High Density Ozone Generation System Using Fuzzy Inference Engine

Ozone (O3) is generated by voltage control inverter of single phase sinusoidal waveform different from current control inverter of three phase used in motor control. Ozone quantity is directly proportional to the frequency as well as the voltage of power supply. In this paper, we propose not only a voltage control inverter of 600Hz and step-up transformer from 220V to 12KV using IGBT, but also fuzzy inference engine using MADANI Min-Max composition so as to generate the high density ozone generation. We substantiate that the proposed Ozone generation system produces the double quantity of ozone and higher efficiency than conventional ozone system using the current control inverter through lots of real experiments on the developed ozone system.


Introduction
Ozone (O 3 ) is generated by Ozone generator using single phase inverter combined with step-up transformer to 12KV at 600Hz as well as Air Preparation System (APS). The inverter used in ozone generation is different from the three phase inverter used in motor control and the inductive load characteristics of the electric circuit.
The ozone generator has capacitive load characteristics because of the charging and discharging taken place between the two electrodes between discharging tubes arranged in parallel and steel contacts encompassing the tubes in high frequency alternatively, the tubes filled with pressurized air.
The conventional ozone generator controls the supplying current of the inverter output by adjusting not only the frequency, but also the voltage level of the PWM square waveform so as to maintain the current level. These cause the voltage waveform required in the ozone generation to be fluctuated so as to track the desired current levels continuously.
This current type inverter used in ozone generator has a short discharging period which is critical parameters of efficient ozone generation and the spikes caused by this impulse current destroys the discharging tubes at the rising and falling edge of square wave.
Because of these defects from the conventional current control inverter [CCI], in this paper, we proposes system for the high density concentration and high efficiency of ozone generation system [OGS]; the first, one phase PWM inverter with adjustable amplitude and frequency, the second, LC filter for smoothing PWM voltage of inverter into sinusoidal waveform as well as for compensating the power factor (PF). Finally, the fuzzy controller for the high density ozone generation using MAMDANI MAX-MIN fuzzy inference, where parameters such as ozone concentration as well as supplied voltage level and the supplying voltage as output are used as input and output of the proposed FIS, respectively.
Ozone Generation Technologies. The word "Ozone" is originated from the Greek word "Ozein" meaning a peculiar smell of fish, Schöbein used the word in 1840 for the first time. From then, the Ozone generation technologies have been advanced to a silent discharge through electrolysis, Oprochemical combination, high frequency electric field and illumination of radiation.
However, the silent discharging technology is considered to be practical in industrial production. The glass (or ceramic) discharge tube is enclosed by metal electrode with a clearance of air gap. The air or oxygen are passed through hese electrodes of 6~18KVAC sinusoidal voltage of ceramic(anode contact) and metal (cathode contact) as shown in Fig.1(a). High pressurized air (or oxygen) is blown into the inlet, and passed through the discharging air with gap of 3mm clearance, power supplying of 6000Vac~12000Vac,600Hz.
The generated ozone is expelled out through the Ozone outlet as shown in Fig.1 (a). The cooling water is circulated so as to ban the reduction of the generated ozone to Oxygen when Ozone is exposed in environment exceeding 40°C.  The discharging electric circuit is constructed by the current flow from the inverter; the current is boosted up by using the step-up transformer and discharged from the Pyrex discharging electrode to the metal contact within the ozone tank, and then return to the ground of step-up transformer. Table 1 shows the generated ozone quantity according to the supplying power frequency. Role of power supply in Ozone generation system. Ozone quantity is directly proportion to supplying voltage from 600 to 2KVac of the gas cell if the other parameters such as the relative humidity and pressurization of the air are well conditioned. The governing equation of ozone generator is described by the following equation (1): (1) where f-input frequency, V a -supply voltage at air gap, V o -maximum value of supply voltage, C ddielectric capacitance, C a -air capacitance at the air gap. The ozone generation system has capacitive features because of capacitive loads of single phase high voltage electrically. Although the generated ozone quantity is proportional to the frequency and supplying voltage, in some case, the specific OGS takes advantage of the frequency adjustment to control the quantity and concentration while fixing the voltage control the frequency in a specific case.
Because the power factor (PF) in the OGS is very low (0.3~0.5) because of capacitive characteristics of ozone tubes, the matching transformer like a choke must be inserted between boosting transformer and ozone generator so as to improve power factor [PF] Cos(θ) to almost 1 so that the effective maximum energy mighty be transmitted to the OGS

