JP2020082043A - Electrostatic precipitator - Google Patents

Abstract

To provide an electrostatic precipitator capable of suppressing wasteful power consumption while suppressing deterioration of dust collection performance even when corona discharge is generated in a dust collection section.SOLUTION: An electrostatic precipitator includes: a charging section; a dust collection section; a power supply section; and a control section. The charging section electrically charges dust. The dust collection section has a plurality of dust collecting electrodes and a plurality of high voltage electrodes formed of a semi-insulating resin, which are alternately arranged, and collects dust charged in the charging section. The power supply section applies voltage to the high voltage electrodes. The control section determines the presence or absence of generation of corona discharge in the dust collection section. When determining the generation of corona discharge, the control section detects discharge start applied voltage in which corona discharge is started and causes the power supply section to apply voltage smaller than the detected discharge start applied voltage to the high voltage electrodes.SELECTED DRAWING: Figure 7

Description

The present invention relates to an electrostatic precipitator.

Conventionally, as an electrostatic precipitator that removes dust from sucked air, a charging unit that charges dust by corona discharge and multiple ground electrodes (dust collecting electrodes) and multiple high-voltage electrodes formed of semi-insulating resin alternate. An electrostatic precipitator having a dust collecting section arranged in the above and collecting the dust charged by the charging section by the dust collecting section is known (for example, refer to Patent Document 1).

When the high-voltage electrode is formed of a semi-insulating resin as in the electrostatic precipitator disclosed in Patent Document 1, the high-voltage electrode has a larger volume resistance value than that formed of a metal, so that the discharge is difficult. It is possible to prevent the occurrence of spark discharge that requires a large current.

JP-A-8-71451

However, even if the spark discharge can be prevented from occurring between the dust collecting electrode of the dust collecting portion and the high voltage electrode, it is not possible to prevent the corona discharge which is generated even with a minute current. When corona discharge occurs in the dust collector, the operation as an electrostatic precipitator can be continued, but the power consumed by the discharge from the high-voltage electrode is wasted, and a voltage drop occurs due to the discharge, and the electric field strength in the dust collector is reduced. It may weaken and the dust collection performance may deteriorate. As described above, unlike the charging section in which the corona discharge is intentionally generated in order to charge the dust, the generation of the corona discharge in the dust collecting section wastes electric power and lowers the dust collecting performance.

The disclosed technology is made in view of the above, and provides an electric dust collector that can suppress unnecessary power consumption while suppressing deterioration of dust collecting performance even when corona discharge occurs in the dust collecting portion. The purpose is to do.

One aspect of the electrostatic precipitator disclosed in the present application includes a charging unit, a dust collecting unit, a power supply unit, and a control unit. The charging unit charges the dust. The dust collecting portion has a plurality of dust collecting electrodes and a plurality of high voltage electrodes formed of semi-insulating resin alternately arranged, and collects the dust charged by the charging portion. The power supply unit applies a voltage to the high voltage electrode. The control unit determines whether or not corona discharge has occurred in the dust collecting unit, and when determining that corona discharge has occurred in the dust collecting unit, detects a discharge start applied voltage at which the corona discharge is started, and The control is performed so that a voltage lower than the detected discharge start applied voltage is applied to the high voltage electrode.

According to one aspect of the electrostatic precipitator disclosed in the present application, wasteful power consumption can be suppressed while suppressing deterioration of the dust collecting performance even if corona discharge occurs in the dust collecting portion.

FIG. 1 is a schematic configuration diagram of an air cleaner including the electric dust collector of the embodiment. FIG. 2A is a block diagram of an air cleaner including the electrostatic precipitator of the embodiment. FIG. 2B is an explanatory diagram of the dust collecting unit output control unit shown in FIG. 2A. FIG. 3 is a schematic view showing a dust collecting portion of the electric dust collector of the embodiment. FIG. 4 is a graph showing the change characteristics of the discharge current corresponding to the voltage applied to the high voltage electrode of the dust collector of the electrostatic precipitator. FIG. 5 is a graph showing the change characteristics of the electric field strength corresponding to the voltage applied to the high-voltage electrode of the dust collector of the electrostatic precipitator. FIG. 6 is a graph showing the relationship between the current corresponding to the voltage applied to the high voltage electrode of the dust collector of the electrostatic precipitator and the potential beyond the discharge point. FIG. 7 is an explanatory diagram showing a flow of processing of discharge suppression applied voltage control performed by the control unit of the electrostatic precipitator in the embodiment. FIG. 8: is explanatory drawing which shows the equivalent circuit of the dust collection part of the electrostatic precipitator of an Example.

Hereinafter, embodiments of the electrostatic precipitator disclosed in the present application will be described in detail with reference to the drawings. The structure and control method of the electrostatic precipitator disclosed in the present application are not limited by the following embodiments. Further, the constituent elements according to the following description include those that can be easily replaced by those skilled in the art, or those that are substantially the same, that is, those in the so-called equivalent range.

First, an outline of an air cleaner including the electric dust collector of the embodiment will be described. FIG. 1 is a schematic configuration diagram of an air cleaner including the electric dust collector of the embodiment. As shown in FIG. 1, the air cleaner 1 according to the embodiment includes a housing 10 that houses devices for cleaning the air. The housing 10 is formed of a synthetic resin material into a substantially rectangular parallelepiped shape, and has an inlet 11 for sucking air in the room and an outlet 12 for blowing the cleaned air into the room.

In the housing 10, there are provided a prefilter 14 for removing large dust from the sucked air, a plurality of electric dust collectors 2 for collecting dust in the air passing through the prefilter 14 by electrostatic force, and an electric dust collector 2. A deodorizing filter 5 that deodorizes the passing air is provided. The electrostatic precipitator 2 includes a charging unit 3 and a dust collecting unit 4 described in detail later. In addition, in the present embodiment, the three electrostatic precipitators 2 are arranged in the housing 10 in the housing 10, but the number of the electrostatic precipitators 2 arranged is not limited at all.

