JP2022136435A - Power supply system - Google Patents

Abstract

To prevent switching hunting of a changeover switch at an open power failure, in a power supply system that achieves both an uninterruptible power supply function and a load leveling function by using a common distributed power supply while satisfying FRT requirements.SOLUTION: A power supply system 100 provided between a commercial power system 10 and an important load 30 to supply a power to the important load, comprises: a distributed power supply 2; a changeover switch 3; an impedance element 4 connected in parallel to the changeover switch; a system side voltage detector 61; non-fundamental wave current injection means; and a non-fundamental wave voltage detector 82. In a case where a system voltage becomes lower than a first setting value, the changeover switch is opened to continuously operate the distributed power supply in a state where the distributed power supply and the commercial power system are connected with each other via the impedance element, and injection of a non-fundamental wave current by the non-fundamental wave current injection means is started. After the changeover switch is opened, in a case where the detected system voltage becomes equal to or more than the first setting value and a non-fundamental wave voltage becomes equal to or less than a second setting value, the changeover switch is closed again.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 is restored to a healthy state, the changeover switch is turned on to resume normal operation.

Japanese Patent No. 6338131

However, in the power supply system described above, during an open-circuit power outage in the commercial power system, depending on the system conditions, the system voltage rise due to the opening of the changeover switch may be misidentified as recovery (recovery) from the instantaneous drop, and the changeover switch may be immediately turned on again. There is a risk of Immediately after the changeover switch is turned on again, the system voltage drops, misidentifying it as an instantaneous voltage drop and reopening the changeover switch. Critical loads may be adversely affected.

As examples of system conditions that cause such opening and closing hunting, two cases are conceivable as shown in FIG. 4, for example.

For example, when the impedance elements connected in parallel to the changeover switch are capacitors (C) and coils (L), the receiving point voltage V There is a risk that _r will increase, and opening/closing hunting of the changeover switch will occur (Case 1).

In addition, after opening the changeover switch due to the drop in the receiving point voltage _Vr due to the occurrence of an open-circuit power failure, L of high reactance such as the receiving trans-reactance of other consumers with distributed power sources and the internal reactance of the generator and large capacity on the line side Due to the LC series resonance caused by the SC, the power receiving point voltage _Vr increases, which may cause opening/closing hunting of the changeover switch (Case 2).

Therefore, the present invention has been made to solve the above problems, and in 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, open-circuit power failure The main object is to prevent the opening and closing hunting of the changeover switch.

That is, a power supply system according to the present invention is provided between a commercial power system and an important load, supplies power to the important load, and includes a power line for supplying power from the commercial power system to the important load. a connected distributed power source, a changeover switch provided on the power line closer to the commercial power system than the distributed power source and opening and closing the power line, and an impedance element connected in parallel to the changeover switch on the power line; and a non-basic current for injecting a non-fundamental current having a frequency different from the fundamental frequency of the commercial power system into the power line. wave current injection means; and a non-fundamental wave voltage detection unit that detects a non-fundamental wave voltage that is the voltage of the non-fundamental wave current on the commercial power system side of the changeover switch, and the detected system voltage is detected in advance. When the value falls below a predetermined first set value, the changeover switch is opened, and the distributed power supply continues to operate in a state in which the distributed power supply and the commercial power system are connected via the impedance element. and after starting injection of the non-fundamental wave current by the non-fundamental wave current injection means and opening the changeover switch, the detected system voltage becomes equal to or higher than the first set value, and the detected non-fundamental wave The changeover switch is configured to be turned on again when the voltage drops below a predetermined second set value.

In such a power supply system, a changeover switch is provided on the commercial power system side of the power line rather than the distributed power supply, and an impedance element is connected in parallel to the changeover switch, so that the voltage on the commercial power system side is the second. Since the change-over switch is opened when the voltage falls below one set value, the demand-side facility is connected to the commercial power system via the impedance element even during the voltage drop. This makes it possible to prevent voltage drops to important loads during voltage sags while satisfying the FRT requirements for distributed power supplies. After the changeover switch is opened, the changeover switch is turned on again when the detected system voltage becomes equal to or greater than the first set value and the non-fundamental wave voltage becomes equal to or less than the second set value. For example, when the system voltage rises due to LC series resonance during an open-circuit power failure, it is possible to prevent hunting in which the change-over switch is repeatedly turned on and off again, thereby preventing adverse effects on important loads.

