JP2003275541A - Plasma device and control method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a plasma device in which a voltage drop in a plasma electrode is reduced and a gas cleaning effect is maintained. <P>SOLUTION: Inside the flow path member 12 of the plasma device 10, electrodes 21, 22, 23, 31, 32, 33, 41, 42, 43, 44, 45 and 46 formed in a net shape are installed parallelly along the flow direction of an exhaust gas. The electrodes 21, 22 and 23 and the electrodes 31, 32 and 33 are anodes and the electrodes 41, 42, 43, 44, 45 and 46 are cathodes. The anodes 21, 22 and 23 constitute an anode group 20 and the anodes 31, 32 and 33 constitute an anode group 30. The electrodes 41, 42, 43, 44, 45 and 46 constitute a cathode group 40. The cathode group 40 is connected to an exhaust pipe and an engine which are metal parts and grounded. To an electrode group constituted of the anode group 20 and the cathode group 40 and the electrode group constituted of the anode group 30 and the cathode group 40, high voltage pulses are impressed at respectively different timings and frequencies. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma device for purifying gas by discharge plasma and a control method therefor.

[0002]

2. Description of the Related Art A gas polluted with harmful substances, for example, NOx, SOx, which are harmful substances in exhaust gas from vehicles, are decomposed into harmless substances by discharge plasma, or the harmful substances are ionized by discharge plasma. As a plasma device for purifying gas by activating and improving the reduction rate of a catalyst, JP-A-11-128674 and JP-A-2001
The ones disclosed in Japanese Patent Laid-Open No. 87620 and Japanese Patent Laid-Open No. 2001-164927 are known. In order to generate the discharge plasma, it is necessary to apply an ultrashort high voltage pulse of several tens of kV or more and 100 ns or less to the plasma electrode because of its purification effect and energy efficiency.

[0003]

However, when a high voltage pulse is applied from the pulse generating circuit to the plasma electrode to supply energy, the applied voltage drops due to the capacitance of the plasma electrode. If the pulse voltage applied to the plasma electrode drops, the gas purification effect may decrease. When a high voltage pulse containing a voltage drop is generated in order to obtain a desired purification effect, it becomes necessary to increase the withstand voltage of the circuit. When the electrode area of the plasma electrode is reduced to reduce the capacitance in order to reduce the voltage drop at the plasma electrode,
The area of the plasma electrode for purifying the gas is narrowed.

There is also a problem that a special switching element is required to generate an ultrashort pulse. Further, in the configuration of the pulse generation circuit that accumulates the high voltage in the capacitor in order to generate the high voltage pulse, the high voltage is constantly applied to the capacitor, which may cause electric shock.

An object of the present invention is to provide a plasma device that reduces the voltage drop at the plasma electrode and maintains the gas purification effect. Another object of the present invention is to provide an inexpensive plasma device that does not require a special switching element to generate a high voltage pulse applied to a plasma electrode. Another object of the present invention is to generate a high voltage on the secondary coil side only when generating a high voltage pulse,
It is an object of the present invention to provide a plasma device and a control method thereof that reduce the possibility of electric shock. Another object of the present invention is to provide a method for controlling a plasma device, which efficiently supplies electric power to the plasma device according to the degree of gas contamination or the flow rate thereof to reduce the power consumption.

[0006]

According to the plasma apparatus of claim 1 of the present invention, a plasma electrode is constituted by a plurality of electrode groups electrically connected in parallel, and a plasma generating electrode and each electrode group are connected. A pulse generation switch installed for each electrode group is connected and disconnected electrically. Since the electrode group to which the high voltage pulse is applied at the same time can be selected, the electrode area of the electrode group to which the high voltage pulse is applied at the same time can be made smaller than the electrode area of the entire plasma electrode. Since the voltage drop for each electrode group becomes small and the desired discharge plasma is generated,
The gas can be satisfactorily purified. Further, since the voltage drop of each electrode group is small, it is not necessary to further increase the voltage of the pulse voltage generated by the pulse generation circuit including the voltage drop. Therefore, it is easy to ensure the withstand voltage of the pulse generation circuit.