The pre-filter 14 has a mesh structure in which, for example, a thread-shaped PET material is woven, and is held by a resin frame (not shown). The pre-filter 14 collects relatively large dust contained in the air sucked into the housing 10. The deodorizing filter 5 performs a deodorizing process for removing odorous components such as ammonia and methyl mercaptan and harmful components such as formaldehyde from the air from which dust has been removed by the prefilter 14 and the electrostatic precipitator 2, by using a catalyst filter.

Further, in the housing 10, a fan 6 arranged on the downstream side of the deodorizing filter 5, a fan motor 61 for rotating the fan 6, and a power supply functioning as a control unit 7 for controlling the electrostatic precipitator 2 and the fan motor 61. A control board is provided.

Further, in the housing 10, a dust sensor 13 that detects the dust concentration of air sucked from the suction port 11 and an operation display board 15 that performs operation start operation, operation stop operation, and the like are provided.

In the present embodiment, the housing 10 is provided with a single constant-voltage high-voltage power supply unit 40 for supplying dust to each dust collecting unit 4 of each electrostatic dust collector 2. The constant-current high-voltage power supply unit 30 for the charging unit that supplies electric power to the charging unit 3 is arranged in each of the three charging units 3.

Thus, the indoor air sucked from the suction port 11 is dedusted by the dust in the air being collected by the prefilter 14 and the electrostatic precipitator 2 as shown by the arrow f, and the deodorizing filter 5 The deodorized clean air is blown out into the room through the air outlet 12.

Here, the dust collecting action of the electrostatic precipitator 2 will be briefly described. A preset positive high voltage (for example, +4.5 kV) is applied to a plurality of discharge electrodes (not shown) included in the charging unit 3 of the electrostatic precipitator 2, and a plurality of counter electrodes (not shown) are supplied with a constant current and high voltage. It is connected to the ground electrode (ground) of the power supply unit 30. By doing so, corona discharge occurs between the discharge electrode and the counter electrode. The plurality of discharge electrodes and the plurality of counter electrodes have different polarities and are alternately arranged in a state of being held by a frame portion (not shown). Here, the different polarities mean a combination of two polarities among three polarities of positive polarity, negative polarity, and nonpolarity (earth).

When corona discharge occurs between the discharge electrode and the counter electrode, the space between the discharge electrode and the counter electrode is filled with air containing positively charged ions. Then, when the dust passes through the space filled with positive ions, depending on the passing time and the strength of the electric field created by the discharge electrode and the counter electrode, the movement of charges due to the collision of the ions and the dust occurs, The dust is charged with a positive charge.

On the other hand, in the dust collecting part 4, a preset high positive voltage (for example, +4.5 kV) is applied to the plurality of high voltage electrodes 42 (see FIG. 3) forming the high voltage side electrode part. On the other hand, the plurality of ground electrodes 43 (see FIG. 3) forming the electrode part on the dust collecting side are connected to the ground electrode (earth) of the constant voltage high voltage power supply part 40. By doing so, a predetermined electrostatic field is formed between both electrodes.

In FIG. 1, when the dust positively charged by the charging unit 3 moves to the dust collecting unit 4, it receives a repulsive force from the high-voltage electrode 42 in the high-voltage side electrode unit having the same polarity. Then, the dust reaches the ground electrode 43 by receiving an attractive force in the direction of being attracted by the ground electrode 43 having a polarity opposite to that of the dust. In this way, dust is collected by the dust adhering to the ground electrode 43. Further, when the positively charged dust touches the ground electrode 43, the positively charged dust is flown to the ground. Therefore, it is possible to prevent the ground electrode 43 from being charged to the positive electrode due to the adhesion of the charged dust, and to suppress the decrease in the collection force.

Next, the function of the air cleaner 1 including the electrostatic precipitator 2 of the embodiment will be mainly described with reference to FIGS. 2A and 2B. FIG. 2A is a block diagram of an air cleaner 1 including the electric dust collector 2 of the embodiment, and FIG. 2B is an explanatory diagram of a dust collector output control unit shown in FIG. 2A.

As shown in FIG. 2A, the air purifier 1 includes, in addition to the electric dust collector 2 and the fan 6 and the fan motor 61 according to the present embodiment, an AC input processing unit 8, an AD converter 9, a control unit 7, a constant current high voltage power supply unit. 30 and a constant-voltage high-voltage power supply unit 40.

As described above, the electric dust collector 2 according to the present embodiment includes the charging unit 3 and the dust collecting unit 4, and as shown in the figure, the dust collecting unit 4 has the potential measuring unit 48 (see FIG. 3). It is provided. As the potential measuring unit 48, for example, a well-known surface potential measuring device having a detection electrode capable of measuring the potential of the high voltage electrode 42 in a non-contact manner can be used, and the actual potential at the high voltage electrode 42 can be measured. ..

The AC input processing unit 8 inputs 100 V AC from a commercial power source, for example. The AD converter 9 converts the 100V alternating current input by the AC input processing unit 8 into, for example, 12V direct current.

The control unit 7 includes a charging unit output control unit 71, a dust collection unit output control unit 72, and a motor output control unit 73. The control unit 7 has, for example, a microcomputer such as a CPU and a memory, and functions as the charging unit output control unit 71, the dust collection unit output control unit 72, and the motor output control unit 73 by reading and processing a predetermined program. Fulfill. The motor output control unit 73 is electrically connected to the air volume changeover switch 62 for setting the air volume and controls the output of the fan motor 61 according to the operation of the air volume changeover switch 62.

