U.S. patent application number 09/800258 was filed with the patent office on 2001-11-22 for speed sensorless vector control apparatus.
This patent application is currently assigned to Fuji Electric Co., Ltd.. Invention is credited to Tajima, Hirokazu, Umida, Hidetoshi.
Application Number | 20010043048 09/800258 |
Document ID | / |
Family ID | 18590882 |
Filed Date | 2001-11-22 |
United States Patent
Application |
20010043048 |
Kind Code |
A1 |
Tajima, Hirokazu ; et
al. |
November 22, 2001 |
Speed sensorless vector control apparatus
Abstract
A control apparatus for estimating the flux, the current, and
the speed of an AC motor using the current and the voltage, and
controlling the vector of an AC motor using the estimated speed, a
flux command, and a torque current command. The speed is estimated
by adding a product of the deviation between the actual value and
the estimated value of a magnetization current, the level of a
torque current correspondence value, the sign correspondence value
of a primary frequency command value, and a gain to an outer
product of an estimated current deviation and an estimated flux.
Thus, a stable speed estimating operation can be performed to
successfully operate the motor in a low speed area in which a
voltage frequency applied to the motor is extremely low.
Inventors: |
Tajima, Hirokazu; (Mie,
JP) ; Umida, Hidetoshi; (Kanagawa, JP) |
Correspondence
Address: |
GREER, BURNS & CRAIN, LTD.
Suite 2500
300 South Wacker Drive
Chicago
IL
60606
US
|
Assignee: |
Fuji Electric Co., Ltd.
|
Family ID: |
18590882 |
Appl. No.: |
09/800258 |
Filed: |
March 6, 2001 |
Current U.S.
Class: |
318/727 |
Current CPC
Class: |
H02P 21/18 20160201;
H02P 21/26 20160201 |
Class at
Publication: |
318/727 |
International
Class: |
H02P 001/24; H02P
001/42; H02P 003/18; H02P 007/36; H02P 005/28 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 10, 2000 |
JP |
2000-072482 |
Claims
What is claimed is:
1. A speed sensorless vector control apparatus, comprising: a
current/flux operation unit computing a primary current estimated
value (hereinafter referred to as an estimated current) and a
secondary flux estimated value (hereinafter referred to as an
estimated flux) from a primary current, a primary voltage, and an
estimated speed of an AC motor without a speed sensor; a coordinate
conversion unit converting a primary current into a torque current
and a magnetization current with an estimated flux vector set as a
reference of a rotation coordinate; a current adjustment unit
adjusting a torque current and a magnetization current such that
the currents match respective commands; a coordinate conversion
unit generating a primary voltage command by converting coordinates
of an output signal of said current adjustment unit with an
estimated flux vector set as a reference of a rotation coordinate;
an inverter for driving the AC motor operated at a primary voltage
command; and a speed estimation unit receiving an estimated
current, an estimated flux, a primary current, a torque current, a
magnetization current, and a primary frequency command value, and
estimating speed of the motor, wherein said speed estimation unit
adds a product of magnetization current deviation between an actual
value of a magnetization current and an estimated value, a level of
a torque current correspondence value, a sign correspondence value
of a primary frequency command value, and a gain to an outer
product of estimated current deviation between a primary current
and an estimated current and an estimated flux, thereby estimating
speed.
2. The apparatus according to claim 1, wherein said torque current
correspondence value is a torque current estimated value.
3. The apparatus according to claim 1, wherein said torque current
correspondence value is a torque current actual value.
4. A speed sensorless vector control apparatus, comprising:
current/flux operation means for computing a primary current
estimated value (hereinafter referred to as an estimated current)
and a secondary flux estimated value (hereinafter referred to as an
estimated flux) from a primary current, a primary voltage, and an
estimated speed of an AC motor without a speed sensor; coordinate
conversion means for converting a primary current into a torque
current and a magnetization current with an estimated flux vector
set as a reference of a rotation coordinate; current adjustment
means for adjusting a torque current and a magnetization current
such that the currents match respective commands; coordinate
conversion means for generating a primary voltage command by
converting coordinates of an output signal of said current
adjustment means with an estimated flux vector set as a reference
of a rotation coordinate; an inverter for driving the AC motor
operated at a primary voltage command; and speed estimation means
for receiving an estimated current, an estimated flux, a primary
current, a torque current, a magnetization current, and a primary
frequency command value, and estimating speed of the motor, wherein
said speed estimation means adds a product of magnetization current
deviation between an actual value of a magnetization current and an
estimated value, a level of a torque current correspondence value,
a sign correspondence value of a primary frequency command value,
and a gain to an outer product of estimated current deviation
between a primary current and an estimated current and an estimated
flux, thereby estimating speed.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a speed sensorless vector
control apparatus capable of controlling the vector of an AC motor
such as an induction motor, etc. without a speed sensor.
