JP2018018778A - Abnormal discharge detector of plasma reactor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an abnormal discharge detector which can detect abnormality of discharge, becoming the possible cause of discharge variation, upon occurrence thereof.SOLUTION: When voltage application to the primary coil of a flyback step-up transformer is stopped, energy accumulated in the primary coil is released, and a secondary voltage is generated in the secondary coil, and applied between the electrodes of a plasma reactor. When voltage application to the primary coil of the flyback step-up transformer is stopped, measurement of the lapsed time from that stoppage is started. Thereafter, first peak value of a reactor application current, flowing to the electrode of the plasma reactor, is acquired. When the time elapsed from stoppage of voltage application to the primary coil until acquisition of the peak value of a reactor application current is equal to or less than a prescribed value, a determination is made that discharge in the plasma reactor is abnormal.SELECTED DRAWING: Figure 5

Description

  The present invention relates to an apparatus for detecting a discharge abnormality in a plasma reactor.

  The exhaust gas discharged from an engine, particularly a diesel engine, includes CO (carbon monoxide), HC (hydrocarbon), NOx (nitrogen oxide), PM, and the like.

  As a technique for removing PM contained in exhaust gas, a technique for removing PM contained in exhaust gas using a plasma reactor has been proposed. The plasma reactor includes a plurality of electrode panels. The electrode panel has, for example, a configuration in which an electrode is built in a dielectric, and the plurality of electrode panels are arranged to face each other with a gap in a direction orthogonal to the flow direction of the exhaust gas. When a voltage is applied between the electrodes from the power supply device for the plasma reactor, dielectric barrier discharge occurs, low temperature plasma (non-equilibrium plasma) is generated between the electrode panels, and PM in the exhaust gas flowing between the electrode panels is oxidized. Is removed.

  The power supply device of the plasma reactor is provided with a flyback type step-up transformer. A switching element is connected in series to the primary coil of the flyback type step-up transformer, and a DC power source is connected to a series circuit of the primary coil and the switching element. The secondary coil of the flyback type step-up transformer is connected to the electrode of the plasma reactor.

  When the switching element is turned on, a current flows through the primary coil of the flyback type step-up transformer, and energy is stored in the primary coil. After that, when the switching element is turned off, the energy accumulated in the primary coil is released, an electromotive force is generated in the primary coil, and a secondary voltage corresponding to the turn ratio is generated in the secondary coil of the flyback step-up transformer. To do. By repeatedly turning on / off the switching element, a secondary voltage is generated in a pulsed manner, and a secondary voltage that changes in a pulse waveform is applied between the electrodes of the plasma reactor.

JP 2007-75778 A JP 2010-203401 A

  In the plasma reactor, when the reactor applied voltage (secondary voltage output from the plasma reactor power supply device) applied between the plasma reactor power supply device and the plasma reactor electrode reaches a certain discharge start voltage, Begin to discharge uniformly throughout.

  However, if PM or foreign matter adheres to the surface of the electrode panel and the interval between the electrode panels is locally narrowed, the interval between the electrode panels starts when the reactor applied voltage is lower than the normal discharge start voltage. Discharge starts at the narrowed area. When the voltage applied to the reactor rises to the normal discharge start voltage, discharge is performed between the electrode panels as a whole, but the discharge intensity is uneven (discharge variation) between the electrode panels. Since the discharge variation causes a decrease in PM removal performance (PM removal rate), it is desirable for the plasma reactor to detect a discharge abnormality that causes the discharge variation.

  An object of the present invention is to provide a discharge abnormality detecting device capable of detecting an abnormality when a discharge abnormality that causes discharge variation occurs.

  In order to achieve the above object, a discharge abnormality detection device for a plasma reactor according to the present invention is a discharge abnormality detection device for a plasma reactor that generates a discharge between electrodes by applying a secondary voltage of a flyback step-up transformer, After stopping the application of voltage to the primary coil of the flyback step-up transformer, obtain the peak timing to obtain the peak timing at which the current applied to the plasma reactor from the secondary coil of the flyback step-up transformer takes the first peak value Means, time measuring means for measuring the time from when the voltage application to the primary coil is stopped until the peak timing is acquired by the peak timing acquiring means, and when the time measured by the time measuring means is a predetermined time or less , An abnormality determining means for determining that the discharge in the plasma reactor is abnormal Including the.