According to the plasma device of the second or fourth aspect of the present invention, since the flyback voltage generated when the reverse current flows through the diode is used as the high voltage pulse, special switching is performed to generate the high voltage pulse. No element is needed. According to the plasma device of claim 3, 5 or 6 of the present invention or the control method of the plasma device according to claim 11, the power switch is turned on and off only when a high voltage pulse is generated, and the secondary coil side, That is, since a high voltage is generated in the pulse generation circuit, it is not necessary to constantly store the high voltage in the pulse generation circuit in order to generate a high voltage pulse. Therefore, the risk of electric shock is reduced.

According to the control method of the plasma apparatus of the eighth aspect of the present invention, since the high voltage pulse is applied to only one of the plurality of electrode groups at the same time, the power consumption can be reduced. According to the plasma device control method of the ninth aspect of the present invention, the plasma device is installed at a position where the flow velocity is slower in the flow path, that is, at a position where the flow velocity is higher than the electrode group installed at a position where the flow velocity is low, that is, a position where the flow velocity is high. A high-voltage pulse is applied to the electrode group being applied with high frequency. Power can be efficiently supplied to the plasma device to effectively purify the gas.

According to the plasma device control method of the tenth aspect of the present invention, the number of electrode groups to which the high-voltage pulse is applied is increased or decreased according to the degree of contamination of the gas, so that the plasma device is efficiently supplied with electric power. The power consumption can be reduced.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a plasma device according to an embodiment of the present invention. The plasma device 10 shown in FIG. 1 is used, for example, in an exhaust gas treatment device of an internal combustion engine (hereinafter, “internal combustion engine” is referred to as an engine), and is installed near the upstream side of the reduction catalyst. The plasma device 10 decomposes harmful substances such as NOx and SOx in exhaust gas into harmless substances or ionizes and activates harmful substances by discharge plasma to enhance the reduction effect of the reduction catalyst.

The plasma device 10 has a flow path member 12 formed of ceramic in a circular or elliptical shape, and exhaust gas passes through the flow path formed in the flow path member 12. Electrodes 21, 22, 23, 31, which are formed in a mesh shape,
32, 33, 41, 42, 43, 44, 45 and 46 are installed in parallel in the flow path member 12 along the flow direction of the exhaust gas. Electrodes 21, 22, 23 and electrodes 31, 3
2, 33 are positive electrodes, and electrodes 41, 42, 43, 4
4, 45 and 46 are negative electrodes. Positive electrodes 21, 22, 2
3 constitutes a positive electrode group 20, and positive electrodes 31, 32 and 33 constitute a positive electrode group 30. The positive electrode group 20 and the positive electrode group 30 are electrically connected in parallel. Positive electrode group 20
Is installed in the flow path member 12 at a central portion where the flow velocity is high, that is, the flow rate is high. The positive electrode group 30 is located on both sides of the central portion where the positive electrode group 20 is installed, that is, the flow path member 1
It is installed at a position where the flow velocity is slower and the flow rate is smaller than that in the central portion in the area 2. Electrodes 41, 42, 43, 44, 4
Reference numerals 5 and 46 form the negative electrode group 40. Cathode electrode group 40
Is connected to the exhaust pipe, which is a metal part, and the engine and is grounded. The positive electrode group 20 and the negative electrode group 40 form the electrode group 120 shown in FIG. 2, and the positive electrode group 30 and the negative electrode group 40 form the electrode group 140 shown in FIG. The electrode group 120 and the electrode group 140 form a plasma electrode. In this embodiment, high voltage pulses are applied to the electrode groups 120 and 140 at different timings and frequencies. That is, the high voltage pulse is not applied to the electrode groups 120 and 140 at the same time.