[0003] 2. Description of the Related Art
[0004] In vector control known as a high-performance and
high-precision system of controlling an induction motor, speed
information about a motor is required, and is normally obtained by
a pulse generator (PG), etc. However, it is desired to realize the
speed sensor vector control as a variable speed drive system
capable of performing torque control and obtaining the maximum
torque in a wide operation range without a necessity of the high
performance of the conventional speed sensor vector control at a
request to restrict the environment of setting a speed sensor,
simplify the wiring, reduce the cost, etc.
[0005] FIG. 1 is a block diagram of the function of the
conventional speed sensorless vector control apparatus using a
common speed adaptive secondary flux observer, and shows the speed
sensor vector control of an AC motor 102 such as an induction
motor, etc. by combining an inverter 101, a current detection unit
103, current adjustment units 104 and 105, coordinate conversion
units 106 and 109, 3 phase to 2 phase conversion units 107 and 108,
a current/flux estimation unit 110, and a speed estimation unit
301.
[0006] The current/flux estimation unit 110, the speed estimation
unit 301, etc. configure the speed adaptive secondary flux
observer.
[0007] In FIG. 1, a primary current 118 of the AC motor 102 through
the 3 phase to 2 phase conversion unit 108 is converted into a d-q
axis rotation coordinate component by the coordinate conversion
unit 109 with an estimated flux (vector) 122 set as the standard of
a rotation coordinate, and then into a torque current (i.sub.q) 117
and a magnetization current (i.sub.d) 116. The current adjustment
units 104 and 105 perform control such that the torque current
(i.sub.q) 117 and the magnetization current (i.sub.d) 116
respectively match a torque current command (i.sub.q*) 113 and a
magnetization current command (1.sub.d*) 115. The magnetization
current command (1.sub.d*) 115 is computed by a magnetization
current command operation unit 112 which receives a flux command
(.PHI.*) 114.
[0008] The coordinate conversion unit 106 generates a primary
voltage command 119 by converting the output of the current
adjustment units 104 and 105 into a static coordinate system,
generating a primary voltage command 119, and providing the
generated command for the inverter 101 such as a three-phase
voltage type inverter, etc. The inverter 101 performs DC-AC
conversion based on the primary voltage command 119, and provides
the voltage (primary voltage 120) of each of the three phases for
the AC motor 102.
[0009] In addition, the primary voltage 120 and a primary current
118 detected by the current detection unit 103 are converted into
two components respectively by the 3 phase to 2 phase conversion
units 107 and 108. The two-phase component of the primary voltage
120 is input to the current/flux estimation unit 110, the two-phase
component of the primary current 118 is input to the current/flux
estimation unit 110, the speed estimation unit 301, and the
coordinate conversion unit 109.
[0010] Described mainly below are the operations by the
current/flux estimation unit 110 and the speed estimation unit 301
to explain about the speed estimating operation in the conventional
speed sensorless vector control.
[0011] First, the principle of the speed sensorless vector control
is introduced by:
[0012] Document 1: Power and Electric Application Study of Electric
Society of Japan, material IEA-91-11, 1991, pp.41-48 "Speed
Adaptive Secondary Flux Observer of an Induction Motor and its
Characteristics".
[0013] Document 2: IEEE Transaction on Industry Application,
Vol.30, No.5, September/0 ct 1994, pp.1219-1224 "Speed Sensorless
Field Oriented Control of Induction Motor with Rotor Resistance
Adaptation".
[0014] Document 3: "Vector Control of AC Motor" (published by Daily
Industrial News in 1996, pp9l-110, Chapter 5 `Speed Sensor Vector
Control of Induction Motor`.
[0015] According to the above mentioned documents, the speed can be
estimated based on the algorithm described below with the
configuration shown in FIG. 2 described later.
