JP5278414B2 - Distributed power supply, distribution facility, and power supply method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress fluctuation in an interconnection point voltage which is caused by an effective power output from a distributed power supply, in the case where the distributed power supply is interconnected with an existing power distribution system to supply power to a load. <P>SOLUTION: The distributed power supply that is interconnected with an existing power distribution system to supply power to a load, comprises a power generating means which generates an effective power and a reactive power and outputs them to an interconnection point, and a control means which controls the power generating means so that an optimum value is output according to the effective power by acquiring an optimum value of the reactive power which suppresses fluctuation in the interconnection point voltage caused by the effective power. When the control means judges that the effective power is in a rising state based on the effective power acquired in the previous detecting opportunity and current detecting opportunity, the control means detects an interconnection point voltage by successively changing the reactive power output to the interconnection point, and searches for the reactive power which the detected interconnection point voltage becomes equal to the interconnection point voltage acquired in the previous detecting opportunity as the optimum value. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

 The present invention relates to a distributed power source, a power distribution facility, and a power supply method.

  In recent years, distributed power sources such as wind power generators and solar cells are connected to existing power distribution systems to supply power to consumers. Of the technical requirements for connecting such distributed power sources to the power grid, the Ministry of Economy, Trade and Industry It has been formulated as “Guidelines for grid interconnection technical requirements”.

  On the other hand, for electric utilities, the voltage of electricity to be supplied is stipulated as a value that should be maintained by the Electricity Business Act and the Ordinance of the Ministry of Economy, Trade and Industry. When there is a risk that the voltage of the low voltage consumer may rise beyond the appropriate value due to reverse power flow from the distributed power source, the voltage is automatically adjusted by the phased reactive power control function or output control function of the distributed power source. It describes that measures to be adjusted are taken.

Grid interconnection technical requirement guidelines for ensuring power quality (Agency for Natural Resources and Energy)

  By the way, in the existing power system, as is well known, a reactive power compensator is used to maintain the system voltage at an appropriate value. The reactive power compensator controls the system voltage by adjusting the reactive power in the system power by adjusting the phase difference between the system current and the system voltage. However, such a reactive power compensator is relatively expensive. According to the above guidelines, the reactive power compensator is not provided in a distributed power source that requires a low cost. A means for controlling the interconnection point voltage by a simple (low cost) method using power control or output control function is adopted.

According to the advanced phase reactive power control function, it is possible to perform control to maintain the voltage at an appropriate value by using the reactive power of the distributed power source itself, but the capacity of the distributed power source is generally small, With only one distributed power supply, the capacity limit is reached, and fluctuations in the system voltage cannot be effectively suppressed. In other words, the output limit of the distributed power source is reached and control becomes impossible in an attempt to compensate for voltage fluctuations caused by load fluctuations or changes in system operation conditions.
In addition, in order to share reactive power with multiple distributed power sources, centralized control for controlling communication between distributed power sources and controlling multiple distributed power sources to optimally share reactive power output. A device is required, and it is expensive to install communication equipment and a central control device.
On the other hand, according to the output control function, since the output of the distributed power supply is suppressed, the original function of the distributed power supply for supplying power to the load cannot be achieved. As a result, it becomes impossible to recover the funds required for this, and the economics of the distributed power source are impaired.

The present invention has been made in view of the above-described circumstances, and has the following objects.
(1) When a distributed power source and an existing power system are connected to supply power to a load, fluctuations in the connection point voltage due to active power output from the distributed power source are suppressed.
(2) To provide a low-cost function for maintaining the interconnection point voltage within a specified voltage range in the distributed power source.

  In order to achieve the above object, according to the present invention, as a first solution for a distributed power supply, a distributed power supply that supplies power to a load in conjunction with an existing power system is provided. A power generation means for generating power and outputting it to a connection point, and an optimum value of reactive power that suppresses fluctuations in the connection point voltage caused by the active power are obtained, and the optimum value is output according to the active power Control means for controlling the power generation means, and when the control means determines that the active power is in the rising state based on the active power acquired in the previous detection opportunity and the current detection opportunity, The reactive power output to the interconnection point is sequentially changed to detect the interconnection point voltage, and the optimum reactive power at which the detected interconnection point voltage becomes equal to the interconnection point voltage acquired at the previous detection opportunity Use a method of searching as a value

 Further, as a second solving means related to the distributed power source, in the first solving means, the control means outputs the optimum value of the reactive power obtained by the search to the interconnection point, and at this time, The relationship between the obtained active power and the optimum value of the reactive power is stored in the storage unit. Thereafter, the optimum value of the reactive power corresponding to the detected active power is searched from the storage unit, and the invalidity obtained by the search is stored. A means for instructing the power generation means to output an optimum value of power to the interconnection point is adopted.

 Further, as a third solving means relating to the distributed power supply, in the first or second solving means, the control means causes the optimum value of the reactive power obtained by the search to be output to the interconnection point. The relationship between the active power obtained at this time, the interconnection point voltage, and the optimum value of the reactive power is stored in the storage unit, and the active power is constant based on the active power acquired at the previous detection opportunity and the current detection opportunity. When it is determined that the state or the descent state is present, the connection point voltage when the optimum value of the reactive power corresponding to active power is output differs from the connection point voltage stored in the storage unit, When the interconnection point voltage in the storage unit is rewritten, the data in the storage unit relating to the active power greater than the current active power is deleted, and the active point power is increased again, the rewritten interconnection point voltage Based re searches for an optimum value of the reactive power to active power, to adopt a means of.

 On the other hand, in the present invention, as a first solving means related to the power distribution facility, an existing power system that supplies power to the load, and a power that is connected to the existing power system is supplied to the load. The distributed power source having any one of the third solving means is used.

  Furthermore, in the present invention, as a first solving means related to a power supply method, an existing power system and a distributed power supply are connected to supply power to a load, and the distributed power supply By detecting the connection point voltage when the reactive power output to the load is changed, the optimum value of the reactive power that suppresses the change of the connection point voltage caused by the active power output to the load is obtained, When the effective power and the optimum value of the reactive power corresponding to the active power are output to the load and it is determined that the active power is in the rising state based on the active power acquired at the previous detection opportunity and the current detection opportunity, The reactive power output to the interconnection point is sequentially changed to detect the interconnection point voltage, and the optimum reactive power at which the detected interconnection point voltage becomes equal to the interconnection point voltage acquired at the previous detection opportunity Use a method of searching as a value. To.

