JP2023036148A - Power supply system - Google Patents

Abstract

To prevent, in a power supply system that supplies power to a plurality of important loads connected in parallel, an influence of occurrence of a short-circuit accident on a load side from spreading to all the loads.SOLUTION: Provided is a power supply system 100 that is provided between a commercial power system 10 and a plurality of important loads 30 connected in parallel to each other and supplies power to the plurality of important loads, including: a distributed power supply 2 connected to a main power line L1 for supplying power from the commercial power system to the plurality of important loads; a plurality of open/close switches 9 provided respectively for a plurality of branch power lines L2 that are branched on the main power line at a place closer to the important loads than the distributed power supply, and are configured to supply power to the respective important loads; an impedance measurement unit 93 that measures impedance of each of the branch power lines; and a second control unit 94 that, in a case where impedance of any of the plurality of branch power lines falls below a predetermined setting value, opens the open/close switch provided for the relevant branch power line.SELECTED DRAWING: Figure 1

Description

The present invention relates to power supply systems.

Conventionally, as a power supply system that satisfies the FRT requirements and has both an uninterruptible power supply function and a load leveling function using a common distributed power supply, the system shown in Patent Document 1 has been considered.

In the power supply system of Patent Document 1, a changeover switch such as a semiconductor switch and an impedance element connected in parallel to the changeover switch are provided between the commercial power system and the important load, and distributed to the important load side rather than the changeover switch. It is configured with a type power supply. Further, a parallel-off switch is provided on the commercial power system side of the selector switch. This power supply system connects the commercial power system and distributed power sources via impedance elements by opening the changeover switch when an instantaneous voltage drop (hereinafter also referred to as an instantaneous sag) occurs in the commercial power system. At the same time, the distributed power source continues operation including reverse power flow (FRT operation). On the other hand, when the commercial power system returns to a healthy state, the voltage on the load side is compared with the voltage on the load side, and when synchronization is established, the changeover switch is turned on to resume normal operation.

Patent No. 2019-047656

By the way, in the power supply system as described above, a plurality of important loads are connected in parallel, and a circuit breaker or the like for short-circuit protection may be provided for each of them. In such a power supply system, as shown in FIG. 6, when a short-circuit fault occurs on the important load side during normal operation, the fault current immediately flows from the commercial electrode system and the distributed power supply toward the short-circuit point. Along with this, when the voltage on the commercial power system side drops, the distributed power supply starts the FRT operation by opening the changeover switch. Here, the changeover switch is opened and the commercial power system is connected via the impedance element, thereby limiting the fault current from the commercial power system side and restoring the voltage on the commercial power system side. On the other hand, on the critical load side, the voltage drop and fault current of the distributed power supply continue until the short circuit is broken.

Here, as shown in FIG. 7, it is desirable that the detection of the voltage drop on the commercial power system side and the speed of opening the changeover switch be instantaneous (for example, within 2 milliseconds), assuming the withstand capacity of the important load. On the other hand, load-side circuit breakers and overcurrent relays are often configured to break short-circuit currents (10 times or more of the rated current) in about 20 milliseconds. In this case, if the changeover switch is opened instantaneously (within 2 ms), the fault current from the commercial power system is suppressed by inserting the impedance element before breaking the short-circuit point, and the current flows toward the short-circuit point. The short-circuit current will decrease, for example, to about 1.5 times the rating. As a result, the circuit breaker and the overcurrent relay extend the breaking time due to the anti-time characteristics (in the case of a general low-voltage circuit breaker, about 1 to 30 minutes for 1.3 to 1.5 times the rating). As a result, the voltage drop caused by a short circuit in a healthy important load will be prolonged, the overcurrent supply time will be prolonged in distributed power sources, and synchronization with the commercial power grid will not be established due to the voltage drop, resulting in dispersion due to equipment protection. The power supply can fail and the effects of the short circuit fault can spread to the entire critical load.