[0016] First, in an example of an induction motor as a motor to be
controlled, a state equation can normally be represented by
equation 1. The transposed matrix is expressed with the character T
added to a matrix as a superscript. 1 / t [ i s r ] = A [ i s r ] +
Bv s i s = [ i s i s ] T ; r = [ r r ] T ; v s = [ v s v s ] T ; A
= [ - ( R s L s + 1 - r ) I L m L s L r ( 1 r I - r J ) L m r I - 1
r I + r J ] ; B = [ 1 L s 0 0 0 0 1 L s 0 0 ] I = [ 1 0 0 1 ] ; J =
[ 0 - 1 1 0 ] ; Equation 1
[0017] In the equation 1 above,
[0018] i.sub.s and v.sub.s indicate the primary current and the
primary voltage;
[0019] .PHI..sub.r indicates the secondary interlinkage flux
(secondary flux);
[0020] Superscripts .alpha. and .beta. indicate the orthogonal
2-axis 15 components of a static coordinate system;
[0021] R.sub.s and R.sub.r indicate the primary resistance and the
secondary resistance;
[0022] L.sub.s, L.sub.r, and L.sub.m indicate the primary
inductance, the secondary inductance, and the mutual inductance
respectively;
[0023] .tau..sub.r=L.sub.r/R.sub.r indicates the secondary time
constant;
[0024] .sigma.=1-L.sub.m.sup.2/(L.sub.sL.sub.r) indicates a leakage
coefficient; and
[0025] .omega..sub.r indicates a rotor angular speed.
[0026] The equation 1 indicates the relationship between the
primary voltage v.sub.s as an input to a control target and the
primary current i.sub.s and the secondary flux .phi..sub.r as
outputs. If the primary voltage vs is provided, the primary current
i.sub.s and the secondary flux .PHI..sub.r can be computed.
[0027] A model in which the above mentioned deviation can be input
to a simulator such that there is no deviation between an output of
a control target which can be measured and an estimated output
value of the simulator is referred to as a same dimensional
observer. According to the principle of the observer, the
current/flux estimation unit 110 computes the estimated value
i.sub.s of the primary current (an estimated current 121 shown in
FIG. 1) and the estimated value .PHI..sub.r of the secondary flux
(an estimated flux 122) by equation 2. In the following
descriptions, " " indicates an estimated value. 2 / t [ i s r ] = A
[ i s r ] + Bv s + G ( i s - i s ) Equation 2
[0028] In the equation 2 above,
[0029] G indicates a gain matrix (optional matrix for determination
of the dynamic characteristic of an observer).
[0030] A matrix A is obtained by replacing the angular speed
.omega..sub.r in the matrix A in the equation 1 with the estimated
speed .omega..sub.r .
[0031] In the equation 2 above, when the rotor angular speed
changes, there arises deviation between the output (primary current
estimated value) of the simulator (equation model) and the actual
primary current. Thus, the speed adaptive secondary flux observer
estimates the secondary flux .PHI..sub.r while estimating and
adapting the angular speed .omega..sub.r using the function of the
current deviation (i.sub.s-i.sub.s ).
[0032] The speed adaptive secondary flux observer can be configured
as expressed by equation 3 described later by adding the adaptive
estimation mechanism of the angular speed as an unknown parameter
to the observer expressed by the equation 2, and can be embodied by
the speed estimation unit 301 shown in FIG. 1 obtaining an
estimated speed 123 from the estimated current 121, the primary
current 118, and the estimated flux (vector) 122.
[0033] That is, as shown in FIG. 2 of an embodiment of the speed
estimation unit 301 shown in FIG. 1, an outer product unit 202
obtains an outer product of the current deviation (i.sub.s-i.sub.s
) obtained by an addition/subtraction unit 203 and the estimated
flux (.PHI..sub.r ) 122, and the speed estimation unit 301 provides
the outer product to a PI adjustment unit 201, and obtains the
estimated speed (.omega..sub.r ) 123.
[0034] That is, the estimated speed .omega..sub.r is computed by
the following equation 3. The symbol x in the equation 3 indicates
an outer product.
.omega..sub.r =(k.sub.p.omega.+k.sub.i.omega./p){(i.sub.s-i.sub.s
).times..phi..sub.r
}=(k.sub.p.omega.+k.sub.i.omega./p){(i.sub.s.alpha.-i-
.sub.s.alpha. ).phi..sub.r.beta. -(i.sub.s.beta.-i.sub.s.beta.
).phi..sub.r.alpha. }
[0035] Equation 3
p=d /dt
[0036] In the equation 3 above,
[0037] k.sub.p.omega. and k.sub.i.omega. indicate a proportional
gain and an integral gain respectively;
[0038] i.sub.s.alpha., i.sub.s.alpha. , i.sub.s.beta., and
i.sub.s.beta. indicate the orthogonal 2-axis component in the
static coordinate system of the primary current is and the
estimated current i.sub.s ; and
[0039] .phi..sub.r.alpha. and .phi..sub.r.beta. indicate the
orthogonal 2-axis component in the static coordinate system of the
estimated flux .phi..sub.r .
