JPS6093537A - Compensating device for reactive power and higher harmonic current - Google Patents

Abstract

PURPOSE:To compensate sufficiently a higher harmonic current which is generated varying complicatedly by providing a higher harmonic current compensating circuit at a point where the current of an arc furnace and the current of a reactive power compensating circuit are made confluent. CONSTITUTION:The reactive power generated by the arc furnace 80 is compensated by a reactive power compensating circuit 70 and the active power of the furnace 70 and the higher harmonic current generated by the circuit 70 flow through a line 6. This current is detected by a current detector 501 and led to a current generator 510. The detected current is inputted to a current higher harmonic detecting circuit in the generator 510 and the basic wave component is removed to extract only the higher harmonic current component, which is inverted in only phase by 180 deg. through a phase inverter and outputted as a current command. The current indicated by this command, i.e. compensated current is returned to a point 5 through a line 550 and mixed with the current flowing through the line 6. The higher harmonic current component is therefore canceled and only the active current component of the furnace 80 flows through a line 4.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a reactive power and harmonic current compensator, which compensates for reactive power fluctuations and harmonic current generation from an AC power system via an AC bus bar. The present invention relates to a reactive power/harmonic current compensation device for effective reactive power compensation and harmonic current compensation in a power supply system.

[Technical background of the invention and its problems] In recent years, large-capacity arc furnace equipment has come to be connected to an AC power system and operated. As is well known, arc furnaces generate reactive power on the power supply side that fluctuates rapidly depending on the state of the molten material in the furnace, and harmonic current that changes in a complex manner on the power supply side as the electrode discharge phenomenon changes. let These sudden changes 4
Incoming reactive power reduces the utilization rate of power supply equipment and causes flickering in lighting equipment, while harmonic current distorts the voltage waveform of the AC power supply system and adversely affects other equipment. Therefore, when installing a large-capacity arc furnace, etc.,
It is necessary to install a reactive power compensator and a filter for absorbing high % wave current in parallel with the equipment,
The power supply system will be as shown in (assuming a three-phase AC power system).

That is, in the same figure, 8o is a loaded arc furnace, and a melted material 83 such as iron is placed in the furnace 82, and an electrode 8 is placed in the furnace 82.
A current of 1U to 81W is applied by discharging to heat and melt. 7° reactive power compensation circuit, arc furnace 80
Leading reactive power equivalent to the lagging reactive power generated by is supplied, and the operating power factor when looking at the load from the power supply system is approximately 1:
This is a device that adjusts the Usually, the reactive power compensation circuit 70 includes phase advance capacitors 74U to 74W and reactor 7.
It is composed of thyristors 2U to 72W and anti-parallel connected thyristors 73U to 73W, but the thyristors 73U to
By adjusting the conduction angle of 73W in relation to the magnitude of the reactive power of the arc furnace 80, the current of the reactors 72U to 72W is controlled, and in combination with the action of the phase advance capacitors 74U to 74W, the generated reactive power of the arc furnace 80 is controlled. An amount of leading reactive power equal to (lag) is generated on lines 71U to 71W.

Therefore, at the three-phase bus lines 6U to 6W, there is no reactive power and only the active power of the load flows.

This is a resonant filter consisting of a 50-meter reactor and a capacitor, which absorbs especially harmful harmonic components of the harmonic current generated by the arc furnace 80, and prevents the harmful harmonic current from flowing toward the three-phase bus 4U to 4W. This is a fixed filter circuit that prevents this from occurring. 3U to 3W are system impedances existing in the three-phase AC power system. 01 is a power supply source such as the three-phase AC power system or a power transmission/distribution bus.

In the power supply system configured in this way, the reactive power generated by the arc furnace 80 is compensated by the reactive power compensation circuit 70, and the harmonic current is absorbed by the filter 50, so that the line 4U
Only the active power consumed by the arc furnace 80 flows through the ~4W and AC power supply system 1, which is effective in making effective use of the power supply equipment, reducing flicker, and preventing troubles caused by harmonic currents. Aaru. However, in reality, this system has the following problems. That is, the harmonic current generated by the arc furnace 80 does not have a single frequency component but changes in a complex manner, and the reactive power compensation circuit 70 itself also changes in a complex manner due to the switching action of the thyristors 73U to 73W. This is to generate harmonic current. As is well known, a reactor is a passive element,
Since the resonant fixed filter 50 made of a capacitor exhibits an absorption effect only on harmonic current of a certain specific frequency,
This type of fixed filter 50 cannot be expected to be very effective against harmonic currents that change in a complicated manner. In fact, a large amount of harmonic current flows into the AC power supply system 4U to 4W, causing voltage waveform distortion and adversely affecting other devices.

As described above, it has been found that although the conventional power supply system having the configuration shown in FIG. 1 can sufficiently obtain a reactive power compensation effect, it cannot sufficiently cope with complexly changing harmonic currents. However, this system configuration has the advantage that the main circuit is relatively simple and the cost is low.

