JP2010226950A - System interconnection inverter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent decrease in efficiency even when output current decreases, when alternating-current power is outputted, while detecting output current and performing feedback control. <P>SOLUTION: An output current detecting section 38 is provided with a CT70B and a CT70A, that have a higher current transformation ratio than CT70B. A signal-generating section 50 is provided with a selecting section 66 that selects the CT70B, when input power to the inverter is high; reads the output from the CT70B as the output current of the inverter; and performs feedback control. When the input current to the inverter becomes low, by having the selecting section select the CT70A and reads the output from the CT70A as the output current, desired feedback gain is secured and decrease in the conversion efficiency, even when the output current decreases, is prevented. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a grid-connected inverter that supplies power generated by a solar power generation device or the like to a grid power supply.

  In recent years, grid interconnection systems such as grid-connected power generation apparatuses that connect (link) solar power generation apparatuses and the like to commercial power grids are becoming widespread. In such a grid interconnection system, DC power generated by a solar cell is converted into AC power by an inverter device and regenerated to the grid.

  In the grid-connected inverter that is an inverter device provided in the grid-connected system, for example, a target value of the output current for one cycle is set, and data that becomes this target value is stored as a ROM table, A current corresponding to the target value can be output by setting an on time (on duty) when driving the switching element based on the data of the ROM table. This target value is set based on the output power of the grid interconnection system, that is, the power generated by the solar power generation device or the like.

  By the way, the grid-connected inverter can be operated most efficiently when the rated power is output. However, in the power generation device using a solar cell, the generated power varies depending on the amount of solar radiation. When the electric power is less than the rated electric power, maximum power follow-up control (MPPT control) is performed so that the output efficiency becomes the highest according to the change in the generated electric power so that the output electric power corresponding to the generated electric power can be obtained.

  Further, in the grid-connected inverter, in order to output a current corresponding to the target value, the output current is measured, and feedback control is performed so that the output current becomes the target value.

  For the measurement of such output current, for example, a CT (Current Transformer) is used, and a voltage output from this CT is read according to the output current.

  By the way, in the measurement of such output current, the current value detected when the grid-connected inverter outputs the rated power is set to be the maximum value. For example, when a voltage in a range of ± 2.5 v (0 v to 5 v) is read with reference to a voltage of 2.5 v, the CT output voltage at the rated power is −2.5 v to +2.5 v. I am doing so.

  However, when the output power of the grid interconnection inverter is low, the output current is also low and the CT output is reduced. For this reason, the feedback gain at the time of performing feedback control of the output current becomes low, and the power factor of the output power may be lowered.

  The present invention has been made in view of the above facts, and when feedback control is performed so that the output current becomes a target value corresponding to the input power, the power of the output power can be reduced even when the output power is lower than the rated power. An object of the present invention is to propose a grid-connected inverter that enables efficient operation without reducing the rate.

  In order to achieve the above object, the present invention provides a grid-connected inverter that converts input DC power into AC power corresponding to the voltage and frequency of the system power supply and outputs the AC power based on a predetermined switching signal. An inverter circuit that converts the DC power into the AC power when an element is driven, and a target current value of the output current of the inverter circuit is set based on the DC power and the voltage or frequency of the system power supply. Generating means for generating a switching signal for driving the switching element based on the target current value and the voltage and frequency of the system power supply, and first current detecting means for detecting an output current converted and output by the switching circuit And second current detection means for detecting the output current at a higher current transformation ratio than the first current detection means, and the first or second current detection means. A selection unit that selects any one of the second current detection units and uses the detection result of the selected current detection unit as an output current, and the generation unit selects a switching signal based on the output current selected by the selection unit. Correction means for correcting the target current value when generating the current value.

  According to the present invention, the target current value is set according to the input DC power, and the switching power is generated based on the set target current value, the system voltage of the system power supply, and the system frequency, whereby the input power is Output as AC power matched to the system voltage and system frequency of the power supply. At this time, an output current of the inverter circuit is detected, and a target current value or a switching signal is corrected based on the output current, thereby performing feedback control for adjusting the phase of the voltage and current of the output power.

  On the other hand, as current detection means for detecting output current, first current detection means and second current detection means having a higher current transformation ratio than the first current detection means are provided. One of the current detection means is selected by the selection means, and an output current for correcting the target current value or the switching signal is read.

