JPH07222362A - Reactive current detection circuit - Google Patents

Abstract

PURPOSE:To detect a reactive current at high speed by detecting the effective current of a load temporarily and subtracting the effective current from a load current thereby detecting the reactive current. CONSTITUTION:An effective power generating circuit 23 generates an effective power P from a load current IL and a load voltage VL detected, respectively, through a current transformer 6 and a potential transformer 7. An effective current generating circuit 24 generates an effective current Ip based on an output from the effective power generating circuit 23. A reactive current generating circuit 25 subtracts the effective current Ip generated by the effective current generating circuit 24 from the load current IL detected by the current transformer 6 thus detecting the reactive current Iq. Consequently, the reactive current Iq can be detected based on the effective current Ip exhibiting high response to the rising of the load current IL. This circuit realizes high speed detection of reactive current Iq.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reactive current detecting circuit, and more particularly, to a reactive current detecting circuit incorporated in a TCR type or self-exciting type reactive power compensating device for detecting a reactive current generated by a variable load.

[0002]

2. Description of the Related Art In a power system, a variable load 4 [hereinafter, simply referred to as load] such as a large-capacity arc furnace, electric iron load, or steel rolling load that causes system voltage fluctuation due to reactive power fluctuation.
, The load 4 is placed between the system power supply 1 and the load 4.
In order to compensate the reactive power generated in the system, for example, as shown in FIG. 4, a self-excited reactive power compensator 5 in which a system power supply 1 and an inverter 2 are interconnected via a transformer impedance 3 is provided. It is common.

This reactive power compensator 5 detects a load current I _L and a load voltage V _L by a current transformer 6 and a transformer 7 connected to a load 4, and a reactive current detection circuit 8 detects a load current I _L.
The reactive current component inside is detected. By controlling the drive of the inverter 2 based on the detection signal of the reactive current, a compensating current having a phase opposite to the reactive current generated in the load 4 is generated following the fluctuation of the load 4, and the compensating current is generated in the system. By doing so, the voltage fluctuation of the system power supply 1 due to the load fluctuation is suppressed.

The above-mentioned reactive current detection circuit 8 specifically detects the load current I _L via the current transformer 6, and
After detecting the load voltage V _L via the transformer 7, the 90 ° delay voltage generation circuit 9 generates a 90 ° delay voltage V _{L ′} with respect to the load voltage V _L [see FIG. 5 (a)]. Then, the above-described load current I _L and 90 ° delay voltage V _{L ′} are multiplied by the reactive power calculation circuit 10, and the reactive power value is calculated using a filter circuit that removes a frequency component that is twice the system frequency. The reactive current value is generated by multiplying the reactive power value by the reference current signal waveform in phase with the 90 ° delay voltage V _{L ′} in the multiplication circuit 11, and this reactive current signal is used as the reactive current command value.

A gate signal generation circuit 12 generates a gate signal based on the reactive current command value, and the inverter 2 is drive-controlled by the gate signal.

[0006]

By the way, FIG. 5 (a)
It is assumed that the load current I _L detected by the reactive current detection circuit 8 is delayed by 60 ° with respect to the load voltage V _L , as shown in FIG. In the conventional reactive current detection circuit 8, as described above, the 90 ° delay voltage V _{L ′} is generated by the 90 ° delay voltage generation circuit 9 with respect to the load voltage V _L. By multiplying the 90 ° delay voltage V _{L ′} and the load current I _L by the reactive power calculation circuit 10, a reactive power signal q is generated as shown in FIG. 5B. Here, based on the waveform of the reactive power signal q shown in FIG.
The average value of the reactive power signal q becomes the reactive power Q to be obtained, and the reactive current signal I _q is obtained by using the current signal delayed by 90 ° from the load voltage V _L.

In the case of a three-phase equilibrium state consisting of a phase, b phase and c phase, the load current I _L between the lines ab, bc, ca is
_{ab = (I a -I b)} / 3, I bc = (I b -I c) / 3,
If I _ca = (I _c −I _a ) / 3, the reactive power signal q _ab between the lines _ab is obtained by q _ab = I _ab × (−√3 · V _C ), where V _C = ( _VL / √3) · cos ωt, I _ab =
If I _L · sin (ωt−θ), the reactive power signal q _ab based on the 90 ° delay voltage V _{L ′} and the load current I _L described above is q _ab = V _L · I _L × {cos (θ−90) °) -cos (2ωt-
90 ° −θ)} / 2, and the reactive power Q _ab becomes Q _ab = V _L · I _L × cos (θ−90 °) / 2. As for the line-to-line bc and ca, the reactive power signals _qbc and _qca and the reactive powers _Qbc and _Qca are obtained in the same manner as described above.

