WO2011069904A2

WO2011069904A2 - Method and device for compensating for interference fields of sensor signals in an electrical power steering system

Info

Publication number: WO2011069904A2
Application number: PCT/EP2010/068826
Authority: WO
Inventors: Rainer Wöger; Rainer Biegert
Original assignee: Zf Lenksysteme Gmbh
Priority date: 2009-12-08
Filing date: 2010-12-03
Publication date: 2011-06-16
Also published as: DE102009047633A1; WO2011069904A3; DE102009047633B4

Abstract

The invention relates to a method and devices acting according thereto, in particular a circuit (ESK) generating a compensation signal (KS) by means of a factorized addition of two sinusoidal signals (sin1, sin2). The fact that sinusoidal drive currents (Iu, Iv, Iw) are already available for an electrical power steering system, and that the addition of phase-shifted sinusoidal signals having the same frequency results in a sinusoidal signal having said frequency, is utilized. The signals (sin1, sin2) are multiplied by factors (F1, F2) prior to addition, whereby the phasing of the resulting sinusoidal signal or sum signal is shifted at the output of the adder (A1). Said sum signal is then multiplied by a factor (F3) corresponding to both the amplitude standardization and the adaptation to the interference field, in order to ultimately obtain a sinusoidal compensation signal (KS) having predefinable phasing and a standardized amplitude that is also optimized with respect to the interference field. The compensation signal (KS) is then subtracted from the sensor signal (HS) having the interference.

Description

Method and apparatus for interference field compensation of sensor signals in an electric power steering system

The invention relates to a method for compensation field compensation according to the preamble of claim 1 and an operating according to the method electronic circuit which is connectable to a sensor arrangement for determining an absolute steering angle and / or torque. Furthermore, the invention relates to a control device and an electric power steering system, which are equipped with such a circuit.

Various methods and devices are known from the prior art which evaluate sensor signals generated by sensor arrangements in order to determine the steering angle and / or the torque in the steering line of a power steering system.

The DE 1 0 2007 01 1 675 A1 besch rubs a Sensoranord nu ng in a steering column of a power steering system, two mutually offset by 90 degrees Hall sensors generate sensor signals for determining the steering angle. For this purpose, the Hall sensors are assigned to a common and with respect to a rotation axis radially or frontally arranged magnetic field generator ring having a magnetic north pole and south pole existing pole pair. In this case, each pole is provided with a half sinusoidal magnetization corresponding to a wavelength, wherein the field generator ring consists of a magnetizable material whose magnetization is artificially introduced.

In DE 1 98 18 799 C2, a sensor arrangement is described, which has a rotation angle sensor with two magnetic rings and d rei zugeord Neten sensor elements. To determine a unique angle within a 360 degree full circle, a combination of Hall and MR sensors will be used used, the signals of the Hall sensors are used for area discrimination.

Although the known sensor arrangements provide clear sensor signals, which are evaluated for the determination of the steering angle and / or torque, but it has been shown that the sensor signals are affected by various disturbing influences. As a result, the measured sensor signals can be heavily corrupted. If, for example, such sensor arrangements are used in a polyphase electric power steering system, it is also possible for interference emissions from individual phase currents to occur on the sensor system. An effective

Interference field compensation would be very desirable here.

The object of the invention is to propose a method and then working device for interfering field compensation. In particular, an electronic circuit for r Störfeld compensation to be proposed or in a Sensoranord n ung to achieve a Störfeldkompensierte determination of steering angles and / or torques in such a power steering system.

This object is achieved by a method having features of claim 1 and by devices having the features of the independent claims.

