JP5018205B2 - Calculation method in reactive power compensator - Google Patents

Description

  The present invention relates to a reactive power compensator that is linked to a power system and suppresses voltage fluctuations of the power system, and more particularly to an improvement in a reactive power calculation method.

FIG. 3 shows a general example of the reactive power compensator.
The reactive power compensator 1 is connected between the system impedance 3 and the load 4 of the power system to which the load 4 is connected from the power system 2 through the system impedance 3 and compensates for the reactive power generated from the load 4. . The reactive power compensator 1 includes a thyristor 5, a reactor 6, a capacitor 7, and the like. Reference numeral 13 denotes a control device of the reactive power compensator 1.

As an operation of the reactive power compensator 1, the reactive power generated by the load 4 is compensated. Here, when the reactive power generated by the load 4 is Qf, the reactive power of the reactive power compensator 1 is Qt, and the reactive power of the system is Qs, the reactive power compensator 1 is controlled so that Qt = Qf. The reactive power of the system is Qs = 0, and the voltage fluctuation of the system voltage can be suppressed.
An example of a control device for the reactive power compensator is shown in FIG.

This is because the reactive power detector 10 detects the reactive power Q from the detected system voltage Vs and the load current If, and the result obtained by multiplying the reactive power Q by the gain by the coefficient unit or the multiplier 11 is the firing angle. This is input to the adjuster 12, where a firing angle command α for firing the thyristor is calculated.
As the reactive power detector 10, for example, an example disclosed in Patent Document 1 is shown in FIG.

  This is composed of multipliers 15 and 16, adder 17, gain element 18, all-pass filter 21, and the like. From the detected system voltage V 1, a voltage V 2 delayed by 90 ° with respect to this, the load current if, etc., the final Specifically, the reactive power Q is calculated. As shown in FIG. 6, the all-pass filter is mainly composed of an operational amplifier Op, which is generally defined as a filter that has no change in frequency-amplitude characteristics and changes only in frequency-phase characteristics.

First, the all-pass filter 21 calculates a current obtained by advancing the load current if by 90 °, and if, V1, and V2 are defined as follows.
V1 = √2E cos θ (1)
V2 = √2Esin θ (2)
if = √2I cos (θ−φ) (3)
The reactive power instantaneous value q is calculated by multiplying V2 and if.

q = V2 × if = E · I {sinφ + sin (2θ−φ)} (4)
The virtual reactive power instantaneous value q ′ is calculated by multiplying V1 and the current if ′ obtained by advancing if by 90 °.
q ′ = V1 × if ′ = E · I {sinφ−sin (2θ−φ)} (5)
When the reactive power instantaneous value q and the virtual reactive power instantaneous value q ′ are added,
q + q ′ = 2E · Isinφ (6)
Thus, the reactive power Q is calculated by multiplying the equation (6) by a gain of 1/2.

Q = (q + q ′) / 2 (7)
JP-A-8-140246

  As described above, in order to calculate the reactive power Q, a PT (transformer: 8, 14 in FIG. 4) and an all-pass filter (21 in FIG. 5) that detect a voltage delayed by 90 ° with respect to the system voltage are necessary. There is a problem to say. In addition, since the all-pass filter is made using an operational amplifier (Op), etc., adjustment to advance the phase by 90 ° is required. As a result, the circuit is complicated and the scale is increased, and it takes time to adjust the filter, resulting in an increase in cost. Will do.

  Accordingly, an object of the present invention is to simplify the circuit and reduce the cost by eliminating the need for an all-pass filter.

In order to solve such a problem, in the invention of claim 1, in the reactive power compensator connected to the power system and suppressing the voltage fluctuation of the power system,
Reactive power instantaneous value calculated by product of system voltage and load current
The reactive power amount is calculated by adding the value of 60 ° before the reactive power instantaneous value and the inverted value of the value 30 ° before.

  According to the present invention, the reactive power can be obtained simply by providing a memory or using an existing memory. Therefore, a PT or an all-pass filter that detects a voltage 90 ° behind the system voltage as in the prior art. As a result, it is possible to reduce the size and cost by simplifying the circuit.