 According to the present invention, a distributed power source that supplies power to a load in linkage with an existing power system obtains reactive power that suppresses fluctuations in interconnection point voltage caused by active power as an optimum value, and And since the said optimal value according to the said active power is output to load, the fluctuation | variation of the connection point voltage resulting from active power can be suppressed more reliably.

   Further, according to the present invention, since the optimum value (reactive power) for the active power can be set by the power factor control of the distributed power source, the connection point can be obtained at low cost without requiring a conventional reactive power compensator. Voltage fluctuation can be suppressed. That is, since the cost for realizing the function for suppressing the fluctuation of the interconnection point voltage is low, it can be easily introduced into a distributed power source that requires low cost.

   Further, according to the present invention, only the voltage fluctuation at the interconnection point caused by the active power of the distributed power supply itself is compensated, so that the capacity of the small capacity distributed power supply can be effectively utilized. In addition, since communication between a large number of distributed power sources is unnecessary, the cost for communication facilities is unnecessary. Furthermore, since the effective power output of the distributed power source is not suppressed, the economic efficiency of the distributed power source is not impaired.

   Furthermore, according to the present invention, since the distributed power source connected to the existing power system suppresses fluctuations in the connection point voltage caused by the active power output by itself, the reactive power compensator is provided on the existing power system side. The connection point voltage can be effectively maintained within the specified voltage range as compared with the case where the connection point voltage is compensated. For example, when a plurality of distributed power sources are connected to an existing power system, it is difficult to compensate the connection point voltages of all connection points on the existing power system side. However, in the present invention, each distributed power source autonomously compensates the interconnection point voltage, so that the interconnection point voltages of a plurality of interconnection points can be more reliably maintained within the specified voltage range.

It is a systematic diagram of the power distribution equipment concerning 1st Embodiment of this invention. It is a schematic diagram for explaining a fluctuation suppression principle of interconnection point voltage V by the reactive power Q _G in each embodiment of the present invention. It is a flowchart which shows the process sequence of the period variation method in 1st Embodiment of this invention. It is a flowchart which shows the process sequence of the optimal value search method in 1st Embodiment of this invention. It is a flowchart which shows the detailed process sequence of the optimal value search method in 1st Embodiment of this invention. It is a block diagram of the distribution system which connected the distributed power supply PW1 in 1st Embodiment of this invention in multiple numbers. It is a systematic diagram of the power distribution equipment concerning 2nd Embodiment of this invention.

Embodiments of the present invention will be described below with reference to the drawings.
[First Embodiment]
FIG. 1 is a system diagram of a power distribution facility according to the first embodiment of the present invention. This first embodiment relates to power distribution equipment having a distributed power PW1 of the type not substantially control the active power P _G to which itself outputs.

  In FIG. 1, S is a distribution substation, C1 is a high voltage distribution line, T1 and T2 are distribution transformers (post transformers), C2 is a low voltage distribution line, PW1 is a distributed power supply, and L is a load. is there. The distribution substation S is connected to the primary side of the distribution transformers T1 and T2 via the high-voltage distribution line C1. The high-voltage distribution line C1 transmits high-voltage power (for example, 6600 V) output from the distribution substation S to the distribution transformers T1 and T2. The distribution transformers T1 and T2 convert the high-voltage power supplied via the high-voltage distribution line C1 into a low-voltage power of 200 V, for example, and supply it to the low-voltage distribution line C2. The low-voltage distribution line C2 is provided between the distribution transformers T1 and T2 and the load L, and supplies low-voltage power to the load L.

  Here, the distribution substation S, the high-voltage distribution line C1, the distribution transformers T1 and T2, and the low-voltage distribution line C2 constitute an existing distribution system laid in a network in the city. On the other hand, the distributed power source PW1 is connected to the low-voltage distribution line C2 at the interconnection point, and supplies low-voltage power to the load L in linkage with the existing distribution system. Moreover, the load L is all the loads connected to the existing power distribution system.

  As shown, the distributed power source PW1 includes a voltmeter 1, an ammeter 2, a detected power calculation unit 3, an optimal output calculation unit 4, a storage unit 5, an output current setting unit 6, as main functional components. An output current control unit 7, an inverter 8, a DC power supply 9, and an interconnection reactor 10 are provided. The voltmeter 1 detects the voltage at the connection point of the low-voltage distribution line C2 (connection point voltage V) and outputs it to the detected power calculation unit 3. The ammeter 2 detects the output current of the distributed power source PW1 and outputs it to the detected power calculation unit 3.

Based on the instantaneous voltage value of the interconnection point input from the voltmeter 1 and the instantaneous output current value input from the ammeter 2, the detected power calculation unit 3 is output from the distributed power source PW1 to the interconnection point. Output power (that is, active power P _G and reactive power Q _G ) is calculated and output to the optimum output calculation unit 4 as detected power, and based on the instantaneous voltage value of the connection point input from the voltmeter 1. The effective value calculation of the system point voltage is performed, and the effective value of the connection point voltage (connection point voltage V) is output to the optimum output calculation unit 4.

The optimum output calculation unit 4 outputs the detected power (active power P _G and reactive power Q _G ) and the interconnection point voltage V input from the detected power calculation unit 3 to the storage unit 5 for storage, while the storage Based on the interconnection point voltage V and the active power P _G or the reactive power Q _G stored in the unit 5, the output power of the inverter 8 is output to the output current setting unit 6 as a power command value. The power command value, the output power of the inverter 8, that is, those that direct and active power P _G and the reactive power Q _G individually.

Although details will be described later, the optimum output calculation unit 4 estimates the system impedance Z of the existing distribution system when generating the reactive power command value for instructing the reactive power Q _G to the output current setting unit 6. Given the estimated value, determined as the optimum value of the reactive power Q _G suppresses fluctuation of interconnection point voltage V due to output active power P _G to a linking point, invalid instructing the output of the optimum value The power command value is output to the output current setting unit 6. The storage unit 5 orders the detected power (active power P _G and reactive power Q _G ) and the connection point voltage V when the reactive power is optimally adjusted in the order of the magnitude of the active power P _G as one record. Is stored, and the record is read out and output to the optimum output calculation unit 4 when necessary.

The output current setting unit 6 sets the power factor so that the active power P _G and the reactive power Q _G according to the power command value are output from the inverter 8, and the set value (power factor set value) is output current controlled. Output to unit 7. The output current control unit 7 generates a control signal for controlling the inverter 8 based on the power factor setting value, for example, a PWM (Pulse Width Modulation) signal and outputs the control signal to the inverter 8. The inverter 8 converts the DC voltage supplied from the DC power supply 9 into an AC voltage by switching based on the control signal.

