JPH0625949B2 - Reactive power compensator - Google Patents

Description

Description: TECHNICAL FIELD [0001] The present invention relates to a reactive power compensator, and an effective reactive power compensation system in a system for supplying power from an AC power supply system to an AC power bus to a load with a large fluctuation of reactive power. The present invention relates to a reactive power compensator for performing power compensation.

[Technical background of the invention and its problems]

In recent years, large-capacity arc furnace equipment has been connected to an AC power supply system and operated. As is well known, the arc furnace generates reactive power on the power supply side that fluctuates abruptly depending on the state of the melt in the furnace. This abruptly changing reactive power distorts the voltage waveform due to the interaction with the power supply system impedance, which causes flicker of the lighting equipment and causes the utilization rate of the power supply equipment to decrease. Therefore, when installing a large-capacity arc furnace, etc., a reactive power compensator is installed in parallel with the arc furnace to compensate for the rapidly fluctuating reactive power generated by the arc furnace and to fluctuate the reactive power of the AC power system. Is suppressed.

For such a reactive power compensator, see [Reference] Technical Report of The Institute of Electrical Engineers of Japan (Part II), April 1979, 76th edition.
Nos. P26 to P31, "Power Conversion Technology for Reactive Power / Harmonics Countermeasures," Special Committee for Permanent Rectifiers, the configuration is the power supply system as shown in FIG.

That is, in the figure, 10 is the load of the arc furnace,
Iron or the like is put into the furnace 12, and an electric current is caused to flow through the electrode 11 by electric discharge to heat and melt the iron inside. 9 is a transformer for the furnace.

Reference numeral 100 is a reactive power compensator, which is a reactor unit 300.
And a phase advancing capacitor section 200 that also serves as a harmonic filter. Reactor section 300 is reactor 302U-
302W and anti-parallel thyristor 30 connected in series to it
1U to 301W and load current detectors 81R, 81S, 8
1T, voltage detection transformer 70, and its control circuit 350
The reactive electric power of the arc furnace 10 is detected, the conduction angles of the thyristors 301U to 301W are adjusted according to the detected value, and the reactor current is controlled. That is, in the reactive power compensating apparatus 100, the currents of the reactors 302U to 302W are controlled in combination with the action of the phase advancing capacitor 200, and the amount of lead reactive power equal to the generated reactive power (delay) of the arc furnace 10 is applied to the lines 51R, 51S, It is controlled to occur at 51T, and the reactive power disappears at the point of the three-phase bus 4 and only the active power of the load flows. Therefore, the voltage distortion of the bus bar 4 is reduced and the utilization rate of the power supply equipment is improved. Reference numeral 3 is a system impedance existing in a three-phase AC power supply system, and 1 is a power supply source such as a three-phase AC power supply system or a transmission and distribution bus.

In the reactive power compensator 100 having the above configuration, the control circuit 3
How accurately the reactive power generated by the load 10 is detected by 50 is a key to the device performance. An example of this reactive power detection circuit is shown in FIG.

That is, FIG. 6 shows the method disclosed in FIG. 2 of Japanese Patent Laid-Open No. 59-139416. First, when the product q of the 90 ° delayed waveform e _{90 of the} bus voltage e and the load current i _L is created, q has a form in which a direct current component (reactive power component) and an alternating current component that oscillates at twice the fundamental frequency are included. This signal is passed through a low-pass filter and the direct current component q _VAR (amount of reactive power) Is detected, and the current of the reactor part 300 is controlled based on this.

Besides, various reactive power detection methods have been proposed, but the gist thereof can be reduced to the principle disclosed in Japanese Patent Laid-Open No. 59-139416.

The above is the description of the conventional reactive power compensator, but this device has the following drawbacks. That is, when the fluctuating power (including active power and reactive power) generated by an arc furnace is analyzed, the component of the DC amount that does not fluctuate (that is, the positive phase power due to the positive phase voltage and the positive phase current) ) And a fluctuating component (that is, the negative phase power caused by the positive phase voltage and the negative phase current), the conventional reactive power detection method clearly separates these positive phase power and negative phase power. There is no concept, therefore, the electric power is regarded only as a fluctuation component in which the positive-phase electric power and the negative-phase electric power are mixed together, and the reactor current is controlled based on the fluctuation. Therefore, what is to be compensated in the conventional reactive power compensator, that is, whether the positive-phase reactive power (component that does not fluctuate) is controlled or the negative-phase reactive power (component that fluctuates) is controlled. In principle, it was not possible to discriminate between, and it was impossible to develop into more advanced control.