  Since the second current detection means has a high current transformation ratio, the detection value of the second current detection means is larger than the detection value of the first current detection means. Therefore, when the output current is small and sufficient feedback gain cannot be obtained when the detection value of the first current detection unit is used, the second current detection unit is selected and the second current detection unit A desired feedback gain can be obtained by using the detected value.

  Thereby, it can prevent that the conversion efficiency at the time of converting an output electric current from the direct current power by an inverter circuit to alternating current power falls at least.

  In the present invention, it is sufficient if the first and second current detection units having different current transformation ratios are provided, but three or more current detection units having different current transformation ratios may be provided.

  In the above-mentioned invention, each of the first and second current detecting means includes an equivalent current transformer for an instrument, and the current transformation ratio is changed by changing the number of turns of the primary winding. It is characterized by.

  According to the present invention, equivalent current transformers are used as the first and second current detection means, and the current transformation ratios are made different by changing the number of turns of the primary winding. Thereby, the 1st and 2nd electric current detection means from which a current transformation ratio differs by a desired ratio can be obtained easily.

  Moreover, in the above-mentioned invention, the selection means selects one of the first and second current detection means based on the DC power.

  According to the present invention, one of the first and second current detection means is selected based on the DC power input to the inverter circuit. Since the system voltage of the system power supply is substantially constant, the output current varies depending on the input power. For this reason, by selecting one of the first and second current detection means from the input power, an appropriate selection according to the output current is possible.

According to the present invention, by providing at least the first and second current detection means having different current transformation ratios, a sufficient feedback gain can be ensured even when the output power is low. Thereby, the outstanding effect that an efficient driving | operation becomes possible even if output electric power is low is acquired.

It is a block diagram which shows schematic structure of the solar power generation device applied to this Embodiment. It is a block diagram which shows schematic structure of the signal generation part which produces | generates a switching signal. It is a schematic block diagram which shows the output current detection part to which this invention is applied. (A) And (B) is a schematic diagram of CT applied to this embodiment, A) shows CT70A with a high current transformation ratio, and (B) shows CT70B with a low current transformation ratio. (A) And (B) is a diagram which shows the outline of the output voltage according to the output current of CT, and the output voltage input into a microcomputer, (A) shows CT70A with a high current transformation ratio, B) shows CT70B having a low current transformation ratio. It is a flowchart which shows an example of the front-end | tip of CT70 based on input electric power.

Embodiments of a grid-connected inverter according to the present invention will be described below with reference to the drawings.

  In FIG. 1, the schematic structure of the solar power generation device 10 applied to this Embodiment is shown. The solar power generation device 10 includes a solar battery 12 and a grid-connected inverter (hereinafter referred to as “inverter 14”) each of which is constituted by a solar battery array in which a plurality of solar battery modules each formed by connecting solar battery cells are connected. Say). In addition, in FIG. 1, the solar cell 12 which connected the solar cell array formed of the several module is shown.

  The solar power generation device 10 uses a frequency corresponding to a commercial power system (hereinafter referred to as “system power supply 16”) by the inverter 14 to generate direct-current power generated when each solar battery cell of the solar battery 12 receives sunlight. Convert to AC power.

  The solar power generation device 10 regenerates the generated power to the system power supply 16 by being connected to the system power supply 16 via, for example, a distribution board (not shown). At this time, the photovoltaic power generation apparatus 10 is connected to the line of the system power supply 16 through the disconnecting conductor 30, the protective relay 54, and a wiring breaker (not shown), and is disconnected from the system power supply 16 by the disconnecting conductor 30 or the protective relay 54. Can be separated. As a result, an abnormality occurring in the system power supply 16 is prevented from spreading to the inverter 14. In addition, the solar power generation device 10 applied to this Embodiment shall supply 200V alternating current power to the line of the system power supply 16 of a single phase three-wire 100V / 200V.

  The inverter 14 of the solar power generation device 10 includes an inverter circuit 20 and a microcomputer (hereinafter referred to as “microcomputer 22”) that controls the inverter circuit 20 and the like. The direct-current power generated by the solar cell 12 is supplied to the inverter circuit 20 through a backflow prevention diode 24, a protective circuit breaker (NFB) 25, and a noise filter 26.

  In the inverter circuit 20 of the inverter 14, the DC power is switched based on the PWM theory to generate a pseudo sine wave having substantially the same frequency as that of the system power supply 16. As a result, the DC power generated by the solar cell 12 is converted into AC power of the system power supply 16 and output. The output power of the inverter circuit 20 is output to the line of the system power supply 16 through the filter circuit 28 and the noise filter 29. That is, the solar power generation apparatus 10 uses a transformerless system in which the inverter 14 is connected to the system power supply 16 without using a transformer.

