JP4543754B2 - Power supply method for discharge reactor - Google Patents

Description

  The present invention relates to a power supply control method for a discharge reactor, particularly a discharge reactor for purifying exhaust gas from an internal combustion engine or the like.

At present, various purification systems using discharge have been proposed for exhaust gas purification of automobiles, exhaust gas purification of garbage incineration plants, generation of ozone for sterilization and deodorization, and the like. Particularly in the field of automobile exhaust gas purification, it is known to use discharge in combination with an exhaust gas purification catalyst to purify NO _x , CO (carbon monoxide), HC (hydrocarbon components) and PM (particulates). ing.

  When a discharge reactor is used in a moving medium such as an automobile, the performance of the discharge reactor itself is also important, but how to control the power supply is important from the viewpoint of reliability and energy efficiency. . Therefore, conventionally, various modes and power supply circuits for supplying power to the discharge reactor have been proposed.

  For example, in Patent Document 1, low voltage power for control and high voltage power for a discharge (plasma) reactor are respectively generated by an engine as a power source for vehicle travel. When such a pulsed power supply is used in combination with a discharge reactor for purifying automobile exhaust gas, as shown in Patent Document 1, power supply is intermittently turned on and off according to the exhaust gas purification catalyst and / or the engine warm-up state. And / or to regulate.

Further, for example, Patent Documents 2 and 3 show discharge reactors for purifying exhaust gas from a stationary combustion device such as a private power generation device. In particular, in Patent Document 2, the presence / absence, magnitude, frequency, etc. of the voltage applied to the discharge reactor are determined based on the NO _x concentration, CO / HC concentration and O ₂ concentration in the exhaust gas, exhaust gas flow rate, exhaust gas temperature, etc. (Paragraph 0016).

Japanese Patent Laid-Open No. 7-253014 JP 7-139338 A JP-A-9-299762

When a conventionally known pulse power source is used in combination with a discharge reactor for exhaust gas purification, for example, as shown in Patent Documents 1 and 2, the exhaust gas purification catalyst and the engine are warmed up, the NO _x concentration in the exhaust gas, CO It is known to determine the presence / absence, magnitude, frequency, etc. of voltage applied to the discharge reactor based on HC concentration and O ₂ concentration, exhaust gas flow rate, exhaust gas temperature, and the like.

  As described above, adjusting the voltage applied to the discharge reactor according to the state of the exhaust gas or the like is preferable in order to favorably perform exhaust gas purification by discharge. However, in these methods, the state in the discharge reactor is not detected, and therefore, it may not be possible to perform optimum applied voltage control according to the deterioration of the discharge reactor and the power source and the change in exhaust gas conditions.

  Accordingly, the present invention provides a method for controlling a power source for a discharge reactor that can appropriately apply a voltage according to the state of the discharge reactor, particularly the discharge state in the discharge reactor.

  The control method of the power source for the discharge reactor according to the present invention calculates the impedance of the discharge reactor from the voltage applied to the discharge reactor and the current flowing through the discharge reactor, and applies the impedance to the discharge reactor so that the impedance falls within a predetermined range. The voltage to be applied, for example, the voltage magnitude, the pulse width, and the pulse frequency are changed.

  The impedance of the discharge reactor can represent the state of the reactor, particularly the discharge state within the reactor. Therefore, by changing the voltage applied to the discharge reactor so that this impedance becomes a predetermined impedance, the discharge in the discharge reactor can be optimized according to the deterioration of the discharge reactor and the power source, the change of exhaust gas conditions, and the like.

  In one aspect of the method of the present invention, when the magnitude of the calculated impedance is smaller than a predetermined value, the calculated magnitude of the impedance is higher than the predetermined value at a frequency higher than the predetermined frequency. When the voltage decreases, the voltage applied to the discharge reactor is decreased.

  When the discharge in the discharge reactor shifts from corona discharge to spark discharge or arc discharge, the impedance value of the discharge reactor decreases. Therefore, if the impedance value indicating the occurrence of spark discharge or arc discharge is determined in advance, and the voltage applied to the discharge reactor is reduced when the impedance of the discharge reactor becomes smaller than this value, the occurrence of spark discharge or arc discharge will occur. Can suppress the deterioration of the discharge reactor. When the exhaust gas temperature is low, for example, 100 ° C. or lower, the moisture in the exhaust gas aggregates to become water and adheres to the reactor, which may promote the generation of this spark discharge or arc discharge. In addition, if an allowable frequency or period of impedance reduction is set, more appropriate control may be achieved.

