Ozone generator abnormality detection device and ozone generator

Abstract

To provide a detector that accurately detects the failure of a discharge tube constituting an ozone generator with a simple configuration.SOLUTION: A malfunction detector of an embodiment is used for an ozone generator equipped with a power converter that converts an input first AC voltage into a preset second AC voltage and outputs the second AC voltage, a transformer that boosts the AC voltage output from the power converter to a high voltage, and an ozone generator that incorporates a discharge tube and generates ozone when the AC voltage boosted by the transformer is applied to the discharge tube. The malfunction detector includes: a voltage dividing circuit that converts an AC voltage boosted to a high voltage by a transformer to a low voltage; two or more signal conversion units that convert the AC voltage passed through the voltage dividing circuit into a pulse signal, output the pulse signal, and use different comparison voltages when converting the AC voltage into the pulse signal; and a malfunction detection unit that detects a malfunction in the ozone generator based on a change in a pulse width of the pulse signal output from at least one of the two or more signal conversion units.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] An embodiment of the present invention relates to an abnormality detection device for an ozone generator and an ozone generator. [Background technology]

[0002] There is a technology for detecting an abnormality in an ozone generator when a discharge tube constituting the ozone generator breaks and the ozone generator becomes abnormal. For example, this technology determines that the ozone generator is abnormal when the input power input to an inverter that generates an AC voltage to be applied to the ozone generator is below a specified value and the output current output from the inverter is above a specified value. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 4071017 [Patent Document 2] Japanese Patent Application Publication No. 8-146071 [Patent Document 3] Patent Publication No. 2021-27677 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the above-mentioned conventional technology requires both an input power detector that detects input power and an output current detector that detects output current, which results in a complicated and expensive circuit configuration for the device that detects abnormalities in the ozone generator. Also, while there are devices that detect abnormalities based on changes in the frequency of the inverter power supply voltage, it is difficult to detect abnormalities based on frequency changes that occur during operation because the frequency of an ozone generator changes when the amount of ozone generated changes.

[0005] Therefore, an object of the present invention is to provide an abnormality detection device and an ozone generator that can accurately detect damage to a discharge tube that constitutes an ozone generator with a simple configuration. [Means for solving the problem]

[0006] An embodiment of the abnormality detection device is an abnormality detection device used for an ozone generator including: a power conversion device that converts an input first AC voltage into a predetermined second AC voltage and outputs the second AC voltage; a transformer that boosts the AC voltage output from the power conversion device to a high voltage; and an ozone generator that has a built-in discharge tube and generates ozone when the AC voltage boosted by the transformer is applied to the discharge tube. The abnormality detection device includes: a voltage divider circuit that converts the AC voltage boosted to a high voltage by the transformer into a low voltage; two or more signal conversion units that convert the AC voltage that has passed through the voltage divider circuit into a pulse signal and output the pulse signal, each using a different comparison voltage when converting into a pulse signal; and an abnormality detection unit that detects an abnormality in the ozone generator based on a change in the pulse width of the pulse signal output from at least one of the two or more signal conversion units. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a diagram showing an example of a schematic configuration of an ozone generator according to an embodiment of the present invention. [Figure 2] FIG. 1 is a diagram illustrating an example of a functional configuration of an abnormality detection device according to an embodiment of the present invention. [Figure 3] 2 is a diagram illustrating an example of a functional configuration of a signal conversion circuit included in the abnormality detection device according to the present embodiment. FIG. [Figure 4] 3 is a diagram illustrating an example of signal conversion by a signal conversion circuit included in the abnormality detection device according to the present embodiment. FIG. [Figure 5] 3 is a diagram illustrating an example of signal conversion by a signal conversion circuit included in the abnormality detection device according to the present embodiment. FIG. [Figure 6] FIG. 2 is a diagram illustrating an example of the functional configuration of a PLC included in the abnormality detection device according to the present embodiment. [Figure 7]10A and 10B are diagrams showing an example of measurement results of pulse widths in a PLC included in the abnormality detection device according to the present embodiment. [Figure 8] 10A and 10B are diagrams showing an example of measurement results of a pulse width ratio in a PLC included in the abnormality detection device according to the present embodiment. [Figure 9] 7, this is a diagram showing an example of the measurement result of the pulse width in the PLC included in the abnormality detection device. [Figure 10] 8, this is a diagram showing an example of the measurement result of the pulse width ratio in the PLC included in the abnormality detection device. [Figure 11] 10 is a diagram illustrating a method for calculating a weighted moving average in a PLC included in the abnormality detection device according to the present embodiment. FIG. [Figure 12] 10 is a diagram showing an example of a pulse width ratio calculated by a PLC included in the abnormality detection device according to the present embodiment. FIG. [Figure 13] 4A to 4C are diagrams illustrating voltage waveforms and abnormality determination when an abnormality occurs in the ozone generator according to the present embodiment. [Figure 14] 4 is a flowchart showing a process performed by a PLC according to the present embodiment. [Figure 15] 3 is a diagram illustrating an example of signal conversion by a signal conversion circuit included in the abnormality detection device according to the present embodiment. FIG. [Figure 16] 2 is a diagram illustrating an example of a functional configuration of a signal conversion circuit included in the abnormality detection device according to the present embodiment. FIG. [Figure 17] 3 is a diagram illustrating an example of signal conversion by a signal conversion circuit included in the abnormality detection device according to the present embodiment. FIG. [Figure 18] 3 is a diagram illustrating a signal conversion circuit and abnormality determination included in the abnormality detection device according to the present embodiment. FIG. [Figure 19] 3 is a diagram illustrating a signal conversion circuit and abnormality determination included in the abnormality detection device according to the present embodiment. FIG. [Figure 20] 3 is a diagram illustrating a signal conversion circuit and abnormality determination included in the abnormality detection device according to the present embodiment. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, an example of an ozone generator and an abnormality detection device according to an embodiment of the present invention will be described with reference to the accompanying drawings.

