Study of Corona Discharge Treaters consisting of Voltage-Source Inverter Fed Series Resonant Circuits using IGBT's

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Over the last 5-10 years, remarkable progress has been made in the development of fast switching devices such as power transistors, static induction transistors, power MOSFET's, and so on. Notably, attention is paid to Insulated Gate Bipolar Transistors (IGBT's) which are suitable for high-frequency-inverters with the frequency range of 20-60kHz.A high-frequency high-voltage power supply is essential for corona discharge treatment. The object of corona discharge treatment for film is to render the affinity to inks, glues and coatings. So far, vacuum tubes have been used for such a power supply at the expense of efficiency and feliability.In this study, a new inverter system for a corona discharge treater is developed, which consists of a 50kHz 5kW voltage-source inverter using IGBT's and a step-up transformer of turn ratio 1:20. A leakage inductor of the step-up transformer plus a stray capacitor of the step-up transformer and the corona discharge treater forms a series resonant circuit without any externally connected inductor or capacitor. The series resonant circuit is considered a matching circuit between the inverter of output voltage 250V and the treater of input voltage 20KV. This plays an important role in maintaining proper corona discharge. The following results are obtained :1. A three-phase diode rectifier is used as an ac to dc power converter. This results in a simple power circuit.2. Although output power control is achieved by power factor control, the inverter efficiency is 96% with the help of lossless snubbing circuits.3. A new PLL circuit developed in this study is introduced to the control circuit, leading to proper corona discharge.