The DC power supply 9 is a solar cell, for example, and outputs a predetermined DC voltage to the inverter 8. Since the DC power source 9 depends on the amount of light generated power is irradiated from the sun, the inverter 8 can not output the active power P _G which is controlled to a constant value to the interconnection point. That is, distributed power PW1 in the distribution equipment can not control the active power P _G to a constant value, and outputs the active power P _G which varies randomly. The interconnecting reactor 10 is provided at the output end of the inverter 8 to provide inductance.

Here, the distributed power source PW1 includes the voltmeter 1, the ammeter 2, the detected power calculation unit 3, the optimum output calculation unit 4, the storage unit 5, the output current setting unit 6, as main functional components as described above. output current controller 7, an inverter 8 is provided with the DC power source 9 and the interconnection reactor 10, of these functional components, an inverter 8, the DC power source 9 and the interconnection reactor 10, the effective power P _G and reactive power constitute a power generating means for outputting to the interconnection point to generate Q _G.

The voltmeter 1 ammeter 2, detection power calculation section 3, the optimum output calculation unit 4, storage unit 5, the output current setting unit 6 and the output current controller 7, linking point voltage caused by the active power P _G calculated reactive power Q _G so as to suppress variations in V based on system impedance Z, constitute a control means for controlling the power generating means to generate the reactive power Q _G. Such a distributed power source PW1 is a characteristic component of the power distribution facility.

Next, the operation of the power distribution equipment configured as described above will be described in detail.
In this power distribution facility, the existing power distribution system and the distributed power source PW1 link the power to supply the load L. Here, interconnection node voltage V is generally but will vary depending on the active power P _G which is output from the distributed power source PW1, distributed power PW1 of the power distribution facility may, itself communicating and it outputs the linking point to optimize the reactive power Q _G so as to suppress the fluctuation of interconnection point voltage V caused by the active power P _G to be output to the system point.

Figure 2 is a schematic diagram for explaining a fluctuation suppression principle of interconnection point voltage V due to such reactive power Q _G. In this schematic diagram, the system impedance Z is “R + jX”, the output voltage of the distribution substation S is “E”, the power output from the distributed power source PW1 is “P _G + jQ _G ”, and the load L from the interconnection point Is assumed to be “P + jQ”. Of the load power P + jQ, “P” indicates load effective power, and “Q” indicates load reactive power.

  In this power distribution facility, the following approximate expression (1) is established with each value as a variable or constant.

The approximate expression (1) is due to active power P _G to a voltage fluctuation ΔV output from the voltage fluctuation ΔV1 (= R · P + X · Q) and distributed power source PW1 due to variation of the load L at the interconnection node It shows that the voltage fluctuation ΔV2 (= R · P _G + X · Q _G ).

That is, the voltage variation ΔV2 due to the active power _{P G} of distributed power PW1 by optimizing reactive power _{Q G} of the dispersed power source PW1, i.e. the conditional expression: the _{R · P G + X · Q} G = 0 It is possible to minimize by setting the reactive power Q _G to satisfy. This voltage fluctuation ΔV2 are those active power P that _G flows into the existing distribution system and the active power P _G of the dispersed type power supply PW1 is generated by varying. In order to obtain the reactive power Q _G (that is, the optimum value of the reactive power Q _G ) for minimizing such voltage fluctuation ΔV2, it is necessary to obtain the system impedance Z.

Now, fluctuation suppressing principles of interconnection point voltage V is as described above, in order to set the optimum value of reactive power Q _G on the basis of such a change inhibition principle, it is necessary to know the system impedance Z . If there is no change in the configuration of the existing distribution system and the system impedance Z is fixed, the reactive power Q _G may be optimally set using the system impedance Z obtained by measurement, but the actual distribution system is The configuration is often changed for various reasons, and therefore cannot be considered as a fixed value in practice.

Under such circumstances, the optimum output calculation unit 4 obtains the system impedance Z by obtaining the connection point voltage V of the connection point when the reactive power Q _G is intentionally changed among the powers P _G + jQ _G. presume. In the case of distributed power PW1 in the power distribution facility, so it can not effective control for active power P _G, as described above, varying only the reactive power Q _G intentionally.

That is, the optimum output calculation unit 4 sets the reactive power Q _G to the specified values Q _{G1 to} Q _G3 for the three times t1, t2, and t3 within a relatively short period so that the load power P + jQ does not vary. Is output to the output current setting unit 6, and the connection point voltages V _{1 to} V ₃ , active powers P _{G1 to} P _G3, and reactive powers Q _{G1 to} Q _G3 at this time are acquired from the detected power calculation unit 3. Then, the optimum output calculation unit 4 substitutes these interconnection point voltages V _{1 to} V ₃ , active powers P _{G1 to} P _G3, and reactive powers Q _{G1 to} Q _G3 into the above equation (1) ( The real part R and the imaginary part X of the system impedance Z are obtained by solving 2) to (4).

 The following expression (5) is obtained by subtracting the expression (2) from the expression (3), and the following expression (6) is obtained by subtracting the expression (2) from the expression (4).

_{Here, ΔP 2 = P G1 -P G2} , ΔP 3 = P G1 -P G3, ΔQ 2 = Q G1 -Q G2, ΔQ 3 = Q G1 -Q G3, also _{ΔV 2 = V 1 -V 2,} ΔV _{When 3} = V ₁ −V ₃ is set, the above equations (5) and (6) are expressed as the following determinant (7).

Then, from this determinant (7), the real part R and the imaginary part X of the system impedance Z are obtained by the following expression (8). The optimum output calculation unit 4 includes the connection point voltages V _{1 to} V ₃ , the active powers P _{G1 to} P _G3 and the reactive powers Q _{G1 to} Q _G3 acquired from the detected power calculation unit 3 in the equation (8). The system impedance real part R and imaginary part X are obtained by substituting.

Here, distributed power PW1 can not be substantially controlled active power P _G, as described above. Therefore, the grid point voltage V _{1 to} V ₃ , the active powers P _{G1 to} P _G3 and the reactive powers Q _{G1 to} Q _G3 obtained for the three times t1, t2, and t3 are substituted into the above equation (8). The impedance Z is obtained. However, when the active power P _G1 and the active power P _G2 are equal, the imaginary part X of the system impedance Z can be obtained by an equation (9) simpler than the above equation (8).