The constant-current high-voltage power supply unit 30 is a power supply for applying a constant-current high voltage to the charging unit 3, and the applied voltage is controlled by the charging-unit output control unit 71 of the control unit 7. The constant voltage/high voltage power supply unit 40 is a power supply (power supply unit) for applying a constant high voltage to the dust collecting unit 4, and the applied voltage is controlled by the dust collecting unit output control unit 72 of the control unit 7. Controlled. That is, in order to increase the dust collection efficiency as much as possible, it is desirable to supply a constant large current to the charging unit 3 and a constant high voltage to the dust collecting unit 4, so Separate power supplies are provided for the unit 4 and the unit 4, respectively.

As shown in FIG. 2B, the dust collector output control unit 72 includes a discharge determination unit 721, an applied voltage control unit 722, and an expected potential calculation unit 723.

The discharge determination unit 721 determines whether corona discharge has occurred in the dust collection unit 4. As will be described later in detail, the dust collecting unit 4 includes an electrode unit 41 (see FIG. 3) in which a plurality of high-voltage electrodes 42 and a plurality of ground electrodes (dust collecting electrodes) 43 are arranged in parallel and alternately, When a high voltage is applied to the high-voltage electrode 42 from the constant-voltage high-voltage power supply unit (power supply unit) 40, corona discharge is generated between the adjacent high-voltage electrode 42 and the ground electrode 43 due to electrode contamination due to moisture and deterioration over time. May occur. The discharge determining unit 721 determines whether corona discharge has occurred in the electrode unit 41 of the dust collecting unit 4.

When the applied voltage control unit 722 determines by the discharge determination unit 721 that corona discharge has occurred in the electrode unit 41 of the dust collecting unit 4, the applied voltage control unit 722 applies a voltage smaller than a discharge start applied voltage described later to the constant voltage high voltage power supply unit 40. The high voltage electrode 42 of the electrode portion 41 can be applied to continue the dust collection operation.

That is, when corona discharge occurs in the electrode portion 41 and a discharge current (a current flowing by causing insulation breakdown of air) flows, a voltage drop occurs and the dust collection performance deteriorates. Therefore, in order to suppress the deterioration of the dust collecting performance as much as possible, the applied voltage control unit 722 sets the constant voltage and high voltage power supply unit 40 so that the applied voltage is such that the corona discharge does not occur and the dust collecting process can be performed without any trouble. To control.

More specifically, when the discharge determination unit 721 determines that the corona discharge has occurred in the electrode unit 41 of the dust collecting unit 4, the applied voltage control unit 722 performs the discharge start voltage search process of searching the discharge start applied voltage. Run. Then, the applied voltage control unit 722 performs the discharge start voltage search process and then controls the high voltage electrode 42 to be applied with a voltage smaller than the searched discharge start applied voltage. A detailed method of determining whether corona discharge has occurred will be described later.

The expected potential calculation unit 723 calculates an expected potential that is expected to be measured by the potential measurement unit 48, assuming that corona discharge has not occurred in the electrode unit 41 of the dust collecting unit 4. The detailed method of calculating the expected potential will also be described later.

As will be described in detail later, the discharge determination unit 721 in the present embodiment is configured to determine the presence or absence of corona discharge based on the actually measured potential measured by the potential measurement unit 48.

FIG. 3 is a schematic diagram showing the dust collector 4 of the electric dust collector 2 of the embodiment. As shown in FIG. 3, the dust collecting part 4 includes an electrode part 41 in which a plurality of high voltage electrodes 42 and a plurality of ground electrodes (dust collecting electrodes) 43 are arranged in parallel and alternately. The plurality of high-voltage electrodes 42 are each formed in a sheet shape, and each base is held by the insulating holding member 45 and connected to the high-voltage power supply member 46. The plurality of ground electrodes 43 are also formed in a sheet shape, and each base is held by the insulating holding member 45 and connected to the ground power feeding member 47. Further, the insulating holding member 45 and the ground power supply member 47 are provided with a discharge prevention insulating member 44.

The high-voltage electrode 42 is formed in a flat plate shape with a semi-insulating resin having a volume resistivity of 10 ⁹ Ωcm to 10 ¹³ Ωcm mixed with, for example, PA (polyamide) or ABS resin. The ground electrode 43 is formed in a flat plate shape with a semiconductive resin having a volume resistivity of about 10 ² Ωcm, which is a mixture of carbon and ABS resin. Then, the high voltage electrodes 42 and the ground electrodes 43 are alternately arranged with a predetermined interval of, for example, 2 mm or less.

Further, the dust collecting unit 4 is provided with the potential measuring unit 48 as described above. As the potential measuring unit 48, a well-known surface potential measuring device having a detection electrode capable of measuring the voltage of the high voltage electrode 42 in a non-contact manner can be used.

Here, when the electrostatic precipitator 2 is used for a long time and the high voltage electrode 42 is contaminated and deteriorates over time, corona discharge is likely to occur between the position S that is the closest to the high voltage power supply member 46 and faces the adjacent ground electrode 43. Become. Then, when corona discharge occurs, the potential drops on the high-voltage electrode 42 at a position farther from the discharge point (position S) than the high-voltage power supply member 46 (hereinafter, referred to as “discharging point”). Therefore, in the present embodiment, the potential measuring unit 48 is provided at a position distant from the high voltage power supply member 46, that is, at the tip end side of the high voltage electrode 42. Thereby, the potential of the high-voltage electrode 42 connected to the high-voltage power supply member 46 via the insulating holding member 45 beyond the discharge point (potential on the tip end side of the high-voltage electrode 42) is measured.

In particular, since the high-voltage electrode 42 in this embodiment is formed of the semi-insulating resin having a high volume resistivity as described above, even if the current flowing due to the discharge is a minute corona discharge, it is immediately after the discharge. The potential drops sharply. Therefore, the presence or absence of corona discharge can be accurately measured by detecting a rapid change in the potential of the high-voltage electrode 42 by the potential measuring unit 48.

