JP2009050111A - Control system of reactive power compensator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable compactly and inexpensively obtaining reactive power of a load without increasing a circuit scale. <P>SOLUTION: In the reactive power compensator interlocked with a power system and controlling voltage fluctuation of the power system, in order to compensate the reactive power of the load, a multiplier 15 obtains a reactive power instantaneous value q from the product of a voltage v2 delayed by 90° from a system voltage v1 and a load current if, while a multiplier 16 obtains the product q of a differential value obtained by averaging the load current for a predetermined period and the system voltage, and the values are added to obtain the reactive power. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a control method for a reactive power compensator that is connected to a power system using a semiconductor device and suppresses voltage fluctuations of the power system.

FIG. 2 shows a general example of a reactive power compensator.
That is, the reactive power compensator 1 in FIG. 2 is installed between the system impedance 3 and the load 4 in the system in which the load 4 is connected from the power system 2 through the system impedance 3, and is generated by the load 4. Compensate for reactive power.

  The reactive power compensator 1 includes a thyristor 5, a reactor 6, a capacitor 7, a control device 13, and the like. As the operation, in order to compensate for the voltage flicker, the reactive power generated by the load 4 is compensated. If 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 is set to Qs = 0, and as a result, voltage fluctuation of the system voltage can be suppressed and voltage flicker can be suppressed.

  A specific example of the control device 13 is shown in FIG. Here, the system voltage, the system voltage of 90 ° phase lag and the load current if are detected by PT and CT, and the reactive power detector 10 calculates the reactive power Q. The result of multiplying the detected reactive power Q by the gain from the gain element 11 is input to the firing angle control circuit 12, and the firing angle control circuit 12 calculates a firing angle command α for firing the thyristor. To do.

FIG. 4 shows a specific example of the reactive power detector 10 disclosed in Patent Document 1, for example.
In the figure, the reactive power Q is calculated as follows.
(A) The system voltage v1, the voltage v2 delayed by 90 ° with respect to the system voltage v1, and the load current if are detected, and the current if ′ obtained by advancing the load current if by 90 ° is calculated by the all-pass filter 21 shown in FIG. Here, v1, v2, and if are expressed as follows.

v1 = √2Esinωt− (1)
v2 = −√2Ecosωt− (2)
if = √2I sin (ωt−φ) − (3)

(B) The reactive power instantaneous value q is calculated by multiplying v2 and if.
q = v2 × if = E · I {sinφ−sin (2ωt−φ)} − (4)
(C) 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 {sin φ + sin (2ωt−φ)} − (5)

(D) The reactive power instantaneous value q and the virtual reactive power instantaneous value q ′ are added.
q + q '= 2E · I · sinφ-(6)
(E) The reactive power Q is calculated by multiplying the above equation (6) by 1/2.
Q = (q + q ') / 2 = E · I · sinφ-(7)

Japanese Patent Laid-Open No. 08-140268

According to Patent Document 1, in order to calculate the reactive power Q, a transformer (PT) that detects a voltage 90 degrees behind the system voltage and an all-pass filter are required. In particular, since the all-pass filter is made using an operational amplifier or the like as shown in FIG. 5, adjustment to advance the phase by 90 ° is required. For this reason, the circuit is complicated and large, and it takes time to adjust the filter. The all-pass filter is instantaneous,
Since the instantaneous value is phase-shifted, there is a possibility that a calculation error becomes large depending on a sudden load current change.

  Accordingly, an object of the present invention is to provide a reactive power calculation method with a small calculation error and without making a circuit complicated and large-scale.

In order to solve such a problem, the invention of claim 1 compensates the reactive power of the load by the reactive power compensator that is connected to the power system and suppresses voltage fluctuations of the power system.
The reactive power value is obtained by adding the product of the derivative value obtained by averaging the load current for a certain period and the system voltage to the reactive power instantaneous value calculated by the product of the voltage delayed by 90 ° from the voltage of the power system and the load current. The calculation is performed, and the reactive power of the load is compensated by the calculated value.
In the invention of claim 1, the differential value obtained by averaging the load current for a certain period is obtained by differentiating the load current before n (natural number of 2 or more) sampling is obtained by differentiating the load current before one sampling. The phase can be shifted so that they have the same phase and the same amplitude, and the operations can be performed with the same amplitude (invention of claim 2).