The present invention was made to solve the above problems. In a power supply system that supplies power to a plurality of important loads connected in parallel, when a short-circuit accident occurs on the load side, the effect spreads to all the important loads. Its main task is to prevent

That is, a power supply system according to the present invention is a power supply system provided between a commercial power system and a plurality of important loads connected in parallel to each other and supplying power to the plurality of important loads, wherein the commercial power system a distributed power source connected to a main power line for supplying power to the plurality of important loads from the main power line; and a changeover switch provided on the main power line closer to the commercial power system than the distributed power source and opening and closing the main power line. an impedance element connected in parallel to the changeover switch on the main power line; a system side voltage detection unit that detects a voltage on the commercial power system side of the changeover switch; A plurality of open/close switches respectively provided in a plurality of branch power lines branching from the important load side and supplying power to each of the important loads, an impedance measuring unit for measuring impedance of each of the branch power lines, and the grid side voltage detection. a first control unit that opens the changeover switch when the detected voltage of the unit becomes equal to or less than a predetermined set value and connects the distributed power supply and the commercial power system via the impedance element; and a second control unit that opens the open/close switch provided for the corresponding branch power line when any of the impedances of the plurality of branch power lines becomes equal to or less than a predetermined set value.

In such a power supply system, the impedance of each branch power line connected to an important load is measured, and if the impedance of any branch power line falls below a set value, the corresponding branch power line is cut off. Therefore, even if a short-circuit accident occurs on the side of an important load during constant operation, the short-circuit point can be immediately cut off. It is possible to prevent the supply of current and prevent the influence of the short-circuit accident from spreading to the entire important load.

A specific configuration of the power supply system includes a load-side voltage detection unit that detects a voltage value applied to the branch power line, a load-side current detection unit that detects a current value that flows through the branch power line, and the impedance measurement unit. calculates the impedance of the branch power line based on the detected voltage value and current value.

Further, in the power supply system, the second control unit controls when any of the current values of the plurality of branch power lines is equal to or greater than a predetermined set value, or when any of the impedances of the plurality of branch power lines is set in advance. It is preferable to open the opening/closing switch provided for the corresponding branch power line when it becomes equal to or less than a predetermined set value.
By doing so, the branch power line can be cut off immediately when a large current flows toward the important load before the changeover switch is opened.

As a specific configuration of the power supply system, the open/close switch may be a semiconductor switch, or a hybrid switch combining a semiconductor switch and a mechanical switch, or the like, capable of high-speed switching.
By doing so, it is possible to more effectively prevent the influence of the short-circuit accident from spreading to the entire important load.

According to the present invention configured as described above, in a power supply system that supplies power to a plurality of important loads connected in parallel, when a short-circuit accident occurs on the load side, it is possible to prevent the effect from spreading to the entire load. can be done.

1 is a schematic diagram showing the configuration of a power supply system according to an embodiment; FIG. FIG. 2 is a schematic diagram showing the state of the power supply system of the same embodiment during normal operation; FIG. 4 is a schematic diagram showing the state of the power supply system of the same embodiment during an instantaneous voltage drop; FIG. 4 is a schematic diagram showing a state of the power supply system of the same embodiment when the load side is short-circuited; FIG. 5 is a diagram showing simulation results of the operation of the power supply system of the same embodiment when the load side is short-circuited; FIG. 4 is a schematic diagram showing a state of a conventional power supply system when a short circuit occurs on the load side; The figure which shows the simulation result of the operation|movement at the time of the load side short circuit of the conventional power supply system.

A power supply system according to an embodiment of the present invention will be described below with reference to the drawings.

A power supply system 100 of the present embodiment, as shown in FIG. Function as an uninterruptible power supply system that supplies power to each important load 30 in the event of an abnormality (uninterruptible power supply function), and a distributed power supply system that levels the load by forward power flow and reverse power flow to the commercial power system 10 function (load leveling function).

Specifically, the power supply system 100 includes a distributed power supply 2 connected to a main power line L1 for supplying power from the commercial power system 10 to each important load 30, and the commercial power system 10, the distributed power supply 2, and the important load 30. A changeover switch 3 to be connected, an impedance element 4 connected in parallel to the changeover switch 3, a system side voltage detection unit 5 for detecting the voltage on the commercial power system 10 side rather than the changeover switch 3, and a system side voltage detection unit 5. A first control unit 6 for opening the changeover switch 3 when the detected voltage becomes equal to or less than a set value.

