JPH0112544B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for quickly detecting the occurrence of a reverse ionization phenomenon occurring in a dust collecting electrode of an electrostatic precipitator.

In an electrostatic precipitator, the electrical resistance of dust is 1
It is well known that when it exceeds ×10 ¹¹ Ω·cm, a phenomenon called reverse ionization occurs, and the dust collection performance is significantly reduced. This reverse ionization phenomenon causes dielectric breakdown due to the excessive accumulation of charge in the dust layer deposited on the dust collection electrode. Therefore, in order to prevent a decrease in dust collection efficiency, it is necessary to remove the dust collector at the same time as reverse ionization occurs. After the applied voltage has been lowered and the charge accumulated in the dust layer has substantially disappeared, the required time for dust discharge has elapsed.
It is effective to control the applied voltage so that it recovers again, and for such a control method, he proposed another invention (patent application (b) dated September 28, 1981) entitled "Automatic Voltage Control in Electrostatic Precipitator". Device").

However, for such control, a detection method that detects the occurrence of reverse ionization as quickly as possible is essential.

Therefore, the present applicant focused on the fact that when reverse ionization occurs, the characteristics of the secondary voltage V and secondary current I (V-I characteristics) differ greatly from those in the normal case, as shown in FIG. We previously proposed a method of detecting reverse ionization from the magnitude of dV/dI by taking advantage of the difference in V-I characteristics, especially the large change in skewed dV/dI (Patented on September 28, 1982). wish (a)
"Method for detecting reverse ionization in electrostatic precipitators").

However, this method calculates the voltage and current as average values over a half-cycle period of the AC power source, so it takes half a cycle to calculate the average value.
Furthermore, in order to calculate dV/dI, it is necessary to calculate two sets of average voltage and current values (V, I), and the time required for one cycle (half cycle x 2) is equal to dV/dI. Necessary for calculation. Furthermore, in the process of increasing the dust collector voltage, the "charging current" (described later) increases, so in order to prevent malfunctions at this time, the detection function must be disabled during the period when the dust collector voltage is rapidly increasing. It won't happen.

This invention improves the detection method described above to shorten the detection time, and provides a high-speed reverse ionization detection method that can detect reverse ionization in half a cycle of the power supply frequency without changing the control voltage when detecting reverse ionization. be.

If the occurrence of reverse ionization can be detected from the instantaneous values of voltage and current, it will be possible to detect reverse ionization much more quickly than with the above method.

However, since electrostatic precipitators have the function of a capacitor in an electric circuit (called capacitance), the instantaneous value of the observed secondary current is not the true corona discharge current (including that due to reverse ionization). , the charging current is added.

FIG. 3 shows an equivalent circuit of the electrostatic precipitator shown in FIG. 2.

In Figure 3, V is the discharge electrode, T is the dust collection electrode, and S
is the rectifier, W is the transformer, C is the capacitance of the dust collector, R is the resistance equivalent to corona discharge, I ₀ is the secondary current, I ₃ is the corona current, and I ₂ is the charging current.

The absolute value V ₀ of the electromotive force of the transformer secondary winding is the fourth
When the voltage changes as shown by the solid line in Figure A, the voltage (secondary voltage) of the dust collector changes as shown by the dotted line due to the capacitance C. During the period when V ₁ >V ₀ , the silicon rectifier S is reverse biased and blocks the current, so that the secondary current has an intermittent waveform as shown by the solid line in FIG. 4b. However, in this case as well, the corona current I ₃ is continuous, and the two have different waveforms.

(Note that I ₃ cannot be directly observed.) According to the equivalent circuit shown in FIG. 3, I ₀ =I ₃ +CdV ₁ /dt. Here, the second term on the right side is the charging current _I2 .

As can be seen from the above, the instantaneous value of the observed secondary current I ₀ cannot be regarded as the corona current I ₃ , and it can be seen that the charging current becomes large, especially when the precipitator voltage is rapidly increased. .

By the way, in FIG. 4b, in the period when I ₀ =0, it is shown as I ₃ =-CdV ₁ /dt, so the true corona current can be estimated from the speed of voltage attenuation of the secondary voltage waveform.