As a result, when the load current I _L rises from 0 [see FIG. 5 (a)], the reactive power Q whose average value is the reactive power Q is based on the rising time of the load current I _L. The phase of 60 ° of ⅛ cycle or more is required to reach [1] (see FIG. 5B), and a considerable delay occurs in the detection of the reactive power Q to be obtained and the reactive current signal I _q. was there. In the reactive power compensator 5, in order to suppress the voltage fluctuation of the system power supply due to the load fluctuation, even a compensation operation delay of about 5 ms from the voltage fluctuation occurrence to the compensation current output has a great influence, and at least 1/8. The current situation is that the delay of detection itself in the cycle [2 ms] cannot be ignored.

Therefore, the present invention has been proposed in view of the above problems, and an object thereof is to provide a reactive current detection circuit capable of speeding up the detection of a reactive current by a simple means. To do.

[0010]

As a technical means for achieving the above object, the present invention provides a reactive power for generating a compensation current having a phase opposite to that of the variation of the reactive current of a fluctuating load connected to a system power supply. In a reactive current detection circuit that is incorporated in a compensator and detects a reactive current generated by a fluctuating load through a current transformer and a transformer, the active power from the load voltage and load current detected by the current transformer and transformer. And an active current generation circuit that generates an active current based on the output from the active power generation circuit,
And a reactive current generating circuit for subtracting the active current output from the active current generating circuit from the load current detected by the current transformer.

Further, the active power generation circuit removes a frequency component twice the system frequency from the active power operation circuit for multiplying the load voltage and the load current and the active power signal output from the active power operation circuit. A filter circuit, and the active current generating circuit divides a direct current signal value of active power output from the filter circuit by a direct current signal value (effective value) of a load voltage, and an effective current operation circuit thereof. It is characterized in that it is configured by an active current waveform calculation circuit for multiplying the DC signal value (effective value) of the active current output from the current calculation circuit by the current signal waveform in phase with the load voltage.

[0012]

In the reactive current detection circuit according to the present invention, the effective current is detected with a good response to the rising of the load current, and the effective current is subtracted from the load current based on the effective current to detect the reactive current to be obtained. Detect current. By once detecting the active current in this way, the detection delay with respect to the rise of the load current can be reduced as much as possible as compared with the case where the reactive current is directly detected, and the reactive current can be detected at high speed.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a reactive current detection circuit according to the present invention will be described with reference to FIGS. The same parts as those in FIGS. 4 and 5 are designated by the same reference numerals, and a duplicate description will be omitted.

The reactive current detection circuit 22 incorporated in the reactive power compensator 21 is connected to a load 4 via a current transformer 6 and a transformer 7 as shown in FIG.
And an active power generation circuit 23 that generates an active power signal p from the load voltage V _L and the load current I _L detected by the transformer 7, and an active current I _p based on the output from the active power generation circuit 23. And a reactive current generating circuit 25 that subtracts the active current I _p output from the active current generating circuit 24 from the load current I _L detected by the current transformer 6. It

The following description is based on a three-phase equilibrium state consisting of a-phase, b-phase and c-phase, but in FIG.
Since the same reactive current detection circuit 22 is configured for ab, bc, and ca, the reactive current detection circuit 2 in the line ab is shown in FIG.
2 shows only the reactive current detection circuit 2 between the lines bc and ca.
The circuit configuration of 2 is omitted.

The active power generation circuit 23 described above is specifically, as shown in FIG. 3, a load voltage V of the lines ab, bc, ca.
_L [V _ab , V _bc , V _ca ] and load current I _L [I _ab , I _bc ,
I _ca ], and a filter circuit 27 that removes a frequency component that is twice the system frequency from the active power signal output from the active power calculation circuit 26. The generation circuit 24 divides the active power P (DC signal value) output from the filter circuit 27 by the DC signal value (effective value) of the load voltage V _L , and the active current operation circuit 28. It is composed of an active current waveform calculation circuit 29 for multiplying the DC signal value (effective value) of the output active current by the load signal V _L of the lines ab, bc, ca and the current signal waveform of the same phase.

