JP3729616B2 - Active filter operation / control method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an active filter operation / control method applied to a distribution system, and more particularly to an active filter operation / control method capable of improving the influence of harmonic suppression characteristics due to system switching.
[0002]
[Prior art]
When an active filter is applied to a power distribution system, the following two methods are usually used.
(1) Voltage detection method A system voltage is detected and controlled according to a harmonic voltage included in the system voltage.
(2) Current detection method The system current is detected and controlled according to the harmonic current contained in the system current.
It is known that the active filter of the above (1) voltage detection system has a great effect when it is installed at the end of a system with a large harmonic voltage for the purpose of suppressing voltage distortion caused by the harmonic expansion of the system.
[0003]
On the other hand, the active filter of the current detection method of (2) is a harmonic current for the purpose of suppressing the harmonic current flowing into the phase advance capacitor in the system due to the harmonic current and voltage distortion generated in the system. It is known that it is more effective to install in the higher rank of the system where the
However, in an actual power distribution system, there are many opportunities to switch the system due to a load shift or a ground fault. In this case, for example, when a ground fault occurs at the upper level of the system, in order to avoid a power failure at the customer at the end of the system, the section switch at the ground fault point is disconnected and the section switch at the lower side of the system is turned on. Power is supplied from a healthy system to consumers connected to the power distribution system, and consumers at the end of the system may be connected to a higher rank. Similarly, a customer connected to the upper side of the system may be connected to the terminal side of the system.
[0004]
When applying the active filter to such a distribution system, if the voltage detection method of (1) is used, the voltage detection type active filter installed at the lower level has a small voltage distortion after switching the distribution line. It will be installed on the upper side and it will not be able to demonstrate the effect of suppressing harmonics.
In addition, when the current detection method of (2) above is used, the current detection type active filter installed in the upper part of the system is supplied with power from the lower system after switching the distribution line. Since it will be arranged at the end of a few systems, the effect of the active filter cannot be fully demonstrated.
[0005]
FIG. 3 shows a system configuration in a normal power flow mode when this type of conventional active filter is applied to the lower side of the system.
In the figure, 1 is a receiving point of a distribution substation, 2 is its transformer, 10a, 10b and 10c are lead wires in the substation. In the same figure, the case where electric power is supplied to the 1st distribution line from the leader line 10b to 11a-11c, and the electric power is supplied to 2 circuits of the 2nd distribution line from the leader line 10c to 12a-12g is shown.
31, 35 and 41, 47 installed at the main points of these distribution lines are division switches using vacuum switches or the like that disconnect or switch the distribution system at their respective points. With the back coating, the open state is shown without the back coating. The figure shows a state in which the section switch 35 is opened and all other switches are turned on. In this example, the voltage detection type active filter 50 is connected to the second distribution line 12f. .
[0006]
FIG. 4 is an enlarged view of a part of the distribution system where the active filter is installed at this time.
7a-7g is a branch point for supplying to each consumer, and many consumers are generally distributed and installed in the distribution line. In the figure, as an example, one customer is collectively shown above and below the installation point of the active filter 50. The active filter 50 is connected to the distribution line 12f at the branch point 7e, detects the current of the distribution line with the current transformer 6a, and detects the voltage of the distribution line with the instrument transformer 6b to control the active filter 50. It is taken in. In this figure, since the section switch 35 is open, the power at this point is supplied from the section switch 46 side, and the active filter 50 is connected to the end of the second distribution line.
[0007]
The power receiving facilities 90a and 90b of the customer are supplied with power from the branch points 7d and 7g via manual switches 48a and 48b. The power receiving facilities 90a and 90b of the customer are composed of phase-advancing capacitors 91a and 91b for power factor improvement and power receiving transformers 92a and 92b. After the voltage is stepped down to a required voltage by the power receiving transformers 92a and 92b, its secondary It is supplied to load equipment including electronic equipment that generates harmonics from the side.
[0008]
[Problems to be solved by the invention]
In the above distribution line system, when a ground fault occurs at a point 7h of the distribution line 12d in FIG. 5, the switch 35 is used to avoid a power failure at a customer connected to the lower side. A method is used in which the switches 44 and 45 are opened and electric power is supplied from the first distribution line to the distribution line below the ground fault point 7h. FIG. 5 is exactly the same as FIG. 3 except that the ground fault current generation location 14 at the time of the occurrence of the ground fault and the switching states of the switches 35, 44, and 45 are changed.
In this case, since the voltage detection type active filter 50 is connected to the upper side of the system having a low voltage distortion, the suppression target is changed and the suppression effect is also reduced.