Accordingly, it is proposed to apply to the at least one sensor signal generated by the sensor arrangement a compensation signal which is generated by adding two frequency-identical sinusoidal signals, these signals being derived from drive currents of an electric motor mounted in the electric power steering system. Preferably, two sinusoidal drive currents of a multi-phase induction motor are used. The selection of the two drive currents takes place as a function of which different phase positions the sinusoidal signals (input signals) should have, in order to generate them

Compensation signal (output signal) to achieve the desired phase position. The association is preferably stored in a look-up table. The invention thus utilizes the already existing drive currents of the electric motor to derive two sinusoidal, frequency-equal, but phase-different input signals, from which then by means of addition a compensation signal desired amplitude and phase angle is generated. Since the two input signals (two individual sinusoidal signals) are derived from drive currents which are shifted by a fixed phase, for example by 30 degrees, it is advantageous if the two sinusoidal signals are added in a factorized manner, thus providing a sum signal with one for the compensation to form the desired phase position. By further factoring, the amplitude of the sum signal is normalized to a desired amount. This factored

Sum signal forms the compensation signal, with which the disturbed sensor signal is applied, this is preferably done by the compensation signal is subtracted from the sensor signal to finally obtain a compensated sensor signal.

By accessing the drive currents and the addition of sinusoidal signals derived therefrom, in particular by a factorized or weighted addition, a compensation signal with predeterminable phase position and amplitude can be formed very effectively and with very little computational complexity.

Also proposed are an electronic circuit operating according to the method for connection to a sensor arrangement (sensor system), as well as a control unit equipped therewith for an electric power steering system. In addition, an electric power steering system equipped therewith is proposed.

Advantageous embodiments of the invention will become apparent from the dependent claims.

The invention will now be described by way of example and with reference to the accompanying drawings which show the following schematic views: Fig. 1 shows the structure of an electric power steering system, in which a circuit according to the invention is installed;

Fig. 2 shows the structure of the circuit which is connected to a sensor and performs an interference field compensation to the sensor signal;

Fig. 3 shows a flow chart for a method according to the invention, which executes the circuit for interference field compensation;

Fig. 4 relates to a step of the method and illustrates an addition or superposition of two equal frequency sinusoidal signals to a sinusoidal sum signal;

Fig. 5 refers to a further step of the method and

illustrates the dependence of the phase position of the sum signal on a factorization or weighting of the sine signals;

Fig. 6 refers to a further step of the method and

illustrates the dependence of the amplitude of the sum signal on a factorization of the sine signals;

Fig. 7 relates to a further step of the method and

illustrates the normalization of the sum signal to a certain amplitude;

Fig. 8 relates to a further step of the method and

illustrates the selection of the sinusoidal signals used for the interference field compensation in a three-phase system (three-phase motor).

He and Fig. Power Steering 1 (also known as electric power steering) for a vehicle in which a rack 2 arranged in an axially displaceable manner is arranged in a steering housing. In this rack 2, a pinion 3 meshes a, which is operatively connected to a steering shaft or steering column 4, via which the steering force applied by the driver is transmitted.

To support this manually applied force, an electric motor EM is provided, which is controlled by means of an electronic control unit ECU and a downstream power unit PU. The electric motor EM is, for example, a brushless DC motor (BLDC motor), which is designed as a DC-operated multi-phase AC motor (AC motor) and acts on the rack 2 via a pinion to assist the servo. For the control of the motor EM, a control unit SAN upstream of the control unit ECU is used, which, for. B. magento-resistive sensors and / or Hall sensors may include, in particular, detect the rotor position of the electric motor and transmitted as a sensor signal HS to the control unit ECU or to an electrical circuit located therein ESK. Preferably, the sensor assembly is in proximity to the power lines through which the drive currents flow to the electric motor.

In the example shown in FIG. 2, the control signals CS are fed to the power stage PU upstream of the electric motor EM, which is also referred to herein as a ballast and contains controllable power semiconductors. These then generate e.g. three drive currents lu, Iv and Iw for the electric motor EM, so for each phase a sinusoidal drive current (see also Fig. 8). To control the electric motor EM, the sensor signals HS should be as accurate as possible and undisturbed.

However, the invention is based on the recognition that the sensor signals coming from the sensor arrangement SAN or the sensors mounted therein (eg MR or Hall) can be severely disturbed. Investigations by the inventor have shown that, in particular, nth-order disturbances occur in the sensor signal HS, where n corresponds to the pole-pair number of the electric motor EM. In order to propose an effective interference field compensation, an electronic circuit ESK is used in the control unit ECU, which will be described in more detail below. The invention is also based on the knowledge that the required compensation signal KS can be generated by superposition of two sinusoidal signals, for which purpose it is possible to make use of the already existing sinusoidal signals with which the electric motor is energized, that is to say that the already existing drive currents can be used.

