WO2012172321A1 - Measurement of motor rotor position or speed - Google Patents

Measurement of motor rotor position or speed Download PDF

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Publication number
WO2012172321A1
WO2012172321A1 PCT/GB2012/051323 GB2012051323W WO2012172321A1 WO 2012172321 A1 WO2012172321 A1 WO 2012172321A1 GB 2012051323 W GB2012051323 W GB 2012051323W WO 2012172321 A1 WO2012172321 A1 WO 2012172321A1
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WO
WIPO (PCT)
Prior art keywords
circuit
signals
motor
input signals
signal
Prior art date
Application number
PCT/GB2012/051323
Other languages
French (fr)
Inventor
Peter Geoffrey Scotson
Original Assignee
Trw Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Trw Limited filed Critical Trw Limited
Priority to US14/126,122 priority Critical patent/US9989384B2/en
Priority to BR112013032059A priority patent/BR112013032059A2/en
Priority to CN201280029433.9A priority patent/CN103703377B/en
Priority to EP12745711.7A priority patent/EP2721420B1/en
Publication of WO2012172321A1 publication Critical patent/WO2012172321A1/en

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
    • G01D5/12—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means
    • G01D5/243—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the phase or frequency of ac
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
    • G01P3/00—Measuring linear or angular speed; Measuring differences of linear or angular speeds
    • G01P3/42—Devices characterised by the use of electric or magnetic means
    • G01P3/44—Devices characterised by the use of electric or magnetic means for measuring angular speed
    • G01P3/48—Devices characterised by the use of electric or magnetic means for measuring angular speed by measuring frequency of generated current or voltage
    • G01P3/481—Devices characterised by the use of electric or magnetic means for measuring angular speed by measuring frequency of generated current or voltage of pulse signals
    • G01P3/489—Digital circuits therefor
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R25/00—Arrangements for measuring phase angle between a voltage and a current or between voltages or currents
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P23/00—Arrangements or methods for the control of AC motors characterised by a control method other than vector control
    • H02P23/22—Controlling the speed digitally using a reference oscillator, a speed proportional pulse rate feedback and a digital comparator