Here, an example of discharge prevention control performed by the electrostatic precipitator 2 according to the present embodiment will be described with reference to FIGS. 2 to 6. Here, the discharge prevention control refers to control for executing the dust collection operation with an applied voltage that is smaller than the discharge start applied voltage at which corona discharge is started. Such control is performed by the dust collector output controller 72. As will be described later in detail, in the present embodiment, the dust collector output control unit 72 performs a discharge start voltage search process for searching for a discharge start applied voltage, and after performing the discharge start voltage search process, the searched discharge start The voltage applied to the high voltage electrode 42 is lower than the applied voltage.

FIG. 4 is a graph showing the change characteristics of the discharge current corresponding to the voltage applied to the high voltage electrode 42 of the dust collector 4 of the electrostatic precipitator 2, and FIG. 5 shows the characteristics of the high voltage electrode 42 of the dust collector 4 of the electrostatic precipitator 2. It is a graph which shows the change characteristic of the electric field strength corresponding to an applied voltage. 6 is a graph showing the relationship between the current corresponding to the voltage applied to the high-voltage electrode 42 of the dust collector 4 of the electrostatic precipitator 2 and the potential beyond the discharge point, and FIG. 7 is the graph of the electrostatic precipitator 2 in the example. It is explanatory drawing which shows the flow of the process of discharge suppression applied voltage control which the dust part output control part 72 performs.

4 and 5, the solid line indicates changes in voltage and current of the high-voltage electrode 42 of the electrostatic precipitator 2 at the start of use (initial state) after long-term use. In FIG. 4, the horizontal axis represents applied voltage (voltage applied to the high-voltage electrode 42), and the vertical axis represents discharge current (discharge current flowing in the high-voltage electrode 42). In FIG. 5, the horizontal axis represents the applied voltage (voltage applied to the high-voltage electrode 42), and the vertical axis represents the electric field strength (index indicating the dust collecting capability) between the high-voltage electrode 42 and the ground electrode 43. taking it.

The electrostatic precipitator 2 applies a predetermined reference voltage (hereinafter referred to as “reference voltage”) Vx, which has been confirmed that corona discharge does not occur in the initial state (at the start of use), to the high-voltage electrode 42 of the dust collector 4. Can be used in any setting. However, when the applied voltage is continuously set to the reference voltage Vx, the high voltage electrode 42 and the ground electrode (dust collecting electrode) 43 are contaminated due to moisture or deterioration over time, and the high voltage electrode 42 of the dust collecting part 4 is grounded. It is known that a corona discharge is generated between the electrode 43 and the dust collecting ability. For example, at the start of use (initial state) of the electrostatic precipitator 2 and after long-term use, the current flowing through the high-voltage electrode 42 changes due to the occurrence of corona discharge after long-term use.

Here, the points on the graph showing the discharge current with respect to the applied voltage in FIG. 4 and the points on the graph showing the electric field strength with respect to the applied voltage in FIG. 5 are hereinafter referred to as “operating points”. A to D in FIGS. 4 and 5 represent different operating points. When the symbols indicating the operating points are the same in FIGS. 4 and 5 (for example, the operating point A in FIG. 4 and the operating point A in FIG. 5), the characteristics when the applied voltage to the high voltage electrode 42 is the same are shown. Represent

Normally, the electrostatic precipitator 2 is set so that the applied voltage becomes the reference voltage Vx so that a good dust collecting operation is performed without corona discharge during the manufacturing. Assuming that the operating point corresponding to the applied voltage Vx set at the time of manufacturing (at the start of use) is the first operating point A, the discharge current value is 0 at the first operating point A as shown in FIG. That is, the operating point corresponds to the applied voltage at which corona discharge does not occur. For example, the applied voltage applied to the high voltage electrode 42 is set here to 4.5 kV. The operating point A, which is the electric field strength (here, 22.5 kV/cm) when the applied voltage is applied, takes a linear value in which the applied voltage and the electric field strength are proportional, as shown in FIG.

However, when the electrostatic precipitator 2 is used for a long time and the high-voltage electrode 42 is contaminated, the corona discharge may be generated even at the reference voltage Vx which is the applied voltage of the magnitude that did not cause the corona discharge in the initial state. become. Therefore, after long-time use, for example, when the applied voltage (the voltage applied to the high voltage electrode 42) is set to 4.0 kV, corona discharge occurs, and the operating point corresponding to the applied voltage at this time is D It is a point. That is, corona discharge occurs even when a voltage of 4.5 kV is applied as in the initial state, and a slight discharge current flows through the high-voltage electrode 42 with corona discharge. If even a slight discharge current flows, the electric resistance of the high-voltage electrode 42 formed of the semi-insulating resin is large, so that the potential of the high-voltage electrode 42 drops significantly. As a result, even if the applied voltage remains 4.5 kV, the discharge current and the electric field strength move from the first operating point A in the initial state to the second operating point B after long-term use. In this way, the characteristics of the discharge current with respect to the applied voltage and the characteristics of the electric field strength with respect to the applied voltage differ between the initial state and after long-term use. Therefore, the potential of the high-voltage electrode 42 is significantly reduced in proportion to the magnitude of the discharge current, and as a result, at the second operating point B, the electric field strength indicating the dust collecting performance is large, as shown in FIG. descend. Here, the electric field strength is reduced from 22.5 kV/cm to 15.0 kV/cm.

On the other hand, if the voltage applied to the high-voltage electrode 42 is set to be smaller than 4.0 kV which is the applied voltage at which corona discharge starts (discharge start applied voltage), corona discharge does not occur in the dust collecting part 4. Therefore, the dust collector output control unit 72 of the control unit 7 in the present embodiment applies the constant voltage high-voltage power supply unit (power supply unit) 40 so that the operating point becomes the third operation point C at which corona discharge does not occur. Control the voltage. That is, control is performed so that an applied voltage lower than the discharge start applied voltage is applied to the high voltage electrode 42. As shown in FIG. 4, the applied voltage is set to 3.8 kV here so that the discharge current value becomes 0 and the third operating point C at which corona discharge does not occur.

