Comparative Analysis of Energy Efficiency in High-Voltage Ozone Generators: Resonant Versus Non-Resonant Systems ^†

Abstract

The effective generation of ozone by high-voltage systems is essential for several industrial and environmental purposes. This paper performs a thorough comparative examination of energy efficiency in ozone generators, emphasizing resonant and non-resonant systems. Resonant ozone generators, which utilize tuned electrical circuits for optimal efficiency, are assessed in comparison to non-resonant systems that function without frequency tuning. The comparison analysis includes measures like energy use, ozone generation, and overall system efficiency. Experimental results demonstrate considerable differences in energy consumption between the two generator types, with resonant systems exhibiting substantially more efficiency in the conversion of electrical power into ozone. The resonant systems, producing 120 g/kWh, demonstrate 50% greater efficiency than the non-resonant systems, which generate 80 g/kWh, in terms of ozone production per unit of energy. This study clarifies the operational features, benefits, and drawbacks of each system, offering essential insights for the advancement of ozone-generating technologies in diverse applications.

1. Introduction

Ozone (O₃), which is known for its powerful oxidizing powers, is utilized extensively in a variety of industrial sectors, including the purification of water, the treatment of air, and the synthesis of chemicals. When it comes to these operations, high-voltage ozone generators [1], which achieve the production of ozone through the use of electrical discharges, play an essential part. A key target that has evolved as a result of the intensification of focus on energy efficiency and sustainability is the enhancement of the energy consumption of ozone generators. The purpose of this inquiry is to evaluate the energy efficiency of resonant high-voltage ozone generators in comparison to non-resonant generators [2,3], to identify technology that demonstrates superior efficiency, and to offer suggestions for improvements that might be implemented in future designs. Ozone production can be accomplished through various circuit configurations that utilize high-voltage electrical discharges.

The system’s performance largely depends on the efficacy of its power supply for ozone generation. Despite its pulsed characteristics making it unsuitable for continuous operation, a Marx generator is highly effective at producing high-voltage pulses, making it ideal for initiating high-energy discharges. A 50 Hz high-voltage transformer, on the other hand, provides consistent AC, which is less effective for ozone generation, as pulsed or high-frequency systems are more effective. A high-voltage, high-frequency half-bridge power supply is the best option for continuous ozone generation because it provides better energy efficiency through the precise control of high-voltage pulses or high-frequency alternating current. Full-wave resonance increases efficiency by optimizing energy transfer at the resonant frequency, resulting in improved discharge stability. When compared with the half-wave power supply, full-wave resonance enhances performance, making it the best system for dependable and efficient ozone generation [3,4,5,6,7,8].

Resonant systems use inductors and capacitors to generate oscillating electric energy, improving energy transfer efficiency by minimizing energy losses. Conversely, non-resonant systems utilize high voltages directly, without oscillating components, which frequently leads to increased energy consumption. Although earlier studies have explored different facets of ozone generation, there remains a gap in thorough comparative analyses that specifically address the energy efficiency of resonant systems compared to non-resonant systems. This review seeks to synthesize our current understanding, emphasizing the operational mechanisms, advantages, and limitations of each system, while also identifying the gaps that this study aims to address.

2. Materials and Methods

A high-voltage ozone generator consists of a power frequency converter, a high-frequency high-voltage transformer, and an ozone tube. Descriptions of these components are given in the following subsections.

2.1. Power Frequency Converter

The power frequency converter converts the DC power supply to the specific frequency that is necessary for the efficient operation of the ozone generator. A rectifier and an insulated-gate bipolar transistor (IGBT) bridge configuration are shown in the power conversion circuit diagram in Figure 1. A bridge rectifier converts AC to DC voltage. The DC output voltage, V_dc, is then stored across a capacitor C₁. The four IGBTs (S₁, S₂, S₃, and S₄) constituting the IGBT bridge are linked to their respective freewheeling diodes. The individual units responsible for managing these IGBTs are referred to as IGBT drivers. Upon activation, these drivers can receive control signals from a microcontroller, designated STM32F407. Thus, the microcontroller is responsible for controlling the on/off states of the IGBTs, resulting in the production of the requisite square waveform output voltage for the ozone generator system [8,9,10].

2.2. High-Frequency High-Voltage Transformer

A transformer designed for high-frequency applications was employed to augment the voltage necessary for ozone production. It was equipped with a primary winding that contained 23 turns of SWG 34 copper wire and a secondary winding that contained 1280 turns. This configuration was intended to accommodate high-frequency inputs that are within the 1–25 kHz frequency range. Regarding the high-frequency operation of these high-voltage transformers, the IGBT bridge produced a high-frequency signal that was delivered to the primary winding of the high-frequency transformer. The transformer elevated the voltage from the input level to 3 kV, functioning at a frequency of 18.5 kHz.