Definitions

  • This invention relates to a measurement circuit for, and a method of, measuring at least one of the rotational position and rotational speed of the rotor of an electric motor, and to related motor control circuits and electric power assisted steering systems.
  • the permanent magnet synchronous motor In motor control, in order to correctly control the operation of the motor, it is often required to be able to measure the position of the motor rotor, for example in order to switch the current supply to different phases of a multiple-phase motor.
  • One motor commonly used in EPAS systems is the permanent magnet synchronous motor. This comprises a plurality of permanent magnets mounted on the motor rotor, with a plurality of phase windings surrounding the rotor to form the stator. By cyclically energising the phase windings, the rotor can be forced to rotate.
  • a measurement circuit for measuring at least one of the rotational position and rotational speed of the rotor of an electric motor, the circuit comprising: • first and second inputs for receiving first and second input signals which vary cyclically with the rotational position of the rotor, the first and second input signals at the first and second inputs varying in quadrature with each other;
  • the observer circuit is arranged to generate estimates indicative of the frequency and phase of the first and second input signals
  • phase detector circuit is arranged to determine the phase difference between first and second estimated signals varying cyclically and at the frequency indicated by the estimates with a phase difference dependent on the phase difference indicated by the estimates, the first and second estimated signals varying in quadrature with each other on the one hand and the first and second input signals on the other by adding a multiplicative combination of the first input signal with the first estimated signal to a multiplicative combination of the second input signal with the second estimated signal to result in a sum signal dependent upon the phase difference;
  • the circuit may further comprise a velocity estimation circuit, which is arranged to take the first and second input signals and to output a velocity signal indicative of the rotational speed of the motor rotor by determining the rate of change of one of the first and second input signals and dividing the rate of change by the other of the first and second input signals.
  • the velocity determining circuit may be arranged such that the first or second input signal used to divide the rate of change is the larger of the first and second input signal, so as to avoid errors due to dividing by a number clos e to zero, or an error due to dividing by zero itself.
  • the observer circuit may be arranged so as to generate the estimates based upon the phase difference and the output of the velocity determining circuit.
  • the observer circuit may be arranged to determine the first and second estimated signals based upon its estimates. As such, by making the estimates depend upon the velocity estimate, the precision with which the circuit will follow the actual velocity and/or position of the rotor as the velocity changes has been found to improve over prior art phase lock loops, which merely measure the phase difference.
  • the circuit may further comprise a normalisation circuit, arranged so as to normalise the first and second input signals.
  • the amplitude of the signals is not particularly important (only the phase and frequency), and so by normalising the signals, any deleterious effects of amplitude variation can be avoided.
  • the normalisation circuit may be arranged to divide each of the first and second signals by the square root of the sum of the squares of the first and second input signals; given that the first and second signals are cyclically varying in quadrature, this divisor is likely to represent the amplitude of each of the signals, and so result in a normalised amplitude of unity.
  • the first and second signals may be indicative of the inductance of the motor, and as such may depend upon or be the derivative of the current flowing at least one phase winding of the motor.
  • ⁇ a sensor arranged to output first and second input signals, which vary cyclically with the rotational position of the rotor, to the first and second inputs of the measurement circuit;
  • the motor control circuit is arranged so as to vary the output dependent upon the estimates output by the measurement circuit.
  • a third aspect of the invention there is provided a combination of an electric motor having a rotor and the motor control circuit of the second aspect of the invention arranged so as to control the motor, with the sensor of the motor control circuit being arranged so as to sense the rotational position of the rotor.
  • an electric power assisted steering system comprising a steering wheel, a steering mechanism which operatively couples the steering wheel to road wheels of a vehicle, a electric motor being arranged so as to apply in use a force to part of the steering mechanism, a torque sensor which, in use, provides a torque signal indicative of the torque carried by part of the steering mechanism and a motor control circuit arranged to control the motor by generating, in use, a current signal indicative of the current to be applied to the electric motor in accordance with the second aspect of the invention.
  • a method of measuring at least one of the rotational position and rotational speed of the rotor of an electric motor comprising:
  • the method may further comprise the step of estimating the velocity of the motor rotor by determining the rate of change of one of the first and second input signals and dividing the rate of change by the other of the first and second input signals.
  • the method may comprise determining which of the first or second input signal is the larger and using the larger of the first and second input signals to divide the rate of change, so as to avoid errors due to dividing by a number close to zero, or an error due to dividing by zero itself.
  • the method may comprise estimating at least one of the rotational position and the rotational speed of the motor rotor based upon the phase difference and the output of the velocity determining circuit. As such, by making the estimates depend upon the velocity estimate, the precision with which the circuit will follow the actual velocity and/or position of the rotor as the velocity changes has been found to improve over prior art phase lock loops, which merely measure the phase difference.
