JP5716961B2 - Control device for reactive power compensator - Google Patents

Description

  The present invention relates to a technique for compensating for reactive power generated by an arc furnace load or the like and suppressing voltage flicker in an electric power system.

  FIG. 5 shows a use state of the reactive power compensator for compensating the reactive power of the load. In FIG. 5, the reactive power compensator 1 is installed between the system impedance 3 of the power system 2 and the load 4, and reacts with the reactive power generated by the load 4 such as an arc furnace load, and thus the voltage flicker caused by the reactive power. The compensation device main body 1 ′ including the thyristor 5, the reactor 6, and the capacitor 7, and the control device 13 for controlling conduction of the thyristor 5 are configured.

The reactive power compensator 1 compensates reactive power generated by the load 4 in order to compensate for voltage flicker. That is, as shown in FIG. 5, _assuming that the reactive power generated by the load 4 is Q _f , the reactive power of the compensation device main body 1 ′ is Q _t , and the reactive power of the power system 2 is Q _s , Q _t = Q _f By controlling the compensator body 1 ′ so that the reactive power of the power system 2 becomes Q _s = 0, fluctuations in the system voltage and thus voltage flicker can be suppressed.

Next, the configuration and operation of the control device 13 will be described with reference to FIG. In FIG. 6, the same components as those in FIG.
The control device 13 shown in FIG. 6 is described, for example, in FIG. 6 of Patent Document 1. This control device 13 includes a reactive power detection circuit 10, a gain 11, and a firing angle control circuit 12. ing. Disable power detection circuit 10, from the a system voltage _{V s} detected by the load current _{I f} and PT8 detected by CT9, calculates the reactive power _{Q f} of the load 4 in FIG. The reactive power Q _f is multiplied by the value K of the gain 11 obtains the K × Q _f, the thyristors 5 compensation device body 1 'is conductive in accordance with a firing angle α that was computed by a subsequent firing angle control circuit 12, Reactive power _Qt is generated.

Here, since the reactive power detection circuit 10 is a circuit that predicts the reactive power Q _f from the load current _If and the system voltage V _s , the load 4 is an arc furnace load or the like, and the load current _If is steep and random. If you change to, the prediction error is generated in the reactive power Q _f. Therefore, in the prior art of FIG. 6, by multiplying the gain 11, which is set in advance in the reactive power Q _f, and corrects the prediction calculation result.

The voltage flicker is also called ΔV ₁₀ and is measured by a flicker meter 18 as shown in FIG. According to the Institute of Electrical Engineers of Japan Technical Report II No. 72, the voltage flicker ΔV ₁₀ is obtained by changing the fluctuation width of the voltage fluctuation component of the fluctuation frequency f _n obtained as a result of frequency analysis of the voltage fluctuation for 1 minute to ΔV _n and the fluctuation frequency f _n . When the corresponding luminous coefficient and a _n, defined by equation 1 below, luminous coefficient a _n are defined as in FIG.

On the other hand, the above-described prediction error correction gain 11 is adjusted by changing its value little by little so that the reactive power compensation effect becomes the highest according to the load 4. That is, since the compensation effect is measured by changing the gain and the operation of changing the gain again according to the measurement result is repeated, the adjustment operation for setting the gain 11 as the optimum compensation gain requires a lot of time.
The compensation effect may not be improved by adjusting the gain 11, and in this case, the capacity of the reactive power compensator 1 must be increased.

For such a problem, for example, as shown in FIG. 8, a signal obtained by multiplying a detection value by the reactive power detection circuit 10 by a plurality of gains is subjected to various calculations to calculate a plurality of voltage flickers, A method for determining the optimum compensation gain from the above is provided, and this prior art is described in FIG.
8, 13A is a control device, 111 to 113 are gains, 121 to 123 are firing angle control circuits, 141 to 143 are reactive power compensator models, 151 to 153 are system models, and 161 to 163 are voltage flicker detection circuits. , 17 are minimum value selection circuits, 201 to 203 are adders, and the other components are given the same numbers as in FIG. Incidentally, in FIG. 8, alpha ₁ to? ₃ are firing _angle, I t1 _{~I t3} compensation _current, V 1 ~V ₃ shows the amount of voltage variation.
Here, the reactive power compensation device model 141 to 143, has a function of calculating the compensation current _I t1 _{~I t3} when driving the thyristors 5 in FIG. 5 in accordance with the firing angle alpha ₁ to? _3, system model 151 ～153 has a function of calculating the voltage change amount _V 1 ~V ₃ strains of when the compensation current _I t1 _{~I t3} the load current _{I f} is superimposed respectively.

