Electricity: power supply or regulation systems – Output level responsive – Using a three or more terminal semiconductive device as the...
Reexamination Certificate
2000-03-30
2001-02-27
Han, Jessica (Department: 2838)
Electricity: power supply or regulation systems
Output level responsive
Using a three or more terminal semiconductive device as the...
C323S286000, C363S039000, C363S050000
Reexamination Certificate
active
06194885
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a system technique which utilizes a boosting active filter which functions as a DC power-supply circuit for a load, and a technique for controlling the active filter.
(1) First, the present invention relates to a system which uses a boosting active filter as an AC-DC converter or a DC-DC converter which provides (a) control of DC output voltage, (b) power-factor improvement of the power supply, and (c) a measure to counter power-supply harmonics, and a device for controlling the active filter.
More specifically, the present invention relates to a technique which is used for such an active filter to certainly limit the variation of the DC output voltage within a given range around the set value over the entire load range including a situation in which the load condition largely changes from the no-load or light load to the rated load or heavy load and the opposite situation.
(2) The present invention further relates to a system for supplying a DC output voltage to the load by using a boosting active filter as an AD-DC converter or a DC-DC converter which provides (a) control of variable DC output voltage, (b) power-factor improvement of the power supply, and (c) a measure to counter power-supply harmonics, and a device for controlling the active filter.
More specifically, the present invention relates to a boosting active filter system having an overvoltage preventing control function which can certainly control a variable DC output voltage within a given range around a certain set value over the entire load range including a situation in which the load condition largely changes from the light load or no-load to the rated load or heavy load and the opposite situation, and which can follow a new set voltage even if the set voltage is changed, and to a device for controlling the active filter.
2. Discussion of the Background
The basic circuit configurations of the boosting active filters have conventionally been studied and known. For example, Japanese Patent No.2624793 (Japanese Patent Publication No.7-89743) discloses a basic circuit configuration thereof.
FIG. 13
shows the structure of the main circuit corresponding to the basic circuit.
As shown in
FIG. 13
, the main circuit includes converter diodes D
1
to D
2
forming a full-wave rectifying circuit, a DC reactor L, a switching element Q
1
, a rectifier diode D
5
, a load capacitor C, and a load R.
Some methods for controlling this main circuit have also been suggested and used in practice. Many ICs specialized to realize the control systems are commercially available.
FIG. 14
shows an example of circuit configuration of the entirety of an actually used active filter system.
As shown in
FIG. 14
, this system generally includes a single-phase AC power supply
1
, a noise filter
25
, a main circuit (active filter)
100
, a control circuit
200
P for controlling the main circuit
100
, and a load
10
. Among these components, the main circuit
100
includes diodes
2
to
5
forming a single-phase full-wave rectifying circuit, a reactor
6
, a switching element
7
, a rectifier diode
9
, a load capacitor
11
connected to the load
10
in parallel, and a current detecting resistor
12
. The control circuit
200
P includes resistors
29
to
32
for dividing the DC output voltage v
o
, a voltage setter
13
for indicating a set value of the load voltage, a voltage amplifier (a differential amplifier)
14
for amplifying the difference between the load voltage and the voltage set value, and a multiplier
15
receiving a current obtained by applying full-wave rectification to the AC power-supply current at its one input and an output from the voltage amplifier
14
at its other input, for calculating and outputting the product.
The control circuit
200
P further includes a current amplifier
16
for amplifying the difference between the AC power-supply current detected by the current detecting resistor
12
and the output from the multiplier
15
, an oscillator
17
for generating a signal having a triangular waveform, and a comparator
18
having its one input connected to the output of the oscillator
17
and its other input connected to the connection point “a” between a constant-current source
26
and the anode of a diode
28
having its cathode connected to the output of the current amplifier
16
.
The comparator
18
makes comparison between its two input signals to output a control signal at a given frequency, whose waveform has a duty factor varying in accordance with the result of the comparison. The control signal is amplified by a gate driver
19
and then applied to the gate electrode of the switching element
7
, and the switching element
7
turns on and off in correspondence with the duty factor of the control signal.
When the switching element
7
is on, the current inputted from the AC power supply I flows in the closed circuit including the rectifier diodes
2
to
5
, the reactor
6
, the switching element
7
and the current detecting resistor
12
. After that, when the switching element
7
turns off, the current flowing through the reactor
6
cannot flow to the switching element
7
, and it flows to the load
10
and the load capacitor
11
parallel-connected to the load
10
through the rectifier diode
9
. Then the load capacitor
11
is charged and the DC output voltage or load voltage v
o
rises. As a result, in the period in which the switching element
7
is in the OFF state, the rectifier diode
9
is reverse-biased by the charge voltage of the load capacitor
11
and the current does not flow. Thus, in the OFF period of the switching element
7
, electric charge is discharged from the load capacitor
11
to the load
10
and current is supplied to the load
10
.
The control circuit
200
P further includes a soft start DC power supply
23
which directs the main circuit to make soft start immediately after an activation command signal ON is inputted and activation after the soft start, and a start switch
22
which connects the DC power supply
23
to the cathode of the diode
27
series-connected to the constant-current source
26
in response to the input of the activation command signal ON. When the start switch
22
operates to apply the power-supply voltage of the soft start DC power supply
23
to the point “b,” the control circuit
200
P and therefore the entire system including the active filter is started. To stop the entire system, an activation stop command signal OFF is applied to control the start switch
22
to the ground potential.
The control circuit
200
P also has a hysteresis comparator
20
for the object described later; when the voltage obtained by dividing the DC output voltage v
o
at the resistors
31
and
32
exceeds an overvoltage determining reference level (trip operation point) determined by the set value
24
, the comparator
20
outputs an overvoltage detect signal to a flip-flop
21
to latch the flip-flop
21
. In response, an overvoltage detect signal F
o
is outputted to the outside.
When detecting the output of the signal F
o
, an external microcomputer
500
generates the activation stop command signal OFF and sends it to the start switch
22
to switch the start switch
22
to the ground potential.
In this way, the conventional system is constructed so that the entire system is stopped by external control when the voltage obtained by dividing the DC output voltage across the load terminals at the two resistors
31
and
32
rises to or over a level corresponding to the overvoltage (the trip operation point).
In this conventional circuit, when the load
10
changes from the rated heavy load condition to the light load or no-load condition, the output voltage v
o
of the active filter rises higher and higher by the mechanism described below over the range in which the output voltage can be controlled constant.
The “heavy load condition” means a condition in which the load operates while satisfying the 100% condition with respect to the rating, and the “light load cond
Han Jessica
Mitsubishi Denki & Kabushiki Kaisha
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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