Here, the commercial power system 10 is a power supply network of an electric power company (electric utility), and has a power plant, a power transmission system, and a power distribution system. Moreover, each important load 30 is a load to which electric power should be stably supplied even in the event of a system abnormality such as a power failure or momentary voltage drop. Each important load 30 is connected to a plurality of branch power lines L2 branching from the important load side 30 of the distributed power supply 2 in the main power line L1.

The distributed power supply 2 is interconnected to the commercial power system 10, and includes, for example, a DC power generation facility 21a such as a solar power generation or a fuel cell and a power conversion device 22, a secondary battery (storage battery) or the like. One having a power storage device (storage device) 21b and a power conversion device 22, and after rectifying the electric energy output by AC such as wind power generation and micro gas turbine to DC, grid interconnection using the power conversion device power generation equipment (not shown), or AC power generation equipment 21c such as a synchronous generator or an induction generator. The power supply system 100 includes at least the power storage device 21b, and may include any of the distributed power sources 2 described above.

The changeover switch 3 is provided on the main power line L1 closer to the commercial power system 10 than the connection point of the distributed power source 2 and opens and closes the main power line L1. For example, a semiconductor switch or a semiconductor switch and a mechanical switch. A changeover switch capable of high-speed switching, such as a hybrid switch combining For example, when a semiconductor switch is used, the switching time can be set to 2 ms or less, and the power can be cut off regardless of the zero point. Moreover, when a hybrid switch is used, the switching time can be reduced to 2 msec or less, and not only is it possible to cut off regardless of the zero point, but also the conduction loss can be reduced to zero. The changeover switch 3 is controlled to open and close by the first control section 6 .

The impedance element 4 is connected in parallel to the switch 3 on the main power line L1, and is a current limiting reactor in this embodiment.

The system-side voltage detection unit 5 detects the voltage on the commercial power system 10 side of the changeover switch 3 in the main power line L1 via a voltage transformer. Specifically, the grid-side voltage detector 5 is connected to the commercial power grid 10 side of the parallel circuit composed of the changeover switch 3 and the impedance element 4 via a voltage transformer.

The first control unit 6 compares the detected voltage detected by the grid-side voltage detection unit 5 with a predetermined set value, and controls the changeover switch 3 when the detected voltage is equal to or less than the set value. A signal is output to open the switch 3 . Note that the set value in this embodiment is a voltage value for detecting a voltage drop. By opening the changeover switch 3 by the first control unit 6 in this way, the commercial power system 10 , the distributed power supply 2 and the important load 30 are connected via the impedance element 4 . In this state, the distributed generation continues operation including reverse power flow.

In the power supply system 100, the parallel-off switch 7 provided closer to the commercial power system 10 than the distributed power source 2 on the main power line L1 and the voltage on the distributed power source 2 side of the parallel-off switch 7 are detected. A power source side voltage detector 8 is further provided.

The parallel-off switch 7 is an open/close switch for paralleling off the commercial power system 10 and the distributed power supply 2, and is, for example, a mechanical switch. In FIG. 1 , the parallel-off switch 7 is provided closer to the commercial power system 10 than the changeover switch 3 , but may be provided closer to the distributed power supply 2 than the changeover switch 3 . The parallel-off switch 7 is controlled to be opened/closed by the first control unit 6 .

Specifically, the first control unit 6 opens the parallel-off switch 7 when the voltage detected by the grid-side voltage detection unit 5 satisfies a predetermined parallel-off condition. Here, the predetermined parallel-off condition is that the duration of the system voltage drop (state in which the detected voltage is equal to or less than the set value) is equal to or greater than a predetermined value (longer duration than the voltage sag duration). be. With the parallel-off switch 7 opened, the distributed power supply 2 enters the self-sustained operation mode and supplies power to the important load 30 . Since the selector switch 3 has already been released, the reactor 4 suppresses overcurrent due to the opening of the parallel-off switch 7 .