  According to this configuration, when the application of the voltage to the primary coil of the flyback type step-up transformer is stopped, the energy accumulated in the primary coil is released, and a secondary voltage is generated in the secondary coil. A secondary voltage is applied between the electrodes of the plasma reactor.

  When the application of the voltage to the primary coil of the flyback type step-up transformer is stopped, measurement of the elapsed time from the stop is started. Thereafter, the peak timing at which the current applied to the plasma reactor from the secondary coil of the flyback type step-up transformer takes the first peak value is acquired. When the time elapsed from the stop of the voltage application to the primary coil until the peak timing is acquired is equal to or shorter than the predetermined time, it is determined that the discharge in the plasma reactor is abnormal.

  As a result of experiments by the inventors of the present application, when control is performed so that the peak value of the current matches the target peak value, the voltage to the primary coil is changed even if the temperature of the reactor or the density of gas flowing into the reactor changes. There is no change in the time difference from the stop of the application until the peak timing of the current applied to the reactor is obtained. However, when the discharge can be started from a time lower than the discharge start voltage at which the discharge between the electrodes starts uniformly, that is, when the discharge starts locally between the electrodes, the reactor starts from the stop of the voltage application to the primary coil. It has been found that the time until the peak timing of the current applied to is acquired is shortened.

  Therefore, when the time from the stop of the voltage application to the primary coil of the flyback step-up transformer to the peak timing at which the current applied to the plasma reactor takes a peak value is less than a predetermined time, the discharge in the plasma reactor Is determined to be abnormal, it is possible to detect the abnormality when a discharge abnormality that causes discharge variation, such as a local discharge between the electrodes, occurs.

  According to the present invention, when a discharge abnormality that causes discharge variation, such as a local discharge between electrodes of a plasma reactor, occurs, the abnormality can be detected. Therefore, it is possible to prevent the PM removal performance from being deteriorated due to discharge variation.

It is sectional drawing which shows the structure of a plasma reactor schematically. It is a circuit diagram which shows the structure of the power supply device for plasma reactors in which the discharge abnormality detection apparatus which concerns on one Embodiment of this invention is integrated. It is a circuit diagram which shows the structure of a current peak timing detection circuit. It is a flowchart which shows the flow of a discharge abnormality detection process. It is a figure which shows the outline of the time change of a reactor application voltage, a reactor application current, the inclination of a reactor application current, a current peak timing signal, and a timer count value.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

<Plasma reactor>
FIG. 1 is a cross-sectional view schematically showing the configuration of the plasma reactor 1.

  The plasma reactor 1 is interposed in the middle of an exhaust pipe 2 such as an exhaust pipe, for example, in order to remove PM from exhaust gas discharged from a vehicle engine (not shown). The plasma reactor 1 includes a case (body) 3 and a plurality of electrode panels 4 accommodated in the case 3.

  The case 3 is made of metal and is formed in a tubular shape (tubular shape). One opening of the case 3 is an inflow port through which exhaust gas flows in, and the other opening is an outflow port through which exhaust gas flows out. The exhaust gas discharged from the engine to the exhaust pipe 2 flows into the case 3 from the inlet while flowing through the exhaust pipe 2, flows through the case 3, and flows out from the outlet.

The electrode panel 4 has a configuration in which an electrode 6 is sandwiched between a flat dielectric plate 5 made of a dielectric in the thickness direction. Examples of the dielectric that is the material of the dielectric flat plate 5 include Al ₂ O ₃ (alumina). An example of the material of the electrode 6 is tungsten.

