U.S. patent application number 09/751387 was filed with the patent office on 2001-09-06 for motor control device.
Invention is credited to Nakazawa, Yosuke.
Application Number | 20010019251 09/751387 |
Document ID | / |
Family ID | 18530855 |
Filed Date | 2001-09-06 |
United States Patent
Application |
20010019251 |
Kind Code |
A1 |
Nakazawa, Yosuke |
September 6, 2001 |
Motor control device
Abstract
The present invention is a motor control device for controlling
current command values in relation to a permanent magnet reluctance
motor which generates torque corresponding to the combined value of
the torque resulting from the permanent magnet and the reluctance
torque through field-weakening control in such a manner that the
motor terminal voltage does not exceed the maximum inverter output
voltage. In particular it controls the angle of the current
relative to the motor rotor which is required for the purpose of
field-weakening control, and ensures that this is stable and
effective whatever torque is output.
Inventors: |
Nakazawa, Yosuke; (Tokyo,
JP) |
Correspondence
Address: |
Richard L. Schwaab
FOLEY & LARDNER
Washington Harbour
3000 K Street, N.W., Suite 500
Washington
DC
20007-5109
US
|
Family ID: |
18530855 |
Appl. No.: |
09/751387 |
Filed: |
January 2, 2001 |
Current U.S.
Class: |
318/701 |
Current CPC
Class: |
H02P 25/08 20130101;
H02P 21/0089 20130101; H02P 21/06 20130101 |
Class at
Publication: |
318/701 |
International
Class: |
H02P 001/46; H02P
003/18; H02P 005/28; H02P 007/36 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 7, 2000 |
JP |
2000-001652 |
Claims
What is claimed is:
1. A motor control device for controlling a permanent magnet
reluctance motor which generates torque corresponding to a combined
value of a torque resulting from a permanent magnet and a
reluctance torque, comprising: correction means for correcting a
current command value so as to prevent a motor terminal voltage
from exceeding a maximum inverter output voltage; and variation
means in response to a magnitude of a given torque command for
varying an angle of a motor to an current command value output from
said correction means.
2. A motor control device for controlling a permanent magnet
reluctance motor which generates torque corresponding to a combined
value of a torque resulting from a permanent magnet and a
reluctance torque, comprising: a dq axes current command setting
unit which calculates both a d-axis current command corresponding
to an axial direction of a permanent magnet and a q-axis current
command in a direction at right angles thereto on the basis of a
given torque command in accordance with previously supplied
patterns; a d-axis current control unit which calculates a d-axis
voltage in order to permit a d-axis current feedback value to track
said d-axis current command; a q-axis current control unit which
calculates a q-axis voltage in order to permit a q-axis current
feedback value to track said q-axis current command; a voltage
vector length calculation unit which determines a voltage vector
whereof a d-axis voltage and q-axis voltage are components; a
voltage vector length restriction unit which compares said voltage
vector length and an inverter direct-current input voltage, and
calculates a voltage vector length restriction value which is
restricted in such a manner that said voltage vector length does
not exceed a maximum inverter output voltage as determined in
accordance with said inverter direct-current input voltage; a
terminal voltage uniformity control unit which calculates said
voltage command correction value required in order to ensure that
said voltage vector length tallies with said voltage vector length
restriction value; a dq axes current command correction value
calculation unit which calculates said d-axis current command
correction value and q-axis current command correction value in
accordance with said torque command; a dq axes current command
correction unit which corrects said d-axis current command by said
d-axis current command correction value, and said q-axis current
command by said q-axis current command correction value; and a dq
three-phase transformation unit which transforms said d-axis
voltage command and q-axis voltage command into a three-phase
command on the basis of said d-axis voltage output from said d-axis
current control unit, said q-axis voltage output from said q-axis
current control unit, and a motor rotor position detection
angle.