  • the motor may be a permanent magnet motor, typically a permanent magnet synchronous motor.
  • Figure 1 shows an electric power assisted steering (EPAS) system having a measurement circuit according to an embodiment of the invention
  • Figure 2 shows a cross section through the motor of the EPAS system of
  • Figure 3 shows schematically the function of the measurement circuit of the EPAS system of Figure 1 ;
  • Figure 4a shows a graph of estimated and actual rotor position in a test procedure carried out according to the embodiment of Figure 1 ;
  • Figure 4b shows a graph of the difference between the estimated and actual rotor position of Figure 4a.
  • FIG 4c shows the current applied to the motor in the test procedure of Figure 4a.
  • An electric power assisted steering assembly is illustrated in Figure 1 of the accompanying drawings.
  • the apparatus comprises an electric motor 1 which acts upon a drive shaft 2 through a gearbox 3 of the rack and pinion type.
  • the drive shaft terminates with a worm gear 4 that co-operates with a wheel provided on a portion of a steering column 5 or a shaft operatively connected to the steering column.
  • the steering column carries a torque sensor 6 that is adapted to measure the torque carried by the steering column. This torque is produced by the driver turning the steering wheel, either to turn a corner or to counter pull of the vehicle to one side.
  • the output signal T from this sensor is fed to a signal processing means in the form of a signal processor 7, which takes the torque input signals and outputs commands to a drive circuit for the motor 9 over line 8a.
  • the drive circuit in turn returns a signal indicative of the current flowing in the windings of the motor 9 over line 8b.
  • the motor 9 is a three phase brushless motor, which comprises a rotor 12 having six embedded magnets 14 within it which in this instance are arranged so as to provide six poles which alternate between north and south around the rotor.
  • a stator 16 comprises a nine slot copper wound element having three groups of three teeth 18A, 18B, 18C each group of teeth having a common winding (example shown as 13) forming a respective phase. There are therefore three electrical cycles in each full rotation of the rotor 12, as the rotor and its magnets 14 have threefold circular symmetry, meaning that each 120 degree rotation of the rotor leaves it in an equivalent position.
  • the signal processor 7 is provided a measurement circuit 19 with the functionality shown in Figure 3 of the accompanying drawings.
  • the measurement circuit 7 is provided with a di/dt sensor 20, which takes the currents flowing through the motor (typically through a ground return in common to each of the phases) and differentiates them, in order to arrive at two cyclically varying indications of the rate of change of current. These signals are indicative of the inductance of the phase windings at that particular instant.
  • the di/dt sensor 20 outputs the two signals As t + ⁇ 1 ) and A cos ⁇ t + ⁇ 1 ) to a normalisation circuit 22.
  • the two signals are normalised to an amplitude of unity. This is done by dividing each of the signals by the square root of the sum of the squares of the two signals; this divisor will always be A as follows:
  • the output of the normalisation circuit 22 is passed to a phase detector circuit 24. This determines the phase difference between estimates of the phase difference and frequency calculated by an observer circuit 28 discussed below and the normalised signals from the normalisation circuit 22.
  • the output of the normalisation circuit is also passed to a velocity detector 26. This determines the speed C0 1 of the motor by differentiating one of the normalised signals and dividing the differentiated signal by the other. Taking, for example, the sine component as the component to be differentiated:
  • the phase difference circuit outputs a value that is dependent upon the sine of the phase difference (measured in radians).
  • the system uses the small angle approximation to avoid needing to carry out an inverse sine operation; when the phase difference is small, the sine of the phase difference will be approximately equal to the phase difference; as the difference increases, the error in the phase difference will increase, but will still have the same sign and will therefore cause the estimate to be corrected in the correct direction.
  • the output of the phase difference circuit is used directly as the phase difference below.
  • the estimates C0 2 and ⁇ are updated in two ways: firstly, in accordance with the physical dynamics of a rotating motor; and secondly according to the phase difference and speed measurement estimate already determined.
  • the position ⁇ is increased or decreased in proportion to the current speed estimate ⁇ 3 ⁇ 4.
  • ⁇ + 1) ⁇ ( + ⁇ 12 ⁇ 2 ( ⁇ ) + ⁇ 11 ⁇ + & 12 ( ⁇ 1 - ⁇ 2 ( ⁇ ))
  • ⁇ is the phase difference
  • a l2 is the proportion of the current speed estimate, usually set equal to
  • b u is the proportion of the phase difference used to update the position estimate, usually set less than one.
  • b 12 is the porportion of the measured speed estimate used to update the position estimate, usually set less than the time between samples
  • the speed estimate can be computed in a similar way:
  • b 22 is the proportion of the measured speed estimate used to update the observer speed estimate
  • the values of the a and b coefficients can be adjusted to control and adapt the performance of the observer as desired.
  • the estimated values of the motor rotor rotational position ⁇ and the rotor speed C0 2 are then output, and can be used in the signal processor 7 in order to control the switching of the phases 13 in any suitable manner.
  • Figure 4c shows the current applied to the phases of a test motor over an approximately 37 second long test run.
  • Figure 4a shows both the actual motor position (measured by a suitable position encoder, the trace shown as "enc") and the estimated value ⁇ determined by the observer circuit ("est"). From Figure 4a, the two traces appear practically indistinguishable.
  • Figure 4b shows the difference between the actual and estimated measurements, and as such represents the difference between the "enc" and “est” traces of Figure 4a. This shows that there is some error in the measurement, but it is generally at a low level, but increasing as the current applied to the motor increases.

