JP2008072869A - System interconnecting inverter device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a system interconnection inverter device which surely detects individual operation, when a commercial power system is not interconnected, without erasing the fluctuation outputs by each inverter circuit, respectively, under the condition that a plurality of the system interconnection inverter devices be interconnected and operated on the same wiring. <P>SOLUTION: The system interconnection inverter device 105 includes an output fluctuating portion 105d which gives fluctuations to the output current of the inverter circuit 105a, based on the fluctuation pattern of a period T. The fluctuation patterns of the output fluctuation portion 105d are set different in the absolute values of the fluctuations between the periods 0 to T/2 and T/2 to T. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a grid-connected inverter device that prevents an inverter circuit of the grid-connected inverter device from operating independently in a grid connection between a commercial power system and a grid-connected inverter device.

  Conventionally, this type of grid-connected inverter device has a voltage at the connection point between the inverter circuit and the commercial power system when the switch of the commercial power system is opened for the purpose of accident or construction (power failure state). In addition, it is necessary to disconnect the inverter circuit from the commercial power system by the system voltage abnormality and frequency abnormality detection function.

  However, if the active power and reactive power are balanced between the output power of the inverter circuit and the power consumption of the load, the inverter circuit will continue to operate even if the commercial power system switch opens, and the load May continue to supply power. This is called an isolated operation state, and there is a risk of an unexpected situation such as an electric shock when the commercial power system is maintained and maintained.

  There are various methods for detecting such an isolated operation state, and one of them is, for example, as shown in FIG. 9 (see, for example, Patent Document 1).

That is, the output from the oscillator 26 is converted by the frequency divider 27 and the amplifier 28 into a minute fluctuation signal Δφ having a constant period, and this signal is given to the output current phase adjustment circuit 20 as a phase fluctuation command. The output current phase adjustment circuit 20 detects a phase difference between the output current reference value i _unit and the system voltage Vs by a phase difference detection circuit (not shown), and controls the phase difference to be equal to the phase fluctuation command Δφ. A frequency fluctuation command signal Δf is output by a phase adjuster (not shown).

The commercial frequency signal f is added to the frequency fluctuation command signal Δf to obtain the frequency command f ^* of the output current reference sine wave. This command value is converted into a clock signal according to the frequency command f ^* by the voltage / frequency converter (V / F) 21. This clock signal is converted into a sine wave i _unit by an up / down counter (U / D) 22, an input / output interface (I / O) 23, a sine wave ROM 24, a digital / analog converter (D / A) 25, and the like. Since a frequency command is added to this, i _unit becomes a sine wave signal whose phase varies with respect to the interconnection voltage. The inverter output current command i ^* is obtained by multiplying the i _unit by the current amplitude command output from the DC voltage regulator 30 by the multiplier 31.

The deviation between the output current command i ^* and the actual output current value (detected value) i is given to the current regulator 32, where a predetermined adjustment calculation is performed so as to eliminate the deviation, whereby the output voltage command Vi. Is obtained. This output voltage command Vi is compared with the carrier signal from the carrier generator 34 in the comparator 33, and a pulse width modulation (PWM) signal is generated in the gate signal generation circuit 35 in accordance with the comparison result to constitute an inverter. On / off control of the switching device is performed.

By the way, although output current fluctuation occurs in the inverter during grid connection, there is almost no influence on the power system, and the voltage frequency at the connection point is stable. On the other hand, after the system is shut down, the interconnection point voltage is a voltage generated by itself, and the phase difference between the interconnection point voltage and the output current is in a fixed relationship that can be loaded. Since the inverter outputs the current given by the current phase fluctuation command, the commanded current phase cannot be generated, and the inverter further greatly changes the frequency of the output voltage. Therefore, this frequency fluctuation is detected by a frequency fluctuation detection circuit including a frequency / voltage converter (F / V) 36, a commercial frequency elimination filter 37, a bandpass filter 38, and a discrimination circuit 39, and the isolated operation state is discriminated. .
JP-A-6-113467

  However, the above method has the following problems. FIG. 7 is a waveform diagram for explaining this. This shows the case where the inverter is connected to the system by a single machine after the system is shut down. FIG. 7 (a) shows the phase fluctuation command of the output current command, and FIG. 7 (b) shows the frequency fluctuation amount. Show. That is, by changing the output current command at an appropriate cycle as shown in FIG. 7 (a), the same frequency fluctuation as the output current command cycle appears as shown in FIG. 7 (b). The isolated operation is detected by the set level LV.