3. A motor control device for controlling a permanent magnet
reluctance motor which generates torque corresponding to a combined
value of a torque resulting from a permanent magnet and a
reluctance torque, comprising: a dq axes current command setting
unit which calculates both a d-axis current command corresponding
to an axial direction of a permanent magnet and a q-axis current
command in a direction at right angles thereto on the basis of a
given torque command in accordance with previously supplied
patterns; a field-weakening axis angle setting unit which
calculates a field-weakening axis angle on the basis of said torque
command; an ft coordinates transformation unit which transforms
said d-axis current command and q-axis current command into an
f-axis current command corresponding to a direction of said
field-weakening axis angle and a t-axis current command in a
direction at right angles thereto; an f-axis current command
correction unit which corrects said f-axis current command by a
current command correction value; an ft inverse coordinates
transformation unit which transforms said f-axis current command
and said t-axis current command corrected by said f-axis current
command correction unit into new d-axis and q-axis current
commands; a d-axis current control unit which calculates a q-axis
voltage in order to permit a d-axis current feedback value to track
said d-axis current command obtained through said ft inverse
coordinates transformation unit; a q-axis current control unit
which calculates a q-axis voltage in order to permit a q-axis
current feedback value to track said q-axis current command
obtained through said ft inverse coordinates transformation unit; a
voltage vector length calculation unit which determines a voltage
vector whereof a d-axis voltage and q-axis voltage are components;
a voltage vector length restriction unit which compares a voltage
vector length and inverter direct-current input voltage, and
calculates a voltage vector length restriction value which is
restricted in such a manner that said voltage vector length does
not exceed a maximum inverter output voltage as determined in
accordance with an inverter direct-current input voltage; a
terminal voltage uniformity control unit which calculates a voltage
command correction value required in order to ensure that said
voltage vector length tallies with said voltage vector length
restriction value; and a dq three-phase transformation unit which
transforms a d-axis voltage command and q-axis voltage command into
a three-phase command on the basis of said d-axis voltage output
from a d-axis current control unit, said q-axis voltage output from
said q-axis current control unit, and a motor rotor position
detection angle.
4. The motor control device according to claim 3, wherein said
field-weakening axis angle setting unit calculates said
field-weakening axis angle on the basis of said d-axis and q-axis
current commands deduced from said torque command.
5. The motor control device according to claim 3, wherein said ft
coordinates transformation unit transforms a ft coordinates by
determining an origin of a ft coordinates axis as a point on a dq
coordinates axis at which a short-circuit current flows when a
motor is rotated with terminals thereof short-circuited.
6. The motor control device according to claim 3, further
comprising: a t-axis current command correction unit which based on
said torque command, a motor rotation angle speed, and said d-axis
and q-axis current commands and voltage commands output from said
ft inverse coordinates transformation unit calculates a t-axis
current command correction value required in order to correct
derivations in a motor output torque relative to said torque
command caused by correction of said f-axis current command as a
result of terminal voltage uniformity control.
7. A motor control device for controlling a permanent magnet
reluctance motor which generates torque corresponding to a combined
value of a torque resulting from a permanent magnet and a
reluctance torque, comprising: a dq axes current command setting
unit which calculates both a d-axis current command corresponding
to an axial direction of a permanent magnet and a q-axis current
command in a direction at right angles thereto on the basis of a
given torque command; a field-weakening axis angle setting unit
which calculates a field-weakening axis angle on the basis of said
torque command; an ft coordinates transformation unit into which a
d-axis current command and q-axis current command are input to
obtain a t-axis current command in a direction at right angles to a
direction of a field-weakening axis angle; an actual current ft
coordinates transformation unit which calculates a t-axis current
on the basis of d-axis and q-axis current feedback values and said
field-weakening axis angle; a t-axis current control unit which
calculates a voltage potential angle on the basis of a deviation
between said t-axis current command and said t-axis current; and a
one-pulse waveform voltage calculation unit which uses said voltage
phase angle, inverter input direct-current voltage and a motor
rotor phase to calculate a one-pulse waveform three-phase voltage
command required in order to turn inverter switch elements on and
off once for each output frequency cycle.
Description
BACKGROUND TO THE INVENTION
[0001] 1. Field of the invention
[0002] The present invention relates to a motor control device for
controlling a permanent magnet reluctance motor. 2. Description of
the related art
[0003] It has hitherto been common practice to implement
field-weakening control during constant output operation in
permanent magnet and reluctance motors when inverter-driven for use
in electric trains, electric motor vehicles and similar
applications, the aim being to ensure that the motor terminal
voltage is lower than the maximum voltage which the inverter is
capable of outputting.
[0004] FIG. 1 illustrates an example of a conventional motor
control device with field-weakening control of this kind. This
control device has a dq axes current command setting unit 11, a
d-axis current command correction unit 14, a d-axis current control
unit 16, a q-axis current control unit 17, a voltage vector length
calculation unit 18, a voltage vector length restriction unit 19, a
terminal voltage uniformity control unit 20, and a dq three-phase
transformation unit 21. It should be added that in this example of
the prior art it is assumed that the permanent magnet reluctance
motor is driven under vector control.
