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II-System configuration
Arc discharge: this is a high power thermal discharge of very high temperature ~10,000 K. It can be generated using various power supplies. It is commonly used in metallurgical processes. Corona discharge: this is a non-thermal discharge generated by the application of high voltage to sharp electrode tips. It is commonly used in ozone generators and particle precipitators. Dielectric barrier discharge (DBD): this is a non-thermal discharge generated by the application of high voltages ( a range of about 20-100 kHz, 0-2.4 kV peak) across small gaps wherein a non-conducting coating prevents the transition of the plasma discharge into an arc. It is often mislabeled 'Corona' discharge in industry and has similar application to corona discharges. It is also widely used in the web treatment of fabrics. Capacitive discharge: this is a non-thermal discharge generated by the application of RF power (e.g., 13.56 MHz) to one powered electrode, with a grounded electrode held at a small separation distance on the order of 1 cm. Such discharges are commonly stabilized using a noble gas such as Helium or Argon.
Design and implementation of a high-voltage high-frequency pulse
power generation system for plasma applications
I-Introduction
The inverter has five stages, determined by the power switching elements of the two legs. The stages in which two diagonally opposite power switches are conducting are called active. On the contrary, the stages in which two switches on the same site of power switches are conducting are called passive. The switching of the leg can moves the inverter from active stage to passive stage is called the leading leg (QC , QD). The other leg which switches only from passive stage to active is called the trailing leg (QAQB).
Fig.2. The switching relationship of the power elements and the corresponding inverter output voltage and current.
The PAM controls the inverter input voltage by controlling the PFC stage output voltage to achieve the adjusting inverter output power.
The PWM controls the pulse width of the inverter output voltage by shifting the phase difference of the control phase with respect to the standard phase to adjust the output power.
The PFM controls the frequency of the inverter output voltage to achieve the adjustable output power.
The PDM controls the output power by controlling the number of inverter output voltage pulses.
V- Conclusion
DLg
i
OC
SR
AC QgV
Li
K1
LR Vdc
+Vin_
Iin
Fig. 1(a). PFC stage control structure. Fig. 1(b). Inverter stage control structure.
IR2110Driver
IR2110Driver
UC3895PWM controller
PIC16F877 controller
+AQ
BQ
CQ
DQ
1
2
RL+
-PV
SP NN :+
-AB
V
QAD
QDDQBD
QCDQAC
QDC
QCC
QBC
Vdc
-
Rig
C
VZ
dC
Lm+
Vs-
PDM/PWM Select logicIII-Control circuit
abV
Ri
AQ
BQ
CQ
DQ
0t 1t 2t 3t 4t 5t
abV
Ri
t
AQ
BQ
CQ
DQ
RL+
-AB
V
QAD
QDDQBD
QCD
QAC
QDC
QCC
QBC
INV
RiA
B
+
PV
SP NN :
-
gC
ZV
dC
Power control strategies
Fig. 3. PSIM based simulation for plasma reactor characteristic, (a) plasma reactor input voltage and gas discharger, (b) gas discharge voltage verse
charger, (c) plasma reactor input voltage verse charger.
(a) (b) (c)
IV Experimental result
CH1-20A CH2-200V M-5ms/div Fig. 4. The source voltage and current
VAB
iR
Vs
(400V/div)
(10A/div)
(5kV/div) (10uS/div)
VAB
iR
Vs
(400V/div)
(10A/div)
(5kV/div) (10uS/div)
VAB
iR
Vs
(400V/div)
(10A/div)
(5kV/div) (10us/div)
(a) (b) (c) Fig. 5. The experimental results of PWM control at 40 kHz switching frequency.
GSV
DSV
CH1
CH2
Fig. 6. ZVS switching case for the inverter
D
CK
Q
Q
D
CK
Q
Q
SignalOutPIC
3895U
CC
AQ
BQ
CQ
DQ
組A
組B
ABCD
輸出信號PIC
輸出信號OUTA
驅動信號AQ
驅動信號DQ
PDM implementation
Vs
iR
VAB (400V/div)
(10A/div)
(5kV/div) (100us/div)
VAB (400V/div)
Vs (5kV/div) (100us/div)
iR (10A/div)
Fig. 7. The corresponding waveforms for PDM control
Vs
iR
VAB
(400V/div)
(10A/div)
(5kV/div) (10us/div)
VAB
iR
Vs
(400V/div)
(10A/div)
(5kV/div) (10us/div)
(a) (b)
Fig. 8. PFM control for 50 kHz switching frequency.
Fig. 9. PFM control for 40 kHz switching frequency.
As the experimental results, some conclusions can be made as follows:The only PAM control is not encouraged as it needs a complicated front stage to achieve voltage regulation function, and is hardly used to less that half of the full range due to the required gas breakdown voltage level The PWM control can fulfill the full load range conditions. However, a small pulse width tends to a discontinuous load current or leading load current, which is adverse to the switching loss, thus it is disapproved for a low pulse width control.The only PFM control is also not encouraged as it should be large than the load resonant frequency to realize zero voltage switching. Thus, one can see that the inverter power fact should decline in low power range, and it is difficult to adjust the discharge power to less than half of the full power as the electrodes voltage would be lower than the gas discharge breakdown voltage. The PDM can work well over a range of pulse densities from 3/30 to 1, however, the environment temperature fluctuations should disturb the stability of the inverter output power. To compensate this influence, a hybrid control such as PDM plus PFM or PDM plus PWM is suggested.
M. T. Tsai C. W. KeDepartment of Electrical Engineering
Southern Taiwan UniversityTainan, TAIWAN. R.O.C. 710
3895 PWM
PIC OUT
PDM
PDM
3895 PWM
PIC OUT
T
Period onT Period offT
PDM
3895 PWM
PIC OUT
T
Period onT Period offT
PDM control signals