Further, the first control unit 6 ensures that the detected voltage of the grid-side voltage detector 5 satisfies the predetermined parallel off condition, and that the detected voltage of the grid-side voltage detector 5 and the detected voltage of the power supply-side voltage detector 8 are synchronously verified. When the conditions are satisfied, the switch 7 for parallel off is turned on.

Thus, in the power supply system 100 of the present embodiment, in order to prevent the influence of a short-circuit accident on the load side from spreading to the entire load, the opening/closing switches 9 provided for each of the plurality of branch power lines L2, A load-side voltage detection unit 91 that detects the voltage value applied to each branch power line L2, a load-side current detection unit 92 that detects the voltage value flowing through each branch power line L2, and an impedance measurement unit that measures the impedance of each branch power line L2. 93 and a second control section 94 that opens the open/close switch 9 based on the measured value of the impedance measurement section 93 .

The open/close switch 9 opens and closes the branch power line L2 and is provided for each important load 30 . Specifically, as the open/close switch 9, a switch capable of high-speed switching (high-speed switch) such as a semiconductor switch or a hybrid switch combining a semiconductor switch and a mechanical switch can be used. For example, when a semiconductor switch is used, the switching time can be set to 2 ms or less, and the power can be cut off regardless of the zero point. Moreover, when a hybrid switch is used, the switching time can be reduced to 2 msec or less, and not only is it possible to cut off regardless of the zero point, but also the conduction loss can be reduced to zero. The opening/closing switch 9 is controlled to be opened/closed by the second control section 94 .

The load-side voltage detection unit 91 is connected to the distributed power supply 2 side of the branch power line L2 rather than the open/close switch 9, and detects the voltage applied to the branch power line L2 via the instrument transformer. The voltage value detected by the load-side voltage detector 91 is desirably a three-phase instantaneous voltage effective value, and its frequency may be a fundamental wave or a harmonic wave. The voltage value detected by the load-side voltage detection section 91 is input to the impedance measurement section 94 and used for impedance measurement.

The load-side current detection unit 92 is connected to the distributed power supply 2 side of the branch power line L2 rather than the opening/closing switch 9, and detects the current flowing through the branch power line L2 via the instrument current transformer. The current value detected by the load-side current detection section 92 is input to the impedance measurement section 94 and used for impedance measurement. The current value detected by the load-side current detector 92 is preferably a three-phase instantaneous current effective value, and its frequency may be a fundamental wave or a harmonic wave. This current value is also input to the second control section 94 and used to control the open/close switch 9 .

The impedance measurement section 93 measures the impedance of the branch power line L2 based on the voltage value detected by the load side voltage detection section 91 and the current value detected by the load side current detection section 92 . The measured impedance is input to the second controller 94 and used to control the open/close switch 9 .

When any of the impedances of the plurality of branch power lines L2 becomes equal to or less than a predetermined set value (impedance set value), the second control unit 94 controls the opening/closing switch 9 provided in the corresponding branch power line L2. A signal is output to open the open/close switch 9 . This impedance set value is a value for detecting a short circuit (load side short circuit) in the branch power line L2, and is set to, for example, about 30% of the steady impedance value. When the measured impedance becomes equal to or less than the impedance set value, the second control section 94 opens the opening/closing switch 9 after a predetermined determination time (for example, about 20 ms) has passed.

Also, when any of the current values of the plurality of branch power lines L2 is equal to or greater than a predetermined set value (current set value), the second control unit 94 controls the open/close switch provided for the corresponding branch power line L2. A control signal is output to 9 to open the open/close switch 9 .

Next, the operation of the power supply system 100 of the present embodiment (during constant operation, instantaneous voltage drop, and short circuit on the load side) will be described.

(1) Normal Operation In the power supply system 100, as shown in FIG. 3 is connected to the commercial power grid 10 . Although the reactor 4 is connected in parallel to the changeover switch 3, since the impedance of the changeover switch 3 is smaller than the impedance of the reactor 4, the commercial power system 10, the distributed power supply 2, and each important load 30 are connected to the changeover switch Power is exchanged between the three sides. Peak cut/peak shift can be realized by reverse power flow by the distributed power source 2 .