  The inverter 14 includes a power generation voltage detection unit 32 that includes an isolation amplifier that detects the voltage of the power generated by the solar battery 12, and a power generation current detection unit that includes a current transformer (CT) that detects a direct current of the power generated by the solar battery. 34, a system voltage detector 40 for detecting the system voltage, voltage waveform and frequency of the system power supply 16 by a transformer (PT) and an output current detector 38 for detecting an alternating current (output current) output from the inverter circuit 20 These are provided and connected to the microcomputer 22.

  The inverter circuit 20 is provided with switching elements 42Xa, 42Xb, 42Ya, 42Yb (hereinafter collectively referred to as “switching element 42”) such as IGBTs in a bridge connection. A diode (flywheel diode) 44 is provided corresponding to each of the switching elements 42Xa, 42Xb, 42Ya, and 42Yb.

The microcomputer 22 detects the duty ratio of the switching signal that drives the switching element 42 of the inverter circuit 20 based on the generated power detected by the generated voltage detection unit 32 and the generated current detection unit 34 and the voltage detected by the voltage waveform detection unit 40. To control. Thereby, in the inverter circuit 20, each of the switching elements 42 is driven on / off according to the switching signal output from the microcomputer 22. At this time, the microcomputer 22 generates a switching signal in accordance with the phase (zero cross) of the AC voltage of the system power supply 16 detected by the voltage waveform detector 40.

  The voltage waveform of the AC power output from the inverter circuit 20 when the switching element 42 is turned on / off has a sawtooth waveform. In the inverter 14, the filter circuit 28 removes higher harmonic components, and a predetermined waveform is obtained. Outputs waveform AC power. In addition, a booster circuit is provided between the inverter circuit 20 and the noise filter 26, and the generated power of the solar battery 12 is boosted to a predetermined voltage corresponding to the system voltage by the rising circuit and then input to the inverter circuit 20. Also good.

  As shown in FIG. 2, the microcomputer 22 is formed with a signal generation unit 50 that generates a switching signal for obtaining a sine wave signal based on the PWM theory. FIG. 2 shows a functional block diagram of the signal generation unit 50 formed in the microcomputer 22.

  The signal generator 50 includes a ROM 52 (hereinafter referred to as “ROM data”) for storing data (an on / off signal pattern) for generating a preset current waveform, A control unit 56 that reads ROM data and generates a switching signal based on the ROM data, and a drive unit 58 that drives the switching element 42 based on the switching signal output from the control unit 56 are provided. In the inverter 14 applied to the present embodiment, the switching element 42 is driven by generating a switching signal of 15 kHz to 20 kHz.

  As described above, the ROM 52 of the signal generation unit 50 stores the target value of the ON time (ON duty) of the switching signal when generating a preset current waveform such as a sine wave as ROM data. . The ROM data is set on the basis of a predefined current waveform that does not include a DC component, such as a sine wave.

  The control unit 56 outputs a switching signal in accordance with the phase of the ROM data and the frequency fs of the system power supply 16 (for example, fs = 50 Hz when the power supply frequency of the system power supply 16 is 50 Hz) and the power supply voltage of the system power supply 16.

  At this time, the control unit 56 outputs, for example, a switching signal Xa for driving the switching element 42Xa and a switching signal Ya (for the switching element 42Ya) whose phase is shifted by 180 ° with respect to the switching signal Xa. Switching signals Xb and Yb generated by inputting the switching signals Xa and Ya to the inverter 60 are input to the drive unit 58 together with the switching signals Xa and Ya. The drive unit 58 switches (ON / OFF) the switching elements 42Xa, 42Xb, 42Ya, and 42Yb by the switching signals Xa, Xb, Ya, and Yb. Thereby, the inverter 14 outputs power corresponding to the frequency and voltage of the system power supply 16.

  On the other hand, as shown in FIG. 1, a disconnecting contactor 30 is connected to the microcomputer 22, and the microcomputer 22 operates the disconnecting contactor 30 to intermittently connect the photovoltaic power generation apparatus 10 and the system power supply 16. I do.

  For example, the microcomputer 22 disconnects the photovoltaic power generation device 10 and the system power supply 16 when the generated power by the solar battery 12 is low or is not generating power and the operation of the inverter 14 is stopped, and the generated power reaches a predetermined value. When operating the inverter 14 beyond, the circuit is closed by the disconnecting contactor 30 immediately before the inverter 14 starts to operate, and the photovoltaic power generator 10 and the system power supply 16 are connected.