[0009]
That is, in the normal power flow mode before the occurrence of the ground fault, the harmonic current is low on the lower side of the system 12f where the active filter is installed, but the voltage drop due to the harmonic current is added to the lower side of the system and the voltage is added. The distortion increases, and this harmonic voltage is suppressed by the active filter 50.
However, in the mode where the power flow after the occurrence of a ground fault is reversed, the voltage detection type active filter 50 is connected to the upper side of the system where the harmonic current of each part that is generated in the system is collected although the voltage distortion is low. Thus, the voltage detection type active filter cannot effectively suppress the harmonic current. That is, in this case, it is more effective to suppress the harmonic current using a current detection type active filter.
[0010]
As described above, in a distribution system where system switching is performed, the installation point of the active filter changes due to system switching. Conventionally, an active filter of current detection type or voltage detection type is connected to the system according to the purpose of suppressing harmonics. Therefore, there is a problem that it is impossible to cope with system switching, and it becomes impossible to effectively suppress harmonics after system switching.
The present invention has been made in view of the above-described circumstances, and the object of the present invention is that the active filter can be operated with an optimal detection method according to the system state, and the harmonics of the distribution system are used according to the purpose. It is an object to provide an active filter operation / control method that can be effectively suppressed.
[0011]
[Means for Solving the Problems]
As described above, the installation point of the active filter in the system changes before and after the system switching. Since the purpose of suppressing harmonics also changes at the upper and lower levels of the system, it is desirable to switch the method of detecting harmonics at the time of system switching and control with a detection signal corresponding to the installation point of the active filter.
Therefore, in the present invention, system voltage detection means for detecting system voltage, system current detection means for detecting system current, and power flow direction monitoring means are provided, and active filter connection is performed by the power flow direction monitoring means provided in the active filter. The power flow direction at the point is monitored, and the output of either the system voltage detection means or the system current detection means is selected according to the power flow direction to suppress the harmonic voltage or harmonic current of the system.
In the present invention, the harmonic voltage or harmonic current of the system is suppressed according to the flow direction as described above, so that the harmonics of the distribution system can be effectively suppressed even when the system is switched. be able to.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a diagram illustrating a main configuration inside an active filter according to an embodiment of the present invention and a manner of connection of the active filter to a power distribution system.
In the figure, an active filter 50 includes an active filter main circuit unit 55 connected to a connection point 7e of the distribution line 12f via a transformer 56. Based on the voltage detection signal or current detection signal, the output of the reverse phase that cancels the harmonics is generated to suppress the harmonics of the distribution system.
[0013]
The active filter 50 takes in the distribution line current detected by the instrument current transformer 6a, and converts the output of the instrument current transformer 6a into a voltage proportional to the current flowing through the distribution line by the current signal converter 51. Further, the distribution line voltage detected by the instrument transformer 6b is captured, and the voltage signal converter 52 converts the output of the instrument transformer 6b into a voltage signal having a signal level proportional to the distribution line voltage.
The voltage signal proportional to the distribution line current output from the current signal converter 51 or the voltage signal proportional to the distribution line voltage output from the voltage signal converter 52 is taken into the control circuit 54 via the sequence switching circuit 53. The control circuit 54 calculates a compensation command value to the active filter main circuit unit 55 based on the voltage signal proportional to the distribution line current or the voltage signal proportional to the distribution line voltage. As the active filter main circuit section 55 and the control circuit 54, for example, Japanese Patent Application No. 8-215504, edited by the Institute of Electrical Engineers of Japan, March 31, 1987 "Semiconductor Power Conversion Circuit" P223-P235 A well-known circuit described in the above can be used.
[0014]
The voltage signal detected by the instrument transformer 6b and the signal proportional to the distribution line current detected by the auxiliary current transformer 6c attached to the output line of the instrument current transformer 6a are sent to the power flow monitoring device 80. Entered.
As shown in FIG. 2, the power flow monitoring device 80 is composed of a power transducer 81 and a signal generator 82. The power transducer 81 calculates three-phase power from both the voltage signal and current signal detection signals. . In FIG. 2, for the sake of simplicity, a single-wire connection is shown. However, if three phases of voltage and current are detected, the calculated three-phase power becomes a direct current amount, and the direction of power flow can be determined based on the positive / negative.
That is, when the three-phase power calculated by the power transducer 81 outputs a signal that is proportional to the calculated power in the positive flow and negative in the reverse flow, the signal generator 82 receives a positive signal accordingly. When a negative signal is received from the H terminal, a power flow signal is sent to the sequence switching circuit 53 from the L terminal.
[0015]
The sequence switching circuit 53 includes relay exciting coils 531 and 532 and contact points 533 and 534 thereof.
