U.S. patent application number 15/687042 was filed with the patent office on 2017-12-07 for motor controller and motor control method.
This patent application is currently assigned to PANASONIC INTELLECTUAL PROPERTY MANAGEMENT CO., LTD.. The applicant listed for this patent is Panasonic Intellectual Property Management Co., Ltd.. Invention is credited to Yasushi KATO, Ryuta SASAKI, Toru TAZAWA, Yasuyuki YOKOUCHI.
Application Number | 20170350404 15/687042 |
Document ID | / |
Family ID | 49081770 |
Filed Date | 2017-12-07 |
United States Patent
Application |
20170350404 |
Kind Code |
A1 |
SASAKI; Ryuta ; et
al. |
December 7, 2017 |
MOTOR CONTROLLER AND MOTOR CONTROL METHOD
Abstract
A motor controller of the present invention comprises units
which obtain information indicative of a motor speed (.omega.) and
information indicative of motor torque (T), an air flow calculation
section which calculates an air flow (Q) of a fan based on the
motor speed (.omega.) and the motor torque (T); and a speed command
generation section which generates a speed command (.omega.*) of a
motor such that the air flow (Q) coincides with the predetermined
air flow command (Q*).
Inventors: |
SASAKI; Ryuta; (Osaka,
JP) ; YOKOUCHI; Yasuyuki; (Osaka, JP) ; KATO;
Yasushi; (Kyoto, JP) ; TAZAWA; Toru; (Osaka,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Panasonic Intellectual Property Management Co., Ltd. |
Osaka |
|
JP |
|
|
Assignee: |
PANASONIC INTELLECTUAL PROPERTY
MANAGEMENT CO., LTD.
|
Family ID: |
49081770 |
Appl. No.: |
15/687042 |
Filed: |
August 25, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14382239 |
Aug 29, 2014 |
9771944 |
|
|
PCT/JP2012/005849 |
Sep 13, 2012 |
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15687042 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F24F 7/007 20130101;
H02P 23/14 20130101; F24F 11/77 20180101; F24F 2110/00 20180101;
F05D 2200/14 20130101; F04D 25/06 20130101; F04D 27/00 20130101;
Y02B 30/746 20130101; F24F 11/0001 20130101; F04D 27/004 20130101;
F24F 11/30 20180101; F04D 25/08 20130101; H02P 6/06 20130101; Y02B
30/70 20130101; F05D 2270/3061 20130101; F05D 2270/02 20130101;
F05D 2200/12 20130101; F24F 11/74 20180101 |
International
Class: |
F04D 27/00 20060101
F04D027/00; F24F 7/007 20060101 F24F007/007; F24F 11/04 20060101
F24F011/04; H02P 6/06 20060101 H02P006/06; F04D 25/06 20060101
F04D025/06; H02P 23/14 20060101 H02P023/14; F24F 11/00 20060101
F24F011/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 2, 2012 |
JP |
2012-046204 |
Claims
1. A motor controller for controlling a motor which drives a fan
for supplying air to a desired location through an air flow
passage, the motor controller comprising: an air flow calculator
configured to obtain speed information indicative of a motor speed
at which the motor is running and torque information indicative of
a motor torque which the motor is outputting and calculate an air
flow of the fan from the motor speed and the motor torque; and a
speed command generator configured to generate a speed command
given to rotate the motor at a target motor speed so that the air
flow coincides with a predetermined air flow command, wherein the
speed command generator is configured to compare the calculated air
flow and the predetermined air flow command and subject to a
comparison result between the calculated air flow and the
predetermined air flow command, use a ratio of the predetermined
air flow command with respect to the air flow to derive the speed
command.
2. The motor controller according to claim 1, wherein the speed
command generator is further configured to use a difference between
the calculated air flow and the predetermined air flow command to
derive the speed command when the difference between the calculated
air flow and the predetermined air flow command falls within a
predetermined range.
3. The motor controller according to claim 1, wherein the speed
command generator is further configured to: receive the
predetermined air flow command which directs a target air flow;
compare the predetermined air flow command and the calculated air
flow; and upon a determination that a difference between the
predetermined air flow command and the calculated air flow falls
outside a first predetermined range, multiply the ratio between the
predetermined air flow command and the calculated air flow by a
target motor speed of previous update to derive the speed command
which directs the motor to rotate at the target motor speed.
4. The motor controller according to claim 1, further comprising a
motor driving controller configured to generate a signal used for
controlling a driving voltage to the motor in such a way that the
motor speed will track the target motor speed.
5. The motor controller according to claim 1, wherein the speed
command generator is configured to integrate a difference between
the predetermined air flow command and the calculated air flow to
derive the target motor speed when the difference between the
predetermined air flow command and the calculated air flow falls
within a predetermined range.
6. The motor controller according to claim 1, wherein the speed
command generator is configured to multiply, by a gain, a
difference between the predetermined air flow command and the
calculated air flow and add the motor speed to a result of
multiplication to derive the target motor speed, when the
difference between the predetermined air flow command and the
calculated air flow falls within a predetermined range.
7. The motor controller according to claim 1, wherein the speed
command generator is configured to correct the speed command in
such a way that a difference between the speed command and the
motor speed will fall within a predetermined speed range, when the
difference between the speed command and the motor speed falls
outside the predetermined speed range.
8. The motor controller according to claim 1, wherein the speed
command generator is configured to update the target motor speed at
intervals, the speed command generator being configured to replace
the speed command, when a difference between the motor torque and a
motor torque obtained previously falls within a predetermined
torque range.
9. The motor controller according to claim 1, wherein the speed
command generator is configured to store a minimum motor speed and
a maximum motor speed and further configured to adjust the target
motor speed to fall within a range between the minimum and the
maximum motor speeds.
10. The motor controller according to claim 1, wherein the air flow
calculator is configured to divide the motor torque with a square
of the motor speed and multiply the motor speed with the result of
division.