[0009] First, an example of the schematic configuration of an ozone generator A and an abnormality detection device 6 according to this embodiment will be described with reference to Fig. 1 and Fig. 2. Fig. 1 is a diagram showing an example of the schematic configuration of an ozone generator A according to this embodiment. Fig. 2 is a diagram showing an example of the functional configuration of the abnormality detection device 6 and the like according to this embodiment.

[0010] Ozone generator A is an example of a single-tube ozone generator. It includes an ozone generator 1, a power supply 3, a fuse 4, and a high-voltage power supply 5. Ozone generator 1 incorporates a discharge tube 10, and generates ozone when an AC voltage that has been boosted by a transformer 32 and passed through a reactor 33 is applied to an electrode 11 of discharge tube 10. Specifically, ozone generator 1 includes the discharge tube 10, an electrode 11 attached to discharge tube 10, a metal electrode 12, and a spacer 13 for forming a discharge gap 14 between discharge tube 10 and electrode 11.

[0011] The power supply device 3 includes a power conversion device 31, a transformer 32, and a reactor 33. The power conversion device 31 converts an AC voltage (first AC voltage) input from a commercial power supply into an AC voltage (second AC voltage) of a preset frequency (predetermined frequency) and outputs the converted AC voltage.

[0012] The transformer 32 boosts the AC voltage output from the power conversion device 31 to a high voltage. The reactor 33 is connected between the ozone generator 1 and the transformer 32. The reactor 33 further boosts the AC voltage output from the transformer 32 and suppresses high-frequency noise generated by the switching operation of the power conversion device 31. The reactor 33 also suppresses high-frequency components that occur in the AC voltage applied to the transformer 32 due to abnormal discharge in the ozone generator 1, for example, arc discharge generated in a pinhole (e.g., about 1 mm in diameter) caused by damage to the discharge tube 10 built into the ozone generator 1.

[0013] In this way, the power supply 3 applies an AC voltage Vop to the electrode 11 of the discharge tube 10 via the fuse 4 and the high-voltage power supply 5. This causes a discharge in the source gas flowing into the discharge gap 14 between the electrode 11 and the metal electrode 12, and this discharge generates ozone (O3). The power supply 3 applies an AC voltage of a frequency less than 600 Hz, for example, to the electrode 11.

[0014] The discharge occurring in the discharge gap 14 is a so-called dielectric barrier discharge, and is also simply called a barrier discharge or a silent discharge. The source gas is oxygen, a mixed gas of oxygen and nitrogen, air, etc. The gas pressure of the source gas flowing into the discharge gap 14 is, for example, an absolute pressure of 0.17 to 0.28 MPa.

