JPS6321207B2 - - Google Patents

Description

Detailed Description of the Invention For example, in order to suppress flicker caused by the operation of an arc furnace, it is necessary to compensate for the fluctuations in reactive power. The application of the device is considered. FIG. 1 is a schematic diagram for explaining the configuration of a thyristor type reactive power compensator. Arc furnaces F ₁ and F ₂ are connected to the grid via transformers T ₁ and T ₂ , and a reactor is connected in parallel to this via transformer T ₃ .
A phase-advancing capacitor/filter circuit consisting of a capacitor C and an inductance L is connected to a lagging reactive power adjustment circuit in which Re is connected in series with a energization control element in which a thyristor Th is connected in antiparallel so that current can be passed in both directions. . Then, the reactive power detector DD calculates the reactive power component from time to time by the current transformers CT ₁ and CT ₂ and the voltage transformer PT that detect the currents of the arc furnaces F ₁ and F ₂ , and the reactive power component is calculated from time to time. is compared with a reference value, and the pulse phase applied to the firing control terminal of the thyristor is controlled according to the positive or negative magnitude of the reference value.
The output terminal of the control pulse generator PG is connected to the ignition control terminal of the thyristor to control the reactive power. If the pulse is delayed from a certain phase, the current flowing through the reactor Re decreases and the grid voltage increases.

In order to detect the above-mentioned reactive power, the 90 degree phase-lag waveform of the voltage is multiplied by the current, and the second harmonic component generated by the multiplication is removed by a low-pass filter (hereinafter referred to as LPF). Although some configurations are known, such configurations cannot follow rapid changes in reactive power Q due to the nature of the LPF, and therefore,
It is not suitable for things such as anti-flicker measures, where rapid fluctuations need to be detected and these fluctuations immediately reflected in system control.

As described above, the present invention provides a reactive power compensator equipped with a reactive power detection circuit that eliminates the detection delay caused by the use of an LPF and prevents the generation of control signals that may cause erroneous control during control. be.

The present invention will be described below based on the embodiment shown in FIG. 2 and the waveform explanatory diagram in FIG. In FIG. 2, a series circuit of a voltage transformer PT, a variable load Lv, a reactor Re, an antiparallel-connected thyristor Th that conducts current in both directions, and a phase advance/filter capacitor C are connected in parallel to the bus bar. In addition
L ₁ indicates the inductance of the power line.

The secondary side of the voltage transformer PT is connected to a 90 degree phase shifter PS, and the output side of the 90 degree phase shifter PS is connected to a multiplier X ₁ , while the current transformer CT detects the current I of the variable load Lv. is coupled to a variable load Lv, and its secondary side is connected to a multiplier _X1 .

If the system voltage V ₉₀ with a 90-degree phase-lag waveform and the load current I are input into the multiplier X ₁ , the reactive power can be calculated.
By taking the product of the two, an alternating current component of twice the frequency remains in the direct current component, as described above. To remove and smooth this alternating current component, the output from multiplier _X1 is
T ₁ = 1/4f, that is, input to a delay circuit TC that provides a time delay equivalent to a 1/4 thyristor, and a delayed reactive power signal Q that passes through this delay circuit TC and a direct reactive power signal Q that does not go through this delay circuit. is an adder
A ₁ is added and 2Q is added as shown in Figure 3.
appears on its output side. At this time, the system voltage V
The second harmonic components of both reactive power signals Q generated by multiplying by the load current I and the load current I cancel each other out, and the ripple is eliminated.

In this way, the output of the adder _A1 contains almost no second harmonic component, and generates a reactive power signal Q with extremely small errors that quickly responds to load reactive power fluctuations.
This signal Q passes through the reactive power phase conversion circuit QPS,
It is input to the control pulse generator PG, and its output controls the compensation reactive power by controlling the firing of the thyristor Th connected to the reactor Re.

Next, the embodiment shown in FIG. 4 will be described. The same parts as in FIG. 2 are indicated by the same reference numerals.

As explained in the embodiment of FIG. 2, the instantaneous value of reactive power can be output at the adder _A1 , but of the load current input to the multiplier _X1 ,
By subtracting the current corresponding to the active power component, the amplitude of the current input to this multiplier _X1 can be reduced, and the second harmonic contained in the multiplier _X1 output (reactive power output) can be reduced. Ripple can be reduced.

In the embodiment of FIG. 4, a circuit is added to the circuit of the embodiment of FIG. 2 to generate a current component corresponding to the active power component, subtract it from the load current I, and input it to the multiplier _X1 . ing.

As shown in the figure, the system voltage V and load current I are multipliers.
X ₂ and the output of multiplier X ₂ is the low pass filter LPF ₁
, and is input to the multiplier X ₃ , and the system voltage V is input to the multiplier X ₃ .

An active power component is generated by multiplying the system voltage V and the load current I, but since this contains a second harmonic, it is removed and smoothed by LPF ₁ . Since a waveform in phase with the voltage waveform and proportional to the active power P is a current component corresponding to the target active power component, this is generated by the multiplier _X3 . If this current component is Ip, Ip sinωt∝P×V
It is expressed as sinωt.

Since the active power component is passed through LPF ₁ as described above, even if there is a change in the active power component, Ip appears as Ipav with a gentle change. this
Ipav has a small second harmonic ripple,
Ip is subtracted from the load current I by subtractor S and multiplier
Enter _X1 . As a result, the effective current component in the load current I is removed and input to the multiplier _X1 , so it is possible to reduce the second harmonic component included in the output from the multiplier _X1 . The following operation is similar to the embodiment shown in FIG.

Next, the embodiment shown in FIG. 5 will be described. The same parts as in FIG. 2 are indicated by the same reference numerals.

