JP2012235588A - System interconnection apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a system interconnection apparatus that reduces a load on switch elements when electrically discharging capacitors connected to an input side of a bridge circuit by means of an ON resistance of the switch elements.SOLUTION: When an output of AC power from an inverter circuit 10 is shut off and an output of DC power from a DC power source 1 is equal to or lower than a predetermined value, the system interconnection apparatus returns AC power output from a bridge circuit 5 to capacitors 3a and 3b via a feedback circuit.

Description

  The present invention relates to a grid interconnection device that converts DC power output from a DC power source such as a solar cell, a fuel cell, or a storage battery into AC power and superimposes the AC power on a commercial power system.

  2. Description of the Related Art Conventionally, there is provided a grid interconnection device that converts DC power of a solar cell, a fuel cell, a storage battery, or the like into AC power and links to a commercial power system via a grid interconnection relay.

  The grid interconnection device includes a booster circuit that boosts a DC voltage output from a DC power supply, an inverter circuit that converts output power of the booster circuit into AC power, and a grid interconnection relay connected between a filter circuit and a commercial system. The control circuit is composed of a microcomputer and provides an open / close signal to each switch element of the booster circuit and the inverter circuit and the relay for system interconnection.

  The inverter circuit includes a bridge circuit in which an arm circuit in which a first switch element and a second switch element are connected in series is connected in parallel between two DC power sources, and is connected between the input side of the bridge circuit and the DC power source. And a filter circuit through which the AC power output from the bridge circuit passes.

  Since the capacitor of the inverter circuit uses a large capacity (about 3000 to 5000 μF) electrolytic capacitor, etc., the AC power output from the inverter circuit is cut off after the grid interconnection device performs the interconnection operation. This will leave a lot of charge on this capacitor. Since it takes about half a day to spontaneously discharge all the electric charge remaining in this capacitor, it is necessary to wait for a long time in order to perform maintenance of the grid interconnection device safely.

For this reason, conventionally, after the grid interconnection device performs the interconnection operation, a technique for discharging the capacitor after the output of the AC power from the inverter circuit is interrupted has been proposed (Patent Document 1). . The grid interconnection device described in Patent Document 1 consumes the capacitor charge by the ON resistance of the switch element by closing all the switch elements constituting the bridge circuit when disconnected (after turning off the grid interconnection relay). (Discharge the capacitor).
JP-A-7-20956

  However, in the grid interconnection device described in Patent Document 1, since all the switch elements constituting the inverter circuit are closed, both ends of the capacitor are short-circuited, and a large direct current continues to flow through the switch elements. There was a problem that it took a burden.

  The present invention has been made in view of the above-described problems, and reduces the burden on the switch element when discharging the capacitor connected to the input side of the bridge circuit using the ON resistance of the switch element. It aims at providing the grid connection apparatus which can do.

  In order to achieve the above object, each switching element of a bridge circuit in which an arm circuit in which a first switch element and a second switch element are connected in series is connected in parallel between at least two rows between DC power supplies is periodically opened and closed. In the inverter circuit for converting direct current power output from the direct current power source into alternating current power, the inverter circuit is connected to the input side of the bridge circuit and connected between the direct current power sources, and from the bridge circuit A filter circuit through which the output AC power passes, and a feedback circuit configured to be able to feed back a part of the AC power from the filter circuit to the capacitor, wherein the output of the AC power is cut off from the inverter circuit; The AC power output from the bridge circuit when the DC voltage output from the DC power source is a predetermined value or less Changed through the circuit and returning to the capacitor.

  According to the present invention, the AC power output from the bridge circuit is returned to the capacitor via the feedback circuit when the output of AC power from the inverter circuit is interrupted and the DC power output from the DC power source is equal to or lower than a predetermined value. ing. Thereby, when the charge of the capacitor returns to the capacitor through the feedback circuit, it is consumed through the bridge circuit and the filter circuit. For this reason, since the impedance is increased by the amount of the filter circuit as compared with the case of the closed loop with only the switch element, the current flowing through the switch element is reduced, and the burden on the switch element can be reduced. Further, by periodically opening and closing one of the switch elements of each arm so as to be in a conductive state and the other to be in a cut-off state, the current flowing through the switch element becomes an alternating current. For this reason, a large current does not continue to flow, and the load on the switch element can be reduced.