11. The motor controller according to claim 1, further comprising a
first detector configured to detect the motor speed and output the
speed information.
12. The motor controller according to claim 1, further comprising a
second detector configured to detect a current flowing through the
motor and output the torque information.
13. A motor control system comprising: a motor; the motor
controller according to claim 1; and a motor driving controller
configured to drive the motor based on a speed command provided by
the motor controller, wherein the motor driving controller is
disposed outside the motor controller.
14. A motor control system comprising: a motor; the motor
controller according to claim 1; and a motor driving controller
configured to drive the motor based on a speed command provided by
the motor controller, wherein the motor driving controller is
disposed inside the motor controller.
15. A method of controlling a motor which drives a fan for
supplying air to a desired location through an air flow passage,
the method comprising: obtaining speed information indicative of a
motor speed at which the motor is running and torque information
indicative of motor torque which the motor is outputting;
generating a speed command given to rotate the motor at a target
motor speed so that the air flow coincides with a predetermined air
flow command, wherein generating a speed command comprises
comparing the air flow and the predetermined air flow command and,
subject to a result of comparison between the air flow and the
predetermined air flow command, use a ratio of the predetermined
air flow command with respect to the air flow to generate the speed
command; and controlling the motor with the generated speed command
in such a way that the fan will output a target air flow.
Description
RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 14/382,239, filed Aug. 29, 2014 and which is a
371 application of PCT/JP2012/005849 having an international filing
date of Sep. 13, 2012, which claims priority to JP2012-046204 filed
on Mar. 2, 2012, the entire contents of which are incorporated
herein by reference.
TECHNICAL FIELD
[0002] The present invention relates to a motor controller and a
motor control method. Particularly, the present invention relates
to an air flow control method for a fan motor such as an air
conditioner, which performs motor control, or a blower such as a
ventilation fan.
BACKGROUND ART
[0003] In recent years, in an air conditioning system of a
ventilation fan or an air conditioner, to optimize a status of a
room or the air conditioning system, it is required that an air
flow (air volume) be controlled to become a predetermined air flow
value even though a static pressure changes due to clogging of a
filter or a state of a vent provided in an air outlet.
[0004] For example, as a technique for controlling the air flow
such that the air flow becomes the predetermined air flow value,
for example, Patent Literature 1 is known. According to the
conventional technique disclosed in Patent Literature 1, a command
speed of a motor for driving a fan is calculated from a formula
(1).
S*=S+K.times.(S-Sa) (1)
[0005] S* indicates the command speed of the motor, S indicates a
motor speed, Sa indicates a target motor speed, and K indicates a
gain. The target motor speed Sa is calculated from a formula
(2).
Sa = n = 0 j ( m = 0 i ( k nm T n Q * m ) ) ( 2 ) ##EQU00001##
[0006] T indicates motor torque, Q* indicates a predetermined air
flow value, k.sub.nm (n=0, 1, 2, j, m=0, 1, 2, . . . , i) indicates
a constant, i indicates a finite value, and j indicates a finite
value. The formula (2) represents a relationship in which the motor
speed required to allow the air flow to become the predetermined
air flow command Q* in a case where the motor torque is T is
Sa.
[0007] Hereinafter, a description will be given of control of the
motor in the case where a motor controller disclosed in Patent
Literature 1 controls the air flow of the fan such that the air
flow becomes the predetermined air flow value Q*, with reference to
FIG. 7.
[0008] In FIG. 7, a curve F indicates a motor speed and motor
torque at which the air flow becomes the predetermined air flow
value Q* (hereinafter this curve will be referred to as "constant
air flow curve"). A curve C indicates an environment curve unique
to an air conditioning environment in which the motor is mounted
(hereinafter will be referred to as "air conditioning environment
curve").
[0009] It is supposed that the operation point of the motor is a
point A1 on the air conditioning environment curve C. In this case,
the target motor speed Sa calculated from the formula (2) is a
motor speed Sa1 at a point B1 on the constant air flow curve F at
which motor torque T1 corresponding to the operation point A1 is
obtained.
[0010] According to the formula (1), a difference (indicated by A S
in FIG. 7) obtained by subtracting Sa1 from the motor speed S1 is
multiplied by the gain K and the motor speed S1 is added to the
resulting value, thereby resulting in a command speed S* (not
shown) of the motor. Then, the command speed S* is output. The
motor speed is controlled in accordance with the command speed S*,
and thereby the operation point is shifted.
[0011] At the shifted operation point, a new command speed S* is
calculated according to the formula (2) and the formula (1). This
is repeated. The operation point is shifted to an operation point
A2 and then to an operation point A3 in FIG. 7. Finally, obtained
is an operation point at which the difference between the motor
speed S and the target motor speed Sa becomes zero, i.e., an
intersection E of the air conditioning environment curve C and the
constant air flow curve F.
[0012] As described above, the motor controller disclosed in Patent
Literature 1 is configured to calculate a compensation value
required for the motor speed using the motor torque and the
predetermined air flow value and the command speed is output based
on the compensation value. This makes it possible to control the
air flow such that the air flow becomes the predetermined air flow
value, even if the predetermined air flow value changes or the
static pressure changes due to clogging of the filter or
opening/closing of the vent.
CITATION LIST
Patent Literature
[0013] Patent Literature 1: International Publication No.
2008/117515
SUMMARY OF INVENTION
Technical Problem
[0014] In the conventional technique disclosed in Patent Literature
1, how the motor speed changes and converges depends on the value
of the gain K of the formula (1). For example, in a case where the
value of the gain K is small, the changing magnitude of the command
speed S* with respect to a calculation cycle is small, and
therefore, it takes time for the motor speed to converge.
[0015] On the other hand, in a case where the value of the gain K
is large, the changing magnitude of the calculated command speed S*
is large. The motor speed changes back and forth, crossing a
convergence point E in FIG. 7 (the motor speed repeatedly exceeds
and falls below the convergence point E). Thus, the motor speed
does not stably converge at the convergence point E. To avoid this,
an experiment is conducted while changing the value of the gain K
to find an optimal value.
