JP2002125318A - Tidal current controlling method for distribution system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power flow control method for distribution system, capable of stabilizing the current and voltage of respective distribution systems, even if there is fluctuating tidal current, for increasing the equipment utilization rate of the respective distribution systems, and reducing power loss. SOLUTION: A series active filter 10, constituted of a combination of a converter 5, an inverter 6, a filter 7, and a transformer 8, is connected between the respective distribution systems 3, 4. The currents of the respective distribution systems 3, 4 are detected, and correction current calculated, based on the detected current value, is passed through the distribution systems of different feeders via the series active filter 10, thereby controlling the power flow of the respective distribution systems.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power flow control method for a distribution system.

[0002]

2. Description of the Related Art For maintaining the power quality of a distribution system,
Conventionally, there are problems such as harmonics and instantaneous voltage fluctuation. However, in the future, distributed power sources such as wind power generators and solar cells will be increasingly connected to the distribution system, adding new challenges such as reverse power flow from these distributed power sources. However, it will be more difficult.
For example, if a distributed power supply is connected to one of two distribution systems extending from a substation and a reverse power flow occurs, a large imbalance occurs in voltage and current with the other distribution system.

[0003] Such an imbalance between the distribution systems of different feeders has conventionally existed due to load fluctuations and the like. Conventionally, however, the load connection system is switched using a load switch. , The load distribution connected to the distribution system was changed. Such switching of the connection system is also performed in a case where power is supplied in a loop from another system when the distribution system fails.

However, since the load switch is provided with a contact that mechanically opens and closes, it is not possible to control the current between the distribution systems in a steady and continuous manner. For this reason, in the past, each distribution system was designed with sufficient margin,
By always operating at a lower level than the equipment capacity,
I had to prepare for voltage fluctuations and current fluctuations. In addition, when the current is expected to increase due to the connection of the distributed power supply, the entire power distribution system must be remodeled for a large current to have a margin.

However, providing a margin for daily operation in preparation for an emergency means that the utilization rate of power distribution equipment is low. Further, since the power generation capacity of the distributed power source fluctuates greatly depending on weather conditions, the power utilization rate of a distribution system adapted to the maximum power generation capacity will decrease for many hours. As described above, the conventional concept cannot avoid the tendency that the capacity factor further decreases with the increase of distributed power sources in the future.

[0006] Further, conventionally, since each distribution system is operated independently, voltage and current imbalance occurs as described above, and a large power loss occurs when the feeder of the substation is viewed as a whole. Has occurred. That is, when the voltage and current of each feeder are balanced, the power loss should be minimum, but with the conventional technology, the imbalance between the distribution systems of different feeders cannot be eliminated constantly and continuously. The power loss could not be minimized.

[0007]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problems and stabilizes the current and voltage of each distribution system even when there is a load fluctuation or a power flow fluctuation from a distributed power supply. The present invention has been made in order to provide a power flow control method for a power distribution system that can improve the capacity factor of each power distribution system and reduce power loss.

[0008]

SUMMARY OF THE INVENTION To solve the above-mentioned problems, a power flow control method for a power distribution system according to the present invention is characterized in that a series active filter combining a converter, an inverter, a filter, and a transformer is provided with two or more feeders. The power flow of each distribution system is controlled by connecting a commercial frequency correction current between distribution systems of different feeders through this series type active filter. It is preferable that the power flow control is performed while detecting the current of each distribution system and calculating the correction current based on the detected current value.

As described in detail below, according to the present invention, a correction current flows between distribution systems of different feeders through a series-type active filter, and the power flow in each distribution system is optimally controlled constantly and continuously. Can be. For this reason, it is possible to always operate each distribution system in a balanced manner, thereby improving the facility utilization rate and reducing the power loss.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below. FIG. 1 is a simplified model diagram illustrating the basic form of the present invention, wherein 1 is a transformer, 2 is its bus,
Reference numerals 3 and 4 are distribution systems of different feeders. In this example, 20
A load of about 10 kW is connected to the 0 V distribution system 3, and a load of about 3.5 kW is connected to the distribution system 4. For this reason, the current of the distribution system 4 is 10 A while the current of the distribution system 3 is 30 A, and a significant imbalance occurs.