In the controller 13A, when the current value of the gain 111 to K1, the gain 112 and 113 respectively K1 + .DELTA.G, is set to K1-.DELTA.G, firing angle control circuit 121 to 123 is the reactive power _{Q f} and the respective gains The firing angles α _{1 to} α ₃ are respectively calculated from the multiplication results of.
Compensator model 141 to 143 calculates the compensation current _I t1 _{~I t3} corresponding to firing angle alpha ₁ to? _3, adders 201 to 203 at a load current _{I f} and added value of the system model 151 to 153 To obtain voltage fluctuation amounts V _{1 to} V ₃ . The voltage flicker detection circuits 161 to 163 have the same function as the flicker meter, and calculate voltage flicker from the voltage fluctuation amounts V _{1 to} V ₃ , respectively. The minimum value selection circuit 17 selects a minimum value from the voltage flickers output from the voltage flicker detection circuits 161 to 163, and sets this as a gain 11 as an optimum compensation gain.
That is, in this prior art, the compensation amount is calculated by each of a plurality of compensation device models having different gains, and the control amount when the compensation amount is the smallest among them is adopted as the control amount of the actual compensation device, thereby shortening the time. Therefore, optimal reactive power compensation control can be realized.

Here, the reactive power compensator has a purpose of suppressing voltage flicker generated by a load and a purpose of performing power factor compensation by reactive power. In other words, the reactive power compensator is required to suppress voltage flicker caused by fluctuations in load reactive power and compensate for power factor reduction caused by fixed load reactive power.
Therefore, according to the method of setting the gain 11 according to only the voltage flicker detection value as shown in FIG. 8, there is a problem that the power factor reduction due to the fixed load reactive power cannot be sufficiently compensated.

The above problem will be described with reference to FIG.
Now, the reactive power at the front stage of the gain 11 in FIG. 8 is Q ₁ (indicated as Q _{f in} FIG. 8), and the reactive power at the rear stage of the gain 11 is Q ₂ . Here, the reactive power Q ₁ is decomposed into a reactive power fixed frequency Q _1A and reactive power fluctuation Q _1B, also the reactive power Q ₂ is decomposed into a reactive power fixed frequency Q _2A and reactive power fluctuation Q _2B The reactive power fixed components Q _1A and Q _2A cause a power factor decrease, and the reactive power fluctuation components Q _1B and Q _2B cause a voltage flicker.

For example, when the reactive power fixed part Q _1A and the reactive power fluctuation part Q _1B are expressed as shown in FIG. 9A, the value of the gain 11 is ½ of the value up to that time by the conventional technique shown in FIG. 9B, as shown in FIG. 9B, the reactive power fixed portion Q _2A and the reactive power fluctuation portion Q _{2B in} the latter stage of the gain 11 are both the reactive power fixed portion Q _1A and the reactive power fluctuation portion Q _1B. 1/2 of this.
Therefore, even if the voltage flicker can be suppressed to some extent, the power factor decrease can be compensated only about half.

  For this reason, in order to enhance the power factor reduction compensation function, the load reactive power is separated into the reactive power fixed component and the reactive power fluctuation component, and only the reactive power fluctuation component is used in the manner shown in FIG. It can be considered that the reactive power is compensated by multiplying the optimum gain 11 and adding the result to the fixed reactive power.

Japanese Examined Patent Publication No. 7-104739 (page 2, left column, lines 6 to 39, FIG. 6 and the like) JP 2004-336948 A (paragraphs [0008] to [0013], FIG. 1 etc.)

As described above, the method of compensating the reactive power by multiplying the reactive power fluctuation by the gain 11 and adding the result to the fixed reactive power can be referred to as a compensation method giving priority to the compensation of the power factor reduction. . However, with this method, when the load reactive power exceeds the capacity of the compensation device, there is a concern that the compensation capability of the voltage flicker will be significantly reduced.
That is, as shown in FIG. 10A, when the load reactive power Q exceeding the capacity of the compensator is generated, the compensation beyond the capacity of the compensator cannot be made, so the load shown in FIG. The reactive power Q _comp is to be compensated. For this reason, it becomes impossible to compensate for the reactive power fluctuation portion exceeding the device capacity, and as a result, the compensation capability of the voltage flicker is lowered.

  Therefore, the problem to be solved by the present invention is that the reactive power exceeding the capacity of the compensator is limited by limiting the fixed reactive power according to the excess, thereby compensating for the voltage flicker caused by the reactive power fluctuation. It is an object of the present invention to provide a control device for a reactive power compensator that can be realized in parallel with compensation for power factor reduction.