FIG. 1 is a block diagram showing an embodiment of the present invention.
As illustrated, the reactive power detector 10 is characterized by the addition of memories 20 and 22 for storing the reactive power instantaneous value q. The calculation is performed as follows.
First, the phase shifter 19 obtains a voltage V2 delayed by 90 ° from the detected system voltage V1. The system voltage V1 is the same as the above equation (1).
V1 = √2E cos θ (8)
Therefore, the voltage V2 is V2 = √2Esin θ (9)
It is. Further, the load current if is the same as the above equation (3),
if = √2I cos (θ−φ) (10)
It becomes.

The multiplier 15 calculates the reactive power instantaneous value q by multiplying V2 and if.
q = V2 × if = E · I {sinφ + sin (2θ−φ)} (11)
The calculated reactive power instantaneous value q is sequentially stored in the memories 20 and 22 here. The memory 20 only needs to store the reactive power instantaneous value q up to 60 ° before. Assuming that the reactive power instantaneous value data is stored in the memory 20 in increments of 1 °, it is sufficient that data up to 60 ° before can be stored, so it can be said that a capacity of 60 words is sufficient. Since the memory having this capacity can use the internal memory of the computer, there is no cost increase due to the addition of a new memory.

The memory 22 only needs to be able to store the reactive power instantaneous value q up to 30 ° before. For example, if the reactive power instantaneous value data is stored in the memory in increments of 1 °, it can be said that a capacity of 30 words is sufficient. Since the memory having this capacity can use the internal memory of the computer, there is no increase in cost due to the addition of a new memory.
Next, the reactive power instantaneous value q ′ 60 ° before stored in the memory 20 and the inverted value q ″ of the reactive power instantaneous value 30 ° before stored in the memory 22 are read, and q ′ and q ″. And add.

q ′ = V1 × if ′ = E · I {sinφ + sin (2 (θ−φ′−60))}
= E · I {sinφ + sin (2θ−φ′−120)} (12)
q ″ = − V1 × if ′ = − E · I {sinφ + sin (2 (θ−φ′−30))}
= −E · I {sin φ + sin (2θ−φ−60)} (13)
Q = q + q ′ + q ″ = E · Isinφ (14)
FIG. 2 shows the waveform of each part of FIG.

That is, FIG. 2A shows the output V2 of the phase shifter 19 that is delayed by 90 degrees with respect to the detection voltage V1, in addition to the detection voltage V1 and the detection current If, and FIG. The output q of the multiplier 15, the output q ′ of the memory 20, the output q ″ of the memory 22, and the reactive power Q and the like are shown in FIG.
In addition, in the Japanese Patent Application No. 2006-13453, the applicant has applied for an invention for calculating reactive power using a reactive power instantaneous value 90 degrees before, but in the present invention, a reactive power instantaneous 60 degrees before Since the value is used, the error is reduced by the phase of 30 °.

  As described above, reactive power can be obtained simply by providing a memory or using an existing memory. Therefore, a PT or an all-pass filter that detects a voltage that is 90 ° behind the system voltage as in the prior art is used. As a result, miniaturization and cost reduction can be realized by simplifying the circuit.

Block diagram showing an embodiment of the present invention Waveform diagram showing the waveform of each part in FIG. Configuration diagram showing a typical power system The block diagram which shows the specific example of the control apparatus of FIG. The block diagram which shows the specific example of the reactive power detector provided in the control apparatus of FIG. Circuit diagram showing a specific example of the all-pass filter used in FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Reactive power compensator, 2 ... Power system, 3 ... Inductance, 4 ... Load, 5 ... Thyristor, 6 ... Reactor, 7 ... Capacitor, 8, 14 ... PT (transformer), 9 ... CT (8 current transformer) ) 10... Reactive power detector, 11 and 18... Gain element, 12... Firing angle control circuit, 13... Control device, 15 and 16. ... memory, 21 ... all-pass filter.

Claims (1)

In the reactive power compensator connected to the power system and suppressing the voltage fluctuation of the power system,
Reactive power instantaneous value calculated by product of system voltage and load current,
A value 60 degrees before the reactive power instantaneous value,
An inverted value of the value 30 ° before the reactive power instantaneous value,
A reactive power calculation method characterized by calculating a reactive power amount by adding.

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