Electricity: motive power systems – Induction motor systems – Primary circuit control
Reexamination Certificate
2001-11-20
2004-06-15
Fletcher, Marlon (Department: 2837)
Electricity: motive power systems
Induction motor systems
Primary circuit control
C310S181000, C310S199000, C318S802000, C318S803000
Reexamination Certificate
active
06750629
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an inverter control apparatus which is used for variable speed drive of a rotary machine, and a motor driving system using the same.
2. Description of the Related Art
FIG. 1
is a block diagram showing the circuit structure of a motor driving system using a conventional inverter control apparatus. A method of changing the frequency of 3-phase AC (alternating current) power Acc supplied to an induction motor is known as one method of controlling rotation speed of the induction motor. The conventional motor driving system is composed of a 3-phase AC power supply
50
, an inverter control unit
20
, a variable speed driving unit
60
, and an induction motor
11
with a rotation frequency detecting unit
12
for a load. The variable speed driving unit
60
is composed of a rectifier
61
and an inverter
62
. The variable speed driving unit
60
is used to control the rotation frequency of the induction motor.
The 3-phase AC power supply
50
supplies 3-phase AC power with a constant frequency (60 Hz) to the variable speed driving unit
60
. The variable speed driving unit
60
is composed of a rectifying unit
61
and a current type inverter
62
. The rectifying unit
61
rectifies the 3-phase AC power into DC power in response to a rectifier current instruction signal Id* from the inverter control unit
20
. The current type inverter
62
inverts the DC power into 3-phase AC power Acc in response to an inverter frequency instruction signal fe* from the inverter control unit
20
. Thus, the variable speed driving unit
60
controls the frequency of the 3-phase AC power Acc. The 3-phase AC power Acc is supplied to the multi-polar induction motor
11
.
The inverter control unit
20
is composed of converters
21
and
22
, adders
23
and
26
, a speed control section
24
, a slide calculating section
25
, and a current calculating section
27
.
For slide frequency control, a rotation frequency of the multi-polar induction motor
11
(the number of poles is p) is detected by the rotation frequency detecting unit
12
such as an encoder and a signal form indicative of the detected rotation frequency is supplied to the converter
22
of the inverter control unit
20
. The converter
22
converts the detected rotation frequency signal form into a 2-pole conversion detected rotation frequency signal fr
2
which is supplied to the adders
23
and
26
. A multi-polar rotation frequency instruction signal form* is supplied to the converter
21
from the outside, and the converter
21
converts the multi-polar rotation frequency instruction signal form* into a 2-pole conversion rotation frequency instruction signal fr
2
*, which is supplied to the adder
23
.
The adder
23
subtracts the 2-pole conversion detected rotation frequency signal fr
2
from the 2-pole conversion rotation frequency instruction signal fr
2
*, and supplies the subtracting result to the speed control unit
22
. The speed control unit
22
generates a 2-pole conversion torque instruction signal T
2
* from the subtracting result, and supplies to the current calculating section
27
and the slide calculating section
25
. The current calculating section
27
calculates the rectifier current instruction signal Id* from the 2-pole conversion torque instruction signal T
2
* and supplies to the rectifying unit
61
of the variable speed driving unit
60
.
The slide calculating section
25
calculates a slide frequency instruction signal Fs* from the 2-pole conversion torque instruction signal T
2
*. The adder
26
adds the slide frequency instruction signal Fs* and the 2-pole conversion detected rotation frequency signal fr
2
to produce the inverter frequency instruction signal fe*, which is supplied to the current type inverter
62
of the variable speed driving unit
60
.
In conjunction with the above description, an inverter control apparatus is disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 11-69880). In this reference, an inverter inputs DC power from a DC power supply through a filter capacitor which is provided on the input side of the inverter, and supplies AC power with a variable voltage and a variable frequency to an AC motor to drive the AC motor. A voltage increase suppressing torque instruction correcting section of the inverter control apparatus inputs a capacitor DC voltage applied to the filter capacitor and an operation torque instruction, and outputs a first torque instruction to reduce regenerative torque for suppressing the increase of the DC voltage when the DC voltage increases. A change rate limiting section of the inverter control apparatus limits the change rate of the first torque instruction to output a second torque instruction.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an inverter control apparatus in which the stationary characteristics (such as effective values of voltage and current) of an inverter can be improved, and a motor driving system using the inverter control apparatus.
In an aspect of the present invention, a motor driving system for driving an induction motor with a rotation frequency detector, wherein the induction motor drives a load, and the rotation frequency detector detects a rotation frequency of the induction motor, includes a variable speed driving unit, and an inverter control unit. The variable speed driving unit is connected to the induction motor and has a capacitance at output. The variable speed driving unit rectifies first 3-phase AC power to produce DC power, and converts the DC power into second 3-phase AC power with a frequency, and drives the induction motor with the second 3-phase AC power. The inverter control unit generates a frequency instruction and a temporary current instruction based on the detected rotation frequency and a rotation frequency instruction at least. Then, the inverter control unit corrects the temporary current instruction based on at least one of first correction depending on the capacitance and second correction depending on a predetermined frequency component of the temporary current instruction to produce a current instruction, and controls the variable speed driving unit based on the frequency instruction and the current instruction.
The variable speed driving unit may include a rectifying unit and a current type inverter. The rectifying unit rectifies the first 3-phase AC power in response to the current instruction to produce the DC power. The current type inverter has the capacitance at the output, and inverter converts the DC power into the second 3-phase AC power with the frequency in response to the frequency instruction.
Also, the inverter control unit may include a first correcting section which corrects the temporary current instruction for current flowing into the capacitance in the first correction to produce the current instruction. In this case, the first correcting section may correct the temporary current instruction based on a first correction factor to produce the current instruction. The first correction factor is determined based on the capacitor, a self-inductance of a stator of the induction motor stator, a mutual inductance between the stator and a rotor in the induction motor, a self-inductance of the rotor of the induction motor, a resistance of the stator of the induction motor, a resistance of the rotor of the induction motor rotor, and slide.
Also, the inverter control unit may include a second correcting section which corrects the temporary current instruction based on a second correction factor in the second correction to produce the current instruction, wherein the second correction factor is determined such that the predetermined frequency component is set to a predetermined value.
Also, the inverter control unit may include a first correcting section and a second correcting section. The first correcting section corrects the temporary current instruction for current flowing into the capacitance in the first correction to produce a next temporary current instruction.
Akasaka Noriyuki
Kawabata Osamu
Kayuki Yoshio
Nonaka Mitsuyuki
Shigemizu Tetsuro
Armstrong Kratz Quintos Hanson & Brooks, LLP
Fletcher Marlon
Mitsubishi Heavy Industries Ltd.
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