Electricity: single generator systems – Automatic control of generator or driving means – Plural conditions
Reexamination Certificate
2000-01-11
2001-08-28
Ponomarenko, Nicholas (Department: 2834)
Electricity: single generator systems
Automatic control of generator or driving means
Plural conditions
C322S020000, C322S025000
Reexamination Certificate
active
06281664
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a generator equipped with a dual voltage inverter having two inverter system, and a generator apparatus having these generators connected in parallel.
2. Description of Related Art
There has been known a generator equipped with an inverter for converting a direct current (DC) into an alternating current (AC) of a desired frequency. Further, there has also been known a generator having two inverters connected in parallel. For example, in Japanese Patent Application Laid-Open No. 8-205543, there is a description of an apparatus for an inverter operation capable of stable parallel operation of two inverters.
It has been desired to obtain two-level output voltages in the above-described generator having one or more inverters. In a generator having an inverter (s), it is possible to obtain two kinds (two levels) of AC output voltages, such as, for example, 120 V and 240 V, by switching an output of a rectification device, that is, a DC voltage input to the inverter, at two levels.
However, in the case of switching over a DC voltage between two levels as described above, it is necessary to make the dielectric strength of the inverter correspond to a higher-voltage side and to make the output current capacity correspond to a higher-current side, respectively. Therefore, it is necessary to increase the size of an inverter circuit and to increase the size of what is called a power element such as an electrolytic capacitor, a choke coil or the like.
There has also been a desire to obtain many kinds of output power, other than changing over an output voltage at two levels or changing over an output power into two levels. However, at present, it is not possible to meet these requirements in an efficient manner by using a compact apparatus.
It is considered possible to obtain two-level AC output voltages by operating two inverters in series or in parallel.
FIG. 13
is a connection diagram of a generator having two inverters connected in series. As shown in
FIG. 13
, it is possible to obtain two-level output voltages of 120 V and 240 V by serially connecting two inverters A and B capable of outputting an AC voltage of 120 V based on a power generated by a generator G. According to the kind of serial operation, however, the balance between the outputs of the two inverters A and B may be broken in some cases depending on the load taken by the inverters.
Further, there is a case where a control method is employed for adjusting a rotational speed of an engine to an optimum value according to the magnitude of a load when a generator is driven by an engine (hereinafter, “eco-throttle control” method). When an electronic governor is set in only one inverter to carry out the eco-throttle control by the CPU of said one inverter and when a heavy load is connected to the other inverter not provided with the electronic governor, for example, there is a problem that it is not possible to secure a sufficient level of an output voltage because the two inverters are out of balance.
In the case of connecting two inverter systems as described above, it is necessary to provide a ground fault interrupter for each series.
FIG. 14
is a circuit diagram showing a structure of a generator equipped with a conventional ground fault interrupter. Referring to the drawing, a ground fault interrupter
110
is provided at the output side of a generator
100
, and a plug socket
120
for taking out power is connected through the ground fault interrupter
110
. The ground fault interrupter
110
is comprised of a detecting section
121
and an operating section
122
. The detecting section
121
comprises of a current transformer (ZCT)
121
a
and an oscillation coil
121
b
provided on an output line of the generator
100
, and a controller
121
c
for energizing a relay coil
122
a
of the operating section
122
based on detected signals. A contact point
122
b
of the operating section
122
is “normally closed”, and it is “opened” when the relay coil
122
a
is energized by the controller
121
c.
As the ground fault interrupter
110
is manufactured and marketed as a single integrated unit, it is usually large in size and expensive. When the interrupter is externally installed on the generator, it leads to an increase in the overall size of the generator.
SUMMARY OF THE INVENTION
It is a first object of the present invention to provide a generator capable of efficiently obtaining output voltages and power at a plurality of levels, and a generator apparatus using such generator.
It is a second object of the invention to provide a generator capable of obtaining an output voltage at two levels in good balance when two inverters are connected with each other.
It is a third object of the invention to provide a generator having a compact and low-cost ground fault interrupter capable of detecting a ground occurring in any one of two inverter systems.
A generator having a first feature of the present invention includes two power source systems each of which comprises a rectifier circuit for rectifying an input alternating current into a direct current and an inverter circuit for converting the direct current inputted from the rectifier circuit into an alternating current of a predetermined frequency, one of said systems further comprising target waveform generating means for producing a reference waveform to determine an output frequency of the inverter circuit means for producing a reference waveform clock signal representative of the reference a waveform to the other system means for receiving a second reference waveform clock signal transmitted from the other system phase difference detecting means for detecting a phase difference between the first and second reference waveform clock signals; and frequency adjusting means for adjusting the output frequency so that the phase difference detected by the phase difference detecting means is within a predetermined range wherein the generator includes switching means for selectively connects the two power source systems in series connection or in parallel connection.
According to a first aspect of the present invention, it is possible to connect in series or in parallel the outputs of two inverter circuits. Further, it is possible to synchronize the outputs of the two inverter circuits connected with each other by mutually communicating reference wave clock signals.
A generator apparatus having a second feature of the present invention includes two generators recited in claim
1
connected in parallel, wherein one of said two systems incorporated in each of the generators comprises current detecting means for detecting an output current of the intra-systems voltage detecting means for detecting an output voltage of the intra-systems second phase difference detecting means for detecting a second phase difference between the output current and the output voltage and second frequency adjusting means for adjusting the output frequency so that the second phase difference is within a second predetermined range, and wherein when a phase difference between the reference waveform clock signals is within a predetermined range, the generator starts a power generation by energizing the inverter circuit, and the function of the frequency adjusting means recited in claim
1
is stopped in response to the starting of the power generation.
According to a second aspect of the invention, there are a plurality of parallel-connected generators each having two series of inverter circuits capable of switching over between series connection and parallel connection. Therefore, it is possible to obtain many kinds of outputs (power) . When the parallel-connected generators are not synchronized, phase differences of output currents and output voltages of the two series of inverter circuits included in the generators are not kept within a predetermined range. To avoid this problem, according to the second aspect of the invention, the parallel-connected generators are made synchronized by adjusting frequencies or phas
Nakamura Masashi
Shimizu Motohiro
Armstrong Westerman Hattori McLeland & Naughton LLP
Honda Giken Kogyo Kabushiki Kaisha
Ponomarenko Nicholas
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