In recent years, there has been a strong demand for improving the quality of power in the AC power system,
In order to meet this demand, there is a strong demand for more advanced control of reactive power compensators for flicker countermeasures in arc furnaces, etc., and reactive power compensators for AC power system stabilization measures, and this requirement is satisfied. Therefore, the emergence of a reactive power compensator equipped with a highly accurate power detection method (including active and reactive components) based on a new control concept is desired.

[Object of the Invention]

The present invention has been made in view of the above-mentioned problems of the prior art,
The purpose is to separate and detect the positive-phase component and the negative-phase component in the load current in a device that compensates the reactive power generated by the load of an arc furnace, etc. Another object of the present invention is to provide a reactive power compensator capable of performing highly accurate compensation control.

[Outline of Invention]

In order to achieve the above object, the present invention relates to a reactive power compensator for compensating reactive power generated by a load connected to an AC power system, and a two-phase current signal obtained by converting a detected load current into two phases. , A unit two-phase voltage signal synchronized with the AC bus voltage connected to the load and a unit two-phase voltage signal having a frequency twice the frequency of the AC bus voltage are used, and the positive phase in the load current is calculated through the calculation of these signals. The reactive component and the anti-phase component are separately detected, a current command for the reactive power compensator is created based on this detection signal, and the reactive power compensator is controlled based on this current command value.

Example of Invention

The power supply system including the reactive power compensator of the present invention (for the convenience of the following description, it will be described as a three-phase system) is the same as that in FIG. 5, and the elements referred to in the above description of the conventional example will be described. The description is omitted here.

In FIG. 5, reference numerals 81R, 81S and 81T denote current detectors, which detect the currents (i _RL , i _SL , i _TL ) of the arc furnace 10 and guide them to the control circuit 350. 70 is a voltage detector which is an arc furnace 1
0 (including furnace transformer 9) bus voltage (e
_RS , e _ST , e _TR ) are detected and guided to the control circuit 350. Thirty
Reference numeral 0 denotes a reactor portion, which is normally delta connected, and the magnitude of the current is adjusted by adjusting the firing angle of the thyristors 301U to 301W. The reactor current usually has a distorted waveform including harmonics in addition to the fundamental wave.

Reference numeral 400 is an arithmetic circuit incorporating the present invention.
_RL , i _SL , i _TL and voltage signals e _RS , e _ST , e _TR are input and various calculations are performed, and a current command of DC value ▲ I ^* _U for instructing the fundamental current that the reactor unit 300 should flow ▼, ▲ I
Output ^* _V ▼, ▲ I ^* _W ▼.

Reference numeral 500 denotes an ignition controller, which is a current command value ▲ I ^* _U ▼, ▲ I
Operates in response to ^* _V ▼, ▲ I ^* _W ▼, ▲ I ^* _U ▼, ▲ I ^* _V ▼,
Thyristor 3 so that reactors 302U, 302V, 302W flow the current (fundamental wave component) designated by ▲ I ^* _W ▼.
Ignition control of 01U, 301V, and 301W.

A combination of the arithmetic circuit 400 and the ignition controller 500 is called a control circuit 350, and the details of this circuit are shown in FIG.

Next, the main part of the present invention will be described with reference to FIGS.
In the present invention, the following description will be given by taking the case where the reactor part 300 of FIG. 5 is delta-connected as an example. The same symbols in FIGS. 1 and 5 represent the same elements and the same signals.

In FIG. 1, reference numeral 402 is a line / phase converter, and the load current signals i _RL , i _SL , and i _TL detected as the line current in FIG.
Is calculated by the equation (1), the phase currents i _UL , i _VL of the delta connection,
i _WL is converted (the conversion of the formula (1) is necessary for the reactor section 300 in FIG. 5 at the time of delta connection, and the star connection does not require this conversion).

_{Reference numeral} 403 denotes a two-phase converter which converts the current signals i _UL , i _VL , i _WL into two-phase current signals i _1dL , i _1qL by the calculation of the equation (2).

