JPH04331422A - Lag reactive power compensator - Google Patents

Abstract

PURPOSE:To realize a lag reactive power compensator having high performance and a low cost by effectively combining a capacitor type and an active filter type. CONSTITUTION:A capacitor unit 3 in which capacitors are formed to be able to be connected or disconnected at a group capacity unit, and an active filter unit 4 having at least the same capacity as the group capacity, are connected in parallel with a load 2. A control regulator 7 detects a lag reactive power and a harmonic current and a harmonic capacity from outputs of a voltage transformer 5 and a current transformer 6, and sends a control command signal to the units 3 and 4. Thus, a reactive power control having a high responding speed substantially equal to that of an active filter type is performed, and an effect of suppressing a harmonic wave is also provided. A price rise when compared with a capacitor type is small.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a delayed phase reactive power compensator for improving the power factor of a power distribution system.

0002

2. Description of the Related Art A capacitor device has been most widely used as a power factor correction system, that is, a slow phase reactive power compensator. The power factor is improved by compensating for the lagging reactive power of the load using the leading phase reactive power of the capacitor. Also, as a relatively recently developed product, for example, Mitsubishi Electric Technical Report Vol. 56, NO6, 1982, P455
There is an active filter device disclosed in . this is,
The inverter outputs a current that offsets the slow phase reactive current of the load to improve the power factor.

In the former method, a reactor with a capacity of 6% of the capacitor is usually inserted in series to prevent resonance with the fifth harmonic, which is relatively abundant in the system. In addition, for devices exceeding a certain capacity, a method is adopted in which the load is divided into multiple groups in consideration of fluctuations in the delayed phase reactive power of the load, and the number of groups to be applied is adjusted according to changes in the capacity to be compensated. The latter is
For example, a voltage source inverter under PWM control can be used to output a current with an arbitrary waveform, and it is also possible to compensate not only for lagging reactive power but also for advancing reactive power and harmonic current.

0004

[Problems to be Solved by the Invention] As mentioned above, conventional power factor correction methods include the capacitor method and the active filter method, but the former is generally relatively simple in configuration and inexpensive. , maintenance is also easy. On the other hand, (1
) It is necessary to take measures against the inrush current that occurs when the capacitor is turned on. (2) Power factor control becomes discontinuous step-like, and in order to reduce the step, a small-capacity multi-group configuration is required, increasing the price and making maintenance complicated. (3) It has drawbacks such as being unable to cope with sudden load changes.

[0005] Furthermore, the latter active filter method is
It is possible to control the power factor to always maintain it at 1.0 even in response to sudden load fluctuations, and it is also possible to compensate for harmonic components. However, in order to take advantage of these advantages, it is necessary to have a capacity that can sufficiently compensate for the maximum value of delayed phase reactive power and harmonic components that may occur, and this method is generally expensive per unit capacity. However, the disadvantage is that the entire device is extremely expensive.

[0006] Therefore, a method of using both methods in combination is envisaged, but simply combining them will not effectively eliminate the drawbacks of both methods, nor will their advantages be effectively utilized. This invention has been made to solve the above-mentioned problems, and it is an object of the present invention to obtain a delayed phase reactive power compensator that can effectively combine a capacitor method and an active filter method and effectively utilize their advantages. With the goal.

[0007]

[Means for Solving the Problems] A lagging phase reactive power compensator according to the present invention includes a capacitor device comprising a plurality of groups of capacitors having predetermined group capacitances and configured to be able to turn on and off in units of the group capacitances; An active filter device having the same capacitance as the group capacitance is connected in parallel with the load.

[0008]

[Operation]Then, the number of input groups of the capacitor device is set so that the difference between the delayed phase reactive power to be compensated for in the load and the input capacity of the capacitor device is minimized, and the active filter device performs the compensation as described above. In addition to compensating the reactive power of the difference between the delayed phase reactive power to be output and the input capacity of the capacitor device, harmonics of the load are compensated within the range of the difference between the capacitance of the active filter device and the compensating capacity of the differential reactive power. Compensate ingredients.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing a delayed phase reactive power compensator according to an embodiment of the present invention. In the figure, 1 is a system power supply, 2 is a load connected to this system power supply 1, and 3 is a capacitor device connected in parallel with the load 2, which is composed of multiple groups each having a predetermined group capacity K. Group, switch 3
1. It is composed of a series reactor 32 and a capacitor 33. 4 is an active filter device,
For example, it is composed of a DC voltage source, a voltage source inverter using switching elements such as power transistors, and an output transformer, which are well known as described above, so detailed explanation will be omitted. And its capacity A is K
It is set to a predetermined value within the range of ≦A≦2·K. 5 is a voltage transformer, 6 is a current transformer, 7 is a voltage transformer 5 and a current transformer 6
This is a control adjustment device that detects slow phase reactive power, harmonic current, and harmonic capacitance from the output of and sends a control command signal to capacitor device 3 and active filter device 4.

Next, the operation will be explained with reference to the flowchart shown in FIG. This flowchart shows the content of processing that is repeated at regular time intervals within the control adjustment device 7. First, lagging reactive power, harmonic current, and harmonic capacity are detected from the outputs of voltage transformer 5 and current transformer 6 (steps S1 and S2). Next, the number N of input groups of the capacitor device 3 is set based on the following formula (step S3). −0.5<Q/K−N≦0.5 In other words, the number of groups N is set such that the difference between the value of the delayed phase reactive power to be compensated and the value of the input capacitance of the capacitor device 3 is minimum. This is the translation. Based on this, each switch 31 of the capacitor device 3 is operated to open and close. Then, the active filter device 4 supplements the deficiency or excess of the compensation capacity.
Fix it. Therefore, the compensation capacity Q1 for this supplement etc.
is calculated by the following formula (step S4). Q1 = |Q-K・N|

Next, the harmonic compensation capacitance Q2 that the active filter device 4 has at this point is calculated using the following formula (step S5). Q2=H When H≦A-Q1, Q2
=A-Q1 H>A-Q1 Finally, the harmonic compensation current Ih of the active filter device 4 is calculated from Q2 obtained above (step S6). Ih = I·Q2 /H Therefore, when H≦A−Q1, Ih = I, and the harmonic components are 100% compensated. Also, H>A-
When Q1, the maximum harmonic current compensation is obtained within the capability of the active filter device 4.

As described above, in this embodiment, most of the capacitance to be compensated is composed of relatively inexpensive capacitor devices, and the expensive active filter device has at least the capacity of one group of capacitor devices. Therefore, the price increase compared to when the entire device is constructed using a capacitor type can be kept to a small level. In addition, continuous control that follows the slow phase reactive power that changes moment by moment in the load is possible, and the power factor can always be kept at 1. In this respect, it has the same performance as the case where the entire device is constructed using an active filter method, which is extremely expensive. Furthermore, of the capacity of the active filter device 4, the remaining capacity used for compensating for reactive power is used for compensating for harmonics, so the utilization rate of the active filter device 4 is improved and the power factor is improved. In addition, harmonics can be suppressed.

Note that the capacity A of the active filter device 4
It is sufficient to have the value of the capacitance K for one group of the capacitor device 3, but it is desirable to set it slightly larger than the value of K in order to smoothly control the opening and closing of the switch 31 of the capacitor device 3. Furthermore, the larger the capacity, the greater the harmonic suppression effect. However, in order to control reactive power, the capacity does not need to be more than twice K.

[0014]

[Effects of the Invention] Since the present invention is constructed as described above, the advantages of the capacitor method and the active filter method are effectively utilized, making it possible to continuously control reactive power at a relatively low cost and suppressing harmonics. It's also effective.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing a lagging reactive power compensator according to an embodiment of the present invention.

FIG. 2 is a flowchart illustrating the operation of the embodiment of FIG. 1;

[Explanation of symbols]

2 Load 3 Capacitor device 4 Active filter device 7 Control adjustment device K group capacity Q lagging reactive power I Harmonic current H Harmonic capacity

Claims (1)

[Claims] 1. A capacitor device comprising a plurality of groups of capacitors having predetermined group capacitances and configured to be able to be turned on and off in units of the group capacitances, and an active filter device having at least the same capacitance as the group capacitances are connected in parallel with a load. The number of input groups of the capacitor device is set so that the difference between the delayed phase reactive power to be compensated for in the load and the input capacity of the capacitor device is minimized, and the active filter device While compensating for the reactive power of the difference between the delayed phase reactive power and the input capacity of the capacitor device, harmonic components of the load are compensated within the range of the difference between the capacitance of the active filter device and the compensating capacity of the differential reactive power. A lagging reactive power compensator designed to compensate.