The ozone generation process within the ozone tube was initiated by a high-voltage, high-frequency output that facilitated corona discharge and improved the efficiency of ozone production. The basic high-frequency power generation setup, as shown in Figure 2, includes a power frequency converter, a high-frequency transformer, and an ozone tube [11].

This system transforms 50 Hz power into a frequency range of 1–25 kHz while elevating the voltage, yielding a straightforward and efficient design appropriate for fundamental applications. Conversely, the diagram in Figure 3 shows a series resonance circuit situated between the power converter and the transformer. This circuit comprises a capacitor and an inductor. This resonant circuit facilitates accurate frequency regulation and increases efficiency by eliminating undesirable frequencies, minimizing noise, and enhancing overall performance. The incorporation of the resonance circuit enhances this design’s suitability for industrial or high-performance applications that necessitate precise frequency tuning and reduced power losses.

Resonant systems achieve high voltage with minimal energy dissipation by utilizing a resonant circuit, which typically consists of capacitors and inductors. The voltage across the ozone-generating unit is optimized with minimal power input when the inductive and capacitive reactances are equal and antipodal, resulting in resonance [12,13]. To determine the resonant frequency of a series resonance circuit, we apply the provided parameters: a capacitance of 33 nanofarads (nF) and an inductance of 2.25 millihenries (mH), encompassing the high-frequency transformer. The internal resistance of 38 ohms does not influence the resonant frequency directly; however, it affects the quality factor and bandwidth of the resonance. We utilized the resonant frequency formula to compute the resonant frequency, which was found to be 18.5 kHz in this instance.

$$f_0={\displaystyle \frac{1}{2\pi \sqrt{LC}}}$$

(1)

$$A_v\left(resonance\right)={\displaystyle \frac{V_{out}}{V_{in}}}$$

(2)

$$V_{out}\left({\omega }_r\right)=V_{in}\left({\omega }_r\right)\times {\displaystyle \frac{R_L{C}_L}{\sqrt{L{C}_L{R}_S{R}_L{C}_L+L}}}$$

(3)

$$3O_3\left(g\right)\to 2O_3\left(g\right)$$

(4)

Equation (1) defines the resonant frequency (f₀) of a series LC circuit, which consists of a capacitor (C) and an inductor (L), connected in series. The relationships between the circuit’s output voltage (V_out) and input voltage (V_in) at its resonant frequency (ω_r) are described by Equations (2) and (3). The circuit’s behavior at the resonant angular frequency (ω_r) is influenced by factors such as resistance (R_L), capacitance (C_L), inductance (L), and series resistance (R_s). In resonant circuits, resistance (R_L) signifies the load resistance, which represents the resistive component across the output that dissipates power. Capacitance (C_L) denotes the load capacitance, which considers the capacitive influences of the load or parasitic components on the resonant frequency of the circuit. The series resistance (Rs) represents the inherent losses that occur in both the inductive and conductive pathways. The quality factor and damping of the circuit are significantly impacted by this factor. The parameters outlined collectively influence the circuit’s selectivity, energy dissipation, and frequency response in proximity to resonance. These equations emphasize the complex interactions between these components, offering a detailed understanding of the energy transfer between the input and output during resonance.

Equation (4) illustrates the chemical process of ozone generation through high-voltage corona discharge, wherein a high voltage converts molecular oxygen (O₂) to ozone (O₃) [14]. The oxygen concentration in Earth’s atmosphere is roughly 21% by volume. In a sample of air, approximately 21% consists of oxygen, while the remaining 79% is composed of other gases, predominantly nitrogen (approximately 78%), along with trace quantities of argon, carbon dioxide, and additional gases [15].

Conversely, non-resonant systems provide power to the ozone-generating tube through direct high-voltage transformers. Although their design is simpler, non-resonant systems are more likely to experience higher energy losses as a result of the need for higher input power to maintain operation and a less efficient power transfer mechanism.

2.3. Ozone Generation

A corona discharge was induced in the oxygen by the high-voltage alternating signal generated by the high-frequency high-voltage transformer, which was then applied to the ozone tube. This process produced ozone, which was collected for the purpose of conducting color elimination tests on water [16,17].