406 inputs the AC bus voltage signals e _RS , e _ST , and e _TR of FIG. 5, and based on them, the phase lock loop circuit (PLL
A two-phase signal generator obtained by configuring a circuit), and as its output, the first phase is the R phase and the second phase is the S phase in FIG.
Assuming that the phase and the third phase are T phases, the unit sine wave signal ▲ e ^* _1d1 ▼ synchronized with the line voltage e _RS of the first and second phases and the unit sine wave signal ▲ e advanced by 90 ° ^* _1q1 ▼ and its phase signal ▲ θ ^* _1d1 ▼ are output, and ▲ e ^* _1d1 ▼, ▲ e ^* _1q1 ▼ are the formula
(3) (Note that when the reactor part 300 of FIG. 5 is star connected, ▲ e ^* _1d1 ▼, ▲ e ^* _1q1 ▼ are synchronized with the phase voltage of the first phase).

407 is also a two-phase generator, which operates by receiving the phase angle signal ▲ θ ^* _1d1 ▼ and has a frequency twice the AC bus voltage frequency.
(4) two-phase voltage signals _{^{▲ e * 1d2 ▼, ▲ e}} * 1q2 ▼ generates.

_{Reference numeral} 404 denotes an arithmetic unit that outputs signals i _1dL , i _1qL and ▲ e
^* _1d1 ▼, ▲ e ^* _1q1 ▼ is input, and the signal Q _1N ,
Calculate P _1N .

When the load currents i _RL , i _SL , and i _TL include a positive phase component / a negative phase component, Q _1N and P _1N become a pulsating flow that includes a DC component and an AC component that oscillates at a frequency twice the fundamental wave. .

Reference numeral 409 denotes a separator, which is composed of the DC detection filters 410 and 411 and the adders 412 and 413, receives the signals Q _1N and P _1N , and receives the DC detection filters 410 and 411.
Detects the DC components of Q _1N and P _1N and outputs them as signals Q _1ND and P _1ND , and at the places of the adders 412 and 413, the DC components of the signals Q _1N and P _1N , that is, Q _1ND and P _1ND, are output. It is removed and only the AC component is output as the signals Q _1NA and P _1NA . The P _1ND and Q _1ND thus obtained are the components (P _1ND ) in phase with the reverse phase current included in the first phase current i _UL of the equation (1) in the line voltage of the first phase and the second phase, and 90 ° _Indicates the current of each component when it is decomposed by components with different phases (Q _1ND ), where P _1ND is the in-phase reverse-phase current signal of the first phase, Q _1ND
Will be referred to as a first-phase 90 ° anti-phase current signal.

_{Reference numeral} 408 denotes an arithmetic unit which outputs signals Q _1NA , P _1NA and ▲ e
^{_{* 1d2 ▼, ▲ e * 1q2}} ▼ enter a calculates the signal Q _1PD by equation (6).

^{_{Q 1PD = ▲ e * 1d2 ▼}} · Q 1NA - ▲ e * 1q2 ▼ · P 1NA ......
(6) The signal Q _1PD becomes a DC signal, and this Q _1PD represents the positive-phase reactive current included in the load currents i _RL , i _SL , and i _TL .

Reference numeral 420A denotes a distributor, which receives signals Q _1PD , Q _1ND and P _1ND to perform calculation, and current command values ▲ I ^* _U ▼, ▲ I ^* _V for instructing the current flowing through the reactor unit 300 shown in FIG. ▼ 、
Output ▲ I ^* _W ▼. The details of the distributor 420A are shown in FIG.

Reference numeral 500 denotes an ignition controller, which is a current command value ▲ I ^* _U ▼, ▲ I
Operates in response to ^* _V ▼, ▲ I ^* _W ▼, ▲ I ^* _U ▼, ▲ I ^* _V ▼,
Thyristors 301U, 301V, 3 so that the current (fundamental wave component) instructed by ▲ I ^* _W ▼ flows through reactor _1ND 300
Ignition control of 01W.

Next, the distributor 420A will be described with reference to FIG. Signals having the same symbols in FIGS. 1 and 2 are connected according to the symbols.
In FIG. 2, 421A and 424A are arithmetic units,
The first-phase 90 ° negative-phase current signal Q _1ND and the first-phase in-phase negative-phase current signal P _1ND are input, and the second-phase 90 ° negative-phase current is calculated through the equations (7) and (8), respectively. The signal Q _2ND , the second-phase in-phase reverse-phase current signal P _2ND, the third-phase 90 ° reverse-phase current signal Q _3ND , and the third-phase in-phase reverse-phase current signal P _3ND are output.

