1. 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. Arc dischargemetallurgical 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. Corona discharge ozone 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. Dielectric barrier discharge 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. Capacitive discharge 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 Fig. 1(a). PFC stage control structure. Fig. 1(b). Inverter stage control structure. III-Control circuit 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 ( a) (b)(b) (c) Fig. 5. The experimental results of PWM control at 40 kHz switching frequency. Fig. 6. ZVS switching case for the inverter PDM implementation Fig. 7. The corresponding waveforms for PDM control (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. Ke Department of Electrical Engineering Southern Taiwan University Tainan, TAIWAN. R.O.C. 710 PDM control signals