Abstract

Circuit for measuring the rotational position and/or speed of the rotor of an electric motor, comprising: first and second inputs receiving first and second input signals varying cyclically with the rotational rotor position and in quadrature with each other; a phase detector circuit; and an observer circuit generating estimates indicating the frequency and phase of the input signals; the first and second estimated signals varying cyclically but in quadrature with each other and having the same frequency; whereby the phase detector circuit determines the phase difference between the first and second estimated signals on the one hand and the first and second input signals on the other by adding a multiplicative combination of the first input signal with the first estimated signal to a multiplicative combination of the second input signal with the second estimated signal to result in a sum signal dependent upon the phase difference; and whereby the observer circuit varies the estimates dependent upon the sum signal.

Description

MEASUREMENT OF MOTOR ROTOR POSITION OR SPEED
This invention relates to a measurement circuit for, and a method of, measuring at least one of the rotational position and rotational speed of the rotor of an electric motor, and to related motor control circuits and electric power assisted steering systems.
The field of control of electric motors, such as may be used in such fields as driving electric power assisted steering (EPAS) systems, has been well explored in the prior art.
In motor control, in order to correctly control the operation of the motor, it is often required to be able to measure the position of the motor rotor, for example in order to switch the current supply to different phases of a multiple-phase motor. One motor commonly used in EPAS systems is the permanent magnet synchronous motor. This comprises a plurality of permanent magnets mounted on the motor rotor, with a plurality of phase windings surrounding the rotor to form the stator. By cyclically energising the phase windings, the rotor can be forced to rotate. Such motors often have relatively low resolution position sensors, such as Hall-effect sensors mounted relative to the stator, which can indicate the passing of a permanent magnet pole on the rotor, and so indicated to a motor control circuit the appropriate moment to switch (or "commutate") the energisation of the phase windings. However, it has been desired to remove the need to provide such sensors, and potentially to measure the rotational speed of the rotor also. One method of doing so is to determine the inductance of the motor by measuring the rate of change of motor current, as proposed in the PCT patent application published as WO2004/023639. It is desirable to improve the performance of such position sensing techniques.
According to a first aspect of the invention, there is provided a measurement circuit for measuring at least one of the rotational position and rotational speed of the rotor of an electric motor, the circuit comprising: • first and second inputs for receiving first and second input signals which vary cyclically with the rotational position of the rotor, the first and second input signals at the first and second inputs varying in quadrature with each other;
• a phase detector circuit; and
· an observer circuit;
in which the observer circuit is arranged to generate estimates indicative of the frequency and phase of the first and second input signals;
in which the phase detector circuit is arranged to determine the phase difference between first and second estimated signals varying cyclically and at the frequency indicated by the estimates with a phase difference dependent on the phase difference indicated by the estimates, the first and second estimated signals varying in quadrature with each other on the one hand and the first and second input signals on the other by adding a multiplicative combination of the first input signal with the first estimated signal to a multiplicative combination of the second input signal with the second estimated signal to result in a sum signal dependent upon the phase difference; and
in which the observer circuit is arranged to vary the estimates dependent upon the sum signal. By doing so, we have determined that there is no longer the need to employ a low pass filter as in a prior-art phase lock loop system, as the sum signal will not have a term dependent upon the sum of the frequency of the first and second estimated signals and the frequency of the first and second input signals. The circuit may further comprise a velocity estimation circuit, which is arranged to take the first and second input signals and to output a velocity signal indicative of the rotational speed of the motor rotor by determining the rate of change of one of the first and second input signals and dividing the rate of change by the other of the first and second input signals. The velocity determining circuit may be arranged such that the first or second input signal used to divide the rate of change is the larger of the first and second input signal, so as to avoid errors due to dividing by a number clos e to zero, or an error due to dividing by zero itself.
The observer circuit may be arranged so as to generate the estimates based upon the phase difference and the output of the velocity determining circuit. The observer circuit may be arranged to determine the first and second estimated signals based upon its estimates. As such, by making the estimates depend upon the velocity estimate, the precision with which the circuit will follow the actual velocity and/or position of the rotor as the velocity changes has been found to improve over prior art phase lock loops, which merely measure the phase difference.
The circuit may further comprise a normalisation circuit, arranged so as to normalise the first and second input signals. The amplitude of the signals is not particularly important (only the phase and frequency), and so by normalising the signals, any deleterious effects of amplitude variation can be avoided. As such, the normalisation circuit may be arranged to divide each of the first and second signals by the square root of the sum of the squares of the first and second input signals; given that the first and second signals are cyclically varying in quadrature, this divisor is likely to represent the amplitude of each of the signals, and so result in a normalised amplitude of unity.
The first and second signals may be indicative of the inductance of the motor, and as such may depend upon or be the derivative of the current flowing at least one phase winding of the motor.
According to a second aspect of the invention, there is provided a motor control circuit for controlling an electric motor having a rotor, the motor control circuit comprising:
• a measurement circuit according to the first aspect of the invention;
· a sensor arranged to output first and second input signals, which vary cyclically with the rotational position of the rotor, to the first and second inputs of the measurement circuit; and
• at least one output indicative of an electric current to be applied to the electric motor;
in which the motor control circuit is arranged so as to vary the output dependent upon the estimates output by the measurement circuit.
According to a third aspect of the invention, there is provided a combination of an electric motor having a rotor and the motor control circuit of the second aspect of the invention arranged so as to control the motor, with the sensor of the motor control circuit being arranged so as to sense the rotational position of the rotor.