Here, P _2ND and Q _2ND are obtained by _converting the opposite phase component of the second phase current i _{VL in} the equation (1) into a component in phase with the line voltage of the second and third phases and a component having a 90 ° phase difference with it. The in-phase component current (P _2ND ) when decomposed and the current component (Q _2ND ) having a 90 ° phase difference are shown.

Similarly, P _3ND and Q _3ND are _obtained by _converting the negative phase component of the third phase current i _WL of the equation (1) into the third phase and the first phase, which are in-phase with the line voltage, and different from the phase with 90 ° phase. The in-phase component current (P _3ND ) when decomposed and the current component (Q _3ND ) having a 90 ° phase difference are shown.

A setter 437 outputs a reactive current setting signal Q _1MAX for instructing the maximum value of the reactive current (delay) to be generated by the reactor unit 300 in FIG.

430A is a distributor, in which the positive-phase reactive current signal Q _1PD detected from the load current of the arc furnace, the first phase,
Second-phase and third-phase 90 ° negative-phase current signals Q _1ND , Q _2ND , Q
_{Input 3ND} , in-phase and out-of-phase current signals P _1ND , P _2ND , P _3ND and reactive current setting signal Q _1MAX , and formula based on these signals
The calculation of (9) is performed, and the reactor unit 30 of FIG.
0 first phase current command ▲ I ^* _U ▼ for indicating the current to be generated by the first phase reactor 302U, and second phase current command ▲ I ^* _V ▼ for the reactor 302V, and Third-phase current command for reactor 302W ▲ I ^* _W
Output ▼. Here, the following elements are included in the distributor 430A. That is, 431A, 432A, 43
3A is a coefficient unit for input signal Double and output. 434A, 435A and 436A are adders which add the outputs of the coefficient units 431A, 432A and 433A with the polarities shown. The outputs of the adders 434A, 435A and 436A correspond to the calculation of the third term of the equation (9). An adder 438A calculates the setting signal Q _1NAX and the signal Q _1PD with the polarities shown. That is, the output of the adder 438A corresponds to the calculation of the first term of Expression (9). Reference numerals 439A, 440A and 441A denote adders which add the signals Q _1ND , Q _2ND and Q _3ND and the output signal of the adder 438A and the output signals of the coefficient multipliers 434A, 435A and 436A with the polarities shown.

Signals obtained by the above calculation ▲ I ^* _U ▼, ▲ I ^* _V ▼, ▲ I ^* _W
▼ is a DC amount signal, and this signal includes all the information about the positive phase current and the information about the negative phase current. Therefore, by controlling the reactor part 300 of FIG. 5 based on these ▲ I ^* _U ▼, ▲ I ^* _V ▼, and ▲ I ^* _W ▼, the load current of the arc furnace or the like is reversed in addition to the positive phase component. Even when the phase component is included in a large amount, the current at point 4 in FIG. 5 can be freely balanced.

The above is a typical configuration of the present invention.

Next, the operation of the present invention will be described.

First, in FIG. 5, the electric current of the arc furnace is the signal i _RL ,
Although detected as i _SL and i _TL , this current is usually an unbalanced current including a positive phase component and a negative phase component. On the other hand, the power source line voltage to which the arc furnace is connected is also the signal e _RS , e _ST , e.
_It is detected as _TR and is introduced into the reactive power compensator 100 control circuit.

Next, referring to FIG. 1, the two-phase generator 406 outputs the signal e _RS ,
Two-phase signal ▲ e based on equation (3) in response to e _ST and e _TR
^* _1d1 ▼, ▲ e ^* _1q1 ▼ and its phase angle signal ▲ θ ^* _1d1 ▼ are output, and then the two-phase generator 407 receives the phase angle signal ▲ θ ^* _1d1 ▼ and outputs the two-phase based on the equation (4). signal ▲ e ^* _1d2 ▼, to generate the _▲ e ^* 1q2 ▼.

