Electricity: battery or capacitor charging or discharging – Capacitor charging or discharging
Reexamination Certificate
2001-06-26
2002-05-07
Toatley, Gregory (Department: 2838)
Electricity: battery or capacitor charging or discharging
Capacitor charging or discharging
Reexamination Certificate
active
06384579
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a capacitor charging apparatus and charging method using an inverter, a switching regulator and an inductance circuit. More particularly, this invention relates to the capacitor charging apparatus and charging method which charge in two stages. This invention particularly relates to the capacitor charging apparatus and charging method which use resonant charging to achieve a highly accurate level of voltage stability, such that the charge voltage accuracy of the energy accumulating capacitor comprising the load is highly accurate to less than approximately 0.1%.
2. Description of the Related Art
In a pulse laser such as an excimer laser, the charge of a capacitor for accumulating energy, which has been charged to a high voltage of approximately several kV to several ten kV, is discharged at high speed to a laser tube via a magnetic compressor or the like, thereby exciting laser light. In the application apparatus of the pulse laser, the higher the number of laser light excitations (i.e. the higher the number of repetitions of charging and discharging the capacitor) the greater its capability as a laser apparatus. For this reason, in recent years there have been attempts to achieve a high repetition of several kHz. Consequently, the charging apparatus of the capacitor must be capable of repeating high-speed charge/discharge to completion below several hundred &mgr;s. Excimer lasers require a highly accurate level of voltage stability, detecting fluctuations in the output of laser light in each cycle and controlling the output of laser light in the subsequent cycle accordingly. Therefore, the charge voltage must be controlled in each cycle, making high-speed controllability an important feature.
FIG. 19
is a circuit diagram showing one example of the constitution of a conventional resonant charging-type capacitor charging apparatus. Reference numeral
1
represents a dc (direct current) power such as a rectifier which rectifies a commercial ac (alternating current) voltage. The output of the dc power
1
is supplied to a voltage-type bridge inverter
2
(hereinafter abbreviated as “inverter
2
”). The inverter
2
comprises four IGBTs
4
A-
4
D (insulated gate bipolar transistors) which feedback diodes
3
A,
3
B,
3
C and
3
D are connected to in reverse parallel.
The ac side output of the inverter
2
connects via an inductance circuit
5
to a primary winding
6
A of a high-voltage transformer
6
(hereinafter abbreviated as “transformer
6
”), becomes an ac high voltage boosted to a predetermined value at a secondary winding
6
B, is converted to a dc high voltage by a high-voltage rectifier
7
(hereinafter abbreviated as “rectifier
7
”), and is supplied to a load capacitor
8
. The black dots appended to the primary winding
6
A and the secondary winding
6
B represent the polarities of the windings. The rectifier
7
is a bridge rectifier comprising four diodes
7
A,
7
B,
7
C, and
7
D. The inductance circuit
5
also includes the inductance leaked from the transformer
6
.
Reference numerals
9
and
10
represent voltage division resistances for detecting charge voltage; the resistances
9
and
10
convert a charge voltage Vc of the load capacitor
8
to a charge voltage detect signal Vd of several V (hereinafter abbreviated as “detect voltage Vd”), which is input to a voltage comparator
11
. Reference numeral
12
represents a reference voltage source for setting the charge voltage, and outputs a reference voltage Vr. The voltage comparator
11
compares the detected voltage Vd with the reference voltage Vr, outputting a comparison signal Vh at the H (high) level until the detected voltage Vd reaches the reference voltage Vr and outputting the comparison signal Vh at the L (low) level when the detected voltage Vd reaches the reference voltage Vr. To prevent the output comparison signal Vh from oscillating at the switchover point, the hysteresis of the voltage comparator
11
is set to approximately 0.1% of the charge voltage. Reference numeral
13
represents an inverter controller which supplies two A-phase and B-phase opposite phase signals through AND gates
14
and
15
, one signal switching ON the pair of IGBTs
4
A and
4
D and the other signal switching ON the pair of IGBTs
4
B and
4
C alternately. In
FIG. 19
, a pair of IGBT gate signals is shown in common in order to illustrate the path of the signals, but in reality the gate signal of the IGBTs are separately insulated from each other.
The inductance circuit
5
which includes the leakage inductance from the transformer
6
, the rectifier
7
, and the load capacitor
8
form a half-wave series resonant circuit. The inductance circuit
5
is usually comprised of an inductor comprising the leakage inductance of the transformer
6
and an appropriate inductance, but when the inductance required for series resonance can be obtained by using only the leakage inductance of the transformer
6
, the transformer
6
alone is sufficient. When the pair of IGBTs of the inverter
2
are switched ON in resonant half-cycles, the load capacitor
8
is charged by resonance to a voltage which is approximately twice the value obtained by multiplying the dc power voltage by the transform ratio n of the transformer
6
. For example, when the dc power voltage Vd is 250 V, the capacity of the load capacitor
8
(Co) is 50 nF, and the boost ratio n of the transformer
6
is 20, the charge voltage Vc becomes Vc=2×n×Vdc=2×20×250=10 kV. The time during which the pair of IGBTs are ON corresponds to the charge time, that is, a resonant half-cycle. When the charge time (i.e. the resonant half-cycle) T/2=100 &mgr;s, the primary conversion value Co′ of the load capacitor Co becomes Co′=20
2
×50 nF=20 &mgr;F. Since 2 &pgr;{square root over ( )}LC=T, the inductance value L of the inductance circuit
5
becomes L=(T/2&pgr;)
2
/Co′=25.3 &mgr;H. In actual conventional systems, the dc power voltage Vdc changes due to fluctuation in the commercial power voltage; for example, when the commercial power voltage fluctuates between AC 180 V to 220 V, the dc power voltage Vdc changes from 240 V to 300 V. Furthermore, the resonant effect decreases to less than twice as a result of circuit loss. For these reasons, the boost ratio n of the transformer
6
is set at more than 20, e.g. 25, and the circuit constant is set so that, when the pair of IGBTs are switched ON in a resonant half-cycle while the dc power voltage Vdc is at its lowest value, the charge voltage of the load capacitor Co is greater than the set voltage 10 kV. Therefore, the IGBT of the inverter are switched OFF when the charge voltage of the load capacitor Co has reached the set voltage 10 kV, stabilizing the charge voltage within the range of power voltage fluctuation.
Subsequently, the operation will be explained by referring to FIG.
20
. In
FIG. 20
, symbol (
1
) shows the current IL of the inductance circuit
5
, which is equivalent to a compound current of the current of the IGBT
4
A and the diode for feedback
3
A, connected in reverse parallel thereto, and the current of the IGBT
4
B and the diode for feedback
3
B, connected in reverse parallel thereto. In
FIG. 20
, the currents of the diodes for feedback
3
A and
3
B are shown by diagonal shading. In
FIG. 20
, symbol (
2
) shows the charge voltage Vc of the load capacitor
8
, and symbol (
3
) shows a gate signal VgA of the IGBT
4
A and
4
D, and a gate signal VgB of the IGBT
4
B and
4
C. When the load capacitor
8
is being discharged at time t
0
and the detect voltage Vd is lower than the reference voltage Vr, the voltage comparator
11
outputs an H signal, and the A-phase side signal of the inverter controller
13
passes through the AND gate
14
, switching ON the pair of IGBT
4
A and
4
D which are on the diagonal line of the inverter
2
. When the IGBT
4
A and
4
D are switched ON, a dc power voltage is app
Hoffmann & Baron , LLP
Origin Electric Company Limited
Toatley Gregory
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