Electrical characteristics of Ozone generation system
The equivalent electrical circuit of ozone generation system using silent discharging can be modeled in  Equivalent model in Fig.3 shows lots of capacitance are cascaded in parallel or in electrical network, which are the reason why the OGS has capacitive load characteristics. Fig. 4 shows electrical phenomena within the discharging tube for one period of supplying voltage.
(a) Ionization level (b) Alternating ionization (c) Electrical potential changes of Ozone generation electric potential discharge tube within gas states Fig. 4. Discharging condition according to the supplying voltage waveform [2] [3] Owing to the changing of electrical characteristics, the ionization potential also changes alternatively as in Fig.2  The gases exist as an ionized state partly and then dropped below than the ionized potential. Waveform of electric potential the gas is shown as Fig.4 (c) The ionization voltage in ozone generation system V i is proportional to the gas pressure and applied voltage between electrodes as Eq (5). i V pg  (5) where p-gas pressure, g-applied pressure. Fig 5 shows a series of ozone generation dynamic sequences according to the electric potential variation within the air passing space.
The boxed areas denotes the ionized periods explained as in Fig.4 (b), take placed alternatively along the periodical sinusoidal waveform which are ionized time. Lots of Oxygen (O -2 ) are combined with a single oxygen in ionized Oxygen (O -1 +O -1 ) and becomes Ozone (O 3 ) Fig.5 Ozone generation mechanism at air gap [4] Ozone Generation System Fig.6 shows PWM inverter used in the OGS. Three phase line voltage is converted to DC voltage after rectification by bridge circuit and the DC voltage is used in IGBT PWM inverter. The basic waveform of the PWM inverter has sinusoidal waveform of PWM inverter as shown in Fig.6 Fig.7 (b) shows the screen of PC based main controller implementing FIS while monitoring all states of the OGS. We can see the fired crisp result by Min-Max composition of FIS in Fig.7 (b)

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Mechatronics and Information Technology

Experimental results
In this paper, we pretest the ozone concentration to examine the capability of the proposed OGS while changing input frequency with other conditions such as air pressure and supplying voltage fixed at 6000Vac and 1.3Bar, respectively. The test result is shown in Fig. 9. Comparing this result with Fig. 2 of ozone generation characteristics, we conclude that the proposed OGS has the same characteristics as explained in Fig.2 for the ozone generation. Fig.10 shows another test result while only changing the air flow into the ozone generation tubes with other parameters such as frequency at 600Hz and voltage at 6000VAc fixed with a view to compare the ozone concentration.
We analyze the efficiency of the OGS comparing with conventional current control inverter [CCI]. The proposed OGS has a characteristic of increased Ozone quantity according to the increased air flow. Finally, Table2 represents the comparison results of the proposed OGS using FIS and PWM sinusoidal inverter with the conventional CCI of square waveform without any feedback control Ozone Concentration Fig.9 Ozone generation according to Fig.10 Test results while maintain frequency at 600Hz and the only frequency changes the supplying voltage at 6000VAc

Conclusion
We proposed the OGS using not only voltage control inverter with PWM sinusoidal waveform generation, but also FIS for control the optimal ozone generation. The PWM square waveform from the proposed inverter is filtered for converting the square into analog sinusoidal waveform before inserted in step-up transformer. The FIS plays parts in controlling the ozone concentration by adjusting frequency as well as voltage into ozone tubes.