The three times t1, t2, and t3 are invalid because they are set within a relatively short period in which the load power P + jQ does not fluctuate, that is, within a period in which the operating point of the load L can be regarded as constant without fluctuating. The optimum value of the electric power Q _G is expressed by the following expression (10) obtained by modifying the conditional expression: R · P _G + X · Q _G = 0 with the voltage fluctuation ΔV2 described above being zero.

That is, the optimum output computing section 4 of system impedance Z and active power P _G obtained based on equation (8) the optimum value of the reactive power Q _G by substituting the equation (10), that is to interconnection node instructing the output of active power P reactive power suppresses the voltage fluctuation ΔV of the interconnection point voltage V caused by the output of the _G Q _{G (i.e.,} the optimum value) to the current setting portion 6. As a result, the voltage fluctuation ΔV of the interconnection point voltage V is suppressed to the minimum. In addition, the optimal output calculation part 4 always estimates the optimal optimal value with respect to the fluctuation | variation of the system impedance Z by the structure change of the existing distribution system by performing the estimation process of the system impedance Z at a fixed time interval. To do.

When the system impedance Z is estimated based on the simultaneous equations (2) to (4) as described above, it is necessary to detect the connection point voltage V for a period in which the operating point of the load L can be considered constant without fluctuation. However, the load L connected to the actual power distribution system includes a load that constantly varies in a certain period or a load that varies instantaneously. If such a load L is connected, the voltage change ΔV of interconnection point voltage V, in addition to voltage variation when varying the intentionally reactive power Q _G, variations in load L, as described above As a result, an error occurs in the estimated value of the system impedance Z. Further, measurement noise when detecting the interconnection point voltage V also causes an error in the estimated value of the system impedance Z.

Such load L in order to eliminate the influence of measurement noise of voltage fluctuation and connecting point voltage V interconnection node voltage V caused by the change of interconnection point voltage detecting when varying the reactive power Q _G System impedance Z is estimated based on a value obtained by passing V through a low-pass filter. Thereby, the influence of the measurement noise of the connection point voltage V as well as the voltage change of the connection point voltage V due to the high frequency load change can be removed, and the error of the estimated value of the system impedance Z can be reduced.

   As another method, an estimated value of the system impedance Z is stored in the storage unit 5 as time series data, an average value of the time series data is obtained, and the value is used as a final estimated value of the system impedance Z. By using it, the influence of the measurement noise of the connection point voltage V as well as the voltage change of the connection point voltage V due to the high frequency load change can be removed, and the error of the estimated value of the system impedance Z can be reduced. The averaging process may be performed by applying a digital low-pass filter to the time series data of the estimated value of the system impedance Z.

   On the other hand, when the load fluctuation of the load L is known in advance, the estimation accuracy of the imaginary part X of the system impedance Z can be increased by the following method.

In FIG. 1, an inrush current generated when a load L (in this case, an induction machine) is started is represented by ΔI _Q. Here, when it is considered that the inrush current ΔI _Q at the time of starting the load L is mostly ineffective components, the voltage fluctuation ΔV of the interconnection point voltage V caused by the inrush current ΔI _Q is detected to detect the imaginary impedance of the system impedance Z. Part X can be determined by X = ΔV / ΔI _Q.

Therefore, if the value of the inrush current ΔI _Q at the start of the load L is known in advance, the inrush current ΔI _Q is stored in the storage unit 5 of the distributed power source PW1, and the connection point voltage V is always detected. When the voltage fluctuation ΔV due to the inrush current ΔI _Q is detected, the optimum output calculation unit 4 reads the inrush current value ΔI _Q from the storage unit 5 and calculates the imaginary part X = ΔV / ΔI _Q of the system impedance Z. Here, since the voltage fluctuation ΔV caused by the inrush current ΔI _Q is a spike-like large voltage fluctuation, a threshold value is set in advance in the optimum output calculation unit 4, and the optimum output calculation unit 4 has a voltage exceeding the threshold value. When the fluctuation ΔV is detected, it is determined that the voltage fluctuation ΔV is caused by the inrush current ΔI _Q , and the imaginary part X of the system impedance Z is calculated.

The value of the rush current [Delta] I _Q reaches several times the rated capacity of the load L, inrush current [Delta] I _Q voltage fluctuation ΔV of the interconnection points by the far the voltage fluctuation range of the interconnection point voltage V by the output of the reactive power Q _G Therefore, the estimation accuracy of the imaginary part X of the system impedance Z can be increased without being affected by disturbances such as measurement noise. Therefore, when estimating the system | strain impedance Z based on simultaneous equations (2)-(4), estimation accuracy can be raised about the imaginary part X by using the imaginary part X calculated | required by said method.

In the case of estimating the imaginary part X of the system impedance Z by spike-like voltage variations ΔV caused by such inrush current [Delta] I _Q, it can not be used a low-pass filter described above. Therefore, when the real part R of the system impedance Z is obtained, the real part R estimated based on the simultaneous equations (2) to (4) is stored as time series data, and the average value of the time series data is obtained as an actual value. Let it be the final value of part R. As a result, the real part R can be estimated with high accuracy.

Incidentally, instead of the method of determining the optimum value of the reactive power Q _G with seeking system impedance Z by solving the simultaneous equations as described above (2) to (4), and the system impedance Z and the formula (10) Te, we determined using periodic variation method described the system impedance Z below, also employs the optimum value search method described below as a method for determining the optimum value of the reactive power Q _G without obtaining a system impedance Z Also good.

According to the periodic variation method, although the processing is complicated, it is not necessary to perform the low-pass filter and the averaging processing as described above, and the influence of the fluctuation of the connection point voltage V due to disturbance (load fluctuation and measurement noise) is removed. Therefore, the system impedance Z can be obtained with high accuracy.
Further, determined according to the optimum value search method, without estimating the system impedance Z of which similar processing is complicated, and the optimum value of the reactive power Q _G without using the equation (10) is an approximate equation directly since, it is possible to more accurately determine than the case of using the periodic variation method the optimum value of the reactive power Q _G.

FIG. 3 is a flowchart showing a processing procedure of the periodic variation method.
As shown in this figure, the optimum output calculation unit 4, at the prescribed time (step S1), the detected power and active power P _G and the interconnection point voltage V which varies randomly in accordance with the output fluctuation of the DC power source 9 It acquires sequentially from the calculating part 3 in time series (step S2).

