Prime-mover dynamo plants – Electric control – Engine control
Reexamination Certificate
2002-06-26
2003-12-09
Ramirez, Nestor (Department: 2834)
Prime-mover dynamo plants
Electric control
Engine control
C290S00100C, C290S04000F, C290S04000F
Reexamination Certificate
active
06661110
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a portable generator which generates an AC voltage of 100 V or the like by being turned by an engine.
BACKGROUND ART
Today, small generators driven by a gasoline engine or a diesel engine, permitting conveyance to where they are needed and capable of developing a per-unit output of several kilowatts, have come into extensive use.
Such portable generators permitting ready conveyance include generators enabled, by keeping the frequency of engine revolutions constant, to develop a single-phase AC voltage of around 100 V in average output voltage at a frequency of 50 or 60 Hz.
However, more recently, there have been proposed systems whereby the output of an engine-driven AC generator is once rectified into a DC voltage and this DC voltage is further converted with an inverter into an output voltage having a constant frequency of 50 Hz or 60 Hz (e.g. JP 63-114527 A and JP 63-302724 A).
Incidentally, an engine-driven small portable generator capable of developing an output of several kilowatts to about 10 kW is not only carried to where they are needed and used for power generation always in a movable state but also may be semi-permanently installed in a fixed position where it is required to operate continually for some time.
This inverter-equipped portable generator, as shown in
FIG. 10
, has an engine-driven AC generator
50
, a DC-voltage-generating circuit
110
using rectifier diodes
115
and thyristors
111
, a DC-power-source unit
120
using a large-capacitance capacitor
121
consisting of a required number of capacitors connected in parallel, an inverter circuit
130
using a power transistor, and a low pass filter
140
using a coil and a capacitor.
Further, it has, as control circuits for driving and controlling such power circuits as these DC-voltage-generating circuit
110
and inverter circuit
130
, a PWM-signal-generating circuit
250
, a voltage-limiting circuit
240
, an overload-detecting circuit
260
and an inverter-drive circuit
255
. This portable generator
100
also has, as power-supply units for driving these control circuits, a smoothing circuit
210
and a constant-voltage circuit
235
.
Many of the AC generator
50
in use whose rotor is turned by such an engine has a three-phase output coil
51
and a single-phase output coil
55
. In many cases, the three-phase output coil
51
can develop a maximum output of tens of amperes at hundreds of V, while the single-phase output coil
55
can develop an output of tens of amperes at tens of V.
The DC-voltage-generating circuit
110
to which the output terminal of this three-phase output coil
51
is connected is configured of a rectifier bridge circuit using three rectifier diodes
115
and three thyristors
111
. The both output terminals of this rectifier bridge circuit is connect to both ends of the main smoothing capacitor
121
, which uses the DC-power-source unit
120
, to charge the capacitor
121
.
Incidentally, the gate terminal of each thyristor
111
in the DC-voltage-generating circuit
110
is connected to the voltage-limiting circuit
240
to control the continuity angle of each thyristor
111
, and the voltages at both ends of the main smoothing capacitor
121
, which uses the DC-power-source unit
120
, are thereby regulated.
Then, the inverter circuit
130
is configured of a bridge circuit using four power transistors. In this inverter circuit
130
, a first transistor
131
and a third transistor
133
, arranged in series, are connected to the DC-power-source unit
120
, and a second transistor
132
and a fourth transistor
134
, arranged in series, are connected to the DC-power-source unit
120
. The midpoint between the first transistor
131
and the third transistor
133
is connected to a first output terminal
151
via the low pass filter
140
, and the midpoint between the second transistor
132
and the fourth transistor
134
is connected to a second output terminal
152
via the low pass filter
140
. Further the base of the first transistor
131
and the base of the fourth transistor
134
are commonly connected to the inverter-drive circuit
255
, and the base of the second transistor
132
and the base of the third transistor
133
are commonly connected to an inverter-drive circuit
255
.
A first PWM signal supplied from this inverter-drive circuit
255
to the first transistor
131
and the fourth transistor
134
and a second PWM signal supplied to the second transistor
132
and the third transistor
133
are high-frequency pulse signals of several kHz or more. The pulse width of each pulse signal is successively varied between 50 Hz and 60 Hz, and the varying quantity of the pulse width is successively increased or decreased in a sine-wave shape.
Further, the first PWM signal and the second PWM signal are reverse in phase to each other. For this reason, continuity is established between the first transistor
131
and the fourth transistor
134
by the first PWM signal, while discontinuity is ensured between the second transistor
132
and the third transistor
133
by the second PWM signal, and when the midpoint between the first transistor
131
and the third transistor
133
has a voltage VD, which is the voltage of the DC-power-source unit
120
, the midpoint between the second transistor
132
and the fourth transistor
134
is at 0 V. When continuity is established between the second transistor
132
and the third transistor
133
by the second PWM signal, the first PWM signal ensures discontinuity between the first transistor
131
and the fourth transistor
134
, sets the midpoint between the first transistor
131
and the third transistor
133
to 0 V, and the midpoint between the second transistor
132
and the fourth transistor
134
then to the voltage VD of the DC-power-source unit
120
.
This midpoint potential between the first transistor
131
and the third transistor
133
changes over at high speed between 0 V and the voltage VD of the DC-power-source unit
120
as shown in
FIG. 11A
, and the duration of the DC source voltage VD successively varies. Also, the midpoint potential between the second transistor
132
and the fourth transistor
134
also changes over at high speed between 0 V and the voltage VD of the DC-power-source unit
120
as shown in
FIG. 11B
, and the duration of the DC source voltage VD successively varies.
As a result, a first output voltage and a second output voltage having passed the low pass filter
140
are are turned into sine-wave voltages of 50 Hz or 60 Hz as shown in FIG.
11
. Then, the voltage of the first output terminal
151
and the voltage of the second output terminal
152
are generated as AC output voltages of 50 Hz or 60 Hz, with their peak level and bottom level staggered by a half period.
On the other hand, the single-phase output coil
55
of the AC generator
50
is connected to the smoothing circuit
210
in the control-power-supply circuit as shown in FIG.
10
.
This smoothing circuit
210
is configured of a rectifier diode
211
and a smoothing capacitor
215
. The rectifier diode
211
is inserted between the output terminal of the single-phase output coil
55
and the smoothing capacitor
215
, and the smoothing capacitor
215
is charged with the output voltage of the single-phase output coil
55
to form a DC voltage.
Incidentally, the number of the rectifier diode
211
is not limited to one as shown in
FIG. 10
, but sometimes four rectifier diodes are used as an all-wave rectifier bridge to charge a smoothing capacitor.
Then, the output terminal of the smoothing circuit
210
is connected to the constant-voltage circuit
235
, and this constant-voltage circuit
235
generates a prescribed voltage for driving control circuits.
Moreover, the terminal on the − side of this constant-voltage circuit
235
is connected to the + side of the DC-power-source unit
120
, and the terminal on the + side of the constant-voltage circuit
235
is connected to the voltage-limiting circuit
240
, the PWM-signal-generating circuit
250
and an inve
Shinohara Takeshi
Suzuki Kouji
Takahashi Jun
Cuevas Pedro J.
Finnegan Henderson Farabow Garrett & Dunner LLP
Keihin Corporation
Ramirez Nestor
LandOfFree
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