TECHNICAL FIELD
The present invention relates to a control device for an
electric power steering apparatus which adopts a vector control system where a steering
assist power is applied to a steering system of an automobile or a vehicle by a
motor. The present invention particularly relates to the control device for an electric
power steering apparatus in which a delay of a motor current in the vector control
system is compensated by an advance angle and thus the performance is improved.

BACKGROUND ART
An electric power steering apparatus, in which a steering
apparatus of an automobile or a vehicle is energized by an assist load using rotary
force of a motor, driving force of the motor is applied to a steering shaft or a
rack shaft via reduction gears or by a transmitting mechanism such as gears or a
belt so that the steering shaft or the rack shaft is energized by the assist load.
Since such conventional electric power steering apparatus generates an assist torque
(steering assist torque) accurately, it controls the feedback of motor currents.
The feedback control adjusts a motor applied voltage so that a difference between
a current command value and a motor current detected value becomes small or zero.
The adjustment of the motor applied voltage is made generally by a duty ratio of
PWM (pulse width modulation) control.

Japanese Patent Application Laid-Open No. 2003-189658 A
(Patent Document 1) discloses a technique such that a motor present position
of an electric power steering apparatus is made to respond at a high speed. A control
device in the above Patent Document 1 has a command generator 4 which provides a
command &thgr;ref, a load machine 1 and a motor driving device 2 which drives the
load machine 1 based on the torque command Tref. The control device is a delay-compensating
motor control device which

provides a torque command Tref based on a motor present position &thgr;m of the
motor driving device 2. This control device is provided with a monitoring device
3 which monitors a state of the motor driving device 2 and provides a motor delay
position &thgr;n which delays from the motor present position &thgr;m, a delay
compensating observer 6 which provides an estimated motor present position h&thgr;m
based on the motor delay position &thgr;n and the torque command Tref, and a first
control device 5 which provides the torque command Tref based on the command &thgr;ref
and the estimated motor present position h&thgr;m.

The electric power steering apparatus in the Patent Document
1 is provided with the delay observer which inputs the delay position &thgr;n and
the torque command Tref therein and outputs the estimated present position so that
the motor present position &thgr;m is estimated by the estimated motor present
position h&thgr;m.

In the device of the Patent Document 1, however, an estimating
arithmetic expression is complicated, and it is difficult to determine an inertia
moment Jm in an electric power steering. In the electric power steering, a lot of
parts such as a motor, reduction gears, an intermediate joint, a rack pinion, tires
and so on are subjects for driving. Since respective connecting portions have looseness,
it is difficult to obtain the inertia moment Jm.

The present applicant of this invention proposes a delay
compensation of a back EMF, but it is supposed that a delay between actual motor
information (position, angular velocity, voltage, electric current, back EMF and
the like) and an information which is used for the control contributes heavily to
occurrence of torque ripples (
Japanese Patent Application No. 2003-163446
). That is to say, when the delay of the information is compensated, the
torque ripples are reduced.

The present invention is devised from the viewpoint of
the above circumstances and its object is to provide a control device for an electric
power steering apparatus in which torque ripples at the time of rotation of a motor
are reduced by a simple arithmetic so that smooth and safe assist control can be
made with a steering feeling being improved.

DISCLOSURE OF THE INVENTION
The present invention relates to a control device for an
electric power steering apparatus which adopts a vector control system for applying
an assist force of a motor to a steering system. The object of the present invention
is achieved by that a phase delay according to an angular velocity is obtained,
a corrected electric angle is calculated by adding the phase delay to an electric
angle, and generation of a current command value in the vector control is compensated
based on the corrected electric angle.

Further, the object of the present invention is achieved
more effectively by that the phase delay includes a response delay of an electric
current control, the phase delay is obtained by a linear function of an offset and
a gain, or the corrected electric angle is limited to 0 to 360°.

Furthermore, the object of the present invention is achieved
by that a first phase delay according to an angular velocity is obtained, a first
corrected electric angle is calculated by adding the first phase delay to an electric
angle, generation of a current command value in the vector control is compensated
based on the first corrected electric angle, a second phase delay according to the
angular velocity is obtained, a second corrected electric angle is calculated by
adding the

second phase delay to the electric angle, and a back EMF in the vector control is
compensated based on the second corrected electric angle.

Still further, the object of the present invention is achieved
more effectively by that the first phase delay and the second phase delay include
a response delay of electric current control, the first phase delay and the second
phase delay are obtained by a linear function of an offset and a gain, or the first
corrected electric angle and the second corrected electric angle are limited to
0 to 360°.