  When the microcomputer 22 detects a voltage increase, voltage decrease, frequency increase, or frequency decrease of the system power supply 16, the circuit is opened by the disconnecting conductor 30 or the protective relay 54, and the inverter 14 and the system power supply 16 are disconnected. Protection is to be done. With respect to voltage rise, voltage drop, frequency rise, and frequency drop for system interconnection protection, set values are set in advance, and the microcomputer 22 has the voltage or frequency of the system power supply 16 reach this set value. Then, grid connection protection is performed.

  Note that the configuration and control of the solar power generation apparatus 10 can apply conventionally known configurations and control methods, and detailed description thereof is omitted in the present embodiment.

  As shown in FIGS. 1 to 4, the output current detection unit 38 is provided with a plurality of CTs (Current Transformers: instrument current transformers) 70 as first and second current detection means. Yes. In the present embodiment, description will be made using two CTs 70A and 70B (referred to collectively as “CT70”) as an example.

  As shown in FIG. 1, the CTs 70 </ b> A and 70 </ b> B are provided between the inverter circuit 20 and the filter circuit 28. As shown in FIGS. 4A and 4B, the CT 70 has a general configuration in which a coil is wound around, for example, an iron core formed in a ring shape, and the wiring inserted through the shaft center portion. An input / output current corresponding to the current passing through 72 is generated. By using the wiring 72 as a wiring between the inverter circuit 20 and the filter circuit 28, the output current of the inverter circuit 20 can be measured by the CT 70.

On the other hand, as shown in FIG. 4B, the wiring 72 is inserted as it is into the CT 70B, but as shown in FIG. 4A, the wiring 72 is turned once in the CT 70A twice. It is inserted. Thus, CT70A, current transformer ratio between 70B is changed, the voltage V _a in accordance with the current generated in CT70A by the current passing through the wire 72, and approximately twice the voltage V _b in accordance with the current generated in the CT70B It is trying to become. That is, when the voltage corresponding to the output current of CT70B is ± 1.25v, the voltage corresponding to the output current of CT70A is set to ± 2.5v (see FIGS. 5A and 5B). ).

  As shown in FIG. 3, the output current detection unit 38 is provided with a conversion circuit 74 for each of the CTs 70A and 70B, and the outputs of the CTs 70A and 70B are sent to the A / D of the microcomputer 22 via the conversion circuit 74. Input to the input port. The conversion circuit 74 is configured by resistors R1 and R2 and a capacitor C, for example, and the voltage is changed so that the voltage corresponding to the output current of the CTs 70A and 70B changes around a predetermined reference voltage (for example, 2.5 V). shift.

When the voltages V _A and V _B output from the CTs 70A and 70B and converted by the conversion circuit 74 are input to the microcomputer 22, the voltage V _A or the voltage V _B is output by A / D conversion. It converts into the output current _IO of the inverter circuit 20 (inverter 14) which the current detection part 38 detects, and reads it.

On the other hand, as illustrated in FIG. 2, the signal generation unit 50 includes a correction unit 62, a current difference calculation unit 64, and a selection unit 66. The selection unit 66 outputs the detection result of the output current detection unit 38 to the current difference calculation unit 64 as the output current I _O. At this time, the selection unit 66 selects one of the detection results of the CTs 70A and 70B based on the generated power of the solar cell 12 input to the inverter circuit 20.

  In the present embodiment, the microcomputer 22 performs A / D conversion on a voltage in the range of 0 v to 5 v input to the A / D input port. Moreover, the solar power generation device 10 applied to this Embodiment sets the rated electric power generation of the solar cell 12 to 4Kw, and, thereby, the rated output of the inverter 14 (inverter circuit 20) is 4Kw.

CT70B, when the inverter 14 outputs the rated power P _A, as shown by the solid line in FIG. 5 (B), the output voltage V _b is varied in a range of ± 2.5v centered on 0 v. Thus, when the inverter 14 outputs the rated power P _A is so with respect to the 2.5v to the microcomputer 22 the output voltage V _B of the range of 0v~5v inputted. The CT 70B outputs an output voltage as shown by a two-dot chain line in FIG. 5B when the inverter 14 outputs about half the rated power P _A (P _A / 2). Vb changes in the range of ± 1.25 v centered on 0 v, and the output voltage VB to the microcomputer 22 becomes 1.25 v to 3.75 v.