2 shows the structure of an arrangement comprising a sensor or sensor array SAN and an associated electronic circuit ESK for the interference field compensation of sensor signals generated by the sensor. Before the circuit ESK is described in greater detail, the sensor system SAN and the sensor signals (for example HS) which it generates, which should be susceptible to interference, will first of all be described.

The sensor SAN is arranged on the rotor shaft of the electric motor and has a magneto-resistive sensor and two Hall sensors, which are each offset by 90 degrees. On the shaft itself, a field sensor ring is arranged radially or frontally, which has a pole pair with a magnetic north pole and a magnetic south pole. This may be e.g. to act a magnetized disc (magnetic tablet). By means of the sin / cos evaluation method known from the prior art, the so-called quadrature method, an associated angle value can be determined from the analog signals of the Hall sensors. With the magneto-resistive sensor alone, which can only detect the magnetic field strength, but not the field direction, an absolute measurement of the angle would only be possible in the range of 0-180 degrees with this arrangement. This limitation is overcome by the use of the Hall sensors, which also controls the field direction, i. H . the polarity of a detected magnetic pole can be detected. By an evaluation of all sensor signals, an unambiguous determination of the absolute angle can be performed. Such a sensor arrangement SAN is known per se (see DE 198 18 799 C2) and will therefore not be described further here.

It has now been shown that in particular the sensor signals HS coming from the Hall sensors are falsified or disturbed by interfering radiation could be. A compensation according to the invention is described below by way of example on the generated sensor signal HS. For compensation measures are proposed, which are also illustrated by the other figures. Reference is made in particular to FIG. 3, which shows a flow diagram for a method for interference field compensation, according to which the circuit ECU operates or is designed.

As can be seen with reference to FIG. 2, two of the drive currents, in this case Iu and Iv, are fed into the circuit ESK, each of which represents a sine signal sin1 or sin2. This is done in step 1 10 of the method 100 (see Fig. 3). The use of own sine generators can therefore be dispensed with. The sinusoidal signals derived from the drive currents Iu and Iv have the same frequency f0, but have different phase angles (see also FIG. In the consideration of the fourth order of a three-phase system shown here, the sin ussignals u m obtained from the drive currents are each shifted 30 degrees to each other. If e.g. used the signals lu and Iv, it can be generated by the circuit ESK a compensation signal KS whose phase angle is between 0 and 30 degrees (range 1 in Fig. 8). If the phase position of KS or HS 'are in the range between 30 and 60 degrees, the signals Iv and Iw should be supplied to the circuit ESK, etc .. In order to obtain the desired phase position for the compensation signal KS, so is a selection of made two drive currents, which are assigned to the corresponding area (see Fig. 8), ie whose zero crossings are at the beginning or at the end of the respective range. The table TAB is used for this. Depending on the area in which the desired phase angle (reference angle of HS 'or KS) should lie, the two matching drive currents are selected on the basis of this assignment table TAB, and consequently the two matching sinusoidal signals sin1 and sin2 are provided.

Referring to FIG. 4, the superimposition of two frequency-identical sinusoidal signals (sin1 and sin2) carried out by the circuit ESK to a resulting sinusoidal signal (compensation signal KS) is illustrated. For example, the signal sin1 has the phase position zero and the signal sin2 is leading and, for example, around -60 Degrees shifted. Addition of both signals results in a sum signal sin1 + sin2 which also corresponds to a sinusoidal signal which has the same frequency but whose amplitude and phase position result from the superimposition of the two signals sin1 and sin2. The amplitude can be greater than any single amplitude. The phase position, in turn, can assume any value between the phase positions of the individual signals, that is to say between -60 and 0 degrees in the example shown. I n the F ig. 4, the amplitudes of the input signals sin1 and sin2 are normalized to the value one. Due to the superimposition, a phase angle of -30 degrees results for the sum signal sin1 + sin2. If the input signals (individual signals) sin1 and sin2 are each multiplied by a pre-factor F1 or F2 and then added together, the following applies to the phase position of the resulting sum signal:

(pres = F1 * (psinl + F2 * (psin2 (formula 1)

This means that even with defined phase positions for the individual signals sin1 and sin2 by factoring or weighting of the individual signals, a resulting signal can be generated whose resulting phase position lies between the defined phase positions of the individual signals. Thus, the factors F1 and F2 correspond to shift factors because they shift the resulting

The factorization is realized in the circuit ESK by corresponding multipliers M1 and M2, respectively (see Fig. 2 and step 120 in Fig. 3) For simplicity, the factors F1 and F2 are given so that their sum always is equal to one, so that is: F1 + F2 = 1.