  However, the decrease in impedance can also occur when the voltage applied to the discharge reactor is small and the phase of the impedance is thereby delayed. Therefore, it may be preferable to combine the control method of this aspect with other control methods as needed.

  In another aspect of the present invention, the voltage applied to the discharge reactor is increased when the calculated impedance phase is delayed from a predetermined phase. In still another aspect of the present invention, the voltage applied to the discharge reactor is reduced when the calculated impedance phase is ahead of a predetermined phase. In addition, by combining these aspects, when the calculated impedance phase is delayed from the first predetermined phase, the voltage applied to the discharge reactor is increased, and the calculated impedance phase is The voltage applied to the discharge reactor can be reduced when the phase is ahead of the predetermined phase of 2.

  When the voltage applied to the discharge reactor is large, the impedance phase is advanced, and when the voltage applied to the discharge reactor is small, the impedance phase is delayed. Therefore, a predetermined impedance phase or phase range is set as an impedance phase corresponding to a desired discharge state in the discharge reactor, and the voltage applied to the discharge reactor so that the calculated impedance phase falls within the predetermined phase range. By adjusting the voltage, it is possible to apply an appropriate voltage to the discharge reactor, and to suppress a decrease in efficiency and / or deterioration of the discharge reactor.

  In the following, the present invention will be described in detail based on the embodiments shown in the drawings. However, these drawings are diagrams showing an outline of an apparatus that can be used for the control method of the present invention. The form is not limited.

  An apparatus that can be used in the control method of the present invention will be described with reference to FIG.

  As shown in FIG. 1, a device 10 that can be used for the control method of the present invention surrounded by a two-dot broken line includes a voltage measuring unit 14 that measures a voltage applied to the discharge reactor R, a discharge reactor. A current measuring unit 16 that measures a current flowing through R and a control unit 18 that controls the high-voltage power supply 12 are provided. Here, the voltage measurement unit 14 and the control unit 18 are connected by a signal line 15, the current measurement unit 16 and the control unit 18 are connected by a signal line 17, and the control unit 18 and the control unit 18 are connected to a high voltage. The power supply 12 is connected by a signal line 19. The control means 18 calculates the impedance of the discharge reactor R from the measured values at the voltage measuring unit 14 and the current measuring unit 16, and based on this, particularly based on the magnitude and / or phase of the impedance, The high voltage power supply 12 is controlled so that an appropriate voltage is applied.

  The impedance of the discharge reactor can be calculated by detecting the voltage and current applied to the discharge reactor R over a period determined by the gate signal and dividing the voltage value by the current value.

Control Based on the Impedance of the Discharge Reactor When the device 10 shown in FIG. 1 is used to reduce the voltage applied to the discharge reactor when the calculated impedance falls below a predetermined value, the flowchart of FIG. Can be performed as shown in FIG.

  Here, first, an initial value of a voltage to be applied to the discharge reactor R is determined (S101), and this voltage is applied to the discharge reactor (S103). In determining the initial voltage, the exhaust gas flow rate, the temperature in the exhaust pipe, the humidity, and the like can be referred to. Further, when the exhaust gas temperature is equal to or higher than a certain temperature, it is also possible to apply no voltage because exhaust gas purification can be achieved without discharge. On the other hand, when the exhaust gas temperature is below a certain temperature, for example, 100 ° C. or less, the moisture in the exhaust gas aggregates into water, causing arc discharge, which can easily deteriorate the reactor, and no voltage can be applied. .

  Next, the voltage measurement unit 14 and the current measurement unit 16 measure the voltage applied to the discharge reactor R and the current flowing through the discharge reactor R, and calculate the impedance of the discharge reactor R based on these values (S105).