[0005] The dq axes current command setting unit 11 inputs the
torque command Tref, determining the d-axis current command Idref
and q-axis current command Iqref required in order to output this
torque. The d-axis current command Idref is corrected by the d-axis
current command correction unit 14 by adding the d-axis current
command correction value .DELTA.Idref from the terminal voltage
uniformity control unit 20, and this is input to the d-axis current
control unit 16. The q-axis current command Iqref is input to the
q-axis current control unit 17.
[0006] The d-axis current control unit 16 inputs the d-axis current
command Idref fed from the d-axis current command correction unit
14 and the d-axis current feedback value Id, and generates a d-axis
voltage command Vd in such a manner that the d-axis current
feedback value Id tracks the d-axis current command Idref. This is
input to the dq three-phase transformation unit 21. Similarly, the
q-axis current control unit 17 inputs the q-axis current command
Iqref fed from the q-axis current command correction unit 11 and
the q-axis current feedback value Iq, and generates a q-axis
voltage command Vq in such a manner that the q-axis current
feedback value Iq tracks the q-axis current command Iqref. This is
input to the dq three-phase transformation unit 21. The dq
three-phase transformation unit 21 generates the three-phase
voltage commands Vu, Vv and Vw on the basis of the d-axis voltage
command Vd, the q-axis voltage command Vq and the motor rotor
potential .theta. r, controlling the motor by way of a voltage
transformer not illustrated in the drawing in order to achieve
this.
[0007] The voltage vector length calculation unit 18 inputs the dq
axes voltage commands Vd and Vq and calculates the voltage vector
length (absolute voltage value) Vl. The voltage vector length
restriction unit 19 inputs the resultant voltage vector length Vl
and the inverter input direct-current voltage Vdc, and determines
the restricted voltage vector restriction length Vllim. The
terminal voltage uniformity control unit 20 calculates the current
command correction value .DELTA.Idref on the basis of the voltage
vector length Vl and the voltage vector restriction length Vllim,
and inputs it to the d-axis current command correction unit 14 as
already mentioned.
[0008] In the drawing, the circuit elements represented by the
codes 18, 19, 20 and 14 are for the purpose of field-weakening
control. Field-weakening control of a permanent magnet motor
generally involves running an armature current or minus d-axis
current, so to speak, so that the magnetic flux of the permanent
magnet and the magnetic flux created by the current flowing to the
motor armature are in opposite directions. In a reluctance motor,
on the other hand, where there is a large inductance value axis
(q-axis) and a small inductance value axis (d-axis), it is normal
to achieve field-weakening control by reducing the more effective
q-axis current.
[0009] However, when it is sought to implement field-weakening
control in a motor which generates a combination of reluctance
torque and torque resulting from a permanent magnet, this can prove
ineffective depending on the magnitude of the current amplitude
rendered variable by the torque which it is desired to output if
the current which is allowed to flow for this purpose is fixed on
either the d-axis or the q-axis. The result is that it becomes
impossible to control the motor terminal voltage below the maximum
inverter output voltage, and control becomes unstable. A similar
phenomenon can be produced also in a so-called embedded-type
permanent magnet motor which outputs combined permanent magnet and
reluctance torque by virtue of the fact that the permanent magnet
is embedded within the rotor core.
SUMMARY OF THE INVENTION
[0010] Accordingly, one object of the present invention is to
provide a novel motor control device wherein it is possible to
implement field-weakening control in a stable and effective manner
whatever torque is output, thus solving the abovementioned
problem.