Thus, only one of the factors, e.g. F2 be specified as a shift factor. The relationship between shift factor F2 and the resulting phase angle is shown in FIG. It shows a region-wise cosinusoidal dependence according to the following formula:

(pres = (COS (180 ° + F2 * 180 °) + 1) * ((psin2 - (psinl) 12 (Formula 2) By converting the formula, it is therefore possible to carry out a calculation of F2 for a desired phase position (pres.) The addition of the factorized individual signals results at the output of the first adder (see A1 in Fig. 2 and step 130 in Fig. 3). the following resulting sinusoidal signal:

Sinres = (1-F2) * Sin1 + F2 * Sin2 (Formula 3)

It should be noted that the variation of the amplitude does not depend linearly on the angular displacement, but follows a particular function, which is shown in Fig. 6 and which also can not be approximated by a trigonometric function. Therefore, the following approach is used to determine the amplitude:

Since a sinusoidal signal has its maximum function value at 90 degrees, only the function value at the corresponding location needs to be calculated to determine the value of the amplitude. It should be noted that the signal whose amplitude is to be calculated to be shifted by any angle between the phase angles of the individual signals sin1 and sin2. Thus, the amplitude can be calculated using the following formula:

A = (1-F2) ^* sin1 (P1) + F2 ^* sin2 (P1)

= (1 -F2) ^* sin (<p1 + 90 ° + Versch ^* Ord) + F2 ^* sin ((p2 + 90 ° + Versch ^* Ord) = (1-F2) ^* cos ((p1 + Versch ^* Ord) + F2 ^* cos ((p2 + Versch ^* Ord)

(Formula 4)

FIG. 7 shows these relationships using the example of a function value to be calculated. By means of the calculated amplitude A, the signal can be normalized such that its amplitude has the value one for all shifts. The inverse value 1 / A corresponds to the normalization factor F3. The normalization takes place in the multiplier M2 (see Fig. 2) or in step 140 (see Fig. 3). This results in the following formula: Sinres = ((1-F2) ^* Sin1 + F2 ^* Sin2) ^* F3 (Formula 5)

With the aid of this formula, it is possible, by means of two sinusoidal signals with the amplitude 1 and an arbitrary phase position φ (φΐ <φ <φ 2) which are phase-shifted with one another, to produce a resulting sinusoidal

Compensation signal KS = sinres to produce the desired phase position

(pres and a desired maximum amplitude Amax = F3.) The resulting

Compensation signal KS is then subtracted from the noisy sensor signal HS, resulting in the suppressed sensor signal HS 'results (see Fig.2 and step 150 in Figure 3).

In multi-phase systems (e.g., three-phase motors), due to the constraint (φΐ <φ <φ2), it may be necessary to first select the appropriate phase currents for compensation.

This is described below using the example of a fourth-order interference signal in a three-phase system: this means that a fourth-order error is to be compensated in a three-phase system and therefore the phase difference between the individual sine signals is 30 degrees (= 360 degrees / 3/4) ,

Due to the fact that it is a fourth-order signal, the phase angle can be limited by subtracting all multiples of 90 degrees to a range of 0 to 90 degrees.

Since only a range of 30 degrees can be covered with a fixed selection of two phase currents used for compensation, an area distinction must first be made. FIG. 8 and the table TAB below illustrate this. Depending on the area in which the determined phase angle is, the corresponding Phase currents used for signal generation (see also TAB in Fig. 2 and step 1 10 in Fig. 3).

The assignment is taken from the following table TAB:

After the area discrimination, the signal to be generated need only be shifted in a range of 0 to 30 degrees. The necessary parameters (shift factor VF = F2 and normalization factor NF = F3) can be calculated according to the above formulas.