  The magnitude of the impedance obtained in step S105 is observed, and it is determined whether this value suggests the occurrence of spark discharge or arc discharge instead of corona discharge (S107). In determining the discharge state based on the magnitude of this impedance, the magnitude of the impedance corresponding to the spark discharge or arc discharge is set, and when the calculated impedance becomes smaller than this, the spark discharge or arc is set. It can be determined that a discharge has occurred. In setting the magnitude of impedance corresponding to spark discharge or arc discharge, the saturated water vapor amount, exhaust gas temperature, and exhaust gas flow rate in the exhaust gas can be taken into consideration. Note that the impedance of the discharge reactor decreases when the discharge shifts from corona discharge to spark discharge or arc discharge.

  If it is determined in step S107 that spark discharge or arc discharge is occurring in the discharge reactor R, it is further determined whether or not the spark discharge or arc discharge is within an allowable range (S109). When the spark discharge or arc discharge is within the allowable range, the voltage application to the discharge reactor is continued (S103). Further, when the spark discharge or arc discharge exceeds the allowable range, the voltage applied to the discharge reactor is lowered to prevent the spark discharge or arc discharge and suppress the deterioration of the discharge reactor (S111), and then decrease. The applied voltage is applied to the discharge reactor (S103).

Control Based on Impedance Phase of Discharge Reactor Using the apparatus 10 shown in FIG. 1, when the measured impedance phase is behind the first predetermined phase, the voltage applied to the discharge reactor is increased, In addition, when the impedance phase is ahead of the second predetermined phase, the voltage applied to the discharge reactor can be reduced as shown in the flowchart of FIG.

  Here, first, an initial value of a voltage to be applied to the discharge reactor R is determined (S201), and this voltage is applied (S203). This determination of the initial voltage can be performed as shown with respect to step S101 in the flowchart of FIG.

  Next, the voltage measurement unit 14 and the current measurement unit 16 measure the voltage applied to the discharge reactor R and the current flowing through the discharge reactor R, and calculate the impedance of the discharge reactor R based on these values (S205).

  The phase of the impedance obtained in step S205 is observed, and it is checked whether this phase is within a predetermined phase range, that is, between the first predetermined phase and the second predetermined phase (S207). This impedance phase can be set as a phase corresponding to an appropriate voltage application in the discharge reactor.

  When the calculated impedance phase is within the predetermined phase range, it is determined that appropriate discharge is being performed in the discharge reactor, and voltage application to the discharge reactor is continued (S203). If the impedance phase is behind the first predetermined phase, it is determined that the voltage applied to the discharge reactor is insufficient, and the voltage applied to the discharge reactor is increased (S209). The applied voltage is applied to the discharge reactor (S203). If the impedance phase is further advanced than the second predetermined phase, it is determined that the voltage applied to the discharge reactor is excessive, and the voltage applied to the discharge reactor is decreased (S211) and decreased. The applied voltage is applied to the discharge reactor (S203).

  Below, each part which comprises the apparatus shown in FIG. 1 is demonstrated more concretely.

  An arbitrary voltmeter can be used as the voltage measuring unit 14, but it must be capable of measuring a high voltage applied to the discharge reactor, for example, a voltage of several kV to 50 kV. In addition, an arbitrary ammeter can be used as the current measuring unit 16, but it is preferable that the current measuring unit 16 can cope with an instantaneous change in the current value.

  The control means 18 may be an electronic device only for controlling the high-voltage power supply 12, or may have other functions like an ECU (electronic control unit) in the case of an automobile.

  The high voltage power supply 12 may generate a pulsed or steady DC or AC voltage. As the applied voltage and the pulse period, general values can be used for generating discharge. For example, a pulse voltage of 1 kV to 50 kV and a pulse period of 10 Hz to 2,000 Hz can be used. A DC voltage, an AC voltage, a periodic waveform voltage, or the like can be applied between both electrodes, and a DC pulse voltage is particularly preferable because corona discharge can be caused satisfactorily. When a DC pulse voltage is used, the applied voltage, pulse width, and pulse period can be arbitrarily selected as long as corona discharge can occur between both electrodes. The voltage of the applied voltage may be subject to certain restrictions due to device design, economy, etc., but a high voltage and a short pulse period voltage are desirable from the viewpoint of generating corona discharge satisfactorily. .