According to a fourth aspect of the invention, there is provided an electric power assisted steering system, comprising a steering wheel, a steering mechanism which operatively couples the steering wheel to road wheels of a vehicle, a electric motor being arranged so as to apply in use a force to part of the steering mechanism, a torque sensor which, in use, provides a torque signal indicative of the torque carried by part of the steering mechanism and a motor control circuit arranged to control the motor by generating, in use, a current signal indicative of the current to be applied to the electric motor in accordance with the second aspect of the invention.
According to a fifth aspect of the invention, there is provided a method of measuring at least one of the rotational position and rotational speed of the rotor of an electric motor, the method comprising:
• receiving first and second input signals which vary cyclically with the rotational position of the rotor, the first and second input signals varying in quadrature with each other;
• generating first and second estimated signals, the first and second estimated signals varying cyclically and having the same frequency but varying in quadrature with each other;
• determining the phase difference between the first and second estimated signals on the one hand and the first and second input signals on the other by adding a multiplicative combination of the first input signal with the first estimated signal to a multiplicative combination of the second input signal with the second estimated signal to result in a sum signal dependent upon the phase difference; and
• varying the frequency of the first and second estimated signals dependent upon the sum signal.
By doing so, we have determined that there is no longer the need to employ a low pass filter as in a prior-art phase lock loop system, as the sum signal will not have a term dependent upon the sum of the frequency of the first and second estimated signals and the frequency of the first and second input signals. The method may further comprise the step of estimating the velocity of the motor rotor by determining the rate of change of one of the first and second input signals and dividing the rate of change by the other of the first and second input signals. The method may comprise determining which of the first or second input signal is the larger and using the larger of the first and second input signals to divide the rate of change, so as to avoid errors due to dividing by a number close to zero, or an error due to dividing by zero itself.
The method may comprise estimating at least one of the rotational position and the rotational speed of the motor rotor based upon the phase difference and the output of the velocity determining circuit. As such, by making the estimates depend upon the velocity estimate, the precision with which the circuit will follow the actual velocity and/or position of the rotor as the velocity changes has been found to improve over prior art phase lock loops, which merely measure the phase difference.
The method may further comprise normalisation of the first and second input signals. The amplitude of the signals is not particularly important (only the phase and frequency), and so by normalising the signals, any deleterious effects of amplitude variation can be avoided. As such, the method may comprise dividing each of the first and second signals by the square root of the sum of the squares of the first and second input signals; given that the first and second signals are cyclically varying in quadrature, this divisor is likely to represent the amplitude of each of the signals, and so result in a normalised amplitude of unity. The first and second signals may be indicative of the inductance of the motor, and as such may depend upon or be the derivative of the current flowing at least one phase winding of the motor. The method may comprise generating the first and second signals, typically by differentiating the current flowing through at least one phase of the motor.
In the above aspects, the motor may be a permanent magnet motor, typically a permanent magnet synchronous motor.
There now follows, by way of example only, an embodiment of the present invention, described with reference to the accompanying drawings, in which: Figure 1 shows an electric power assisted steering (EPAS) system having a measurement circuit according to an embodiment of the invention; Figure 2 shows a cross section through the motor of the EPAS system of
Figure 1 ;
Figure 3 shows schematically the function of the measurement circuit of the EPAS system of Figure 1 ;
Figure 4a shows a graph of estimated and actual rotor position in a test procedure carried out according to the embodiment of Figure 1 ;
Figure 4b shows a graph of the difference between the estimated and actual rotor position of Figure 4a; and
Figure 4c shows the current applied to the motor in the test procedure of Figure 4a. An electric power assisted steering assembly is illustrated in Figure 1 of the accompanying drawings. The apparatus comprises an electric motor 1 which acts upon a drive shaft 2 through a gearbox 3 of the rack and pinion type. The drive shaft terminates with a worm gear 4 that co-operates with a wheel provided on a portion of a steering column 5 or a shaft operatively connected to the steering column.
The steering column carries a torque sensor 6 that is adapted to measure the torque carried by the steering column. This torque is produced by the driver turning the steering wheel, either to turn a corner or to counter pull of the vehicle to one side. The output signal T from this sensor is fed to a signal processing means in the form of a signal processor 7, which takes the torque input signals and outputs commands to a drive circuit for the motor 9 over line 8a. The drive circuit in turn returns a signal indicative of the current flowing in the windings of the motor 9 over line 8b.
The motor is shown in more detail in Figure 2 of the accompanying drawings. The motor 9 is a three phase brushless motor, which comprises a rotor 12 having six embedded magnets 14 within it which in this instance are arranged so as to provide six poles which alternate between north and south around the rotor.
A stator 16 comprises a nine slot copper wound element having three groups of three teeth 18A, 18B, 18C each group of teeth having a common winding (example shown as 13) forming a respective phase. There are therefore three electrical cycles in each full rotation of the rotor 12, as the rotor and its magnets 14 have threefold circular symmetry, meaning that each 120 degree rotation of the rotor leaves it in an equivalent position.
In order to determine the rotational position of the rotor 12 within an electrical revolution (that is, to one of three rotational positions of the rotor 12, spaced apart by 120 degrees), the signal processor 7 is provided a measurement circuit 19 with the functionality shown in Figure 3 of the accompanying drawings.
The measurement circuit 7 is provided with a di/dt sensor 20, which takes the currents flowing through the motor (typically through a ground return in common to each of the phases) and differentiates them, in order to arrive at two cyclically varying indications of the rate of change of current. These signals are indicative of the inductance of the phase windings at that particular instant.
