Power supply device for ozone generator

Abstract

To provide a power supply device with which power supply to an ozone generator is stopped when a short circuit or ground fault occurs in wiring between the ozone generator and the power supply device.SOLUTION: A power supply device for an ozone generator comprises an ozone generator for generating ozone by applying AC power to a discharge member, wherein the device comprises a control part for controlling output power based on a power command value. The control part stops power supply to the ozone generator when detecting that an output voltage of the power supply device obtained from a voltmeter is equal to or lower than a voltage threshold preset according to the magnitude of the output voltage.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] An embodiment of the present invention relates to a power supply for an ozone generator. [Background technology]

[0002] In general, in an ozone generator, an ozone generator is connected to a high-voltage, high-frequency power supply. A discharge tube is inserted in the ozone generator, and ozone is generated by supplying a high-voltage, high-frequency AC voltage to the discharge tube. When an abnormality occurs in this discharge tube, causing a short circuit or a ground fault (hereinafter also referred to as "short circuit, etc."), the fuse attached to the discharge tube melts to cut off the current.

[0003] There is also a technology that monitors the output voltage and output current of the power supply device, and when the voltage is below a threshold and the current is above a threshold, it determines that a short circuit has occurred and cuts off the current. There is also a technology that cuts off the current by using a pre-installed overcurrent protection circuit when an abnormality occurs inside the power supply device, causing a short circuit, etc. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 3978902 [Patent Document 2] JP 2010-159178 A [Patent Document 3] Patent Publication No. 2021-46331 [Patent Document 4] International Publication No. 2019 / 229865 Summary of the Invention [Problem to be solved by the invention]

[0005] In the above conventional technology, when an abnormality occurs inside the ozone generator or the power supply device, the current can be cut off. However, when a short circuit or the like occurs in the wiring connecting the ozone generator and the power supply device, the short circuit or the like cannot be detected by the fuse or the overcurrent protection circuit of the power supply device, and the current cannot be cut off. One of the reasons for this is that the ozone generator is a capacitive load because it generates ozone by dielectric barrier discharge, and a reactor is placed in the power supply device to improve the power factor.

[0006] Specifically, if a short circuit or the like occurs in the wiring between the ozone generator and the power supply, no current is passed to the ozone generator, and the power factor of the power supply deteriorates, so that the current output by the power supply when a short circuit or the like occurs is reduced compared to the current when the ozone generator is in normal operation. Therefore, a short circuit or the like protection circuit that detects a sudden increase in current cannot detect a short circuit or the like. In addition, the above-mentioned technology for determining a short circuit is a method for detecting when a short circuit or the like occurs inside the ozone generator, and is not suitable for detecting a short circuit or the like in the wiring connecting the ozone generator and the power supply.

[0007] If a short circuit or the like occurs in the wiring between the ozone generator and the power supply device, it is necessary to stop the supply of power to the ozone generator. However, if the occurrence of a short circuit or the like in the wiring cannot be detected, it is naturally impossible to stop the supply of power to the ozone generator.

[0008] Therefore, the present invention has been made in consideration of the above-mentioned circumstances, and an object of the present invention is to provide a power supply device for an ozone generator that is capable of stopping the supply of power to the ozone generator when a short circuit or a ground fault occurs in the wiring between the ozone generator and the power supply device. [Means for solving the problem]

[0009] The power supply device for an ozone generator of an embodiment is a power supply device for an ozone generator that includes an ozone generator that generates ozone by applying AC power to a discharge member, and includes a control unit that controls output power based on a power command value, and when the control unit detects that the output voltage of the power supply device obtained from a voltmeter is equal to or lower than a voltage threshold that is preset according to the magnitude of the output voltage, it stops supplying power to the ozone generator. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram showing an example of a schematic configuration of an ozone generator according to the present embodiment. [Diagram 2] FIG. 2 is a diagram showing an example of a circuit diagram of the ozone generator and the power supply device of this embodiment. [Diagram 3] FIG. 3 is a diagram showing an example of a circuit diagram of the ozone generator and the power supply device of this embodiment. [Figure 4] FIG. 4 is a diagram showing an example of a voltage and current waveform output by the power supply device of this embodiment. [Diagram 5] FIG. 5 is a diagram showing a flow for determining the output power in this embodiment. [Figure 6] FIG. 6 is a diagram showing the correlation between the voltage and current output by the power supply device of this embodiment and the power command value (output level). [Figure 7] FIG. 7 is a diagram showing a flow of detection of a short circuit or the like in this embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, the power supply device for the ozone generator of this embodiment will be described with reference to the accompanying drawings. FIG. 1 is a diagram showing an example of a schematic configuration of an ozone generator 1000 of this embodiment. The ozone generator 1000 of this embodiment is a dielectric barrier type ozone generator. In FIG. 1, the y-axis is an axis along the central axis of an airtight container 14 described later. The x-axis is an axis perpendicular to the y-axis and extends from the back to the front of the paper. The z-axis is an axis perpendicular to the y-axis and the x-axis.