BRIREF DESCRIPTION OF THE DRAWINGS

- FIG. 1 is a block diagram illustrating the principle of the present invention;
- FIG. 2 is a diagram illustrating a feature example of an advance angle control
according to the present invention;
- FIG. 3 is a block diagram illustrating a constitutional example of the present
invention;
- FIG. 4 is a waveform chart illustrating an example of a delay of a current response;
- FIG. 5 is a diagram for explaining a correction of a current command;
- FIG. 6 is a characteristic chart illustrating an example of an advance angle;
- FIG. 7 is a characteristic chart illustrating an example of an advance angle;
- FIG. 8 is a constitutional diagram for explaining the advance angle control
with respect to a back EMF; and
- FIGs. 9A and 9B are diagrams for explaining the advance angle control with respect
to the back EMF.

BEST MODE FOR CARRYING OUT THE INVENTION
In vector control using a control device for an electric
power steering apparatus in which an assist force is applied to a steering system
by a motor, it is necessary to generate a current command value which eliminates
torque ripples theoretically. In order to eliminate the torque ripples, a delay
should not occur in a motor current, but the motor current delays from a current
command value due to delay of a sampling cycle and current control. In the present
invention, the delay is compensated by advancing an angle to be used when the current
command value is generated.

In the present invention, it is understood that an amount
of the delay is proportional to a constant delay amount and an angular velocity,
and the delay is compensated by a simple primary expression "y = a.x + b". That
is to say, the present invention is characterized greatly in that an item whose
delay amount is compensated is narrowed down (electric current) and a simple linear
function is used so that the effect on an arithmetic amount becomes maximum.

An embodiment of the present invention is explained below
with reference to the drawings.

FIG. 1 illustrates the principle constitution of the present
invention. An estimated (or detected) motor rotation number (speed) &ohgr; is subject
to an advance angle control by an advance angle element 11 composing an advance
angle control section, an angle estimated value &thgr;e is added to the angle &Dgr;&thgr;
which is subject to the advance angle control by an adding section 12, the angle
estimated value is limited to within "0° to 360°" by a limiting section
13, and an angle estimated value &thgr;ea which is subject to the advance angle
control is outputted and the angle estimated value &thgr;ea is used for a vector
arithmetic. The limiting section 13 has a function for limiting the angle estimated
value &thgr;ea within the range of "0° to 360°". That is to say, the
angle estimated value &thgr;e is limited within the range of "0° to 360°",
but when the angle &Dgr;&thgr; is added, the angle

estimated value &thgr;e occasionally exceeds 360°. The exceeded value is returned
to the range of "0° to 360°". For example, when the angle estimated value
&thgr;e is "350" and the angle &Dgr;&thgr; is "20",

an added value is "370", but the "10" is obtained by "370 - 360" by the limiting
section 13.

As shown in FIG. 2, in the constitution of the advance
angle element 11, a linear function, which is obtained by adding (or subtracting)
a gain "Gain" to (from) an offset "Offset", is outputted. That is to say, the advance
angle element 11

performs an arithmetic of the following expression (1):
$$\mathrm{\&Dgr;}\mathrm{\&thgr;}=\mathrm{\&ohgr;}\times \mathrm{Gain}+\mathrm{sign}\left(\mathrm{\&ohgr;}\right)\cdot \mathrm{Offset}$$

When the rotation number &ohgr; is subject to the advance
angle control so as to be added to the angle estimated value &thgr;e and the added
result is used when the current command value is generated, the delay amount of
the motor current can be compensated, and thus the torque ripples and an operation
noise can be reduced.

FIG. 3 illustrates an entire constitutional example to
which the present invention is applied. A current command Iref is inputted to the
limiting section 1, the current command Iref1 whose upper and lower values are limited
by the limiting section 1 is inputted to an Id calculating section 2 and an Iq calculating
section 3. The Id calculating section 2 calculates a d-axis current in the vector
control. The d-axis current is used for controlling a magnetic force of the motor
(torque constant), making weakening magnetic field control which weakens an electric
field and thus improving the feature of the high-speed rotation. Further, the Iq
calculating section 3 calculates a q-axis current in the vector control, and obtains
the q-axis current based on a relationship of input/output energy of the motor 10.

