JP3322728B2 - Distributed power supply device and method for preventing reverse charging of interconnected commercial frequency power line by distributed power supply device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a system for operating a distributed power supply device such as a fuel cell or a solar cell by connecting it to a commercial frequency power line. The present invention relates to a distributed power supply device for preventing reverse charging from a distributed power supply device operated in connection with a power line to a commercial frequency power line due to reverse power flow, and a method for preventing reverse charging of a commercial frequency power line using the device.

[0002]

2. Description of the Related Art In order to cope with the depletion of energy resources expected in the future, development of new power generation systems such as solar cells, wind power generators and fuel cells has been advanced, and a large number of small and medium-sized power supply devices utilizing these have been developed. (Hereinafter referred to as a distributed power supply) and a grid connection technical requirement guideline (hereinafter referred to as a guideline) for connecting to a commercial frequency power system have been developed. The guidelines describe conditions necessary for the sound operation of the commercial frequency power line, and by providing these, it is possible to safely connect the distributed power source to the commercial frequency power line.

By the way, the guidelines revised in March 1993 have enabled reverse power flow interconnection in high-voltage distribution lines. However, the following problems can be considered in the isolated operation state at the time of reverse power flow interconnection. Under special conditions where the power generation output of the distributed power supply unit and the total amount of distribution line load are balanced, if the loss of the commercial frequency power supply due to a distribution line accident or work outage occurs, the distribution line voltage and system frequency Does not fluctuate, and neither the system over / under voltage detection element nor the system frequency abnormality detection element operates. Therefore,
The distributed power supply does not disconnect from the distribution line and the distribution line continues to be charged by the distributed power supply. As a result, there is a risk that a worker who is confident that the distribution line has become zero voltage due to the loss of the commercial frequency power supply may be at risk of electric shock. In addition to this, when the commercial frequency power supply is restored, for example, when the distribution line is reclosed, the distributed power supply and the commercial frequency power supply are not synchronized, and a synchronization collision may occur. It has been pointed out that there is a danger of breaking the interconnection and it is regarded as a problem.

[0004] The reason will be described below. FIG.
Supplies the active power Ps and the reactive power Qs from the distributed power supply A to the distribution line L whose impedance is omitted, when the commercial frequency power supply C is in a normal state. Schematically shows a state in which there is a load B having a power consumption of active power PL and reactive power QL. Distributed power supply A
It has an internal voltage Es and an internal impedance Zs, and shows a voltage VL at an output point a of the distributed power supply A. Further, the distributed power supply device A has an internal circuit (control circuit) Sy. The control circuit Sy has an internal oscillator whose natural frequency determines Fo, which determines the frequency F of the internal voltage Es. Based on the frequency and the phase, the frequency F
And the internal voltage with respect to the voltage VL at the link point a according to the values of the active power Ps and the reactive power Qs to be supplied from the distributed power supply A to the distribution line L. This is a circuit for adjusting the phase angle of Es. The commercial frequency power supply C operates at the frequency Fu at the voltage Eu. Therefore, the distribution line load is now inductive, and the active power Ps and the reactive power Qs to be supplied from the distributed power supply A to the distribution line L and the active power P consumed by the distribution line load B are considered.
Assuming that L and reactive power QL are completely equal, the power flow at point b in the figure, which is the connection point between commercial frequency power supply C and distribution line L, is zero. Accordingly, FIG. 3 shows a voltage vector relationship composed of the distributed power supply A and the load B of the distribution line L. The internal voltage Es of the distributed power supply A is
, A shared voltage Vx due to the inductance of the load B, and a shared voltage Vr due to the resistance of the load B. In this state, the voltage VL at the link point a is the commercial frequency power supply C And the output frequency of the distributed power supply A is equal to the internal circuit Sy.
The frequency Fu of the commercial frequency power supply C.