[0012] 1, the ozone generator 1000 includes an ozone generator 11, which is the main body of the device, an AC power source 12, a fuse 18, a power supply device 20, etc. The ozone generator 11 includes an airtight container 14, a dielectric electrode 15 (discharge member), a metal electrode 16, etc.

[0013] The airtight container 14 is a cylindrical container. Specifically, the airtight container 14 is a cylindrical container having a central axis along the y-axis direction. The airtight container 14 accommodates a dielectric electrode 15 and a metal electrode 16 therein. A gas inlet 141, a gas outlet 142, a cooling water inlet 143, and a cooling water outlet 144 are formed on the outer periphery of the airtight container 14.

[0014] A raw material gas containing oxygen is supplied to the airtight container 14 from the outside through the gas inlet 141. The raw material gas pressure, which is the pressure of the raw material gas, is preferably 0.1 to 0.3 MPa (megapascals). The airtight container 14 discharges unreacted raw material gas and ozone to the outside through the gas outlet 142. Cooling water is introduced into the airtight container 14 through the cooling water inlet 143. The airtight container 14 discharges the cooling water to the outside through the cooling water outlet 144.

[0015] The dielectric electrode 15 is provided inside the airtight container 14. The dielectric electrode 15 has a dielectric portion 151, a conductive film 152, and a high voltage supply terminal 153. The dielectric portion 151 contains a dielectric material and is formed in a cylindrical shape having a central axis along the y-axis direction. The central axis of the dielectric portion 151 is parallel (including approximately parallel) to the central axis of the airtight container 14. The high voltage supply terminal 153 is provided inside the conductive film 152 and is electrically connected to the conductive film 152.

[0016] The metal electrode 16 includes a conductive material. The metal electrode 16 is provided inside the airtight container 14 and outside the dielectric electrode 15. The metal electrode 16 is grounded and has a ground potential. The metal electrode 16 also has a spacer 161. The spacer 161 protrudes from a part of the metal electrode 16 toward the dielectric electrode 15 to form (maintain) a discharge gap 17 between the metal electrode 16 and the dielectric electrode 15.

[0017] In addition, a water channel 162 into which cooling water flows is formed between the metal electrode 16 and the inner circumferential surface of the airtight container 14. The water channel 162 is connected to a cooling water inlet 143 and a cooling water outlet 144 of the airtight container 14. Therefore, the cooling water flowing in from the cooling water inlet 143 passes through the water channel 162 and is discharged from the cooling water outlet 144.

[0018] The AC power supply 12 is electrically connected to the high voltage supply terminal 153 via the fuse 18 and the power supply device 20. The AC power supply 12 applies a voltage to the dielectric electrode 15 (conductive film 152) via the power supply device 20, the fuse 18, and the high voltage supply terminal 153. This generates a discharge in the raw material gas flowing into the discharge gap 17, and the discharge generates ozone. The cooling water supply unit 13 is, for example, a pump. The cooling water supply unit 13 supplies cooling water from a cooling water inlet 143 of the airtight container 14.

[0019] Next, an example of a circuit diagram of the ozone generator 11 and the power supply device 20 of this embodiment will be described with reference to Fig. 2. Fig. 2 is a diagram showing an example of a circuit diagram of the ozone generator 11 and the power supply device 20 of this embodiment.

[0020] The power supply device 20 converts AC power supplied from the AC power supply 12 into AC power of a preset voltage, and applies the voltage of the AC power to the dielectric electrode 15. In this embodiment, the power supply device 20 has an input reactor 21, a VVVF inverter (Variable Voltage Variable Frequency) 22, a zero-phase reactor 23, a resistor 24, a transformer 25, an output reactor 26, a voltmeter 27, an ammeter 28, and a control device 40, as shown in FIG.

[0021] The input reactor 21 is connected between the AC power supply 12 and the VVVF inverter 22 , and suppresses harmonics contained in the AC power output from the VVVF inverter 22 .

[0022] The VVVF inverter 22 converts the input DC power into AC power and outputs it. For example, the VVVF inverter 22 turns on and off a switching element by PWM control to convert the DC power into AC power and output it. In this embodiment, the VVVF inverter 22 has a converter that converts the AC power supplied from the AC power source 12 into DC power. The VVVF inverter 22 converts the DC power output from the converter into AC power by PWM control. Thereafter, the VVVF inverter 22 applies the voltage of the AC power to the dielectric electrode 15 of the ozone generator 11.

[0023] The zero-phase-sequence reactor 23 is a reactor that cancels out the zero-phase-sequence current of the carrier frequency component that flows through the wiring that connects the VVVF inverter 22 and the high voltage supply terminal 153.

[0024] Resistor 24 prevents a current from flowing to the zero phase of VVVF inverter 22, thereby preventing a short circuit in transformer 25. If there is no possibility of a short circuit, resistor 24 is not necessary.

[0025] The transformer 25 boosts the AC voltage output from the VVVF inverter 22. Specifically, for example, the transformer 25 is connected between the VVVF inverter 22 and the dielectric electrode 15, and boosts the voltage of the AC power output from the VVVF inverter 22 to a preset voltage (for example, 2000V, 4000V).

[0026] The output reactor 26 is an example of a reactor that reduces an inrush current flowing through the ozone generator 11. Specifically, for example, the output reactor 26 is connected in series to the dielectric electrode 15, and reduces an inrush current flowing through the dielectric electrode 15 when the switching element is switched from off to on by PWM control in the VVVF inverter 22.

[0027] Voltmeter 27 measures the output voltage of power supply device 20. Note that voltmeter 27 may measure the AC voltage by stepping it down via a transformer. For example, when the output side of output reactor 26 is several kV, if a transformer that steps it down to 1 / 100 is used, the voltage measured by voltmeter 27 will be several tens of volts, and can be measured with a low-voltage voltmeter. Also, other than the method of stepping down the voltage via a transformer, the voltage may be step-down by capacitive voltage division using a capacitor or resistive voltage division using a resistor.

[0028] The ammeter 28 measures the output current of the power supply device 20. In Fig. 2, the ammeter 28 is attached to the low-voltage wiring on the output side of the power supply device 20. Note that the location of the ammeter 28 is not limited to the location shown in Fig. 2, and may be located elsewhere, for example, between the output reactor 26 and the fuse 18.

[0029] The equivalent circuit of the ozone generator 11 can be represented by a capacitor 29, a capacitor 30, and a Zener diode 31. The capacitor 29 represents the dielectric portion 151 in an equivalent circuit. The capacitor 30 represents the discharge gap 17 in an equivalent circuit. When a high voltage is applied to the discharge gap 17, a barrier discharge occurs in the gas. The Zener diode 31 represents the discharge maintenance voltage of this barrier discharge. The Zener diode is an element that does not allow current to flow up to a voltage that is a threshold (variable, for example, about 1000 V), but allows infinite current to flow above the threshold voltage.

[0030] The ozone generator 11 is a capacitive load because it can be represented by an equivalent circuit using capacitors 29 and 30 and a Zener diode 31. For the ozone generator 11, which is a capacitive load, the power supply device 20 is provided with an output reactor 26, which has the effect of increasing the power factor of the power supply device 20.

[0031] The control device 40 includes a current detection unit 41, a voltage detection unit 42, a storage unit 43, a threshold calculation unit 44, a control unit 45, and a short circuit signal output unit 46. The operation of the control device 40 will be described.

[0032] The current detection unit 41 is connected to the ammeter 28 and detects the output current of the power supply device 20. The voltage detection unit 42 is connected to the voltmeter 27 and detects the output voltage of the power supply device 20.

[0033] The control unit 45 executes various controls. For example, the control unit 45 controls the output power of the power supply device 20 based on a power command value acquired from the storage unit 43. The control unit 45 also acquires an output current (value) from the current detection unit 41 and an output voltage (value) from the voltage detection unit 42. The threshold calculation unit 44 calculates thresholds (current threshold, voltage threshold) for detecting a short circuit, etc., based on the output current, output voltage, and power command value.

[0034] The control unit 45 judges the presence or absence of a short circuit, etc., based on the output current, the output voltage, and thresholds (current threshold, voltage threshold). For example, when the control unit 45 detects that the output voltage is equal to or lower than a voltage threshold that is preset according to the magnitude of the output voltage, the control unit 45 sends an instruction to the short circuit signal output unit 46 to stop the supply of power to the ozone generator 11.

[0035] Also, for example, when the control unit 45 detects that the output current is equal to or lower than a current threshold value that is preset according to the magnitude of the output current, the control unit 45 sends an instruction to the short-circuit signal output unit 46 to stop the supply of power to the ozone generator 11.

[0036] The short-circuit signal output unit 46 sends a gate signal to the gate of a switching element such as an IGBT (Insulated Gate Bipolar Transistor) of the inverter element of the VVVF inverter 22, and stops (cuts off) the power supply to the ozone generator 11.

[0037] 3 is a diagram showing an example of a circuit diagram of the ozone generator 11 and the power supply device 20 of this embodiment. In FIG. 3, a ground fault occurs in the wiring between the output reactor 26 and the fuse 18.

[0038] Examples of when a ground fault occurs include when an arc discharge occurs from the wiring to the ground, when the wiring directly contacts the ground, etc. In Fig. 3, an arc discharge 32 occurs on the output side of the output reactor 26 and is connected to the ground.

[0039] Due to the arc discharge 32, the potential between the output reactor 26 and the fuse 18 becomes the sum of the voltage across the ground resistance and the voltage of the arc discharge, and the voltage becomes much lower than before the occurrence of the arc discharge 32. Therefore, a current flows toward the arc discharge 32 not only from the power supply device 20 but also from the capacitor included in the ozone generator 11. Then, since no power is supplied to the ozone generator 11 after the occurrence of the arc discharge 32, the current flowing from the ozone generator 11 to the arc discharge 32 decreases over time.

[0040] 4 is a diagram showing an example of voltage and current waveforms output by the power supply device 20 of the present embodiment. In FIG. 4, a voltage and current waveform is shown when a ground fault occurs in the wiring between the output reactor 26 and the fuse 18.

[0041] In (a) to (c), the horizontal axis is time. The vertical axis of (a) is the output voltage (value) of the power supply device 20. The vertical axis of (b) is the output current (value) of the power supply device 20. The vertical axis of (c) is the current (value) of the arc discharge 32.

[0042] Assume that a ground fault occurs at time t1. As shown in (c), immediately after the ground fault occurs, the current increases instantaneously due to arc discharge 32, but then the current decreases exponentially in a short period of time. However, as shown in (b), the current of power supply device 20 continues to flow even after the ground fault occurs. This is because the current cannot be interrupted because arc discharge 32 continues to occur.

[0043] If a short circuit or the like occurs in the ozone generator 11, the current can be cut off by the fuse 18. If a short circuit or the like occurs in the power supply device 20, the overcurrent protection circuit can detect it and cut off the current. However, in the case of a ground fault shown in Figures 3 and 4, the current cannot be cut off by using the fuse 18 or an overcurrent protection circuit (not shown).

[0044] When multiple dielectric electrodes 15 are inserted in the ozone generator 11, a fuse 18 is attached to each of the dielectric electrodes 15. However, in the case of the ground fault in Fig. 3, the current flowing through the fuse 18 is not an overcurrent strong enough to melt the fuse, and so the current cannot be cut off. In addition, in the current waveform of the power supply device 20 shown in Fig. 4(b), the current decreases after the occurrence of a ground fault, so that the overcurrent protection circuit cannot detect a short circuit, etc.

[0045] Therefore, as described above, the control unit 45 detects a short circuit or the like using the output voltage (value) and output current (value) of the power supply device 20. The method for detecting a short circuit or the like will be described again with reference to Fig. 5. Fig. 5 is a diagram showing a flow for determining the output power in this embodiment.

[0046] The control unit 45 (power supply device 20) compares the output power of the power supply device 20 with the power command value as shown in FIG. 5, and controls the output power so that the output power approaches the power command value. The output voltage and output current of the power supply device 20 can be obtained by solving the electric circuit in FIG. 2 for each power command value. The output voltage and output current obtained for each power command value are shown in FIG. 6. FIG. 6 is a diagram showing the correlation between the voltage and current output by the power supply device 20 of this embodiment and the power command value (output level). In (a), discretely arranged triangular marks indicate the correlation between the output voltage and the power command value (output level). Also, in (b), discretely arranged square marks indicate the correlation between the output current and the power command value (output level).

[0047] In both (a) and (b), when the power command value is near 0%, there is a sudden change, but when it is about 5% or more, there is an almost linear correlation between the output voltage and the output current. When a short circuit or the like occurs, the output voltage and the output current decrease to nearly 0V and 0A, respectively, relative to the power command value.

[0048] Therefore, when focusing on voltage, the voltage threshold is set to a value lower than the calculated value for the power command value. In FIG. 6(a), the voltage threshold is determined by a linear function (a line sloping upwards to the right) for the power command value. Similarly, when focusing on current, the current threshold is determined by a linear function (a line sloping upwards to the right) for the power command value. The reason why each threshold (voltage threshold, current threshold) is not set to near 0V or 0A is that there may be a partial ground fault before the occurrence of an arc discharge, as well as a complete ground fault that generates an arc discharge 32. In this partial ground fault, the voltage and current may decrease by several tens of percent. Therefore, each threshold is set for each power command value.

[0049] Fig. 7 is a diagram showing a flow of detection of a short circuit or the like in this embodiment. The series of processes shown in Fig. 7 is executed, for example, every several tens of milliseconds, but the processing cycle is not limited to this. When detecting a short circuit or the like by voltage, the voltage is detected by the voltage detection unit 42 using the voltmeter 27. Then, the voltage comparison unit 47 (control unit 45) compares the detected voltage with a voltage threshold, and detects a short circuit or the like when the detected voltage falls below the voltage threshold.

[0050] Furthermore, when detecting a short circuit or the like by a current, the current is detected by the current detection unit 41 using the ammeter 28. Then, the current comparison unit 48 (control unit 45) compares the detected current with a current threshold, and detects a short circuit or the like when the detected current falls below the current threshold.

[0051] 7 shows a case where short circuit detection is performed for both voltage and current, and if a short circuit or the like is detected in only one of them, the short circuit is detected by the calculation unit 49 (control unit 45). However, this is not limited to this, and a short circuit or the like may be detected in only one of the voltage and current.

[0052] In this way, according to the power supply device 20 for the ozone generator 1000 of this embodiment, by comparing the output voltage and output current of the power supply device 20 with threshold values, it is possible to detect a short circuit, etc., and stop the supply of power to the ozone generator 11.

[0053] Although an embodiment of the present invention has been described, this embodiment is presented as an example and is not intended to limit the scope of the invention. This novel embodiment can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. This embodiment and its modifications are included in the scope and spirit of the invention, and are included in the invention and its equivalents described in the claims.

[0054] For example, the voltmeter 27 and the ammeter 28 may be installed outside the power supply device 20, rather than inside the power supply device 20. In addition to the configuration shown in Fig. 1, the ozone generator 11 may use flat-plate structures as the dielectric electrode and metal electrode housed in an airtight container, and may be arranged such that the dielectric electrode and the metal electrode are overlapped to form a discharge gap, as disclosed in, for example, International Publication No. 2016-067382 and International Publication No. 2000-032514. [Explanation of symbols]

[0055] 11... ozone generator, 12... AC power source, 14... airtight container, 15... dielectric electrode, 16... metal electrode, 17... discharge gap, 20... power supply device, 21... input reactor, 22... VVVF inverter, 23... zero-phase reactor, 24... resistor, 25... transformer, 26... output reactor, 40... control device, 41... current detection unit, 42... voltage detection unit, 43... memory unit, 44... threshold calculation unit, 45... control unit, 46... short-circuit signal output unit, 47... voltage comparison unit, 48... current comparison unit, 49... calculation unit, 1000... ozone generator

Claims

1. A power supply device for an ozone generator including an ozone generator that generates ozone by applying AC power to a discharge member, a control unit that controls an output power based on a power command value; The control unit is A power supply device for an ozone generator that stops supplying power to the ozone generator when it is detected that an output voltage of the power supply device obtained from a voltmeter is equal to or lower than a voltage threshold that is preset in accordance with the magnitude of the output voltage.

2. A power supply device for an ozone generator including an ozone generator that generates ozone by applying AC power to a discharge member, a control unit that controls an output power based on a power command value; The control unit is A power supply device for an ozone generator that stops supplying power to the ozone generator when it is detected that an output current of the power supply device obtained from an ammeter is equal to or lower than a current threshold that is preset in accordance with the magnitude of the output current.

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