[0016] However, the optimal value of the gain K is varied depending
on the air conditioning environment in which the motor is mounted.
For example, in some cases, a gain which is sufficiently stable in
an air conditioning environment of a virtual model becomes
excessive and the operation point does not stably converge, in a
real air conditioning environment provided in a house and changed
due to clogging of the air filter or opening/closing of the vent.
In light of this, assuming a change in the air conditioning
environment to be used, it is desired that the gain K be set to a
sufficiently small value so that the fan can operate stably in an
operation range in which the motor speed tends to fluctuates
unstably.
[0017] However, if the value of the gain K is small, it takes time
for the motor speed to converge. Therefore, when the predetermined
air flow value is changed significantly, it takes a long time for
the air flow to converge at a new predetermined air flow value, in
some cases.
[0018] The present invention is directed to solving the above
described problem associated with the prior art, and provides a
motor controller and a motor control method which allow the air
flow of a fan to track a predetermined air flow value at a high
speed and to stably converge at the predetermined air flow value,
even when the predetermined air flow value changes
significantly.
Solution to Problem
[0019] According to a first aspect of the present application,
there is provided a motor controller for controlling a motor which
drives a fan, the motor controller comprising: an air flow
calculation section which obtains information indicative of a motor
speed and information indicative of motor torque and calculates an
air flow of the fan based on the motor speed and the motor torque;
and a speed command generation section which generates a speed
command of the motor based on a comparison calculation value of the
air flow and a predetermined air flow command and by using a ratio
of the predetermined air flow command with respect to the air flow
such that the air flow coincides with the predetermined air flow
command. According to a second aspect of the present invention, in
the motor controller according to the first aspect, the speed
command generation section generates the speed command by using the
ratio of the predetermined air flow command with respect to the air
flow when the comparison calculation value falls outside a first
predetermined range; and the speed command generation section
generates the speed command by using a difference between the air
flow and the predetermined air flow command when the comparison
calculation value falls within the first predetermined range.
[0020] According to a third aspect of the present application, in
the motor controller according to the first aspect, the speed
command generation section generates as the speed command a value
obtained by multiplying the motor speed by the ratio of the
predetermined air flow command with respect to the air flow, or a
value obtained by multiplying the speed command output at a
previous time by the ratio of the predetermined air flow command
with respect to the air flow, when the comparison calculation value
falls outside the first predetermined range.
[0021] According to a fourth aspect of the present invention, the
motor controller according to the first aspect, further comprises a
motor driving control section which generates a signal used for
controlling a driving voltage given to the motor such that the
motor speed coincides with the speed command.
[0022] According to a fifth aspect of the present application, in
the motor controller according to the first aspect, the speed
command generation section generates the speed command by using a
value obtained by integrating a difference between the air flow and
the predetermined air flow command, when the comparison calculation
value falls within the first predetermined range.
[0023] According to a sixth aspect of the present application, in
the motor controller according to the first aspect, the speed
command generation section generates the speed command by using a
value which is a sum of the motor speed and a value obtained by
multiplying by a gain, a difference between the air flow and the
predetermined air flow command, when the comparison calculation
value falls within the first predetermined range.
[0024] According to a seventh aspect of the present application, in
the motor controller according to the first aspect, the speed
command generation section compensates the speed command such that
a difference between the speed command and the motor speed falls
within a second predetermined range, when the difference between
the speed command and the motor speed falls outside the second
predetermined range.
[0025] According to an eighth aspect of the present application, in
the motor controller according to the first aspect, the speed
command generation section compensates the speed command such that
the speed command coincides with the speed command output at a
previous time, when a difference between the motor torque obtained
at a present time and the motor torque obtained at a previous time
falls within a third predetermined range.
[0026] According to a ninth aspect of the present application, in
the motor controller according to the first aspect, the speed
command generation section contains a minimum speed command and a
maximum speed command, and outputs the speed command limited within
a range between the minimum speed command and the maximum speed
command.
[0027] According to a tenth aspect of the present application, in
the motor controller according to the first aspect, the air flow
calculation section calculates the air flow as a product of the
motor speed and a polynomial of variables in which the motor torque
is divided by a square of the motor speed.
[0028] According to an eleventh aspect of the present application,
in the motor controller according to the first aspect, the motor
speed is obtained by a first detector which detects the motor
speed.
[0029] According to a twelfth aspect of the present application, in
the motor controller according to the first aspect, the motor
torque is obtained by a second detector which detects a current
flowing in the motor.
[0030] According to a thirteenth aspect of the present application,
there is provided a method of controlling a motor which drives a
fan, the method comprising: obtaining at least one of information
indicative of a motor speed and information indicative of motor
torque; calculating an air flow of the fan based on the motor speed
and the motor torque; and generating a speed command of the motor
based on a comparison calculation value of the calculated air flow
and a predetermined air flow command, and by using a ratio of the
predetermined air flow command with respect to the air flow such
that the air flow coincides with the predetermined air flow
command.
Advantageous Effects of Invention
[0031] A motor controller of the present invention generates a
speed command which is equal to a motor speed which realizes an air
flow value of a predetermined air flow command, when the motor
controller determines that a difference between an air flow
calculated by an air flow calculation section and the predetermined
air flow command is large. This allows the air flow to track a
predetermined air flow value at a high speed and to stably converge
at the predetermined air flow value.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] FIG. 1 is a block diagram showing the exemplary
configuration of a motor control system including a motor
controller according to Embodiment 1 of the present invention.
[0033] FIG. 2 is a flowchart showing the exemplary process of a
speed command generation section 12 according to Embodiment 1 of
the present invention.
[0034] FIG. 3 is a flowchart showing the exemplary process of speed
command compensation steps within the speed command generation
section 12 according to Embodiment 1 of the present invention.
[0035] FIG. 4 is a view showing the exemplary air flow control
performed by a motor controller 8a according to Embodiment 1 of the
present invention.
[0036] FIG. 5 is a view showing the exemplary air flow control
performed by the motor controller 8a according to Embodiment 1 of
the present invention.
[0037] FIG. 6 is a block diagram showing the exemplary
configuration of a motor control system including a motor
controller according to Embodiment 2 of the present invention.
[0038] FIG. 7 is a view showing air flow control performed by a
motor controller according to a conventional technique.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0039] (View Point of the Present Invention)
[0040] In order to allow the air flow (air volume) of a fan to
track a predetermined air flow value at a high speed and stably
converge at the predetermined air flow value even when the
predetermined air flow value changes significantly, inventors of
the present application focused an attention on a rule in which the
air flow is generally proportional to a rotational speed in a
blower device such as the fan or a blower, as a rule derived from
similarity of flows in fluid dynamics. Specifically, according to
this rule, a relationship is satisfied, in which the ratio of a
predetermined air flow command (commanded air flow) with respect to
the air flow is equal to the ratio of "motor speed which realizes
an air flow value of the predetermined air flow command" with
respect to the motor speed. Therefore, the inventors decided as a
speed command, a value obtained by multiplying the motor speed by
the ratio of the predetermined air flow command with respect to the
air flow (product of the motor speed and the ratio of the
predetermined air flow command with respect to the air flow). In
this configuration, the speed command is changed into the value of
the motor speed which realizes the air flow value of a new
predetermined air flow command even when the predetermined air flow
command changes significantly. This allows the air flow to track
the predetermined air flow command at a high speed.
[0041] Specifically, a motor controller of the present invention is
a motor controller for controlling a motor which drives a fan, the
motor controller comprising: an air flow calculation section which
calculates an air flow of the fan based on a motor speed and motor
torque; and a speed command generation section which generates a
speed command of the motor based on a comparison calculation value
of the air flow and a predetermined air flow command and by using a
ratio of the predetermined air flow command with respect to the air
flow such that the air flow coincides with the predetermined air
flow command.
[0042] In this configuration, the generation method of the speed
command is changed depending on the magnitude of the comparison
calculation value of the air flow and the predetermined air flow
command. When the comparison calculation value falls outside the
first predetermined range, the speed command which is equal to the
"motor speed which realizes the air flow value of the predetermined
air flow command" is generated by multiplying the motor speed by
the ratio of the predetermined air flow command with respect to the
air flow, as described above.
[0043] On the other hand, when the comparison calculation value
falls within the first predetermined range, the motor speed is
compensated based on an integral calculation value of the
difference between the air flow and the predetermined air flow
command, i.e., feedback control by integral compensation.
[0044] In this case, a control gain is set to a small value to make
sensitivity of the control low, and thus the speed command is
allowed to change gently.
[0045] Hereinafter, embodiments of the present invention will be
described with reference to drawings. Note that the present
invention is not limited by the embodiments described below.
Embodiment 1
[0046] FIG. 1 is a block diagram showing the exemplary
configuration of a motor control system including a motor
controller according to Embodiment 1 of the present invention. The
motor control system of FIG. 1 includes a fan 1, an air flow
passage 2 through which air blown by the fan 1 flows, a motor 3
which drives the fan 1, an inverter 4 which supplies electric power
to the motor 3, a motor driving control section 5a which controls
the inverter 4, a position detector 6 which detects the position of
a rotor of the motor 3, a current detector 7 which detects a
current of the motor 3, and a motor controller 8a which controls
air flow (air volume) Q of the fan 1 such that the air flow Q
becomes a predetermined air flow command Q*.
[0047] The motor controller 8a includes a speed detection section 9
which detects a motor speed .omega. from the output signal of the
position detector 6, a torque detection section 10 which detects
motor torque T from the output signal of the current detector 7, an
air flow calculation section 11 which calculates the air flow Q of
the fan 1 based on the motor .omega. and the motor torque T, and a
speed command generation section 12 which generates a speed command
.omega.* of the motor 3 such that the air flow Q coincides with the
predetermined air flow command Q*. The speed detection section 9
may detect the motor .omega. using other known means (e.g.,
rotation meter, speed sensor, etc.). The torque detection section
10 may detect the motor torque T using other known means (e.g.,
torque meter, etc.).
[0048] Next, the operation and constituents of the sections in the
example of FIG. 1 will be described. The fan 1 supplies air to a
desired location through the air flow passage 2. The motor 3
rotates in a state in which it is joined to the fan 1, to drive the
fan 1. The structure of the motor 3 is not particularly limited,
and may be, for example, a brushless DC motor. Or, other motor,
such as an induction motor or a DC motor with brush may be
used.
[0049] The inverter 4 performs semiconductor switching in
accordance with a control signal received from the motor driving
control section 5a, converts a DC voltage from an electric power
supply (not shown) into an AC voltage and supplies the AC voltage
to the motor 3. A switching configuration or switching method
within the inverter 4 is not particularly limited so long as they
are adapted to an aim of driving the motor 3.
[0050] The motor driving control section 5a calculates by speed
control a driving voltage for allowing the motor speed .omega. to
track a speed command .omega.* received from the motor controller
8a, and outputs a control signal for causing the inverter 4 to
supply this driving voltage. The position detector 6 is attached to
the motor 3, and outputs a signal corresponding to the position of
the rotor of the motor 3.
[0051] In a case where the position or speed of the rotor can be
detected by estimation, the position detector 6 may be omitted. In
the present embodiment, the current detector 7 directly detects a
phase current value of the motor and outputs a signal corresponding
to the phase current value. The current detector 7 may detect the
current in any location so long as the motor torque can be
estimated. For example, the current detector 7 may be inserted into
a DC line (not shown) connected to the inverter 4 and detect the
motor current.