On the other hand, the signals i _RL , i _SL , and i _TL detected as the line currents are converted by the equation (1) in the line / phase converter 402,
As a result, the phase currents i _UL , i _VL , and i _WL of the delta connection (that is, for example, the reactor section 30 in the delta connection of FIG. 5).
Taking 0 as an example, Actors 302U, 302V, 302W
Corresponding to the current flowing in). The signals i _UL , i _VL , and i _WL are converted by the equation (2) in the two-phase converter 403, and two-phase signals i _1dL and i _1qL are obtained. Next, the arithmetic operation of the equation (5) is performed in the arithmetic unit 404 to output the signals Q _1N , P
_1N is obtained, and this is passed through a separator 409 to be separated into DC component signals Q _1ND and P _1ND and AC component signals Q _1NA and P _1NA .

The signals Q _1ND and P _1ND obtained in this way are such that the reverse phase current included in the first phase current i _UL of the equation (1) is the same phase component as the line voltage of the first phase and the second phase and 90 ° phase with it. _Represents the current of each component when decomposed into different components of P, ie, the in-phase current component (P _1ND ) and the current component with a 90 ° phase difference (Q _1ND ) (P _1ND : in-phase reverse phase of the first phase). Current, Q _1ND : 90 of the first phase
Reverse phase current).

On the other hand, the arithmetic unit 408 the signal _{^{▲ e * 1d2 ▼, ▲ e}} * 1q2 ▼ and Q _1NA, the operation is performed DC signal of formula (6) and P _1NA Q _1PD
Which is the load current signal i _RL , i _SL , i
_It represents the positive-phase reactive current contained in _TL (or may be paraphrased as i _UL , i _VL , and i _WL in Expression (1)).

Next, in the distributor 420A of FIG.
Equation (7) in 424A, performs an operation of (8), a second phase of the in-phase reverse-phase current P _2ND, 90 ° reverse-phase current Q _2ND, third phase of the in-phase reverse-phase current P _3ND, 90 ° A reverse phase current Q _3ND is obtained.

The signal Q _1PD obtained as described above is the load current i _RL ,
i _SL , i _TL is a signal related only to the positive-phase component current contained in i _TL and i _TL . Further, if the positive-phase component current can be decomposed into an active current and a reactive current, it is only the reactive current. It is a signal that is relevant, ie, only the positive-phase reactive current.
Note that the calculation of various quantities related to the positive phase component of the current, for example, equation (6)
In the conversion of etc., the exact same amount is calculated regardless of which phase the calculation is performed. Therefore, the calculation for the positive phase component may be performed for one phase.

Also, the signals P _1ND , Q _1ND and P _2ND , Q _2ND and P _3ND ,
Focusing on Q _3ND , these signals are i in load current equation (1).
_UL , i _VL , and i _WL (or i _RL , i _SL , and i _TL may be paraphrased) are signals related only to the negative-phase component current, and further, P _1ND and Q _1ND are currents. i _UL 's reverse phase component only, P _2ND , Q _2ND only i _VL 's reverse phase _component P _3ND , Q
_3ND is a signal related only to the reverse phase _component of the current i _WL . More specifically, taking P _1ND and Q _1ND as an example, P _1ND has the same phase as the line voltage in the reverse phase component of the current i _UL . It is a current component, and Q _1ND is a signal related only to the current component that is 90 ° out of phase with the voltage.

As described above, all the information of the load currents i _RL , i _SL , and i _TL are DC signals Q _1PD , P _1ND , P _2ND , P _3ND , Q _1ND , Q _2ND , Q.
It will be clear that they are separately detected in the form of _3ND .

The signals thus obtained are distributed along the equation (9) in the distributor 430A of FIG. 2 and the current commands ▲ I ^* _U ▼, ▲ I ^* _V ▼, ▲
I ^* _W ▼ is made, but this current command ▲ I ^* _U ▼, ▲ I ^* _V ▼, ▲
When the current of the reactor part of FIG. 5 is controlled on the basis of I ^* _W ▼, regarding the control of the anti-phase current, the anti-phase current of the current generated by the arc furnace and the compensation current generated by the rear acrylic part 300 are controlled. Since the opposite-phase currents are controlled so that their phases are exactly opposite to each other, these are the points 51R and 51 for the opposite-phase component.
Since they are combined at S and 51T and cancel each other out, the reverse-phase current does not flow toward the power source 1 and the current of the power source 1 is balanced. Next, regarding the positive-phase reactive current, the output signal of the adder 438A in FIG. 2 acts, and as a result, the positive-phase reactive component (delay) of the current generated by the load and the reactor unit 3 in FIG.
00 is controlled so that the sum of the compensation current generated by 00 and the positive-phase reactive component (delay) is exactly equal to the reactive current setting signal Q _1MAX (delay) shown in FIG. The reactive current and the advance reactive current of the phase advancing capacitor shown in FIG. 5 cancel each other out. As a result, the reactive current does not flow to the AC current 1 shown in FIG. Only the phase active current will flow.