  FIG. 8 shows a case where a plurality of (two) inverters are connected after the system is shut off. FIG. 8 (a) shows a phase fluctuation command of an output current command of a certain inverter. (B) indicates the phase fluctuation command of the output current command of another inverter. In other words, there is no problem as long as the phase fluctuation commands of the output current commands of the respective inverters are synchronized with each other, but since these are usually not synchronized, the phase variation is canceled out, and the frequency variation amount is as shown in FIG. Therefore, the set level LV may not be reached and the isolated operation may not be detected.

  In other words, in the conventional configuration, when a plurality of grid-connected inverter devices are connected and operated on the same wiring, the output fluctuations of the respective inverter circuits interfere with each other and the single operation cannot be detected. Had the problem of occurring.

  The present invention solves the above-described conventional problems, and cancels fluctuations output from each inverter circuit under the condition that a plurality of grid-connected inverter devices are connected to and operated on the same wiring. An object of the present invention is to provide a grid-connected inverter device that can reliably detect an isolated operation when a commercial power system is disconnected.

  In order to solve the above-described conventional problems, a grid-connected inverter device according to the present invention is a grid-connected inverter device linked to a commercial power system, the inverter circuit converting DC power into AC power, and the inverter An isolated operation preventing device for preventing an isolated operation of the circuit, the isolated operation preventing device detecting a voltage at a connection point between the inverter circuit and the commercial power system, and the voltage detecting unit. The commercial power system is stopped based on the voltage detected by the independent operation determination unit that determines that the inverter circuit is in the single operation state, and the single operation determination unit determines that the single operation state is in the single operation state. A grid connection protection unit that disconnects the inverter circuit and the commercial power system, and an output variation unit that varies the output current of the inverter circuit based on a variation pattern of the period T; Variation pattern of the output fluctuation unit is for an absolute value of the variation differs between periods 0 to T / 2 and the period T / 2~T.

  This ensures that the commercial power system can be reliably disconnected when canceling the fluctuations output by each inverter circuit under the condition that a plurality of grid-connected inverter devices are connected and operated on the same wiring. Independent operation can be detected.

  The grid-connected inverter device of the present invention is commercially available without canceling out the fluctuations output by each inverter circuit under the condition that a plurality of grid-connected inverter devices are linked and operated on the same wiring. An isolated operation can be reliably detected when the power system is disconnected.

  1st invention is the grid connection inverter apparatus linked with a commercial power system, Comprising: It has the inverter circuit which converts direct-current power into alternating current power, and the independent operation prevention apparatus which prevents the independent operation of the said inverter circuit The isolated operation prevention device includes a voltage detection unit that detects a voltage at a connection point between the inverter circuit and the commercial power system, and the commercial power system stops based on a voltage detected by the voltage detection unit. An independent operation determination unit that determines that the inverter circuit is in an isolated operation state, and a grid interconnection protection unit that disconnects the inverter circuit and the commercial power system when the isolated operation determination unit determines that the inverter circuit is in an isolated operation state. And an output fluctuation section that varies the output current of the inverter circuit based on the fluctuation pattern of the cycle T. The fluctuation pattern of the output fluctuation section has an absolute value of fluctuation of the period 0 to T. 2 and the period T / 2 to T, the variation output by each inverter circuit is canceled under the condition that a plurality of grid-connected inverter devices are connected and operated on the same wiring. In this way, it is possible to reliably detect the isolated operation when the commercial power system is disconnected.

  According to a second aspect of the invention, in particular, in the grid-connected inverter device of the first invention, the fluctuation pattern of the output fluctuation section is monotonously increased or monotonically decreased, so that a plurality of grid-connected inverter devices on the same wiring Since the output fluctuation of one or more units can be obtained regardless of the phase shift of the output fluctuation of each output fluctuation part due to the difference in the operation start time under the condition that the inverter circuit operates, the inverter circuit It is possible to reliably detect the isolated operation when the commercial power system is disconnected without canceling the fluctuations output.