[0040] The estimated speed .omega..sub.r thus obtained as described
above is used in an arithmetic operation of the deviation between
the speed and the speed target value .omega..sub.r* not shown in
FIG. 1, the deviation is input to a speed adjustment unit, and a
torque current command 113 is generated.
[0041] In the above mentioned conventional speed estimating method,
when the voltage applied to the motor and the frequency of the
current are considerably low (frequency of 0 in an extreme
example), the induction reactance of the motor logically approaches
zero, and the voltage of the inductance approaches zero regardless
of the current. Therefore, the secondary flux cannot be computed
from the primary voltage, and the estimated flux or the estimated
speed cannot be computed, either. That is, the deviation between an
estimated flux and its actual value, and the deviation between an
estimated speed and its are not equal to zero, and do not
successfully converge.
[0042] Generally speaking, since it is difficult to stably estimate
the speed in an area in which the frequency of the voltage applied
to a motor is extremely low, there has been the problem with the
conventional technology that a motor cannot be operated by speed
sensorless vector control. That is, since there is a lower limit
for the output frequency of the sensorless vector control apparatus
using an inverter, there has been a request to extend the range of
speed control in the above mentioned low speed area.
SUMMARY OF THE INVENTION
[0043] To solve the above mentioned problems, the present invention
aims at providing the speed sensorless vector control apparatus
capable of operating a motor without any trouble by successfully
performing a stable speed estimation even in a low speed area in
which the frequency of a voltage applied to the motor is extremely
low.
[0044] The speed sensorless vector control apparatus according to
the present invention includes a current/flux operation unit, a
coordinate conversion unit, a current adjustment unit, a coordinate
conversion unit, an inverter for driving an AC motor, and a speed
estimation unit.
[0045] According to the first aspect of the present invention, the
current/flux operation unit computes the primary current estimated
value (hereinafter referred to as an estimated current) and the
secondary flux estimated value (hereinafter referred to as an
estimated flux) from the primary current, the primary voltage, and
the estimated speed of the AC motor without a speed sensor. The
coordinate conversion unit converts the primary current into a
torque current and a magnetization current with the estimated flux
vector set as the reference of a rotation coordinate. The current
adjustment unit adjusts the torque current and the magnetization
current such that they match respective commands. The coordinate
conversion unit generates the primary voltage command by converting
the coordinates of the output signal of the current adjustment unit
with the estimated flux vector set as the reference of a rotation
coordinate. The inverter for driving an AC motor is operated at the
primary voltage command. The speed estimation unit receives an
estimated current, an estimated flux, a primary current, a torque
current, a magnetization current, and a primary frequency command
value, and adds a product of the magnetization current deviation
between the actual value of the magnetization current and the
estimated value, the size of a torque current correspondence value,
the sign correspondence value of the primary frequency command
value, and the gain to the outer product of the estimated current
deviation between the primary current and the estimated current and
the estimated flux, thereby computing the estimated value of the
speed of the motor.
BRIEF DESCRIPTION OF THE DRAWINGS
[0046] FIG. 1 is a control block diagram of the conventional
technology;
[0047] FIG. 2 is a block diagram of a practical example of the
speed estimation unit shown in FIG. 2;
[0048] FIG. 3 is a control block diagram of an embodiment of the
present invention; and
[0049] FIG. 4 is a block diagram of a practical example of the
speed estimation unit shown in FIG. 3.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0050] To solve the above mentioned problems, the invention
according to claim 1 comprises:
[0051] current/flux operation means for computing an estimated
current and an estimated flux from the primary current, the primary
voltage, and the estimated speed of an AC motor without a speed
sensor;
[0052] coordinate conversion means for converting a primary current
into a torque current and a magnetization current with an estimated
flux vector set as a reference of a rotation coordinate;
[0053] current adjustment means for adjusting a torque current and
a magnetization current such that they match respective
commands;
[0054] coordinate conversion means for generating a primary voltage
command by converting the coordinates of an output signal of the
current adjustment means with an estimated flux vector set as a
reference of a rotation coordinate;
[0055] an inverter for driving an AC motor operated at the primary
voltage command; and
[0056] speed estimation means for receiving an estimated current,
an estimated flux, a primary current, a torque current, a
magnetization current, and a primary frequency command value, and
computing the estimated value of the speed of the motor. The speed
estimation means adds a product of the magnetization current
deviation between the actual value of the magnetization current and
the estimated value, the size of a torque current correspondence
value, the sign correspondence value of the primary frequency
command value, and the gain to the outer product of the estimated
current deviation between the primary current and the estimated
current and the estimated flux, thereby computing the estimated
value of the speed of the motor.