When reverse ionization occurs, the corona current increases significantly, and the attenuation width of the secondary voltage increases. It is possible to detect the occurrence of reverse ionization from the secondary voltage waveform, and it can be detected immediately when it occurs. The present invention relates to a specific method thereof.

As a result of various observations of the waveform of the secondary voltage using an actual dust collector from the above-mentioned perspective, we found the following relationship between the peak value (referred to as V _P ) and the bottom value (referred to as V _B ) of the secondary voltage waveform. I found out.

At the voltage before the start of corona, both V _P and V _B are low, and they almost match. (See Figure 5) When reverse ionization does not occur, as the output increases, both V _P and V _B increase, and the difference V _P -V _B also increases. However, V _P −V _B does not become excessively large. (See Figure 6) When reverse ionization occurs, V _B
does not increase; on the contrary, it decreases. Since V _P becomes large, V _N (=V _P −V _B ) becomes very large.
(See FIG. 7) Furthermore, when the characteristics of V _N (=V _P −V _B ) and V _B were determined, FIG. 8, which is similar to FIG. 1, was obtained.

Therefore, the principle of the present invention is to assume the dotted line in FIG. 8 and detect the occurrence of reverse ionization depending on which side of this line it is on.

In Figure 8, the boundary line ₍ dotted line) between normal charging and reverse ionization is determined as the relationship between V _B and V _{N (} =V _P - V _B ). Find it as the relationship. This is shown in Figure 9. (Approximated by a polygonal line.) The reverse ionization boundary voltage Vn has a function shape with saturation characteristics with respect to the peak voltage V _P. It has been experimentally confirmed that this saturation level (Vn=15 KV in FIG. 9) can be set to a condition where reverse ionization has not yet occurred, for example, 3 to 5 KV lower than the bottom value of the secondary voltage waveform immediately after the start of charging. When reverse ionization does not occur, the bottom value of the secondary voltage waveform is high, but when reverse ionization occurs, the bottom value becomes low, so the highest value of the bottom value of the secondary voltage is detected and the voltage is 3 to 5 KV lower than that. However, it is sufficient to set the saturation level of the reverse ionization boundary voltage.

When the peak voltage V _P is given, if the valley voltage V _B falls below the corresponding value of V _M shown in FIG. 9, it is determined that reverse ionization occurs. Furthermore, at this time, the larger the value of V _M -V _B , the greater the degree of reverse ionization.

By the way, if the instantaneous value of the voltage waveform is V _t , then
The value of V _t at the time of transition from falling to rising, that is, at the end of the falling process, becomes V _B.
Since V _t > V _B in the falling process, V _t is the 9th
If V B is below V _M in the figure, then V _B is always below V _M and is determined to be reverse ionization. Therefore, the instantaneous value V _t is V _M
When the value falls below , it is determined that reverse ionization has occurred. In this way, the determination can be made earlier than the determination based on the valley bottom voltage V _B , which is advantageous for automatic voltage control. (At the valley bottom voltage V _B , the falling process is already about to turn to rising, but in a power supply controlled by a thyristor on the primary side, this is the result of the thyristor firing. In other words, the thyristor This is the result of the gate pulse being emitted, and the reverse ionization detection at this point is
Since this is after the gate pulse has been issued, control is too late. ) When reverse ionization is detected at the instantaneous value V _t , V _t at that point or at a time when V _t further decreases.
The value of is compared with V _M and V _M −V _t is output as a signal representing the magnitude of reverse ionization.

Note that when V _t has fallen to almost 0 at this time, this is not considered to be reverse ionization, since sparks have occurred rather than reverse ionization.

Next, an embodiment of such a detection circuit will be described.

FIG. 10 shows a state in which the detection circuit is incorporated into the dust collector voltage control. The secondary voltage is divided by R ₁ and R ₂ and used as input 1 of the reverse ionization detection circuit.

The thyristor firing start signal 2' is given as a signal that triggers the start of one operation of the reverse ionization detection circuit (one detection operation is repeated for every half cycle of AC power supply).

The reverse ionization detection circuit 3 detects and outputs the occurrence and magnitude of reverse ionization. This output 4 causes the control circuit 5 to operate as described in another invention (patent application (b) ``Automatic voltage control device for electrostatic precipitator'' dated September 28, 1981). That is, the control circuit 5 controls the output 2 of the automatic voltage detection circuit 7 to switch to low charge at the same time as reverse ionization is detected, and to restore the output to high charge after a period of time corresponding to the magnitude of reverse ionization. Control.

