Electricity: motive power systems – Induction motor systems
Reexamination Certificate
2001-08-17
2003-06-10
Nappi, Robert E. (Department: 2837)
Electricity: motive power systems
Induction motor systems
C318S132000, C318S254100, C318S799000, C318S800000, C318S801000, C318S811000
Reexamination Certificate
active
06577096
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a vector control system of an induction motor, and more particularly, to a sensorless vector control system of an induction motor that is capable of estimating a magnetic flux and speed of an induction motor without using a speed measuring device.
2. Description of the Background Art
In general, thanks to its easy control, a DC motor has been for a long time used for a fixed speed and variable speed control apparatus. But the DC current is has shortcomings that its use of a predetermined time consumes a brush, which, thus, requires a maintenance and repairing.
In case of an induction motor, it is superior in the aspect of maintenance and repairing thanks to its firm structure. Especially, it's low in price so that it has been widely used in the industrial field. But, the induction motor has been mainly used for a constant speed operation on account of its difficulty in controlling compared to a DC motor.
Recently, however, with the introduction of a vector control theory which is able to separately control a magnetic flux and a torque component by using a speed sensor, with the advent of a high speed power semiconductor device and with a development of a high performance microprocessor (Central Processing Unit or Digital Signal Processor), variable speed operation of the induction motor is possibly performed and the induction motor can be controlled beyond the level of the DC motor in terms of an efficiency of a speed control characteristic, so that the variable sped control field which has adopted the DC motor, growingly employs the induction motor in place of the DC motor.
In order to vector-control the induction motor, speed or magnetic flux information of the motor should be fedback from the induction motor, for which a speed information sensor or a magnetic flux sensor such as a tacho generator or a resolver or a pulse encoder is required.
However, since the sensors include an electronic circuit, the induction motor having the sensors is also restricted due to a use temperature range of the electronic circuit, and signal wiring between the speed sensor and the inverter incurs much expense.
And even though the speed sensors is possibly installed, since a coupling portion between the induction motor and the speed sensors are weak to an impact, the sensors are preferably avoided for use in terms of a facility reliability.
Thus, in order to solve such problems, researches for a sensorless vector control without a necessity of a speed sensor has been successively conducted.
Accordingly, recently, various speed estimation methods of the induction motor have been proposed with respect to the sensorless vector control without the speed sensor. Among them, researches are conducted on a method for directly estimating and controlling a magnetic flux by using a simultaneous differential equation of a model reference adaptive system (MRAS), a flux observer and a motor.
FIG. 1
is a schematic block diagram of a sensorless vector control system in accordance with a conventional art.
As shown in
FIG. 1
, a sensorless vector control system for receiving a power from a power supply unit
13
and driving an induction motor includes a speed controller for being fedback with a reference speed (&ohgr;
r
*) and an estimation speed value ({circumflex over (&ohgr;)}
r
) from an integration & proportional constant computing unit
20
, operating them and outputting a reference torque component current (i
1&bgr;
*), when the predetermined reference speed (&ohgr;
r
*) and a reference magnetic flux component current (i
1&agr;
*) are given; a current to voltage command unit
10
for receiving the reference magnetic flux component current (i
1&agr;
*) and the reference torque component current (i
1&bgr;
*) and outputting DC reference voltages (v
1&agr;
*, v
1&bgr;
*); a DC to AC converter
11
for receiving the DC reference voltages (v
1&agr;
*, v
1&bgr;
*) and outputting two phase reference AC voltages (v
1d
*, v
1q
*); a phase voltage converter
12