[0011] With a view to achieving the abovementioned object, the
present invention is a motor control device for controlling a
permanent magnet reluctance motor which generates torque
corresponding to the combined value of the torque resulting from
the permanent magnet and the reluctance torque, having a means of
correction which serves to correct the current command value in
such a manner as to prevent the motor terminal voltage from
exceeding the maximum inverter output voltage, and a means of
variation which serves to render the angle between the current
command value from this means of correction and the motor rotor
variable in accordance with the magnitude of the given torque
command.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] A more complete appreciation of the present invention and
many of the attendant advantages thereof will be readily obtained
as the same becomes better understood by reference to the following
detailed description when considered in connection with the
accompanying drawings, wherein:
[0013] FIG. 1 is a block diagram illustrating a conventional motor
control device;
[0014] FIG. 2 is a block diagram of control device illustrating a
first embodiment of the present invention;
[0015] FIG. 3 is a block diagram illustrating the detailed
configuration of the dq-axis current command correction value
calculation unit in the first embodiment;
[0016] FIG. 4 is a graph illustrating the relationship between the
input torque command of the dq-axis current command setting unit
and the output d-axis current command;
[0017] FIG. 5 is a graph illustrating the relationship between the
input torque command of the dq-axis current command setting unit
and the output q-axis current command;
[0018] FIG. 6 is a block diagram of control device illustrating a
second embodiment of the present invention;
[0019] FIG. 7 is a block diagram illustrating a third embodiment of
the present invention;
[0020] FIG. 8 is a characteristic diagram which serves to explain
the content of calculations implemented in the field-weakening axis
angle setting unit;
[0021] FIG. 9 is a block diagram of control device illustrating a
fourth embodiment of the present invention;
[0022] FIG. 10 is a block diagram of control device illustrating a
fifth embodiment of the present invention; and
[0023] FIG. 11 is a block diagram of control device illustrating a
sixth embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0024] With reference now to the drawings, wherein like codes
denote identical or corresponding parts throughout the several
views, and more particularly to FIG. 2 thereof, one embodiment of
the present invention will be described.
[0025] (The First Embodiment)
[0026] FIGS. 2 and 3 illustrate a first embodiment of the motor
control device to which the present invention pertains. The device
as illustrated in FIG. 2 has a dq axes current command setting unit
11, a dq axes current command correction value calculation unit 12,
a dq axes current command correction unit 13, a d-axis current
control unit 16, a q-axis current control unit 17, a voltage vector
length calculation unit 18, a voltage vector length restriction
unit 19, a terminal voltage uniformity control unit 20, and a dq
three-phase transformation unit 21.
[0027] The dq axes current command setting unit 11 inputs a torque
command Tref, and determines and outputs the d-axis current command
Idref and q-axis current command Iqref which are most suitable for
outputting that torque. The values selected for the two axis output
commands Idref, Iqref are, for instance, those at which the motor
current vector length Ilref required to output the same torque is
at its minimum. In this case the two axis current commands Idref,
Iqref can be determined with the aid of the following formula.
I dref={-.PHI.pm-.infin.{square root over
((.PHI.pm.sup.2+8.multidot..DELT- A.L.sup.2.multidot.I
lref.sup.2))}}/(4.multidot..DELTA.L) (1)
[0028] Here, .PHI.pm is the magnetic flux of the permanent magnet,
.DELTA.L=Ld-Lq, Ld is the d-axis inductance, Lq is the q-axis
inductance, and L ref is the current amplitude, whereby the
following condition holds.
I lref={square root}{square root over ((I dref.sup.2+I
qref.sup.2))} (2)
[0029] The d-axis current Id and q-axis current Iq which satisfy
Formula (1) when modified with the current amplitude Ilref as a
parameter are determined, after which the torque T generated by the
motor in such cases is determined with the aid of the following
formula.
T=p.multidot.(.PHI.pm+.DELTA.L.multidot.I d).multidot.I q (3)9
[0030] Here, p is the motor pole number (pole twin number).
[0031] Taking the example of a motor equivalent circuit constant,
FIG. 4 illustrates the functional relationship between the motor
torque command Tref and the d-axis current command where
.PHI.pm=0.09, Ld=15 mH, and the motor pole number p=4. The d-axis
current command Idref is output, having been determined from the
input torque command Tref in accordance with the coefficient graph
of FIG. 4. In the same manner, the q-axis current command Iqref is
output, having been determined from the input torque command Tref
in accordance with the functional characteristic of FIG. 4.
[0032] The action of the dq axes current command correction value
calculation unit 12 will be described with reference to FIG. 3. The
dq axes current command correction value calculation unit 12 has a
divider 121, a multiplier 122, a cosine calculator 123 and a sine
calculator 124. As a whole it inputs the current command correction
value .DELTA.Iref output from the terminal voltage uniformity
control unit 20, determining and outputting the d-axis current
command correction value .DELTA.Idref and q-axis current command
correction value .DELTA.Iqref in accordance with the following
calculation. Firstly, the ratio Trate of the input torque command
Tref to the maximum torque command value Trefmax is determined
as
T rate=T ref/T refmax (4)
[0033] by the divider 121 and output to the multiplier 122. The
multiplier 122 multiplies the ratio Trate by .pi./2 and outputs
Trate.multidot..pi./2. Using this Trate.multidot..pi./2 and the
d-axis current command correction value .DELTA.Iref, the cosine
calculator 123 and sine calculator 124 perform the following
calculation to determine the d-axis current command correction
value .DELTA.Idref and q-axis current command correction value
.DELTA.Iqref as follows.