Here, the active power P _G is a constant value in the context of three-phase balanced for the (effective), the time variation of the active power becomes change in the effective value of the effective power P _G, interconnection node voltage V a similar Shows time change. However, or a three-phase unbalanced, in the case of single-phase power, without effective value is changed, the effective power P _G oscillates at twice the frequency of the system frequency. That is, a constant value (effective value), i.e. the vibration of the frequency doubled system frequency to enable power P _G is a direct current component so that the thus superposed. Therefore, in order to eliminate the influence of extraneous vibration and change of such effective value, removing the frequency doubled component of the system frequency by filtering the time series data of the active power P _G obtained in step S2 .

Since this only by variation of the effective value of the effective power P _G can be extracted, then the optimum output calculation unit 4, a series data FFT (Fast Fourier Transform) processing and when the active power P _G after such filtering Then, only one specific frequency component P _G (ω ₀ ) is selected from the frequency components of the time series data (step S3).

The optimum output calculation unit 4, by treating DFT (Discrete Fourier Transform) with respect to the frequency components P _G of the active power P _G time series data interconnection node voltage V _{(ω 0),} the active power P _G The same frequency component V (ω ₀ ) as the frequency component P _G (ω ₀ ) is extracted (step S4). Here, if the influence of the same frequency components of the loads P and Q on the connection point voltage V can be ignored, and the reactive power Q _G is kept constant during the period, the time series data of the connection point voltage V Since the extracted same frequency component V (ω ₀ ) is only due to the effect of the active power P _G , V (ω ₀ ) ≈R · P _G (ω ₀ ). Optimum output calculation unit 4, and thus to extract the active power P _G frequency component P _{G (omega 0),} the frequency component V (omega ₀₎ interconnection node voltage V that matches to the on the basis The real part R of the system impedance Z is calculated (step S5).

Then, the optimal output computing section 4, the reactive power Q _G which outputs a reactive power command value for varying the reactive power Q _G at a predetermined cycle to the output current setting unit 7 is outputted from the inverter 8 to the interconnection point a predetermined It fluctuates with a cycle (step S6), and the interconnection point voltage V at this time is sequentially acquired from the detected power calculation unit 3 in time series (step S7). Then, the optimal output calculation unit 4, by DFT processing time series data of the interconnection point voltage V, to extract components other variations the same frequency of the reactive power Q _G (step S8), and extracted in this way The imaginary part X of the system impedance Z is calculated based on the frequency component of the connection point voltage V (step S9).

When the series of processes of steps S1 to S9 is completed, the optimum output calculation unit 4 returns the process to step S1. When the next specified time is reached (step S1), the optimum output calculation unit 4 repeats the processes from step S2 onward. System impedance Z is estimated at time intervals. According to such a periodic variation method, since estimates the system impedance Z using the active power P _G and the reactive power Q interconnection node voltage V of frequency that matches the fluctuation frequency of _G, system impedance to eliminate the disturbance Z can be estimated more accurately. Based on the estimated system impedance Z, the optimum reactive power Q _G is obtained from Equation (10) and output. A filter (for example, a band pass filter) may be used instead of the FFT process or the DFT process.

Next, FIG. 4 is a flowchart showing a processing procedure of the optimum value search method.
Optimum output calculation unit 4, first initializes the control variable i to "0" in the processing (step Sa1), more effective power P _G and the reactive power Q _G active and reactive power command to set only "0" for a moment The value is output to the output current setting unit 7 to forcibly set the power output from the inverter 8 to the interconnection point to “0” (step Sa2). Then, the optimal output computing section 4, the value of the interconnection point voltage V obtained from the detection power calculation section 3 (step Sa3), the interconnection point voltage V above the active power P _G and the reactive power Q _G at this time (i.e. "0") causes registered in the correspondence table table set to active power P size order in the storage unit 5 of _G as one record (step Sa4).

Thereafter, the optimum output calculation unit 4 repeatedly increments the control variable i (step Sa5), and calculates the active power P _G , the reactive power Q _G and the interconnection point voltage V in the normal operation state of the distributed power source PW1. series manner are sequentially acquired (step Sa6), to determine the state of change in the active power P _G (step Sa7), the optimum value search processing to obtain the optimum value of the reactive power Q _G in accordance with the changing state (step Sa8), The correspondence table table rewriting process (1) (step Sa9) or the correspondence table table rewriting process (2) (step Sa10) is executed. The determination process of the state of change in the active power P _G at the step Sa7 is to compare the magnitude relationship of the current value (active power current value P _pre) and the previous value of the active power P _G (active power previous value P _last) Is done by.

That is, the optimum value if the case real power current value P _pre is larger than the active power previous value P _last That active power P _G is in the raised state search process (step Sa8) is executed. Further, when the real power current value P _pre is active power previous value P _last equal if that is the effective power P _G is in a steady state is performed rewrite processing of a correspondence table Table (1) (step Sa9) it is more effective so that the rewriting processing of the correspondence table table (2) (step Sa10) is executed when the power current value P _pre is small if that is the effective power P _G than active power previous value P _last is in the lowered state.

   FIG. 5 is a flowchart showing details of the optimum value search process (step Sa8), the correspondence table table rewriting process (1) (step Sa9), and the correspondence table table rewriting process (2) (step Sa10). 5, (a) shows the optimum value search process, (b) shows the rewrite process (1) of the correspondence table, and (c) shows the rewrite process (2) of the correspondence table.

As shown in FIG. 5 (a), in the optimum value search process (step Sa8), the current value of the connection point voltage V (the connection point voltage current value V _pre ) and the previous value (the previous value of the connection point voltage). V _last) and to search the reactive power _{Q G} equal (step Sa81). That is, the optimum output calculation unit 4, by sequentially changing the reactive power Q _G to output the output reactive power command value sequentially changing the reactive power Q _G to the output current setting unit 7 from the inverter 8 to the interconnection point, the By sequentially acquiring the connection point voltage V from the detected power calculation unit 3, the reactive power Q _{G in} which the connection point voltage current value V _pre and the connection point voltage previous value V _last are equal is searched.

Then, the optimal output computing section 4, the interconnection node from the inverter 8 Thus the reactive power command value for instructing the output of the search value of the reactive power Q _G obtained by re-output to the output current setting unit 7 The searched optimum value is output (step Sa82), and the active power current value P _pre obtained from the detected power calculation unit 3 at this time, the search value of the reactive power Q _G and the connection point voltage current value V _pre are obtained. New registration is made in the correspondence table (step Sa83).

Such active power P _G is the optimum value search processing executed in raised state (step Sa8), the plurality of the correspondence table table sampled in step Sa6 over the output capacity range of the dispersed power source 1 active power the optimum value of the reactive power Q _G about P _G and the interconnection point voltage V at that time is stored as a number of the record corresponding to the active power P _G.