In order to solve the above-described problem, the invention according to claim 1 is a reactive power compensator that at least compensates for voltage flicker that is linked to a power system and that is caused by a variation in reactive power of a load connected to the power system. In the reactive power compensator configured to control a semiconductor element that operates to exchange reactive power with the power system by a drive signal based on an optimal compensation gain,
Means for detecting reactive power of the load;
Means for separating the detected reactive power into a reactive power fixed component and a reactive power fluctuation component;
Means for generating the drive signal based on a signal obtained by multiplying the reactive power fluctuation by the optimum compensation gain;
Means for calculating a plurality of voltage flickers corresponding to each auxiliary gain based on a result obtained by multiplying the reactive power fluctuation by different auxiliary gains;
Means for selecting the auxiliary gain corresponding to the minimum value among the plurality of calculated voltage flickers and setting the optimum compensation gain;
Means for calculating a ratio between the capacity of the compensation device and the maximum value of reactive power of the load;
Means for limiting the fixed reactive power to less than or equal to the capacity of the compensator by multiplying the fixed reactive power by the ratio;
Means for adding the fixed reactive power after the limit to the output of the optimum compensation gain and the output of the auxiliary gain, respectively.

  According to the present invention, voltage flicker compensation and power factor reduction compensation can be performed in parallel, and in the range where the load reactive power exceeds the capacity of the compensation device, the excess reactive power fixed amount is limited. Thus, a decrease in voltage flicker compensation capability can be avoided.

It is a block diagram which shows embodiment of this invention. It is a block diagram of the isolation | separation computing unit in FIG. It is explanatory drawing for the reactive power fixed part and reactive power fluctuation part before and behind the optimal compensation gain 11 in embodiment of this invention. Load reactive power Q in the embodiment of the present invention, showing the maximum value detected value _{Q max,} the reactive power fixed frequency _{Q A,} the ratio _{G base.} It is a figure which shows the use condition of a reactive power compensation apparatus. It is a block diagram of the control apparatus in FIG. It is an explanatory view of a luminous coefficient a _n. It is a block diagram of the prior art described in patent document 2. FIG. It is explanatory drawing of the part for the reactive power fixed part and fluctuation | variation before and behind the gain 11 in FIG. It is waveform diagrams, such as load reactive power, for demonstrating the problem of a prior art.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows the configuration of the control device 13B according to this embodiment. The same components as those in FIG. 8 are given the same reference numerals, and the description thereof will be omitted. Hereinafter, the parts different from FIG. explain.

In FIG. 1, the load reactive power Q calculated by the reactive power detection circuit 10 is separated into a reactive power fixed part Q _A and a reactive power fluctuation part Q _B by a separation calculator 21. Here, as shown in FIG. 2, the separation calculator 21 inputs the calculation result of the load reactive power Q to the primary delay filter 21a and outputs the calculation result as a fixed reactive power Q _A. and outputs as the reactive power fluctuation Q _B the result of subtracting the reactive power fixed frequency Q _a from the load reactive power Q by 21b.

Referring again to FIG. 1, the gain 11 (hereinafter referred to as the optimum compensation gain 11) is added to the reactive power fluctuation amount Q _B output from the separation computing unit 21. 113 is referred to as an auxiliary gain) and the output of the multiplier 29 is added by the adder 24, and the result is input to the firing angle control circuit 12 so that the point for the thyristor 5 in FIG. Calculate the arc angle α. Here, the multiplier 29 multiplies the reactive power fixed amount Q _A by a ratio G _base from an upper / lower limiter 28 described later.

The reactive power fluctuation Q _B is multiplied by an auxiliary gain 111 (the current value K1 of the optimum compensation gain 11), an auxiliary gain 112 (K1 + ΔG), and an auxiliary gain 113 (K1−ΔG), respectively. the output of the multiplier 29 by the adder 221, 222, 223, that is the product of the reactive power fixed frequency _{Q a} and the ratio _{G base} is added, respectively. The outputs of the adders 221, 222, and 223 are added to the firing angle control circuits 121, 122, and 123, and the subsequent configuration and operation are the same as those in FIG.

That is, the firing angle control circuits 121 to 123 calculate the firing angles α _{1 to} α ₃ based on the input signals (outputs of the adders 221, 222, and 223), respectively. Compensator model 141 to 143 calculates the compensation current _I t1 _{~I t3} corresponding to firing angle alpha ₁ to? _3, adders 201 to 203 at a load current _{I f} and added value of the system model 151 to 153 To obtain voltage fluctuation amounts V _{1 to} V ₃ . The voltage flicker detection circuits 161, 162, and 163 calculate three types of voltage flicker corresponding to the auxiliary gains 111, 112, and 113 (K1, K1 + ΔG, K1−ΔG), and select a minimum value from these voltage flickers. The minimum value is obtained by the circuit 17, and the voltage flicker of the minimum value is updated as the value of the optimum compensation gain 11.