.DELTA.I dref=.DELTA.I ref.multidot.cos(T rate.multidot..pi./2)
(5)
.DELTA.I qref=.DELTA.I ref.multidot.sin(T rate.multidot..pi./2)
(6)
[0034] The dq axes current command correction unit 13 inputs the
d-axis current command Idref and q-axis current command Iqref
output from the dq axes current command setting unit 11, together
with the d-axis current command correction value .DELTA.Idref and
q-axis current command correction value .DELTA.Iqref output from
the dq axes current command correction value calculation unit 12,
determining and outputting a new d-axis current command Idref and
q-axis current command Iqref corrected according to the following
calculations.
I dref=I dref+.DELTA.I dref (7)
I qref=I qref+.DELTA.I qref (8)
[0035] The d-axis current control unit 16 inputs the d-axis current
command Idref output from the dq axes current command correction
unit 13 and the d-axis current feedback value Id, determining and
outputting the d-axis voltage command Vd as
Vd=(Kp+Ki/s).multidot.(I dref-I d) (9)
[0036] so that the d-axis current Id traces the d-axis current
command Idref. Here, s is a Laplace operator, Kp is the relative
gain, and Ki is the integral gain.
[0037] Similarly, the q-axis current control unit 17 inputs the
q-axis current command Iqref output from the dq axes current
command correction unit 13 and the q-axis current feedback value
Id, determining and outputting the q-axis voltage command Vq as
Vq=(Kp+Ki/s).multidot.(I qref-I q) (10)
[0038] so that the q-axis current Iq traces the q-axis current
command Iqref.
[0039] The voltage vector length calculation unit 18 inputs the
d-axis voltage command Vd output from the d-axis current control
unit 16 and the q-axis voltage command Vq input from the q-axis
current control unit 17, determining and outputting the voltage
vector length Vl as
Vl={square root}{square root over ((Vd.sup.2+Vq.sup.2))} (11)
[0040] The voltage vector length restriction unit 19 inputs the
voltage vector length Vl output from the voltage vector length
calculation unit 18, and the inverter input direct-current voltage
Vdc, determining the restricted voltage vector restriction length
Vllim. As a result, the maximum voltage Vlmax is here first
determined as
Vl max=0.9.multidot.{square root}{square root over
(6.multidot.)}Vdc/.pi. (12)
[0041] This Formula (12) represents fundamental wave voltage
amplitude in one-pulse waveform voltage mode, which is to say a
mode wherein one-pulse waveform voltage is output so as to turn the
inverter switching element on and off once for each output
frequency cycle. The coefficient 0.9 in the formula is the one
required to set this at a value 10% lower in order to give control
margin.
[0042] Next, the terminal voltage Vl and maximum voltage Vlmax
obtained in Formula (12) are compared with the aid of the following
formulae.
When Vl<Vlmax, Vllim=Vl (13)
When Vl>Vlmax, Vllim=Vlmax (14)
[0043] In this manner, the restricted voltage vector restriction
length Vllim is output.
[0044] The terminal voltage uniformity control unit 20 inputs the
voltage vector length Vl output from the voltage vector length
calculation unit 18 and the voltage vector length Vllim output from
the voltage vector length restriction unit 19, determining the
current command correction value .DELTA.Iref as
.DELTA.I ref=G(s).multidot.(Vllim-Vl) (15)
[0045] Here, s is a Laplace operator, and G (s) is the control
gain. The control gain of proportional/integral control may be
thought of as the control gain G(s). It has already been noted that
current command correction value .DELTA.Iref determined here is
used by the dq axes current command correction value calculation
unit 12.