The d-axis current Idref from the Id calculating section
2 is inputted to the Iq calculating section 3 and a dq/abc (two-phase/three-phase)
converting section 4. The q-axis current Iqref calculated in the Iq calculating
section 3 is also inputted to the dq/abc converting section 4, and converted three-phase
currents Iaref, Ibref and Icref are outputted from the dq/abc converting section
4. Differences (errors) between the three-phase currents Iaref, Ibref, Icref and
the motor

currents (Im) Ia, Ib, Ic are obtained by subtracters SB1, SB2 and SB3, respectively.
The differences are PI-controlled by PI control sections 101, 102 and 103, respectively,
and the PI-controlled voltages are added to back EMFs EMFa, EMFb and EMFc, respectively,
by adders AD1, AD2 and AD3 so that the added values are inputted to a PWM circuit
5. The motor 10 is controlled to be driven via a driving circuit 6.

The three-phase motor currents Ia, Ib and Ic are feedbacked
to the subtracters SB1, SB2 and SB3, respectively, and are

inputted to an EMF (back electromotive voltage) calculating section 7 and an estimating
section 100. Three-phase motor voltages Va, Vb and Vc are inputted to the EMF calculating
section 7 and the estimating section 100. The three-phase back EMFs Ea, Eb and Ec
calculated by the EMF calculating section 7 are inputted to an abc/dq (three-phase/two-phase)
converting section 8, and voltages Ed and Eq converted into two-phase voltages are
inputted to the Iq calculating section 3 which calculates the q-axis

current. A Hall signal is inputted from a Hall sensor which detects a rotor position
of the motor 100 to the estimating section 100.

Further, the rotation number &ohgr; estimated by the estimating
section 100 is inputted to advance angle control sections 110 and 120, and to the
Iq calculating section 3. The advance angle control section 110 is composed of an
advance angle element 111 and an adder 112, and the advance angle control section
120 is composed of an advance angle element 121 and an adder 122. An angle &Dgr;&thgr;1
which is subject to the advance angle control by the advance angle element 111 is
inputted to the adder 112, and an angle &Dgr;&thgr;2 which is subject to the
advance angle control by the advance angle element 121 is inputted to the adder
122. An angle estimated value &thgr;e estimated by the estimating section 100 is
inputted to the adder 112 of the advance angle control section 110 and the adder
122 of the advance angle control section 120. An angle estimated value &thgr;1
which is subject to the advance angle control by the advance angle control section
110 is inputted to the abc/dq converting section 8 and the dq/abc converting section
4. Further, an angle estimated value &thgr;2 which is subject to the advance angle
control by the advance angle control section 120 is inputted to a look-up table
130, and the look-up table 130 generates three-phase voltages EMFa, EMFb and EMFc,
and they are inputted to the adders AD1, AD2 and AD3, respectively. The limiting
sections which limit the ranges of the angles are omitted in the advance angle control
sections 110 and 120.

The operation in the above constitution is explained below.

In the advance angle control of the back EMFs in the advance
angle control section 120, the back EMFs EMFa, EMFb and EMFc from the look-up table
130 are used for a feed-forward control of the electric current control, and the
angle &thgr;2 which is subject to the advance angle control is used for correcting
an error based on a delay of the angle estimated value &thgr;e. Further, in the
advance angle control of the current command in the advance angle control section
110, the angle &thgr;1 which is subject to the advance angle control is used for
correcting a delay of the motor current Im.

The advance angle estimated value &thgr;e estimated by
the estimating section 100 is estimated from motor voltages Va, Vb and Vc and motor
currents Ia, Ib and Ic using a motor model (for example,
Japanese Patent Application No. 2003-101195
) and a Hall signal (for example,
Japanese Patent Application No. 2003-101195
). For this reason, a small amount of error based on measurement of voltage
or electric current and a delay of a signal process (filter, reading of voltage
or electric current, a Hall signal or the like) is always present in the angle estimated
value &thgr;e. The delay is a function of the rotary speed of the rotor, and as
the speed is higher, the delay becomes larger. That is to say, the back EMFs EMFa,
EMFb and EMFc for the

feed-forward control are read from the look-up table 130 based on the angle &thgr;2,
and the input into the look-up table 130 is controlled so that the delay can be
easily corrected.