[0057] The torque current correspondence value can be a torque
current estimated value or a torque current actual value as
described in claim 2 or 3.
[0058] The embodiment of the present invention is described below
by referring to the attached drawings.
[0059] FIG. 3 is a control block diagram of an embodiment of the
present invention. The difference from the block diagram shown in
FIG. 1 if the configuration of a speed estimation unit 111. The
speed estimation unit 111 further receives a primary frequency
command value (.omega..sub.1*) 401, a magnetization current
(i.sub.d) 116, and a torque current (i.sub.q) 117. Other units are
the same as those shown in FIG. 1. Therefore, the same reference
numerals as those shown in FIG. 1 are assigned, and the explanation
is omitted here.
[0060] FIG. 4 shows the internal configuration of the speed
estimation unit 111.
[0061] The configuration is described below by referring to FIG. 2.
As compared with FIG. 2, the configuration shown in FIG. 4 further
comprises addition/subtraction units 205 and 305, multiplication
units 306 and 309, a gain element 304, an absolute value operation
unit 307, a sign operation unit 308, and a coordinate conversion
unit 310.
[0062] That is, according to the present embodiment, the following
operations are performed in addition to the outer product operation
of the current deviation (i.sub.s-i.sub.s ) and the estimated flux
.phi..sub.r performed by the outer product unit 202 shown in FIG.
2, and the PI operation performed by the PI adjustment unit 201 on
the output of the outer product operation.
[0063] That is, in FIG. 4, the coordinate conversion unit 310
converts coordinates based on the estimated flux (.phi..sub.r )
122, separates the estimated current (i.sub.s ) 121 into a
magnetization current estimated value (i.sub.d ) 302 and a torque
current estimated value (i.sub.q ) 303, and outputs the result.
[0064] Then, the addition/subtraction unit 305 obtains the
deviation (i.sub.d-i.sub.d ) between the actual magnetization
current (i.sub.d) 116 and the magnetization current estimated value
(i.sub.d ) 302, and the multiplication unit 306 multiplies the
deviation by the torque current estimated value (i.sub.q ) 303
obtained by the absolute value operation unit 307 or the absolute
value of the torque current actual value (i.sub.q) 117.
[0065] In FIG. 4, the absolute value operation unit 307 in the
speed estimation unit 111 receives the torque current actual value
(i.sub.q) 117 to match FIG. 4 with FIG. 3, and only has to compute
the absolute value using one of the torque current estimated value
(i.sub.q ) 303 and the torque current actual value (i.sub.q)
117.
[0066] Furthermore, the multiplication unit 309 multiplies the sign
correspondence value sgn (.omega..sub.1*) of a primary frequency
command value (.omega..sub.1*) 401 obtained by the sign operation
unit 308 by the output of the multiplication unit 306, the gain
element 304 multiplies the output by k.sub..omega., and the
addition/subtraction unit 205 adds the output to the output of the
outer product unit 202. Then, the output of the
addition/subtraction unit 205 is input to the PI adjustment unit
201, and the estimated speed (.omega..sub.r ) 123 is obtained.
[0067] That is, according to the present embodiment, the
magnetization current deviation (i.sub.d-i.sub.d ) is amplified
depending on the value corresponding to the level of the torque,
the sign of the output signal is adjusted depending on the rotation
direction of a motor, and the addition/subtraction unit 205 adds a
correction signal obtained by multiplication by a gain k.omega. to
the output signal of the outer product unit 202, and inputs the
result to the PI adjustment unit 201.
[0068] When the actual speed (.omega..sub.r) of the AC motor 102
matches the estimated speed (.omega..sub.r ) 123, the direction of
the actual flux vector of the AC motor 102 matches the direction of
the estimated flux vector, and the magnetization current estimated
value (i.sub.d ) 302 matches the actual magnetization current
(i.sub.d) 116. As a result, the output of the addition/subtraction
unit 305 is zero, and the output of the gain element 304 is also
zero. Therefore, the configuration shown in FIG. 4 is practically
the same as that of the conventional technology shown in FIG.
2.