[0046] The dq three-phase transformation unit 21 inputs the d-axis
voltage command Vd output from the d-axis current control unit 16,
the q-axis voltage command output from the q-axis current control
unit 17, and the motor rotor phase .theta.r, determining the UVW
three-phase voltage commands Vu, Vv and Vw as
Vl={square root}{square root over ((Vd.sup.2+Vq.sup.2))} (16)
.DELTA.V=tan.sup.-1 (Vq/Vd) (17)
Vu={square root}(2/3).multidot.Vl.multidot.cos (.theta.+.delta.V)
(18)
Vv={square root}({square root over (2/3)}).multidot.Vl.multidot.cos
(.theta.+.delta.V-2.pi./3) (19)
Vw={square root}(2/3).multidot.Vl.cndot.cos
(.theta.+.delta.V-4.pi./3) (20)
[0047] By controlling a permanent magnet reluctance motor in this
manner it is possible to implement field-weakening control, and
ensure that this is stable and effective whatever torque is
output.
[0048] (The Second Embodiment)
[0049] There follows a description of a second embodiment with
reference to FIG. 6. This motor control device has a dq axes
current command setting unit 11, a field-weakening axis angle
setting unit 22, an ft coordinates transformation unit 23, an
f-axis current command correction unit 24, an ft inverse
coordinates transformation unit 25, a d-axis current control unit
16, a q-axis current control unit 17, a voltage vector length
calculation unit 18, a voltage vector length restriction unit 19, a
terminal voltage uniformity control unit 20, and a dq three-phase
transformation unit 21. Those component elements which are the same
as or correspond to component elements of the control device
illustrated in FIG. 2 have been allocated the same codes, and will
not be described separately.
[0050] The field-weakening axis angle setting unit 22 inputs the
torque command Tref, outputting the maximum field-weakening angle
value or an approximation thereto as the field-weakening angle
establishment value Qft. To give an example here of an output
approximation, the field-weakening angle setting value Qft may be
determined by the following formula
Qft=(.pi./2).multidot.(Tref/Trefmax) (21)
[0051] with the maximum torque command value as Trefmax.
[0052] On the basis of the d-axis current command Idref and the
q-axis current command Iqref output from the dq axes current
command setting unit 11, and the field-weakening angle
establishment value Qft output from the field-weakening axis angle
setting unit 22, the ft coordinates transformation unit 23
determines the f-axis current command Ifref and t-axis current
command Itref as 1 ( I fref I tref ) = ( cos ( Qft ) sin ( Qft ) -
sin ( Qft ) cos ( Qft ) ) ( I dref I qref ) ( 22 )
[0053] The f-axis current command correction unit 24 inputs the
f-axis current command Ifref output from the ft coordinates
transformation unit 23 and the f-axis current command correction
value .DELTA.Ifref output from the terminal voltage uniformity
control unit 20, determining the corrected new f-axis current
command Ifref as
Ifref=Ifref+.DELTA.Ifref (23)
[0054] and feeding it to the ft inverse coordinates transformation
unit 25.
[0055] The ft inverse coordinates transformation unit 25 inputs the
f-axis current command Ifref output from the f-axis current command
correction unit 24, the t-axis current command Itref output from
the ft coordinates transformation unit 23, and the field-weakening
angle establishment value Qf t output from the field-weakening axis
angle setting unit 22, determining a new d-axis current command
Idref and q-axis current command Iqref as 2 ( I dref I qref ) = (
cos ( Qft ) - sin ( Qft ) sin ( Qft ) cos ( Qft ) ) ( I fref I tref
) ( 24 )
[0056] Using the d-axis current command Idref and q-axis current
command Iqref determined in this manner makes it possible in the
end to obtain the phase voltage commands Vu, Vv and Vw with the aid
of Formulae (18)-(20), thus facilitating motor control and ensuring
that this is stable and effective whatever torque is output.
[0057] (The Third Embodiment)
[0058] There follows a description of a third embodiment with
reference to FIGS. 7 and 8. This embodiment closely resembles the
control device illustrated in FIG. 6, and the majority of the
component elements are common to both. The only difference is the
field-weakening axis angle setting unit 26. This does not determine
the field-weakening angle establishment value Qft from the torque
command Tref, but instead inputs the d-axis current command Idref
and q-axis current command Iqref output from the dq axes current
command setting unit 11, referring to the characteristic diagram of
terminal voltages (FIG. 8) determined experimentally in advance on
the dq current command coordinates to set and output the
field-weakening angle setting value Qft in a direction centripetal
to the terminal voltage uniformity curve where the terminal voltage
is low.