From the above description, when the reactive power compensator of the present invention operates, even if the load of the arc furnace or the like generates an unbalanced current including a positive phase component and a negative phase component, the reactive current is compensated and Since the phase current is compensated, only the positive-phase active current flows through the AC power supply, and therefore the voltage fluctuation (that is, flicker).
It can be seen that the power consumption can be suppressed and the utilization factor of the power source (that is, reactive power need not be handled) can be improved.

The above is a typical embodiment of the present invention.

Next, another embodiment of the present invention will be described with reference to FIG. That is, FIG. 3 is a modification of the distributor 420A of FIG. 2 of the invention described above, and FIG. 3 is used by inserting it into the distributor 420A of FIG. Therefore, this modified example has many parts that overlap with the invention described above, and the description of the overlapping parts will be omitted. The same symbols in FIGS. 3 and 1 are connected according to the symbols.

In FIG. 3, 421B and 424B are arithmetic units,
The first-phase 90 ° anti-phase current signal Q _1ND and the first-phase in-phase anti-phase current signal P _{1ND described above} are input, and equations (10) and (11) are respectively inputted.
The second phase 90 ° anti-phase current signal Q _2ND and the third phase 90 ° anti-phase current signal Q _3ND are output through the above calculation. These Q _2ND and Q _3ND are the signals Q obtained by the equations (7) and (8) described above.
It is the same as _2ND and _Q3ND .

A setter 437 outputs a reactive current setting signal Q _1MAX . 430B is a distributor, which is a positive-phase reactive current signal Q
_1PD , 1st phase, 2nd phase, 3rd phase 90 ° negative phase current signal Q
_1ND , Q _2ND , Q _3ND and reactive current setting signal Q _1MAX are input, and the calculation of formula (12) is performed based on these signals, and the first
Phase, second phase, third phase current command ▲ I ^* _U ▼, ▲ I ^* _V ▼, I
Output ▲ ^* _W ▼. Here, 446B, 447B, 44
8B is a coefficient unit which doubles the input signal and outputs it. Further, reference numerals 438A, 439B, 440B, and 441B are adders, which add the illustrated signals with the illustrated polarities.

The current commands ▲ I ^* _U ▼, ▲ I ^* _V ▼, and ▲ I ^* _W ▼ are the above-mentioned formulas.
It is exactly the same as the current command value obtained in (9). Therefore, based on this ▲ I ^* _U ▼, ▲ I ^* _V ▼, ▲ I ^* _W ▼
If the current of the reactor portion 300 in the figure is controlled, the same compensation effect as that of the invention shown in FIGS. 1 and 2 can be obtained.

As described above, in this embodiment, the arithmetic units 421B and 424B shown in FIG.
Can be simplified by the arithmetic units 421A and 424A shown in FIG.

Next, another embodiment of the present invention will be described with reference to FIG. This embodiment also relates to the modification of FIG. 2 of the invention described above, and FIG. 4 is inserted into the distributor 420A of FIG. 1 for use. Therefore, the description of the same parts as those of the above-mentioned invention will be omitted.

In FIG. 4, 421C and 424C are arithmetic units,
The first-phase 90 ° negative-phase current signal Q _1ND and the first-phase in-phase negative-phase current signal P _{1ND described above} are input, and the equations (13) and (14) are respectively inputted.
2nd phase in-phase current signal P _2ND , 3rd phase
The in-phase and out-of-phase current signal P _3ND of the phase is output. This P _2ND , P
_3ND is the same as the signals P _2ND and P _3ND obtained by the above described equations (7) and (8).