The circuit shown in FIG. 2 has an electrode group 120, 140.
1 is a pulse generation circuit 100 of a plasma device 10 for generating a high voltage pulse to be applied to. The electrode group 120 includes a capacitor component (C3) 122 and a resistance component (R3) 124.
, The electrode group 140 has a capacitor component (C
4) 142 and resistance component (R4) 144.

The pulse generation circuit 100 includes power supplies 102, 1
Secondary coil (L1) 104, secondary coil (L2) 106,
Power switch (SW1) 108, resonance capacitor (C
1) 110, diode (D1) 112, thyristor (SW2) 116, coil (L3) 118, resonance capacitor (C2) 130 and diode (D2) 132. The pulse generation switch 114 is a switch that connects and disconnects the electrical connection between the pulse generation circuit 100 and the electrode group 120. The pulse generation switch 134 is a switch that connects and disconnects the electrical connection between the pulse generation circuit 100 and the electrode group 140.

The power supply 102 is a vehicle-mounted battery. Primary coil (L1) 104 and 2 as a resonance coil
The next coil (L2) 106 constitutes a transformer.
The power switch (SW1) 108 is the primary coil (L1) 1
The current flowing through 04 is interrupted. Secondary coil (L2) 10
6, the resonance capacitor (C1) 110 and the diode (D1) 112 form a resonance circuit for the electrode group 120. Secondary coil (L2) 106, resonance capacitor (C
2) 130 and diode (D2) 132 are electrode group 1
A resonant circuit for 40 is configured.

The thyristor (SW2) 116 is a switch for generating a flyback voltage in the diode (D1) 112 or the diode (D2) 132. The inductance of the coil (L3) 118 is equal to that of the secondary coil (L3).
2) It is sufficiently smaller than the inductance of 106.

Next, the operation of the pulse generation circuit 100 shown in FIG. 2 will be described with reference to the time chart shown in FIG. When the power generation switch (SW1) 108 is turned on and off in a pulse shape while the pulse generation switch (SW3) 114 is turned on, and the current flowing through the primary coil (L1) 104 is interrupted, the secondary coil (L2) 106 A high-voltage induced voltage is generated at. Pulse generation switch (SW3) 1
When 14 is on, this induced voltage causes the diode (D1) 112, the resonance capacitor (C1) 110,
A current flows through the pulse generation switch (SW3) 114 and the secondary coil (L2) 106 in the forward direction of the diode (D1) 112 (L2 current).

The thyristor (SW2) 116 is turned on at the same time as or before the reversal of the current flowing in the resonance circuit composed of the secondary coil (L2) 106, the resonance capacitor (C1) 110 and the diode (D1) 112. When set to
Thyristor (SW2) 116, coil (L3) 118,
A slightly steep current flows through the pulse generation switch (SW3) 114, the resonance capacitor (C1) 110, and the diode (D1) 112 in the reverse direction of the diode (SW3 current). Since the inductance of the coil (L3) 118 is sufficiently smaller than the inductance of the secondary coil (L2) 106, the current flowing through the secondary coil (L2) 106 is negligibly small. Since the resistance value of the resistance component 124 of the electrode group 120 is very large, the current flowing through the electrode group 120 is also small enough to be ignored.

The reverse current flows for several hundreds of nanoseconds until the diode (D1) 112 blocks the reverse current that tries to flow in the reverse direction through the diode (D1) 112.
When the diode (D1) 112 abruptly cuts off the reverse current in about 10 nanoseconds, a flyback voltage of about several tens of kV is generated. This flyback voltage is applied as a high voltage pulse to the electrode group 120 (C3 voltage), and discharge plasma is generated in the electrode group 120.

Also in the electrode group 140, the diode (D2) 132 is turned on by turning on and off the power switch (SW1) 108 and the thyristor (SW2) 116 while the pulse generation switch (SW4) 134 is turned on.
Then, a flyback voltage can be generated and applied as a high voltage pulse to the electrode group 140 (C4 voltage). The pulse generation switch (SW3) 124 is turned on and the electrode group 12
The frequency of applying the high voltage pulse to 0 is twice the frequency of applying the high voltage pulse to the electrode group 140 by turning on the pulse generation switch (SW4) 134.