Next, FIG. 2 shows an example in which reactive power compensation and harmonic current compensation are performed at the same time. In addition, in the following explanation, 701. . Yugaagawayu, Eya, 3. Well, we will deal with it using the K-1 diagram. Also, among the symbols on the diagram, the remaining numerical symbols after removing U, V, and W (Alphabella) are assumed to represent the same element. In other words, 600 is a Japanese patent, JP-A-56-1599.
The fault current compensator described in No. 36 is composed of a controlled rectifier 601, 602, a DC reactor 603, and a phase advance capacitor 604 connected in series, and compensates for the reactive power and harmonic current generated by the arc furnace 80. Compensation is performed at the same time in one circuit, and only active power is allowed to flow to the main circuit 4. Focusing on the harmonic current compensation effect, this device should be able to deal with the harmonic current that changes in the detection line generated by the arc furnace in principle, but as a practical matter, this device can In order to compensate for high harmonic current components, the control rectifier in the main circuit must be made multi-phase, which complicates the control circuit, leading to problems such as increased main circuit loss and increased main circuit cost. It tends to become unrealistic as a system.

As is clear from the above explanation, when compensating for reactive power and harmonic current of an arc furnace, etc. using the configuration method shown in Figure 1 or Figure 2, the practical problem is that the compensation effect of reactive power is However, there is a problem in compensating for harmonic current that it is not possible to adequately compensate for high frequency components in response to harmonic current that changes in a complex manner. In recent years, there has been a strong push to improve the quality of power in AC power systems, and for that purpose,
There is a strong need for a low-cost, effective reactive power/harmonic current compensator that can cope with arbitrary fault currents.

[Object of the Invention] The present invention has been made in view of the problems of the prior art described above, and its purpose is to compensate for harmonic current in a device that compensates for reactive power and harmonic current generated by a load such as an arc furnace. A harmonic current compensation circuit that actively performs compensation is provided to provide sufficient compensation for harmonic currents that occur with complex fluctuations. An object of the present invention is to provide a 1i JH wave current compensator.

[Summary of the Invention] In order to achieve the above object, the present invention provides a device for compensating for the reactive power and harmonic current of an AC power supply system that supplies power to a load that generates reactive power and harmonic current. A reactive power compensation circuit that compensates for the reactive power is connected to an AC bus that connects the grid and the load, and the harmonic current is actively transmitted to the AC bus through which the current of the reactive power compensation circuit and the current of the load are combined. This is a reactive power/multiple harmonic current compensator that is connected to a harmonic current compensation circuit that compensates for the current, and is capable of sufficiently compensating for harmonic currents that occur while fluctuating in a complicated manner.

[Embodiment of the Invention] FIG. 3 shows an embodiment of the reactive power and harmonic current compensating device according to the present invention. Elements with the same symbols as those in FIG. 1 of the conventional example described above have the same functions, and their explanations will be omitted here.

In Figure 3, the AC power supply system l and the load 8 such as an arc furnace
When a reactive power compensation circuit 7o is installed from the AC power supply system 1 of the power supply bus connecting the power supply line 0, the composite value of the current of the arc furnace 8° and the current of the reactive power compensation circuit 7o flows to line 6, but this composite value Harmonic current compensation port #650 where current flows
Set 0. The combination of the reactive power compensation circuit 7o and the harmonic current compensation circuit 500 configured in this manner is referred to as a reactive power and harmonic current compensation device 1000. In the same figure, 5o1 is a current detector (detects three phases) and the load 8
A current value that is a combination of the current of o and the current of the reactive power compensation circuit 70 is detected. A voltage detector 502 (detects three phases) detects the voltage of the line 6. These extracts, the current emitted,
A voltage is introduced into a current generator 510. Current generator 51
0 will be described later. The harmonic current compensation circuit 500 actively acts to generate a compensation current that is exactly 180° different in phase and has the same amplitude as the harmonic current component contained in the current detected by the current detector 501. is generated on line 550. When the circuit is installed in this manner, the harmonic current flowing in line 6 and the compensation current flowing in line 550 are combined at point 5 and cancel each other out, so that no harmonic current flows in line 4'.

Next, an example of the current generator 510 will be explained with reference to FIG.

Reference numerals 503 and 504 are detection signal lines for current detection and voltage detection, which are introduced into the current harmonic detection circuit 511. Here, the fundamental wave component of the current is removed from the detected current value, and
It functions to extract only the harmonic component of current LII'U -LH'w (assuming three-phase alternating current). 515 is a phase inverter, and the harmonic current AHU − detected by the above-mentioned 511 is
bm'w (7) Invert each phase by 180' and output as harmonic current command Ll (UR-LHwi.52
0 is the main circuit, harmonic current command = uUR - AHWR
The current indicated by, that is, the harmonic compensation current LHU −LH
Generate W. The current Lmu -Luw is the current flowing into point 5 through line 550 in FIG. 3 above.