[0015] The discharge tube 10 is formed into a cylindrical shape from a dielectric material such as glass or ceramic, with one end open and the other end U-shaped, and has an electrode 11 with a conductive metal (e.g., stainless steel) vapor-deposited on its inner surface.

[0016] In this embodiment, the electrode 11 deposited on the inner surface of the discharge tube 10 is a cylindrical electrode, and a metal electrode 12 is provided across the dielectric discharge tube 10 and a discharge gap 14. The conductive electrode of the electrode 11 is connected to a high-voltage feeder 5.

[0017] The metal electrode 12 is a cylindrical electrode made of, for example, stainless steel, etc. Specifically, the metal electrode 12 is a cylindrical electrode coaxial with the electrode 11, and is provided on the outer peripheral surface side of the electrode 11 with a discharge gap 14 interposed therebetween.

[0018] Metal electrode 12 also has a plurality of spacers 13 for forming a discharge gap 14 between itself and electrode 11. Spacers 13 are protrusions that form discharge gap 14 of, for example, about 0.3 to 1.3 mm.

[0019] Furthermore, in ozone generator A, cooling water is supplied to the side of metal electrode 12 opposite to the side where electrode 11 is provided. This allows the heat generated by the dielectric barrier discharge in discharge gap 14 to be cooled by the cooling water, thereby suppressing a temperature rise in the source gas in discharge gap 14 and enabling the production of ozone at a high concentration and with a high yield. The ozone generated by ozone generator A is used for water treatment, such as deodorizing, decolorizing, and sterilizing the water to be treated.

[0020] The abnormality detection device 6 includes a signal conversion circuit 61 and a PLC (Programmable Logic Controller) 62. The signal conversion circuit 61 is a circuit that converts the waveform of the AC voltage Vop applied to the ozone generator 1 into a pulse signal. The PLC 62 (abnormality detection unit) recognizes changes in the pulse width of the pulse signal output from the signal conversion circuit 61, detects an abnormality in the ozone generator 1 based on the changes, and controls the power conversion device 31 to cut off the supply of power to the ozone generator 1 if an abnormality is detected.

[0021] Furthermore, for example, for three or more consecutive pulse signals, the PLC 62 generates information on the normal range of pulse widths by statistical processing using the pulse widths of the previous plurality of pulse signals, and if the pulse width of the latest pulse signal is not within the normal range, determines that there is an abnormality in the ozone generator 1. Furthermore, the PLC 62 generates information on the normal range by statistical processing using the pulse widths of the previous plurality of pulse signals, with a lower limit being a value obtained by multiplying a weighted moving average of the pulse widths of the previous plurality of pulse signals by a predetermined first coefficient less than 1, and an upper limit being a value obtained by multiplying the weighted moving average by a predetermined second coefficient greater than 1. This will be described in detail below.

[0022] 3 is a diagram showing an example of the functional configuration of the signal conversion circuit 61 included in the abnormality detection device 6 according to this embodiment. As shown in Fig. 3, the signal conversion circuit 61 includes a voltage dividing circuit 611, a low-pass filter 612, an amplifier 613, and a comparator 614 (signal conversion unit). Note that if high-frequency noise is not generated in the voltage dividing circuit 611, the low-pass filter 612 may be omitted.

[0023] There is provided a plurality of comparators 614. Here, three comparators 614A, 614B, and 614C are provided.

[0024] The voltage divider circuit 611 converts the AC voltage that has been boosted to a high voltage by the transformer 32 and input via the reactor 33 into a low voltage. Specifically, the voltage divider circuit 611 converts the high AC voltage Vop (for example, about 10 kV) that is applied to the ozone generator 1 into a voltage level (for example, about 5 V) that can be processed by electronic circuits such as a low-pass filter 612, an amplifier 613, and a comparator 614.

[0025] The low-pass filter 612 attenuates high-frequency noise components contained in the output voltage Vb from the voltage dividing circuit 611, and prevents malfunction of the comparator 614 (described later) due to chattering caused by high-frequency noise.

[0026] The amplifier 613 amplifies the AC signal (AC voltage) that has passed through the low-pass filter 612 by a predetermined amplification factor, and outputs an AC signal Vo.