In this way, by controlling the applied voltage so that the operating point becomes the third operating point C, the operating point becomes the first point as a result of corona discharge occurring without any control while continuing the dust collecting operation. It is possible to obtain a higher dust collecting performance as compared with the case of moving to the second operation point B. That is, as shown in FIG. 5, compared to the electric field strength of 15.0 kV/cm when no control is performed, the dust collecting operation with the electric field strength of 19.0 kV/cm becomes possible.

However, the discharge start applied voltage does not always take a constant value, and changes depending on the shape and material of the electrode, the operating environment such as temperature and humidity, and the type of dirt accumulated on the electrode. Therefore, even when the voltage applied to the high-voltage electrode 42 is controlled to be a predetermined applied voltage (for example, 3.8 kV) in advance when the occurrence of corona discharge in the dust collecting portion 4 is detected, the corona discharge is generated. It does not always occur. Therefore, in the present embodiment, the discharge start voltage searching process described below is performed so that the discharge start applied voltage can be detected regardless of the use environment and the type of dirt.

Here, the discharge start voltage searching process for detecting the discharge start applied voltage will be briefly described with reference to FIG. The straight line L in FIG. 6 is defined by the linear function shown in Expression 1.
E=pV... (Equation 1)
E: Potential beyond the discharge point
V: Applied voltage (V<V ₀ , V ₀ : Applied voltage to start discharge)
p: Proportional constant (p≈1)

Further, in FIG. 6, I _L is a leak current (current flowing through the surface of the object), I _D is a discharge current (current flowing due to dielectric breakdown of air), and I _total which is a detectable collector current is , I _total =I _L +I _D.

As shown in FIG. 6, first, the expected potential calculation unit 723 (see FIG. 2B) of the control unit 7 causes the potential measurement unit 48 (see FIGS. 2A and 3) to assume that corona discharge has not occurred. The expected potential E _es expected to be measured is calculated (estimated). As shown in Expression 1, when corona discharge is not occurring, the potential E of the high voltage electrode 42 beyond the discharge point is proportional to the applied voltage V to the high voltage electrode 42 (E=pV). Therefore, assuming that no corona discharge has occurred, the potential E beyond the discharge point can be calculated (estimated) based on the applied voltage V. That is, the expected potential E _es can be obtained by the equation (E _es =pV) of the straight line L showing the proportional relationship with the applied voltage. The proportionality constant p≈1, and here p=1 for simplicity. For example, when the applied voltage V is 4.0 kV which is equal to or lower than the discharge start voltage, the expected potential E _es is E _es =pV=4.0 kV.

Then, the measured potential E _ac , which is the actual potential measured by the potential measuring unit 48, is compared with the expected potential E _es . Here, the expected potential E _es is calculated on the assumption that no corona discharge has occurred. Therefore, if corona discharge has occurred, the measured potential E _ac, which is the actual potential measured by the potential measuring unit 48, becomes a value significantly smaller than the expected potential E _es due to the voltage drop accompanying the corona discharge. It is assumed that Therefore, when the difference between the measured potential E _ac and the expected potential E _es is larger than a predetermined threshold value (for example, the amount of change in potential due to voltage drop that occurs when corona discharge occurs), the discharge determination unit 721 (FIG. 2B). (See) determines that corona discharge has occurred.

Next, the control unit 7 searches for a discharge start applied voltage V _{0 at} which corona discharge is started. Here, the discharge start applied voltage V ₀ is searched for on the basis of the actually measured potential E _ac measured by the potential measuring unit 48. That is, while gradually changing the applied voltage V, each applied voltage V is compared with the corresponding actually measured potential E _ac to search for the discharge start applied voltage V ₀ .

That is, the applied voltage control unit 722 (see FIG. 2B) of the control unit 7 searches for the discharge start applied voltage V ₀ by changing the applied voltage V to the high voltage electrode 42 so as to be gradually smaller in the discharge start voltage search process. To do. At this time, when the amount of change in the actually measured potential E _ac corresponding to the applied voltage V that has been changed becomes significantly larger than the amount of change up to now in the vicinity of a certain applied voltage V, the discharge current _ID flows. It is determined that the measured potential E _ac has changed suddenly due to the disappearance. That is, when the applied voltage V to the high-voltage electrode 42 is changed to be gradually decreased, the measured potential E _ac suddenly increases (for example, the fluctuation amount of the measured potential E _ac accompanying the applied voltage V changes. with the detection of that) is equal to or greater than a predetermined value, it is possible to determine that the corona discharge is stopped, then the applied voltage V which has been applied to the high-voltage electrode 42 to be detected as the discharge starting voltage V applied _0. Note that it may be possible to determine whether corona discharge has occurred or not based on a change in I _total ( _{total of} leak current I _L and discharge current I _D ) that is a detectable current value. However, since the discharge current I _D flowing through the high-voltage electrode 42 when the corona discharge occurs in the dust collecting part 4 is weak, the fluctuation of I _total near the discharge start applied voltage V ₀ is small as shown in FIG. It is loose. Therefore, it is desirable to determine the presence/absence of corona discharge based on the change in the potential of the high-voltage electrode 42, which changes significantly.