  In the above-mentioned invention, the first voltage sensor for detecting the voltage of the capacitor is provided, and when the voltage detected by the first voltage sensor becomes smaller than a predetermined value, all the switching elements are cut off. It is characterized by.

  In the above-described invention, a booster circuit that boosts DC power supplied from the DC power supply is provided between the DC power supply and the capacitor, and a second voltage sensor that detects an input voltage of the booster circuit is provided. The DC voltage output from the DC power supply is a voltage detected by the second voltage sensor.

  Moreover, in the above-described invention, power necessary for operating each of the switching elements is supplied from the commercial power system.

  According to the present invention, it is possible to provide a system interconnection device capable of reducing the burden on a switch element when discharging a capacitor connected to the input side of the bridge circuit using the ON resistance of the switch element. Can do.

It is a lineblock diagram showing photovoltaic power generation system 100 concerning this embodiment. It is a figure which shows the feedback circuit 11 according to the switching pattern of the switch elements 51 and 52 in this embodiment. It is a figure which shows the operation | movement flow of the grid connection apparatus 2 at the time of discharging a capacitor | condenser. It is a figure which shows the functional block diagram of the control circuit 8 at the time of discharging the capacitor | condensers 3a and 3b in the modification 1. FIG. It is a figure which shows the feedback circuit 11 according to the switching pattern of the switch elements 51 and 52 in the modification 2. FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a configuration diagram illustrating a photovoltaic power generation system 100 according to the present embodiment. As shown in this figure, the photovoltaic power generation system 100 includes a solar cell 1 (DC power supply) and a grid interconnection device 2.

  The grid interconnection device 2 includes a booster circuit 4, an inverter circuit 10, a grid interconnection relay 7, a control circuit 8, a power supply circuit 9, current sensors CTi, CT1, CT2, and voltage sensors VSi, VS1, VS2, VSuv, VSwv. Is provided. The grid interconnection device 2 superimposes the AC power output from the inverter circuit 10 on the commercial power grid 30 via the grid interconnection relay 7.

  The booster circuit 4 boosts the DC voltage output from the solar cell 1. Then, the booster circuit 4 outputs the boosted DC voltage to the inverter circuit 10. As shown in FIG. 1, the booster circuit 4 includes a reactor 41, a switch element 42 such as an IGBT (insulated gate bipolar transistor), and a diode 43. A solar cell 1 is connected to the input side of the booster circuit 4, and a reactor 41 and a diode 43 are connected in series with the positive electrode of the solar cell 1. The switch element 42 is connected between the connection point of the reactor 41 and the diode 43 and the negative electrode of the solar cell 1, and opens and closes between them.

  The operation of the booster circuit 4 is controlled by the control circuit 8. Specifically, the control circuit 8 determines the ON duty ratio, and periodically applies a pulse signal having the duty ratio to the gate of the switch element 42. Then, the switch element 42 is periodically opened and closed, and the booster circuit 4 obtains a predetermined boost ratio corresponding to (for example, proportional to) the duty ratio.

  The inverter circuit 10 has a bridge circuit 5 in which an arm circuit 53 in which a first switch element 51 and a second switch element 52 are connected in series is connected in parallel between at least two rows between DC power supplies (between the output terminals of the booster circuit). doing. The inverter circuit periodically opens and closes the switching elements 51 and 52 of the bridge circuit 5 to convert the DC power output from the solar cell 1 into AC power.

  The inverter circuit 10 includes capacitors 3a and 3b connected to the input side of the bridge circuit 5 and connected between the DC power supplies, a filter circuit 6 through which AC power output from the bridge circuit 5 passes, and the filter circuit 6 and a feedback circuit configured to be able to return a part of the AC power to the capacitors 3a and 3b.

  As the capacitors 3a and 3b, electrolytic capacitors having a large capacity (about 3000 to 5000 μF) are used. The capacitors 3 a and 3 b are connected in series, and the capacitors 3 a and 3 b connected in series are connected to the diode 43 and the negative electrode of the solar cell 1.

  As the switch elements 51 and 52 of the bridge circuit 5, a switch element such as an IGBT may be used. The operation of the bridge circuit 5 is controlled by the control circuit 8. The bridge circuit 5 periodically opens and closes the switch elements 51 and 52 according to PWM (Pulse Width Modulation) control of the control circuit 8 to convert the input DC power into three-phase AC power. The three-phase AC power includes a U-phase output line u extending from the connection point between the first switch element 53b and the second switch element 54b, a V-phase output line v extending from the connection point between the capacitor 3a and the capacitor 3b, and the first switch element. Supplied to a W-phase output line w extending from a connection point between 51a and the second switch element 52a.

  The filter circuit 6 includes reactors 61 and 62 and capacitors 63a, 63b, and 63c. The filter circuit 6 is connected to the connection point of the first switch element 51a and the second switch element 52a, the connection point of the first switch element 51b and the second switch element 52b, and the connection point of the capacitor 3a and the capacitor 3b. (Provided on the output side of the bridge circuit 5). Specifically, a reactor 61 is interposed in the U-phase output line u, and a reactor 62 is interposed in the W-phase output line w. A U-phase output line u, a V-phase output line v, and a W-phase output line w are connected to the connection points where the capacitors 63a, 63b, and 63c are delta-connected, respectively. The filter circuit 6 removes a ripple component (harmonic component) of the three-phase alternating current generated when the switch elements 51 and 52 of the bridge circuit 5 are opened and closed.

  The feedback circuit is configured by the bridge circuit 5 and the filter circuit 6, and the current path for feedback to the capacitors 3 a and 3 b varies depending on the switching pattern of the switch elements 51 and 52. FIG. 2 shows the feedback circuit 11 for each switching pattern of the switch elements 51 and 52.

  The feedback circuit 11a shown in FIG. 2A has a switching pattern in which the first switch element 51a is conductive, the second switch element 52a is cut off, the first switch element 51b is cut off, and the second switch element 52b is conductive. It is a feedback circuit in the case of a state. In the feedback circuit 11a, a current flows through a path indicated by a dotted line L1, and a part of the AC power is fed back from the filter circuit 6 to the capacitors 3a and 3b.

  In the feedback circuit 11b shown in FIG. 2B, the switching pattern is such that the first switch element 51a is cut off, the second switch element 52a is turned on, the first switch element 51b is turned on, and the second switch element 52b is cut off. It is a feedback circuit in the case of a state. In the feedback circuit 11a, a current flows through a path indicated by a dotted line L2, and a part of the AC power is fed back from the filter circuit 6 to the capacitors 3a and 3b.

  In the feedback circuit 11c shown in FIG. 2C, the switching pattern is such that the first switch element 51a is conductive, the second switch element 52a is cut off, the first switch element 51b is conductive, and the second switch element 52b is cut off. It is a feedback circuit in the case of a state. In the feedback circuit 11c, a current flows through a path indicated by a dotted line L3, and a part of the AC power is fed back from the filter circuit 6 to the capacitors 3a and 3b.

  In the feedback circuit 11d shown in FIG. 2D, the switching pattern is such that the first switch element 51a is cut off, the second switch element 52a is turned on, the first switch element 51b is cut off, and the second switch element 52b is turned on. It is a feedback circuit in the case of a state. In the feedback circuit 11d, a current flows through a path indicated by a dotted line L4, and a part of the AC power is fed back from the filter circuit 6 to the capacitors 3a and 3b.

  The grid interconnection relay 7 is interposed in the output lines u, v, and w connected to the commercial power system 30, and opens and closes the output lines u, v, and w. In addition, the grid interconnection relay 7 is controlled to be closed or open by a control signal from the control circuit 8 to link or disconnect the grid interconnection device 2 (solar cell 1) and the commercial grid 30. It is.

  The power supply circuit 9 is connected to the commercial power system 30, and includes a booster circuit 4, an inverter circuit 5, a control circuit 8, a system interconnection relay 7, and various sensors CTi, CT1, CT2, VSi, VS1, VS2, VSuv, and VSwv. Is supplied from the commercial power system 30.

  A current transformer is used for each of the current sensors CTi, CT1, and CT2. The current sensor CTi is provided between the positive electrode of the solar cell 1 and the reactor 41 and detects the current Iin input to the booster circuit 4. The current sensor CT1 is provided between the connection point of the capacitors 63a and 63c and the reactor 61, and detects the U-phase current Iu output from the bridge circuit 5. Current sensor CT <b> 2 is provided between capacitor 63 b and the connection point of capacitor 63 c and reactor 62, and detects W-phase current Iw output from bridge circuit 5.