[0052] The operation and constituents of sections of the motor
controller 8a will be described. The speed detection section 9
calculates the motor speed .omega. based on the output signal of
the position detector 6. The speed detection section 9 may
calculate the motor .omega. by estimation using the motor current
or the driving voltage, without using the output signal of the
position detector 6. The torque detection section 10 calculates the
motor torque T based on the output signal of the current detector
7.
[0053] Unlike the configuration of FIG. 1, the speed detection
section 9 and the torque detection section 10 need not be placed
within the motor controller 8a. In a case where the speed detection
section 9 and the torque detection section 10 are placed outside
the motor controller 8a, they output the calculated motor speed
.omega. and the calculated motor torque T to the motor controller
8a.
[0054] The air flow calculation section 11 assigns the motor
.omega. and the motor torque T to the formula (3) to calculate the
air flow Q of the fan 1. The formula (3) represents the
relationship in which the air flow of the fan 1 is Q when the motor
speed of the motor 3 is .omega. and the motor torque of the motor 3
is T.
Q = n = 0 i { K n ( .omega. 0 .omega. ) 2 n - 1 T n } ( 3 )
##EQU00002##
[0055] K.sub.n(n=0, 1, 2, . . . , i) indicates a constant, i
indicates a finite value, and .omega..sub.0 indicates a particular
motor speed.
[0056] Next, basis for the formula (3) and how to derive the
formula (3) will be described.
[0057] Initially, an experiment is conducted, in which a particular
fan is driven at a particular motor speed .omega..sub.0 by the
motor 3. In this case, when the air flow and motor torque in a case
where the pressure in the air flow passage accommodated with this
fan is changed are Q.sub.0 and T.sub.0, respectively, the
relationship between Q.sub.0 and T.sub.0 is approximated as the
formula 4.
Q 0 = n = 0 i ( K n T 0 n ) ( 4 ) ##EQU00003##
[0058] K.sub.n (n=0, 1, 2, . . . , i) indicates a constant, and i
indicates a finite value. By deriving the formula (3) described
below, K.sub.n and i in the formula (4) coincide with K.sub.n and i
in the formula (3), respectively.
[0059] An approximation method for deriving the formula (4) is not
particularly limited. For example, a least square method, a
regression analysis, or the like is used. i indicates the order of
an approximation formula. Approximation accuracy and calculation
accuracy of the air flow are varied depending on the value of
i.
[0060] Next, how the formula (3) is derived from the formula (4)
will be described. In general, in a fan or a blower, there exists a
rule in which the air flow is proportional to the rotational speed
of the fan under the same pressure loss conditions, and a rule in
which shaft power is proportional to a cube of the rotational speed
of the fan, due to similarity of flows.
[0061] When the fan and the shaft of the motor are joined together
without a deflection or detachment, it can be supposed that the
rotational speed of the fan is equal to that of the motor speed,
and the shaft power of the fan is equal to a motor output (=motor
speed.times.motor torque). Therefore, the following formulas (5)
and (6) are satisfied.
Q Q 0 = .omega. .omega. 0 ( 5 ) T .omega. T 0 .omega. 0 = ( .omega.
.omega. 0 ) 3 ( 6 ) ##EQU00004##
[0062] The formula (6) can be transformed into the following
formula (7).
T T 0 = ( .omega. .omega. 0 ) 2 ( 7 ) ##EQU00005##
[0063] The formula (5) and the formula (7) represent the
relationship in which when the motor speed at which the particular
fan is driven is changed from .omega..sub.0 into .omega., the air
flow changes from Q.sub.0 into Q and the motor torque changes from
T.sub.0 into T. By applying the formula (5) and the formula (7) to
the formula (4), the above formula (3) is derived.
[0064] As described above, by conducting only the experiment in
which the fan is driven at the particular motor speed .omega..sub.0
and by using in the formula (3), the constant K.sub.n of the
approximation formula (4) thus obtained, the air flow Q in the case
where the same fan is driven at a desired motor speed .omega. can
be calculated.
[0065] The air flow Q may be calculated without using the formula
(3). For example, the relationship among the air flow Q, the motor
.omega. and the motor torque T in a case where the pressure in the
air flow passage is changed is found by conducting an experiment,
and a formula (8) which approximates this relationship may be
used.
Q = g = 0 j { h = 0 i ( K gh .omega. h T g ) } ( 8 )
##EQU00006##
[0066] K.sub.gh (g=0, 1, 2, . . . , j, h=0, 1, 2, i) indicates a
constant, i indicates a finite value, and j indicates a finite
value. The similarity of flows is not used in the formula (8). It
is necessary to measure the air flow Q and the motor torque T at
plural motor speeds w. For this reason, more measurements are
necessary to derive K.sub.gh in the formula (8), than to derive
K.sub.n in the formula (4) and the formula (3). In addition, it is
necessary to derive K.sub.gh in the formula (8), every time the
impeller outer diameter of the fan is changed. However, according
to the formula (8), the air flow Q can also be calculated based on
the motor .omega. and the motor torque T.
[0067] The air flow calculation section 11 has been described
above. Hereinafter, the operation and constituents of the speed
command generation section 12 will be described.
[0068] The speed command generation section 12 generates the speed
command .omega.* of the motor 3 such that the air flow Q coincides
with the predetermined air flow command Q*. The speed command
generation section 12 generates the speed command .omega.*
cyclically and for example, 10 times per second. Although in the
example of FIG. 1, the predetermined air flow command Q* is newly
input outside the motor controller 8a, it is not necessarily input
from outside the motor controller 8a in every cycle.
[0069] For example, the motor controller 8a may include an internal
memory (not shown). This memory may store therein the predetermined
air flow command Q* input outside the motor controller 8a, and
update the predetermined air flow command Q* every time the
predetermined air flow commands Q* is input from outside the motor
controller 8a.
[0070] The predetermined air flow command Q* is not necessarily
input from outside the motor controller 8a. For example, the
internal memory of the motor controller 8a may store plural
predetermined air flow commands Q* and the motor controller 8a may
be manually operated to select a particular predetermined air flow
command Q*.