(2) When voltage drop occurs and when power is restored When a short-circuit accident (for example, a three-phase short circuit) occurs on the commercial power system 10 side, the voltage on the commercial power system 10 side drops. This voltage drop is detected by the grid-side voltage detector 5 . The first control unit 6 opens the changeover switch 3 when the detected voltage detected by the grid-side voltage detection unit 5 is equal to or lower than the set value. As shown in FIG. 3 , when the switch 3 is opened, the distributed power supply 2 and each important load 30 are connected to the commercial power system 10 via the reactor 4 . In this state, the current flowing from the distributed power supply 2 to the short-circuit fault point is limited by the reactor 4 to suppress the fault current flowing to the short-circuit fault point and prevent the voltage drop of each important load 30 . Further, in this state, the distributed power source 2 continues operation including reverse power flow, and continues power generation output.

The grid-side voltage detection unit 5 detects the voltage on the commercial power grid 10 side regardless of whether the changeover switch 3 is open or closed, and the first control unit 6 controls the detection voltage of the grid-side voltage detection unit 5 to a predetermined value. , for example, when the residual voltage of the commercial power system reaches 80% or more, the selector switch 3 is closed.

(3) When a short circuit occurs on the load side When a short circuit accident occurs on the important load 30 side (specifically, the branch power line L2), the voltage on the commercial power system 10 side and the impedance of the branch power line L2 where the accident point is located decrease. This voltage drop is detected by the grid-side voltage detector 5 . The first control unit 6 opens the changeover switch 3 when the detected voltage detected by the grid-side voltage detection unit 5 is equal to or lower than the set value. As shown in FIG. 4 , when the selector switch 3 is opened, the distributed power supply 2 and each important load 30 are connected to the commercial power system 10 via the reactor 4 . Here, the impedance continues to drop in the short-circuited branch power line L2. This drop in impedance of the branch power line L2 is detected by the impedance measuring section 93 . The second control unit 94 detects that the impedance measured by the impedance measurement unit 93 is equal to or lower than the set value (about 30% of the steady state value) for a predetermined determination time (about 20 ms). The on-off switch 9 of the branch power line L2 that is lowered is opened. The on-off switch 9 on the healthy branch power line L2 without a short-circuit accident remains closed.

Next, FIG. 5 shows simulation results of the operation of the power supply system 100 configured as shown in FIG. 1 when the load side is short-circuited.

The simulation results of this operation show that when a load-side short-circuit accident occurs, a drop in voltage on the commercial power system 10 side is detected and the changeover switch 3 is opened within 2 milliseconds, and a drop in load-side impedance is detected. It shows the voltage waveform and current waveform on the commercial power system side and the impedance waveform, voltage waveform and current waveform on the load side when the open/close switch 9 at the fault point is opened within 20 ms. The voltage/current waveform on the commercial power system side indicates the voltage and current detected on the commercial power system side rather than the changeover switch 3 on the main power line, and the voltage/current waveform on the load house side indicates that a short circuit has occurred. It shows the impedance, voltage and current detected in the resulting branch power line.

From the simulation results of FIG. 5, it can be seen that by detecting a drop in impedance at the time of a short circuit on the load side and opening the open/close switch 9 of the branch power line L2 at the fault point, the voltage on the side of the important load 30 recovers and the effects of the short circuit accident are absorbed by the load. It was confirmed that recovery was possible without affecting the entire side.

<Effects of power supply system 100 of the present embodiment>
According to the power supply system 100 of this embodiment configured in this way, the impedance of each branch power line L2 connected to the important load 30 is measured, and the impedance of any branch power line L2 becomes equal to or less than the set value. Since the branch power line L2 corresponding to the case is cut off, even if a short-circuit accident occurs on the side of the important load 30 during normal operation, the short-circuit point can be cut off immediately. It is possible to instantly recover the drop, prevent overcurrent supply of the distributed power supply 2, and prevent the impact of the short circuit accident from spreading to the entire important load 30.

<Other Modified Embodiments>
It should be noted that the present invention is not limited to the above embodiments.