  Next, voltage sensors VSi, VS1, VS2, VSuv, and VSwu will be described. The voltage sensor VSi is provided on the input side of the booster circuit 4 and detects the input voltage Vin of the booster circuit 4. The voltage sensor VS1 is provided on the output side of the booster circuit 4, and detects the output voltage Vc of the booster circuit 4 (the voltage across the capacitor 3a and the capacitor 3b connected in series). The voltage sensor VS2 is connected in parallel with the capacitor 3b and detects the voltage Vcb across the capacitor 3b. Voltage sensor VSuv is connected to U-phase output line u and V-phase output line v, and detects line voltage Vuv between U-phase output line u and V-phase output line v. The voltage sensor VSwv is connected to the W-phase output line w and the V-phase output line v, and detects a line voltage Vwv between the W-phase output line w and the V-phase output line v.

  The control circuit 8 controls the operation of the booster circuit 4, the inverter circuit 10, and the grid interconnection relay 7 using the various sensors CTi, CT1, CT2, VSi, VS1, VS2, VSuv, and VSwv described above.

(Discharge operation of capacitors 3a and 3b)
The discharge (consumption of electric charges) of the capacitors 3a and 3b is mainly performed when (1) a maintenance worker starts work and (2) when the grid interconnection device 2 stops. In either case (1) or (2), the grid interconnection device 2 is stopped (the grid interconnection relay 7 is in the open state, the switch element of the booster circuit is cut off, and the switch element 51 of the bridge circuit 5). , 52 are all in the cut-off state), and the operation flow shown in FIG. 3 is executed by the control circuit 8, whereby the capacitors 3a and 3b can be discharged.

  FIG. 3 shows an operation flow of the grid interconnection device 2 when discharging the capacitors 3a and 3b. In this operation flow shown below, the control circuit 8 mainly controls the grid interconnection device 2. For this reason, although the control circuit 8 is mainly used as a subject, since it becomes the operation | movement of the grid connection apparatus 2, the control circuit 8 of a subject can also be read as the grid connection apparatus 2. FIG.

  When the operation flow in FIG. 3 is started, the control circuit 8 detects the input voltage Vin of the booster circuit 4 (step S11), and determines whether or not the input voltage Vin is smaller than a predetermined value Vith (step S12). If the input voltage Vin is not smaller than the predetermined value Vith, the control circuit 8 returns to step S11. If the input voltage Vin is smaller than the predetermined value Vith, the control circuit 8 proceeds to step S13 and starts driving control of the switch elements 51 and 52. To do.

  In step S13, the control circuit 8 detects the phase currents Iu and Iw using the current sensors CT1 and CT2. When the phase currents Iu and Iw are detected, the control circuit 8 calculates the effective values Iue and Iwe of the phase currents Iu and Iw using the detected phase currents Iu and Iw (step S14). In step S14, the control circuit 8 calculates the average value Iave of the effective values Iue and Iwe of each phase, and in step S15, the difference between the average value Iave and the target value It of the output current of the bridge circuit 5 is the current. It is determined whether or not it is smaller than the threshold value Ith. This target value It is set to zero when starting the operation flow shown in FIG.

  In step S15, when the control circuit 8 determines that the difference between the average value Iave and the target value It of the output current of the bridge circuit 5 is not smaller than the current threshold value Ith, the target value It of the output current of the bridge circuit 5 is changed. Without proceeding to step S18. In step S15, when the control circuit 8 determines that the difference between the average value Iave and the target value It of the output current of the bridge circuit 5 is smaller than the current threshold value Ith, the target value It is greater than the maximum value Itmax of the target value It. It is determined whether it is small (step S16).

  The maximum value Itmax of the target value It is set to a value that does not cause a burden even if it flows through the switch elements 51 and 52.

  In step S16, when the control circuit 8 determines that the target value It is not smaller than the maximum value Itmax of the target value It, the control circuit 8 proceeds to step S18 without changing the target value It of the output current of the bridge circuit 5. If the control circuit 8 determines in step S16 that the target value It is smaller than the maximum value Itmax of the target value It, a predetermined amount Iα is added to the target value It of the output current of the bridge circuit 5 in step S17. As a target value It of the output current of the new bridge circuit 5, the process proceeds to step S18.