  The plurality of electrode panels 4 are arranged, for example, in parallel to each other at intervals in a direction orthogonal to the center line of the case 3 (each extending in the direction of the center line of the case 3). The electrodes 6 of each electrode panel 4 are disposed at the same position in a direction along a plane orthogonal to the stacking direction, and their peripheral edges are opposed to each other in the stacking direction (overlapping in the stacking direction).

  The positive wiring 7 and the negative wiring 8 are alternately connected to the electrode 6 of the electrode panel 4 in order from one side in the stacking direction of the electrode panel 4. The plus wiring 7 and the minus wiring 8 are electrically connected to the plus terminal and the minus terminal of the plasma reactor power supply device 9, respectively.

  Between the electrodes 6 of the electrode panels 4 adjacent to each other in the stacking direction, a pulse-wave-like high voltage output from the plasma reactor power supply device 9 is applied. When this high voltage is applied between the electrodes 6, a dielectric barrier discharge is generated between the electrode panels 4, and plasma is generated by the dielectric barrier discharge. On the other hand, between the electrode panels 4, exhaust gas flows from the end portion on the inlet side of the case 3, and the exhaust gas flows toward the end portion on the outlet side. Due to the generation of plasma between the electrode panels 4, PM contained in the exhaust gas flowing between the electrode panels 4 is oxidized (burned) and removed.

<Power supply for plasma reactor>
FIG. 2 is a circuit diagram showing a configuration of the plasma reactor power supply device 9.

  The plasma reactor power supply device 9 includes a flyback step-up transformer 11, an energization control MOSFET 12, a gate drive circuit 13, and a control device 14.

  The flyback step-up transformer 11 has a primary coil 21 and a secondary coil 22. One end of the primary coil 21 is connected to the wiring 23. The other end of the primary coil 21 is connected (grounded) to the ground via the conduction control MOSFET 12. One end and the other end of the secondary coil 22 are connected to electrodes 6 of the electrode panel 4 adjacent to each other in the stacking direction in the plasma reactor 1 via a plus terminal and a minus terminal, respectively.

  The conduction control MOSFET 12 is, for example, an enhancement type nMOSFET, and its drain is connected to the other end of the primary coil 21 of the flyback step-up transformer 11 and its source is connected to the ground.

  A positive terminal of a battery 25 that is a DC power source is connected to the wiring 23 via a fuse 24. The battery 25 is, for example, a lead battery having a nominal voltage of 12V.

  The gate drive circuit 13 is a circuit that applies a pulse voltage (gate voltage) to the gate of the conduction control MOSFET 12.

  The control device 14 includes a CPU, a memory, and the like, and may be one of a plurality of ECUs (Electronic Control Units) mounted on the vehicle or may be incorporated in one of the ECUs. It may be. The memory includes, for example, a rewritable nonvolatile memory such as a flash memory in addition to a ROM and a RAM.

  The control device 14 controls the gate drive circuit 13 to switch output / stop of the pulse voltage (gate voltage) from the gate drive circuit 13. When an ON instruction signal is input from the control device 14 to the gate drive circuit 13, the pulse voltage output from the gate drive circuit 13 rises, and the pulse voltage is applied to the gate of the conduction control MOSFET 12, thereby controlling energization. MOSFET 12 is turned on. When an off instruction signal is input from the control device 14 to the gate drive circuit 13, the pulse voltage output from the gate drive circuit 13 falls and the pulse voltage is not applied to the gate of the MOSFET 12 for energization control. The control MOSFET 12 is turned off.

  When the energization control MOSFET 12 is turned on, the voltage of the battery 25 is applied to the primary coil 21 of the flyback step-up transformer 11 as the primary voltage, and energy is accumulated in the primary coil 21. Thereafter, when the energization control MOSFET 12 is turned off, the energy accumulated in the primary coil 21 is released, an electromotive force is generated in the primary coil 21, and the secondary coil 22 of the flyback step-up transformer 11 is in accordance with the turn ratio. A secondary voltage is generated. By repeatedly turning on / off the power supply control MOSFET 12, a secondary voltage is generated in a pulsed manner, and a secondary voltage that changes in a pulse waveform is applied between the electrodes 6 of the plasma reactor 1.