After detecting the discharge start applied voltage V ₀ , the applied voltage controller 722 determines the lower limit applied voltage that is the lower limit of the applied voltage V to the high voltage electrode 42 (see FIG. 3) based on the applied voltage V and the measured potential E _ac . Set V _min . Then, the applied voltage control unit 722 causes the constant voltage high voltage power supply unit 40 to apply a voltage smaller than the discharge start applied voltage V ₀ to the high voltage electrode 42 thereafter. As shown in FIG. 6, the lower limit applied voltage V _min is, for example, the measured potential E _ac when corona discharge occurs and a voltage drop occurs (the measured potential E when applied voltage V=discharge start applied voltage V ₀ ). (including _ac ) is E _min, and the applied voltage when the expected potential E _es =E _min on the straight line L (E=pV) showing the expected potential E _es assuming that corona discharge is not generated V may be the lower limit applied voltage V _min .

Thus, the dust collecting unit output control unit 72 of the control unit 7 (see FIG. 2A), after searching the discharge starting voltage applied V _0, than the discharge starting voltage applied V ₀ to the constant-voltage high-voltage power supply unit 40 small applied A voltage is applied to the high-voltage electrode 42 to perform discharge prevention operation control for preventing corona discharge while continuing the dust collection operation. Here, by setting the applied voltage V to a value larger than the lower limit applied voltage V _min , the electric field strength becomes larger than 15 kV/cm, and the electric field strength is higher than that when the electric field strength is lowered by the corona discharge in the dust collecting part 4. The dust performance is maintained. The range F of the applied voltage V when the discharge prevention operation control is executed is a range indicated by Vmin to Vmax.

Here, the discharge suppression applied voltage control for searching the discharge start applied voltage V ₀ and executing the discharge prevention operation control will be described with reference to FIG. 7. In the process of FIG. 7, for the sake of convenience, the proportional constant p=1 in the relationship between the applied voltage and the potential beyond the discharge point is set.

As shown in FIG. 7, the control unit 7 sets the applied voltage V to the high voltage electrode 42 to the reference voltage Vx (step S110). The reference voltage Vx is preset to a voltage at which the discharge current value becomes 0 at the time of manufacturing the electrostatic precipitator 2 and no corona discharge is expected to occur.

Here, if corona discharge is occurring in the dust collecting unit 4, the measured potential E _ac, which is the actual potential measured by the potential measuring unit 48, is larger than the applied voltage V due to the voltage drop due to the corona discharge. It is expected to become small. On the other hand, if corona discharge does not occur in the dust collecting unit 4, it is assumed that the voltage drop does not occur and the measured potential E _ac does not become significantly smaller than the applied voltage V. Therefore, the control unit 7 measures the measured potential E _ac by the potential measuring unit 48 (step S120), and the measured potential E _ac is equal to or more than the difference between the applied voltage V and the threshold ΔE (applied voltage V and measured potential E _ac ). When it is determined that the difference from _ac is less than or equal to the threshold ΔE (step S130: No), it is determined that the potential drop due to discharge has not occurred, that is, corona discharge has not occurred. On the other hand, it is determined that the measured potential E _ac is smaller than the difference between the applied voltage V and the threshold ΔE (the difference between the applied voltage V and the measured potential E _ac is larger than the predetermined threshold ΔE) (step S130: Yes), it is determined that a discharge current due to corona discharge is flowing through the high-voltage electrode 42, that is, corona discharge is occurring, and the process proceeds to step S140.

In order to search for the applied voltage (discharging start applied voltage) applied when the corona discharge occurs, the control unit 7 reduces the applied voltage V by a predetermined decrease width ΔV in step S140 (applied voltage V Is changed to V=V−ΔV), the measured potential E _ac at that time is detected (step S150), and whether or not the measured potential E _ac is larger than the difference between the applied voltage V and the threshold ΔE, in other words, It is determined whether the difference between the applied voltage V and the measured potential E _ac is smaller than a predetermined threshold ΔE (step S160).

When it is determined that the measured potential E _ac is smaller than the difference between the applied voltage V and the threshold ΔE (the difference between the applied voltage V and the measured potential E _ac is larger than the predetermined threshold ΔE) (step S160: No), The control unit 7 determines that the corona discharge still occurs, and moves the process to step S140. Then, the control unit 7 further lowers the applied voltage V by a predetermined decrease width ΔV, and the measured potential E _ac is equal to or more than the difference between the applied voltage V and the threshold ΔE (the difference between the applied voltage V and the measured potential E _ac is predetermined. The process is repeated until it is determined that the threshold value ΔE or less), that is, it is determined that the corona discharge has stopped. In this way, the applied voltage that is the boundary between the applied voltage at which corona discharge has occurred and the applied voltage at which corona discharge has stopped, that is, the corona The applied voltage at which the discharge is started (discharging start applied voltage V ₀ ) is searched for.

Then, when it is determined that the measured potential E _ac is equal to or larger than the difference between the applied voltage V and the threshold ΔE (the difference between the applied voltage V and the measured potential E _ac is equal to or smaller than the predetermined threshold ΔE) (step S160: Yes), The control unit 7 determines that the corona discharge has stopped.

After that, the control unit 7 waits until a predetermined time t1 (for example, 30 minutes) elapses (step S170: No) in order to suppress the influence of the fluctuation due to the passage of time, and when the predetermined time t1 is reached (step S170: Yes). , It is determined whether the applied voltage V is lower than the reference voltage Vx set as the reference (step S180).

When it is determined that the applied voltage V is lower than the reference voltage Vx set as the reference (step S180: Yes), the process proceeds to step S190. On the other hand, when it is determined that the applied voltage V is equal to or higher than the reference voltage Vx set as the reference (step S180: No), this processing ends.

By the way, the discharge start applied voltage V ₀ may temporarily drop due to changes in humidity in the electrostatic precipitator 2. In this case, it is assumed that the discharge start applied voltage V ₀ that has dropped temporarily returns with the passage of time.