  In step S18, the control circuit 8 determines that the difference between the target value It of the bridge circuit 5 and the effective value Iue of the phase currents Iu and Iw and the average value Iave of the bridge circuit 5 is zero. The target value Vt of the average value of the effective values Vuve and Vvwe of the voltage is determined so that the difference between the average value Vave of the line voltage of the bridge circuit 5 and the average value Vave of the Vvwe and the target value Vt of the voltage becomes zero. The switching element of the bridge circuit 5 is controlled by a PWM signal. As a result, AC power is output from the bridge circuit 5, returned to the capacitors 3a and 3b by the feedback circuit, and the capacitors 3a and 3b are discharged. When the operation of step S18 is completed, the control circuit 8 proceeds to step S19. In step S19, the control circuit 8 detects the voltage Vca of the capacitor 3a and the voltage Vcb of the capacitor 3b using the voltage sensors Va and Vb.

  The voltage Vca of the capacitor 3a can be detected by detecting the voltage Vc across the capacitor 3a and the capacitor 3b connected in series by the voltage sensor Va, and Vca = Vc−Vcb.

  When detecting the voltage Vca and the voltage Vcb, the control circuit 8 determines whether or not both the voltage Vca and the voltage Vcb are smaller than the predetermined value Vcth (step S20). If the control circuit 8 determines in step S20 that both the voltage Vca and the voltage Vcb are not smaller than the predetermined value Vcth, the control circuit 8 returns to step S13 because discharging of the capacitors 3a and 3b has not been completed. In step S20, when the control circuit 8 determines that both the voltage Vca and the voltage Vcb are smaller than the predetermined value Vcth, the discharge of the capacitor 3a is completed, and the switch elements 51 and 52 are opened to open the capacitors 3a and 3b. End the discharge.

  According to the present invention, when the output of AC power from the inverter circuit 5 is interrupted (the grid connection relay 7 is in an open state) and the DC power output from the solar cell 1 is less than or equal to a predetermined value (voltage Vin <voltage threshold) The output of the bridge circuit is returned to the capacitors 3a and 3b via the feedback circuit. Thereby, when the discharge charge of the capacitor returns to the capacitor through the feedback circuit, it is consumed through the bridge circuit and the filter circuit. For this reason, since the impedance of the filter circuit 6 increases compared to the case of the closed loop of only the switch elements 51 and 52, the current flowing through the switch elements 51 to 54 is reduced, and the burden on the switch elements 51 to 54 can be reduced. it can. Further, by periodically opening and closing one of the switch elements 51 and 52 of each arm so as to be in a conductive state and the other to be in a cut-off state, the current flowing through the switch elements 51 and 52 becomes an alternating current. For this reason, a large current does not continue to flow, and the burden on the switch elements 51 and 52 can be reduced. Further, since the switch elements 51 to 52 are periodically opened and closed, the electric charges of the capacitors 3a and 3b can be consumed even by a switching loss. For this reason, the electric charge of capacitor 3a, 3b can be consumed rapidly.

  Further, according to the present invention, the charges of the capacitors 3a and 3b are consumed, and when the voltage Vca and Vcb of the capacitors becomes smaller than the predetermined value Vcth, the bridge circuit 5 is stopped (switch of the bridge circuit 5). Shut off all elements). For this reason, the inverter circuit 10 can be stopped immediately after the capacitors 3a and 3b are discharged, and the burden on the switch circuits 51 and 52 can be reduced.

  Further, according to the present invention, after confirming that the input voltage Vin to the booster circuit is smaller than the predetermined value Vith, consumption of the electric charges of the capacitors 3a and 3b is started. For this reason, when the worker who performs maintenance works, the discharge of the capacitors 3a and 3b can be automatically started from the time when the switch between the solar cell 1 and the grid interconnection device 2 is opened. . Thereby, it is not necessary to provide a switch for discharging the capacitors 3a and 3b in the main body of the grid interconnection device 2, and an artificial mistake of forgetting to press the switch can be eliminated.

  Further, according to the present invention, the consumption of the electric charges of the capacitors 3a and 3b is not started unless the input voltage Vin to the booster circuit becomes smaller than the predetermined value Vith. For this reason, even when the grid interconnection device 2 stops, the capacitors 3a and 3b are not discharged when it is desired to perform a self-sustained operation thereafter (for example, when the commercial power system 2 fails during the day). Independent operation can be quickly started without charging the capacitors 3a and 3b. Further, since the capacitors 3a and 3b are not discharged, it is possible to use the power that has not been discharged.