The delay of the motor current in the control system is
caused by an inductance L of the motor 10, and this delay is a function of the speed
&ohgr;. The waveform chart in FIG. 4 illustrates an example of the delay of the
current response, and the current command Iref is changed from positive into negative,
but the motor current Im does not track the current command Iref at a high speed.
That is to say, "dim/dt" is not sufficiently fast. In the case of a one-phase motor,
when the load resistance is designated by R and the motor speed is designated by
&ohgr;m, the following expression (2) is established:
$$\begin{array}{ll}\mathrm{Vs}& =\mathrm{Im}\cdot \mathrm{R}+\mathrm{L}\cdot \mathrm{dim}/\mathrm{d}\mathrm{t}+\mathrm{EMF}\\ \mathrm{\hspace{1em}}& =\mathrm{Im}\cdot \mathrm{R}+\mathrm{L}\cdot \mathrm{dim}/\mathrm{d}\mathrm{t}+\mathrm{K}\mathrm{e}\cdot \mathrm{\&ohgr;m}\end{array}$$
When the above expression (2) is solved for "dim/dt", the following expression
(3) is established:
$$\mathrm{dim}/\mathrm{d}\mathrm{t}=\left\{\mathrm{V}\mathrm{s}-\mathrm{Im}\cdot \mathrm{R}-\mathrm{K}\mathrm{e}\cdot \mathrm{\&ohgr;}\mathrm{m}\right\}/\mathrm{L}$$
However, in the function of the rotor position, "dim/dt" can

be expressed as follows:
$$\mathrm{dim}/\mathrm{d}\mathrm{t}=\mathrm{dim}/\mathrm{d}\mathrm{\&thgr;}\cdot \mathrm{d}\mathrm{\&thgr;}/\mathrm{d}\mathrm{t}=\mathrm{dim}/\mathrm{d}\mathrm{\&thgr;}\cdot \mathrm{\&ohgr;}\mathrm{m}$$
According to the above expression (4), the following expression (5) is established:
$$\mathrm{dim}/\mathrm{d}\mathrm{\&thgr;}=\mathrm{dim}/\mathrm{d}\mathrm{t}\cdot 1/\mathrm{\&ohgr;}\mathrm{m}=\left\{\mathrm{V}\mathrm{s}-\mathrm{Im}\cdot \mathrm{R}-\mathrm{K}\mathrm{e}\cdot \mathrm{\&ohgr;}\mathrm{m}\right\}/\mathrm{L}\cdot 1/\mathrm{\&ohgr;}\mathrm{m}$$

The expression (5) shows the followings. That is to say,
when the inductance L is large, dim/d&thgr; is small and the delay is large. When
the motor speed &ohgr;m is large, dim/d&thgr; is small and the delay is large.
In other words, the delay of the current depends on the impedance of the motor 10
and is the function of the speed &ohgr;.

The delay of the motor current Im can be reduced or cancelled
previously by shifting the current command Iref by the angle &Dgr;&thgr;1. That
is to say, in the control system of the present

invention, since the current commands Iaref, Ibref and Icref from the dq/abc converting
section 4 are calculated by using the look-up table, the delay error can be easily
corrected. In FIG. 3, the following expression (6) is established:
$$\mathrm{\&thgr;}1=\mathrm{\&thgr;}\mathrm{e}+\mathrm{\&Dgr;}\mathrm{\&thgr;}1$$
The angle &thgr;1 is used for calculating the current commands Iaref, Ibref and
Icref (for example,
Japanese Patent Application No. 2002-345135
). The current command Iqref calculated and outputted by the Iq calculating
section 3 is obtained according to the following expression (7):
$$\mathrm{I}\mathrm{q}\mathrm{ref}=2/3\cdot \mathrm{T}\mathrm{ref}\cdot \left(\mathrm{\&ohgr;}\mathrm{m}/\mathrm{E}\mathrm{q}\right)-\mathrm{I}\mathrm{d}\mathrm{ref}\cdot \left(\mathrm{E}\mathrm{d}/\mathrm{E}\mathrm{q}\right)$$

Further, details about conversion of two-phase "dq" into
three-phase "abc" are described in, for example,
Japanese Patent Application No. 2002-345135
), and details about conversion of three-phase "abc" into two-phase "dq"
are described in, for

example,
Japanese Patent Application No. 2002-345135
.

FIG. 5 illustrates a state that the current command Iref
is corrected, and the current command Iref with the same waveform shifts by the
angle (time) &Dgr;&thgr;1. The motor current Im delays from the corrected current
command Iref' but does not delay from the original current command Iref.