  According to a third aspect of the present invention, in particular, in the grid-connected inverter device according to any one of the first and second aspects, the output fluctuation unit outputs an output current with respect to a voltage detected by the voltage detection unit based on the fluctuation pattern. The phase of each phase is advanced or retarded, and reactive power fluctuations are generated at the interconnection point, so that each of the grid connection inverter devices on the same wiring is operated in an interconnected manner. It is possible to reliably detect the isolated operation when the commercial power system is disconnected without canceling the fluctuations output from the inverter circuits.

  According to a fourth aspect of the invention, in particular, in the grid-connected inverter device according to any one of the first and second aspects, the output fluctuation unit increases or decreases the amplitude of the output current based on the fluctuation pattern, and By generating active power fluctuations in the system, under the condition that a plurality of grid-connected inverter devices are connected and operated on the same wiring, the fluctuations output by each inverter circuit are not canceled out. An isolated operation can be reliably detected when the power system is disconnected.

  In the fifth aspect of the invention, in particular, the frequency of the interconnection point between the inverter circuit and the commercial power system is detected from the voltage detected by the voltage detection unit in the grid interconnection inverter device of any one of the first or second invention. Provided with a frequency detection unit, the output fluctuation unit raises or lowers the frequency of the output current with respect to the frequency detected by the frequency detection unit based on the fluctuation pattern, and generates a reactive power fluctuation at the interconnection point Therefore, under the condition that multiple grid-connected inverter devices are connected and operated on the same wiring, the commercial power system can be reliably connected at the time of disconnection without canceling the fluctuations output by each inverter circuit. Single operation can be detected.

  In a sixth aspect of the invention, in particular, the grid-connected inverter device according to any one of the first to fifth aspects includes a frequency detection unit that detects a frequency from a voltage detected by the voltage detection unit, and the output fluctuation unit includes the frequency By increasing or decreasing the fluctuation value of one of the fluctuation patterns of period 0 to T / 2 or period T / 2 to T based on the frequency detected by the detection unit, a plurality of grids are connected on the same wiring. Under the condition that the power system inverter device is linked and operated, the bias of the output fluctuation of each inverter circuit can be given in the same direction, so that the commercial power system reliably detects single operation when disconnected Can do.

  According to a seventh aspect of the invention, in particular, the grid-connected inverter device according to any one of the first to sixth aspects includes an output current detection unit that detects an output current of the inverter circuit, and the output variation unit includes the output current detection unit. By increasing the fluctuation value of the fluctuation pattern as the output current detected in (2) decreases, the output of the inverter circuit varies even when the commercial power system is disconnected when the output current of the inverter circuit is small and a single operation state occurs Can be made sufficiently large, so that an isolated operation can be reliably detected.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to this embodiment.

(Embodiment 1)
FIG. 1 is a block diagram of a grid-connected inverter device according to a first embodiment of the present invention. FIG. 2 is a diagram showing output fluctuations and frequency fluctuations when a plurality of units are connected.

  In FIG. 1, 101 is a DC power supply device that supplies DC power, 102 is a load that consumes power, 103 is a commercial power system that supplies power to the load 102, 104 is a switch of the commercial power system 103, and 105 is commercial power. A grid-connected inverter device 105 that is linked to the grid 103 and supplies power to the load 102. Reference numeral 105 denotes an inverter circuit 105a that converts the DC power of the DC power supply device 101 into AC power, an inverter circuit 105, and a commercial power grid. 103, a parallel disconnection relay 105b, a voltage detection unit 105c for detecting the voltage at the connection point between the inverter circuit 105 and the commercial power system 103, and the inverter circuit 105 based on the fluctuation pattern of the cycle T. The output fluctuation unit 105d that fluctuates the output current and the voltage value of the connection point detected by the voltage detection unit 105c A frequency detection unit 105e for detecting the frequency of the voltage in the frequency, a frequency variation detection unit 105f for detecting a frequency variation amount from the frequency detected by the frequency detection unit 105e, and a voltage at the connection point detected by the voltage detection unit 105c, or When either the frequency detected by the frequency detection unit 105e or the frequency variation detected by the frequency variation detection unit 105f is greater than or equal to a predetermined value, the commercial power system 103 is stopped and the inverter circuit 105a is in an independent operation state. The isolated operation determining unit 105g and the isolated operation determining unit 105g are provided with a grid interconnection protection unit 105h that disconnects the inverter circuit 105a and the commercial power system 103 when it is determined that the isolated operation determination unit 105g is in the isolated operation state.