  A current sensor 31 is connected to the control device 14. The current sensor 31 detects a reactor applied current applied to the plasma reactor 1 from the plasma reactor power supply device 9, and outputs a detection signal corresponding to the current value.

  The control device 14 acquires the first peak value (hereinafter simply referred to as “first peak value”) after the rise of the reactor applied current applied to the plasma reactor 1 from the detection signal output from the current sensor 31. On the other hand, the control device 14 acquires the air-fuel ratio of the exhaust gas discharged from the engine (not shown), and obtains the PM amount contained in the unit volume of the exhaust gas from the air-fuel ratio. A non-volatile memory (ROM, flash memory, EEPROM, or the like) of the control device 14 stores the relationship between the PM amount and the target peak value in the form of a two-dimensional map. The control device 14 sets a target peak value corresponding to the PM amount based on the relationship between the PM amount and the target peak value, and gate drive so that the first peak value of the reactor applied current matches the target peak value. The circuit 13 is controlled.

<Current peak timing detection circuit>
FIG. 3 is a circuit diagram showing a configuration of the current peak timing detection circuit 41.

  The current peak timing detection circuit 41 is an analog circuit for detecting the timing at which the plasma application current applied to the plasma reactor 1 first takes a peak value. The current peak timing detection circuit 41 includes a differentiation circuit 42, an inverting amplification circuit 43, and a Schmitt circuit (hysteresis comparator) 44.

  A detection signal (voltage) of the current sensor 31 is input to the differentiation circuit 42, and a voltage proportional to the time differentiation (slope) of the input voltage is output from the differentiation circuit 42.

  The output voltage of the differentiation circuit 42 is input to the inverting amplifier circuit 43, and the input voltage is inverted and amplified and output from the inverting amplifier circuit 43.

  The Schmitt circuit 44 is supplied with the output voltage of the inverting amplifier circuit 43. When the input voltage exceeds a predetermined reference voltage, a high level voltage is output from the Schmitt circuit 44. When the high-level voltage is output from the Schmitt circuit 44, the high-level voltage continues to be output until the voltage input to the Schmitt circuit 44 drops to zero. When the voltage input to the Schmitt circuit 44 drops to 0, a low level voltage is output from the Schmitt circuit 44.

<Discharge abnormality detection processing>
FIG. 4 is a flowchart showing the flow of the discharge abnormality detection process. FIG. 5 is a diagram showing an outline of the time variation of the reactor applied voltage, the reactor applied current, the slope of the reactor applied current, the current peak timing signal, and the timer count value.

  During the operation of the plasma reactor 1, the control device 14 detects one pulse of a voltage (pulse applied voltage) that changes in a pulse waveform in the primary coil 21 of the flyback type step-up transformer 11 in order to detect an abnormality in the discharge in the plasma reactor 1. Each time it is input, the discharge abnormality detection process shown in FIG. 4 is executed.

  In the discharge abnormality detection process, the falling edge of the pulse application voltage is detected (step S1). Since the falling edge of the pulse application voltage substantially coincides with the falling edge of the pulse voltage (gate voltage) applied to the gate of the MOSFET 12 for energization control, the pulse is replaced with the detection of the falling edge of the pulse application voltage. A falling edge of the voltage (gate voltage) may be detected.

  When the falling edge of the pulse application voltage is detected (YES in step S1). The timer counter provided in the control device 14 starts counting up (step S2).

  When the pulse application voltage falls, that is, when the application of the voltage to the primary coil 21 of the flyback type step-up transformer 11 is stopped, a secondary voltage is generated in the secondary coil 22, and between the electrodes 6 of the plasma reactor 1. A reactor applied voltage is applied, and a current (reactor applied current) flows through the electrode 6. When the value of the current flowing through the electrode 6 rises and the voltage input to the Schmitt circuit 44 of the current peak timing detection circuit 41, that is, the voltage proportional to the slope (differential value) of the reactor applied current exceeds the reference voltage, the current peak The voltage output from the Schmitt circuit 44 as the timing signal is switched from the low level to the high level. Thereafter, when the reactor applied current takes a peak value and the slope of the reactor applied current becomes zero, the current peak timing signal falls from the high level to the low level.