In the following in this way correspondence table table is constructed in the storage unit 3, the optimum output calculation unit 4, the active power by searching the correspondence table table based on the active power P _G acquired from the detection power calculation section 3 Reactive power Q that suppresses fluctuations in interconnection point voltage V by obtaining an optimum value of reactive power Q _G corresponding to P _G and outputting a reactive power command value for outputting the optimum value to output current setting unit 7 _G is output from the inverter 8 to the connection point.

On the other hand, the active power P _G is constant (unchanged) state and decreasing state is rewritten correspondence table table (i.e. maintenance) is performed. As described above, this maintenance is performed in consideration of the configuration change of the existing distribution system. For example, when the active power _{P G} is a constant state, rewrite processing (1) shown in FIG. 5 (b) (step Sa9) is executed. In this rewriting process, the optimum output calculation unit 4 outputs a reactive power command value for outputting the previous value of the reactive power Q _G (reactive power previous value Q _last ) to the output current setting unit 7 and outputs the reactive point from the inverter 8. It is set to an invalid power previous value Q _last reactive power Q _G to be output (step Sa91), and acquires the interconnection point voltage V at this time from the detection power calculation section 3 (step Sa92).

Then, when the connection point voltage V acquired in this way is not equal to the connection point voltage current value V _pre , the optimum output calculation unit 4 causes some change such as a change in connection relation in the existing distribution system. Therefore, the corresponding record in the correspondence table is rewritten to the interconnection point voltage current value V _pre (step Sa93).

Further, when the active power P _G is a decreasing state, as shown in FIG. 5 (c), the rewrite processing of a correspondence table table (2) (Step Sa10), the optimum output calculation unit 4, effective from the correspondence table table power The reactive power Q _G corresponding to the current value P _pre is searched (step Sa101), and the reactive power command value for outputting the search value obtained as the search result is output to the output current setting unit 7 and connected from the inverter 8 to set the reactive power _{Q G} to be output to the point in the search value (step SA 102).

   Then, the optimum output calculation unit 4 newly acquires the connection point voltage V at this time from the detected power calculation unit 3 (step Sa103), and the connection point voltage V corresponds to the search value in the correspondence table. If it is different from the connection point voltage V, the connection point voltage V of the corresponding record in the correspondence table is rewritten to a new connection point voltage V acquired from the detected power calculation unit 3 (step Sa104). Such inconsistency of the connection point voltage V is a case where some change such as a change in connection relation occurs in the existing distribution system as described above.

The optimum output calculation section 4 deletes the record corresponding to the active power P _G is larger than active power current value P _pre of correspondence table table acquired by the optimum value search process (step Sa8) (step SA105) . If the record corresponding to the larger effective power P _G than the effective power current value P _pre Among Thus correspondence table table is erased, the erased portion of the correspondence table table, then active power P _G is raised state It is reconstructed by the optimum value search process (step Sa8) executed when it is executed.

Lowering the effective power P _G to reach the performance of step Sa10, if the example photovoltaic corresponds to obscuration of the day. In addition, the active power P _G does not necessarily decrease and does not always decrease to the active power P _G = 0. Therefore, the active power P _G = 0 and the reactive power Q _G are forcibly forced at regular time intervals. By repeating the above process with = 0, it is possible to remove the cause of voltage fluctuations caused by load fluctuations and changes in system operating conditions, and to search for more accurate optimum values.

   The above is the description of the configuration and operation of the distributed power supply PW1 of the first embodiment. In the above, for the sake of simplification of description, the case where one distributed power supply PW1 is connected to the existing distribution system has been described. . However, actually, as shown in FIG. 6, a plurality of distributed power sources may be linked to an existing distribution system.

In FIG. 6, the same components as those in FIG. The distributed power sources PW11, PW12, and PW13 are connected to the low-voltage distribution line C2 at interconnection points 1, 2, and 3, respectively, and are connected to the existing distribution system to supply low-voltage power to the loads L1, L2, and L3. Supply. These distributed power PW11, PW12 and PW13 is estimated by the method described above the system impedance Z of the existing distribution system viewed from the interconnection point, determines and outputs an optimal reactive power Q _G. Although omitted in FIG. 6, the high-voltage distribution line C1 is connected to a plurality of low-voltage power systems configured by a distribution transformer T1, a low-voltage distribution line C1, loads L1, L2, and L3.

   In the power distribution system having such a configuration, when a plurality of distributed power sources PW11, PW12, and PW13 simultaneously perform system impedance estimation processing, there are the following problems.

First, when the distributed power sources PW11, PW12, and PW13 estimate the system impedance Z by solving the simultaneous equations (2) to (4), each distributed power source is assumed to be constant without fluctuations in the loads L1, L2, and L3. intentionally varying the reactive power Q _G for three times short regarded will detect a voltage variation ΔV at interconnection points 1, 2 and 3. When such an operation is performed simultaneously, the voltage fluctuation ΔV of each interconnection point voltage V is superimposed on the voltage fluctuation caused by the reactive power Q _G output from each distributed power source. A large error occurs in the estimated value of the system impedance Z from the point of view.

Therefore, in the above case, to set the time for varying the reactive power Q _G as different for each distributed power source. For example, to connect each distributed power source online, by detecting the time varying reactive power Q _G of the other dispersed power source, the time is as long as the same time as the self-dispersed power, autonomous self so as to change the time for varying the reactive power Q _G of.

Thus, it is not possible to synchronize the time that other distributed power to vary the reactive power Q _G, interconnection caused by the change of the reactive power Q _G of the distributed power itself was system impedance estimating process Only the voltage fluctuation ΔV of the point voltage V can be extracted. As a result, an error in the estimated value of the system impedance Z can be reduced.

On the other hand, distributed power PW11, PW12 and even when performing system impedance estimation process by PW13 is periodic variation method, since each distributed power source to vary the reactive power Q _G periodically, fluctuation period other distributed A large error occurs in the estimated value of the system impedance Z when it matches the power source.

Therefore, each such distributed power source may performed system impedance estimating process by the periodic variation method, it sets a period for varying the reactive power Q _G as different for each distributed power source. For example, as described above, each distributed power source is connected online, the fluctuation period of the reactive power Q _G of the other distributed power source is detected, and if the fluctuation period coincides with the other distributed power source, Change the fluctuation cycle.

In this way, the interconnected point voltage resulting from the fluctuation cycle of the reactive power Q _G of the distributed power source itself that has performed the system impedance estimation process without matching with the fluctuation cycle of the reactive power Q _G by other distributed power sources. Since only V can be extracted, as a result, an error in the estimated value of the system impedance Z can be reduced.

As described above, even in a distribution system in which a plurality of distributed power sources are connected as shown in FIG. 6, the optimum value of reactive power Q _G is obtained by estimating the system impedance Z as described above. Voltage fluctuation at the interconnection point can be suppressed.

[Second Embodiment]
Next, a second embodiment of the present invention will be described.
The first embodiment is distributed power supply PW1 was for the case of the type not substantially control the active power P _G to which itself outputs, the second embodiment is itself output it relates distribution equipment comprising a distributed power PW2 of the type capable of substantially controlling the active power P _G to.

   FIG. 7 is a system diagram of a power distribution facility according to the second embodiment. In FIG. 7, the same components as those in the first embodiment are denoted by the same reference numerals. In the following description, description of parts common to the first embodiment will be omitted, and only characteristic parts of the second embodiment will be described.

   As shown in the figure, the distributed power source PW2 in the second embodiment includes a voltmeter 1, an ammeter 2, a detected power calculation unit 3, an optimum output calculation unit 4A, a storage unit 5, an output setting unit 11, a governor 12, and an excitation. The current control unit 13, the prime mover 14, the generator 15, and the interconnection reactor 10 are provided. The voltmeter 1 detects the voltage at the connection point of the low-voltage distribution line C2 (connection point voltage V) and outputs it to the detected power calculation unit 3. The ammeter 2 detects the output current of the distributed power source PW2 and outputs it to the detected power calculation unit 3.

   The generator 15 may not be a rotating machine, and may be a combination of a DC power source capable of controlling output, such as a fuel cell, and an inverter. In this case, the governor 12 corresponds to a fuel supply control device to the fuel cell, the prime mover 14 corresponds to the fuel cell, the generator 15 corresponds to the inverter, and the excitation current control unit 13 corresponds to the output current control device of the inverter.

The optimum output calculation unit 4A has the same calculation function as the optimum output calculation unit 4 in the first embodiment, but the content of the calculation process is slightly different from the optimum output calculation unit 4. The calculation process of the optimum output calculation unit 4A will be described in detail later. Output setting unit 11 based on the output instruction input from the optimum output calculation unit 4A sets the value of the active power P _G and the reactive power Q _G, respectively, for the set value of these active power P _G to a governor 12 , whereas for the set value of the reactive power Q _G is outputted to the excitation current control unit 13.

Governor 12 controls the amount of fuel supplied to the engine 14 based on the set value of the active power P _G. On the other hand, the exciting current control unit 13 controls the exciting current supplied to the generator 15 on the basis of the set value of the reactive power Q _G. The prime mover 14 generates power with the fuel supplied from the governor 12 to rotationally drive the generator 15. Generator 15 outputs the interconnection point via the interconnection reactor 10 to generate electric power that is active power P _G and the reactive power Q _G of the power factor corresponding to the exciting current by the excitation current control unit 13.

Here, among the functional components of these distributed power PW2, the prime mover 14, the generator 15 and interconnection reactor 10, power generating means for outputting to the interconnection point to generate active power P _G and the reactive power Q _G The voltmeter 1, ammeter 2, detected power calculation unit 3, optimum output calculation unit 4A, storage unit 5, output setting unit 11, governor 12, and excitation current control unit 13 constitute control means. ing.

In the thus configured distributed power PW2, it is possible by itself to substantially control the active power P _G and the reactive power Q _G outputs the interconnection point, the contents of the arithmetic processing in the optimum output calculation section 4A Is as follows.

(1) When estimating the system impedance Z based on the estimation processing the simultaneous equations of the system impedance Z by simultaneous equations (2) to (4), that also defines the reactive power Q _G active power P _G not only Therefore, the optimum output calculation unit 4A estimates the system impedance Z by obtaining the connection point voltage V of the connection point when the active power P _G and the reactive power Q _G are intentionally changed.

That is, the optimum output calculation section 4A is a valid power _{P G} with to set the reactive power Q _G to the specified value _Q G1 _{to Q G3} for load power P + jQ three times within a short period of time that does not vary t1, t2, t3 The power command value to be set to the values P _{G1 to} P _G3 is output to the output setting unit 11, and the interconnection point voltages V _{1 to} V ₃ , active powers P _{G1 to} P _G3 and reactive powers Q _{G1 to} Q _G3 at this time are output. Obtained from the detected power calculation unit 3. Then, the optimum output calculation unit 4A has simultaneous equations (1) obtained by substituting these interconnection point voltages V _{1 to} V ₃ , active powers P _{G1 to} P _G3 and reactive powers Q _{G1 to} Q _G3 into the above formula (1). By solving 2) to (4), the real part R and the imaginary part X of the system impedance Z are obtained.

In the second embodiment, it is possible to set this way reactive power Q _G active power P _G not only be intentionally respective times as can be seen from the configuration of the formula (8) t1, t2, t3 The real part R and the imaginary part X of the system impedance Z can be easily obtained by setting values of the active powers P _{G1 to} P _G3 and the reactive powers Q _{G1 to} Q _G3 in FIG.
Further, the system impedance Z by implementing a mode of changing only the reactive power Q _G to a constant active power P _G, and a mode of changing only the active power P _G to a constant reactive power Q _G alternately The real part R and the imaginary part X can be obtained separately and alternately.

The method of removing the influence of the voltage fluctuation of the interconnection point voltage V and the measurement noise of the interconnection point voltage V caused by the high frequency load fluctuation is the same as that of the first embodiment. Further, the method for improving the estimation accuracy of the imaginary part X of the system impedance Z when the inrush current ΔI _Q of the load L is known is the same as that of the first embodiment.

(2) Since also the active power P _G not only estimation processing reactive power Q _G of the system impedance Z due to the periodic variation method can be intentionally set, optimum output calculation unit 4A is, the real part R of the line impedance Z estimation varied at a predetermined cycle active power P _G to be estimated based on the interconnection point voltage V obtained.

(3) Although the estimation process basically optimal value of the reactive power Q _G by the optimum value search method is the same as that of the distributed power supply PW1 in the first embodiment, the active power P during operation of the dispersed type power supply PW2 since fluctuation of _G is less than the distributed power PW1, the search process will be performed only if the startup or active power P _G of distributed power PW2 has changed. Further, the search process may be performed at a predetermined time interval in consideration of a change in the existing distribution system or a change in the load power P + jQ.

   In addition, when a plurality of distributed power sources PW2 are connected to an existing distribution system, the system impedance Z with high accuracy can be obtained by estimating the system impedance Z as in the first embodiment.

   In addition, this invention is not limited to the said embodiment, For example, the following modifications can be considered.

 (1) In each of the above embodiments, the case where the distributed power source is connected to the low voltage side of the existing power distribution system has been described, but the present invention is not limited to this. The present invention is also applicable to a case where a distributed power source is connected to an existing power system or a commercial power system, such as a high-voltage side of a distribution system or a power transmission system.

 (2) In the above embodiments, the distributed power source PW1 and the distributed power source PW2 have been described, but the present invention is not limited to these. The distributed power source according to the present invention is a relatively small-capacity power source in general that does not have an influence on the power system so that the system voltage can be determined independently, among the power generation facilities linked to the power system. These include solar power generation, wind power generation, small hydropower generation, fuel cells, combined heat and power generation facilities or waste incineration power generation.

(3) In each of the embodiments described above, the reactive power Q _G that satisfies the conditional expression: R · P _G + X · Q _G = 0, that is, the invalidation that minimizes the voltage fluctuation ΔV2 (= R · P _G + X · Q _G ). Although the optimum value of power Q _G, the definition of the optimum value is not limited thereto. For example, the distributed power source can also be obtained by setting the reactive power Q _G that satisfies the conditional expression R · P _G + X · Q _G = Vref so that the voltage fluctuation ΔV2 becomes a predetermined threshold value Vref, that is, the optimal value. There may be possible to suppress the voltage change of the system voltage resulting from the active power P _G to be output to the interconnection point.

(4) When a plurality of distributed power sources simultaneously estimate the system impedance Z based on the simultaneous equations (2) to (4), the reactive power Q _G (the active power P if the distributed power source PW2) ₍ Including _G ) may be changed to a method of setting different times to change the time, and the time may be randomly changed at a constant cycle for each distributed power source. In addition to this method, the estimated value of the system impedance Z is obtained twice in succession, and it is confirmed that the two estimated values are the same value within a certain error. In this way, even if the time of varying the reactive power Q _G and / or active power P _G is other dispersed power source and temporarily match is unlikely to match two consecutive Therefore, if the system impedance Z becomes the same value within a certain error twice consecutively, it can be determined that it is the system impedance Z obtained by the distributed power source itself that has performed the system impedance estimation processing.

(5) The change in the case where a plurality of distributed power sources to estimate the system impedance Z by periodic variation method simultaneously, the reactive power Q _{G (including} also distributed power PW2 if active power P _G) in the dispersed power source Instead of setting the period to be changed to be different, the reactive power Q _G and the period to be changed may be randomly changed at each distributed power source every certain period. In addition to this method, the system impedance Z is continuously obtained twice by changing the cycle. In this way, even when the period for varying the reactive power Q _G and / or active power P _G is other dispersed power source and temporarily match is unlikely to match two consecutive Therefore, if the estimated value of the system impedance Z becomes the same value twice in succession, it can be determined that it is the system impedance Z obtained by the distributed power source itself that has performed the system impedance estimation processing. Further, the power distribution frequency spectrum of the system voltage by observing, by varying the reactive power Q _G and / or active power P _G at the frequency component that is not in the system may estimate the system impedance Z.

 S ... Distribution substation, C1 ... High voltage distribution line, T1, T2 ... Distribution transformer, C2 ... Low voltage distribution line, PW1, PW2, PW11, PW12, PW13 ... Distributed power supply, L, L1, L2, L3 ... Load, 1 ... Voltmeter, 2 ... Ammeter, 3 ... Detected power calculation unit, 4, 4A ... Optimum output calculation unit, 5 ... Storage unit, 6 ... Output current setting unit, 7 ... Output current control unit, 8 ... Inverter , 9 ... DC power supply, 10 ... interconnected reactor, 11 ... output setting unit, 12 ... governor, 13 ... exciting current control unit, 14 ... prime mover, 15 ... generator

Claims (5)

A distributed power source that supplies power to a load in conjunction with an existing power system,
Power generating means for generating active power and reactive power to output to the interconnection point;
A control unit that obtains an optimum value of reactive power that suppresses fluctuations in interconnection point voltage caused by the active power, and controls the power generation unit to output the optimum value according to active power; and
When the control means determines that the active power is in an increasing state based on the active power acquired at the previous detection opportunity and the current detection opportunity, the control means sequentially changes the reactive power to be output to the connection point. A distributed power source characterized by detecting a point voltage and searching for the reactive power at which the detected connection point voltage is equal to the connection point voltage acquired at the previous detection opportunity as the optimum value.    The control means causes the optimum value of the reactive power obtained by the search to be output to the interconnection point, and stores the relationship between the active power obtained at this time and the optimum value of the reactive power in the storage unit, and thereafter Retrieves the optimum value of reactive power corresponding to the detected active power from the storage unit, and instructs the power generation means to output the optimum value of reactive power obtained by the retrieval to the interconnection point. The distributed power supply according to claim 1, wherein:    The control means causes the optimum value of the reactive power obtained by the search to be output to the interconnection point, and stores a relationship between the active power obtained at this time, the interconnection point voltage, and the optimum value of the reactive power When the active power is determined to be in a constant state or a lowered state based on the active power acquired at the previous detection opportunity and the current detection opportunity, the optimum value of the reactive power corresponding to the active power is output. When the connection point voltage at the time is different from the connection point voltage stored in the storage unit, the connection point voltage in the storage unit is rewritten, and the data in the storage unit relating to the active power larger than the current effective power When the active power is again increased, the optimum value of the reactive power with respect to the active power is searched again based on the rewritten connection point voltage. Distributed power supply according to. An existing power system that supplies power to the load; and
A distribution facility comprising: the distributed power source according to any one of claims 1 to 3, which supplies power to a load in linkage with the existing power system. A method of supplying power to a load by connecting an existing power system and a distributed power source,
The distributed power source detects a connection point voltage when the reactive power output to the load is changed, thereby suppressing a change in the connection point voltage caused by the active power output to the load. The optimal value of the active power and the optimal value of the reactive power corresponding to the active power are output to the load, and the active power increases based on the active power acquired at the previous detection opportunity and the current detection opportunity. The reactive power output to the connection point is sequentially changed to detect the connection point voltage, and the detected connection point voltage is obtained from the connection point voltage acquired at the previous detection opportunity. A power supply method characterized by searching for equal reactive power as the optimum value.

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