  In FIG. 2, (a) shows the fluctuation pattern of the period T for the output fluctuation unit 105d to fluctuate the output current of the inverter circuit 105a, and (b) shows the output fluctuation part 105d based on (b). (C) is a variation pattern generated by another output variation unit 105d based on (a), (d) is a variation of active power or reactive power generated by (b) and (c), ( (E) shows the fluctuation of the frequency at the interconnection point with the fluctuation of the active power or reactive power of (d).

  The operation and action of the grid-connected inverter device configured as described above will be described below with reference to FIGS.

  As shown in FIG. 2 (a), the output fluctuation unit 105d outputs the output current of the inverter circuit 105a based on a fluctuation pattern in which the absolute values of fluctuations differ between periods 0 to T / 2 and periods T / 2 to T. Fluctuate. That is, the fluctuation pattern is obtained by superimposing the periods 0 to T / 2 and the periods T / 2 to T even if the sum of output fluctuations in the periods 0 to T / 2 and T / 2 to T is the same. Sometimes it will not be zero at each hour.

  By varying the output with such a variation pattern, the phase of the output variation of the output variation unit 105d of the two grid-connected inverter devices 105, as shown in FIGS. 2 (B), (C), and (D). Even if the deviation occurs, the fluctuation of the active power or reactive power generated by the output fluctuation does not become zero, so the reactive power or active power between the output power of the inverter circuit 105a existing on the same wiring and the power consumption of the load 102 Can be prevented.

  Thereby, while the inverter circuit 105a and the commercial power system 103 are connected, the output fluctuation by the output fluctuation unit 105d has almost no effect on the commercial power system 103, and the voltage and frequency at the connection point are stable. When the switch 104 of the commercial power system 103 is opened, the reactive power or active power between the output power of the inverter circuit 105a and the power consumption of the load 102 is not in a balanced state due to the output fluctuation by the output fluctuation section 105d. Frequency fluctuations like (e) occur. This frequency variation is detected by the frequency variation detecting unit 105f, and when the detected frequency variation exceeds a predetermined value, the isolated operation determining unit 105g determines that the isolated operation is performed, and the grid interconnection protection device 6e solves the problem. The row relay 105b is opened to disconnect the inverter circuit 105a and the commercial power system 103, and the output of the inverter circuit 105a is stopped.

  Here, the output fluctuation unit 105d advances or delays the phase of the output current output from the inverter circuit 105a with respect to the voltage detected by the voltage detection unit 105c based on the fluctuation pattern of FIG. Make it compatible. Under such conditions, if the phase of the output current is changed as shown in FIGS. 2B and 2C, reactive power fluctuations as shown in FIG. When the switch 104 is opened, frequency fluctuations as shown in FIG. 2 (e) occur, so that the isolated operation determination unit 105g can determine the isolated operation.

  Further, the output fluctuation unit 105d increases or decreases the amplitude of the output current output from the inverter circuit 105a based on the fluctuation pattern of FIG. Under such conditions, when the amplitude of the output current as shown in FIGS. 2 (B) and 2 (C) is changed, the active power changes as shown in FIG. Since the frequency fluctuation as shown in FIG. 2 (e) occurs when the device 104 is opened, it is possible to determine the single operation by the single operation determination unit 105g.

  Further, the output variation unit 105d increases or decreases the frequency of the output current output from the inverter circuit 105a with respect to the frequency detected by the frequency detection unit 105e based on the variation pattern of FIG. Under such conditions, when the frequency of the output current is changed as shown in FIGS. 2B and 2C, the reactive power changes as shown in FIG. Since the frequency fluctuation as shown in FIG. 2 (e) occurs when the switch 104 is opened, the isolated operation determination unit 105g can determine the isolated operation.