During the reactive power component multiplied by multiplier X ₁ ,
Of the reactive power generated during equipment operation, a quasi-stationary component that is not involved in relatively long time fluctuations is included, and according to the calculation by the _multiplier The computation that also includes the component is performed, and therefore the second harmonic component generated by the computation also becomes large. In this example, the second
The circuit of the embodiment shown in the figure is provided with a circuit that subtracts the current corresponding to the quasi-steady portion of the reactive power from the load current I and inputs it to the multiplier _X1 , thereby reducing the second harmonic ripple. It is.

As shown in the figure, the reactive power is calculated by inputting the 90-degree delayed phase waveform of the grid voltage V and the load current I to a multiplier _X4 , and the reactive power output is removed by a low-pass filter _LPF2. , smooth. In this case, by selecting the characteristics of the LPF ₂ to have a long time constant of about several seconds, the fluctuating components of the reactive power are averaged out and do not appear, and quasi-steady reactive power can be obtained.

The waveform that is 90 degrees behind the voltage waveform and whose amplitude is proportional to the quasi-steady reactive power value Q is the current component that corresponds to the target quasi-steady reactive power component, so this is the current component that is 90 degrees behind the voltage waveform. By inputting the voltage and the quasi-stationary reactive power into a multiplier _X5 , an average reactive current component Iqav can be obtained. Iqav sinωt∝Q
×V sin (expressed as ωt−90°. This Iqav has a small second harmonic ripple, and Iqav is subtracted from the load current I by a subtracter S and input to _the multiplier Since the quasi-stationary reactive current component in the current I is removed and input to the multiplier _X1 , it is possible to reduce the second harmonic component included in the output from the multiplier _X1 . It operates similarly to the embodiment shown in the figure.

Figure 6 shows the embodiment of Figures 4 and 5 in which the active current component and the quasi-steady reactive current component in the load current are subtracted, and the input to multiplier _X1 is further reduced to only the variation. It is.

The active current component Ipav and the quasi-steady reactive current component Iqav each have little second harmonic ripple, and if they are added by adder _A2 , the active current component Ipav is in phase with the grid voltage,
Iqav is in a voltage phase delayed by 90 degrees, and by combining these current components, it is possible to generate a current close to the magnitude and phase of the load current I. The active current component and the reactive current component are subtracted from the load current I in the subtracter S, and I-(Ipav+Iqav) is added to the multiplier.
The voltage is input to X ₁ , while the voltage with a phase lag of 90 degrees is input. As already explained, the output of multiplier _X1 is a delay circuit that provides a time delay corresponding to 1/4 cycle.
It is input to TC and its output side is connected to adder A ₁ , and adder A ₁ is also connected to the output end of multiplier X ₁ , so the output corresponding to twice the reactive power Δq is output from adder A _1. appears at the output end of Δq is naturally positive or negative. When instantaneous fluctuations occur in reactive power, as mentioned above, a large LPF ₂ with a specific number is used in the circuit that generates the reactive current corresponding to reactive power, and such sudden fluctuations are smoothed out. Therefore, it appears only as a gentle fluctuation in the average reactive current component Iqav. When reactive current component Iqav and/or active current component Ipav are subtracted from load current I, I-(Ipav+Iqav)
It can be assumed that the reactive power value Δq generated by .
This reactive power value Δq is converted to the reactive power phase conversion circuit QPS.
The thyristor is input to the control pulse generator PG via the
Reactive power is controlled by controlling the firing phase of Th.

In the above description, in order to simplify the explanation, the coefficients and constants of each element constituting the circuit are not explained, but they are omitted because they would be understood by those skilled in the art.

As described above, in the present invention, second harmonic ripple is extremely unlikely to be included in the detected value, and there is no delay in operation unlike when ripples are removed using an LPF, so high-speed invalidation is possible. It can be said that it is extremely suitable for a reactive power compensator used for flicker countermeasures that require power control.

[Brief explanation of the drawing]

FIG. 1 shows an example of a thyristor-type reactive power compensator, and FIGS. 2, 4, 5, and 6 each show a reactive power compensator according to an embodiment of the present invention,
FIG. 3 is a drawing for partially explaining the present invention. PT...Voltage transformer, CT, CT ₁ , CT ₂ ...Current transformer,
_T1 , _T2 , _T3 ...Transformer, C...Capacitor, L, _L1
...Inductance, Th...Thyristor, X ₁ , X ₂ ,
_{X 3 , _ _ _ _} Control pulse generator, F ₁ ,
F ₂ ...Arc furnace, Lv...Variable load, QPS...Reactive power phase conversion circuit.

Claims (1)

[Claims] 1. A multiplier that multiplies a 90-degree phase-lag voltage and a load current, a delay circuit that provides a time delay corresponding to 1/4 cycle to the reactive power component resulting from this multiplication, and the output side of this delay circuit. An adder is connected to the multiplier, and the adder is also connected to the output of the multiplier. The second harmonic component generated by the multiplication is canceled by adding the reactive power signal to the reactive power signal, and the output of this adder generates a reactive power component that hardly contains the second harmonic component. A reactive power compensator characterized in that it controls energization of a reactor according to the following. 2. The reactive power compensator according to claim 1, wherein a current component corresponding to active power is removed from the input load current to reduce the input current value to the multiplier. 3. The invalidity according to claim 1, characterized in that the input current value to the multiplier is reduced by removing a current component corresponding to quasi-steady reactive power from the input load current. Power compensator. 4. A patent claim characterized in that a current component corresponding to active power and a current component corresponding to quasi-steady reactive power are removed from the input load current to reduce the input current value to the multiplier. The reactive power compensator according to item 1.