In the figure, 30 is a BPF circuit for removing harmonic components of the load voltage V _L of the lines ab, bc, ca detected by the transformer 7, 31 is a line ab, bc, ca. DC signal value of the load voltage V _L filter circuit for generating the (rms), 32 between lines ab, bc, the load voltage V _L and the phase waveform generation circuit for generating a reference current signal waveform of the ca And
Further, 33 is an arithmetic circuit for generating a line-to-line ab, bc, the load current I _L of ca from the load current I _L of each phase detected by the current transformer 6.

Reactive current detection circuit 2 having the above-mentioned configuration
In 2, the reactive current I _q is detected by performing signal processing based on the load voltage V _L and the load current I _L according to the following procedure.

First, the line a by the transformer 7 and the current transformer 6
The load voltage V _L and load current I _L of b, bc, and ca are detected, respectively. Regarding the load voltage V _L between the lines ab, bc, and ca detected by the transformer 7, the BPF circuit 30 removes harmonic components, while the load current I of each phase detected by the current transformer 6 is removed.
_{For L} , the arithmetic circuit 33 generates the load current I _L of the lines ab, bc, ca. The active voltage signal is calculated by multiplying the load voltage V _{L of} these lines ab, bc, ca by the load current I _L in the active power calculation circuit 26, and the filter circuit 2 is calculated.
The active powers P _ab , P _bc , and P _ca (DC signal values) are removed by removing the frequency component twice the system frequency from the active power by 7.
To generate.

On the other hand, between the lines output from the BPF circuit 30
ab, bc, and averaging the load voltage V _L ca filter circuit 31 generates a DC signal value of the load voltage V _L (effective value), DC signal value of the load voltage V _L (effective value) It is input to the active current calculation circuit 28. The active current calculation circuit 28
Then, the active power P _ab output from the filter circuit 27,
By dividing P _bc and P _ca by the DC signal value (effective value) of the load voltage V _L output from the filter circuit 31,
Obtain the DC signal value (effective value) of the active currents of ab, bc, and ca.

Between the lines output from the BPF circuit 30
The waveform generator 32 generates a reference current signal waveform in phase with the load voltage V _L of ab, bc, ca, and the effective current waveform calculator 29.
To enter. In the active current waveform calculation circuit 29, the direct current signal value (effective value) of the active current output from the active current calculation circuit 28 is multiplied by the reference current signal waveform output from the waveform generation circuit 32, so that the line ab , Bc, and ca, the effective current I _pab included in the load current I _L can be obtained and input to the reactive current generation circuit 25.

In the reactive current generating circuit 25, the line ab output from the arithmetic circuit 33, the line current ab output from the active current waveform arithmetic circuit 29 from the load current I _L of bc and ca,
By subtracting the active currents I _pab , I _pbc , and I _pca of bc and ca, the reactive currents I _qab , I _qbc , and I _qab in the load current I _L ,
I _qca is output and used as the reactive current command value. The gate signal generation circuit 12 generates a gate signal based on the reactive current command value, and the inverter 2 is drive-controlled by the gate signal.

Here, as shown in FIG. 2A, it is assumed that the load current I _L detected by the reactive current detection circuit 22 is delayed by 60 ° with respect to the load voltage V _L. In the reactive current detection circuit 22 of the present invention, as described above, the active power signal p is once detected based on the load voltage V _L and the load current I _L of the lines ab, bc, ca. Based on the waveform of the active power signal p shown in FIG. 7B, the average value of the active power signal p becomes the active power P,
The active current I _p calculated from the active power P is the load current I _L
By subtracting from, the reactive current I _{q to} be obtained is obtained. In the present invention, since the effective current I _{p having} a good response to the rise of the load current I _L is once detected,
As in the conventional reactive current I _q can be reduced as much as possible the detection delay with respect to the rise of the load current I _L than to directly detect, thereby speeding the detection of reactive current I _q.

