and a reference current vector; and
determining an actual rotation angle of the rotor as a function of the measured rotation angle and the rotation angle offset.

### Claim 2 (depends on 1)

The method of claim 1, wherein the actual current vector is determined in a first direction of rotation of the rotor and the reference current vector is determined analogous to the actual current vector in a second direction of rotation that is opposite to the first direction of rotation.

### Claim 3 (depends on 1)

The method of to claim 1, wherein the rotation angle offset is determined by adding an angle of the reference current vector and a differential angle, said differential angle corresponding to half of an angular difference between the actual current vector and the reference current vector.

### Claim 4 (depends on 1)

The method of claim 1, wherein the rotation angle offset is determined with the equation:
θ
Offset
=
1
2
⁢
arctan
⁡
(
I
1
,
q
⁢
I
2
,
d
-
I
1
,
d
⁢
I
2
,
q
I
1
,
d
⁢
I
2
,
d
-
I
1
,
q
⁢
I
2
,
q
)
+
arctan
⁡
(
I
2
,
q
I
2
,
d
)
-
180
⁢
°
wherein I1,q is a q-component and I1,d is a d-component of the actual current vector, and I2,q is a q-component and I1,d a d-component of the reference current vector.

### Claim 5 (depends on 1)

The method of claim 1, wherein the reference current vector is determined from stored reference data in dependence on the rotational speed of the rotor.

### Claim 6 (depends on 1)

The method of claim 1, wherein the rotation angle offset is determined by subtracting the angle of the actual current vector and the angle of the reference current vector.

### Claim 7 (depends on 1)

The method of claim 1, wherein the rotation angle offset is determined with the equation
θ
Offset
=
arctan
⁡
(
I
2
,
q
I
2
,
d
)
-
arctan
⁡
(
I
1
,
q
I
1
,
d
)
wherein I1,q is a q-component and I1,d is a d-component of the actual current vector and I2,q is a q-component and I2,d a d-component of the reference current vector.

### Claim 8 (depends on 1)

The method of claim 1, wherein the rotation angle offset is determined in dependence on a temperature.

### Claim 9 (depends on 1)

The method of claim 1, further comprising correcting the rotation angle offset with a correction parameter, said correction parameter being determined with the relationship
k
⁡
(
ω
,
ϑ
)
=
arctan
⁡
(
ω
⁢
⁢
L
S
⁡
(
R
Ref
-
R
S
⁡
(
ϑ
)
)
R
Ref
⁢
R
S
⁡
(
ϑ
)
+
ω
⁢
⁢
L
S
2
)
wherein ω is an angular velocity of the rotor, LS is a stator inductivity, RRef is reference resistance and RS is an actual resistance of the stator.

### Claim 10

A multiphase electric machine, comprising:
a rotor and a rotary encoder operatively coupled with the rotor, said electric machine being configured
to bring the rotor to a defined rotational speed;
to measure a measured rotation angle of the rotor with the rotary encoder,
to induce an active short circuit of the electric machine;
to measure current strengths of currents that flow in at least two phases of the electric machine in the induced active short circuit;
to determine an actual current vector from the current strengths and the measured rotation angle by using a dq-transformation;
to calculate a rotation angle offset from the actual current vector and a reference current vector; and
to determining an actual rotation angle of the rotor as a function of the measured rotation angle and the rotation angle offset.

### Claim 11 (depends on 1)

The multiphase electric machine configured for implementing the method of claim 1.