TS-84
Development of PDM Controlled Soft-Switching High-Frequency
Inverter for Ozone Generation for Water Treatment
Oleg KOUDRIAVTSEV*, Shengpei WANG*, and Mutsuo NAKAOKA*
ABSTRACT
In this paper, voltage source type high-frequency high voltage load resonant inverter using MOSFETs or IGBTs for driving a silent discharge type nonlinear load is presented. It is designed for high performance power supply for ultraviolet generation and ozone generation systems in ship onboard drinking water treatment plants, wastewater treatment applications, malodorous air treatment equipment and ultraviolet sterilization systems. Ozone and ultraviolet water treatment have several advantages over traditional methods implying chemicals such as chlorine or germ culture usage. Introduced here power supply system has proved its effectiveness in experiment and considerations on its inverter characteristics are discussed both in ozone and ultraviolet generation systems. The pulse modulated performances of developed inverter system also evaluated and experimental results are described here. Due to simplicity, easy control and high efficiency of developed scheme, ozonation and treatment based on ultraviolet are effective as main or auxiliary process for onboard disinfections or wastewater treatment systems.
Key Words: silent discharge, ozone, ultraviolet high-frequency inverter, PDM modulation, water treatment.
1. INTRODUCTION
At present, ozone gas has been widely utilized for drinking water, wastewater and malodorous air treatment. At 1990 in Western Europe, there were over 40 full-scale municipal ozone facilities installed each year. France alone had over 700 water treatment plants equipped with ozone. Also Germany had over 70 installations using ozone and there were over 80 plants online for disinfecting contaminated water and oxidizing organics in heavily contaminated surface waters in Switzerland. At the same time, there were not less than 40 full-scale ozone installations in the United States. Such intense interest to ozone caused due to unique characteristics of this gas. The most significant of which are: the most rapid destruction of bacteria and inactivation of viruses among disinfectant chemicals, outstanding oxidative strength, which allows to oxidize heavy metals, strong ability to decompose organic materials and liberate organically bound heavy metals, that cannot be achieved by other means. On the other hand, depending of ship size and type, these features are valuable in onboard systems too, especially those concerning water treatment. Together with traditionally applied today chemicals, germ and ultraviolet water processing, using of ozone should be investigated for such purposes separately or along with ultraviolet treatment.
In spite of such wide spread of ozone technologies in land applications and growing variety of needs for ozone gas, there are still problems hindering its use in case of ship systems. Such difficulties as large physical size, low efficiency of ozone generation, high initial cost and high exploitation expenses should be resolved firstly to make using of ozone and ultraviolet onboard economically effective. Own to recent advances in electronic materials and devices technology, especially in power MOSFETs and IGBTs as well as power electronics circuit components, it become possible to improve performances of power supply system radically.
This paper presents novel ozone generation power supply system that is developed and tested with aim to solve the problem of low efficiency and high cost of ozone generation system. It has full-bridge converter topology, however some proposals concerning its structure and control scheme provide unique features and made this design promising for other silent discharge applications for output power regulation.
The pulse density modulated voltage-source inverter type ozonizer can provide excellent ozone generation characteristics wide output power regulation, which ranges from 10% to 100% of full power, 3kW.
2. OVERALL SYSTEM AND GENERATION TUBE DESCRIPTION
Silent discharge principle is one of the most effective methods for ozone gas production and also applied for ultraviolet light generation systems. Although the electric energy-to-ozone gas conversion efficiency is still rather low, it provides high ozone production level in relatively small-scale set-ups. Introduced here power supply system was developed for silent discharge type ozone generation tube; however, it can be applied for ultraviolet generation with slight corrections.
