JPS5927188B2 - silent discharge device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for increasing the operable frequency of a current source thyristor inverter used as a power source for a silent discharge device.

FIG. 1 is a configuration diagram of an ozonizer as an example of a silent discharge device driven by a current source inverter.

In the figure, 1 is a silent discharge electrode, 1' is an equivalent circuit of a silent discharge electrode when not discharging, 1'' is an equivalent circuit of a silent discharge electrode when discharging, 2 is a step-up transformer, and 3 is a forward conversion consisting of a thyristor bridge, etc. 4 is a DC reactor, and 5 is an inverse conversion device consisting of a thyristor bridge. Inverse conversion device 5
The main part is made up of 51 to 54 thyristor bridges. The current converted from the AC power supply to DC by the forward converter 3 is sent to the reverse converter 5 through the DC reactor 4. This DC reactor 4 has an inductance large enough to always flow a constant value of DC current 10 even if the impedance of the circuit after the inverter 5 changes over time. That is, the forward converter 3 and the DC reactor 4 constitute a constant current source (which always supplies a constant current even if the impedance of the load changes). In the inverter 5, alternating current is supplied to the silent discharge electrode 1 by repeating a state in which thyristors 51 and 52 are conductive and thyristors 53 and 54 are disconnected, and a state in which thyristors 53 and 54 are conductive and thyristors 51 and 52 are disconnected. The step-up transformer 2 changes the voltage ratio and current ratio, but does not affect the waveform. Therefore, the voltage and current waveforms indicated by V and I in FIG. 1 are equal to the voltage and current waveforms applied to the silent discharge electrode 1. FIG. 2 shows the current and voltage waveforms of the inverter output and the terminal voltages of the thyristors 51-54. The current I is obtained by reversing the direction of the direct current 10 from a constant current source at regular intervals using an inverter, so it becomes a rectangular wave. Since the voltage V is the voltage induced when a current flows through the silent discharge electrode which is the load, it is as follows. There is a gap and a dielectric plate between the silent discharge electrodes, and if the capacitance per unit area of the gap is Ca) the capacitance per unit area of the dielectric is Cg) the discharge area is s, the discharge in the gap is The capacitance Cl between the electrodes when no discharge is occurring is the series connection of CaS and CgS, and the capacitance C2 between the electrodes when the gap is discharged is only CgS.

C1=-C2=Cg5 In an ozonizer, normally Cg>Ca, so C2>C1.

Discharge begins when the current reverses, the discharge that occurred in the previous half cycle stops, and the electric field becomes stronger in the opposite direction to the previous half cycle, and the voltage in the air gap reaches the discharge voltage Vb. It happens when you do it. At this time, the apparent discharge voltage b' seen from between the electrodes is expressed by the following equation. VC》 Let b be the voltage obtained by converting b' to the low voltage side of the transformer.

Therefore, the voltage waveform changes with a constant slope because load C1 is charged with a constant current during the non-discharge period until the voltage reaches b after current reversal, and when the voltage reaches Vb, the load changes to C2, but the current is Since it is a constant current source, it does not change, and changes with a constant slope determined by C2. Since C1 is smaller than C2, the non-discharge portion has a steeper slope, resulting in the waveform shown in FIG. In FIG. 2, p is the peak value of the voltage waveform. FIG. 2 also shows the voltages applied to the thyristors CR1 to CR4 of the inverter.

By the way, in a switching element such as a thyristor, the transition from cutoff to conduction can be controlled by the gate, but in order to shift from conduction to cutoff, a reverse voltage is applied to the element, and the reverse voltage time Tr is controlled by the forward voltage of the element itself. The stopping ability recovery time must be kept longer than Toff. That is, T in Figure 2
The inverter works only at frequencies such that the reverse voltage time, denoted r, does not become less than Toff. Tr is Toff
If it becomes smaller, all the thyristors become conductive, causing so-called commutation failure. Thyristor Toff is usually 1
It is 0 to 100ttsec. In the case of Fig. 2, Tr=T
If Off is 30μSec, then T. is 500Itsec
The frequency is about 1 KHz, so it can only be operated at 1 KHz or less. An object of the present invention is to provide a silent discharge device that allows the inverter to be used at a higher frequency by matching the discharge conditions of the silent discharge electrodes and the operating conditions of the inverter.

Figure 3 shows the output current of the inverter and the terminal voltage of the voltage thyristor, similar to Figure 2, and in a), the apparent discharge voltage b is greater than the voltage peak value 9, as in Figure 2. b) is the opposite case.

As is clear from FIG. 3, under the condition of b<p, the reverse voltage time Tr applied to the thyristor can be increased, making high frequency operation possible. By the way, p has a limit value determined by the dielectric strength of the silent discharge electrode, and cannot be set larger than that. Since the discharge voltage Vb is determined by the gap length of the silent discharge electrode and the gas pressure in the gap, it is possible to select p to be smaller than b. Considering the purpose of operating the inverter at high frequency, this is to input as much discharge power as possible to the silent discharge electrodes.

Silent discharge power W is given by the following equation. Frequency F as a state.

, voltage PO, F as shown in FIG. At a lower frequency, the current value is increased with the frequency constant, and Vp=b
Tr, tr! By increasing the voltage to VpO so that Toff is greater than Toff, and then increasing the frequency f to FO while keeping PO constant, a steady state of operation can be reached. Although it is troublesome to change b in a normal ozonizer, it is not impossible to change Vb by adjusting the pressure in the gap.

In this case, a method may be adopted in which the frequency is set to the set value from the beginning, Vp is increased to the set value while the pore pressure is small and b is also small, and then the pore pressure is increased to bring b to the set value. Although the silent discharge ozonizer has been described above, it goes without saying that the present invention can also be applied to a laser excitation device having a silent discharge electrode.

The operation method according to this invention allows Toff to be approximately 30 μSe.
By using a thyristor, an inverter that could previously only be operated at a frequency of 1 KHz or less can now be used up to 3 KHz.

This practical value is enormous.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram of a silent discharge ozonizer driven by a current source inverter, Fig. 2 is a diagram showing the current voltage waveform of the inverter output and the terminal voltage waveform of the thyristor, and Fig. 3 is a diagram showing the thyristor terminal voltage waveform.
Similar to the figure, it is a diagram showing waveform changes due to the relationship between Vb and p, Fig. 4 is a diagram showing voltage waveform changes due to increase in current of the output current and voltage waveform of the inverter, and Fig. 5 is an explanatory diagram of the operation method. .

Claims (1)

[Claims] 1 In a silent discharge device driven by a current-source inverter using a thyristor as an inverse conversion device, the peak value of the inter-electrode voltage is increased to the target value at a frequency lower than the final target frequency, and then the frequency is set to the target value while keeping the peak value constant. In addition to adopting a starting method that increases the voltage up to 100%, the interelectrode voltage at the start of each half cycle is made smaller than the peak value of the interelectrode voltage, thereby increasing the time during which the reverse voltage is applied to the thyristor of the inverter. A silent discharge device.