  The timer counter continues to count up until the falling edge of the current peak timing signal is detected (step S2). When the falling edge of the current peak timing signal is detected (YES in step S3), the count value (timer count value) of the timer counter is acquired (step S4).

  Then, it is determined whether or not the acquired timer count value is equal to or smaller than a predetermined determination value (step S5).

  When PM or foreign matter adheres to the surface of the electrode panel 4 of the plasma reactor 1 and the interval between the electrode panels 4 is locally narrowed, the electrode is applied from when the reactor applied voltage is lower than the normal discharge start voltage. The discharge starts at a portion where the interval between the panels 4 is narrow, and the falling edge of the current peak timing signal is detected earlier than in the normal state where the discharge between the electrode panels 4 starts uniformly.

  When the discharge in the plasma reactor 1 starts at a normal timing, the determination value is such that the timer count value exceeds the determination value, and when the discharge starts at an abnormally early timing, the timer count value is equal to or less than the determination value. Is set.

  When the timer count value at the time of detecting the falling edge of the current peak timing signal is equal to or smaller than the determination value (YES in step S5), it is determined that the discharge in the plasma reactor 1 is abnormal (step S6).

  When the timer count value at the time of detecting the falling edge of the current peak timing signal exceeds the determination value (NO in step S5), it is determined that the discharge in the plasma reactor 1 is normal (skip in step S6).

  When it is determined whether the discharge in the plasma reactor 1 is normal or abnormal, the count value of the timer counter is reset to 0 (step S7), and the discharge abnormality detection process is terminated.

<Effect>
As described above, the timer counter starts counting up from the stop of the application of voltage to the primary coil 21 of the flyback type step-up transformer 11. When the reactor applied current takes the first peak value, the count-up of the timer counter is stopped, and it is determined whether or not the count value of the timer counter is equal to or smaller than a predetermined determination value. When the count value of the timer counter is equal to or smaller than the determination value, it is determined that the discharge in the plasma reactor 1 is abnormal. Thereby, when the abnormality of discharge which causes discharge variation, such as local discharge between electrode panels 4, has occurred, the abnormality can be detected. Therefore, it is possible to prevent the PM removal performance from being deteriorated due to discharge variations in the plasma reactor 1.

<Modification>
As mentioned above, although one Embodiment of this invention was described, this invention can also be implemented with another form.

  For example, instead of the energization control MOSFET 12, another switching element such as an IGBT may be employed.

  In the above-described embodiment, the configuration in which the counter value of the timer counter is used for abnormality determination is taken up. However, for example, an analog voltage that increases at a constant rate as time elapses may be used for abnormality determination.

  In addition, various design changes can be made to the above-described configuration within the scope of the matters described in the claims.

1: Plasma reactor 6: Electrode 11: Flyback type step-up transformer 14: Control device (discharge abnormality detection device, time measuring means, abnormality determination means)
21: Primary coil 41: Current peak timing detection circuit (peak timing acquisition means)

Claims (1)

A discharge abnormality detection device for a plasma reactor that generates a discharge between electrodes by applying a secondary voltage of a flyback step-up transformer,
After stopping the application of voltage to the primary coil of the flyback type step-up transformer, the peak timing at which the current applied to the plasma reactor takes the first peak value from the secondary coil of the flyback type step-up transformer is acquired. Peak timing acquisition means;
Time measuring means for measuring the time from when the application of the voltage to the primary coil is stopped until the peak timing is acquired by the peak timing acquiring means;
A discharge abnormality detection device comprising: an abnormality determination unit that determines that the discharge in the plasma reactor is abnormal when the time measured by the time measuring unit is equal to or shorter than a predetermined time.

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