  The discharge reactor R may be any discharge reactor, and examples thereof include a discharge reactor for treating exhaust gas from a waste treatment plant and exhaust gas from an internal combustion engine such as an automobile engine. This may be as shown in the attached FIG. Here, FIGS. 4A and 4B are a perspective view and a sectional view of the discharge reactor, respectively.

  In the discharge reactor 60 shown in FIG. 4, a discharge space 66 exists between the mesh electrodes 62 and 64 connected to the high voltage power supply 12, and fluid to be processed in the discharge reactor passes through the discharge space 66. It is supposed to be distributed.

  Here, the mesh electrodes 62 and 64 can be made of any material capable of applying a voltage between these electrodes. As the material, a conductive material or a material such as a semiconductor can be used, but a metal material is preferable. Specifically, copper, tungsten, stainless steel, iron, platinum, aluminum or the like can be used as the metal material, and stainless steel is particularly preferable from the viewpoint of cost and durability.

An insulating carrier such as a ceramic honeycomb carrier is disposed in the discharge space 66 between the mesh electrodes 62 and 64, and an exhaust gas purification catalyst such as a so-called three-way catalyst, a NO _x storage reduction catalyst, An oxidation catalyst can be supported. Further, instead of or in addition to arranging the exhaust gas purification catalyst in the discharge reactor, the exhaust gas purification catalyst can be arranged in the discharge reactor on the upstream side of the exhaust gas flow and / or on the downstream side of the exhaust gas flow.

  The discharge reactor R may be as shown in FIG. Here, FIGS. 5A and 5B are a perspective view and a sectional view of the discharge reactor, respectively. The discharge reactor 70 shown in FIG. 5 includes a cylindrical outer peripheral electrode 72 around the discharge space 76, instead of applying a voltage between the mesh electrodes 62 and 64 at both ends of the discharge space 66 in the discharge reactor of FIG. 4 is the same as the discharge reactor of FIG. 4 except that a voltage is applied between the cylindrical outer peripheral electrode 72 and the central electrode 74 disposed at the center.

FIG. 1 is a circuit diagram showing one embodiment of an apparatus for carrying out the control method of the present invention. FIG. 2 is a flowchart of one of the control methods of the present invention. FIG. 3 is another flowchart of the control method of the present invention. FIG. 4 is a perspective view and a cross-sectional view showing one embodiment of a discharge reactor that can control power feeding by the limiting method of the present invention. FIG. 5 is a perspective view and a cross-sectional view showing another embodiment of a discharge reactor in which power feeding can be controlled by the discharge reactor power supply circuit of the present invention.

Explanation of symbols

R ... discharge reactor 10 ... device 12 used in the method of the present invention ... high voltage power supply 14 ... voltage measuring unit 16 ... current measuring unit 18 ... control means 60, 70 ... discharge reactors 62, 64 ... mesh electrodes 66, 76 ... Discharge space 72 ... Cylindrical outer peripheral electrode 74 ... Center electrode

Claims (6)

From the voltage applied to the discharge reactor for purifying exhaust gas and the current flowing through the discharge reactor, the impedance of the discharge reactor is calculated, and the voltage applied to the discharge reactor is set so that the impedance falls within a predetermined range. A method for controlling a power source for a discharge reactor , wherein the voltage to be changed and applied to the discharge reactor is a pulsed DC voltage or an AC voltage . The control method of the power supply for discharge reactors of Claim 1 which changes the voltage applied to the said discharge reactor so that the impedance of the said discharge reactor may become a predetermined range based on the magnitude | size and phase of the said impedance. The control method according to claim 1 or 2 , wherein the voltage applied to the discharge reactor is reduced when the calculated magnitude of the impedance becomes smaller than a predetermined value. The control method according to claim 1 , wherein the voltage applied to the discharge reactor is increased when the calculated phase of the impedance is delayed from a predetermined phase. The control method according to claim 1 , wherein the voltage applied to the discharge reactor is reduced when the calculated phase of the impedance is ahead of a predetermined phase. The control method according to claim 1, wherein no voltage is applied when the temperature of the exhaust gas to be purified is equal to or lower than a certain temperature.

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