[0005] In this state, even if the commercial frequency power supply C is lost due to some kind of distribution line accident or power outage, the active power Ps to be supplied from the distributed power supply A to the distribution line L and the reactive power Ps As long as the state where the power Qs and the active power PL and the reactive power QL consumed by the load B of the distribution line L are exactly equal to each other is satisfied, the conditions of Ps = PL and Qs = QL are satisfied, and the distributed power supply A is configured. The voltage vector relationship is not different from the example of FIG.
L does not change. On the other hand, since the voltage Eu of the commercial frequency power supply C, which was the frequency reference, disappears, the frequency of the link point a becomes
The processing shifts to the natural frequency Fo of the internal circuit Sy of the distributed power supply device A shown in FIG.
Since o is designed to be equal to the frequency Fu of the commercial frequency power supply, the frequency is practically hardly changed. For this reason, the protection device described in the guideline without reverse power flow that monitors only the excess and deficiency of the voltage VL at the link point a and the abnormality of the frequency cannot detect the special operation state, and Ps = PL. As long as the condition is satisfied, the charging from the distributed power supply device A to the distribution line L, that is, the reverse charging state, is continued for a long time.
Therefore, it is not possible to prevent the above-mentioned danger of electric shock of the worker or the synchronization collision when the commercial frequency power supply C is restored.

As a method for solving such a problem,
There is a method of installing a transfer interruption device and a no-voltage confirmation device. When a circuit breaker of a commercial frequency power line is opened due to an accident or the like, a system equipped with a transfer breaker transfers a signal indicating the opening of the breaker to a circuit breaker interconnecting a distributed power supply device and switches the circuit breaker. This is a system that disconnects and opens the interconnection of the distributed power supply device. If this system is adopted, the distributed power supply device is disconnected when the breaker of the commercial frequency power line is opened, so that reverse charging due to isolated operation can be reliably prevented. Further, the non-voltage confirmation device is a device that confirms that the secondary side of the switch is not charged and recloses the circuit breaker when the circuit breaker having the open commercial frequency power line is reclosed. . By employing this device, it is possible to prevent a synchronous collision accident due to the asynchronous input of the distributed power supply and the commercial frequency power supply when the commercial frequency power supply is restored, for example, when the distribution line is reclosed. However, since the installation of the transfer cutoff device and the no-voltage confirmation device involves the construction of the commercial frequency power line, a large amount of cost and a long construction period are required, which has been a hindrance factor in promoting grid interconnection. In addition, this method is effective for interconnection to special high-voltage transmission lines or high-voltage dedicated lines that are not opened with a switch in the middle of the power line on the commercial frequency power line. In the interconnection, since there are a large number of switchgears involved in the system including the line switchgear, it is impractical because a large number of communication lines and transmission / reception devices are required as transfer interruption devices. Since the commercial frequency power supply was stopped by a method other than opening the switch, such as the use of a temporary switch, the transfer interruption device and the no-voltage confirmation device alone could not provide a sufficiently reliable measure.

As a method for solving such a problem, a reverse charging prevention method disclosed in Japanese Patent Application Laid-Open No. 63-287328 as shown in FIG. 4 has been proposed. In this method, a DC power supply 1 such as a solar cell, a distributed power supply A composed of an AC / DC conversion inverter 2 and an interconnection reactor 3 are connected to a commercial frequency power supply C and a distribution line L to which a distribution line load B is connected. Control circuit D of the inverter device 2
Is a trip circuit ST for operating a phase difference detector 21, a phase angle calculator 22, a power setter 23, an error integrator 24, a variable frequency oscillator 25, a voltage abnormality detection circuit 26, a frequency abnormality detection circuit 27, and a circuit breaker S. It is composed of

The AC output voltage of the inverter device and the AC voltage at the output connection point a of the interconnection reactor 3 are input to the phase difference detector 21, and the phase difference φ between these two is obtained. The output signal of the output power setter 6 and the voltage at the interconnection point a are input to 22 and the phase difference required to supply the power specified by the setter 23 to the distribution line L, that is, the predetermined power, The target value β of the phase difference to be held between the voltage between the inverter device 2 and the interconnection point a required for the supply is calculated. The output φ of the phase difference detector 21 and the output β of the phase angle calculator 22 are input to the error integrator 24, and a difference Δφ = β−φ between the target phase difference β and the phase difference φ is obtained. The integral value (∫Δφdt) is obtained. The variable frequency oscillator 25 has a natural frequency Fo that determines the output frequency and phase of the inverter device 2, and the oscillation frequency is controlled by the phase integration error output (∫Δdt) detected by the error integrator 24. A frequency F that can cancel the phase integration error, that is, a frequency deviation Δf that is directly proportional to the output of the phase error integrator 24 and whose sign is inverted
It oscillates at a frequency F = Fo + Δf having = α · ∫Δφdt, and determines the frequency and phase of the inverter device 2.