Therefore, in step S190, the control unit 7 changes the applied voltage so as to increase this time. That is, since it is assumed that the applied voltage at the time of step S190 is smaller than the accurate applied voltage at which corona discharge is started, the measured potential E _ac is detected while increasing the applied voltage V by the width ΔV. (Step S200). Next, the control unit 7 determines whether or not the measured potential E _ac is greater than or equal to the difference between the applied voltage V and the threshold ΔE, in other words, whether or not the threshold ΔE is greater than or equal to the difference between the applied voltage V and the measured potential E _ac. It is determined whether or not (step S210).

Then, when it is determined that the measured potential E _ac is smaller than the difference between the applied voltage V and the threshold ΔE (the difference between the applied voltage V and the measured potential E _ac is larger than the predetermined threshold ΔE) (step S210: No), The control unit 7 moves the process to step S140 and repeats the processes of steps S140 to S200 to search for the discharge start applied voltage.

Then, the measured potential E _ac is greater than or equal to the difference between the applied voltage V and the threshold Delta] E (applied voltage V and the measured potential difference between E _ac is equal to or less than the predetermined threshold value Delta] E) when it is determined (step S210: Yes ), the control unit 7 has detected the discharge start applied voltage.

After that, the control unit 7 waits until the predetermined time t1 elapses (step S220: No), and when the predetermined time t1 elapses (step S220: Yes), the applied voltage V is the reference voltage Vx(set as the reference). It is determined whether or not the voltage is equal to or higher than the voltage at which corona discharge does not occur at the time of manufacturing the electrostatic precipitator 2 (step S230).

Unless it is determined that the applied voltage V is equal to or higher than the reference voltage Vx set as the reference, the control unit 7 repeats the processing from step S140 to step S220 (step S230: No), and the applied voltage V is equal to or higher than the reference voltage Vx. Only when it is determined that (step S230: Yes), the main discharge suppression applied voltage control process ends.

FIG. 8 and Table 1 show how the above-described discharge suppression applied voltage control process improves the dust collection performance of the dust collecting unit 4 according to the embodiment as compared with the case where the discharge suppression applied voltage control process is not performed. It will be explained using. FIG. 8 is an explanatory diagram showing an equivalent circuit of the dust collecting unit 4 according to the embodiment, and Table 1 shows a case where the discharge suppressing applied voltage control is performed in the new electric dust collector and an electric dust collector that has been used for a long time. The performance comparison result in the case is shown. For simplicity, the resistance of the ground electrode (dust collecting electrode) 43 in the dust collecting portion 4 is set to 0 in FIG.

In FIG. 8 and Table 1, V is the power supply voltage, R _hv is the high voltage electrode resistance (HV electrode resistance), i is the discharge current, R _d is the discharge resistance, and E is the inter-electrode voltage. Further, V ₀ in Table 1 is a discharge start voltage (actual measurement value).

It has been known that the electric field strength indicating the dust collecting capability is proportional to the interelectrode voltage E. As shown in Table 1, after the electrostatic precipitator 2 was used for a long time, the inter-electrode voltage E was 4 kV when the above-described discharge suppression applied voltage control was executed, whereas the discharge suppression applied voltage control was not executed. The inter-electrode voltage E in this case is 3.29 kV.

Therefore, it becomes 4 kV/3.29 kV=1.22, and it can be seen that the dust collection capability is improved by 22% by the discharge suppression applied voltage control.

By the way, in the above-described embodiments, whether or not the corona discharge has occurred is determined by the control unit 7 calculating based on the measured potential E _ac . However, a discharge detection sensor that detects a corona discharge in the electrode portion 41 of the dust collecting portion 4 is separately provided in the dust collecting portion 4, and the discharge determining portion 721 of the control portion 7 determines whether or not the discharge determining sensor 721 of the dust collecting portion 4 detects the corona discharge. The presence or absence of corona discharge may be determined.

For example, as the discharge detection sensor, a light detection element or a sound detection element can be considered. The discharge determination unit 721 of the control unit 7 collects by detecting light or sound emitted when corona discharge occurs, as a configuration including at least one of the light detection element and the sound detection element. It can be determined that corona discharge is occurring in the dust section 4.

In addition, as the discharge detection sensor, the number of particles after dust removal is measured by, for example, a particle counter, and if a timing at which the number of particles suddenly changes is found, it can be determined that corona discharge has occurred.

Further, a device such as a probe is arranged in the dust collecting unit 4, and the electric field of the electrode unit 41 is monitored. If a timing at which the electric field changes abruptly is found, it is determined that corona discharge has occurred. Is also possible.

Although the embodiments of the present application have been described above with reference to the drawings, they are merely examples, and various modifications and improvements can be made based on the knowledge of those skilled in the art.

The following electrostatic precipitator 2 is realized from the embodiment described above.

(1) The charging unit 3 for charging dust, the plurality of ground electrodes (dust collecting electrodes) 43 and the plurality of high-voltage electrodes 42 formed of semi-insulating resin are alternately arranged, and the charging unit 3 charges the particles. The dust collecting unit 4 for collecting the collected dust, the constant voltage high-voltage power supply unit (power supply unit) 40 for applying a voltage to the high-voltage electrode 42, and the presence or absence of corona discharge in the dust collecting unit 4 are determined to determine the corona discharge. When it is determined that the discharge start applied voltage V _{0 at} which the corona discharge is started is detected, a voltage smaller than the detected discharge start applied voltage V ₀ is applied to the high voltage electrode 42 with respect to the constant voltage high voltage power supply unit 40. An electrostatic precipitator 2 including a dust collector output control unit 72 to be applied.

According to such an electric dust collector 2, it is possible to suppress wasteful power consumption while suppressing deterioration of the dust collecting performance even if corona discharge occurs.

(2) In the above (1), the dust collector output control unit 72 determines that the dust collector 4 determines whether corona discharge has occurred, and the discharge determiner 721 determines that corona discharge has occurred. In this case, an applied voltage control unit 722 that performs a discharge start voltage search process that searches for the discharge start applied voltage V ₀ , and the applied voltage control unit 722 performs the discharge start voltage search process and then the searched discharge. An electrostatic precipitator 2 that controls to apply to the high-voltage electrode 42 with a voltage lower than the start applied voltage V ₀ .