Here, three phases consisting of a phase, b phase and c phase
In the equilibrium state, load current I between lines ab, bc, ca_LI
_ab= (I_a-I_b) / 3, I_bc= (I_b-I_c) / 3,
I_ca= (I_c-I_a) / 3, the effective power of line ab
Signal p_abIs p_ab= I_ab× V _abCalculated by V_ab= V_L
・ Sin ωt, I_ab= I_L・ Assuming sin (ωt−θ),
Load voltage V described above_LAnd load current I_LActive power based on
Signal p_abIs p_ab= V_L・ I_L× {cos θ−cos (2ωt−θ)} / 2, and the active power P_abIs P_ab= V_L・ I_L× cos θ / 2. Note that the line spacings bc and ca are also valid, as described above.
Power p_bc, P_caAnd active power P_bc, P_caIs required.
This required active power P_ab, P_bc, P_caMore load voltage
V_LEffective current I using the current signal in phase with_pIs required,
Furthermore, the load current I_LMore effective current I_pBy subtracting
Reactive current I_qIs required.

As a result, when the load current I _L rises from 0 [see FIG. 2 (a)], the active power signal p, which is the average value of the active power signal p, is based on the rising time of the load current I _L. It takes about 15 ° phase until it reaches [Fig. 2 (b)], and in the conventional case [Fig. 5 (b)].
It is possible to detect 1/8 cycle faster than that, and it is possible to follow this and speed up the detection of the reactive current.

[0026]

According to the reactive current detection circuit of the present invention, the active current of the load is first detected, and the active current is subtracted from the load current to detect the reactive current. Since the reactive current that should be obtained by the active current detection with good response to the rising can be detected, the detection delay for the rising of the load current should be minimized as compared with the case where the reactive current is directly detected. Therefore, it is possible to provide a reactive current detection circuit which has a high responsiveness and is capable of speeding up reactive current detection.

[Brief description of drawings]

FIG. 1 is a schematic configuration circuit diagram showing an embodiment of a reactive current detection circuit according to the present invention.

2A is a waveform diagram showing load voltage and load current, FIG.
(B) is a waveform diagram showing active power and active current obtained by multiplication of load voltage and load current

FIG. 3 is a circuit diagram showing a specific configuration of the reactive current detection circuit of FIG.

FIG. 4 is a schematic configuration circuit diagram showing a conventional example of a reactive current detection circuit.

5A is a waveform diagram showing a load voltage and a load current and a 90 ° delay voltage, and FIG. 5B is a waveform diagram showing a reactive power and a reactive current obtained by multiplying a 90 ° delay voltage and a load current.

[Explanation of symbols]

1 System power supply 2 Inverter 4 Variable load 6 Current transformer 7 Transformer 21 Reactive power compensator 22 Reactive current detection circuit 23 Active power generation circuit 24 Active current generation circuit 25 Reactive current generation circuit 26 Active power calculation circuit 27 Filter circuit 28 Effective Current calculation circuit 29 Active current waveform calculation circuit _VL Load voltage _IL Load current p Active power signal P Active power

Claims (3)

[Claims] 1. A reactive current compensator for generating a compensating current having a phase opposite to that of a fluctuation of a reactive current of a fluctuating load connected to a system power source, and incorporating the reactive current generated by the fluctuating load into a current transformer and a transformer. Based on the output from the active power generation circuit that generates active power from the load voltage and the load current detected by the current transformer and the transformer, and the output from the active power generation circuit. A reactive current generating circuit for generating an active current, and a reactive current generating circuit for subtracting an active current output from the active current generating circuit from a load current detected by a current transformer. Detection circuit. 2. The active power generation circuit includes an active power calculation circuit that multiplies a load voltage and a load current, and a filter that removes a frequency component twice the system frequency from the active power output from the active power calculation circuit. And a circuit, and
The active current generating circuit divides a direct current signal value of active power output from a filter circuit by a direct current signal value (effective value) of a load voltage, and an active current output from the active current operation circuit. 2. The reactive current detection circuit according to claim 1, wherein the DC signal value (effective value) is multiplied by a current signal waveform in phase with the load voltage. 3. The reactive current detection circuit according to claim 1, wherein the active power generation circuit is a product of a reference sine wave signal synchronized with a load voltage and a load current.