Further, it is preferable that the power supply system is configured to stop injection of the non-fundamental wave current by the non-fundamental wave current injection means while turning on the change-over switch again.

A specific aspect of the power supply system is one in which the non-fundamental current is an integer-order harmonic current. This integer-order harmonic means a harmonic whose frequency is an integer multiple (twice or more) of the fundamental wave.

According to the present invention configured in this way, in 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, opening and closing hunting of the changeover switch at the time of an open power failure can be prevented.

It is a figure which shows typically the structure of the power supply system of this embodiment. It is a figure which shows the simulation result of operation|movement at the time of open-circuit power failure occurrence of the power supply system of this embodiment. It is a figure which shows the simulation result of operation|movement at the time of open-circuit power failure occurrence of the power supply system of this embodiment. FIG. 10 is a diagram for explaining an example in which opening/closing hunting occurs in a changeover switch in a conventional power supply system;

A power supply system 100 according to an embodiment of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, the power supply system 100 of the present embodiment is provided between the commercial power system 10 and the important load 30, and supplies power to the important load 30 when the commercial power system 10 malfunctions. function (uninterruptible power supply function) and a function (load leveling function) as a distributed power supply system that levels the load by forward and reverse power flow to the commercial power system 10 .

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. In addition, the 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 a momentary voltage drop.

Specifically, the power supply system 100 includes a distributed power supply 2, a changeover switch 3 that connects the commercial power system 10, the distributed power supply 2, and an important load 30, an impedance element 4 connected in parallel to the changeover switch 3, a switching A parallel-off switch 5 provided closer to the commercial power system 10 than the switch 3, a grid-side voltage detector 61 that detects the voltage on the commercial power system 10 side of the selector switch 3, and detection by the grid-side voltage detector 61. It has a system abnormality detection unit 62 that detects at least an instantaneous voltage drop and a power failure from the voltage, and a control unit 7 that controls the opening/closing states of the changeover switch 3 and the parallel-off switch 5 .

Distributed power supply 2 is connected to power line L<b>1 for supplying power from commercial power system 10 to important load 30 . This distributed power source 2 is connected to a commercial power system 10, and includes, for example, a direct current power generation facility 21 such as a solar power generation system or a fuel cell, and a power storage device (storage device) 22 such as a secondary battery (storage battery). , wind power generation, micro gas turbine, etc. After rectifying the electrical energy output in AC to DC, power generation equipment (not shown) that is connected to the grid using a power converter (not shown), or a synchronous generator or induction AC generator equipment 23 such as a generator. The DC power generation equipment 21 and the power storage device (storage device) 22 are equipped with a power conversion device (not shown). The power supply system 100 includes at least the power storage device 22 and may also include any of the distributed power sources 2 described above.

The changeover switch 3 is provided on the 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 power line L1. For example, a semiconductor switch or a combination of a semiconductor switch and a mechanical switch is used. A changeover switch capable of high-speed switching such as a hybrid 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 changeover switch 3 is controlled to be opened/closed by the controller 7 .

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

The parallel-off switch 5 is provided closer to the commercial power system 10 than the distributed power source 2 (here, more than the changeover switch 3) on the power line L1, and is, for example, a mechanical switch. The parallel-off switch 5 is controlled to be opened/closed by the controller 7 .

The system-side voltage detection unit 61 detects the voltage on the commercial power system 10 side of the changeover switch 3 in the power line L1 via the voltage transformer. Specifically, the grid-side voltage detection unit 61 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 system abnormality detection unit 62 compares the detected voltage detected by the system side voltage detection unit 61 with a predetermined first set value to detect a system abnormality such as an instantaneous voltage drop or a power failure. Specifically, the system abnormality detection unit 62 detects an instantaneous voltage drop when the detected voltage falls below the first set value. Further, the system abnormality detection unit 62 detects a power failure when the duration of the state in which the detected voltage is below the first set value is equal to or longer than a predetermined value (longer than the duration of the voltage sag). Then, after the instantaneous voltage drop or power failure is detected, the grid abnormality detection unit 62 determines that the commercial power grid 10 is in a healthy state when the duration of the state in which the detected voltage is equal to or greater than the first set value is equal to or greater than a predetermined value. detect a return to

The control unit 7 switches the switching state of the changeover switch 3 and the parallel-off switch 5 according to the signal from the system abnormality detection unit 62 to switch the operating state of the power supply system 100 .