In contrast, CT70A, when the inverter 14 is outputting approximately half the power of the rated power, the output voltage V _a is varied within the range of ± 2.5v centered on 0 v, to the microcomputer 22 The output voltage V _A becomes 0 v to 5 v centered on 2.5 v.

Selecting unit 66, when the output power of the inverter 14 is less than 1/2 of the rated power P _A selects the output of CT70A, when the output power of the inverter 14 becomes more than 1/2 of the rated power P _A , Select the output of CT70B. The microcomputer 22 scans the voltage (current value) applied to the A / D input port at a predetermined cycle (for example, 1/220 sec) and captures it as an instantaneous value. At this time, the digital side of the A / D input port only needs to have 10 bits.

The current difference calculation unit 64 compares the output current _IO output from the selection unit 66 with the target value (target current value) of the output current set based on the input power or the corrected target value of the output current, The data is output to the correction unit 62. The correction unit 62 corrects the ROM data based on the calculation result (comparison result) input from the current calculation unit 64. The signal generator 50 feeds back the output current I _O in this way to generate a switching signal so that the output current I _O becomes a target value corresponding to the input power.

In addition, it is detected whether or not a direct current component is included in the output of the inverter 14 by integrating the output current _IO and the direct current component is removed when the direct current component is included in the output current. Further, correction of ROM data may be performed together.

The operation of the present embodiment will be described below. Note that the ROM 52 provided in the signal generation unit 50 stores, for example, 720 data as ROM data for one cycle of the switching signal, and the correction unit 62 has an interval according to the cycle of the switching signal. Read ROM data with. Thereby, for example, when the cycle of the switching signal is 11 kHz and the power supply frequency of the system power supply 16 is 50 Hz (fs = 50 Hz), 220 (11 kHz / 50 Hz) data are read out per cycle to generate the switching signal.

  In the inverter 14, when the generated power of the solar battery 12 exceeds a predetermined value, the operation starts, and the DC power generated by the solar battery 12 is converted into AC power corresponding to the system voltage and the system frequency of the system power supply 16. Output to the system power supply 16.

In the signal generation unit 50 provided in the inverter 14, a target value of output current is set based on the generated power generated by the solar cell 12 and input to the inverter 14, and the set target current value and output current detection unit 38 are set. The difference of the output current _IO detected and read by is calculated. Next, the signal generator 50 corrects the ROM data based on the target current value and the difference between the target current value and the output current _IO , and based on the corrected ROM data, the switching signals Xa, Xb, Ya, Yb are corrected. Generate.

The inverter 14 drives the switching elements 42Xa, 42Xb, 42Ya, and 42Yb with the switching signals Xa, Xb, Ya, and Yb generated in this manner, thereby converting the DC power generated by the solar cell 12 into the system power supply 16. Output as AC power corresponding to the system voltage and system frequency. At this time, the inverter 14 performs the feedback control to generate the switching signals Xa, Xb, Ya, Yb based on the output current I _O detected by the output current detection unit 38, so that the level of the output voltage and the output current I _O The power factor is prevented from decreasing due to the phase difference. That is, power conversion is performed efficiently by suppressing the generation of reactive power.

Incidentally, in the inverter 14, two CTs 70 </ b> A and 70 </ b> B are provided in the output current detection unit 38, and a selection unit 66 is provided in the signal generation unit 50. The signal generating unit 50, the selection unit 66, for example, selecting one of the outputs of CT70A or CT70B as the output power I _O based on the power generated by the solar cell 12, to correct the switching signal based on the selection result Perform feedback control.

As shown in the flowchart of FIG. 6, the microcomputer 22, for example, at step 100, it reads the detection result of the generated voltage detector 32 and the generated current detecting section 34 calculates the generated power P _a (step 102). This flowchart is repeatedly executed at a predetermined timing set in advance.

In step 104, the generated power P _a is exceeded the predetermined value Q, the operation of the inverter 14 is possible (affirmative determination in step 104), the process proceeds to step 106 to start the operation of the inverter 14.

Thereby, when the inverter 14 is not operating, the operation is started. When the inverter 14 is operating, the operation is continued. When the generated power Pa is small and the inverter 14 is not operable, a negative determination is made in step 104 and the process proceeds to step 108. Thereby, when the inverter 14 is stopped, the operation stop state is continued, and when the inverter 14 is operating, the operation is stopped.
At the same time, in step 110, the generated power P _a confirms whether exceeds 1/2 (P _A / 2) of the rated power P _A.