A setter 437 outputs a reactive current setting signal Q _1MAX . 430C is a distributor, which is a positive-phase reactive current signal Q
_{Input 1PD} , first-phase, second-phase, third-phase in-phase reverse-phase current signals P _1ND , P _2ND , P _3ND and reactive current setting signal Q _1MAX, and calculate equation (15) based on these signals. The current command for the first phase, second phase, and third phase ▲ I ^* _U ▼, ▲ I ^* _V ▼,
Output ▲ I ^* _W ▼. Here, 431A, 432A, 4
33A is a coefficient unit for input signal Double and output. 446B, 447B, 448B are also coefficient units, which double the input signal and output it. Also, 438A, 4
39B, 440B, 441B, 434A, 435A, 4
36A is an adder that adds the signals shown in the drawing with the polarities shown.

The current commands ▲ I ^* _U ▼, ▲ I ^* _V ▼, and ▲ I ^* _W ▼ are the above-mentioned formulas.
It is exactly the same as the current command value obtained in (9). Therefore, the current of the reactor part 300 in FIG. 1 is controlled based on these ▲ I ^* _U ▼, ▲ I ^* _V ▼, and ▲ I ^* _W ▼. Then, the above-mentioned first
The same compensation effect as the invention according to FIGS. 2 and 3 can be obtained.

As described above, in this embodiment, the arithmetic units 421C and 424C shown in FIG.
Can be simplified by the arithmetic units 421A and 424A shown in FIG.

〔The invention's effect〕

As is clear from the above description, the reactive power compensator of the present invention has the following effects. That is, (1) the current generated by a fluctuating load such as an arc furnace is an unbalanced current containing a large amount of reverse phase components together with the positive phase components, but in the present invention, these positive phase components and reverse phase components are clearly defined. Since it can be detected separately, the target to be compensated by the reactive power compensator becomes clear, that is, the control focusing only on the positive phase reactive power, the control focusing only on the negative phase current, or the current balancing control (reverse control). Phase current compensation) is prioritized, and positive phase reactive power compensation is performed only when there is extra capacity in the device (priority control), etc. can be freely configured, and more advanced compensation control than the conventional one can be performed. Easy to achieve.

(2) Even if the load current fluctuates, the positive phase component and the negative phase component can be continuously detected in the form of a DC signal regardless of the lead power factor / lag power factor. Since it does not enter, stable compensation control can be realized.

(3) In the control circuit, when detecting the positive-phase component and the negative-phase component of the load current, simple elements such as a coefficient multiplier, an adder, and a multiplier are used as signal processing means to perform a simple calculation. It is possible to obtain an accurate and high-accuracy signal (regarding the positive phase component and the negative phase component) without any ambiguity in the detection signal, only by obtaining the required signal. Also, because the circuit is simple,
The cost will be lower.

(4) Therefore, in the reactive power compensator according to the present invention, since the information regarding the positive-phase current / negative-phase current is accurately separated and detected, even if the load fluctuates rapidly like an arc furnace, Since it is possible to perform control by clarifying the target of compensation (that is, whether to control the positive-phase reactive current, the negative-phase current, etc.), stable and highly accurate reactive power compensation can be performed.

As described above, the reactive power compensator of the present invention incorporates a completely new control concept that "the positive phase component and the negative phase component are separately detected and the compensation control is performed based on them" which is not in the conventional control. Therefore, it is possible to sufficiently meet the demands for the reactive power compensation control which will become more complicated and sophisticated in the future.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIGS. 2 to 4 are block diagrams showing different embodiments of the present invention, and FIG. 5 is a reactive power compensation to which the present invention is applied. FIG. 6 is a main circuit diagram of the device, and FIG. 6 is a block diagram of a reactive power detection circuit adopted in a conventional reactive power compensating device. 1 ... AC power supply system, 3 ... System impedance, 9, 10
… Arc furnace equipment, 100… Reactive power compensator, 200…
Phase advancing capacitor, 300 ... Reactor part, 350 ... Control circuit, 400 ... Arithmetic circuit, 500 ... Firing control circuit, 40
2 ... Line / phase converter, 403 ... 2 phase converter, 404, 40
8 ... Operation unit, 406, 407 ... Two-phase generator, 409 ... Separator, 410, 411 ... DC detection filter, 412, 41
3 ... Adder, 420A ... Distributor, 500 ... Firing controller,
421A, 424A, 421B, 424B, 421C,
424C ... Operation unit, 431A to 433A, 446B to 4
48B ... Coefficient device, 437 ... Setting device, 434A to 436
A, 438A to 441A, 439B to 441B ... Adder.