[0071] FIG. 2 is a flowchart showing the exemplary process of the
speed command generation section 12. The speed command generation
section 12 generates the speed command .omega.* in two stages of
first speed command calculation steps (step ST1 to step ST4) and
subsequent speed command compensation steps (step ST5 to step
ST7).
[0072] The speed command calculation steps (step ST1 to step ST4)
calculate the speed command .omega.* such that the air flow Q
coincides with the predetermined air flow command Q*. The speed
command compensation steps (step ST5 to step ST7) compensate the
calculated speed command .omega.* based on the motor speed .omega.,
the motor torque T, and several predetermined values. Thus, the fan
is operated stably.
[0073] Firstly, the speed command calculation steps (step ST1 to
step ST4) will be described.
[0074] As shown in FIG. 2, initially, the motor controller 8a
derives a comparison calculation value .DELTA.Q of the
predetermined air flow command Q* and the air flow Q calculated by
the air flow calculation section 11, according to a formula (9)
(step ST1).
.DELTA.Q=Q*-Q (9)
[0075] Note that the comparison calculation value is not
necessarily defined by the difference differently from the formula
(9). For example, the comparison calculation value may be defined
by the ratio of Q* to Q. Nonetheless, in the present embodiment,
the comparison calculation value .DELTA.Q defined by the formula
(9) is used.
[0076] Then, the motor controller 8a determines whether the
comparison calculation value .DELTA.Q falls within or outside a
first predetermined range (step ST2). For example, a predetermined
threshold is set and comparison is made as follows. When the
absolute value of .DELTA.Q exceeds the predetermined threshold, the
motor controller 8a determines that the comparison calculation
value .DELTA.Q falls outside the first predetermined range, while
when the absolute value of .DELTA.Q is equal to or less than the
predetermined threshold, the motor controller 8a determines that
the comparison calculation value .DELTA.Q falls within the first
predetermined range.
[0077] When the comparison calculation value .DELTA.Q falls outside
the first predetermined range, the motor controller 8a generates
the speed command .omega.* of the motor 3 according to a formula
(10) (step ST3).
.omega. * = Q * Q .omega. ( 10 ) ##EQU00007##
[0078] .omega. indicates the motor speed of the motor 3, Q
indicates the air flow of the fan 1, and Q* indicates the
predetermined air flow command. According to the similarity of
flows in which the air flow of the fan is proportional to the
rotational speed of the fan, the motor speed .omega.* calculated
according to the formula (10) is equal in value to the motor speed
which realizes the air flow value of the predetermined air flow
command Q*.
[0079] Therefore, even when the predetermined air flow command Q*
changes significantly, the speed command .omega.* quickly changes
into the value of the motor speed which realizes the air flow value
of a new predetermined air flow command Q*. This allows the air
flow Q to track the predetermined air flow command Q* at a high
speed.
[0080] On the other hand, when the comparison calculation value
.DELTA.Q falls within the first predetermined range, the motor
controller 8a generates the speed command .omega.* according to a
formula (11) (step ST4).
.omega.*=.omega..sub.z+K.sub.G(Q*-Q) (11)
[0081] .omega..sub.Z* indicates the speed command output at a
previous time from the speed command generation section 13, K.sub.G
indicates a control gain (constant), Q indicates the air flow of
the fan 1, and Q* indicates the predetermined air flow command. The
formula (11) means that feedback control is performed by integral
compensation. A change in an air conditioning environment is
estimated in advance, and the value of the control gain K.sub.G is
set to a sufficiently small value so that the air flow Q stably
converges at the predetermined air flow command Q*.
[0082] Now, the functions and advantages of the speed command
calculation steps (step ST1 to step ST4) configured as described
above will be described.
[0083] If the speed command .omega.* is always generated according
to the formula (11), irrespective of the comparison calculation
value .DELTA.Q, the air flow Q is allowed to stably converge, but
the speed command .omega.* always changes gently. Because of this,
when the predetermined air flow command Q* is changed
significantly, a long time is required for the air flow Q to
converge at the new predetermined air flow command Q*.
[0084] Instead, if the speed command .omega.* is always generated
according to the formula (10), the calculated speed command
.omega.* changes significantly, the air flow Q changes back and
forth, crossing the predetermined air flow command Q*, which takes
place repeatedly. Thus, it is likely that the air flow Q does not
stably converge at the predetermined air flow command Q*.
[0085] In light of this, in the present embodiment, when the motor
controller 8a determines that the difference between the air flow Q
and the predetermined air flow command Q* is large based on the
magnitude of the comparison calculation value .DELTA.Q, the motor
.omega. is changed significantly according to the formula (10),
while when the motor controller 8a determines that the difference
between the air flow Q and the predetermined air flow command Q* is
small based on the magnitude of the comparison calculation value
.DELTA.Q, the motor speed .omega. is adjusted to be changed gently
according to the formula (11). This allows the air flow Q to track
the predetermined air flow command Q* at a high speed and stably
converge at the predetermined air flow command Q*, even when the
predetermined air flow command Q* changes significantly.
[0086] Next, the speed command compensation steps (step ST5 to step
ST7) will be described. FIG. 3 is a flowchart of the exemplary
process performed within the speed command compensation steps (step
ST5 to step ST7) of FIG. 2.
[0087] As shown in FIG. 3, initially, the motor controller 8a
determines whether or not the speed command .omega.* generated in
the speed command calculation steps falls within a range between a
predetermined minimum speed command and a predetermined maximum
speed command. When the motor controller 8a determines that the
speed command .omega.* falls within this range, it does not
compensate the speed command .omega.*. When the motor controller 8a
determines that the speed command .omega.* is smaller than the
predetermined minimum speed command, it compensates the speed
command .omega.* such that the speed command .omega.* becomes the
predetermined minimum speed command. When the motor controller 8a
determines that the speed command .omega.* exceeds the
predetermined maximum speed command, it compensates the speed
command .omega.* such that the speed command .omega.* becomes the
predetermined maximum speed command (step ST5).