  As described above, in this embodiment, the independent operation determination unit 105g of the grid interconnection inverter device 105 has the absolute values of the fluctuations of the fluctuation pattern of the output fluctuation part 105d as the periods 0 to T / 2 and the periods T / 2 to T. Therefore, under the condition that a plurality of grid-connected inverter devices 105 are connected and operated on the same wiring, the fluctuations output from the inverter circuit 105a are not canceled out. The isolated operation can be reliably detected when the line 103 is disconnected.

  In the present embodiment, the output fluctuation unit 105d of the grid interconnection inverter device 105 advances or delays the phase of the output current with respect to the voltage detected by the voltage detection unit 105c based on the fluctuation pattern, or By increasing or decreasing the amplitude of the output current, or increasing or decreasing the frequency of the output current with respect to the frequency detected by the frequency detector 105e, and generating reactive power or active power at the interconnection point, Under the condition that a plurality of grid-connected inverter devices 105 are connected to each other, the fluctuations output by the respective inverter circuits 105a are not canceled, and the commercial power system is reliably operated independently when disconnected. Can be detected.

(Embodiment 2)
FIG. 3 is a diagram showing output fluctuations and frequency fluctuations during a multi-unit operation when the fluctuation pattern of the output fluctuation part of the grid-connected inverter device in the second embodiment of the present invention is monotonically increased. .

  In FIG. 3, (a) shows a monotonically increasing fluctuation pattern of the period T for the output fluctuation part 105d to fluctuate the output current of the inverter circuit 105a, and (b) shows the output fluctuation part 105d based on (a). The fluctuation pattern to be generated, (C) is the fluctuation pattern generated by another output fluctuation unit 105d based on (A), (D) is the fluctuation of active power or reactive power generated by (B) and (C), (E) shows the fluctuation of the frequency at the interconnection point accompanying the fluctuation of reactive power or active power of (d).

  The operation and action of the grid-connected inverter device configured as described above will be described below with reference to FIGS.

  As shown in FIG. 3 (a), the output fluctuation unit 105d includes the inverter circuit 105a based on a monotonically increasing fluctuation pattern in which the absolute values of fluctuations differ between periods 0 to T / 2 and periods T / 2 to T. Vary the output current. Under such conditions, even if the phase of the output fluctuation of the output fluctuation section 105d of the two grid-connected inverter devices 105 is shifted by 180 °, as shown in FIGS. Thus, the fluctuation of the active power or the reactive power generated by the output fluctuation is not zero, and the magnitude of the output fluctuation of one or more can be ensured. Therefore, even if the switch 104 of the commercial power system 103 is opened, an active power or reactive power balance between the output power of the inverter circuit 105a existing on the same wiring and the power consumption of the load 102 is prevented. Therefore, the frequency fluctuation as shown in FIG. Therefore, the isolated operation determination unit 105g can determine the isolated operation based on the frequency variation detected by the frequency variation detection unit 105f.

  In the present embodiment, the variation pattern of the output variation unit 105d is monotonously increased, but may be monotonously decreased.

  As described above, in the present embodiment, the fluctuation pattern of the output fluctuation portion 105d of the grid interconnection inverter device 105 is monotonously increased or monotonically decreased, so that a plurality of grid interconnection inverter devices on the same wiring. Under the condition that the 105 is connected and operated, output fluctuations of one or more units can be obtained regardless of the phase shift of the output fluctuation of each output fluctuation part 105d due to the different operation start time. Thus, the commercial power system 103 can reliably detect an isolated operation without disconnecting the fluctuations output from the inverter circuits 105a.

(Embodiment 3)
FIG. 4 is a diagram showing an output fluctuation characteristic according to the frequency detected by the frequency detection unit of the grid-connected inverter device in the third embodiment of the present invention.

  Here, in FIG. 4, the reference frequency indicates the reference frequency 50/60 Hz of the commercial power system 103.

  The operation and action of the independent operation device for the grid-connected inverter configured as described above will be described below with reference to FIGS. 1, 3, and 4.

  When the frequency detected by the frequency detection unit 105e is equal to or higher than the reference frequency, the output variation unit 105d determines the variation amount of the output variation based on the variation pattern in the period 0 to T / 2. At T, the fluctuation amount of the output fluctuation is determined by the product of the fluctuation quantity determined by the fluctuation pattern and the fluctuation coefficient calculated from FIG. 4 based on the frequency (in this embodiment, the fluctuation coefficient is shown in FIG. As the detected frequency increases to 50.1, 50.2, 50.3 Hz..., The coefficient of variation is increased to 1, 2, 3%, etc.).