Therefore, in the present invention, these distribution systems 3,
The series type active filter 10 is connected between the four. This series-type active filter 10 is a combination of a converter 6, an inverter 7, a filter 8 and a transformer 9, and is itself known as a filter for removing harmonics. The converter 6 converts AC input from the distribution system 4 into DC, and
Converts DC to AC again. The filter 8 can cut the harmonics and adjust the waveform, adjust the voltage with the transformer 9, and output the current to the distribution system 3.

Each of the distribution systems 3 and 4 is provided with a current sensor 11 such as a CT, and outputs a detected current value to an arithmetic circuit 12. The arithmetic circuit 12 calculates a correction current based on the detected current value, and controls the operation of the series active filter 10. In the case of this example, if a correction current of 10 A flows from the distribution system 4 to the distribution system 3 through the series active filter 10, the currents of the distribution systems 3, 4 between the bus 2 and the series active filter 10 will both increase. 20 A, and the current can be balanced.

As described above, the series type active filter 1
In the conventional case where there is no 0, at least 30
According to the present invention, the power distribution systems 3 and 4 are both required to have a capacity capable of supporting the power distribution of A.
The capacity may be sufficient for the power distribution of A, and the equipment cost can be reduced. Further, by balancing the current in this manner, power loss due to system impedance can be minimized.

FIGS. 2 and 3 are circuit diagrams showing another embodiment of the present invention. In this example, a load is connected only to the power distribution system 3, and the power distribution system 4 and the power distribution system 3 are connected via the same series-type active filter 10 as shown in FIG. R + ΔR, the system impedance of the distribution system 4 is R, and the current of each system is as illustrated. FIG. 2 shows control performed so that currents sent to the respective distribution lines are equalized. Assuming that the current I flows from the power distribution system 4 to the power distribution system 3, a voltage drop of ΔR * I occurs at both ends of the series-type active filter 10 because the power distribution system 3 has a larger voltage drop.

FIG. 3 shows control performed so that the voltage drop to the connection point of the series type active filter is equalized. The power loss can be reduced as compared with the case of FIG. When a correction current of ｛ΔR / (R + ΔR / 2)｝ * I is supplied from the distribution system 4 to the distribution system 3 via the series active filter 10, the potential difference between both ends of the series active filter 10 becomes zero, Power loss for power distribution to the load can be minimized. Thus, the present invention can also be used to prevent power loss due to differences in system impedance.

In the embodiment shown in FIG. 4, a series-type active filter 10 is connected between the distribution systems 3, 4 and 4, 5 of the three feeders. Each distribution system 3, 4, 5
I _1, I ₂ the current supplied to the load, _{respectively,} and I _3, by passing the correction current between the power distribution system 3, 4, 5 via a series-type active filter 10, the series-type active on the bus 2 Each distribution system 3, up to the filter 10,
4 and 5 currents can be made uniform.

On the other hand, each power distribution system 3,
4 and 5 were operated independently, each distribution system 3,
It is necessary to make all of 4 and 5 correspond to the maximum current. For example, even in the case where the distributed power supply 13 having a large current fluctuation is connected to the distribution system 3, according to the present invention, the currents of the distribution systems 3, 4, and 5 can be averaged. Further, voltage fluctuations caused by power flow fluctuations caused by the distributed power supply 13 can be reduced by the series active filter 10.

In the embodiment of FIG. 5, the terminals of the distribution systems 3, 4, and 5 of the three feeders are connected to the series type active filter 10.
Are connected in a loop. Even when such a connection is made, each of the power distribution systems 3, 4,.
5 currents can be averaged.