[0088] The advantages of step ST5 will be described.
[0089] For example, in a certain air conditioning environment, such
as a case where the pressure in the air flow passage 2 is low, the
magnitude of the motor speed .omega. required to obtain the air
flow value of the predetermined air flow command Q* may not be so
large. In such an air conditioning environment, the motor speed
.omega. becomes extremely low.
[0090] In this case, if a rapid state change takes place in the
motor 3 or the air flow passage 2, the speed command .omega.* is in
some cases calculated transiently as a negative value depending on
the value of the constant K.sub.n of the formula (3). In this case,
the fan 1 rotates in a reverse direction. According to the reverse
rotation of the fan 1, a suction operation takes place, and a user
may misunderstand that the fan 1 has an abnormality. To avoid such
a situation, the predetermined minimum speed command as a lower
limit value is set in the speed command .omega.*. In this way, the
reverse rotation can be prevented.
[0091] On the other hand, in a case where the pressure in the air
flow passage 2 is high, the magnitude of the motor .omega. becomes
an excessively large value. In this case, it is likely that control
becomes unstable due to an attempt to realize the operation which
is beyond the motor's capability, or the fan or the motor vibrates
highly due to the high-speed rotation of the motor 3 and hence
fails. To avoid such a situation, the predetermined maximum speed
command as an upper limit value is set in the speed command
.omega.*. In this way, it becomes possible to prevent a situation
in which control becomes unstable, or the fan or the motor
fails.
[0092] Then, the motor controller 8a calculates a speed deviation
.DELTA..omega. which is a difference between the speed command
.omega.* and the motor .omega. according to a formula (12). When
the speed deviation .DELTA..omega. falls within a second
predetermined range, the motor controller 8a does not compensate
the speed command .omega.*, while when the speed deviation
.DELTA..omega. falls outside the second predetermined range, the
motor controller 8a compensates the speed command .omega.* such
that the speed deviation .DELTA..omega. falls within the second
predetermined range (step ST6).
.DELTA..omega.=.omega.*-.omega. (12)
[0093] In an exemplary compensation method, a predetermined
positive limiting magnitude (range) L is set, (.omega.+L) which is
a sum of the motor speed .omega. and L is set as an upper limit
value, (.omega.-L) obtained by subtracting L from the motor speed
.omega. is set as a lower limit value, the speed command .omega.*
is compensated so as to become the upper limit value (.omega.+L),
when the speed command .omega.* exceeds the upper limit value
(.omega.+L), while the speed command .omega.* is compensated so as
to become the lower limit value (.omega.-L), when the speed command
.omega.* is smaller than the lower limit value (.omega.-L).
[0094] The advantages of step ST6 will be described. If the motor
speed .omega. is changed rapidly, the air flow Q calculated by the
air flow calculation section 11 is deviated from an actual air flow
due to a transient change in the motor torque T or the pressure in
the air flow passage 2, so that the air flow cannot be stably
controlled. To avoid such a situation, the second predetermined
range is set in the changing magnitude of the speed command
.omega.* to prevent a rapid change in the motor speed .omega.. In
this way, it becomes possible to prevent a situation in which
control becomes unstable due to the deviation of the air flow
Q.
[0095] Then, the motor controller 8a compares the motor torque T
obtained at a present time to the motor torque T obtained at a
previous time. When its difference falls within a third
predetermined range, the motor controller 8a determines that a
change in the motor torque T is less, and compensates the speed
command .omega.* such that this speed command .omega.* coincides
with the speed command .omega..sub.z* output at a previous time
from the speed command generation section 13 (step ST7).
[0096] The advantages of step ST7 will be described. If an attempt
is made to change the speed command .omega.* according to a slight
change in the motor torque T without performing step ST7, the speed
command .omega.* will track the slight change in the motor torque T
and oscillate, so that the air flow Q will change back and forth,
crossing the air flow value of the predetermined air flow command
Q*, which takes place repeatedly for a long time. Thus, the air
flow Q does not stably converge at the predetermined air flow
command Q*. For this reason, a dead zone for detection of the
torque is set as the third predetermined range, to prevent the
speed command .omega.* from oscillating in a range near a
convergence point, thereby allowing the air flow Q to stably
converge at the predetermined air flow command Q*.
[0097] The operation of the motor controller 8a configured as
described above will be described below, with reference to FIGS. 4
and 5. FIGS. 4 and 5 are views showing the exemplary air flow
control performed by the motor controller 8a according to
Embodiment 1 of the present invention. In FIGS. 4 and 5, each of a
line (straight line) G1, a line (straight line) G2, and a line
(straight line) G3 indicates the relationship between the motor
speed .omega. and the air flow Q in a corresponding air
conditioning environment. The slope of the line is varied depending
on the air-conditioning environment such as the shape of the air
flow passage 2 or the state of the vent provided in an air
outlet.
[0098] Now, it is assumed that the fan 1 is driven (activated) in
the air conditioning environment indicated by the line G1, and an
operation point is a point H1. At this time, the fan 1 blows the
air flow of 400 CFM through the air flow passage 2, and the motor
speed is 300 rpm.
[0099] Hereinafter, a change in the operation point in a case where
1200 CFM is given as the predetermined air flow command Q* will be
described. The first predetermined range of step ST2 of the speed
command generation section 12 is an absolute error 200 CFM, and the
second predetermined range of step ST6 of the speed command
generation section 12 is an absolute error 200 rpm.
[0100] Initially, the air flow calculation section 11 calculates
the air flow 400 CFM at the operation point H1. Then, the speed
command calculation steps (step ST1 to step ST4) of the speed
command generation section 12 calculate the speed command .omega.*.
At this time, the comparison calculation value .DELTA.Q calculated
according to the formula (9) is 800 CFM and exceeds the absolute
error 200 CFM which is the first predetermined range. Therefore,
process moves from step ST2 to step ST3.