On the other hand, the voltage abnormality detecting circuit 26 generates an absolute value ΔV = | VL− of a comparison difference output between a reference value giving the normal voltage value VL (Vu) of the interconnection point a and the abnormal voltage V′L. V'L ｜
A first comparator for comparing the absolute value ΔV with a predetermined value Va, and judging an abnormality when ΔV exceeds Va to output a trip signal to the cutoff switch S and the trip circuit ST. It consists of two comparison circuits. The frequency abnormality detection circuit 27 includes a reference value for providing the frequency FL (fu) when the interconnection point a is normal, and a frequency F′L for abnormality.
A first comparison circuit for detecting an absolute value ΔF = | FL−F′L | of a difference output from the comparator, and comparing the absolute value ΔF with a predetermined value Fa, and judging that an abnormality has occurred when ΔF exceeds Fa. And a second comparison circuit for outputting a trip signal to the trip circuit ST.

In this reverse charging prevention method, the natural frequency Fo of the variable frequency oscillator 25 is changed to Fo> Fu + ΔFa or Fo <F
By setting it to Fu + ΔFa, the loss of the commercial frequency power supply C under the special condition of Ps = PL is reliably detected, the distributed power supply A is separated from the distribution line L, and the reverse charging state is ensured. It is to prevent. However, in this method, the natural frequency Fo of the variable frequency oscillator 25 must be shifted from the frequency Fu of the commercial frequency power supply C by ΔF a, and the control system always operates to make this ΔF a zero. .

Further, in this method, when a commercial power supply is lost in a distribution system in which a plurality of distributed power supplies are connected to a distribution line, the frequency shifts of the two distributed power supplies are set in reverse. In such a case, the control of the frequency of each distributed power supply device is canceled, and there is a possibility that the loss of the commercial frequency power supply cannot be detected. Furthermore, since the frequency shift method is a method in which disturbance is applied to the system in the first place, when this method is adopted, the frequency of the commercial frequency power supply may be affected.

[0012]

SUMMARY OF THE INVENTION The present invention relates to a system in which a distributed power supply is connected to a commercial frequency power line and operated, and the reverse of a distribution line that cannot be detected by the above-described protection method when the commercial frequency power is lost. To provide a method to detect the state of charge quickly and reliably and to immediately shut off the link between the distributed power supply and the distribution line to prevent reverse charging, so that the safety of workers and the danger of synchronous collision can be prevented. The purpose is to do. Another object of the present invention is to solve the drawbacks of the scheme using the frequency shift.

[0013]

A system to which the present invention is applied is such that a distributed power supply comprising a DC power supply, an inverter and an interconnection reactor is connected to a power distribution line to which a commercial frequency power supply and a load are connected. A system, comprising: reactive power detection means for detecting reactive power at a point on a power distribution line; and control means for the inverter device, wherein the control device for the inverter device detects the reactive power at a point on the power distribution line. A reactive power value setting circuit to be set; and a reactive power detection value from the reactive power detection means and a setting value from the reactive power value setting circuit are input and the reactive power at a certain point in the power distribution line is set to the reactive power value setting circuit. An output reactive power control circuit that calculates an output reactive power value of the inverter device that is equal to or greater than the reactive power set value set in An internal voltage setting circuit that sets an internal voltage to output the output reactive power and outputs the same to the inverter device, and a voltage difference between the output voltage of the inverter device and the output voltage of the distributed power supply device (voltage at the interconnection point). An abnormality detection circuit, a voltage abnormality detection circuit that detects that the output voltage of the distributed power supply has deviated from an allowable range, a frequency abnormality detection circuit that detects that the frequency of the output of the distributed power supply has deviated from an allowable range, It is composed of a trip circuit that trips a DC breaker provided at an interconnection point according to an abnormality detection signal from each abnormality detection circuit, and an inverter stop circuit that stops the inverter device according to an abnormality detection signal from each abnormality detection circuit.