[0059] FIG. 8 illustrates the terminal voltage uniformity curve in
a motor and dq-axis coordinates where the magnetic flux of the
permanent magnet .PHI.pm, d-axis inductance Ld and q-axis
inductance Lq are respectively 0.0573[Wb], 1.81[mH] and 4.46[mH].
The field-weakening angle establishment value Qft is set in a
direction centripetal to the equivalent terminal voltage curve
(direction of the arrow in the drawing) at the dq axes current
command point output from the dq axes current command setting unit
11.
[0060] In this manner it is possible to implement stable
field-weakening control in the same manner as in the first and
second embodiments whatever torque is output. Moreover, inasmuch as
the field-weakening control is more apt, it is possible to reduce
the required current capacity by minimizing the field-weakening
current needed in order to ensure that the terminal voltage is
below a certain level.
[0061] (The Fourth Embodiment)
[0062] There follows a description of a fourth embodiment with
reference to FIG. 9. This embodiment closely resembles the control
device illustrated in FIG. 6, and the majority of the component
elements are common to both. The only difference is the content of
the ft coordinates transformation unit 23, the remainder being the
same. The ft coordinates transformation unit 23 inputs the dq axes
current commands Idref, Iqref output from the dq axes current
command setting unit 11 along with the field-weakening angle
establishment value Qft output from the field-weakening axis angle
setting unit 22, determining and outputting the f-axis current
command Ifref and t-axis current command Itref.
[0063] If each of the motor three-phase output terminals is
short-circuited, a negative d-axis current Id flows to the motor
coils as a result of the motor inductive voltage. If the Idz is the
d-axis current at this time, this d-axis current Idz can be
determined with the aid of
Idz=.PHI.pm/Ld (25)
[0064] 3 ( I fref I tref ) = ( cos ( Qft ) sin ( Qft ) - sin ( Qft
) cos ( Qft ) ) ( I dref + I dz I qref ) ( 26 )
[0065] by using the magnetic flux of the permanent magnet .PHI.pm
and the d-axis inductance Ld as motor equivalent circuit
constants.
[0066] The abovementioned coordinate transformation shows that the
point of origin of the ft coordinates axis shifts Idz in the
direction of the d-axis, while the phase angle rotates by the angle
Qft. If field-weakening control is implemented as far as the point
of origin of the ft coordinates axis, the result is that the motor
terminal voltage becomes zero and comes to be in the direction
where field weakening works most reliably.
[0067] The ft inverse coordinates transformation unit 25 inputs the
f-axis current command Ifref output from the f-axis current command
correction unit 24, the t-axis current command Itref output from
the f-axis current command correction unit 27, and the
field-weakening angle setting value Qft output from the
field-weakening axis angle setting unit 22, determining the new
d-axis current command Idref and q-axis current command Iqref by
means of the following calculation.
[0068] If each of the motor three-phase output terminals is
short-circuited, a negative d-axis current Id flows to the motor
coils as a result of the motor inductive voltage. If the Idz is the
d-axis current at this time, this d-axis current Idz can be
determined with the aid of
Idz=.PHI.pm/Ld (27)
[0069] 4 ( I dref I qref ) = ( cos ( Qft ) - sin ( Qft ) sin ( Qft
) cos ( Qft ) ) ( I fref I tref ) - ( I dz 0 ) ( 28 )
[0070] by using the magnetic flux of the permanent magnet .PHI.pm
and the d-axis inductance Ld as motor equivalent circuit
constants.
[0071] In this manner it is possible to implement stable
field-weakening control in the same manner as in the first and
second embodiments whatever torque is output. What is more, its is
also possible to implement field-weakening control in a stable and
effective manner without dispersing terminal voltage uniformity
control even when the torque command changes rapidly during
field-weakening control.
[0072] (The Fifth Embodiment)
[0073] There follows a description of a fifth embodiment with
reference to FIG. 10. The only difference between this and the
embodiment illustrated in FIG. 9 is the addition of a t-axis
current command correction unit 27 which serves to calculate the
t-axis current command correction value .DELTA.Itref in order to
correct the t-axis current command Itref. All other component
elements are the same as those of FIG. 9. This f-axis current
command correction unit 27 inputs the torque command Tref, the
motor rotation angle speed .omega.r, the d-axis voltage Vd output
from the d-axis current control unit 16, the q-axis voltage Vq
output from the q-axis current control unit 17, and the dq axes
current commands Idref, Iqref output from the ft inverse
coordinates transformation unit 25, determining the t-axis current
command correction value .DELTA.Itref. This is achieved firstly by
determining the effective power command Pref as
Pref=Tref.multidot..omega.r (29)
[0074] Next, the effective power calculation value Pcal is
determined as
Pcal=Vd.multidot.Idref+Vq.multidot.Iqref (30)
[0075] The results of these calculations are then used to determine
the t-axis current command correction value .DELTA.tref as
.DELTA.Itref=G(s).multidot.(Pref-Pcal) (31)
[0076] Here, s is a differential operator, and G(s) is the control
gain in proportional/integral control and elsewhere.