[0027] The comparator 614 converts the AC signal (AC voltage) that has passed through the low-pass filter 612 into a pulse signal and outputs it. Specifically, the operation is as follows: The comparator 614 compares the voltage level of the input AC signal Vo with the comparison voltage of the comparator 614, and switches the output level depending on which is larger. Note that, for example, a comparator with hysteresis characteristics (hysteresis comparator) is used as the comparator 614. By using a hysteresis comparator, it is possible to set comparison voltages separately for the rising and falling edges of the input AC signal Vo, thereby preventing malfunctions caused by chattering that occurs at the rising and falling edges due to noise superimposed on the AC signal Vo.

[0028] The three comparators 614 are set so that the comparison voltages used when converting into pulse signals are different from one another, and the output pulse signals are different from one another.

[0029] The operation of the comparator 614 and the operation of the ozone generator 1 in normal and abnormal conditions will be described with reference to Fig. 4 and Fig. 5. Fig. 4 and Fig. 5 are diagrams showing an example of signal conversion by the signal conversion circuit 61 included in the abnormality detection device 6 according to this embodiment.

[0030] Waveform W1 in Figure 4(a) is the output signal Vo (AC signal) of amplifier 613 that is input to comparator 614 when ozone generator 1 is operating normally. Comparator 614A compares the output signal Vo with comparison voltages VthH_A and VthL_A set in comparator 614A and switches the output level. In Figure 4(a), when the signal level of output signal Vo becomes equal to or higher than comparison voltage VthH_A, comparator 614A switches output signal VcompA (Figure 4(b)) from low to high, and when the signal level of output signal Vo becomes equal to or lower than comparison voltage VthL_A, comparator 614A switches output signal VcompA from high to low.

[0031] By setting the voltage level difference between the comparison voltages VthH_A and VthL_A to be equal to or greater than the peak value of noise superimposed on the output signal Vo of the amplifier 613, it is possible to prevent malfunctions due to chattering caused by noise.

[0032] In the above example, the ozone generator 1 is operating normally, so there is no distortion in the waveform of the output signal Vo of the amplifier 613 in FIG. 4(a), and therefore the pulse widths (lengths of time that the pulse is at a High level: t11 to t12, t13 to t14, t15 to t16, t17 to t18) of the pulse signal VcompA in FIG. 4(b) are almost constant.

[0033] The same applies to the output signal VcompB from the comparator 614B and the output signal VcompC from the comparator 614C. Note that the comparison voltages VthH_C and VthL_C set in the comparator 614C are not shown in FIG.

[0034] In this way, the comparison voltages of the three comparators 614 are different, and therefore the pulse widths of the pulse signals of the output signals VcompA, VcompB, and VcompC are different.

[0035] Next, waveform W2 in Figure 5(a) is the output signal Vo actually measured when an arc discharge occurs at a microscopic hole in the discharge tube 10 built into the ozone generator 1. When an arc discharge occurs, the voltage level temporarily drops to near 0 V and then rises. Figure 5(b) shows the output signal VcompA compared with the comparison voltages VthH_A and VthL_A, which are the same as those in Figure 4(a) above. Because the arc discharge temporarily drops to 0 V and then causes pulse rises and falls as the voltage rises, the pulse widths (t21 to t22, t23 to t24, t25 to t26, t27 to t28) are non-uniform, unlike during normal operation in Figure 4(b).

[0036] The same applies to the output signal VcompB when compared with the comparison voltages VthH_B and VthL_B, and the output signal VcompC when compared with the comparison voltages VthH_C and VthL_C.

[0037] Next, we will explain how to detect abnormal operation of the ozone generator 1. Fig. 6 is a diagram showing an example of the functional configuration of the PLC 62 included in the abnormality detection device 6 according to this embodiment. The PLC 62 includes a pulse width detector 621, a pulse width measurer 622, a comparator 623, and a comparison pulse width calculator 624.

[0038] The pulse width detector 621 has a function of detecting the rising and falling edges of each pulse signal of the output signal Vcomp from the signal conversion circuit 61. There are as many output signals Vcomp as there are comparators 614, and pulse width detection is performed for each of them.

[0039] The pulse width measuring device 622 calculates the time of each pulse width from the difference between the rise time and fall time detected by the pulse width detector 621. The results of actual pulse width measurements are shown in FIGS.