  When the frequency detected by the frequency detection unit 105e is less than the reference frequency, the output fluctuation unit 105d determines the fluctuation amount of the output fluctuation based on the fluctuation pattern in the period T / 2 to T. In T / 2, the variation amount of the output variation is determined by the product of the variation amount determined by the variation pattern and the variation coefficient calculated from FIG. 4 based on the frequency (in this embodiment, the variation coefficient is 4, the coefficient of variation is increased to 1, 2, 3%, etc. as the detected frequency decreases to 49.9, 49.8, 49.7 Hz,...

  Here, when the output fluctuation unit 105d fluctuates the phase of the output current of the inverter circuit 105a, the period 0 to T / 2 is a slow phase and the period with respect to the voltage at the connection point detected by the voltage detection unit 105c. T / 2 to T determine the amount of fluctuation to be advanced. Further, when the amplitude of the output current of the inverter circuit 105 is changed, the amount of change is determined such that the period 0 to T / 2 decreases the amplitude and the period T / 2 to T increases the amplitude. Further, when the frequency of the output current of the inverter circuit 105a is changed, the amount of change is determined such that the period 0 to T / 2 decreases the frequency and the period T / 2 to T increases the frequency.

  Therefore, when the switch 104 of the commercial power system 103 is opened and the inverter circuit 105a is in a single operation state, the frequency increases when the frequency increases, and the frequency increases when the frequency decreases. Since the frequency at the interconnection point greatly fluctuates by changing the output current so as to decrease, the isolated operation determination unit 105g can reliably detect the isolated operation in a short time, and the grid connection protection device 6f The train relay 105b is opened to disconnect the inverter circuit 105a and the commercial power system 103, and the output of the inverter circuit 105a can be stopped.

  In the present embodiment, the variation coefficient is a linear pattern with respect to the frequency, but may be a non-linear pattern.

  As described above, in the present embodiment, the output fluctuation unit 105d has one of the fluctuation patterns of the cycle 0 to T / 2 or the cycle T / 2 to T based on the frequency detected by the frequency detection unit 105e. By increasing or decreasing the fluctuation value, the bias of the output fluctuation of each inverter circuit 105a is set in the same direction under the condition that a plurality of grid-connected inverter devices 105 are connected and operated on the same wiring. Therefore, the isolated operation can be reliably detected when the commercial power system 103 is disconnected.

(Embodiment 4)
FIG. 5 shows a block diagram of a grid-connected inverter device according to the fourth embodiment of the present invention. Moreover, FIG. 6 is a figure which shows the output fluctuation characteristic according to the output current of the output fluctuation part of a grid connection inverter apparatus.

  Here, in FIG. 5, the grid interconnection inverter device 105 includes an output current detection unit 105 i that detects an output current of the inverter circuit 105 a in addition to the configuration of FIG. 1.

  The operation and action of the grid-connected inverter device configured as described above will be described below with reference to FIGS.

  The output fluctuation unit 105d calculates a variation coefficient as shown in FIG. 5 based on the output current detected by the output current detection unit 105i, and outputs it from the product of the variation coefficient and the variation amount determined by the variation pattern. The variation amount of the current is determined (in this embodiment, the variation coefficient is 1, 2 as the detected output current is reduced to rated x 90%, rated x 80%, etc. as shown in FIG. 3%, etc.)

  Therefore, even when the single operation state occurs when the output current of the inverter circuit 105a is small and the load of the rotating machine is connected to the load 102, the amount of frequency fluctuation detected by the frequency fluctuation unit 105f is sufficiently large. The operation determination unit 105g can reliably detect an isolated operation in a short time, and the grid connection protection unit 105h disconnects the inverter circuit 105a and the commercial power system 103 by opening the disconnection relay 105b, and the inverter circuit 105a. Output can be stopped.

  In the present embodiment, the output current detection unit 105i detects the current output from the inverter circuit 105a. However, the output current value of the inverter circuit 105a may be calculated from the generated power of the DC power supply device 101.