The two signals, which will be indicated as Asin t + φ1 ) and A cos t + vary in quadrature with each other - that is, they are a quarter cycle out of phase. A suitable di/dt sensor can be found in the PCT publication WO2004/023639, the contents of which are hereby incorporated by reference. In that document, Park's transformation is used to generate these two signals, therein referred to as La and (from equation 7, page 15). In these two signals, t is time, A is the amplitude of the two signals (which will be the same), (ϋγ is the angular speed of the rotor (in radians per second) and φ1 is a phase offset (again in radians) from an arbitrary datum.
The di/dt sensor 20 outputs the two signals As t + φ1 ) and A cos^t + φ1 ) to a normalisation circuit 22. In order to prevent the transient response of the circuit depending on the amplitude of the currents, the two signals are normalised to an amplitude of unity. This is done by dividing each of the signals by the square root of the sum of the squares of the two signals; this divisor will always be A as follows:
TJ ' A2 sin 2 (cOjt + (h ) + A2 cos2 (o + Φι ) = ^A2{s 2 (c^t cos2 (o t + )) = fA2 = A which makes use of the trigonometric identity that sin2 x + cos2 x = 1 , sin2 and similar terms meaning (sin x)2 and so on.
Thus, the output of the normalisation circuit 22 will be the original two signals, normalised to unity, and thus can be represented by 8Ϊη(ω1ί +φ1 ) and cos^t + (f>j ) .
The output of the normalisation circuit 22 is passed to a phase detector circuit 24. This determines the phase difference between estimates of the phase difference and frequency calculated by an observer circuit 28 discussed below and the normalised signals from the normalisation circuit 22. The estimates are provided to the phase detector circuit as a motor position estimate θ = 0)2ί + φ2 , from which the phase detector circuit determines first and second estimated signals as sm(o)2t +§2 ) and cos(co2t + φ2 ) .
The phase detector circuit then calculates the difference between the two products generated by multiplying the sine term of one signal with the cosine term of the other signal, thusly: y(t) = sin (a + ^ )cos(co2t + φ2 ) - cos^t + ^ )sin (co2t + φ2 ) · · j · sin(0 + cp) + sin(0 -φ) , , Applying the trigonometric identity sm0 coscp = to both terms of the subtraction:
1 8ώ(ω1ί + 1 +ω2ί + 2) + 8ΐη(ω1ί + 1 -ω2ί - φ2)
y(f) =—
2 {-sm(o)2t + <>2 +ω1ί + φ1) - sm(o)2t + <>2 -ω^ -φ^
y(t) = smfa + ^ -co2t - φ2) = sin^cOj - ω^ί + ^ - φ2) Thus, the two terms that vary at the sum of the frequencies C01 + C02 cancel each other out, leaving only a term that varies at the difference of the frequencies C01— C02 and that depends upon the phase difference φ1— φ2 between the estimated and measured signals. As such, when the estimated signals correctly estimate C02 and φ2 , the signal y(t) will be zero; if the frequency or the phase deviate slightly, the signal y(t) can be used to indicate the error as explained below.
Unlike prior art phase lock loop (PLL) techniques, there is no higher frequency term that requires filtering. Given that it is desirable to be able to use the present circuit with a motor with wildly varying speed and so frequency, prior art PLL techniques would have required that a variable frequency filter be used to eliminate the higher frequency terms, which is no longer needed with the present invention.
The output of the normalisation circuit is also passed to a velocity detector 26. This determines the speed C01 of the motor by differentiating one of the normalised signals and dividing the differentiated signal by the other. Taking, for example, the sine component as the component to be differentiated:
Figure imgf000010_0001
However, to avoid a possible loss of precision or outright error when calculating the division, the velocity detection circuit will differentiate the smaller in magnitude of the two signals, and use the larger magnitude signal as the divisor. The observer circuit 28 is provided which takes the output of the phase detector and the difference (as calculated by a difference circuit 30) between the measured speed COj and the speed co2 predicted by the observer circuit 28. The observer circuit then takes the inputs and uses them to determine new estimates of the speed C02 and rotational position θ = 0)2ί + φ2 of the rotor 12 (within an electrical revolution); these are then used to generate the two estimated signals sm(o)2t +§2 ) and cos(co2t + φ2 ) . It is to be noted that the phase difference circuit outputs a value that is dependent upon the sine of the phase difference (measured in radians). The system uses the small angle approximation to avoid needing to carry out an inverse sine operation; when the phase difference is small, the sine of the phase difference will be approximately equal to the phase difference; as the difference increases, the error in the phase difference will increase, but will still have the same sign and will therefore cause the estimate to be corrected in the correct direction. As such, the output of the phase difference circuit is used directly as the phase difference below. The estimates C02 and Θ are updated in two ways: firstly, in accordance with the physical dynamics of a rotating motor; and secondly according to the phase difference and speed measurement estimate already determined. According to the physical dynamics, the position Θ is increased or decreased in proportion to the current speed estimate <¾. Next, Θ is updated according to phase difference δφ = φ1— φ2 and speed measurement estimate and in proportion to the phase difference and speed measurement difference calculated as follows:
ΘΟ + 1) = θ( + α12ω2(ί) + δ11δφ + &12(ω1 -ω2(ί)) where
9(t + 1) is the new observer estimate of the position
9(t) is the current observer estimate of the position
δφ is the phase difference
cOj -ω2(7) is the speed measurement difference calculated
£>l is the measured speed estimate
£>2{t) is the current observer estimate of the speed
al2 is the proportion of the current speed estimate, usually set equal to
the time between samples
bu is the proportion of the phase difference used to update the position estimate, usually set less than one.
b12 is the porportion of the measured speed estimate used to update the position estimate, usually set less than the time between samples
The speed estimate can be computed in a similar way:
ω2(ί + ϊ) = ω2(ί) + ΰ22(ωι -ω2(ί)) Where
co2 (t + 1) is the new observer estimate of the speed
b22 is the proportion of the measured speed estimate used to update the observer speed estimate
The values of the a and b coefficients can be adjusted to control and adapt the performance of the observer as desired.
The estimated values of the motor rotor rotational position Θ and the rotor speed C02 are then output, and can be used in the signal processor 7 in order to control the switching of the phases 13 in any suitable manner.
Some graphs showing the results of a prototype system can be seen in Figures 4a to 4c of the accompanying drawings. Figure 4c shows the current applied to the phases of a test motor over an approximately 37 second long test run. Figure 4a shows both the actual motor position (measured by a suitable position encoder, the trace shown as "enc") and the estimated value Θ determined by the observer circuit ("est"). From Figure 4a, the two traces appear practically indistinguishable.
Figure 4b shows the difference between the actual and estimated measurements, and as such represents the difference between the "enc" and "est" traces of Figure 4a. This shows that there is some error in the measurement, but it is generally at a low level, but increasing as the current applied to the motor increases.
Whilst the embodiment above has been described with the functions shown in Figure 3 described as circuits and the like, the method could be implemented in a suitable microprocessor such as field programmable gate array or even any general purpose microprocessor suitably programmed.