  When the reactive power is obtained by adding the virtual reactive power instantaneous value obtained by multiplying the system voltage by the current obtained by advancing the load current by 90 ° and the reactive power instantaneous value as in the conventional case, an all-pass filter or the like According to the present invention, the virtual reactive power instantaneous value is calculated from the product of the differential value obtained by averaging the load current for a certain period and the system voltage. Error can be suppressed.

FIG. 1 is a block diagram showing an embodiment of the present invention.
This is because the reactive power calculation detector 10 shown in FIG. 4 includes a phase shifter 19, n (natural number of 2 or more) average differentiator 22, gains (elements) 23 and 24, a setter 25, a subtractor 26, a division. A device 27 and the like are added. Since the calculation method is the same as that in FIG. 4 until the reactive power instantaneous value q is calculated, the difference will be mainly described below.

First, if is divided by ω and differentiated, the following equation (8) is obtained.

Further, if is divided by ω, and differential calculation is performed by n average differential calculator 22, Equation (9) shown in Formula 2 is obtained. Ns in the equation represents the number of samples per cycle (number of samples / cycle).

Equation (9) can be expressed as Equation (10) in Equation 3.

By synthesizing the curly braces ({}) in the above expression (10), it can be transformed as the expression (11) shown in equation 4.

From equation (11), r and cos α are obtained as in equation (12) shown by the following equation (5).

The previous equation (11) is different from the equation (8) in equation 1 with respect to the amplitude ratio and the phase difference α as in equation (13) in equation 6.

Further, in order to shift the phase difference α, the following equation (14) may be used.

From the relationship of the equation (11), the equation (15) of the equation 8 is obtained.

From Equation (15) and Equation (14) above, Equation (16) in Equation 9 is obtained.

  That is, the operation for obtaining one input (corresponding to if ′) in the multiplier 16 of FIG. 1 is expressed by the above equation (16). In this calculation, n average differentiators 22, gains (elements) 23 and 24, a setter 25, a subtractor 26, and a divider 27 are used. Therefore, the gain 23 has an amplitude ratio of the above equation (13). , Sin α is set in the gain 24, and cos α in the equation (13) is set in the setting unit 25, respectively.

The multiplier 16 obtains q ′ (virtual reactive power instantaneous value) by the same calculation as the above equation (5), and the adder 17 adds the reactive power instantaneous value q and the virtual reactive power instantaneous value q ′. Therefore, the reactive power Q (= E · I · sinφ) is calculated by multiplying this by 1/2 as in the conventional case.
Incidentally, when Ns = 192 and n = 16, the gain of 23 is “1.0115”, the gain of 24 is “0.2588”, and the set value of 25 is “0.9659”.

  As described above, conventionally, a PT that detects a voltage 90 degrees behind the system voltage and an all-pass filter are required, and the circuit scale is complicated and large. By preparing a memory that can hold Ns data instead of the PT and the all-pass filter, the reactive power can be calculated. Therefore, the circuit can be reduced in size and the cost can be reduced. By performing differentiation by averaging the load current for a certain period, it is possible to suppress calculation errors even for a sudden change in load current.

Block diagram showing an embodiment of the present invention System configuration diagram showing a conventional example The block diagram which shows the structure of the control apparatus of FIG. The block diagram which shows the specific example of the reactive power detector of FIG. Circuit diagram showing a specific example of the all-pass filter of FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Reactive power detector, 15, 16 ... Multiplier, 17 ... Adder, 18, 23, 24 ... Gain (element), 19 ... Phase shifter, 25 ... Setter, 26 ... Subtractor, 27 ... Divider .

Claims (2)

When compensating the reactive power of the load by the reactive power compensator connected to the power system and suppressing the voltage fluctuation of the power system,
The reactive power value is obtained by adding the product of the derivative value obtained by averaging the load current for a certain period and the system voltage to the reactive power instantaneous value calculated by the product of the voltage delayed by 90 ° from the voltage of the power system and the load current. A control method for a reactive power compensator, characterized in that the reactive power of a load is compensated by the calculated value.   The differential value obtained by averaging the load current for a certain period is such that the load current differentiated before n (natural number of 2 or more) sampling has the same phase and the same amplitude as those obtained by differentiating the load current before one sampling. 2. The reactive power compensator control method according to claim 1, wherein the calculation is performed by shifting the phase and aligning the amplitudes.

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