When the current is positive, the exciting coil 532 side is excited by the signal received from the H terminal side of the signal generator 82, and the contact 534 makes up. That is, a voltage detection signal is given to the control circuit 54 at the time of a positive power flow, and the main circuit unit 55 configured by the inverter unit of the active filter 50 operates to suppress the harmonic voltage of the distribution system according to the voltage detection signal. To do.
Further, at the time of reverse power flow, the exciting coil 531 side is excited by the signal received from the L terminal side of the signal generator 82, and its contact 533 makes up. That is, during reverse power flow, a current detection signal is given to the control circuit 54, and the main circuit unit 55 including the inverter unit of the active filter 50 operates to suppress the harmonic current of the distribution system according to the current detection signal. To do.
[0016]
Next, the operation of the active filter of this embodiment at the time of system switching will be described with reference to FIG. As an example of the operation state at the time of system switching, this figure shows the system state when the power flow at the installation point of the active filter becomes the reverse power flow from the normal power flow due to the occurrence of a ground fault. In the figure, a case is shown in which a ground fault has occurred at a point 7h of the distribution line 12d that is substantially in the middle of the second distribution system.
When the above-mentioned ground fault occurs in the distribution system, as described above, this ground fault current is detected in the system, and the switches 44 and 45 are opened and the switch 35 is turned on at the same time. The load near the active filter connection point connected to the lower side shifts to the first distribution system side. As a result, the tidal direction is from the switch 35 toward the switch 45, resulting in a reverse tidal current that is opposite to the normal tidal current state.
[0017]
When the reverse power flow occurs as described above, the power flow signal calculated and output by the power transducer 81 of the power flow monitoring device 80 provided in the active filter 50 becomes negative, and the power flow signal is output from the L terminal side of the signal generator 82. Then, the excitation coil 531 side of the sequence switching circuit 53 is excited, and the contact 533 is made.
Therefore, the control circuit 54 of the active filter 50 operates to suppress the harmonic current flowing out from the distribution system according to the current of the distribution system detected by the current detector 6a.
Here, when the ground fault is released and the active filter 50 is connected to the lower side of the system, the power flow in the system also returns to the normal power flow, and the power flow signal calculated and output by the power flow monitoring device 80 is also inverted. The contact of the sequence switching circuit 53 is made on the voltage detection side on the 534 side. Therefore, the control circuit 54 of the active filter 50 operates in a desirable operating state of harmonic suppression so as to suppress voltage distortion of the distribution line according to the voltage of the distribution system detected by the voltage detector 6b.
[0018]
【The invention's effect】
As described above, in the present invention, the power flow at the active filter connection point is monitored, the detection signal is switched to the voltage detection signal or the current detection signal according to the power flow direction at the active filter connection point, and the harmonics of the system are switched. Since the wave is suppressed, the active filter can be operated with an optimum detection method according to the system state, and even if the system is switched, the harmonics of the distribution system can be effectively suppressed.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a configuration of an active filter according to an embodiment of the present invention and a manner of connection to a distribution system.
FIG. 2 is a diagram illustrating a configuration of a power flow monitoring device and a sequence switching circuit according to an embodiment of the present invention.
FIG. 3 is a diagram showing a system state in a normal power flow mode when an active filter is applied to the lower side of the system.
4 is an enlarged view of a power distribution system in the vicinity of an active filter installation point in FIG. 3;
FIG. 5 is a diagram showing a system state in a case where the power flow at the installation point of the active filter at the time of occurrence of a ground fault is a tidal current opposite to the normal tidal current state.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Receiving point of distribution substation 2 Distribution substation transformers 31-35 Division switch 41-47 Division switch 48a, 48b Manual switch 50 Active filter 51 Current signal converter 52 Voltage signal converter 53 Sequence switching circuit 531 , 532 Switching circuit excitation coil 533, 534 Switching circuit contact 54 Control circuit 55 Active filter main circuit part 56 Transformer 6a Current transformer 6b Instrument transformer 6c Auxiliary current transformer 7a-7g Branch point 7h Ground fault occurred Point 80 Power flow monitoring device 81 Power transducer 82 Signal generators 90a, 90b Power receiving equipment 91a, 91b Phase-advancing capacitors 92a, 92b Power receiving transformers 10a, 10b, 10c Lead lines 11a-11d in the substation First distribution Electric wires 12a to 12g Second distribution line

Claims (1)

An active filter operation / control method that is installed in a distribution system where system switching is performed and suppresses harmonics of the system,
The system voltage is detected by the system voltage detection means, the system current is detected by the system current detection means, the system voltage and the system current are taken into the active filter,
The power flow monitoring means provided in the active filter is used to monitor the power flow direction at the active filter connection point,
A method of operating / controlling an active filter, wherein the output of either the system voltage detection means or the system current detection means is selected according to a power flow direction, and the harmonic voltage or harmonic current of the system is suppressed and controlled. .

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