Thus, with the described measures and formulas, an arbitrarily shifted sinusoidal signal having the same order as that of the generated sinusoidal signals sin1 and sin2 can be generated, wherein the amplitude can be normalized to one.

In order to be able to compensate the interference field influences by the field-causing currents, the relationship between the amplitude of the phase current and the amplitude of the interference signal must be determined. This can e.g. metrologically or by means of a simulation. The relationship between phase current and noise amplitude is determined by the

Störfelderinflussfaktor SF represents. If this is multiplied by the formula 5, then the following formula results for the compensation of the interference signal of the fourth order, wherein sin1 and sin2 are selected from the aforementioned table TAB:

KS = ((1 -VF) ^* sin1 + VF ^* sin2) ^* NF ^* SF

= ((1-F2) ^* sin1 + F2 ^* sin2) ^* F3, where F3 = NF ^* SF (Formula 6)

Accordingly, only three multiplications and one addition are required for the generation of the compensation signal KS (see also Fig. 2). The so generated Compensation signal KS then only needs to be subtracted from the disturbed sensor signal HS.

In other words, it is proposed that a compensation signal KS be generated essentially by a factorized addition of two sinusoidal signals sin1 and sin2. It is exploited that the addition of phase-shifted sine signals with the same frequency, again give a sinusoidal signal with this frequency. If the signals sin1 and sin2 are multiplied by factors before addition, here with F1 or F2, then the phase position of the resulting sine signal (at the output of the adder A1) can be shifted. If this sinusoidal signal is then multiplied by a factor F3, the result is a sinusoidal compensation signal KS with a predefinable phase position and with a normalized amplitude that has been optimized for the interference field.

Overall, only three multiplications and two additions are needed for compensation. This, in turn, means much less computing power than, for example, compensation by signal superposition or vector addition. In addition, because the currents causing the interference field are used directly here as a reference variable in the compensation, there is the advantage of a direct coupling between cause and effect. As a result, the susceptibility of the compensation itself is reduced.

In the circuit ESK shown in FIG. 2, three multiplication stages and two adder stages are shown by way of example. The realization may e.g. be implemented by an application-specific integrated circuit (ASIC), which is integrated approximately in the control unit ECU for the engine of an electric steering. Alternatively, the invention may also be implemented by means of a programmed microcontroller or the like.

In summary, a method and devices operating thereafter are proposed, in particular a circuit ESK which generates a compensation signal KS by a factorized addition of two sinusoidal signals sin1, sin2. It is exploited that in an electric power steering system Sinusoidal drive currents lu, Iv, Iw are already available and that the addition of phase-shifted sine signals with the same frequency, again results in a sine signal with this frequency. The signals sin1, sin2 are multiplied by factors F 1, F2 prior to addition, whereby the phase position of the resulting sine signal or sum signal at the output of the adder A1 is shifted. This sum signal is then multiplied by a factor F3, which corresponds to both the amplitude normalization and adaptation to the interference field, in order finally to obtain a sinusoidal compensation signal KS with a predefinable phase position and with normalized and optimized to the interference field amplitude. The compensation signal KS is then disturbed by the

Sensor signal HS subtracted.

LIST OF REFERENCE NUMBERS

SAN sensor arrangement

H1, H2 Hall sensors

MR magnetoresistive sensor

N, S north or south pole (field ring)

HS sensor signal

KS compensation signal

HS 'interference field compensated sensor signal

ECU control unit with:

ESK circuit for compensation

MEM memory for table TAB

M1, M2, M3 multipliers for factorization F1, F2 and F3

A1, A2 adder

100 method for interference field compensation

1 10 Step for generating sinusoidal signals

120 step to factorize the sinusoidal signals (shift factor)

130 step for forming a sum signal

Addition of the factorized sine wave

140 step for factoring the sum signal (normalization factor) to form the compensation signal

150 step to compensate by subtracting the

Compensation signal from the sensor signal

Claims

claims

1 . Method (100) for interference field compensation in a sensor signal (HS) generated by a sensor arrangement (SAN) for determining a steering angle and / or torque in a steering line of a (4) with a

Electric motor (M) equipped electric power steering system (1) is generated, characterized in that

the sensor signal (HS) generated by the sensor arrangement (SAN) is supplied with a compensation signal (KS) which is generated by adding (130) two sinusoidal signals (sin1, sin2) of equal frequency, the signals (sin1, sin2) being composed of drive currents ( lu, Iv, Iw) of the electric motor (EM) are derived.