An advance angle &Dgr;&thgr;2 is the feature shown in
FIG. 6 and is expressed by the following expression (8). " &Dgr;&thgr;0" is offset.
$$\mathrm{\&Dgr;}\mathrm{\&thgr;}2=\mathrm{\&Dgr;}\mathrm{\&thgr;}0+\mathrm{K}2\cdot \mathrm{\&ohgr;}$$

Further, an advance angle &Dgr;&thgr;1 is the feature
shown in FIG. 7 and is expressed by the following expression (9):
$$\mathrm{\&Dgr;}\mathrm{\&thgr;}1=\mathrm{\&Dgr;}\mathrm{\&thgr;}0+\mathrm{K}1\cdot \mathrm{\&ohgr;}$$

Since the compensation of the back EMF using the advance
angle control section 120 and the look-up table 130 is based on the contents described
in
Japanese Patent Application No, 2003-163446
described by the applicant of the present invention, the summary is explained
below.

The back EMFs (EMFa, EMFb and EMFc) are generated by a
back EMF calculating circuit 21 as shown in FIG. 8, and the back EMF calculating
circuit 21 is composed of a normalized back EMF calculating circuit 21-1 and a rotation
number correcting circuit 21-2. The normalized back EMF calculating circuit 21-1
calculates a back EMF EMF_{1000} when the motor is at 1000 [rpm] based on
a corrected electric angle &thgr;2. In the rotation number correcting circuit 21-2,
since the back EMF is proportional to the rotation number and thus is expressed
by the following expression (10). For example, when the motor is at 1100 [rpm],
the value calculated by the normalized back EMF calculating

circuit 21-1 may be made to be 1.1 times.
$$\mathrm{EMF}\mathrm{a},\mathrm{b},\mathrm{c}=\left(\mathrm{\&ohgr;}/1000\right)\cdot {\mathrm{EMF}}_{1000}$$

The normalized back EMF calculating circuit 21-1 is explained.
Since the waveform of the back EMF generated by the electric angle &thgr; varies
with types and design values of actual motors, the normalized back EMF calculating
circuit 21-1 obtains the back EMF EMF_{1000} at 1000 [rpm] according to
the actual

measurement using a designed actual motor. When the corrected electric angle &thgr;2
which does not delay is inputted from the advance angle control section 120 into
the back EMF calculating circuit 21, the accurate back EMFs EMFa, EMFb and EMFc
are calculated. When the normalized back EMF calculating circuit 21-1 and the rotation
number correcting circuit 21-2 calculate the back EMFs EMFa, EMFb and EMFc with
respect to the corrected electric angle &thgr;2 in advance and the look-up table
is formed (look-up table 130), the high-speed calculation can be made.

The meaning of the compensation of the back EMF is explained
below with reference to FIGs. 9A and 9B.

FIG. 9A illustrates a relationship between the delayed
back EMF EMF1 which is calculated by the back EMF calculating circuit and the actual
back EMF. FIG. 9B illustrates a relationship between the actual back EMF and the
back EMF "K·EMF" which is subject to gain adjustment. In FIG. 9B, a portion
where the torque ripples are difficultly reduced by an electric current control
circuit or the like is surrounded by an oval A. A portion surrounded by an oval
B is a portion where the delay of the back EMF can be compensated as an error and
a disturbance by the electric current control circuit. Also in a portion surrounded
by an oval C, similar compensation can be made by the electric current control circuit.
When the back EMF is multiplied by a gain, therefore, it is important to multiply
the gain and the back EMF so that the actual back EMF is superposed on the back
EMF "K·KMF1" multiplied by the gain in the portion surrounded by the oval A.

According to the present invention, since the advance angle
obtained by the simple linear function is given to the current command, the delay
of the motor current can be compensated accurately, thereby reducing the torque
ripples and the operation noise of the motor. The advance angle control can be made
by the simple linear function "y = a·x + b", and the compensation of the delay
can improve the steering feeling.

When the compensation with respect to the back EMF is made,
the steering feeling can be further improved. That is to say, the output torque
ripples of the motor can be reduced, and the electric power steering apparatus whose
handle operation is smooth and whose noise is less can be realized.

According to the present invention, when the delay between
the information about the actual motor and the information used for the control
is compensated by the advance angle control, the motor current Im can be controlled
accurately. For this reason, the torque ripples and the operation noise of the motor
can be reduced. The advance angle control can be made by the simple linear function,
and the steering feeling can be improved by the compensation of the delay.

INDUSTRIAL APPLICABILITY
According to the present invention, since the delay between
the information about the actual motor and the information used for the control
is compensated by the advance angle control, the torque ripples can be reduced and
device can be applied to high-performance electric power steering for automobiles
and vehicles.