# US 2018/0323738 A1 · Stray magnetic field compensation for a rotor position sensor

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- Number: US 2018/0323738 A1
- Document ID: US20180323738A1
- Status: Published application
- Kind: A1
- Application number: 15/771,672
- Filed: 2012-12-02
- Published: 2018-11-08
- Earliest claimed: 2012-12-02
- Assignees: Thyssenkrupp Presta AG; thyssenkrupp AG
- Applicants: Thyssenkrupp Presta AG; thyssenkrupp AG
- Inventors: Roland GÉMESI
- Web page: https://patentgrep.com/patent/US20180323738A1

## CPC

- H02P 21/06: Rotor flux based control involving the use of rotor position or rotor speed sensors
- B62D 5/046: {Controlling the motor}
- G01R 33/0041: {using feed-back or modulation techniques}
- G01R 33/0082: {Compensation, e.g. compensating for temperature changes}
- H02P 6/08: Arrangements for controlling the speed or torque of a single motor (H02P6/10, H02P6/28 take precedence)
- H02P 21/50: {Vector control arrangements or methods not otherwise provided for in H02P21/00- H02P21/36}
- H02P: CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
- B62D: MOTOR VEHICLES; TRAILERS (steering, or guiding on a desired track, of agricultural machines or implements A01B69/00; wheels, castors, axles, increasing wheel adhesion B60B; vehicle tyres, tyre inflation or tyre changing B60C; connections between vehicles of a train or the like B60D; vehicles for use on rail and road, amphibious or convertible vehicles B60F; suspension arrangements B60G; heating, cooling, ventilating or other air treating devices B60H; windows, windscreens, non-fixed roofs, doors or similar devices, protective coverings for vehicles not in use B60J; propulsion plant arrangements, auxiliary drives, transmissions, controls, instrumentation or dashboards B60K; electric equipment or propulsion of electrically-propelled vehicles B60L; power supply for electrically-propelled vehicles B60M; passenger accommodation not otherwise provided for B60N; adaptations for load transportation or to carry special loads or objects B60P; arrangement of signalling or lighting devices, the mounting or supporting thereof or circuits therefor, for vehicles in general B60Q; vehicles, vehicle fittings or vehicle parts not otherwise provided for B60R; servicing, cleaning, repairing, supporting, lifting, or manoeuvring, not otherwise provided for, B60S; brake arrangements, brake control systems or parts thereof B60T; air-cushion vehicles B60V; motor-cycles, accessories therefor B62J, B62K; testing of vehicles G01M)
- G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12)

## Abstract

A method may be used to error compensate a measurement of an electric motor's rotor position in a power steering system of a motor vehicle. The electric motor generates torque for assisting steering of the motor vehicle, and stray magnetic fields of motor currents affect the measurement of the rotor position with a magneto-resistive rotor position sensor. The method may involve calculating at least two compensation values based on a current vector, rotor position, and hardware dependent parameters. The at least two compensation values account for errors in the rotor position measurement due to stray magnetic fields of motor currents. The method may also involve calculating a compensated rotor position signal by subtracting the at least two compensation values of the measured rotor position, as well as transferring the compensated rotor position signal as part of a feed-back loop to a target motor torque determination in the motor control.

## Claims

### Claim at position 1

-9. (canceled)

### Claim 10

A method for error compensating a measurement of a position of a rotor of an electric motor in a power steering system of a motor vehicle, wherein the electric motor generates torque for assisting steering of the motor vehicle, wherein stray magnetic fields of electric motor currents affect the measurement of the rotor position by a rotor position sensor, the method comprising:
measuring the rotor position with the rotor position sensor;
determining a target motor torque based on signals representative of at least a vehicle velocity and a torque applied to a steering wheel;
transferring the target motor torque into target voltages;
transforming the target voltages into a current vector in a rotating reference frame fixed to the rotor of the electric motor;
transforming the current vector into motor currents expressed in a coordinate system fixed to a stator of the electric motor;
calculating at least two compensation values based on the current vector or a current vector transformed from the motor currents into a coordinate system fixed to the rotor, based on the rotor position, and based on hardware dependent parameters, wherein the at least two compensation values account for errors in the measured rotor position due to the stray magnetic fields of electric motor currents;
calculating a compensated rotor position signal by subtracting the at least two compensation values of the measured rotor position; and
transferring the compensated rotor position signal as part of a feedback loop to the determination of the target motor torque.

### Claim 11 (depends on 10)

The method of claim 10 wherein the at least two compensation values are each given for a respective harmonic by a trigonometric function of the rotor position, wherein an amplitude is dependent on a length of the current vector, a phase shift is dependent on an angle of the current vector, and a periodic length is proportional to a number of the respective harmonic.

### Claim 12 (depends on 11)

The method of claim 11 wherein the phase shift includes an electrical offset.

### Claim 13 (depends on 11)

The method of claim 11 wherein the amplitude is dependent on a parameter that accounts for the error in the measured rotor position due to the stray magnetic fields of electrical motor currents and that is linearly dependent on the current vector.

### Claim 14 (depends on 13)

The method of claim 13 wherein the parameter on which the amplitude depends is stored in a look-up table.

### Claim 15 (depends on 13)

The method of claim 13 wherein the parameter's linear dependence on the current vector is constant for a given hardware design of the power steering system.

### Claim 16 (depends on 10)

The method of claim 10 wherein the at least two compensation values account for XB and XA harmonics of the compensated rotor position signal.

### Claim 17 (depends on 10)

The method of claim 10 wherein the XA harmonic=P+1 and the XB harmonic=P−1, wherein P is a number of motor pole pairs of the electric motor.

### Claim 18

An electromechanical motor vehicle power steering mechanism for assisting steering of a motor vehicle by conferring torque generated by an electric motor to a steering mechanism, the electromechanical motor vehicle power steering mechanism comprising:
a magneto-resistive rotor position sensor that measures a position of a rotor of the electric motor;
a steering controller that receives signals representative of at least a vehicle velocity and a torque applied to a steering wheel to determine a target motor torque;
a motor controller that receives the target motor torque from the steering controller and transfers the target motor torque into target voltages;
an inverter that transforms the target voltages into currents in a rotating reference frame fixed to the rotor of the electric motor;
a coordinate transformation that transforms the currents into motor currents expressed in a coordinate system fixed to a stator of the electric motor; and
a compensation unit that calculates a compensated rotor position signal based on the currents or a current vector transformed from the motor currents into a coordinate system fixed to the rotor, based on the rotor position, and based on hardware dependent parameters, wherein the compensated rotor position signal accounts for errors in the measured rotor position due to stray magnetic fields of motor currents, the compensation unit transferring the compensated rotor position signal to the steering controller.