Claims

1. A measurement circuit for measuring at least one of the rotational position and rotational speed of the rotor of an electric motor, the circuit comprising:
• first and second inputs for receiving first and second input signals which vary cyclically with the rotational position of the rotor, the first and second input signals at the first and second inputs varying in quadrature with each other;
• a phase detector circuit; and
• an observer circuit;
in which the observer circuit is arranged to generate estimates indicative of the frequency and phase of the first and second input signals;
in which the phase detector circuit is arranged to determine the phase difference between first and second estimated signals varying cyclically and at the frequency indicated by the estimates with a phase difference dependent on the phase difference indicated by the estimates, the first and second estimated signals varying in quadrature with each other on the one hand and the first and second input signals on the other by adding a multiplicative combination of the first input signal with the first estimated signal to a multiplicative combination of the second input signal with the second estimated signal to result in a sum signal dependent upon the phase difference; and
in which the observer circuit is arranged to vary the estimates dependent upon the sum signal.
2. The measurement circuit of claim 1 , further comprising a velocity estimation circuit, which is arranged to take the first and second input signals and to output a velocity signal indicative of the rotational speed of the motor rotor by determining the rate of change of one of the first and second input signals and dividing the rate of change by the other of the first and second input signals.
3. The measurement circuit of claim 2, in which the velocity determining circuit is arranged such that the first or second input signal used to divide the rate of change is the larger of the first and second input signal.
4. The measurement circuit of any preceding claim, in which the observer circuit is arranged so as to generate the estimates based upon the phase difference and the output of the velocity determining circuit.
5. The measurement circuit of any preceding claim, comprising a normalisation circuit, arranged so as to normalise the first and second input signals.
6. The measurement circuit of claim 5, in which the normalisation circuit is arranged to divide each of the first and second signals by the square root of the sum of the squares of the first and second input signals.
7. A motor control circuit for controlling an electric motor having a rotor, the motor control circuit comprising:
• a measurement circuit according to any preceding claim;
· a sensor arranged to output first and second input signals, which vary cyclically with the rotational position of the rotor, to the first and second inputs of the measurement circuit; and
• at least one output indicative of an electric current to be applied to the electric motor;
in which the motor control circuit is arranged so as to vary the output dependent upon the estimates output by the measurement circuit.
8. A combination of an electric motor having a rotor and the motor control circuit according to claim 7, arranged so as to control the motor, with the sensor of the motor control circuit being arranged so as to sense the rotational position of the rotor.
9. An electric power assisted steering system, comprising a steering wheel, a steering mechanism which operatively couples the steering wheel to road wheels of a vehicle, a electric motor being arranged so as to apply in use a force to part of the steering mechanism, a torque sensor which, in use, provides a torque signal indicative of the torque carried by part of the steering mechanism and a motor control circuit arranged to control the motor by generating, in use, a current signal indicative of the current to be applied to the electric motor according to claim 7.
10. A method of measuring at least one of the rotational position and rotational speed of the rotor of an electric motor, the method comprising:
• receiving first and second input signals which vary cyclically with the rotational position of the rotor, the first and second input signals varying in quadrature with each other;
• generating first and second estimated signals, the first and second estimated signals varying cyclically and having the same frequency but varying in quadrature with each other;
• determining the phase difference between the first and second estimated signals on the one hand and the first and second input signals on the other by adding a multiplicative combination of the first input signal with the first estimated signal to a multiplicative combination of the second input signal with the second estimated signal to result in a sum signal dependent upon the phase difference; and
• varying the frequency of the first and second estimated signals dependent upon the sum signal.
1 1. The method of claim 10, further comprising the step of estimating the velocity of the motor rotor by determining the rate of change of one of the first and second input signals and dividing the rate of change by the other of the first and second input signals.
12. The method of claim 1 1 , comprising determining which of the first or second input signal is the larger and using the larger of the first and second input signals to divide the rate of change.
13. The method of any of claims 10 to 12, comprising estimating at least one of the rotational position and the rotational speed of the motor rotor based upon the phase difference and the output of the velocity determining circuit.
14. The method of any of claims 10 to 13, comprising normalisation of the first and second input signals.
15. The method of claim 14, in which the normalisation comprises dividing each of the first and second signals by the square root of the sum of the squares of the first and second input signals.
16. The method of any of claims 10 to 15, in which the first and second signals are indicative of the inductance of the motor, and as such depend upon or are the derivative of the current flowing at least one phase winding of the motor.
17. The method of any of claims 10 to 16, comprising generating the first and second signals, typically by differentiating the current flowing through at least one phase of the motor.
PCT/GB2012/051323 2011-06-15 2012-06-12 Measurement of motor rotor position or speed WO2012172321A1 (en)

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US14/126,122 US9989384B2 (en) 2011-06-15 2012-06-12 Measurement of motor rotor position or speed
BR112013032059A BR112013032059A2 (en) 2011-06-15 2012-06-12 measuring circuit, motor control circuit, combination of an electric motor, power assisted steering system, and method for measuring at least one rotational position and rotational rotational speed of an electric motor
CN201280029433.9A CN103703377B (en) 2011-06-15 2012-06-12 To the measurement of motor rotor position or speed
EP12745711.7A EP2721420B1 (en) 2011-06-15 2012-06-12 Measurement of motor rotor position or speed