[0101] Step ST3 calculates the speed command .omega.* as
(1200/400).times.300=900 [rpm], according to the formula (10).
Therefore, at this time, a point Z in FIG. 4 becomes a target
operation point.
[0102] Then, the speed command compensation steps (step ST5 to step
ST7) compensate the speed command .omega.*. The speed deviation
.DELTA..omega. calculated according to the formula (12) of step ST6
is 600 rpm and exceeds the absolute error 200 rpm which is the
second predetermined range. Therefore, step ST6 compensates the
speed command .omega.* such that the speed command .omega.* becomes
an upper limit value 500 rpm which is a sum of a present motor
speed 300 rpm and the predetermined absolute error 200 rpm. As a
result of the above, the target operation point is compensated to
be shifted from the point Z to the point Z1 in FIG. 4.
[0103] The speed command generation section 12 outputs the speed
command 500 rpm generated as described above, and the motor driving
control section 5a controls the driving voltage of the motor 3 so
that the motor speed coincides with the speed command 500 rpm. The
motor controller 8a generates the speed command .omega.*
cyclically, and the motor driving control section 5a controls the
speed of the motor 3 based on the speed command .omega.* updated
cyclically. This is repeated, and as a result, the operation point
is shifted to H2, and to H3 of FIG. 5.
[0104] In the example of FIG. 5, when the air flow Q reaches a
point H4 which exceeds 1000 CFM, the comparison calculation value
.DELTA.Q becomes smaller than the absolute error 200 CFM which is
the first predetermined range. Therefore, differently from the
process corresponding to the operation point H3 and the preceding
operation points, the speed command .omega.* is calculated by step
ST4. The control gain K.sub.G of the formula (11) used in step ST4
is set to a sufficiently small value, and hence the speed command
.omega.* changes gently. Therefore, as shown in FIG. 5, the
operation point is shifted a little by little, like H4, H5, . . . ,
and stably converges at the target operation point Z.
[0105] As described above, the motor controller 8a of the present
embodiment includes the air flow calculation section 11 which
calculates the air flow Q of the fan based on the motor .omega. and
the motor torque T, and the speed command generation section 12
which generates the speed command .omega.* of the motor such that
the air flow Q coincides with the predetermined air flow command Q*
based on the comparison calculation value .DELTA.Q of the air flow
Q and the predetermined air flow command Q*, and the speed command
generation section 12 generates as the speed command .omega.* a
value obtained by multiplying the motor .omega. by the ratio of the
predetermined air flow command Q* with respect to the air flow Q
when the comparison calculation value .DELTA.Q falls outside the
first predetermined range, and generates as the speed command
.omega.* a value obtained by integrating the difference between the
air flow Q and the predetermined air flow command Q* when the
comparison calculation value .DELTA.Q falls within the first
predetermined range.
[0106] In the above configuration, when the difference .DELTA.Q
between the air flow Q and the predetermined air flow command Q* is
large, the air flow Q is allowed to track the predetermined air
flow command Q* at a high speed, while when the difference .DELTA.Q
between the air flow Q and the predetermined air flow command Q* is
small, the air flow Q is allowed to converge at the predetermined
air flow command Q* gently and stably.
[0107] As described above, by changing the generation method of the
speed command a)* according to the difference .DELTA.Q between the
air flow Q and the predetermined air flow command Q*, the air flow
Q is allowed to track the predetermined air flow command Q* at a
high speed, and converge at the predetermined air flow command Q*
stably, even when the predetermined air flow command Q* changes
significantly.
Embodiment 2
[0108] FIG. 6 is a block diagram showing the exemplary
configuration of a motor control system including a motor
controller according to Embodiment 2 of the present invention. In
the present embodiment, the motor driving control section 5a of
Embodiment 1 of FIG. 1 is replaced by a motor driving control
section 5b of FIG. 6, and the motor controller 8a of Embodiment 1
of FIG. 1 is replaced by a motor controller 8b of FIG. 6.
[0109] In the example of FIG. 1, the motor driving control section
5a is provided outside the motor controller 8a, while in the
example of FIG. 6, the motor driving control section 5b is provided
within the motor controller 8b.
[0110] The operation of the motor driving control section 5b and
the operation of the motor controller 8b are the same as the
operation of the motor driving control section 5a and the operation
of the motor controller 8a of Embodiment 1 and will not be
described repeatedly. The other constituents are the same as those
of Embodiment 1 and will not be described repeatedly.
[0111] In the present embodiment, with the above configuration, the
functions and advantages similar to those of Embodiment 1 can be
achieved. In addition, in the present embodiment, the motor
controller 8b contains the motor driving control section 5b.
Therefore, without separately providing a device for controlling
the inverter 4, the motor 3 can be controlled so that the air flow
Q of the fan 1 tracks the predetermined air flow command Q* by
directly outputting a control signal to the inverter 4.
[0112] Next, alternative configuration of the present invention
which is common to Embodiment 1 and Embodiment 2 will be
described.
[0113] The control method of the motor is a speed control method.
Therefore, the speed command .omega.* becomes substantially equal
to the motor speed .omega. so long as the speed command .omega.*
does not change so steeply. Therefore, a formula (13) may be used
instead of the formula (10) used in step ST3 in the flowchart of
the process of the speed command generation section 12 of FIG. 2,
or a formula (14) may be used instead of the formula (11) used in
step ST4 in the flowchart of the process of the speed command
generation section 12 of FIG. 2.
.omega. * = Q * Q .omega. z * ( 13 ) .omega. * = .omega. + K G ( Q
* - Q ) ( 14 ) ##EQU00008##
[0114] .omega..sub.z* indicates the speed command output at a
previous time from the speed command generation section 12.
INDUSTRIAL APPLICABILITY
[0115] A motor controller and a motor control method of the present
invention are optimal to a system which controls an air flow such
that the air flow becomes a predetermined air flow value, and is
useful as air conditioning equipment in general houses, business
buildings, vehicles, etc.
* * * * *