(3) In the above (2), the applied voltage control unit 722 searches for the discharge start applied voltage V ₀ by changing the applied voltage to the high voltage electrode 42 so as to become gradually smaller during the discharge start voltage search process. Dust collector 2.

(4) In the above (2) or (3), the dust collecting unit 4 includes a potential measuring unit 48 that measures the potential of the high-voltage electrode 42, and the applied voltage control unit 722 measures the measured value by the potential measuring unit 48. An electrostatic precipitator 2 that searches for a discharge start applied voltage V ₀ based on the potential E _ac .

When corona discharge occurs in the dust collecting portion 4, even if the discharge current _ID flowing through the high voltage electrode 42 is weak, the potential of the high voltage electrode 42 formed of the semi-insulating resin drops sharply. Therefore, according to the electrostatic precipitator 2, the accurate discharge start applied voltage V ₀ is searched for by determining the presence or absence of the occurrence of corona discharge based on the fluctuation of the measured potential E _ac measured by the potential measuring unit 48. be able to.

(5) In (4) above, the applied voltage control unit 722 determines the expected potential E _es expected to be measured by the potential measuring unit 48, assuming that corona discharge has not occurred in the dust collecting unit 4. The discharge determination unit 721 further includes an expected potential calculation unit 723 for calculating, and the discharge determination unit 721 has a difference between the expected potential E _es calculated by the expected potential calculation unit 723 and the actually measured potential E _ac measured by the potential measurement unit 48 larger than a predetermined threshold ΔE. In this case, the electric dust collector 2 that determines that corona discharge has occurred in the dust collector 4.

(6) In (5) above, the applied voltage control unit 722 determines the measured potential E _ac measured by the potential measurement unit 48 and the expected potential calculation unit when the discharge determination unit 721 determines that corona discharge has occurred. based on the expected potential E _es calculated by 723 to set the lower limit applied voltage V _min is the lower limit of the voltage applied to the high-voltage electrode 42, with respect to the constant-voltage high-voltage power supply unit 40, the lower limit applied voltage V _min or more voltage Is applied to the high voltage electrode 42.

(7) In any one of (2) to (6) above, a discharge detection sensor that detects corona discharge in the dust collecting unit 4 is provided, and the discharge determination unit 721 determines the corona discharge based on the detection result of the discharge detection sensor. An electrostatic precipitator 2 that determines the occurrence of

Further, in the present embodiment, since it has the configurations of (2) to (6) above, even if corona discharge occurs, it is possible to sufficiently suppress the deterioration of the dust collection performance and suppress unnecessary power consumption. It will be possible.

1 Air Purifier 2 Electric Dust Collector 4 Dust Collection Part 7 Control Part 40 Constant Voltage High Voltage Power Supply Part 41 Electrode Part 42 High Voltage Electrode 72 Dust Collection Part Output Control Part 721 Discharge Judgment Part 722 Applied Voltage Control Part 723 Expected Potential Calculation Part

Claims (7)

A charging unit that charges dust,
A plurality of dust collecting electrodes and a plurality of high-voltage electrodes formed of a semi-insulating resin are alternately arranged, and a dust collecting portion that collects the dust charged by the charging portion,
A power supply unit for applying a voltage to the high-voltage electrode,
The presence or absence of corona discharge in the dust collecting portion is determined, and when it is determined that the corona discharge has occurred, the discharge start applied voltage at which the corona discharge is started is detected, and the detected discharge is detected with respect to the power supply unit. A control unit that applies a voltage lower than a start applied voltage to the high-voltage electrode, the electrostatic precipitator. The control unit is
A discharge determination unit that determines the presence or absence of corona discharge in the dust collection unit,
If the discharge determination unit determines that the corona discharge has occurred, an applied voltage control unit that performs a discharge start voltage search process for searching the discharge start applied voltage, and
The applied voltage control unit,
The electrostatic precipitator according to claim 1, wherein after performing the discharge start voltage searching process, control is performed to apply the voltage to the high-voltage electrode with a voltage lower than the searched discharge start applied voltage. The applied voltage control unit,
The electrostatic precipitator according to claim 2, wherein, in the discharge start voltage searching process, the discharge start applied voltage is searched by changing the voltage applied to the high-voltage electrode so as to be gradually decreased. The dust collecting section is
Equipped with a potential measuring unit for measuring the potential of the high voltage electrode,
The applied voltage control unit,
The electrostatic precipitator according to claim 2 or 3, wherein the discharge start applied voltage is searched for based on an actually measured potential measured by the potential measuring unit. The control unit is
When it is assumed that the corona discharge has not occurred in the dust collecting unit, further comprises an expected potential calculation unit for calculating an expected potential expected to be measured by the potential measurement unit,
The discharge determination unit,
The corona discharge is determined to have occurred in the dust collecting unit when the difference between the predicted potential calculated by the predicted potential calculation unit and the measured potential by the potential measurement unit is larger than a predetermined threshold value. The described electrostatic precipitator. The applied voltage control unit,
When the discharge determining unit determines that the corona discharge has occurred, application to the high-voltage electrode based on the actually measured potential measured by the potential measuring unit and the expected potential calculated by the expected potential calculating unit. The electrostatic precipitator according to claim 5, wherein a lower limit applied voltage that is a lower limit of the voltage is set, and a voltage equal to or higher than the lower limit applied voltage is applied to the high-voltage electrode with respect to the power supply unit. A discharge detection sensor for detecting corona discharge in the dust collecting portion is provided,
The discharge determination unit,
The electrostatic precipitator according to claim 2, wherein the presence or absence of the corona discharge is determined based on the detection result of the discharge detection sensor.

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