[0014]

With the above arrangement, the present invention controls the output reactive power of the distributed power supply using the reactive power at a certain point in the distribution line as a control amount, so that the distributed power supply output Qs and the load QzL are unbalanced. (Qs ≠ QzL). Under these circumstances, the loss of the commercial frequency due to a distribution line accident or the like causes an imbalance between the reactive power required by the load and the reactive power output by the distributed power supply, and the distributed power supply When the abnormality of the output voltage and the frequency or the abnormality of the voltage difference between the internal voltage and the output voltage is detected, the connection to the distribution line is cut off.

[0015]

FIG. 1 is a circuit diagram showing an embodiment of the present invention. The same reference numerals as in FIG. 2 denote the same parts. The distributed power supply device A connected to the commercial frequency power line C includes a DC power source 1 such as a fuel cell, and an orthogonal exchange inverter controlled by the inverter control means D to convert the output of the DC power source 1 into AC power at the commercial frequency. It is formed by the device 2 and the interconnection reactor 3. The distribution line L whose impedance is omitted from illustration is a commercial frequency power supply C and a distribution line load B for convenience of explanation.
At the interconnection point a, the cutoff switch S
Is connected to the distributed power supply A via In addition, a reactive power detection unit 4 is connected to the commercial frequency power line L, for example, at a power receiving point b. Next, the inverter control means D of the inverter device 2 is formed from the following components. a reactive power value setting circuit 5 at which a reactive power set value at point b is set; an output reactive power control circuit 6; an internal voltage Es setting circuit 7 that sets an internal voltage Es; A voltage difference abnormality detection circuit 8 for detecting a voltage difference between the two, a voltage abnormality detection circuit 9 for detecting a voltage abnormality at a connection point a, a frequency abnormality detection circuit 10 for detecting a frequency abnormality at a connection point a, The trip circuit 11 of the cutoff switch S and the inverter 2 when an abnormality is detected
And an inverter stop circuit 12 for outputting a signal for stopping the operation.

The reactive power control circuit 6 receives the reactive power Q _{0 at the} point b detected by the reactive power detecting means 4 and the reactive power set value at the point b set in the reactive power value setting circuit 5 at the point b. The output reactive power control circuit 6 calculates an output reactive power Qs from these inputs such that the reactive power Q ₀ at the point b becomes equal to or higher than the reactive power set value at the point b set by the reactive power value setting circuit 5 at the point b. I do. Since the output reactive power Qs is proportional to the internal voltage Es (Qs∝Es), the internal voltage Es setting circuit 7 sets the internal voltage Es to output the output reactive power Qs calculated by the output reactive power control circuit 6. After setting, the inverter 2 controls the internal voltage Es based on a command value from the internal voltage Es setting circuit 7.

The voltage difference abnormality detection circuit 8 calculates a voltage Es (output by the output reactive power control circuit 6) before the interconnection reactor 3.
With the internal voltage that outputs the calculated output reactive power Qs
Yes, the reactive power Q ₀ supplied from the commercial power source C became 0
In this case, when the voltage rises or falls greatly) , the voltage VL after the interconnection reactor 3 is detected, and the voltage difference ΔV1 = | Es−VL | is calculated. ΔV1> ΔV1 * (ΔV1 * is (Set value), that is, if the detected voltage difference exceeds the set value ΔV1 *, an abnormal signal is output. The voltage abnormality detection circuit 9 detects the voltage VL at the point a and calculates ΔV2 = | VL−Vo | (Vo is a reference voltage). If ΔV2> ΔV2 * (ΔV2 * is a set value), That is, when the voltage at the point a is separated from the reference voltage Vo by the set value ΔV2 * or more, an abnormal signal is output. The frequency abnormality detection circuit 10 detects the output frequency FL, calculates ΔFL = | FL−Fol | (Fo is a reference frequency), and when ΔFL> ΔFL * (ΔFL * is a set value), a When the frequency of the point deviates from the reference frequency Fo by the set value FL * or more, an abnormal signal is output. Voltage difference abnormality detection circuit 8, voltage abnormality detection circuit 9, frequency abnormality detection circuit 10
Is sent to the trip circuit 11 of the cut-off switch S and the inverter stop circuit 12, the trip circuit 11 of the cut-off switch S opens the cut-off switch S, and the inverter stop circuit 12 The device is pulsed off to stop the inverter.

