Electricity: motive power systems – Generator-fed motor systems having generator control – Automatic generator control and/or with time-delay means
Reexamination Certificate
2000-11-03
2003-05-06
Donels, Jeffrey (Department: 2837)
Electricity: motive power systems
Generator-fed motor systems having generator control
Automatic generator control and/or with time-delay means
Reexamination Certificate
active
06559611
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application relates to and claims priority to corresponding Japanese Patent Application No. 313462/1999, which was filed on Nov. 4, 1999, and which is incorporated by reference herein.
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a generator which is driven by an engine (hereinafter referred to as an “engine-driven generator”), and more particularly to an engine-driven generator having improved starting characteristics and requiring no control of the driving engine for starting the load wherein the heavy load is loaded on the output of the generator, for example, the load of the induction motor.
(2) Description of the Prior Art
In the case when an induction motor as a load is started by an engine-driven generator, since there flows a rush-current in the order of 400-800% of the rated current thereof at the starting, it is necessary that the capacity of the generator be two-three times as that of the induction motor, so that the performances of the generator are not sufficient for such case. In other words, if the generator having substantially the same rated capacity as that of the load is used, the revolution number of the driving engine is greatly lowered, or the engine will stop its operation.
In order to improve the above explained problems, conventionally, the following methods by which the input supplied to the induction motor is limited are taken.
(1) At starting, the output voltage of the generator is lowered and the input to the induction motor is limited accordingly (method of reducing voltage).
(2) In addition to the above reducing voltage method, the revolution number of the driving engine is temporarily lowered by the control operation of the governor (i.e., reduction in the supply amount of the fuel). Or, by utilizing the temporary reduction in the revolution number of the driving engine due to the rush current, the slip of the induction motor at the starting is made small, whereby the input supplied to the induction motor is limited to low with the sufficient torque being maintained.
(3) By utilizing an automatic voltage regulating means as disclosed in the Japanese Patent No. 2889972, the revolution number of the engine is temporarily lowered at the time when the load current is high, a voltage which is proportional to the revolution number of the engine is outputted by the automatic voltage regulating means, and the revolution number of the engine is gradually raised up to the rated number of revolution accordingly.
FIG. 9
is a block diagram of an exemplary construction of a device that includes an automatic voltage regulating means in which A denotes an engine, B denotes a generator, C denotes a motor, D denotes an automatic voltage regulator, E denotes a control selection means, F denotes a load current detection means, and G denotes a speed control means.
FIG. 10
is a more detailed block diagram of an exemplary construction of a device that includes an exemplary automatic voltage regulating means in which numeral
1
shows an engine, numeral
2
shows a generator which is driven by the engine
1
, and numeral
3
shows an induction motor powered by the output of the generator
2
. The induction motor
3
is connected to the generator
2
through a load switch
4
and a breaker
5
. Numeral
6
shows an automatic voltage controller, numeral
7
shows a current transformer which is provided at an output circuit of the generator
2
, numeral
8
shows a fuel pump for the engine
1
, numeral
9
shows an actuator for the fuel pump
8
, numeral
10
shows a speed sensor in combination with a rotation gear
10
a
, for detecting the speed of the engine
1
, numeral
11
shows a control selection switch, and numeral
12
shows a speed controller.
The automatic voltage regulator
6
maintains a rated voltage (for example, 220 volts) where the frequencies are within predetermined ranges higher and lower than the rated frequency (for example, 60 Hz). However, the frequency becomes lower than the above predetermined range, the output voltage lowers.
FIG. 11
shows exemplary characteristics of such regulator. As shown in a solid line, below a predetermined frequency, the voltage becomes a certain voltage which is set lower than the rated voltage, for example, 50% of the rated voltage. Alternatively, the voltage decreases continuously in proportional to the decrease of the frequency as shown in a dotted line.
The above method (1) is effective for such load having small starting inertia as a pump or a fan. Though the input to such load becomes small proportional to the square of the voltage, the torque generated also becomes small in proportional to the square of the voltage. Therefore, the method can be used only for the case where the load is small at the starting, however, for loads other than such load, it is necessary that the generator having enough capacity be selected as in the conventional way.
In the above method (2), as the input is decreased as the induction motor is accelerated, the revolution number of the engine rises. The motor must be accelerated in the state in which the slip is constantly large and, as a consequence, a prolonged time is required before the motor is accelerated up to the rated revolution number and, during this time, an excess current flows so that the generator requires the capacity such that the excess current breaker does not operate in the course of starting the motor.
With the method (3), the starting is easy because, as compared with conventional systems, the output voltage is proportionally controlled by the revolution number of the motor and the automatic voltage regulating means. However, since the revolution number of the engine is changed in a plurality of steps, it requires a fuel control section for precisely controlling the revolution number of the engine, which leads to a high cost of the entire system. Also, since the revolution number of the engine is caused to be lowered, the output of the engine with respect to the torque required by the load side is inevitably lowered.
SUMMARY OF THE INVENTION
In view of the foregoing, an object of the invention is to improve the load capacity which enables the starting by the engine-driven generator without directly controlling the engine and to realize a method of starting an engine-driven generator at a low cost and to provide the engine-driven generator without requiring complicated costly equipment. Also, since the starting time is, in any case, limited by V/F constant characteristics, in order to shorten further the starting time or to increase the load capacity by causing the starting current to be lowered, there is no alternative but to increase the capacity of the generator.
As a means to solve the above problem, the present invention provides a method for starting the load of the engine-driven generator and provides the engine-driven generator which controls the generator excitation current such that, at the starting of the motor to which the power is supplied by the engine generator, when the generator output voltage has become lower than a predetermined voltage, the output frequency of the generator approaches the predetermined value lower than the rated frequency, and subsequently when the generator output voltage has arisen to the second predetermined voltage which is higher than the first predetermined voltage, the generator output voltage becomes the rated voltage.
According to the invention, in order to start the motor which becomes the heavy load with respect to the generator capacity, when after the starting, the output voltage (for example, rated 220 volts) of the generator has become lower than the first predetermined voltage (for example, 200 volts) determined in advance, the revolution number of the engine is such as to be lowered to the predetermined number by the control of the generator excitation current. The generator excitation current is controlled so that the load of the load of the generator is raised and, since the revolution number of the engine rises due to the
Hosaka Yukio
Maruyama Hideharu
Matsumoto Yuuji
Nakaoka Kiyonori
Satake Satoru
Donels Jeffrey
Satake Toshiko
Satake Corporation
Wells St. John P.S.
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