[0040] 7 and 9 are diagrams showing examples of the measurement results of the pulse width in the PLC 62 of the abnormality detection device 6 according to this embodiment. Fig. 7 shows the case of steady operation in which a constant amount of power is supplied to the ozone generator 1, and Fig. 9 shows the case of the start of operation in which power is transiently supplied to the ozone generator 1.

[0041] The comparison pulse width calculator 624 has a function of calculating a comparison time using the time of each pulse width up to the previous time in order to compare with the latest pulse width. One example of a method for calculating the comparison time is a weighted moving average. FIG. 11 is a diagram showing a method for calculating a weighted moving average in the PLC 62 of the abnormality detection device 6 according to this embodiment. As shown in FIG. 11, the time of the latest pulse width is t0, the time of the pulse width one pulse before is t1, ..., the time of the pulse width n pulses before is t2. n n is an integer equal to or greater than 1. The time t^ of the pulse width obtained by taking the weighted moving average of the time of n pulse widths is expressed by the following equation (1).

[0042]

number

[0043] However, m k is the time t of the kth previous pulse width k represents the weighting coefficient for all m k When m k When = 1 / n, t^ represents an unweighted moving average.

[0044] The pulse width ratio y is calculated by taking the ratio between the time t0 of the most recent pulse width and the time t^ of the n pulse widths obtained by the weighted moving average, and then calculating y=t0 / t^ for each pulse detection. The graphs obtained at this time are shown in Figures 8 and 10.

[0045] 8 and 10 are diagrams showing examples of measurement results of the pulse width ratio in the PLC 62 of the abnormality detection device 6 according to this embodiment.

[0046] Figure 8 corresponds to Figure 7 and was calculated for steady-state operation with a constant amount of power supplied to the ozone generator 1. Figure 10 corresponds to Figure 9 and was calculated for a case where power is transiently supplied to the ozone generator 1. In the case of Figure 8, where a constant amount of power is supplied to the ozone generator 1, the ratio has an average of 1 and spreads with a certain variance. On the other hand, in the case of Figure 10, where power is transiently supplied to the ozone generator 1, the amount of change is large immediately after starting to measure the pulse width and gradually approaches a state similar to when a constant amount of power is supplied to the ozone generator 1. From the above, when determining whether the ozone generator 1 is normal, if it is determined to be normal when power is transiently supplied to the ozone generator 1, it can be considered to be determined to be normal at all times.

[0047] FIG. 12 is a diagram showing an example of a pulse width ratio calculated by the PLC 62 of the anomaly detection device 6 according to this embodiment. When the ratio is calculated between the time t0 of the latest pulse width and the time t^ of three pulse widths calculated as a moving average, there is one maximum y (=t0 / t^) in the transient stage of the pulse width change. FIG. 12 shows the maximum y obtained after eight tests. The average μ was approximately 0.884, and the standard deviation σ was approximately 0.0272, so the values ​​were dispersed. For the maximum y to fall within 3σ, the following formula (2) must be satisfied. μ‐3σ<(t0 / t^)<μ+3σ ···Equation (2)

[0048] Similarly, when the pulse width decreases (for example, when the ozone generator 1 stops applying voltage), equation (3) is obtained. μ‐3σ<(t0 / t^)<1+{1‐(μ‐3σ)} Formula (3)

[0049] Furthermore, when the values ​​in FIG. 12 are substituted into equation (3), the following equation (4) is obtained (the word "approximately" is omitted). 0.802<(t0 / t^)<1.20...Equation (4)

[0050] From the above, the following processing is performed. First, the comparison pulse width calculator 624 calculates t^. Then, the comparator 623 determines whether the following formula (5) (the normal range of the pulse width) is satisfied. 0.802 (example of the first coefficient) × t^ < t0 < 1.20 (example of the second coefficient) × t^ ··· Formula (5)

[0051] That is, the comparator 623 uses the pulse width time t0 output from the pulse width measuring device 622 and t^ calculated by the comparison pulse width calculator 624 to determine whether the formula (5) is satisfied. When it is satisfied, it is determined as normal, and when it is not satisfied, it is determined as abnormal. In this method, since it only multiplies the weighted moving average by a coefficient and compares it with t0, the calculation load is reduced and high-speed operation is enabled.

