JPS5826271B2 - 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, 3 is a thyristor bridge, etc. A forward conversion device, 4 a DC reactor, and 5 an inverse conversion device consisting of a thyristor bridge.

The main part of the inversion device 5 is made up of thyristor bridges 51 to 54.

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 always has a constant DC current (■) even if the impedance of the circuit after the inverter 5 changes over time.

It has a large enough inductance to allow .

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, thyristors 51 and 52 are in conduction and thyristors 53 and 54 are in a cut-off state, and thyristors 53 and 54 are in conduction and 5 is in the state.
1 and 52 are repeatedly cut off to supply an alternating current to the silent discharge electrode 1.

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 ■ is a direct current from a constant current source ■.

Since the direction is reversed at regular intervals using an inversion device, it becomes a rectangular wave.

Since the voltage (■) is the voltage induced when the current (I) 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.If the capacitance per unit area of the gap is Ca, the capacitance per unit area of the dielectric is Cg, and the discharge area is S, the discharge in the gap is The capacitance between the electrodes when they are not activated is C1, CaS, and Cg.
When S is connected in series, the capacitance C2 between the electrodes when the air gap is discharged is only CgS.

shall be.

Therefore, the voltage waveform changes with a constant slope because the voltage reaches vb after the current is reversed. In the past, the load C1 was charged to a constant current during the non-discharge period, and when the voltage reached vb, the load changed to C2, but the current remained constant. Since it is a current source, it does not change, and it 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, Vp 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, the inverter operates only at frequencies such that the reverse voltage time indicated by tr in FIG. 2 does not become smaller than toff.

When tr becomes smaller than toff, all the thyristors become conductive, causing so-called commutation failure.

The toff of Cyrisk is usually 10 to 100 μsec.

In the case of FIG. 2, if tr = toff is 30 μsec, then t.

Since the time is about 500 μsec and the frequency is about IKHz, it can only be operated at below IKHz.

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, like Figure 2, shows the output current of the inverter and the terminal voltage of the voltage thyristor, and a is the same as Figure 2 when the apparent discharge voltage vb is greater than the voltage peak value Vp. and b is the opposite case.

As is clear from FIG. 3, under the condition that vb<Vp, the reverse voltage time tr applied to the thyristor can be increased, making high frequency operation possible.

By the way, Vp has a limit value determined by the withstand voltage of the silent discharge electrode, and it 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 Vp to be smaller than vb.

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.

f is the frequency Ca, Cg, and S are as described above.

Therefore, when finding vb that maximizes W when Vp and f are given, vb=vp, and W changes at the same rate whether vb becomes larger or smaller than Vp.

Therefore, the discharge power is the same in FIGS. 3a and 3b.

Since tr can be larger in case b, it becomes an advantageous operating condition.

In other words, b has a higher discharge power W/f per cycle than a.
Same as , higher frequency is possible.

Also, when operating with vb = vp, the discharge power W/f per cycle is maximized, but when Vb < Vp, tr becomes large, and f can be made large, so as W, Vb = Vp
It becomes larger than at O time.

In conclusion, operating under the condition that vb<vp is more advantageous in increasing the frequency and increasing the discharge power.

Although the silent discharge ozonizer has been described above, it can also be applied to laser excitation devices with silent discharge electrodes.
not.

Due to the operation method according to this invention, toff is approximately 30 μs.
Using an EC thyristor, inverters that could previously only be operated at IKHz or below can now be used in 3KHz trenches.

This practical value is enormous.

[Brief explanation of drawings]

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.
It is a diagram similar to the figure, showing waveform changes due to the relationship between vb and Vp. In the figure, 1 is a silent discharge electrode, 2 is a step-up transformer, 3 is a forward converter, 4 is a DC reactor, 5 is an inverse converter, 5
1 to 54 are thyristors.

Claims (1)

[Claims] 1. In a silent discharge device driven by a current source inverter using a thyristor as the inverter, the inter-electrode voltage at the start of discharge in each half cycle is made smaller than the peak value of the inter-electrode voltage. A silent discharge device characterized by a long reverse voltage applied to the thyristor.