  In addition, according to the present invention, the target value It is first set to zero, Iα is added to the target value, and the switch elements 51 and 52 are opened and closed so that the current detected by the current sensor gradually increases. Thereby, since the current flowing through the filter circuit 6 can be gradually increased, the inrush current flowing through the capacitors 63a to 63c of the filter circuit 6 can be reduced.

  Further, according to the present invention, the switch element 42 of the booster circuit 4 is opened while the electric charges of the capacitors 3a and 3b are consumed. Thereby, since the switching element 42 of the booster circuit 4 does not perform switching, the burden due to switching can be reduced.

  Further, according to the present invention, the electric power necessary for operating the switch elements 51 and 52 of the inverter circuit 5 when discharging the capacitors 3 a and 3 b is supplied from the commercial power system 30 via the power supply circuit 9. . As a result, the capacitors 3a and 3b can be stably discharged to the end. Further, if the power is supplied from both ends of the capacitors 3a and 3b instead of from the commercial power system 30, the electric charges of the capacitors 3a and 3b can be quickly consumed.

(Modification 1)
In the present embodiment, the control circuit 8 performs control based on the three-phase currents iu and iw output from the bridge circuit 5, but performs three-phase to two-phase conversion on the three-phase currents iu and iw to obtain a current vector. You may make it control using Id and Iq.

  FIG. 4 shows a functional block diagram of the control circuit 8 that performs the capacitors 3a and 3b in the first modification. In this block diagram, the control circuit 8 includes a dq converter 101, subtracters 102 and 103, a PI controller 104, an inverse dq converter 105, and a PWM modulator 106.

  The dq converter 101 receives the u-phase current Iu, the w-phase current Iw, and the phase θ detected by the current sensors CT1 and CT2, and performs three-phase to two-phase conversion on the u-phase current Iu and the w-phase current Iw. The d-axis current value Id and the q-axis current value Iq on the coordinate system are calculated. Then, the dq converter 101 outputs the calculated current values Id and Iq to the subtracters 102 and 103.

  The subtractor 102 receives the d-axis current target value Idt and the d-axis current Id, and outputs a value (Id−Idt) obtained by subtracting the d-axis current target value Idt from the d-axis current Id to the PI controller 104.

  The subtractor 103 inputs the q-axis current target value Iqt and the q-axis current Iq, and outputs a value (Iq−Iqt) obtained by subtracting the q-axis current target value Iqt from the q-axis current Iq to the PI controller 104.

  The PI controller 104 inputs the subtraction values (Id−Idt) and (Iq−Iqt), calculates the d-axis voltage target value Vdt and the q-axis voltage target value Vqt so that these values become zero, and vice versa. Output to dq converter.

  The inverse dq converter 105 inputs the d-axis voltage target value Vdt, the q-axis voltage target value Vqt, and the phase θ, performs two-phase three-phase conversion, and connects the U-phase output line u and the V-phase output line v to each other. The voltage target value Vuvt and the line voltage target value Vwvt of the W-phase output line w and the V-phase output line v are calculated. Then, the inverse dq converter 105 outputs the calculated target values Vuvt and Vwvt to the PWM modulator 106.

  The PWM modulator 106 receives the target values Vwvt and Vuvt, outputs a PWM waveform, and opens and closes the switch elements 51 and 52 periodically.

  At this time, the control circuit 8 gradually increases the d-axis current target value Idt and the q-axis current target value Iqt from near zero so that the currents detected by the current sensors CT1 and CT2 gradually increase. The elements 51 to 54 can be opened and closed.

(Modification 2)

  Although the inverter circuit 10 that outputs three-phase AC power is used in the present embodiment, the present invention can also be applied to the inverter circuit 10 that outputs single-phase AC power. FIG. 5 shows the feedback circuit 11 for each switching pattern of the switch elements 51 and 52 in the second modification. As shown in FIG. 5, in the case of the inverter circuit 5 that outputs single-phase AC power, one capacitor 3 is used instead of the capacitors 3a and 3b. The filter circuit 6 uses three capacitors 63a to 63c in a delta connection, but uses one capacitor 63.