for receiving the two phase reference AC voltages (v
1d
*, v
1q
*) and three phase reference phase voltages (v
a
*, v
b
*, v
c
*); an inverter
14
for receiving the three phase reference phase voltages (v
a
*, v
b
*, v
c
*) and controlling an induction motor (IM); the induction motor
15
for receiving the three phase reference phase voltages (v
a
*, v
b
*, v
c
*) from the inverter, to be driven; a current detector
16
for detecting a current flowing between the inverter and the induction motor and outputting detected phase currents (i
a
, i
b
, i
c
); a phase current converter
17
for receiving the detected phase currents (i
a
, i
b
, i
c
) and converting them into d-axis current (i
d
) and q-axis current (i
q
); a magnetic flux operator
18
for receiving into d-axis current (i
d
) and q-axis current (i
q
), receiving the two phase reference AC voltages (v
1d
*,v
1q
*), estimating two phase AC magnetic flux ({circumflex over (&lgr;)}
2d
,{circumflex over (&lgr;)}
2q
) and outputting them; an AC/DC converter
19
for receiving the estimated two phase AC magnetic flux ({circumflex over (&lgr;)}
2d
,{circumflex over (&lgr;)}
2q
), estimating a DC magnetic flux ({circumflex over (&lgr;)}
2&agr;
,{circumflex over (&lgr;)}
&bgr;
) and outputting them; an integral/proportional constant computing unit
20
for estimating a speed by using {circumflex over (&lgr;)}
2&bgr;
of the estimated DC magnetic flux components and outputting it; a slip operator
23
for receiving a magnetic flux component current (i
1&agr;
*) and a torque component current (i
1&bgr;
*), obtaining and outputting a slip; and an integrator
25
for receiving the slip and the estimated velocity ({circumflex over (&ohgr;)}
r
), and integrating them to estimate an angle.
The operation of the sensorless vector control system constructed as described above will now be explained.
First, when the integral/proportional constant computing unit
20
receives a reference speed (&ohgr;
r
*) from a user, operates and outputs a value. The speed controller
22
receives the value and outputs a torque component current (i
1&bgr;
*).
Thereafter, the current/voltage command unit
10
outputs DC reference voltages (v
1&agr;
*, v
1&bgr;
*) by using the magnetic flux component current (i
1&agr;
*) and the torque component current (i
1&bgr;
*). The DC reference voltages (v
1&agr;
*, v
1&bgr;
*) are is converted into two phase AC reference voltages (v
1d
*, v
1q
*) by the DC to AC converter
11
.
Then, in order to drive an induction motor, the phase voltage converter
12
receives the two phase AC reference voltages (v
1d
*, v
1q
*) and outputs three phase reference phase voltages (v
a
*, v
b
*, v
c
*), and the inverter
14
drives the induction motor by using power provided from a power supplier and the three phase reference phase voltages (v
a
*, v
b
*, v
c
*).
An estimated velocity ({circumflex over (&ohgr;)}
r
) and an estimated angle ({circumflex over (&thgr;)}
e
), are obtained as follows.
A current flowing between the inverter
14
and the induction motor
15
is detected to obtain three phase currents (i
a
, i
b
, i
c
). The three phase currents (i
a
, i
b
, i
c
) are converted into two phase d-axis current (i
d
) and q-axis current (i
q
), which are easily controlled, and outputted by the phase current converter
17
.
The magnetic flux operator
18
receives the output values (v
1d
*, v
1q
*) of the DC/AC converter
11
and the d-axis current (i
d
) and the q-axis current (i
q
), and estimates two phase AC magnetic flux to estimate two phase AC magnetic flux ({circumflex over (&lgr;)}
2d
,{circumflex over (&lgr;)}
2q
).
The AC/DC converter
19
converts the two phase AC magnetic flux ({circumflex over (&lgr;)}
2d
,{circumflex over (&lgr;)}
2q
) to two phase DC magnetic flux ({circumflex over (&lgr;)}
2&agr;
,{circumflex over (&lgr;)}
2&bgr;
) which can be conveniently controlled, and then the integral/proportional constant computing unit operates and obtains an estimated velocity ({circumflex over (&ohgr;)}
r
)
LG Industrial Systems Co. Ltd.
Smith Tyrone
LandOfFree
Sensorless vector control system of induction motor and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Sensorless vector control system of induction motor and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Sensorless vector control system of induction motor and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3092878