  As described above, in this embodiment, the output fluctuation unit 105d of the grid interconnection inverter device 105 increases the fluctuation value of the fluctuation pattern as the output current detected by the output current detection unit 105i is smaller. Even when the isolated operation state occurs when the output current of the circuit 105a is small, the output fluctuation of the inverter circuit 105a can be sufficiently increased, so that the isolated operation can be reliably detected.

  The grid-connected inverter device of the present invention is commercially available without canceling out the fluctuations output by each inverter circuit under the condition that a plurality of grid-connected inverter devices are linked and operated on the same wiring. Since the power system can reliably detect an isolated operation at the time of disconnection, it can be applied to applications such as a distributed power supply device such as a fuel cell device or a solar power generation device.

The block diagram of the grid connection inverter apparatus in Embodiment 1 of this invention The figure which shows the output fluctuation | variation and frequency fluctuation | variation at the time of the interconnection operation | movement of several units | sets in Embodiment 1 of this invention. The figure which shows the output fluctuation | variation and frequency fluctuation | variation at the time of the multi-unit interconnection operation when the fluctuation pattern of the output fluctuation | variation part in Embodiment 2 of this invention is made to increase monotonously. The figure which shows the output fluctuation characteristic according to the frequency of the frequency detection part in Embodiment 3 of this invention. The block diagram of the grid connection inverter apparatus in Embodiment 4 of this invention The figure which shows the output fluctuation characteristic according to the output current of the output fluctuation part in Embodiment 4 of this invention. The figure which shows the output fluctuation | variation and frequency fluctuation | variation at the time of 1 unit | set connection operation in the conventional grid connection inverter apparatus The figure which shows the output fluctuation and frequency fluctuation at the time of the multi-unit interconnection operation in the conventional grid interconnection inverter device Block diagram of a conventional grid-connected inverter device

Explanation of symbols

105 Grid-connected inverter device 105c Voltage detection unit 105d Output fluctuation unit 105g Independent operation determination unit 105h Grid connection protection unit 105i Output current detection unit

Claims (7)

A grid-connected inverter device linked to a commercial power system, comprising an inverter circuit that converts DC power into AC power, and an isolated operation preventing device that prevents the isolated operation of the inverter circuit, the isolated operation prevention The apparatus includes: a voltage detection unit that detects a voltage at a connection point between the inverter circuit and the commercial power system; and the commercial power system is stopped based on the voltage detected by the voltage detection unit. An isolated operation determination unit that determines that the system is in an isolated operation state, a grid connection protection unit that disconnects the inverter circuit and the commercial power system when the isolated operation determination unit determines that the operation is in an isolated operation state, and a variation in cycle T And an output variation unit that varies the output current of the inverter circuit based on the pattern. The variation pattern of the output variation unit has an absolute value of variation of period 0 to T / 2 and period T Different interconnection inverter device and 2～T. The grid interconnection inverter apparatus according to claim 1, wherein the fluctuation pattern of the output fluctuation section is monotonously increased or monotonically decreased. 3. The grid-connected inverter device according to claim 1, wherein the output fluctuation unit advances or delays the phase of the output current with respect to the voltage detected by the voltage detection unit based on the fluctuation pattern. 3. The grid-connected inverter device according to claim 1, wherein the output fluctuation unit increases or decreases the amplitude of the output current based on the fluctuation pattern. A frequency detection unit that detects the frequency of the connection point between the inverter circuit and the commercial power system from the voltage detected by the voltage detection unit, and the output fluctuation unit is detected by the frequency detection unit based on the fluctuation pattern The grid-connected inverter device according to claim 1 or 2, wherein the frequency of the output current is increased or decreased with respect to the frequency. A frequency detection unit that detects a frequency from a voltage detected by the voltage detection unit is provided, and the output fluctuation unit is either a cycle 0 to T / 2 or a cycle T / 2 to T based on the frequency detected by the frequency detection unit. The grid interconnection inverter apparatus according to any one of claims 1 to 5, wherein a fluctuation value of one of the fluctuation patterns is increased or decreased. 7. An output current detection unit that detects an output current of the inverter circuit, wherein the output variation unit increases the variation value of the variation pattern as the output current detected by the output current detection unit is smaller. The grid interconnection inverter device according to item 1.

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