Here, when the solar cell 12 is outputting the generated power P _a close to the rated power P _A is an affirmative determination is made in step 110 and proceeds to step 112 to select the output of CT70B as an output current I _O.

In contrast, less generated power P _a of the solar cell 12, when it does not reach 1/2 of the rated power P _A is a negative decision is made at step 110, the routine proceeds to step 114. In this step 114, the output of CT70A is set to be selected as the output current _IO .

When the selection unit 66 sets the CT 70 to be read as the output current I _O in this way, the output of the corresponding CT 70 is read as the output current I _O and output to the current difference calculation unit 64.

Thereby, in the signal generation unit 50, when the output power of the inverter 14 is low and sufficient output cannot be obtained when feedback control of the output current is performed, by using the CT 70A having a high current transformation ratio, in particular, Even when the output power is low and the output current _IO is low, a sufficient feedback gain can be obtained. Therefore, even when the output current from the inverter circuit 20 is small, a sufficient gain for performing feedback control can be secured, and the conversion efficiency is reduced due to the phase difference between the output voltage and the output current of the inverter 14. Can be surely prevented. That is, the inverter 14 can ensure a desired gain when performing feedback control even if the output current is low. Therefore, since the output current is low, it is not possible to secure a sufficient gain when performing feedback control, preventing a power factor from decreasing due to a phase difference between the output voltage and the output current. And efficient operation becomes possible.

In this embodiment, two CT70s (CT70A, 70B) having different current transformation ratios are used as the current detection means. However, the present invention is not limited to this, and power generation is performed using three or more CT70s having different current transformation ratios. The output of the CT 70 selected by the power may be read and converted into the output current I _O. This makes it possible to obtain a sufficient feedback gain even when the output current _IO is extremely low.

  In the present embodiment, one of the CTs 70A and 70B is selected based on the generated power. However, the present invention is not limited to this, and whether or not the output of one of the CTs 70 (for example, the CT 70B) exceeds a predetermined value. You may make it select based on.

In addition, although this Embodiment demonstrated above demonstrated using the solar cell power generation apparatus 10 provided with the inverter 14 which converts the direct-current power generated with the solar cell 12 into the alternating current power according to the system power supply 16, this invention Then, it can apply to the grid connection inverter of various structures which convert direct-current power into alternating current power.

10 Solar power generation device 12 Solar cell 14 Inverter (system interconnection inverter)
16 System power supply 20 Inverter circuit 38 Output current detection part (1st and 2nd current detection means)
42 switching element 50 signal generator 52 ROM
62 Correction part (correction means)
66 Selection part (selection means)
70 CT (first and second current detection means)
70A CT (second current detection means)
70B CT (first current detection means)
74 Conversion circuit (first and second current detection means)

Claims (6)

A grid-connected inverter that converts DC power generated by a solar cell into AC power corresponding to the voltage and frequency of the system power supply by an inverter circuit, and outputs the AC power.
The solar cell is composed of a plurality of solar cells, and is configured to supply DC power generated by each solar cell to the inverter circuit through a diode for preventing backflow and a common noise filter in order, and First current detecting means for detecting an output current output from the inverter circuit to the system power supply, and second for detecting an output current output to the system power supply with a higher current transformation value than the first current detection means. And constituting a current detection means,
Provided is a generated power detection means provided between the diode and the noise filter for detecting DC power entering the noise filter, and the first current detection means is configured based on the DC power detected by the generated power detection means. Correction means for selecting either the output current or the output current detected by the second current detection means, and correcting the target value of the output current output from the inverter circuit in accordance with the selected output current value A grid-connected inverter characterized by comprising.   There is a noise filter on the system power supply side between the inverter circuit and the system power supply, and the first current detection means and the second current detection means are output from the inverter circuit to the noise filter on the system power supply side. The grid-connected inverter according to claim 1, wherein a current is detected.   The grid-connected inverter according to claim 2, wherein the first current detection means and the second current detection means are CT.   The grid-connected inverter according to claim 3, further comprising a booster circuit that boosts the generated power to a predetermined voltage between the noise filter and the inverter circuit.   The grid-connected inverter according to claim 4, wherein a rated output of the inverter circuit corresponds to a total rated generated power of the plurality of solar cells.   Selection means for selecting one of the first and second current detection means based on whether or not the DC power detected by the generated power detection means exceeds half of the total rated generated power. The grid interconnection inverter according to claim 5, comprising: