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Design and implementation of a high-voltage high-frequency pulse power generation system for plasma applications M. T. Tsai C. W. Ke Department of Electrical Engineering Southern Taiwan University Tainan, TAIWAN. R.O.C. 710 I-Introduction IV Experimental result 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. L ig Iin D (400V/div) V AB iR VAB iR (10A/div) (400V/div) iR (10A/div) (10A/div) Vs (5kV/div) (10uS/div) (400V/div) VAB Vs Vs (5kV/div) II-System configuration (10uS/div) (5kV/div) (10us/div) (b) (a) (c) Fig. 5. The experimental results of PWM control at 40 kHz switching frequency. PIC OUT iL 3895 PWM DQA + Vin _ AC CH1-20A CH2-200V M-5ms/div Fig. 4. The source voltage and current Vg Q CO RL + Vdc DQC QC CQA QA PDM CQC NP : NS + VAB Vdc LR QB + Lm VP - DQB CQB QD Period Ton Period C PIC OUT g + Vs - VZ CH1 3895 PWM VDS C DQD PDM d CQD Period Ton 2 IR2110 Driver Period Toff T PIC OUT CH2 1 K Toff T iR - VGS 1 RS 3895 PWM IR2110 Driver PDM Fig. 6. ZVS switching case for the inverter PDM/PWM Select logic UC3895 PWM controller PIC16F877 controller Fig. 1(b). Inverter stage control structure. III-Control circuit PDM control signals PIC 輸出信號 CK UCC 3895 Fig. 1(a). PFC stage control structure. QA Q D PIC Out Signal OUTA 輸出信號 A組 Q A B C D D 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). QB Q QC CK B組 Q Q A 驅動信號 Q D驅動信號 QD PDM implementation VAB VAB ( 400V/ div) ( 400V/ div) iR Vab CQA CQC QC + VIN A NP : NS + Vs (5kV/ div) VZ - DQD CQB QD Cd CQD QA QB ( 100us/div) (400V/div) QD t0 t1 t 2 t3 t 4 t5 t 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. (a) (b) (c) 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. VAB iR (10A/div) ( 100 us/ div) (400V/div) (10A/div) Vs (5kV/div) (5 kV/ div) iR Vs Vs VAB Power control strategies (10 A/ div) (b) (a) Fig. 7. The corresponding waveforms for PDM control QC iR iR Cg VP DQB QB (10A/ div) Vab iR LR V AB B iR DQC DQA QA (10us/div) Fig. 8. PFM control for 50 kHz switching frequency. V- Conclusion (5kV/div) (10us/div) 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.