The operation of the above embodiment will be described below. In the circuit described above, the shutoff switch S is closed to perform stable interconnection operation, and the active power Po is not supplied from the commercial power supply C (Po = O), that is, the supply from the inverter device 2 is performed. It is assumed that the active power Ps is equal to the active power consumption PzL of the load B (ZL). At this time, regarding the reactive power Q, the reactive power Qo supplied from the commercial power supply C is equal to or higher than a certain set value Qo due to the operation of the control circuit D. That is, the reactive power Q supplied from the inverter device 2
The relationship between s, the reactive power QzL consumed by the load B, and the reactive power Qo supplied from the commercial power supply C is QzL = Qs + Qo. As long as the circuit of the present invention is used, the above-mentioned state is the state in which the probability of occurrence of islanding is highest. Here, it is assumed that the commercial frequency power line C drops for some reason. Then, the reactive reactive power Qo supplied from the commercial frequency power line C becomes zero, so that the reactive reactive power QzL is different from the reactive reactive power Qs supplied from the inverter device 2 (QzL ≠ Qs), and the reactive power becomes unbalanced. Therefore, since the voltage VL and the frequency FL at the interconnection point a greatly change from the reference values, when the voltage abnormality detection circuit 9 of the inverter control means D detects the voltage abnormality, ΔV ₂ = | VL−Vo │> △ V ₂ * or the frequency abnormality detection circuit 10 detects the frequency abnormality, so that ΔFL = │FL-Fo│ >> LFL * is detected, and the inverter stop circuit 12 outputs an inverter stop signal to output the inverter stop signal. Since the shut-off switch S is opened at the same time as the stop of 2, the reverse charging can be prevented.

If the set value of the reactive power set value Qo * is small, the reactive power Qs
When the difference between the consumption reactive power QzL of the load B and the load B is small, the fluctuation of the voltage VL and the frequency FL is small, and the voltage abnormality detection circuit 9 or the frequency abnormality detection circuit 10 may not be able to detect the abnormality. However, in the present invention, the output reactive power control circuit 6 is included in the inverter control circuit D, and when the reactive power Qo supplied from the commercial power supply C becomes zero, the output reactive power control circuit 6 Since the input deviation does not become 0, the control circuit output value of the reactive power control circuit 6 diverges. Therefore, the output voltage Es depends on the direction of this divergence.
Will rise or fall significantly. As a result,
{V ₁ = | Es−VL |>} by the voltage difference abnormality detection circuit 8
Since V ₁ * is detected, the inverter stops and the cutoff switch S is opened, reverse charging can be prevented.

[0020]

According to the above configuration, when the distributed power supply device A such as a fuel cell is dispersedly connected to the commercial frequency power line L and operated, the reactive power Qo at a certain point in the power distribution line is used as a control amount. Output reactive power Q of the power supply
s, the AC output voltage of the power supply device can be intentionally reduced when the commercial frequency power supply is lost due to a commercial frequency power line accident or the like, and this voltage abnormality is detected in the power supply device, or Since the frequency abnormality caused by the imbalance of the reactive power is detected and the interconnection with the commercial frequency power line is cut off, reverse charging of the interconnected commercial frequency power line by the distributed power supply device can be prevented, and the commercial frequency can be prevented. A worker who is confident that the distribution line has become zero voltage due to the loss of the power supply is not exposed to the risk of electric shock due to reverse charging.

