Plasma-generation power-supply device
A plasma-generation power-supply device includes a transformer connected to an alternating-current power-supply, a rectifier connected to the transformer, an inverter connected to the rectifier, a reactor inserted in series in a power line of an ozonizer that is supplied with power from the inverter, and a controller that controls the inverter. The controller detects the current flowing to the ozonizer with a current detector and provides a control that keeps power applied to the ozonizer constant.
1. A plasma-generation power-supply device that drives a discharging load that generates a plasma, comprising:
an alternating-current power-supply that supplies power to said discharging load; and
a controller that is capable of controlling a frequency of an alternating output of said alternating-current power-supply,
wherein said controller provides control to vary the power-supply frequency of said alternating-current power-supply in accordance with a target applied power to said discharging load, and
said alternating-current power-supply is formed of an inverter, and said alternating output is a pulse output,
and wherein when
Cg: an electrostatic capacity value of a dielectric included in said discharging load,
Ca: an electrostatic capacity value of a gas region included in said discharging load,
Cp: a floating electrostatic capacity value in parallel with said discharging load,
V*: a discharge maintaining voltage,
L: an inductance value in a circuit including said discharging load,
f: said power-supply frequency, and
Cβ: an electrostatic capacity in a non-discharging state,
then, said controller varies said power-supply frequency and a duty of said pulse output within a stable control region that is surrounded by:
a characteristic curve of applied power that is obtained when said power-supply frequency is varied with said duty of said pulse output fixed at a maximum value;
a curve representing 0.9 times a curve of an applied power Poz that is given by an expression below
Poz
=
4
Cg
(
V
*
)
2
f
(
Cg
Cg
+
Cp
-
1
L
(
2
π
f
)
2
-
(
1
+
Ca
Cg
)
)
;
and,
a straight line representing a resonant frequency f max in the non-discharging state that is given by an expression for f max below
f
max
=
1
2
π
LC
β
.
2. The plasma-generation power-supply device according to claim 1 , wherein said controller varies said power-supply frequency and said duty along a curve that is defined by:
a segment, located on a higher-frequency side of a resonance point, of a characteristic curve of the applied power that is obtained when the frequency is varied with the duty of said pulse output fixed at a value from 80% to 90% of the maximum value; and
a straight line that represents a frequency selected from a range between the value of said resonant frequency f max in the non-discharging state defined by said expression for f max and a value corresponding to 80% of the f max .
3. The plasma-generation power-supply device according to claim 2 , wherein said discharging load is an ozonizer that has a gap interval of 0.6 mm or less and operates with a material gas containing oxygen at an atmospheric or higher gas pressure.
4. The plasma-generation power-supply device according to claim 1 , wherein said discharging load is an ozonizer that has a gap interval of 0.6 mm or less and operates with a material gas containing oxygen at an atmospheric or higher gas pressure.
5. A plasma-generation power-supply device that drives a discharging load that generates a plasma, comprising:
an alternating-current power-supply that supplies power to said discharging load; and
resonance means that causes an alternating voltage outputted from said alternating-current power-supply to jump by resonance and applies the jump voltage as a load voltage to said discharging load,
wherein said alternating-current power-supply is connected electrically directly to said resonance means,
said alternating-current power-supply is formed of an inverter, and
said resonance means comprises a reactor connected in series with said discharging load, and said load voltage is obtained by resonance of a capacitive component of said discharging load and said reactor,
and wherein, when
a ratio of said load voltage with respect to the output voltage of said inverter is defined as a voltage jump rate,
Cg: an electrostatic capacity value of a dielectric included in said discharging load,
Ca: an electrostatic capacity value of a gas region included in said discharging load, and
Cp: a floating electrostatic capacity value in parallel with said discharging load,
and a power-supply frequency of said alternating-current power-supply is set approximately equal to a resonant frequency of a circuit including said discharging load, and when a minimum value M 00 of said voltage jump rate on a characteristic curve of said voltage jump rate with respect to said output voltage is defined by an expression below
M
00
=
2
(
(
(
1
+
Ca
Cg
)
(
1
+
Cp
Cg
)
-
1
2
)
+
(
(
1
+
Ca
Cg
)
(
1
+
Cp
Cg
)
-
1
2
)
2
-
1
4
)
≅
2
2
(
(
1
+
Ca
Cg
)
(
1
+
Cp
Cg
)
-
0.5
)
then, said load voltage is set to be larger than (√{square root over (2)}/4)·M 00 times said inverter's bus voltage and smaller than √{square root over (2)}·(M 00 +2) times said inverter's bus voltage.
6. The plasma-generation power-supply device according to claim 5 , wherein said discharging load is a cylindrical multi-tube type ozonizer that has a plurality of coaxially placed cylindrical electrodes, with a gap interval of 0.6 mm or less, and
said load voltage is set to be larger than one times said inverter's bus voltage and smaller than six times said inverter's bus voltage.
7. A plasma-generation power-supply device that drives a discharging load that generates a plasma, comprising:
an alternating-current power-supply that supplies power to said discharging load; and
resonance means that causes an alternating voltage outputted from said alternating-current power-supply to jump by resonance and applies the jump voltage as a load voltage to said discharging load,
wherein said alternating-current power-supply is connected electrically directly to said resonance means,
said alternating-current power-supply is formed of an inverter, and
said resonance means comprises a reactor connected in series with said discharging load, and said load voltage is obtained by resonance of a capacitive component of said discharging load and said reactor,
and wherein when
a ratio of said load voltage with respect to the output voltage of said inverter is defined as a voltage jump rate,
Cg: an electrostatic capacity value of a dielectric included in said discharging load,
Cp: a floating electrostatic capacity value in parallel with said discharging load,
Vd: a bus voltage of said inverter, and
V*: a discharge maintaining voltage,
then, a power-supply frequency of said alternating-current power-supply is set approximately equal to a resonant frequency of a circuit including said discharging load, and the bus voltage Vd of said inverter is set in a range defined by an expression below, as compared with said discharge maintaining voltage V*,
4
V
*
1
+
Cp
Cg
>
V
d
>
V
*
2
(
1
+
Cp
Cg
)
.
8. The plasma-generation power-supply device according to claim 7 , wherein said discharging load is a cylindrical multi-tube type ozonizer that has a plurality of coaxially placed cylindrical electrodes, with a gap interval of 0.6 mm or less, and
the bus voltage of said inverter is set to be larger than 0.5 times said discharge maintaining voltage and smaller than two times said discharge maintaining voltage.