On the other hand, the load reactive power Q calculated by the reactive power detection circuit 10 is input to the maximum value detector 25, and the reactive power maximum value _Qmax is detected. Above The setting value by the setting unit 27 (e.g. to 100% set point capacity of the reactive power compensator) is input to a divider 26, so that the set value is divided by the reactive power maximum value Q _max is It is input to the lower limit device 28.
The upper / lower limiter 28 calculates the ratio G _base = 100% / Q _max (where 100% is the maximum value), and outputs this ratio G _base to the multiplier 29. The multiplier 29 multiplies the ratio G _base by the reactive power fixed amount Q _A and outputs the result to the adders 24, 221 to 223.

Here, FIG. 3A shows the reactive power Q ₁ before the optimum compensation gain 11 in FIG. ₁ , and FIG. 3B shows the reactive power Q ₂ after the optimum compensation gain 11. According to the present embodiment, since the optimum compensation gain 11 acts only on the reactive power fluctuation Q _B , even if the value of the optimum compensation gain 11 becomes ½ of the previous value, FIG. 3) As shown in FIG. 3 (b), only the reactive power fluctuation Q _{2B at} the subsequent stage of the optimum compensation gain 11 becomes 1/2 of the reactive power fluctuation Q _{1B at} the preceding stage, and the reactive power fixed quantity Q _2A is invalid. Same as fixed power Q _1A .
Therefore, the voltage flicker caused by the reactive power fluctuation can be suppressed by the optimum compensation gain 11, and the power factor reduction caused by the fixed reactive power can be sufficiently compensated.

FIG. 4 shows the load reactive power Q, the maximum value detected value Q _max , the reactive power fixed amount Q _A , and the ratio G _base in the present embodiment.
Assuming that the load reactive power Q exceeds the capacity of the compensation device as shown in FIG. 4A, first, the maximum value detector 25 detects the reactive power maximum value Q _max as illustrated. Assuming that the setting value by the setting device 27 is 100% of the compensation device capacity, the divider 26 calculates 100% / Q _max, and the ratio G _base having the upper limit value of 100% as shown in FIG. Is output from the device 28.

For this reason, the multiplier 29 outputs a value obtained by multiplying the fixed reactive power Q _A by a ratio G _base of 100% or less, and the reactive power exceeding the device capacity exceeds the device capacity. The reactive power fixed amount Q _A limited by that amount is added to the reactive power fluctuation Q _B after multiplication by the optimum compensation gain 11 in the adder 24, and after the auxiliary gains 111 to 113 are multiplied in the adders 221 to 223. It is added to the reactive power fluctuation Q _B of.

Therefore, power factor compensation is performed for the reactive power fixed amount Q _A by limiting the amount exceeding the capacity of the compensator, and the optimum compensation gain 11 selected by the minimum value selection circuit 17 for the reactive power fluctuation portion Q _B. Can be used to suppress voltage flicker. Here, a lower limit value of the upper limit 28 in the reactive power fixed frequency Q _A settable arbitrarily, for example, by setting the lower limit value such as 50% or 70% of the compensation device capacity, minimal power factor It is possible to perform voltage flicker compensation while ensuring compensation.

1 Reactive Power Compensator 2 Power System 3 System Impedance 4 Load 5 Thyristor 6 Reactor 7 Capacitor 8 PT
9 CT
10 Reactive power detection circuit 11 Gain (optimum compensation gain)
12 firing angle control circuit 13, 13A, 13B control device 17 minimum value selection circuit 18 flicker meter 111-113 gain (auxiliary gain)
121-123 Firing angle control circuit 141-143 Reactive power compensator model 151-153 System model 161-163 Voltage flicker detection circuit 201-203 Adder 21 Separation calculator 21a Primary delay filter 21b Subtractor 221-223 Adder 24 Adder 25 Maximum value detector 26 Divider 27 Setter 28 Upper / lower limiter 29 Multiplier

Claims (1)

A reactive power compensator that is connected to an electric power system and compensates for at least voltage flicker caused by a change in reactive power of a load connected to the electric power system. The reactive power is exchanged with the electric power system. In a reactive power compensator that controls a semiconductor element that operates in accordance with a drive signal based on an optimum compensation gain,
Means for detecting reactive power of the load;
Means for separating the detected reactive power into a reactive power fixed component and a reactive power fluctuation component;
Means for generating the drive signal based on a signal obtained by multiplying the reactive power fluctuation by the optimum compensation gain;
Means for calculating a plurality of voltage flickers corresponding to each auxiliary gain based on a result obtained by multiplying the reactive power fluctuation by different auxiliary gains;
Means for selecting the auxiliary gain corresponding to the minimum value among the plurality of calculated voltage flickers and setting the optimum compensation gain;
Means for calculating a ratio between the capacity of the compensation device and the maximum value of reactive power of the load;
Means for limiting the fixed reactive power to less than or equal to the capacity of the compensator by multiplying the fixed reactive power by the ratio;
Means for adding the fixed reactive power after the limitation to the output of the optimum compensation gain and the output of the auxiliary gain, respectively;
A control device for a reactive power compensator, comprising:

Images