Electricity: single generator systems – Generator control – With excitation winding and/or circuit control
Reexamination Certificate
1999-09-20
2001-07-24
Ramirez, Nestor (Department: 2834)
Electricity: single generator systems
Generator control
With excitation winding and/or circuit control
C322S028000, C322S020000, C322S019000
Reexamination Certificate
active
06265852
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an excitation controller and an excitation control method for stabilizing voltage in an electric power system.
2. Description of Related Art
FIG. 8
is a block diagram showing a conventional excitation controller disclosed in Japanese patent publication No. Hei. 10-2809833. In
FIG. 8
, the reference numeral
1
designates a synchronous machine;
2
designates a transformer;
3
designates a breaker;
4
designates a transmission line;
5
designates a transmission bus of a power plant;
6
designates a potential transformer (called “PT” from now on) for detecting an output terminal voltage V
G
of the synchronous machine
1
;
7
designates a voltage setter for setting the output terminal reference voltage r
G
of the synchronous machine
1
;
8
designates a subtracter for producing a deviation signal by subtracting the output terminal voltage V
G
from the reference voltage r
G
set by the voltage setter
7
; and
9
designates a reduced gain circuit for multiplying the deviation signal fed from the subtracter
8
by a gain &bgr;.
The reference numeral
10
designates a potential device (called “PD” from now on) for detecting the transmission voltage V
H
on the transmission bus
5
;
11
designates a high side voltage setter for setting a reference voltage r
H
of the transmission bus
5
;
12
designates a subtracter for producing a deviation signal by subtracting the transmission voltage V
H
from the reference voltage r
H
set by the high side voltage setter
11
;
13
designates a high side voltage control gain circuit for multiplying the deviation signal fed from the subtracter
12
by a gain K
H
;
14
designates an adder for adding the multiplication result of the reduced gain circuit
9
and the multiplication result of the high side voltage control gain circuit
13
;
15
designates an automatic voltage regulator (called “AVR” from now on) for controlling the rectifying timing of an exciter
16
using the addition result of the adder
14
as an input condition;
16
designates the exciter for supplying the field current to a field winding
17
of the synchronous machine
1
under the command of the AVR
15
; and
17
designates the field winding of the synchronous machine
1
.
Next, the operation of the conventional excitation controller will be described.
First, the PT
6
detects the output terminal voltage V
G
of the synchronous machine
1
. Then, the subtracter
8
subtracts the output terminal voltage V
G
from the reference voltage r
G
set by the voltage setter
7
, and outputs its subtraction result as the deviation signal, and the reduced gain circuit
9
multiplies the deviation signal by the gain &bgr;.
On the other hand, the PD
10
detects the transmission voltage V
H
of the transmission bus
5
. Then, the subtracter
12
subtracts the transmission voltage V
H
from the reference voltage r
H
set by the high side voltage setter
11
, and outputs its subtraction result as the deviation signal. The high side voltage control gain circuit
13
multiplies the deviation signal by the gain K
H
.
Subsequently, the adder
14
adds the multiplication result of the reduced gain circuit
9
and the multiplication result of the high side voltage control gain circuit
13
, and the AVR
15
generates a timing signal for controlling the rectifying timing of the exciter
16
using the addition result of the adder
14
as the input condition of the following transfer function.
transfer function=K·(1+T
LD
·S)/(1+T
LG
·S)
where, K is the gain constant;
T
LD
and T
LG
are time constants; and
S is the Laplace operator.
In response to the timing signal fed from the AVR
15
, the exciter
16
supplies the field current to the field winding
17
of the synchronous machine
1
.
Incidentally, if the addition result of the adder
14
is positive, the field current supplied to the field winding
17
is increased so that the output terminal voltage V
G
of the synchronous machine
1
increases, whereas if the addition result of the adder
14
is negative, the field current supplied to the field winding
17
is decreased so that the output terminal voltage V
G
of the synchronous machine
1
decreases.
Thus, the voltage on the transmission bus
5
is maintained at a fixed value, and hence, even if an accident takes place on the transmission line
4
, the voltage drop of the entire transmission system can be alleviated, which makes it possible to markedly improve the voltage stability.
With the foregoing configuration, the conventional excitation controller can maintain the transmission voltage V
H
on the transmission bus
5
at the fixed value. However, it has a problem of increasing the manufacturing cost because of the expensive PD
10
which is required for detecting the transmission voltage V
H
of the transmission bus
5
.
Furthermore, since an excitation control cubicle, on which the AVR
15
and adder
14
are mounted, is usually installed far from the transmission bus
5
, a long cable connecting the excitation control cubicle and the transmission bus
5
is needed and is susceptible to noise, and this presents the problem of reducing the reliability of the system.
SUMMARY OF THE INVENTION
The present invention is implemented to solve the foregoing problem. It is therefore an object of the present invention to provide an excitation controller and an excitation control method capable of maintaining the voltage on the transmission bus at a fixed value without detecting the voltage on the transmission bus.
According to a first aspect of the present invention, there is provided an excitation controller comprising: a voltage detector for detecting an output terminal voltage of a synchronous machine which is connected with a transmission system through a transformer; a reactive current detector for detecting a reactive current output from the synchronous machine; a voltage setter for setting an output terminal reference voltage of the synchronous machine from the reactive current detected by the reactive current detector and a high side reference voltage of the transformer; and a controller for controlling an excitation system of the synchronous machine in response to a deviation between the reference voltage set by the voltage setter and the output terminal voltage detected by the voltage detector.
Here, the voltage setter may set the output terminal reference voltage of the synchronous machine such that the high side voltage of the transformer agrees with the high side reference voltage when the reactive current detected by the reactive current detector agrees with a reference value.
The voltage setter may determine the reference value in accordance with the high side reference voltage of the transformer.
The voltage setter, when the high side reference voltage of the transformer is changed, may subtract from the reference voltage after the change the reference voltage before the change, divide a result of the subtraction by a reactance of the transmission system side, add a result of the division to the reference value before the change, and adopt a result of the addition as the reference value.
The voltage setter may estimate the reactance on the transmission system side when obtaining the reference value after the change.
The voltage setter may calculate the reference value from the reactive current detected by the reactive current detector and the high side voltage of the transformer.
According to a second aspect of the present invention, there is provided an excitation control method comprising the steps of: detecting an output terminal voltage of a synchronous machine which is connected with a transmission system through a transformer; detecting a reactive current output from the synchronous machine; setting an output terminal reference voltage of the synchronous machine from the reactive current detected and a high side reference voltage of the transformer; and controlling an excitation system of the synchronous machine in response to a deviation betwe
Kitamura Hitomi
Shimomura Masaru
Tanaka Seiichi
Gonzalez Julio Cesar
Leydig Voit & Mayer Ltd
Mitsubishi Denki & Kabushiki Kaisha
Ramirez Nestor
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