An example of a reverse ionization detection circuit is shown in FIG. (Analog circuit) Since the secondary voltage has a negative value, the secondary voltage signal comes in as a negative signal, but this is inverted to a positive signal.

When the ignition start signal of the thyristor on the primary side of the dust collector power supply is issued, the secondary voltage starts to rise, so
This ignition start signal almost coincides with the bottom point of the dust collector secondary voltage. This signal momentarily turns on transistor Tr ₁ , and the voltage V _P of capacitor C ₁
Set to 0. At the next moment, Tr ₁ turns OFF and receives the secondary voltage signal V _t . If V _t > V _P , the diode
D ₁ turns on and the voltage V _P of C ₁ becomes equal to V _t . This operation continues until the secondary voltage reaches the peak value from the bottom point, but once the peak has passed, V _P > V _t , _D1 is turned OFF, and the peak voltage is stored in V _P.

A ₁ is a high input impedance amplifier circuit,
Outputs the value of V _P as is.

_A2 is a function generating circuit, which outputs the value of the reverse ionization boundary voltage V _M according to the value of V _P as shown by the polygonal line in FIG.

_A3 is a subtraction circuit that outputs the value of V _M −V _t . If this value is negative, D ₂ turns ON and V _put →0. This means that the charge is determined to be normal and the signal is set to 0.

If V _M −V _t is positive, this magnitude becomes the signal V _put indicating the magnitude of reverse ionization. If the magnitude of V _t is less than a certain set value V _SP (set to 1 to 5 ^KV ), this is determined to be a spark. This set value is set with potentiometer R, and comparator _A4 compares this with the value of _Vt . If V _SP > _Vt , _A4 becomes the output, transistor _Tr2 turns on, and the output of _A3 Output even if V _M −V _t is positive
Let _Vput be 0.

Through such an operation, the output V _put appears only when V _M -V _t is determined to be reverse ionization and not a spark. A ₅ is Tr ₂ when sparking
This is a filter to prevent V _M −V _t from appearing on V _put for a short time until V M turns ON.

As a result of the reverse ionization detection signal being emitted by this circuit, if control is performed to turn off the thyristor, the thyristor ignition signal will not come in, so C ₁
The value of V _P stored in will remain without being reset forever. On the other hand, in this case, since the voltage is cut off by the thyristor, V _t continues to fall, and the output V _put of the detection circuit gradually increases.

Therefore, even in the case of weak reverse ionization, if it is left to emit light, the reverse ionization signal V _put will increase. To prevent this, the magnitude of reverse ionization is determined at a certain timing, for example, after a certain period of time (for example, half a cycle of AC power supply) has passed after the thyristor gate signal is applied, and a circuit that latches this value is used. may be necessary. This is selected depending on how the dust collector voltage is controlled by this detector.

Another embodiment of the reverse ionization detection circuit is shown in FIG.
Shown in Figure 3. (Digital circuit) Here, after the voltage peak V _P is detected, the instantaneous value of the voltage is detected only once during the fall of the voltage waveform at a certain predetermined timing. This voltage is called the sampling value _VT .

Figure 12 shows the configuration of the reverse ionization detection device.This device detects the peak value V _P and the sampling value _V
1, an isolation amplifier 13 and a microcontroller 12 for insulating and supplying a secondary voltage. A thyristor firing start signal 111 is input to the peak value/sampling value detection circuit 11 and the microcontroller 12 for synchronizing the start of detection. The microcomputer 12 receives a peak value detection signal 15, a peak value 16, a sampling value detection signal 17, and a sampling value 18 from the peak value and sampling value detection circuit 11, determines whether or not reverse ionization has occurred, and sends the signal. If ionization occurs,
A reverse ionization detection signal 19 and a magnitude 110 of reverse ionization are output.