[0052] If a plurality of comparators 614 are prepared and connected to the pulse width detector 621, the pulse width is detected as many times as the number of connections. As a result, for each, the pulse width is measured and the comparison for determining whether it is normal or abnormal is performed.

[0053] The voltage waveform at the time of abnormality of the ozone generator 1 is shown in FIG. 13. FIG. 13 is a diagram for explaining the voltage waveform and abnormality determination at the time of abnormality of the ozone generator 1 according to the present embodiment. The applied voltage to the ozone generator 1 is shown in FIG. 13(a), and the output signal from the signal conversion circuit 61 input to the PLC 62 is shown in FIG. 13(b). In the region where the time is negative, the ozone generator 1 is operating normally. An abnormality has occurred in the ozone generator 1 after time zero.

[0054] The comparison pulse width calculator 624 calculates t^ by a three-sample moving average. In that case, for the pulse widths (1) to (8), it is possible to compare from the pulse width (4) at the time when the data of the past three samples has been accumulated. In the table of FIG. 13(c), the No. corresponds to the pulse width numbers (1) to (8).

[0055] Here, reference is also made to Figure 14. Figure 14 is a flowchart showing the processing by the PLC 62 according to this embodiment. First, in step S1, the pulse width measuring device 622 measures the pulse width of each pulse signal.

[0056] Next, in step S2, the comparison pulse width calculator 624 calculates the moving average t^ of the pulse widths of the previous pulse signals using the method described above.

[0057] Next, in step S3, comparator 623 uses the time t0 and t^ of the pulse width to determine whether or not equation (5) is satisfied, and if Yes, ends the process, and if No, proceeds to step S4. In the case of Figure 13, pulse widths (4) to (6) satisfy equation (5) (i.e., are determined to be normal), but pulse width (7) does not satisfy equation (5) (i.e., are determined to be abnormal).

[0058] In step S4, the comparator 623 sends a stop signal to the power conversion device 31, and the power conversion device 31 cuts off the power supply to the ozone generator 1.

[0059] As described above, the abnormality detection device 6 according to this embodiment can accurately detect, with a simple configuration, damage to the discharge tube 10 that constitutes the ozone generator 1. In other words, an abnormality in the ozone generator 1 can be detected without an input power detection unit that detects the input power input to the power conversion device 31 or an output current detection unit that detects the output current output from the power conversion device 31, and this prevents the circuit configuration of the device that detects an abnormality in the ozone generator 1 from becoming complicated and expensive.

[0060] Furthermore, as described above, the PLC 62 generates information on the normal range of the pulse width as shown in equation (5) and compares the pulse width of the latest pulse signal with the normal range, thereby simplifying the processing.

[0061] Furthermore, for example, if the ozone generator 1 is small, even if an arc discharge occurs during an abnormality, the overcurrent (arc current) may be small and may not blow the fuse 4. This is particularly effective in such cases.

[0062] 13 shows that it is possible to detect abnormal discharge when it occurs. However, for example, if the AC voltage Vop applied to the electrode 11 of the discharge tube 10 is lower than expected and becomes lower than the comparison voltage of the comparator 614, a pulse signal may not be generated and abnormal discharge may not be detected. Also, for example, if the AC voltage Vop does not fall below the comparison voltage of the comparator 614 when abnormal discharge occurs and the voltage recovers, no change appears in the pulse signal and abnormal discharge may not be detected.

[0063] FIG. 15 shows a case where the AC voltage Vop applied to the electrode 11 of the discharge tube 10 has decreased. The comparison voltages of the comparators 614A, 614B, and 614C are different. Among the three, comparator 614A (comparator A), which has the lowest comparison voltage, and comparator 614B (comparator B), which has the middle comparison voltage, output pulse signals. However, unless the AC voltage Vop exceeds the comparison voltage of comparator 614C (comparator C), comparator 614C does not output a pulse signal. Whether an abnormal discharge is occurring is determined based on the output signals of comparators 614A and 614B, which are outputting pulse signals. As such, because the AC voltage Vop changes depending on the operating conditions, a low comparison voltage for the comparators may be desirable.

[0064] In the following, Vop refers to the maximum AC voltage. The comparison voltage of the comparator 614 is determined based on two voltage indices: the discharge start voltage Vd of the ozone generator 1 and the maximum AC voltage Vop in design. Because abnormal discharge does not occur below the discharge start voltage Vd, there is no need to set a comparison voltage. Therefore, as shown in Figure 16, the comparison voltage is set so that multiple comparators 614 can operate from the discharge start voltage Vd to the maximum AC voltage Vop in design. When three comparators 614 are installed, the comparison voltages should be set as follows, for example:

[0065] Comparison voltage of comparator 614A = Vd Comparison voltage of comparator 614B = Vop / 3 + 2Vd / 3 Comparison voltage of comparator 614C = 2Vop / 3 + Vd / 3

[0066] According to this, the comparison voltages of the three comparators 614 are set in a well-balanced manner based on the trisection points between the discharge start voltage Vd and the design maximum voltage Vop. Although a detailed explanation is omitted here, for each comparison voltage, a comparison voltage VthH at the rising edge and a comparison voltage VthL at the falling edge are set.

[0067] On the other hand, Figure 17 shows a case where the voltage drop does not reach zero even after an abnormal discharge occurs. The comparison voltages of comparators 614A, 614B, and 614C are different. Until the abnormal discharge occurs on the right side of Figure 17, all comparators 614A, 614B, and 614C stably output pulse signals. When an abnormal discharge occurs, the AC voltage temporarily drops but quickly recovers. When multiple discharge tubes 10 are installed, the capacitor discharge phenomenon may supply charge to the abnormal discharge, making it difficult for the voltage to drop. In this case, comparators 614B and 614C confirm that the pulse width shortens, but because the AC voltage does not drop to zero, comparator 614A does not see the pulse width shorten and cannot determine that an abnormal discharge has occurred. As such, since the AC voltage Vop may not drop to zero even after an abnormal discharge occurs, a higher comparison voltage for the comparators may be desirable.

[0068] As can be seen from the above, because the AC voltage changes when the output of the ozone generator 1 is changed, it is desirable to install multiple comparators 614. Furthermore, inputting all of the output signals Vcomp of the multiple comparators 614 to the PLC 62 and determining whether or not there is abnormal discharge using comparator 623 increases the risk of PLC 62 malfunctioning due to noise originating from the ozone generator 1 or noise originating from the power supply for the ozone generator 1. For this reason, a conceivable method is to use, among the comparators 614 outputting pulse signals, only the comparator 614 with the highest comparison voltage, for example, to determine whether or not there is abnormal discharge using comparator 623.

[0069] Below, three methods will be described for determining which of the multiple comparators 614 should be operated to detect an abnormality. In the first method, if any one of the multiple comparators 614 detects an abnormality, the PLC 62 determines that an abnormality has occurred and shuts down the power supply. This method is shown in Figure 18. Figure 18 shows a case where an abnormality is determined based on a pulse signal from comparator 614B. This method simplifies the logical configuration of the PLC 62, operates the fastest of the three methods, and can give top priority to power supply protection.

[0070] The second method is to use only the comparator 614 with the highest comparison voltage VthH among the comparators 614 that detect the pulse width for abnormality detection. This method is shown in Fig. 19. Fig. 19 shows a case where abnormality detection is performed based only on the pulse signal from comparator 614B. With this method, there is always only one comparator 614 that detects abnormalities, so there is the lowest possibility that an abnormality will be determined to be due to a malfunction caused by noise.

[0071] The third method is to select the comparator 614 with the highest comparison voltage VthH and the comparator 614 with the next highest comparison voltage VthH from among the comparators 614 detecting the pulse width, and use them for abnormality detection. This method is shown in Figure 20. Figure 20 shows a case where abnormality detection is performed based on pulse signals from comparators 614B and 614C. When the output voltage Vcomp is approximately equal to the comparison voltage VthH at which the comparator 614 begins to operate, the comparator 614 may or may not operate within the range of voltage error with each cycle.

[0072] Therefore, when the comparator 614 (comparator 614B) with the highest comparison voltage VthH among the multiple comparators 614 in operation is equal to or greater than a certain pulse width (pulse width B≧threshold B), the comparator 614 (comparator 614B) with the highest comparison voltage VthH is selected. Also, when the comparator 614 (comparator 614B) with the highest comparison voltage VthH among the multiple comparators 614 in operation is less than a certain pulse width (pulse width B<threshold B), the comparator 614 (comparator 614A) with the next highest comparison voltage VthH is selected. This method can reduce the risk of falsely detecting an abnormality based on whether or not the comparator 614 is operating when the output voltage Vcomp is near the comparison voltage VthH.

[0073] Although an embodiment of the present invention has been described above, this embodiment is presented as an example and is not intended to limit the scope of the invention. This novel embodiment can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. This embodiment is included within the scope and spirit of the invention, and is also included in the invention described in the claims and their equivalents.

[0074] For example, in the above-described embodiment, the pulse width of the pulse signal is the time length during which the pulse is at a high level, but this is not limiting, and the pulse width of the pulse signal may be the time length during which the pulse is at a low level, for example. [Explanation of symbols]

[0075] 1...Ozone generator, 3...Power supply device, 4...Fuse, 5...High-voltage power supply, 6...Abnormality detection device, 10...Discharge tube, 11...Electrode, 12...Metal electrode, 13...Spacer, 14...Discharge gap, 31...Power conversion device, 32...Transformer, 33...Reactor, 61...Signal conversion circuit, 62...PLC, 611...Voltage divider circuit, 612...Low-pass filter, 613...Amplifier, 614...Comparator, 621...Pulse width detector, 622...Pulse width meter, 623...Comparator, 624...Comparative pulse width calculator, A...Ozone generator

Claims

1. An abnormality detection device used for an ozone generator including: a power conversion device that converts an input first AC voltage into a preset second AC voltage and outputs the second AC voltage; a transformer that boosts the AC voltage output from the power conversion device to a high voltage; and an ozone generator that has a built-in discharge tube and generates ozone by applying the AC voltage boosted by the transformer to the discharge tube, a voltage divider circuit that converts the AC voltage boosted to a high voltage by the transformer into a low voltage; two or more signal conversion units that convert the AC voltage that has passed through the voltage dividing circuit into a pulse signal and output the pulse signal, and that use different comparison voltages when converting the AC voltage into the pulse signal; an abnormality detection unit that detects an abnormality in the ozone generator based on a change in the pulse width of the pulse signal output from at least one of the two or more signal conversion units; An abnormality detection device comprising:

2. 2. The abnormality detection device according to claim 1, wherein the abnormality detection unit generates information on a normal range of pulse widths for three or more consecutive pulse signals by statistical processing using pulse widths of the pulse signals up to a previous time, and determines that the ozone generator has an abnormality when the pulse width of the latest pulse signal is not within the normal range.

3. 3. The abnormality detection device according to claim 2, wherein the abnormality detection unit generates the information on the normal range by performing statistical processing using pulse widths of the plurality of pulse signals up to a previous time, with a lower limit being a value obtained by multiplying a weighted moving average of the pulse widths of the plurality of pulse signals up to a previous time by a predetermined first coefficient that is less than 1, and an upper limit being a value obtained by multiplying the weighted moving average by a predetermined second coefficient that is greater than 1.

4. 2. The abnormality detection device according to claim 1, wherein the abnormality detection unit controls the power conversion device to cut off the supply of power to the ozone generator when an abnormality is detected.

5. a power conversion device that outputs an AC voltage; an ozone generator that generates ozone when AC power output from the power conversion device is applied; a detection device for detecting an abnormality in the ozone generator, The detection device includes: generating at least two pulse signals by comparing the AC voltage output by the power conversion device with at least two reference voltages; The ozone generator detects an abnormality in the ozone generator based on a change in the pulse width of each of the at least two pulse signals generated.

6. 6. The ozone generator according to claim 5, wherein the detection device generates information about a normal range of pulse widths for three or more consecutive pulse signals by statistical processing using pulse widths of the pulse signals up to the last pulse width, and determines that there is an abnormality in the ozone generator if the pulse width of the latest pulse signal is not within the normal range.

7. 7. The ozone generator according to claim 6, wherein the detection device generates the information about the normal range by performing statistical processing using pulse widths of the previous plurality of pulse signals, with a lower limit being a value obtained by multiplying a weighted moving average of the pulse widths of the previous plurality of pulse signals by a predetermined first coefficient that is less than 1, and an upper limit being a value obtained by multiplying the weighted moving average by a predetermined second coefficient that is greater than 1.

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