The distribution of the electric field is critical when determining the efficiency of ozone production in high-voltage ozone generators, as shown in Figure 4, Figure 5, Figure 6 and Figure 7. A high-voltage electric field was applied to three electrode configurations, namely, a non-uniform electric field, uniform electric field, and slightly non-uniform electric field, to study the effect of geometry on field distribution and its implications for ozone generation. The non-uniform electric field gradually increased in intensity from 12.4 to 37.9 kV, indicating localized enhancement near a sharp region. The uniform electric field exhibited the steepest and most consistent rise, reaching 122.17 kV, indicating a highly homogeneous field. The slightly non-uniform electric field followed a smooth nonlinear trend, rising from 17.4 to 78.4 kV due to moderate field concentrations. All field profiles showed quadratic trends, confirming that electrode geometry is critical for field strength and uniformity, with a direct impact on the efficiency and stability of high-voltage ozone generation systems. However, slightly non-uniform fields can improve performance by promoting more consistent ozone production and reducing localized hotspots, despite minor variations in field strength. Furthermore, in order to achieve a balance between uniformity and practical constraints, advanced electrode designs can be implemented to optimize the field distribution. By effectively managing the degree of non-uniformity, the efficiency of ozone generation can be improved, resulting in a more stable and effective high-voltage ozone generator [18].

The breakdown of air between electrodes is a fundamental process in systems such as corona discharge ozone generators, which results in the generation of ozone (O₃).

A high-voltage electric field is applied between the electrodes, ionizing the air or oxygen and initiating chemical reactions that lead to the formation of ozone. This is the beginning of the process. In a conventional ozone generator, multiple kilovolts of high voltage are applied between two electrodes, which are separated by a dielectric material, such as glass, along with an air- or oxygen-filled interval [19], as shown in Figure 8 and Figure 9. When the applied voltage surpasses the breakdown threshold of air or oxygen, the intense electric field ionizes the gas molecules in the gap, generating a plasma consisting of free electrons, positive ions, and radicals.

A corona discharge is the consequence of ionization, which occurs when the electric field is sufficiently intense to induce partial air breakdown without establishing a complete electrical arc between the electrodes. The dissociation of oxygen molecules (O₂) into singular oxygen atoms (O) is facilitated by the resulting non-thermal plasma, which simultaneously minimizes the thermal output and facilitates chemical reactions that generate ozone, as shown in Figure 10. Figure 11 shows the development of an ozone generator system.

Our comparative analysis utilized the experimental setups of both resonant and non-resonant high-voltage ozone generators. Key parameters, including energy efficiency, input power, and ozone production rate, were systematically measured and recorded under controlled experimental conditions. These factors were thoroughly evaluated. Energy efficiency is defined as the ratio of ozone output to the corresponding energy consumption. Standardized methods for assessing gas flow and concentration were employed to quantify ozone production rates in grams per hour (g/h). In evaluating the system performance, the focus was placed on the uniformity of the ozone output and the durability of the components.

3. Results and Discussion

3.1. Power Frequency Converter with Non-Resonant Systems in an Ozone Generator

Increased losses may result from the harmonic content inherent to the square wave when a square wave input is introduced into a transformer [20,21]. The 3rd, 5th, and 7th harmonics [22] are among the numerous higher-frequency harmonics that significantly impact both core and copper losses in a square wave. Core losses [23,24] escalate due to augmented hysteresis and eddy current losses as the core material reacts to elevated frequencies. Moreover, the abrupt transitions in a square wave can cause the core to reach saturation more easily, resulting in increased power losses [25,26]. Copper losses are heightened due to augmented skin and proximity effects in the windings, leading to increased AC resistance and, consequently, greater I2R losses. Core losses and copper losses may increase when employing a square wave input. This results in an estimated total loss of approximately 6 W, encompassing both core and copper losses, thereby indicating a substantial effect on transformer efficiency. Figure 12 shows the development of a test setup for ozone color removal. The evaluation of non-resonant systems indicates the output voltage of the high-frequency transformer. Figure 13 shows the output voltage waveform with no load, while Figure 14 shows the output voltage waveform under load conditions.

3.2. Power Frequency Converter with Resonant Systems in an Ozone Generator

A resonant condition is achieved by precisely matching the circuit’s inductance and capacitance at a specific frequency, resulting in lower energy losses and higher power transfer efficiency. Resonant systems are designed to operate at this frequency. These systems typically employ sinusoidal waveforms with low harmonic content, which aids in reducing energy losses in the transformer core and windings. The energy efficiency of practical resonant systems is significantly increased, with an average ozone production efficiency of 120 g/kWh. Reduced core losses, such as hysteresis and eddy currents, as well as copper losses, can be attributed to increased efficiency. The total loss, which includes both core and copper losses, is approximately 4 W in a resonant system with a total power input of 100 W, according to the test results. This results in a system that is notable for its exceptional overall efficiency. Figure 15 depicts the high-frequency transformer’s output voltage waveform when no load is present, whereas Figure 16 depicts the voltage waveform when the ozone tube receives power during resonant system operation.