Specifically, the control unit 7 opens the changeover switch 3 when the system abnormality detection unit 62 detects an instantaneous voltage drop. Then, with the commercial power system 10, the distributed power supply 2, and the important load 30 connected via the impedance element 4, the operation by the distributed power supply 2 is continued, and the voltage and frequency of the important load 30 are stabilized. to adjust the power flow balance.

Further, when the system abnormality detection unit 62 detects a power failure, the control unit 7 opens the parallel-off switch 5 in addition to opening the changeover switch 3 and causes the distributed power supply 2 to operate in a self-sustained manner. Specifically, the control unit 7 opens the parallel-off switch 5 , and with the parallel-off switch 5 open, the distributed power supply 2 enters the self-sustained operation mode and supplies power to the important load 30 .

Thus, the power supply system 100 of the present embodiment injects a non-fundamental current, which is a current with a frequency different from the fundamental frequency of the commercial power system 10, into the power line L1 in order to prevent the switching switch 3 from opening and closing hunting during an open power failure. a non-fundamental wave current injection means 81, a non-fundamental wave voltage detector 82 for detecting a non-fundamental wave voltage which is the voltage value of the injected non-fundamental current, a detected non-fundamental wave voltage and a predetermined second set value and a non-fundamental wave voltage monitoring unit 83 that compares the

The non-fundamental wave current injection means 81 injects a non-fundamental wave current to the commercial power system 10 side of the changeover switch 3 in the power line L1. Specifically, the non-fundamental wave current injection means 81 injects the non-fundamental wave current to the commercial power system 10 side of the parallel circuit composed of the switch 3 and the impedance element 4 . The non-fundamental wave current injection means 81 is a current injection device configured to be able to inject a current of any frequency into the power line L1. It is an injection. This integer-order harmonic is a harmonic whose frequency is an integral multiple of two or more times the fundamental wave, and includes, for example, second-order, fourth-order, and other even-orders. The non-fundamental wave current injection means 81 of the present embodiment is connected to the power line L1 through an open/close switch 81s, and the non-fundamental wave current injection means 81 is opened and closed based on the control signal from the control unit 7 by opening/closing the open/close switch 81s. It is configured to start and stop current injection.

The non-fundamental wave voltage detection unit 82 detects the non-fundamental wave voltage on the commercial power system 10 side of the changeover switch 3 in the power line L1 via the voltage transformer. Specifically, the non-fundamental wave voltage detector 82 is connected to the commercial power system 10 side of the parallel circuit composed of the changeover switch 3 and the impedance element 4 via a voltage transformer. The non-fundamental wave voltage detector 82 is configured to detect a harmonic voltage of the same order as the injected non-fundamental wave current.

The non-fundamental wave voltage monitoring unit 83 compares the non-fundamental wave voltage detected by the non-fundamental wave voltage detection unit 82 with a predetermined second set value, and determines that the non-fundamental wave voltage is equal to or less than the second set value. It determines whether or not, and outputs the determination result to the control unit 7 .

In this embodiment, after detecting an instantaneous voltage drop or power failure, the control unit 7 switches the changeover switch 3 based on the detection result of the system abnormality detection unit 62 and the determination result of the non-fundamental wave voltage monitoring unit 83. Configured to be re-injected. Specifically, when the system abnormality detection unit 62 detects a system abnormality (that is, the detected voltage falls below the first set value), the control unit 7 opens the changeover switch 3 and turns on the opening/closing switch 81s. Injection of the non-fundamental wave current by the non-fundamental wave current injection means 81 is started. In the control unit 7, the recovery of the system abnormality is detected by the system abnormality detection unit 62 (that is, the duration of the state in which the detected voltage is equal to or greater than the first set value is equal to or greater than the predetermined value), In addition, when the non-fundamental wave voltage monitoring unit 83 determines that the non-fundamental wave voltage is equal to or less than the second set value, the changeover switch 3 is turned on again, and the opening/closing switch 81s is opened to turn on the non-fundamental wave current injection means 81. stop the injection of non-fundamental currents by That is, if the non-fundamental voltage detected by the non-fundamental voltage monitoring unit 83 exceeds the second set value even if the voltage detected by the system abnormality detection unit 62 is equal to or higher than the first set value, the control unit 7 , the switch 3 is not turned on again.