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2015198039A1 (en) * 2014-06-25 2015-12-30 Trw Limited An electric power assisted steering system

Families Citing this family (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102014117718A1 (en) 2014-12-02 2016-06-02 Trw Automotive Gmbh Steering device and method for controlling a steering device
CN105882736A (en) * 2014-12-16 2016-08-24 重庆邮电大学 Damping control method for vehicle electric power steering system
DE102015211247A1 (en) * 2015-06-18 2016-12-22 Robert Bosch Gmbh Method and device for processing a signal
CN108700620B (en) * 2015-10-14 2021-03-05 无线电力公司 Phase and amplitude detection in wireless energy transfer systems
KR101835406B1 (en) * 2016-08-26 2018-03-09 현대모비스 주식회사 Motor driven power steering control apparatus
CN106526214A (en) * 2016-11-02 2017-03-22 中车株洲电力机车研究所有限公司 Angular velocity calculation method and apparatus
US20210165011A1 (en) * 2019-12-03 2021-06-03 Deere & Company Systems, methods and computer-readable mediums for detecting position sensor faults
DE102021105880A1 (en) * 2021-03-11 2022-09-15 Infineon Technologies Ag Angle of rotation sensor device and method for determining an angle of rotation and control device for an electric motor

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20020149335A1 (en) * 2001-02-16 2002-10-17 Honda Giken Kogyo Kabushiki Kaisha Rotor angle detecting apparatus for DC brushless motors
US20030030406A1 (en) * 2001-04-26 2003-02-13 Honda Giken Kogyo Kabushiki Kaisha Motor control apparatus
WO2004023639A1 (en) 2002-09-03 2004-03-18 Trw Limited Motor drive control
EP1630526A2 (en) * 2004-08-23 2006-03-01 Sony Corporation Resolver signal processing system
US20090034641A1 (en) * 2007-07-30 2009-02-05 Mitutoyo Corporation System and method for dynamic calibration of a quadrature encoder
US20100303460A1 (en) * 2009-05-27 2010-12-02 Bradley Hunter Encoder interpolator with enhanced precision

Family Cites Families (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3883785A (en) 1973-09-27 1975-05-13 Nasa Low speed phaselock speed control system
US4772839A (en) 1987-10-27 1988-09-20 General Electric Company Rotor position estimator for switched reluctance motor
US5134404A (en) 1991-04-01 1992-07-28 Aerotech, Inc. Quadrature error correction
US5325026A (en) 1992-06-29 1994-06-28 General Electric Company Microprocessor-based commutator for electronically commutated motors
US5637974A (en) 1995-04-21 1997-06-10 Itt Automotive Electrical Systems, Inc. Method and apparatus for hybrid direct-indirect control of a switched reluctance motor
US5864217A (en) 1997-05-08 1999-01-26 General Electric Company Switched reluctance machine with toothed-wheel rotor sensor
DE60227721D1 (en) 2001-11-02 2008-08-28 Gsi Group Corp Encoder self-calibration device and method
US6556153B1 (en) 2002-01-09 2003-04-29 Anorad Corporation System and method for improving encoder resolution
JP4395313B2 (en) 2003-04-04 2010-01-06 日本精工株式会社 Motor drive control device and electric power steering device
JP4260544B2 (en) * 2003-05-19 2009-04-30 株式会社日立製作所 Rotation angle detection device and rotation control device
JP3968525B2 (en) 2004-03-04 2007-08-29 ソニー株式会社 Phase synchronization circuit and information reproducing apparatus
JP5557021B2 (en) * 2009-08-26 2014-07-23 株式会社ジェイテクト Rotation angle detector

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20020149335A1 (en) * 2001-02-16 2002-10-17 Honda Giken Kogyo Kabushiki Kaisha Rotor angle detecting apparatus for DC brushless motors
US20030030406A1 (en) * 2001-04-26 2003-02-13 Honda Giken Kogyo Kabushiki Kaisha Motor control apparatus
WO2004023639A1 (en) 2002-09-03 2004-03-18 Trw Limited Motor drive control
EP1630526A2 (en) * 2004-08-23 2006-03-01 Sony Corporation Resolver signal processing system
US20090034641A1 (en) * 2007-07-30 2009-02-05 Mitutoyo Corporation System and method for dynamic calibration of a quadrature encoder
US20100303460A1 (en) * 2009-05-27 2010-12-02 Bradley Hunter Encoder interpolator with enhanced precision

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2015198039A1 (en) * 2014-06-25 2015-12-30 Trw Limited An electric power assisted steering system
CN106573648A (en) * 2014-06-25 2017-04-19 Trw有限公司 An electric power assisted steering system
US10005491B2 (en) 2014-06-25 2018-06-26 Trw Limited Electric power assisted steering system
CN106573648B (en) * 2014-06-25 2019-04-02 Trw有限公司 Electrical power assisted steering system

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