2. Method (100) according to claim 1, characterized in that in a first step (110) a first sinusoidal signal (sin1) and a second sinusoidal signal (sin2) are generated from two drive currents (lu, Iv), the same Frequency (fO), but different phase angles (φ1, φ2) have.

3. The method (100) according to claim 1 or 2, characterized in that the electric motor (EM) is a polyphase n-pole induction motor, which is operated with k sinusoidal drive currents (lu, Iv, Iw), each by 2π / (k ^* n) are out of phase with each other.

4. The method (100) according to claim 3, characterized in that the

Generation of the two sinusoidal signals (sin1, sin2) as a function of which different phase positions (φ1, φ2) they should have, two of the sinusoidal drive currents (lu, Iv) are used, in particular by means of a look-up table (TAB)

be used.

5. The method (100) according to any one of claims 2 to 4, characterized

characterized in that in a second step (120) the sinusoidal Signals (sin1, sin2) are factohosiert by the first and second signals are multiplied by a respective first and second factor (F1, F2), wherein the sum of the factors gives the value one.

6. Method (100) according to claim 5, characterized in that in a third step (130) the factorized signals are added to a sinusoidal sum signal.

7. Method (100) according to claim 6, characterized in that the

Factors (F1, F2) correspond to shift factors and are determined so that the sinusoidal sum signal is one for the

Interference compensation desired phase position ((pres) has, wherein this phase position between the phase positions (φ1, φ2) is located.

8. Method (100) according to claim 6 or 7, characterized in that in a fourth step (140) the sinusoidal sum signal is factored by multiplying the sum signal by a third factor (F3), resulting in the compensation signal (KS) ,

9. Method (100) according to claim 8, characterized in that the third factor (F3) corresponds to a normalization factor ....

10. The method (100) according to claim 8 or 9, characterized in that in a fifth step (150), the sensor signal (HS) with the

Compensation signal (KS), which corresponds to the factorized sum signal, is applied.

1 1. Method (100) according to claim 10, characterized in that the sensor signal (HS) with the compensation signal (KS) is applied by the compensation signal (KS) is subtracted from the sensor signal (HS), whereby an interference field-compensated sensor signal (HS ') results.

12. Electronic circuit (ESK) for interference field compensation in a sensor signal (HS), which generates a sensor arrangement (SAN) for determining a steering angle and / or torque in a steering column (4) of an electric power steering system (1), which is connected to an electric motor ( M), characterized in that

the circuit (ESK) generates a compensation signal (KS) by means of addition (130) of two sinusoidal signals (sin1, sin2) of equal frequency by the circuit (ESK) producing the sinusoidal signals (sin1, sin2)

Drive currents (lu, Iv, Iw) of the electric motor (EM) derived, and that the circuit (ESK), the signal generated by the sensor array (SAN) sensor signal (HS) with the compensation signal (KS) applied.

13. Control unit (ECU) for an electric power steering system (1), wherein the control unit (ECU) an electronic circuit (ESK) for

Interference compensation in a sensor signal (HS), which generates a sensor arrangement (SAN) for determining a steering angle and / or torque in a steering line (4) of the electric power steering system (1), which is equipped with an electric motor (M), characterized that

14. Electric power steering (1) equipped with an electric motor (EM)

equipped with a sensor arrangement (SAN) which generates at least one sensor signal (HS) for determining a steering angle in a steering line (4) of the power steering system (1), and the electronic circuit (ECU) connected to the sensor arrangement (SAN). for interference field compensation in the sensor signal (HS), characterized in that the circuit (ECU) generates a compensation signal (KS) by means of addition (130) of two equal-frequency sinusoidal signals (sin1, sin2) by the circuit (ECU) outputting the sinusoidal signals (sin1, sin2)

Driving currents (lu, Iv, Iw) of the electric motor (EM) derived, and that the circuit (ECU) generated by the sensor assembly (SAN)

Sensor signal (HS) with the compensation signal (KS) acted upon.