Next, the operation of the power supply system 100 of this embodiment (during constant operation, during momentary voltage drop, and during power failure) will be described.

(1) Normal Operation When the system abnormality detection section 62 does not detect a system abnormality, the control section 7 closes the changeover switch 3 and the parallel-off switch 5 . In this case, the distributed power source 2 and the important load 30 are connected to the commercial power system 10 via the changeover switch 3 . The impedance element 4 is connected in parallel to the changeover switch 3, but current flows through the changeover switch 3 side with the lower impedance value. exchange electricity. Peak cut/peak off can be realized by the reverse power flow by the distributed power source 2 . In this normal operation, the open/close switch 81s is open and no non-fundamental wave current is injected into the power line L1.

(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 61 . The control unit 7 opens the changeover switch 3 when the detected voltage detected by the grid-side voltage detection unit 61 is less than the first set value. As a result, the impedance element 4 connected in parallel to the changeover switch 3 is inserted, and power is supplied while maintaining reverse power flow in a form that limits the overcurrent flowing from the distributed power source 2 to the commercial power system 10 side. Prevents a voltage drop in the supply voltage of the important load 30 (performs UPS operation for the important load 30). At this time, the control unit 7 turns on the opening/closing switch 81s to start the injection of the non-fundamental wave current by the non-fundamental wave current injection means 81 into the power line L1. After opening the changeover switch 3, when the detected voltage becomes equal to or greater than the first set value and the detected non-fundamental wave voltage becomes equal to or less than a predetermined second set value, the changeover switch 3 is turned on again, and the opening/closing switch 81s is opened to stop the injection of the non-fundamental current.

(3) Operations during and after parallel-off due to grid voltage drop (occurred by power failure, etc.) the duration of the state in which the detected voltage is lower than the first set value is equal to or greater than a predetermined value), the control unit 7 opens the parallel-off switch 5 and the open/close switch 81s to cause the non-fundamental current stop the injection of As a result, the distributed power supply 2 is disconnected from the commercial power system 10 and enters the isolated operation mode. Since the selector switch 3 has already been opened, the parallel-off switch 5 is opened without overcurrent.

(4) Operation when the system is restored to normal state after parallel off (when power is restored) The duration of the state in which the voltage detected by the system side voltage detection unit 61 is equal to or greater than the first set value is equal to or greater than a predetermined value. When the non-fundamental wave voltage detected by the non-fundamental wave voltage detection unit 82 is equal to or less than the second set value, the control unit 7 turns on the switch 3 again. After that, the detection voltage of the grid-side voltage detection unit 61 and the detection voltage of the power supply-side voltage detection unit satisfy the synchronization test condition (the voltage magnitude, frequency, and phase of the distributed power supply 2 and the voltage magnitude of the commercial power grid 10 are satisfied). , the frequency and the phase match), the control unit 7 turns on the parallel-off switch 5 . As a result, the above-described (1) normal operation is resumed.

Next, FIG. 2 and FIG. 3 show simulation results of the operation of the power supply system 100 of this embodiment at the time of an open-circuit power failure.

Fig. 2 shows the open/closed state of the changeover switch 3 at the time of an open power failure, the injected current [A] of the second harmonic, the instantaneous effective value of the detected second harmonic [V], the open power failure determination signal, and the grid side voltage. Each time change of the power recovery detection signal based on the system voltage detected by the detection unit 61 is shown. _Further , _FIG . 3 shows, at the same time as FIG. Each time change of the critical load voltage [V] is shown.