In the above-described embodiment, the plasma electrode is composed of a plurality of electrode groups 120 and 140, and the electrode group 12
No high voltage pulse is applied to both 0 and electrode group 140 at the same time. Therefore, the capacitance of the electrode group to which the high voltage pulse is applied at the same time is smaller than the capacitance of the entire plasma electrode. Since the voltage drop in the electrode groups 120, 140 is small, a high voltage pulse for generating discharge plasma necessary for purifying exhaust gas can be applied to the electrode groups 120, 140.

In this embodiment, the positive electrode group 20 is the flow path member 1
2 is installed in the central part where the flow rate is high, and the positive electrode groups 30 are installed in the flow path member 12 on both sides of the central part where the flow rate is lower than the central part. The frequency of the high voltage pulse applied to the electrode group 120 is set to twice the frequency of the high voltage pulse applied to the electrode group 140. By increasing the frequency of high voltage pulses applied to the electrode group 120 installed in the central portion where the flow rate is high, the electric power supplied to the plasma device 10 for purifying the exhaust gas is effectively used and the exhaust gas is effectively used. Can be purified.

It is desirable that the frequency at which the power switch (SW1) 108 is turned on and off to generate an induced voltage in the secondary coil (L2) 106 is increased or decreased according to the amount of exhaust gas flowing through the flow path member 12. For example, by increasing the frequency of generating the induced voltage in proportion to the fuel injection amount per intake time corresponding to the exhaust gas amount, the intake air amount, etc., the optimum frequency can be set according to the amount of the exhaust gas purified. . Thereby, the power consumption of the plasma device 10 can be effectively controlled and the power consumption can be reduced.

A high voltage pulse is applied to the electrode group 120 by turning on / off the power switch (SW1) 108.
Secondary coil (L2) 1 only when applied to 140
An induced voltage is generated at 06, and a current is caused to flow through the diode (D1) 112 and the diode (D2) 132 by this induced voltage. Since the induced voltage is generated in the secondary coil (L2) 106 only when necessary, the risk of electric shock is reduced as compared with the configuration of the pulse generation circuit that accumulates a high voltage in the capacitor.

In this embodiment, the high voltage pulse applied to each electrode group is generated by the flyback voltage generated by the diode (D1) 112 and the diode (D2) 132 when the reverse current is cut off. Therefore, no special switching element is needed to generate the high voltage pulse,
The pulse generation circuit can be constructed at low cost.

In this embodiment, the primary coil (L1) 104
A high voltage is generated by a transformer composed of the secondary coil (L2) 106 and the flyback voltage generated by the diode 112 (D1) and the diode (D2) 132 is applied to the electrode groups 120 and 140 as a high voltage pulse.
On the other hand, the high voltage may be generated without using the transformer including the primary coil (L1) 104 and the secondary coil (L2) 106. Further, the high voltage pulse may be generated by an element for switching without using the diode (D1) 112 and the diode (D2) 132.

In this embodiment, the high voltage pulse is not applied to the electrode group 120 and the electrode group 140 at the same time. However, when the exhaust gas amount is large, the high voltage is applied to both the electrode group 120 and the electrode group 140 at the same time. When the pulse is applied and the amount of exhaust gas is small, it is possible to perform the control of applying the high voltage pulse to only one of the electrode group 120 and the electrode group 140.

In this embodiment, two electrode groups 120 and 140 are electrically connected in parallel to form a plasma electrode, but three or more electrode groups are electrically connected in parallel to form a plasma electrode. You may comprise. Further, in the present embodiment, the plasma device of the present invention is used for the exhaust gas purifying device for purifying the exhaust gas of the vehicle, but the plasma device of the present invention can be used for the purifying device for purifying not only the exhaust gas but also gas contamination. Is.

[Brief description of drawings]

FIG. 1A is a sectional view of a plasma device according to an embodiment of the present invention taken along a plane orthogonal to an exhaust gas flow,
(B) is a BB line sectional view of (A).