The experimental results show that resonant and non-resonant technologies consume significantly different amounts of energy. In comparison with non-resonant systems, resonant systems have a higher energy efficiency, meaning that they require less electricity to generate the same quantity of ozone. The performance metrics for each system are presented in tabular and graphical formats, and statistical analysis is used to validate the differences that have been observed. When compared with other types of systems, resonant systems have a distinct efficiency advantage. The system’s losses are measured only at the DC link from the power supplied to the system before the conversion stages. This represents partial system efficiency, not total system power consumption.

The study found that resonant systems outperformed non-resonant systems in terms of energy efficiency and overall performance. Resonant systems achieved a much higher average ozone production efficiency of 120 g/kWh, compared with the 80 g/kWh produced by non-resonant systems. The system producing 120 g/kWh demonstrates 50% greater efficiency than the system generating 80 g/kWh in terms of ozone production per unit of energy.

In comparison with the current state of affairs, this could be considered a significant improvement. Furthermore, resonant systems require a lower amount of power in order to achieve the same level of ozone output as other systems. Non-resonant systems, although simpler to implement and more economical, necessitate higher input power and demonstrate increased variability in ozone production rates, due to inefficiencies in power transfer. This can be attributed to the fact that they are simpler to put into action.

It is possible to attribute the superior performance of resonant systems to the optimized power transfer that takes place as a result of resonance. Consequently, this reduces the amount of energy that is wasted and makes it possible to achieve higher ozone yields while using less power. However, the complexity of resonant systems, requiring precise calibration and potentially higher upfront costs, may limit their widespread use in smaller-scale applications or in those with strict budget limitations. This is because resonant systems require precise tuning. In contrast, non-resonant systems, despite being less efficient, offer a solution that is both simpler and more reliable for circumstances in which the primary concern is either the cost or the complexity of the situation.

Resonant systems are able to achieve higher levels of energy efficiency, as demonstrated by the findings of the study, because they are able to minimize the amount of energy that is lost as a result of the generation of oscillating electrical fields. An investigation into the underlying mechanisms that are responsible for the increased efficiency of resonant systems is presented in this section. When it comes to the generation of ozone in industrial settings, the practical implications suggest that the implementation of resonant designs could result in significant energy savings. In addition, the challenges that are generally associated with the implementation of resonant systems, such as their increased complexity and cost, are discussed. The primary focus of research in the future ought to be on optimizing resonant designs and determining whether or not they are scalable for use in applications that are on a large scale [3].

4. Discussion

4.1. Resonant Systems in an Ozone Generator Test with Wastewater

A test to investigate the color-removal characteristics of ozone at a concentration of 19 ppm requires 400 mL of distilled water. To this volume, 5 g of textile color powder is added. The examination focuses on observing changes in the water’s color before and after exposure to ozone. Figure 12 shows the development of an ozone generator system over a 30-min period. Figure 17 shows a graphical representation of the test results. This experiment seeks to determine the usefulness of ozone, specifically its capacity to remove color from water. The findings are offered for analysis and application to actual wastewater.

In this section, a series of evaluations were performed to assess the efficacy of ozone in removing color from wastewater collected from a canal in Chong Nonsi, Bangkok, Thailand. The results of these examinations are presented in Figure 18, and the detailed data on wastewater treatment with ozone over a period of 0–30 min are provided in

Table 1. Test results using wastewater from Chong Nonsi Canal in Bangkok, Thailand: ozone treatment for 0–30 min.

Parameter	Treatment with Ozone for a Duration of 0–30 min							Quality Std.
	Sample	5	10	15	20	25	30
pH	7.66	8.32	8.34	8.35	8.37	8.38	8.38	5–9
DO, mg/L	2.78	6.46	6.70	6.75	6.82	6.88	6.91	≥6
Color	Black tea	Tea	Tea	Tea	Tea	Clear	Clear	Clear

. This analysis aims to determine the effectiveness of ozone treatment in achieving color removal in real-world wastewater conditions.

Ozone treatment of wastewater over a 30-min period effectively improved water quality across several parameters. The pH value gradually increased from 7.66 to 8.38, consistently remaining within the acceptable range of 5–9. Dissolved oxygen (DO) levels increased from 2.78 mg/L to 6.91 mg/L, exceeding the threshold of ≥ 6 mg/L after 5 min and continuing to improve. The color of the wastewater transitioned from black tea to clear within 25 min, achieving the desired clarity standard by the end of the treatment. These results demonstrate the efficacy of ozone in enhancing pH, oxygenation, and color clarity in wastewater.

The results of wastewater testing from the Saen Saep Canal in Bangkok, Thailand are depicted in Figure 19 and show the findings of these analyses visually, while

Table 2. Test results for wastewater from the Saen Saep Canal in Bangkok, Thailand, with ozone treatment for 0–30 min.

Parameter	Treatment with Ozone for a Duration of 0–30 min.							Quality Std.
	Sample	5	10	15	20	25	30
pH	7.32	8.29	8.30	8.30	8.30	8.31	8.31	5–9
DO, mg/L	3.65	6.15	6.22	6.29	6.38	6.44	6.50	≥6
Color	Black Tea	Tea	Tea	Tea	Clear	Clear	Clear	Clear

offers comprehensive data on ozone wastewater treatment over a period of 0–30 min.

The pH of the wastewater rose marginally from 7.32 to 8.31, still remaining within the permissible range of 5–9, indicating that the ozone treatment did not cause detrimental acidification or alkalinity. Dissolved oxygen (DO) levels concurrently increased from 3.65 mg/L to 6.50 mg/L, satisfying the ≥6 mg/L standard, indicating successful oxygenation. Furthermore, the water’s color changed from tea-colored to clear, indicating a successful decrease in organic pollutants [19].

4.2. Safety and Environmental Conditions in an Ozone Generator Test with Wastewater

In an ozone generator test concerning wastewater, safety and environmental considerations are paramount, due to the inherent hazards linked to ozone production and wastewater handling. Therefore, we examined the following critical elements.

Ozone exposure: Ozone (O₃) is a powerful oxidizing agent that can be detrimental when inhaled, potentially leading to irritation of the respiratory system, eyes, and skin. It is important to ensure that the ozone generator functions in a well-ventilated area or that ozone is adequately neutralized prior to atmospheric release.

Personal protection: Operators are required to wear appropriate personal protective equipment (PPE), comprising ozone-resistant masks or respirators, safety goggles, and gloves, to reduce ozone exposure.

Ozone Monitoring: Ongoing assessment of ozone levels is crucial. Install ozone sensors or detectors in the specified area to guarantee that ozone levels remain within safe parameters.

Ventilation: The assessment must occur in a regulated environment with sufficient ventilation, such as under a fume hood or exhaust system that is engineered to capture and neutralize ozone prior to its release into the atmosphere [16,17,18].

5. Conclusions

The experimental results show that high-voltage ozone producers using resonant systems have significantly higher energy efficiency than non-resonant models. Resonant systems can generate a greater output of ozone per kilowatt-hour of input power while experiencing less energy loss, mainly due to their efficiency in mitigating harmonic distortion. In contrast, non-resonant systems undergo heightened energy loss, especially in the core, due to the harmonic components in the square wave input. A power frequency converter with resonant systems generates 120 g/kWh of ozone, exhibiting 50% greater efficiency than the non-resonant system, which produces 80 g/kWh in terms of ozone generation per unit of energy. The experiments performed for this study indicate that ozone treatment is an efficacious way to decolorize wastewater, especially when removing textile dye contaminants. In a controlled experiment with 19 ppm of ozone, notable decolorization occurred, as demonstrated by the alteration in the water’s color pre- and post-ozone exposure. Empirical assessments of wastewater from a canal in Chong Nonsi, Bangkok, corroborate these findings. During a 30-min ozone treatment, wastewater quality improved significantly: the pH remained below acceptable levels, dissolved oxygen (DO) levels increased substantially, and the water’s color changed from black tea to clear, indicating a significant reduction in organic contaminants.

The findings confirm that ozone treatment improves the visual clarity of wastewater and optimizes critical water quality parameters, making it a feasible approach for urban wastewater management, especially in addressing textile dye contamination. Future research should explore methods to enhance the effectiveness of ozone treatment for various pollutants. This technology improves ozone treatment methods for the effective removal of color from wastewater, as demonstrated by our laboratory tests.

These research findings may facilitate the development of innovative technological applications aimed at adjusting the operating frequency within the 1–25 kHz range upon the installation of additional ozone tubes. This adjustment is essential, as the resulting changes in capacitance directly impact the increased generation of ozone.