In addition to this, when the commercial power supply is restored, for example, when the distribution line is reclosed, the distributed power supply causes an abnormality with the frequency of the commercial power supply and immediately stops the inverter of the distributed power supply. Excessive current flowing through both power supply circuits due to a periodic collision between the power supply device and the commercial frequency power supply can be prevented, and the possibility of destruction of the power supply can be avoided.

Further, since the present invention is a system for monitoring reactive power and collapsing the internal voltage based on the abnormality of the reactive power to control interconnection of the distributed power supply device, frequency disturbance is applied to the power distribution line. Therefore, it is possible to reliably cope with a case where a plurality of distributed power supply devices are interconnected, and to easily control a large-capacity distributed power supply device.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a power distribution system to which a reverse charging prevention method according to the present invention is applied.

FIG. 2 is a conceptual diagram illustrating a state of reverse charging from a distributed power supply to a distribution line when a commercial frequency power supply is lost.

FIG. 3 is a vector diagram of the state of FIG. 2;

FIG. 4 is a conceptual diagram of a conventional reverse charging prevention method.

[Explanation of symbols]

 Reference Signs List A distributed power supply B load C commercial frequency power supply D inverter control circuit 1 DC power supply 2 inverter device 3 interconnection reactor 4 reactive power detection means 5 point b reactive power value setting circuit 6 output reactive power control circuit 7 internal voltage setting circuit 8 voltage Difference abnormality detection circuit 9 Voltage abnormality detection circuit 10 Frequency abnormality detection circuit 11 Trip circuit 12 Inverter stop circuit 21 Phase difference detection circuit stage 22 Phase angle calculation circuit 23 Output power setting circuit 24 Error integration circuit 25 Variable frequency oscillation circuit 26 Voltage abnormality detection Circuit 27 Frequency abnormality detection circuit

Claims (2)

(57) [Claims] 1. A distributed power supply device in a system in which a distributed power supply device comprising a DC power supply, an inverter device, and an interconnection reactor is connected to a power distribution line connected to a commercial frequency power supply and a load, wherein the power supply line is provided. a reactive power detection means for detecting the reactive power, the reactive power value setting circuit for setting a reactive power value at the point with a power distribution line, said reactive power value and the reactive power detected value from the reactive power detecting means set at point An output reactive power for calculating an output reactive power value of an inverter device such that a set value from a circuit is input and a reactive power at a certain point of a power distribution line is equal to or greater than a reactive power set value set in the reactive power value setting circuit. a control circuit, and the internal voltage setting circuit for outputting to set the internal voltage so as to output an output reactive power calculated by the output reactive power control circuit inverter Inverter
The output voltage of the device and the output voltage of the distributed power supply are
Output an error detection signal when the difference between the two exceeds the set value
Voltage difference detection circuit and the output voltage of the distributed power supply
Detects out of range and outputs abnormality detection signal
The frequency of the voltage abnormality detection circuit and the output of the distributed power supply
Detects out of range and outputs abnormality detection signal
Frequency abnormality detection circuit and abnormality detection from each abnormality detection circuit
Signal to trip the circuit breaker provided at the interconnection point.
Lip circuit and the abnormality detection signal from each abnormality detection circuit.
And a control device for the inverter device comprising an inverter stop circuit for stopping the inverter device. 2. A distributed power supply device is connected to a commercial frequency power line in a distributed manner.
This is a method for preventing reverse charging in a system that operates continuously.
The reactive power at a certain point in the power distribution line
Control the output reactive power of the power supply by comparing the
In this way, the commercial frequency power line
In the event of a power loss, the AC output voltage of the distributed power
A control device for the distributed power supply
In addition, the control means of the distributed power supply
Reactive power is input as a control amount, and the output voltage of the inverter device and the
Abnormal difference with the voltage at the coordination point or when the commercial frequency power supply is lost
Generated from abnormal voltage at connection point or imbalance of reactive power
Frequency abnormalities, voltage difference abnormalities or voltage abnormalities or frequency abnormalities.
When the distributed power supply device is connected to the commercial frequency power line.
Shut down the system and stop the inverter device
To commercial frequency power line using distributed power supply
How to prevent reverse charging.