As shown in FIGS. 2 and 3, when the instantaneous effective value of the system voltage falls below the first set value, the changeover switch 3 is opened and injection of secondary harmonic current is started. Then, the instantaneous effective value of the second harmonic soon rises and exceeds the second set value (open power failure determination level). When the duration time during which the secondary harmonic exceeds the second set value exceeds a predetermined set time, the open circuit failure determination signal is turned on. Note that this set time is (Condition 1) "a time or longer in which an open-circuit power failure is not detected due to the transient phenomenon at the time of occurrence and recovery of a momentary sag" and (Condition 2) "The number of interharmonic It is set to be "more than or equal to the time for the transient phenomenon of the instantaneous effective value to converge". This open power failure determination signal masks the subsequent power recovery detection signal, and even if the time when the instantaneous effective value of the system voltage exceeds the first set value exceeds the set time, the changeover switch 3 is turned on again. will not be As a result, when an open power failure occurs, opening and closing hunting of the changeover switch 3 does not occur, and a transient waveform does not occur in the important load voltage.

According to the power supply system 100 of the present embodiment configured as described above, the changeover switch 3 is provided on the commercial power system 10 side of the power line L1 rather than the distributed power supply 2, and the impedance element 4 is connected in parallel with the changeover switch 3. is connected, and the switch 3 is opened when the voltage on the commercial power system 10 side falls below the first set value. It will be in a state of being connected to the commercial power system 10 . In this way, the power supply system 100 does not disconnect the distributed power supply 2 and the important load 30 from the commercial power system 10 at any time during normal operation or during an instantaneous voltage drop. It is possible to prevent the voltage drop to the important load 30 at low time. After opening the changeover switch 3, the changeover switch is turned on again when the detected system voltage becomes equal to or greater than the first set value and the voltage of the injected non-fundamental component is equal to or less than the second set value. As a result, for example, when the system voltage rises due to LC series resonance during an open power failure, it is possible to prevent hunting in which the changeover switch 3 is repeatedly closed and reopened, and the important load 30 can be prevented from being adversely affected. . As a result, in the power supply system 100 that satisfies the FRT requirements and has both an uninterruptible power supply function and a load leveling function using a common distributed power supply 2, the occurrence of opening and closing hunting of the changeover switch 3 during an open power failure can be prevented. .

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

For example, 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 61 of the above-described embodiment may be included in the grid interconnection protection 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 control unit 7 opens the parallel-off switch 5 when any one of the link protection devices operates. In addition, the control unit 7 disconnects 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 61 and the detection voltage of the power supply side voltage detection unit satisfy the synchronization verification condition. Switch 5 can also be turned on. 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.

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.

100... Power supply system 10... Commercial power system 30... Important load L1... Power line 2... Distributed power supply 3... Changeover switch 4... Impedance element 5... Parallel switch 61 ... system side voltage detection unit 62 ... system abnormality detection unit 7 ... control unit 81 ... non-fundamental wave current injection means 82 ... non-fundamental wave voltage detection unit 83 ... non-fundamental wave Voltage monitor

Claims (3)

A power supply system provided between a commercial power system and a critical load to supply power to the critical load,
a distributed power supply connected to a power line for feeding the critical load from the commercial power system;
a changeover switch provided on the power line on the commercial power system side of the distributed power supply to open and close the power line;
an impedance element connected in parallel to the switch on the power line;
a system side voltage detection unit that detects a system voltage on the commercial power system side of the changeover switch;
non-fundamental wave current injection means for injecting a non-fundamental wave current, which is a current having a frequency different from the fundamental frequency of the commercial power system, into the power line;
a non-fundamental wave voltage detection unit that detects a non-fundamental wave voltage that is the voltage of the non-fundamental wave current on the commercial power system side of the switch,
When the detected system voltage falls below a predetermined first set value, the changeover switch is opened, and the dispersed power supply and the commercial power system are connected to each other through the impedance element. while continuing to operate the model power source, starting injection of the non-fundamental wave current by the non-fundamental wave current injection means;
After opening the changeover switch, when the detected system voltage becomes equal to or greater than the first set value and the detected non-fundamental wave voltage becomes equal to or less than a predetermined second set value, the changeover switch A power system configured to cycle the A power supply system configured to turn on the switch again and stop injection of the non-fundamental wave current by the non-fundamental wave current injection means. 3. The power supply system according to claim 1, wherein the non-fundamental current is an integer-order harmonic current.

Images