[0069] However, when the actual speed of the AC motor 102 does not
match the estimated speed 123 in a low speed area in which the
voltage frequency applied to the AC motor 102 is nearly zero, the
direction of the flux vector of the AC motor 102 does not match the
direction of the estimated flux vector, thereby causing the
deviation depending on the different angle of the flux vector
between the magnetization current estimated value 302 and the
magnetization current 116.
[0070] The speed estimation unit 111 generates a correction signal
for the magnetization current deviation (i.sub.d-i.sub.d ) with the
level of the torque and the rotation direction of a motor taken
into account, and the correction signal is added to the outer
product of the estimated current deviation and the estimated flux.
Based on the resultant signal, the estimated speed (.omega..sub.r )
123 is computed.
[0071] That is, the speed estimation unit 111 shown in FIG. 4
computes the estimated speed 123 by equation 4 instead of the
equation 3 above, and the magnetization current estimated value 302
performs feedback control to suppress dispersion on the
magnetization current 116, thereby matching the estimated speed 123
with the actual speed.
[0072] The equation 4 is an example in which the absolute value
operation unit 307 shown in FIG. 4 selects an absolute value
.vertline.i.sub.q.vertline. of the torque current actual value, and
multiplies it by the magnetization current deviation
(i.sub.s-i.sub.s ) However, as described above, the absolute value
.vertline.i.sub.q.vertlin- e. of the torque current actual value
can be replaced with the absolute value .vertline.i.sub.q
.vertline. of the torque current estimated value.
.omega..sub.r =(k.sub.p.omega.+k.sub.I.omega./p)[{(i.sub.s-i.sub.s
).times..phi..sub.r
}+k.sub..omega..multidot.sgn(.omega..sub.1*).multidot-
.(i.sub.d-i.sub.d
).multidot..vertline.i.sub.q.vertline.]=(k.sub.p.omega.+-
k.sub.I.omega./p)[{(i.sub.s.alpha.-i.sub.s.alpha.
).phi..sub.r.beta. (i.sub.s.beta.-i.sub.s.beta. ).phi..sub.r.alpha.
}+k.sub..omega..multidot-
.sgn(.omega..sub.1*).multidot.(i.sub.d-i.sub.d
).multidot..vertline.i.sub.- q.vertline.]
[0073] Equation 4
[0074] In the equation 4 above, k.sub..omega. indicates the gain of
the gain element 304, and x indicates an outer product.
[0075] The first term (i.sub.s-i.sub.s ).times..phi..sub.r in the
brackets on the right side of the equation 4 is just the same also
in the signal of the rotation coordinate system. Therefore, the
equation 4 can be transformed as shown in equation 5. The equation
5 is equivalent to the equation 4. Also in the equation 5, the
absolute value .vertline.i.sub.q .vertline. of the torque current
estimated value can replace the absolute value
.vertline.i.sub.q.vertline. of the torque current actual value.
.omega..sub.r
=(k.sub.p.omega.+k.sub.i.omega./p)[{(i.sub.d,i.sub.q)-(i.sub- .d
,i.sub.q )}.times.(.phi..sub.dr ,.phi..sub.qr
)+k.sub..omega..multidot.-
sgn(.omega..sub.1*).multidot.(i.sub.d-.sub.d
).multidot..vertline.i.sub.q.-
vertline.]=(k.sub.p.omega.+k.sub.i.omega./p)[{(i.sub.d-i.sub.d
).phi..sub.qr -(i.sub.q-i.sub.q ).phi..sub.dr
}+k.sub..omega..multidot.sg-
n(.omega..sub.1*).multidot.(i.sub.d-i.sub.d
).multidot..vertline.i.sub.d.v- ertline.]
[0076] Equation 5
[0077] Thus, according to the present embodiment, the estimated
speed 123 is amended in the direction such that the deviation
between the magnetization current actual value and the estimated
value can be suppressed depending on the level of the torque and
the sign of the primary frequency command value although the
voltage frequency applied to the motor is extremely low. Then, the
current/flux estimation unit 110 estimates the flux using the
amended estimated speed 123. Therefore, the flux vector of the
motor can converge in a desired status, thereby matching the
estimated speed with the actual speed.
[0078] The principle of the present invention can be applied not
only to the induction motor in the above mentioned embodiment, but
also to a synchronous motor.
[0079] As described above, according to the present invention, the
flux and the speed can be stably estimated although the voltage
frequency applied to an AC motor is extremely low. Therefore, the
motor speed control range can be extended than in the conventional
technology.
* * * * *