Returning to the main circuit 520 in FIG. 4, 533-535 are current detectors which detect harmonic compensation currents LHU-LHW and output detection signals LHUP-LHWF. This signal Anup~↓HWF is fed back to the comparators 521~523, where it is compared with the command AHUR-Li+wn, and a voltage command pH13B-IPR is generated. 580 is a power amplifying section, and an example of its circuit will be explained with reference to FIG. This power amplifying section 580 uses voltage command VHUR-? Generates the output voltage "HU -" MW specified by HWR. In the detailed diagram of the power amplifying section 580 in FIG. 5, 581 is a DC power supply, 582 is a three-phase inverter composed of, for example, a gate turn-off thyristor, and 583 is a three-phase inverter 58.
2 gate control circuit, and the voltage command ?2 as explained in Fig. 4 above. HUR-”HWR is input, and the corresponding output voltage tHU-?HW is the output 5 of the three-phase inverter 582.
This is a circuit that performs gate control so that the signal occurs between 30 and 532.

When the main circuit 520 is configured in this way, the current command LHU
With respect to R-LHWR, the harmonic compensation current LH is
υ~LHW occurs.

Returning to FIG. 3, the reactive power generated by the arc furnace 80 is compensated by the reactive power compensation circuit 70, and the line 6 shows the active power of the arc furnace, which is a load, the harmonic current generated by the arc furnace, and reactive power compensation. A harmonic current generated by the circuit 70 flows.

This current is detected by a current detector 501, and a current generator 5
Guided by 10. Turning to FIG. 4, the aforementioned detected current is input to a current harmonic detection circuit 511, in which the fundamental wave component is removed and only the harmonic current component is output from the signal LH'u-L.
It is extracted as u'w. Detected harmonic current bai
+ -Ln'W is when only the phase is 1 in the phase inverter 515.
800 and output as a harmonic current component AHUR-LHWR. The command LHUR-LHWR is the main circuit 52
0, but the main circuit 520 is LHt+R−Lnw
It outputs the current indicated by i, ie the compensation current LHU -LHW, which is returned to point 5 through line 550 of FIG. 3 and is combined with the current flowing through line 61 mentioned above. From this, it can be seen that the harmonic current component flowing through the line 6 and the output current of the current generator 510, that is, the harmonic compensation current, have the same amplitude and a phase difference of exactly 180°, so that these harmonic current components It can be understood that they cancel each other out, and therefore only the effective current component of the arc furnace load flows through the wire 4. [Effects of the Invention] As is clear from the above explanation, as shown in Fig. 3, the arc furnace 80, and a harmonic current compensation circuit 500 is installed at a point where the current of the arc furnace and the current of the reactive power compensation circuit are combined and flow. The device 1000 provides the following advantages. That is, (1) Even with a load that generates rapidly changing reactive power and complexly changing harmonic current, such as an arc furnace, only the active current component flows through the AC power source 1 or line 4, so the power supply equipment cannot be used. rate is increased, flicker is eliminated, and the harmful effects of harmonic currents on other equipment can be eliminated.

(2) In addition to the harmonic current generated by the arc furnace 800, the harmonic current generated by the reactive power compensation circuit 70 can also be compensated by the harmonic current compensation circuit 0 (8) Therefore, the reactive power compensation circuit 70 A circuit that generates a somewhat large harmonic current may be used, which expands the range of circuit selection and allows the adoption of low-cost circuits.

(4) Since the harmonic current compensation circuit only generates harmonic current excluding the fundamental wave component, the circuit capacity becomes small, and the constraints on manufacturing are reduced. Therefore, the range of circuit selection is expanded, and high-performance, low-cost circuits can be adopted. If the wave current (2) is sufficient, a compensation effect can be expected (=).

As mentioned above, the point is that a reactive power compensation circuit is installed near a load that generates a large amount of current, such as an arc furnace, and that the current of the load such as the arc furnace and the current of the reactive power compensation circuit flow together. (The configuration of the present invention with a harmonic current compensation circuit that uses two-phase dynamic The proposed reactive power harmonic current compensator H is of great significance because it is effective and effective in dealing with 26 solar disasters.

[Brief explanation of the drawing]

1 and 2 are diagrams showing a conventionally used reactive power compensation and harmonic current compensation device, and FIG. 3 is a diagram showing a reactive power and harmonic current compensation device according to an embodiment of the present invention. , FIG. 4 is a diagram showing a specific example of the current generator 510 in FIG. 3, and FIG. 5 is a diagram showing a specific example of the power amplifying section 580 in FIG. 4. l... AC power supply system 3... System impedance 5
0... Fixed filter 70... Reactive power compensation circuit 8
0... Arc! P5oo...Harmonic current compensation circuit 5
10... Current, current generator 511... Current harmonic detection circuit 515... Phase inversion circuit 520... Main circuit 582... Inverter circuit

Claims (1)

[Claims] A device for compensating the reactive power and harmonic current of an AC power supply system that supplies power to a load that generates reactive power and harmonic current (= a device that compensates for the reactive power and harmonic current in an AC bus connecting the AC power supply system and the load) A harmonic current compensation circuit that actively compensates for the harmonic current is connected to the AC bus through which the current of the reactive power compensation circuit and the current of the load are combined and flows. A reactive power and harmonic current compensator characterized by: