JP2000032666A - Running method of reactive power compensating apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To compensate for a large reactive power within a short period of time generated when a load apparatus stops the operation or changes the operation mode in order to reduce the reactive power to be leaked to the power supply by operating a reactive power compensating apparatus when an output of a reactive power detecting unit is larger than the first specified value or by stopping the operation of the compensating apparatus when an output is smaller than the second specified value. SOLUTION: An operation stop determining circuit 80a is provided to a reactive power compensating apparatus 4 to always monitor the reactive power. When the reactive power becomes large, a reactive power compensating apparatus 4 is immediately started and then stops when the reactive power becomes small. Moreover, an output of the operation stop determining circuit 80a changes the control constant of a control circuit 60 as required. Thereby, when the reactive power of a load apparatus is smaller, the reactive power compensating apparatus 4 stops to reduce the total loss of the load apparatus 3 and reactive power compensating apparatus 4. In addition, the reactive power of load apparatus 3 becomes large, operation of the reactive power compensating apparatus 4 is started immediately. Moreover, the time constant of the primary delay filter is changed to assure quick response for transitional change of reactive power.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reactive power compensator for compensating for a reactive current generated by a load device, and more particularly to a method of operating a reactive power compensator for controlling a transient reactive current to be compensated.

[0002]

2. Description of the Related Art The configuration of a conventional reactive power compensator is shown in FIG. In FIG. 5, 1 is a power supply, and 3 is a load device. In FIG. 5, a current transformer 2 for detecting a current to the load device 3 is provided between the power source 1 and the load device 3 to compensate for a reactive current taken by the load device 3 and to reduce a power factor for the power source 1. To increase the resistance, a reactive power compensator 4 is provided in parallel with the load device 3.

The reactive power compensator 4 includes a main circuit 50
And a control unit 60. The main circuit unit 50 includes a converter circuit 54, a capacitor 51, a reactor 52, and a current transformer 5 provided between the converter circuit 54 and the power supply 1.
3. It is composed of a DC capacitor 55 provided on the DC side of the converter circuit 54. The converter circuit 54 generates a current corresponding to the reactive current taken by the load device 3 and supplies it to the load device 3 in order to prevent the reactive current taken by the load device 3 from flowing out to the power supply 1. Capacitor 51 and reactor 5
The filter circuit constituted by 2 absorbs a ripple current and a ripple voltage generated by the switching operation of the converter circuit 54 and prevents the converter circuit 54 from flowing out to the power supply 1. The DC capacitor 55 is connected to a power supply 1 that occurs within one cycle or a short time of the power supply due to the reactive power generated by the converter circuit 54.
It is installed to absorb the transfer of electric power with. The main circuit unit 50 includes a transformer 5 as a charging circuit for initially charging the DC capacitor 55 when the apparatus is started.
6. A rectifier circuit 57 may be added.

The control section 60 comprises a reactive current detection section 61, a first-order lag filter circuit 62, a current command generation section 63, a current control section 64, and a gate generation section 65. The reactive current detector 61 detects a reactive current taken by the load device 3 from the current to the load device 3 detected by the current transformer 2. As a specific example, calculations as shown in the following equations (1), (2) and (3) are performed.

[0005]

(Equation 1)

The load current and the power supply voltage are subjected to three-phase / two-phase conversion according to equations (1) and (2), and active power and reactive power are calculated according to equation (3). Where, ir, i
s and it are three-phase load currents detected by the current transformer 3, vr and v
s and vt are power supply voltages. Iα, iβ, eα,
eβ is a three-phase load current ir, is, it, a power supply voltage vr,
This is a three-phase / two-phase conversion of vs, vt. p is instantaneous active power and q is instantaneous reactive power. In some cases, sine waves having the same phase as the power supply voltage are converted into three-phase / two-phase as eα and eβ. Instantaneous active power p and p described later
Although 0 is necessary for DC voltage control and the like, it is not the subject of this patent and is omitted in FIG.

The instantaneous reactive current q obtained here also contains a harmonic component. When only the reactive current is to be compensated by the reactive current compensator, the primary delay filter circuit 6
In step 2, only the DC component q0 of the instantaneous reactive power is extracted. As a result, harmonics are removed from the compensation target, and only the reactive current is compensated, so that the capacity of the converter circuit can be reduced. The first-order lag filter circuit 62 has, for example, a transfer function 1 /
It is indicated by (1 + Ts). In FIG. 5, p0 and q0 are DC components of the instantaneous active current and the instantaneous reactive current. As described above, p0 may be a constant value of zero if only the subject matter of the present patent is considered. The current command generator 63 is represented by the following equations (4) and (5).

[0008]

(Equation 2)

A current isα expressed as a two-phase expression for generating q0 from the DC component q0 of the instantaneous reactive power according to equation (4).
1, isβ1 is obtained, two-phase / three-phase conversion is performed according to the equation (5), and the three-phase current component is returned again. The current commands isu, isv, i
sw. The current command is sent to the current control circuit 64. In the current control circuit 64, the AC current of the converter circuit 54 detected by the current transformer 53 is converted into a current command isu, is
A gate signal that matches v and isw is generated and sent to the gate amplifier 65. The semiconductor element of the converter circuit 54 is controlled by the output of the gate circuit 65.

With the above configuration, even when reactive power is generated in the load device 3 and the power factor is low, the reactive power to the load device 3 is reduced by operating the reactive power compensator 4. The reactive current supplied from the reactive power compensator 4 and viewed from the power supply 1 is small and has a high power factor. Therefore, it is possible to reduce the size of the power supply equipment and save electricity costs.

[0011]

Some electric devices, such as an induction motor, require a short but large current at the time of starting or the like. Further, a large current may transiently occur when the operation mode is switched.
In the case of such a device, the capacity of a power transformer or a circuit breaker that can withstand a short-time current must be used, and the power capacity must be larger than that required in a steady state. The short-time large current as described above is often a reactive current like a starting current of an induction motor. Therefore, if the reactive power compensating device is provided, the above-mentioned transient reactive power can be compensated, so that the power supply only needs to have a capacity required in a steady state. However, if the reactive power compensating device is constantly operated, the loss of the reactive power compensating device always occurs, and wasteful power is consumed. In addition, there is an increased danger of disturbing the distribution line when the device fails. SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and aims to solve these disadvantages and to start the operation promptly only when a reactive power compensator is required, and to provide a large and short-time operation. It is an object of the present invention to provide a method of operating a reactive power compensator that compensates for a reactive current and reduces the size of a power supply.

[0012]

Means for achieving the object are as follows: 1) The operation of a reactive power compensating device connected in parallel with a load device and compensating for the reactive current of the load device according to claim 1 A reactive current detection unit, wherein when the output of the reactive current detection unit increases to a first specified value or more, the reactive power compensator is operated, and the output of the reactive current detection unit is set to a second value. A method for operating a reactive power compensator, characterized in that control is performed so as to stop when the value decreases below a prescribed value.

2) The method according to claim 1, wherein the filter time constant of the control circuit is changed according to the operation or stoppage of the reactive power compensator. is there.

According to a third aspect of the present invention, when the primary delay signal of the output of the reactive current detector increases to a third specified value or more, the reactive power compensator is operated and the output of the reactive current detector is output. 2. The method according to claim 1, wherein the control is performed such that the operation is stopped when the value decreases to a value equal to or less than a fourth prescribed value.

That is, in the present invention, the reactive power compensator is provided with an operation stop determination circuit. This operation stop determination circuit constantly monitors the magnitude of the reactive current, activates the reactive power compensator immediately when the reactive current increases, and stops when the reactive current decreases. The output of the operation stop determination circuit changes the control constant of the control circuit as needed. By doing so, when the reactive current of the load device is small, the reactive power compensator is stopped,
The entire loss between the load and the reactive power compensator is reduced, and when the reactive current of the load device increases, the reactive power compensator is operated immediately to start the reactive power compensation operation. Further, by changing the time constant of the first-order lag filter, the response to the transient change of the reactive power is increased. Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing an embodiment of the first aspect of the present invention. In FIG. 1, the same reference numerals as those in FIG. 5 denote portions having the same configuration and function. In FIG.
An operation stop determination circuit 80a is provided, and the operation stop circuit 80a includes a comparator circuit 81.
The comparator circuit 81 generates an output when the instantaneous reactive current q detected by the reactive current detector 61 exceeds a first predetermined amount, and the output is sent to the gate amplifier 65, and the gate amplifier 65 outputs the gate signal. To the converter circuit 54 to start the compensation operation.

FIG. 2 is a block diagram showing a second embodiment of the present invention. In FIG. 2, a delay circuit 82 is added to the operation stop judging circuit 80b. Delay circuit 82
Receives the output of the comparator circuit 81 and generates an output delayed by a specified time from the output. The output is sent to a first-order lag filter circuit 62 included in the control unit 60, and changes the filter time constant.

FIGS. 3A, 3B and 3C are characteristic diagrams for explaining the operation.
The operation of b will be described. FIG. 3A shows a reactive current detector 61.
(B) shows the comparator circuit 8
1 (c) shows the output of the delay circuit 82. The comparator circuit 81 generates an output at a time T1 at which the instantaneous reactive current detected by the reactive current detector 61 exceeds a predetermined amount q1. This output is sent to the gate amplifier 65,
Gate amplifier 65 provides a gate signal to converter circuit 54 to start a compensation operation. Further, the comparator circuit 8
The output of 1 is also supplied to a delay circuit 82, which generates an output at a time T2 which is later than the comparator circuit 81 by a specified time Td, and is supplied to a first-order lag filter circuit 62. The output of the delay circuit 82 sets the time constant of the primary delay filter circuit 62. When there is no output, the time constant is set short, and when there is an output, the time constant is set long.
The specified time Td is set in consideration of the length of the period in which the reactive current is largely changing. Therefore, the converter circuit 5
The filter time constant is set short until the reactive current is stabilized to some extent even after the start-up of 4, and can respond to a sudden change in the reactive current.