The configuration of the peak value and sampling value detection circuit 11 is shown in FIG. In addition, the processing flowchart is shown in the 14th
As shown in the figure. This circuit first checks the presence or absence of the thyristor firing signal 111 (block (hereinafter abbreviated as BK) 1 in FIG. 14). When the thyristor firing signal 111 comes, the A register 113, the B register 115, the C register 116, the peak value detection signal (hereinafter referred to as V _P FLAG) 15, and the base value detection signal (hereinafter referred to as V _T FLAG) 17 are all cleared. (BK2)
A clear signal is issued from the control section 117.

Next, a conversion start command is given to the A/D converter 112 from the control unit 117 (BK3), and after the A/D conversion is completed, the A register 11 is
3 stores the conversion result. (BK4) A register 1
The contents of 13 and the contents of B register 115 are constantly compared by comparator 114, and the comparison result is checked by control section 117 (BK5). As a result, if A<B, it is determined that the secondary voltage is in the process of increasing, and the contents of the A register are stored in the B register (BK6). Then, A/D conversion is performed continuously and the above processing is repeated.

If A<B, that is, A<B signal 11
If 8 is set, the control unit 117 controls the B register 11.
The value stored in 5 is determined to be the peak value, and V _P
Set up FLAG15 (BK7). and control section 11
7 starts the V _T timer in the control unit 117 in order to measure the timing of measuring the sampling value (BK8). When the V _T timer times up (BK9), the control unit 117 instructs the A/D converter 112 to start conversion (BK10). The conversion result is stored in the C register 116 according to an instruction from the control unit 117 (BK11). Then, the control unit 117 sets V _T
Set FLAG17 (BK12) and wait for the next thyristor firing start signal 111 (BK1).

FIG. 15 is a flowchart of the processing carried out in the microcomputer 12. First, the microcontroller 12 receives the thyristor firing start signal 1 similarly to the detection circuit 11.
Waiting for 11 to come (BK21). When the thyristor firing start signal 111 comes, the reverse ionization detection signal (hereinafter referred to as V _BC FLAG) 19 and the magnitude of reverse ionization (hereinafter referred to as V _BC ) 110 are cleared if they are set or set (BK22). Then, it waits for V _P FLAG 15 to be sent from the detection circuit 11 (BK23). When V _P FLAG15 is sent, the peak value (hereinafter referred to as V _P )6 is read (BK24). The microcomputer 12 determines the corresponding reverse ionization boundary voltage V _M from the peak value V _P according to the graph of FIG.
(BK25) If the sampling value _VT is less than _VM , it is reverse ionization. However, when V _T is almost 0,
It is thought to be a spark, not reverse ionization.

Then, the microcontroller 12 outputs the detection signal 11.
Sampling voltage detection signal (V _T FLAG) 1
Wait for 9 to be sent (BK26). V _T FLAG
When received, the microcontroller 12 reads the sampling voltage (V _T ) (BK27). The value of V _T becomes extremely small when a spark occurs, so if the boundary value is V _SP , if reverse ionization occurs, the sampling voltage (V _T ) is lower than the reverse ionization boundary voltage (V _M ). is small, and the sampling value (V _T ) is larger than the spark generation boundary value (V _SP ). Therefore, the microcontroller 12 checks that V _SP <V _T <V _M (BK28). If V _T is outside this range, no reverse ionization has occurred, so return to BK21.
Wait for the next thyristor firing start signal 111 to arrive.

If V _T is within the range of V _SP < V _T < V _M , back ionization has occurred, so the back ionization detection signal (BC-
FLAG) is immediately output (BK29), and the difference between the reverse ionization boundary voltage (V _D ) and the sampled value (V _T ) is determined and determined as the magnitude of reverse ionization (V _put ) (BK30). Then, the magnitude of the reverse ionization (V _put ) is output (returns to BK31 and BK21 and waits for the next thyristor firing start signal 111 to arrive).

FIG. 16 shows the thyristor firing start signal, secondary voltage waveform, and detector output.

The value of V _P in the detector is reset by the thyristor firing start signal. Almost simultaneously, the value of V _P at the peak of the secondary voltage waveform is stored in the capacitor or register of the detector, and the reverse ionization limit voltage V _M is calculated accordingly.