In the embodiment shown in FIG. 6, two power distribution systems 3 and 4 extending from different transformers 1 are connected by a series active filter 10. By making such a connection, when the load of one of the power distribution systems increases, the current can be supplied from the other power distribution system, and as in the other embodiments, there is an advantage that it is easy to balance between different feeders. is there.

The amplification factor k of the serial type active filter is defined as amplification factor k = power flow control capacity / active filter input, and is calculated by the circuit of FIG. If e is the active filter output voltage and I is the active filter output current, then the active filter output = 3eI. Also e
= Active filter input = 3 ΔRI ² / η from ΔRI
It is. Here, η is the active filter efficiency.
On the other hand, when the system voltage is V, the power flow control capacity S = 3 ^1/2
VI. As described above, amplification factor k = power flow control capacity /
Substituting these equations as the active filter input gives: k = S / active filter input = 3 ^1/2 VI / 3
ΔRI ² / η = Vη / 3 ^1/2 ΔRI.

Now, V = 6600 volts, η = 0.9, Δ
When R = 0.4Ω and I = 100A and these values are substituted into the above equation and calculated, the amplification factor k becomes 86. Further, when the distribution impedance is low, if the same calculation is performed with ΔR = 0.1Ω, the amplification factor k becomes 343. As described above, when operating so that the currents are equal, the amplification factor is about 80 times or more. Therefore, assuming an average power system, power flow control can be performed with a small capacity of about 1.2% of the power of the distribution line.

Therefore, a practical scale of 6600 V, 100 A
(Equivalent to 1140 kVA), the capacity of the series type active filter required to control is about 5 to 15 kW,
There is an advantage that a large facility cost is not required.

[0023]

As described above, according to the power flow control method for the power distribution system of the present invention, the current of each power distribution system can be controlled regardless of the magnitude of the system impedance and the load. Further, even if the number of distributed power sources increases, the distribution system can be stabilized and voltage fluctuation can be suppressed. Further, the power loss of the distribution line can be reduced by balancing the current of the distribution system. Further, there are many advantages such that the utilization rate of the power equipment can be improved, and even when the load capacity increases, the cost of upgrading the distribution line equipment can be reduced.

[Brief description of the drawings]

FIG. 1 is a simplified model diagram illustrating a basic embodiment of the present invention.

FIG. 2 is a circuit diagram showing a second embodiment of the present invention.

FIG. 3 is a circuit diagram showing a second embodiment of the present invention.

FIG. 4 is a circuit diagram showing a third embodiment of the present invention.

FIG. 5 is a circuit diagram showing a fourth embodiment of the present invention.

FIG. 6 is a circuit diagram showing a fifth embodiment of the present invention.

FIG. 7 is a circuit diagram showing a model circuit for calculating an amplification factor of an active filter.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 transformer 2 bus 3 distribution system 4 distribution system 5 distribution system 6 converter 7 inverter 8 filter 9 transformer 10 serial active filter 11 current sensor 12 arithmetic circuit 13 distributed power supply

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Shigeaki Ogawa 1 Higashi-Shinmachi, Higashi-ku, Nagoya City, Aichi Prefecture Inside (72) Inventor Gen Ueda 1 Higashi-Shinmachi, Higashi-ku, Nagoya City, Aichi Prefecture Chubu Electric Power Co., Ltd. (72) Inventor Chihiro Ishibashi 17-3, Maruikedai, Ogawa, Oji, Higashiura-cho, Chita-gun, Aichi Prefecture (72) Inventor Yuji Yamada 38F term of 39, Higashi-Matsumoto, Nakajima, Kitakata-cho, Ichinomiya-shi, Aichi (Reference) 5G066 DA08 HA10 HB02

Claims (2)

[Claims] 1. A series active filter combining a converter, an inverter, a filter, and a transformer,
The power distribution system is connected between two or more power distribution systems and controls the power flow of each power distribution system by flowing a correction current of a commercial frequency between the power distribution systems of different feeders through this series type active filter. Power flow control method. 2. The power flow control method for a distribution system according to claim 1, wherein a current of each distribution system is detected, and a correction current is calculated based on the detected current value.