Further, in the power supply system 100 of the above-described embodiment, even when any one of the current values of the plurality of branch power lines L2 becomes equal to or greater than a predetermined setting value (current setting value), Although it is configured to open the open/close switch 9, it is not limited to this. The power supply system 100 of another embodiment does not compare the current value of the branch power lines L2 and the current set value, and when any of the impedances of the plurality of branch power lines L2 becomes equal to or less than a predetermined set value, Only the opening/closing switch 9 provided on the corresponding branch power line L2 may be opened.

A capacitor may be used as the impedance element 4, or a combination of a reactor, a resistor, or a capacitor may be used.

Furthermore, the grid-side voltage detector 5 of the above-described embodiment may be included in the grid-connection protective device. Examples of grid interconnection protection devices stipulated in grid interconnection regulations include overvoltage relays (OVR), undervoltage relays (UVR), short-circuit direction relays (DSR), ground fault overvoltage relays (OVGR), overfrequency relays ( OFR), under-frequency relays (UFR), transfer interrupters, and the like. In this case, it is conceivable that the first control unit 6 opens the parallel-off switch 7 when any one of the link protection devices operates. Further, the first control unit 6 is controlled when all the protection devices for grid connection are in a non-operating state and the detection voltage of the grid side voltage detection unit 5 and the detection voltage of the power supply side voltage detection unit 8 satisfy the synchronization verification condition. It is also possible to turn on the parallel-off switch 7 at . With this configuration, since the voltage detection section provided in the interlocking protective device is used, there is no need to provide a separate grid-side voltage detection section, and the device configuration can be simplified.

Also, in the above-described embodiment, two important loads 30 are connected in parallel, but the present invention is not limited to this. In another embodiment, three or more important loads 30 are connected in parallel, and each important load 30 may be provided with an open/close switch 9 .

Also, the power supply system 100 of another embodiment may not include the parallel-off switch 7 .

Further, the power supply side voltage detection unit 8 in the above embodiment was provided between the parallel-off switch 7 and the changeover switch 3. good too.

In addition, the present invention is not limited to the above-described embodiments, and it goes without saying that various modifications are possible without departing from the spirit of the present invention.

DESCRIPTION OF SYMBOLS 100... Power supply system 10... Commercial power system 30... Important load L1... Main power line L2... Branch power line 2... Distributed power supply 3... Switch 4... Impedance element 5 . . . System side voltage detection unit 6 .. First control unit 7 .. Parallel-off switch 8 .. Power supply side voltage detection unit 9 . . . . Load-side current detection unit 93 .. Impedance measurement unit 94 .

Claims (4)

A power supply system provided between a commercial power system and a plurality of important loads connected in parallel to supply power to the plurality of important loads,
a distributed power source connected to a main power line for feeding the plurality of critical loads from the utility grid;
a changeover switch provided on the main power line on the commercial power system side of the distributed power supply for opening and closing the main power line;
an impedance element connected in parallel to the switch on the main power line;
a grid-side voltage detection unit that detects a voltage on the commercial power grid side of the changeover switch;
a plurality of open/close switches respectively provided in a plurality of branch power lines for branching from the important load side of the distributed power supply in the main power line and supplying power to each of the important loads;
an impedance measuring unit that measures the impedance of each branch power line;
A first method for connecting the distributed power supply and the commercial power system via the impedance element by opening the changeover switch when the detected voltage of the system side voltage detection unit becomes equal to or less than a predetermined set value. a control unit;
A power supply system comprising: a second control unit that opens the opening/closing switch provided for the corresponding branch power line when any one of the impedances of the plurality of branch power lines becomes equal to or less than a predetermined set value. a load-side voltage detection unit that detects a voltage value applied to the branch power line;
a load-side current detection unit that detects a current value flowing through the branch power line,
2. The power supply system according to claim 1, wherein said impedance measuring unit calculates the impedance of said branch power line based on said detected voltage value and said current value. When any of the current values of the plurality of branch power lines is greater than or equal to a predetermined set value, or the impedance of any of the plurality of branch power lines is less than or equal to a predetermined set value 3. The power supply system according to claim 2, wherein the open/close switch provided in the corresponding branch power line is opened when the condition becomes. 2. The power system according to claim 1, wherein said open/close switch is capable of high-speed switching.

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