Study On High Frequency Pulse Power Supply For Polytetrafluoroethylene Film Surface Modification

The low temperature plasma, induced by Atmospheric Pressure Dielectric Barrier Discharge (APDBD) and applied to Polytetrafluoroethylene(PTFE) film surface modification, have several advantages like better treatment effect, higher treatment efficiency, lossless and non-pollution. While now there exists two main problems, electrodes pollution and low power efficiency, which lead to the lower treatment efficiency. One primary reason of these problems is that traditional APDBDs are driven by AC or bipolar-pulsed power supply, which brings out two opposite discharge current pulses during a high-voltage pulse duration.Based on analysis of these problems, an APDBD excited with a unipolar pulsed power is taken into account, and only one discharge current pulse during a voltage pulse duration, a unipolar pulsed power with regulating repetition frequency from0to20kHz, pulse voltage from0to20kV, pulse rise time about500ns to2us, pulse fall time>20us, is developed. Also the experimental study about surface modification effects of PTFE film by using this unipolar pulsed power is carried out initially.The high voltage pulse generator and related theory are stated firstly. After choosing the Insulated Gate Bipolar Transistor (IGBT) semi-conductor solid switch which can operate with tens of kHz, high voltage and current, the generator structures based IGBT switch are stated totally. And the pulse transformer electrical circuit is chose. The factors effecting the output pulse rise time mainly are leakage inductance and distributed capacitance, the dominant factors effecting pulse fall time are magnetization inductance and distributed capacitance, and the dominant factor of pulse duration voltage is magnetization inductance.the design of unipolar pulsed power is stated in detail. The ratio of pulse transformer is38, the geometry of pulse transformer is a coaxial cylinder for smaller leakage inductance, the primary number of turns is8, and the distributed factors including magnetization inductance, leakage inductance, distributed capacitance are calculated by empirical formulas. Taking the properties of DBD based on the pulsed equivalent model by Liu and Neiger into consideration, we design fake load to release the charges of DBD dielectric layer caused by unidirectional current pulse and call this fake load and DBD reactor as the load of pulsed power. Similarly, we make a pulse transformer equivalent circuit combined with the electrical properties of load like the equivalent resistor and capacitance. And then the output voltage pulse effects caused by these factors are analysed synthetically.The experimental study of the designed pulsed power is carried out. The voltage pulse rise time is a factor dominating the discharge current effect, the oscillating of pulse fall time may damage the whole electrical circuit, so these two factors are paid more attentions. The distributed parameters of pulse transformer are measured, the output voltage pulse, switch voltage pulse and discharge current pulse are measured under different number of primary turns and transformer ratio, the results are investigated, such as the widen pulse rise time. It is shown that the pulse rise time aberration is related to repetition frequency, ratio and DBD; the oscillating of pulse fall time is related to ratio and the number of primary turns. Larger is the pulse repetition frequency and ratio, larger is the level of widen pulse rise time, the reason is increasing of leakage inductance and distributed capacitance by larger frequency and ratio; the reason from DBD is the capacitance of DBD is larger when the discharge occurs. On the other hand, larger is the number of primary turns, larger is the amplitude of oscillating, the reason is increasing of magnetization inductance by larger number of primary turns; similarly, larger is the ratio, larger is the distributed capacitance, and then the period of oscillating is enlarged. So, the number of primary is decreased to7, ensuring enough inductance and output amplitude. Besides, the results from different switch RCD absorbing circuits show that the hot produced by resistors is very serious, and there is a better method of choosing a switch of more voltage and current.Finally, the discharge efficiency of DBD in atmospheric pressure Ar is calculated and analysed initially. And the effect study of PTFE plasma surface treatment is carried out initially. Under the10kHz-20kV conditions, the gap voltage, discharge current and power are calculated by using the pulsed equivalent model. Meanwhile, the DBD emission spectrum is compared to the traditional bipolar discharge’s initially, it is shown immediately that this DBD plasma have the same particles, the surface water contact angle and T-mode peel intensity are also improved very well.