Thereafter, when the delay circuit 82 generates an output at time T2, the time constant of the filter circuit is set long.
Therefore, thereafter, the harmonic component of the instantaneous reactive current q is filtered, and q0 contains only the fundamental component, and the current commands isu, isv, and isw also contain only the fundamental frequency component necessary for power factor compensation. Wave components are no longer compensated, and the burden on converter circuit 54 is reduced. Thereafter, the comparator circuit 8 at time T3 when the reactive current of the load suddenly decreases and the instantaneous reactive current q becomes equal to or less than the second prescribed amount q2.
1 stops its output, stops the gate amplifier 65,
The operation of the converter circuit 54 also stops. The output of the delay circuit 82 also stops thereafter, and the time constant of the filter circuit is set short in preparation for the next rapid increase in the reactive current.

If the converter circuit has room or harmonics are to be compensated at the same time, it is not necessary to provide the first-order lag filter circuit 62 of the control circuit as shown in FIG. Also, the delay circuit 82 is unnecessary. As described above, according to the present invention, the converter is started and stopped according to the change in the reactive current of the load current, and the time constant of the filter circuit is appropriately changed. Therefore, only when the reactive current of the load becomes large, Drive the converter circuit,
Moreover, it is possible to quickly obtain a device exhibiting the compensation performance. In addition, the filter time constant is shortened only at the time of a stop and a transient change, and when the steady state is reached, the filter time constant is set longer, and the harmonic compensation is discontinued to control only the fundamental wave. The load on the circuit can be reduced, and the converter can be downsized.

FIG. 4 is a block diagram showing one embodiment of the third embodiment. In FIG. 3, the operation stop judging circuit 80c includes a second circuit between the reactive current detector 61 and the comparator circuit 81b. A first-order lag filter circuit 83 is provided. The output of the reactive current detector 61 is the second primary lag filter circuit 8
By the operation of 3, the change in the reactive current is suppressed and transmitted to the comparator circuit 81b. Comparator circuit 81b
Generates an output when the output of the second primary delay circuit 83 is equal to or greater than a third specified value, and stops the output when the output is equal to or smaller than a fourth specified value. Therefore, in the case where the reactive current repeatedly increases and decreases remarkably, it is possible to prevent the comparator circuit 81b from repeatedly turning on and off the output, thereby preventing unnecessary stoppage of the operation of the converter circuit.

[0022]

As described above, according to the present invention, it is possible to satisfactorily compensate for a large amount of short-time reactive power generated when the operation of a load device is stopped or a mode is changed, and to reduce the reactive current flowing to a power supply. Therefore, it is not necessary to increase the power supply capacity in consideration of the transient load fluctuation. Further, since the reactive power compensator is operated only at the minimum necessary time, the loss occurring in the reactive power compensator is reduced, and power is saved. Further, the chance of causing disturbance to the load or the power supply due to the failure of the reactive power compensator can be reduced. Therefore, the method of operating the reactive power compensator of the present invention is extremely useful in practice.

[Brief description of the drawings]

FIG. 1 shows a reactive power compensator according to an embodiment of the present invention.

FIG. 2 shows a reactive power compensator according to a second embodiment of the present invention.

FIG. 3 is an explanatory diagram of the operation of the present invention.

FIG. 4 shows a reactive power compensator according to a third embodiment of the present invention.

FIG. 5 is a reactive power compensating apparatus showing an example of the related art.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Power supply 2,53 Current transformer 3 Load device 4 Reactive power compensator 50 Main circuit part 51 Capacitor 52 Reactor 54 Converter circuit 55 DC capacitor 56 Transformer 57 Rectifier circuit 60 Control part (control circuit) 61 Reactive current detection part 62 1 Next delay filter circuit 63 Current command generator 64 Current controller 65 Gate amplifier 80a, 80b, 80c Operation stop determiner 81, 81b Comparator circuit 82 Delay circuit 83 Second primary delay filter circuit

Claims (3)

[Claims] 1. A method of operating a reactive power compensator connected in parallel with a load device and compensating for a reactive current of the load device, comprising a reactive current detector, wherein an output of the reactive current detector is a first regulation. Operating the reactive power compensating device when the value of the reactive power compensating device is increased to a value equal to or greater than the second specified value. Method. 2. The method for operating a reactive power compensator according to claim 1, wherein the filter time constant of the control circuit is changed in accordance with the operation or stoppage of the reactive power compensator. 3. A reactive power compensator is operated when a first-order lag signal of the output of the reactive current detector increases to a third specified value or more, and the output of the reactive current detector is set to a fourth specified value. 2. The method according to claim 1, wherein the control is performed so as to stop when the value decreases to a value equal to or less than the value.