FIG. 2 is a circuit diagram showing a pulse generation circuit of this embodiment.

FIG. 3 is a timing chart showing the operation of the pulse generation circuit.

[Explanation of symbols]

10 Plasma device 12 flow path member 20, 30 Positive electrode group 21, 22, 23, 31, 32, 33 Positive electrode 40 negative electrode group 41, 42, 43, 44, 45, 46 Cathode 100 pulse generation circuit 104 primary coil 106 secondary coil (resonance coil) 108 power switch 110, 130 resonant capacitors 112, 132 diode 114,134 pulse generation switch 120,140 electrode group

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H05H 1/24 F term (reference) 3G091 AA02 AB04 AB14 BA01 BA14 BA20 BA39 HA07 4D002 AA02 AA12 AC10 BA07 GA03 GB20 HA01 4G075 AA03 AA37 AA62 BA05 BD12 CA47 DA03

Claims (11)

[Claims] 1. A plasma device for purifying gas by discharge plasma, comprising: a flow path member for forming a flow path of gas; and a plurality of electrode groups installed in the flow path and electrically connected in parallel. A plasma electrode for generating a discharge plasma, a pulse generation circuit for generating a high voltage pulse applied to the plasma electrode, and an electrical connection between the pulse generation circuit and each electrode group installed for each electrode group. Pulse generation switch for intermittent connection
A plasma device comprising: 2. The pulse generation circuit constitutes a resonance circuit with a resonance coil, a resonance capacitor and a diode,
2. The plasma apparatus according to claim 1, wherein a flyback voltage generated when a reverse current flows through the diode after a forward current flows through the diode is a high voltage pulse. 3. The pulse generation circuit includes a primary coil that forms a transformer with the resonance coil, and a power switch that connects and disconnects a current flowing through the primary coil. Alternatively, the plasma device according to item 2. 4. A plasma device for purifying gas by discharge plasma, comprising: a flow path member for forming a flow path of gas; a plasma electrode installed in the flow path; and a high pressure applied to the plasma electrode. A pulse generating circuit for generating a voltage pulse, wherein the pulse generating circuit constitutes a resonant circuit with a resonant coil, a resonant capacitor and a diode, and a forward current flows through the diode, and then a reverse current flows through the diode. A plasma device characterized in that a flyback voltage generated when a current flows is a high voltage pulse. 5. The pulse generation circuit has a primary coil that forms a transformer with the resonance coil, and a power switch that connects and disconnects a current flowing through the primary coil. The plasma device described. 6. A plasma device for purifying gas by discharge plasma, comprising a flow path member for forming a flow path of gas, a plasma electrode installed in the flow path, and a high pressure applied to the plasma electrode. A pulse generating circuit that generates a voltage pulse; the pulse generating circuit includes a primary coil, a secondary coil that forms a transformer with the primary coil, and a power switch that interrupts a current flowing through the primary coil. The plasma device having the above-mentioned, and using the induced voltage generated in the secondary coil as a source pressure of a high-voltage pulse applied to the plasma electrode. 7. The plasma device according to claim 1, which is mounted on a vehicle and purifies exhaust gas of an internal combustion engine. 8. The plasma device control method according to claim 1, 2, or 3, wherein a high voltage pulse is applied to only one electrode group at a time among the plurality of electrode groups. Control method. 9. The high-voltage pulse is applied to the electrode group installed at a position where the flow velocity is higher in the flow path at a higher frequency than the electrode group installed at a position where the flow velocity is slow. 8. The method for controlling the plasma device according to item 8. 10. The plasma device control method according to claim 1, 2, or 3, wherein the number of electrode groups to which a high-voltage pulse is applied is increased or decreased according to the degree of gas contamination. Control method. 11. The method for controlling a plasma device according to claim 3, 5 or 6, wherein the power switch is turned on and off to generate an induced voltage in the secondary coil only when a high voltage pulse is generated. A method for controlling a plasma device, comprising: