JP3279085B2 - Control method of power supply for electric precipitator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling a power supply of an electric precipitator operated by using high-frequency AC power output from an inverter as a power supply.

[0002]

2. Description of the Related Art Although not shown, a conventional electric precipitator insulates and boosts AC power of a commercial frequency with a transformer, converts the AC power into high-voltage DC power with a rectifier, and converts this into high-voltage DC power. By applying a voltage between the discharge electrode and the dust collection electrode, the dust contained in the gas (combustion gas generated when burning coal or heavy oil) passing between the two electrodes is removed. ,
Since the nature of the dust contained in the generated gas differs depending on the type of fuel and the place of production, in order to improve the efficiency of dust removal, the DC high voltage applied between the electrodes must be appropriately controlled. For this purpose, the conventional circuit has taken measures such as changing the width of the pulse applied between the electrodes by controlling the phase of the alternating current of the commercial frequency, or thinning out the pulse to change the interval between the pulses. However, since a commercial frequency alternating current is used as a power source, such a measure cannot be taken even if the dust removal efficiency can be improved by shortening the pulse interval (ie, increasing the pulse frequency).
Further, even if an abnormal discharge such as a spark discharge occurs, even if an attempt is made to quickly suppress the abnormality, a delay of up to a half cycle (10 milliseconds in a 50 Hz region) occurs. That is, as long as the commercial frequency AC is used as a power source, there is a limit in control, and it has been difficult to maintain a high dust removal efficiency.

[0003] Therefore, an inverter device is used to generate AC power having a frequency higher than the commercial frequency, and this high-frequency AC power is boosted and rectified to obtain DC power having a high pulse frequency, and the operation of thinning out pulses from this is performed. If so, the control delay time described above can be significantly reduced.

[0004]

In order to operate the electrostatic precipitator efficiently, the electric field strength is always at a critical level without causing abnormal discharge such as spark discharge between the electrodes of the electric precipitator. It is desirable to do so. However, it is difficult to maintain the electrode-to-electrode voltage at the optimal critical electric field strength level only by performing pulse thinning operation with DC power obtained by rectifying AC power at a frequency higher than the commercial frequency. In the case where is changed, it takes a long time to reach the optimum operation state.

[0005] Therefore, an object of the present invention is to apply a DC power obtained by rectifying AC power having a frequency higher than the commercial frequency between the electrodes and always operate the electrostatic precipitator so that the voltage between the electrodes is always set to the electric field strength critical. Level to improve dust collection efficiency.

[0006]

In order to achieve the above object, a method of controlling a power supply for an electrostatic precipitator according to the present invention comprises a rectifier for converting input AC power into DC power and outputting the DC power to a DC intermediate circuit. An inverter unit for converting the DC power of the DC intermediate circuit into AC power having a frequency higher than the frequency of the input AC power is connected to a commercial power supply, and the AC power output from the inverter is transformed. In the power supply device for an electrostatic precipitator, the boosted AC power is converted into high-voltage DC power by a high-voltage rectifier, and the high-voltage DC power is applied between the electrodes of the electrostatic precipitator. When the electrostatic precipitator discharges abnormally during operation, the discharge current at this time and the inter-electrode voltage are detected, and the lowest voltage applied between the electrodes during the abnormal discharge and until the voltage is reduced to the lowest voltage Time and calculates a minimum voltage duration by controlling the frequency and pulse width of the AC voltage <br/> the DC intermediate circuit voltage and an inverter unit for the rectification section after completion of the minimum voltage duration output by output The voltage between the electrodes is returned to the electric field intensity critical level in the shortest time.

[0007]

According to the present invention, when the DC power obtained by rectifying the high-frequency AC power output from the inverter device is applied between the electrodes of the electrostatic precipitator and operated, the interelectrode voltage, the electrode current, and the inverter The DC intermediate circuit voltage can be adjusted by detecting the DC intermediate circuit voltage and current of the device and controlling the rectifier of the inverter device so that the voltage between the electrodes of the electrostatic precipitator maintains the electric field intensity critical level. In addition, the frequency and pulse width of the output AC power can be adjusted by controlling the inverter unit. Thus, the voltage between the electrodes of the electrostatic precipitator is always maintained at the electric field intensity critical level in the shortest time.

[0008]

FIG. 1 shows a power supply for an electric precipitator used in the present invention.
FIG. 2 is a circuit diagram of the device, showing an electric precipitator operated with high-voltage DC power obtained from high-frequency AC power. In the circuit of the first embodiment, the inverter device 4 includes a rectifier 41.
And an inverter unit 42 and a DC intermediate circuit connecting both of them. The commercial frequency AC power output from the AC power supply 2 is once converted into DC power by the rectifier 41 and then converted into high-frequency AC power by the inverter 42. The rectifier 41 and the inverter 42 By controlling, the voltage of the DC intermediate circuit and the inverter 42
Can be controlled to arbitrary values.

The AC power output from the inverter device 4 is insulated and boosted by the transformer 5, and then converted to high-voltage DC power by the high-voltage rectifier 6. DC high voltage, for example, as shown in FIG. 1, the transformer 5 has a plurality of secondary windings,
It is obtained by connecting the DC output side of the rectifier separately connected for each winding in series. The capacitors and resistors connected in parallel for each rectifier are for balancing the voltage sharing. The negative potential of the DC high voltage obtained in this manner is applied to the discharge electrode of the electrostatic precipitator 7, and the medium contained in the gas passing between the ground potential precipitator and the discharge electrode is discharged. Remove dust.

In the DC intermediate circuit connecting the rectifier 41 and the inverter 42, a DC intermediate circuit voltage detector 43 and a DC intermediate circuit current detector 44 are provided to detect the voltage and current of the circuit. , To the control device 8. Further, the inter-electrode voltage detector 73 and the electrode current detector 74 are
The electrode voltage and the electrode current are detected and supplied to the control device 8. The control device 8 detects from these input signals that an abnormal discharge state such as spark discharge has occurred, and reduces the inter-electrode voltage to eliminate the abnormal discharge state. The rectifier 41 and the inverter 42 are controlled so as to reach the level.

FIG. 2 is an operation waveform diagram of the present invention.
FIG. 2 shows a change in the DC voltage on the secondary side of the transformer 5 corresponding to the electric field intensity critical level, and FIG. 2 shows a change in the primary side voltage of the transformer 5 (output of the inverter unit 42). In the operation waveform diagram of FIG. 2, a period A is a period in which, when an abnormal discharge such as a spark discharge occurs between the electrodes, control is performed in accordance with the abnormal discharge. After terminating the abnormal discharge,
By changing the pulse width, the inter-electrode voltage is quickly raised to the electric field intensity critical level. The period B is a period during which the load is stable, and the pulse width and the pulse frequency maintain constant values. In the period C, when the load fluctuates, the control that follows the change is performed, and the height of the pulse output from the inverter unit 42 is changed by a change in the DC intermediate circuit voltage.

FIG. 3 is a waveform diagram of a transformer secondary voltage showing a first operation pattern for suppressing spark discharge. A dotted line indicates a critical field intensity level, and a solid line indicates a transformer secondary voltage. Represents. Time Δ at which electric field strength critical level decreases
T, a value Δ below the electrode-to-electrode voltage below the electric field intensity critical level
V, a time T for which the value of ΔV is continued is calculated from each detected value, and the rectifier 41 and the inverter 42 are controlled correspondingly.

FIG. 4 is a waveform diagram of a transformer secondary voltage showing a second operation pattern for suppressing spark discharge. A dotted line indicates a critical field intensity level, and a solid line indicates the transformer secondary voltage. Represents. FIG. 5 is a waveform diagram of the transformer secondary voltage showing the third operation pattern for suppressing the spark discharge, in which the dotted line indicates the electric field intensity critical level, and the solid line indicates the transformer secondary voltage. .

[0014]

According to the present invention, DC power obtained by boosting and rectifying high-frequency AC power output from an inverter device configured by combining a rectifying unit and an inverter unit is applied between electrodes to generate electric power. When operating the dust collector, if the abnormal discharge is detected by monitoring the voltage and current of the DC intermediate circuit connecting the rectifier and the inverter, and the electrode voltage and current of the electric dust collector, the rectification is performed. Since the voltage between the electrodes is always maintained at the critical level of the electric field intensity by controlling the section and the inverter section, an effect that the operation of always maintaining the highest dust collection efficiency can be obtained.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a power supply unit for an electrostatic precipitator used in the present invention.
Figure

FIG. 2 is a waveform chart showing an operation state of the present invention .

FIG. 3 is a waveform diagram of a transformer secondary voltage showing a first operation pattern for suppressing spark discharge.

FIG. 4 is a waveform diagram of a transformer secondary voltage showing a second operation pattern for suppressing spark discharge.

FIG. 5 is a waveform diagram of a transformer secondary voltage showing a third operation pattern for suppressing spark discharge.

[Explanation of symbols]

 2 AC power supply 4 Inverter device 5 Transformer 6 High voltage rectifier 7 Electric precipitator 8 Control device 41 Rectifier unit 42 Inverter unit 43 DC intermediate circuit voltage detector 44 DC intermediate circuit current detector 73 Inter-electrode voltage detector 74 Electrode current detection vessel

Claims (1)

(57) [Claims] A rectifying unit that converts input AC power into DC power and outputs the DC power to a DC intermediate circuit; and converts DC power of the DC intermediate circuit into AC power having a frequency higher than the frequency of the input AC power. An inverter device serving as an inverter unit is connected to a commercial power supply, AC power output from the inverter device is boosted by a transformer, and the boosted AC power is converted into high-voltage DC power by a high-voltage rectifier. In an electric precipitator power supply device in which DC power is applied between electrodes of an electric precipitator, when the electric precipitator abnormally discharges during operation, a discharge current and an inter-electrode voltage at this time are detected. Then, the minimum voltage applied between the electrodes during the abnormal discharge, the time until the voltage is reduced to the minimum voltage, and the minimum voltage duration are calculated, and the rectification unit outputs the voltage after the minimum voltage duration ends. Controlling the frequency and pulse width of the DC intermediate circuit voltage and the AC voltage output by the inverter unit to return the inter-electrode voltage to the electric field intensity critical level in the shortest time; Method.