Claims (4)

[Claims] 1. A reactive power compensator for compensating for unbalanced power and reactive power generated by a load connected to a multi-phase AC power supply system, wherein a phase is synchronized with a first phase of an N-phase multi-phase AC power supply. θ ^* _1d1 ▼
Unit sine wave signal ▲ e ^* _1d1 ▼ that changes with
° Means to obtain a unit sine wave signal ▲ e ^* _1q1 ▼ whose phase advances and changes, and N-phase multi-phase load currents i _1L , i _2L …… i _NL are detected, and the d-axis is aligned with the voltage of the first phase. The two-phase current signal i _1dL , i
Means for obtaining a _1QL, the signal _{^{▲ e * 1d1 ▼, ▲ e}} * 1q1 ▼ and i _{1 dL,} with ^{_{i 1qL P 1N = ▲ e *}} 1d1 ▼ · i 1dL + ▲ e * 1q1 ▼ · i 1qL Q 1N _{^{= ▲ e * 1d1 ▼ · i}} 1qL - ▲ e * 1q1 ▼ · i means for obtaining signals P _1N, the Q _1N by calculation of _{1 dL,} the signal P _1N, detects the AC component of the Q _1N signal P _1NA, Q
_1NA is obtained and the DC component of P _1N and Q _1N is detected to obtain the signal P
_A means for obtaining _1ND and Q _1ND , and a unit sine wave signal ▲ e ^* _1d2 ▼ and a 90 ° phase which operates based on the phase angle signal ▲ θ ^* _1d1 ▼ and whose phase angle changes by ▲ 2θ ^* _1d ▼ means for obtaining a unit sine wave signal _▲ e ^* 1q2 ▼ delayed, the signal _{^{▲ e * 1d2 ▼, ▲ e}} * 1q2 ▼ and P _1NA, Q based on the _{^{Q 1NA 1PD = ▲ e * 1d2}} ▼ · Q 1NA -▲ e ^* _1q2 ▼ Means for obtaining the signal Q _1PD by calculating P _1NA , and the first and second phases of N-phase polyphase alternating current by performing the calculation using the signals Q _1PD , P _1ND and Q _1ND as input signals A means for creating an N-th phase current command, and controlling the reactive power compensator based on the current command obtained by the means. 2. A means for creating the current command, means for setting a reactive current setting signal Q _1MAX for instructing the maximum value of the reactive power to be compensated by the reactive power compensator, and the signals P _1ND , Q Based on _1ND To obtain the signals P _2ND , Q _2ND , P _3ND , Q _3ND , and the signals Q _1MAX , Q _1PD , Q _1ND , Q _2ND , Q _3ND ,
Based on P _1ND , P _2ND , P _3ND The current command signal ▲ I ^* _U ▼, ▲ I ^* _V ▼, ▲ I ^* _W
3. The reactive power compensator according to claim 1, further comprising: means for creating ▼. 3. A means for generating the current command, means for setting a reactive current setting signal Q _1MAX for instructing a maximum value of reactive power to be compensated by the reactive power compensator, and the signals P _1ND , Q Based on _1ND Signal Q _2ND performs an operation of, the means for obtaining the Q _3ND, the signal _{Q 1MAX, Q 1PD, Q 1ND} , Q 2ND, based on the _{^{Q 3ND ▲ I * U ▼ =}} -Q 1MAX + Q 1PD -2Q 1ND ▲ I ^* _V ▼ = -Q _1MAX + Q _1PD -2Q _2ND ▲ I ^* _W ▼ = -Q _1MAX + Q _1PD -2Q _3ND , and current command signal ▲ I ^* _U ▼, ▲ I ^* _V ▼, ▲ I ^* _W
3. The reactive power compensator according to claim 1, further comprising: means for creating ▼. 4. A means for generating the current command, means for setting a reactive current setting signal Q _1MAX for instructing a maximum value of reactive power to be compensated by the reactive power compensator, and the signals P _1ND , Q Based on _1ND Based on the signals Q _1MAX , Q _1PD , P _1ND , P _2ND , P _3ND , and means for obtaining the signals P _2ND , P _3ND And a means for producing current commands ▲ I ^* _U ▼, ▲ I ^* _V ▼, ▲ I ^* _W ▼.