If the instantaneous voltage value does not drop to V _M , it is determined that charging is normal. (In the case of the first peak in Figure 16) Even if the instantaneous value of the voltage is below V _M ,
If the value falls below the V _SP set value, it is determined to be a spark and no reverse ionization detection signal is output. (In the case of the second peak in Figure 16) If the instantaneous value of the voltage is lower than V _M and larger than the set value of V _SP , it is determined that reverse ionization has occurred, and a signal V _put is output according to the magnitude. . (In the case of the third peak in Figure 16) At this time, in the analog example, the instantaneous value
As soon as V _t falls below V _M , the output V _put appears.
In a digital concrete example, the detection of V _T is performed at a certain timing, so if it is determined that reverse ionization is caused by this detection, the output V _put appears and a detection flag is set at the same time.

In summary, the present invention detects the peak voltage of the secondary voltage waveform of an electrostatic precipitator and the instantaneous value of the voltage after the peak voltage, and compares the peak voltage with the boundary voltage of reverse ionization obtained as a function of the peak voltage. This is a reverse ionization detection method that detects the occurrence of reverse ionization based on the magnitude of the value, and it is possible to detect the occurrence of reverse ionization instantaneously (less than half a cycle of the power frequency). By feeding back the detection signal to the voltage control device, we can expect the effect of enabling optimal control of the electrostatic precipitator.
This greatly contributes to improving dust collection efficiency.

[Brief explanation of drawings]

Figure 1 shows the V-
I characteristic diagram, Figures 2 and 3 are diagrams showing a general electrical circuit diagram of an electrostatic precipitator and its equivalent circuit, and Figures 4a and b are diagrams of the transformer secondary winding in an electrostatic precipitator, respectively. Figures 5, 6, and 7 are diagrams showing the relationship between the peak value and trough value of the secondary voltage waveform, respectively. Figure 8 shows the relationship between the difference between the peak value and the valley bottom value of the secondary voltage waveform and the valley bottom value, Figure 9 shows the relationship between the reverse ionization boundary voltage and the peak voltage, and Figure 10 shows the relationship between the peak value and the valley bottom value of the secondary voltage waveform. Figure 11 is a diagram showing an example of a reverse ionization detection circuit, Figures 12 and 13 are diagrams showing an automatic voltage control circuit of a dust device.
The figure is a digital circuit diagram showing another embodiment of the reverse ionization detection circuit, FIG. 14 is a diagram showing the processing flow, and FIG. 15 is a flow chart of the processing included in the microcontroller 12.
FIG. 16 is a diagram showing a thyristor firing start signal and a secondary voltage waveform detector output. In addition, the 14th
Numbers 1 to 29 in the figure and FIG. 15 indicate the order of the processing flow. 1...Input of the reverse ionization detection circuit, 2, 2'...Signal, 3...Reverse ionization detection circuit, 4...Output of the reverse ionization detection circuit, 5...Control circuit, 6...Signal, 7...
automatic voltage control circuit, 11... peak value, sampling value detection circuit, 12... microcontroller, 13...
...Isolation amplifier, 14...Secondary voltage, 15...Peak value detection signal (V _P FLAG), 16...Peak value (V _P ), 17... Sampling value detection signal (V _T
FLAG), 18... Sampling value (V _T ), 19
...Reverse ionization detection signal (V _BC FLAG), 110...
Magnitude of reverse ionization ( _Vput ), 111...Thyristor firing start signal, 112...A/D converter, 113
...A register, 114...Comparator, 115...
B register, 116...C register, 117...
Control unit, 118...A<B signal, V...discharge electrode,
T... Dust collecting pole, S... Rectifier, W... Transformer, C... Capacitance, R... Resistance equivalent to corona discharge.

Claims (1)

[Claims] 1. Detecting the peak voltage of the secondary voltage waveform of the electrostatic precipitator and the instantaneous value of the voltage after the peak voltage, and comparing it with the boundary voltage of reverse ionization determined as a function of the peak voltage. A method for detecting a reverse ionization phenomenon in an electrostatic precipitator, characterized in that the occurrence of reverse ionization is detected based on the magnitude of the value. 2. Claim 1 above, characterized in that the boundary voltage of reverse ionization has a function shape with saturation characteristics with respect to the peak voltage, and the saturation level is given by the highest value of the bottom values of the secondary voltage waveform. The described reverse ionization phenomenon detection method.