  When PWM control for outputting single-phase AC power is applied, the feedback circuit 11 for each switching pattern of the switch elements 51 and 52 is as shown in FIGS. 5 (a) and 5 (b).

The feedback circuit 11e shown in FIG. 5A has a switching pattern in which the first switch element 51a is conductive, the second switch element 52a is cut off, the first switch element 51b is cut off, and the second switch element 52b is conductive. It is a feedback circuit in the case of a state. In the feedback circuit 11e, a current flows through a path indicated by a dotted line L5, and a part of the AC power is fed back from the filter circuit 6 to the capacitor 3.
The feedback circuit 11f shown in FIG. 5B has a switching pattern in which the first switch element 51a is cut off, the second switch element 52a is turned on, the first switch element 51b is turned on, and the second switch element 52b is cut off. It is a feedback circuit in the case of a state. In the feedback circuit 11e, a current flows through a path indicated by a dotted line L6, and a part of the AC power is fed back from the filter circuit 6 to the capacitor 3.

  As mentioned above, although one Embodiment of this invention was described, the above description is for making an understanding of this invention easy, and does not limit this invention. It goes without saying that the present invention can be changed and improved without departing from the gist thereof, and that the present invention includes equivalents thereof.

  For example, the control circuit 8 controls the operation of the bridge circuit 5 using the effective values iue and iwe of the three-phase currents iu and iw output from the bridge circuit 5, but uses the amplitude and average value of the phase currents. Also good.

  For example, in this embodiment, although the example of the solar power generation system 100 was given, DC power supplies, such as a storage battery and a fuel cell, can be used instead of the solar cell 1.

  Further, for example, an LED may be connected to both ends of the electrolytic capacitor to indicate to the user that charges are stored in the capacitor. If it does in this way, a user can judge whether it can work safely by seeing this LED.

  Further, for example, when the grid connection relay 7 is in a welded state, the discharge of the capacitors 3a and 3b may be prohibited. By doing in this way, when switch elements 51 and 52 are operated at the time of discharge of capacitors 3a and 3b, it can prevent unintentionally supplying electric power to a commercial power system.

For example, in the present embodiment, the three-phase half-bridge type inverter circuit 10 having two arms in parallel is used, but a three-phase full-bridge type inverter circuit having three arms in parallel can also be used.

DESCRIPTION OF SYMBOLS 1 Solar cell 2 System interconnection apparatus 3 Electrolytic capacitor 4 Booster circuit 5 Bridge circuit 6 Filter circuit 7 System interconnection relay 8 Control circuit 9 Power supply circuit 10 Inverter circuit 11 Feedback circuit 30 Commercial power system 45 Voltage sensor 91 Load relay 92 AC load CTi Current sensor CT1 Current sensor CT2 Current sensor VSi Voltage sensor VS1 Voltage sensor VS2 Voltage sensor VSuv Voltage sensor VSwv Voltage sensor

Claims (4)

Each switching element of the bridge circuit in which the arm circuit in which the first switch element and the second switch element are connected in series is connected in parallel between at least two rows between the DC power supplies is periodically opened and closed and output from the DC power supply. In an inverter circuit that converts DC power into AC power,
The inverter circuit is connected to the input side of the bridge circuit and connected between the DC power supplies, a filter circuit through which AC power output from the bridge circuit passes, and one AC power from the filter circuit. A feedback circuit configured to be able to return the part to the capacitor,
The AC power output from the bridge circuit is returned to the capacitor via the feedback circuit when the output of the AC power from the inverter circuit is cut off and the DC voltage output from the DC power source is a predetermined value or less. An inverter circuit characterized by A first voltage sensor for detecting the voltage of the capacitor;
2. The grid interconnection device according to claim 1, wherein when the voltage detected by the first voltage sensor becomes smaller than a predetermined value, all of the switching elements are turned off. A booster circuit that boosts the DC power supplied from the DC power supply is provided between the DC power supply and the capacitor, and includes a second voltage sensor that detects an input voltage of the booster circuit;
3. The grid interconnection apparatus according to claim 1, wherein the DC voltage output from the DC power supply is a voltage detected by a second voltage sensor. The grid interconnection apparatus according to any one of claims 1 to 3, wherein electric power necessary to operate each of the switching elements is supplied from the commercial power grid.