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　　Circuit design and implementation of high-voltage sine wave variable frequency inverter power supply

　　Currently, high-voltage inverter power supplies are being increasingly used in technical fields such as ozone generators, sewage treatment, flue gas desulfurization, high-power lasers, and plasma discharges. Traditional high-voltage inverter power supplies are generally obtained by direct boosting of power frequency or medium frequency transformers or LC series resonance, which inevitably has the disadvantages of large size and low efficiency. In many current occasions where high-voltage power is required, it is better to use high-frequency high-voltage power supplies that are much higher than the industrial frequency. Moreover, high-frequency power supplies are small in size and light in weight, which is the direction of future development. This article introduces a high-voltage sine wave inverter power supply dedicated to the dielectric barrier discharge generator. The dielectric barrier discharge generator consists of two parts: an insulating material and a discharge electrode etched at both ends of the insulating material, as shown in Figure 1. Adding a dielectric layer to the discharge electrode gap can effectively suppress the increase in discharge current and help form a stable plasma layer at both ends of the dielectric. Its equivalent circuit can be approximately regarded as a capacitor and a resistor connected in parallel. The impact of this capacitive load on the filter characteristics must be considered when designing the power supply. In order to study the characteristics of the discharge device under different voltages and frequencies, the output voltage and frequency of the supporting power supply need to vary within a wide range. As far as this device is concerned, the power supply requirements are: the output voltage should reach 20kV, the output current should reach 1A, the frequency range should be 5~20kHz, and the waveform should be pure sinusoidal. The design points of this power supply are introduced below.

　　(a) Schematic diagram of generator (b) Equivalent circuit

　　Design of high-voltage sine wave variable frequency inverter power supply

　　The schematic diagram of the high-voltage sine wave inverter power supply designed in this article is shown in Figure 2. The input power supply is three-phase 380V. After rectification by the three-phase bridge, a DC voltage of about 540V can be obtained (fluctuates with the change of the grid voltage). The DC voltage passes through the DC/DC converter to obtain a DC voltage with a variable output amplitude, and the variation range is designed to be 0~500V. This conversion can be achieved using an ordinary Buck step-down conversion circuit. The variable DC voltage is passed through the DC/AC full-bridge inverter circuit to obtain a square wave output. After the square wave is filtered by LC, a sine wave output can be obtained. The filter inductor is composed of the external inductance and the leakage inductance of the transformer itself, and the filter capacitor is composed of the stray capacitance of the transformer itself and the capacitance of the load itself. The low-voltage sine wave is finally boosted by a high-voltage and high-frequency transformer to obtain the required high-voltage sine wave. A general inverter can achieve both frequency conversion and voltage conversion functions by only relying on one-stage DC/AC conversion. However, this example has higher requirements for the output waveform and a higher output frequency, making it difficult to achieve high-frequency modulation. Therefore, Two-stage conversion is used to realize the functions of frequency conversion and voltage conversion respectively.

　　The DC/DC part is controlled by SG3525, which changes the DC output voltage by changing the duty cycle of its output. The function of the DC/AC part is only to convert DC into AC. Therefore, the control chip of this part also uses SG3525, and its duty cycle basically remains unchanged during the working process, and only the frequency changes within the set range. The 80C196KC microcontroller mainly plays the role of a human-machine interface in the entire circuit. It is responsible for receiving control instructions and displaying some parameters and status during the work process. The keyboard and display interface circuit communicate with the CPU through the 8255 chip. The parameter adjustment interface is mainly responsible for transmitting the output instructions of the 80C196KC to the SG3525 power control chip to adjust the output voltage and frequency of the power supply. All power switch tubes use IGBT, and all power tubes are driven by a dedicated IGBT drive control chip M57959L. The chip has a photoelectric isolator and an overcurrent protection circuit inside, which is more convenient to use.

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