[0077] The t-axis current command correction value .DELTA.Itref
obtained in this manner is added in the adder 28 to the t-axis
current command Itref output by the ft coordinates transformation
unit 23 to yield the new t-axis current command Itref, which is fed
to the ft inverse coordinates transformation unit 25. In other
words, the function of the adder 28 is
Itref=Itref+.DELTA.Itref (32)
[0078] In this manner it is possible to implement stable
field-weakening control in the same manner as in the first and
second embodiments whatever torque is output. Moreover, it is
possible to improve the degree of matching between the output
torque and the torque command value.
[0079] (The Sixth Embodiment)
[0080] There now follows a description of a sixth embodiment with
reference to FIG. 11. The control device of this embodiment has a
dq axes current command setting unit 11, a field-weakening axis
angle setting unit 22, an ft coordinates transformation unit 29, an
actual current ft coordinates transformation unit 30, a t-axis
current control unit 31, and a one-pulse waveform voltage
calculation unit 32.
[0081] The functions of the dq axes current command setting unit 11
and the field-weakening axis angle setting unit 22 are the same as
those of the respective component elements of the control device
illustrated in FIG. 6 and already described.
[0082] The ft coordinates transformation unit 29 inputs the dq axes
current commands Idref, Iqref output from the dq axes current
command setting unit 11 and the field-weakening angle establishment
value Qft output from the field-weakening axis angle setting unit
22, determining the t-axis current command Itref as
Itref=-Idref.multidot.sin(Qft)+Iqref.multidot.cos(Qft) (33)
[0083] The actual current ft coordinates transformation unit 30
inputs the dq axes current feedback values Id, Iq and the
field-weakening angle establishment value Qft output from the
field-weakening axis angle setting unit 22, determining the t-axis
current command It as
It=-Id.multidot.sin(Qft)+Iq.multidot.cos(Qft) (34)
[0084] The t-axis current control unit 31 inputs the t-axis current
command Itref of Formula (33) output from the ft coordinates
transformation unit 29 and the t-axis current command It output
from the actual current ft coordinates transformation unit 30,
determining the voltage phase angle .delta.V as
.delta.V=G(s).multidot.(Itref-It) (35)
[0085] Here, s is a differential operator, and G(s) is the control
gain in proportional/integral control and elsewhere.
[0086] The one-pulse waveform voltage calculation unit 32 inputs
the voltage phase angle .delta.V of Formula (35) output from the
t-axis current control unit 31, the motor rotor potential .theta.
r, and the inverter input direct-current voltage Vdc, determining
the three-phase one-pulse waveform voltages Vu, Vv and Vw. Here,
the first step is to determine the three-phase sine waves Vuo, Vvo
and Vwo as
Vuo=cos (.theta.r+.delta.V) (36)
Vvo=cos (.theta.r+.delta.V-2.pi./3) (37)
Vwo=cos (.theta.r+.delta.V-4.pi./3) (38)
[0087] Next, the three-phase one-pulse waveform voltages Vu, Vv and
Vw are determined from the results of the calculations in
accordance with the following condition portions.
When Vuo>0, Vu=+Vdc/2 (39)
When Vuo<0, Vu=-Vdc/2 (40)
When Vvo>0, Vv=+Vdc/2 (41)
When Vuo<0, Vv=-Vdc/2 (42)
When Vwo>0, Vw=+Vdc/2 (43)
When Vwo<0, Vw=-Vdc/2 (44)
[0088] In this manner it is possible to implement stable and
effective field-weakening control in the same manner as in the
first and second embodiments whatever torque is output. What is
more, the adoption of one-pulse waveform voltages allows the
inverter voltage utilization ratio to be improved, leading to lower
cost and greater efficacy of the device.
[0089] The present invention makes it possible for stable and
effective field-weakening control to be implemented in a motor
control device which implements field-weakening control whatever
torque is output.
* * * * *