JP5828126B2 - Grid interconnection device - Google Patents

Description

  The present invention relates to a grid interconnection device that converts DC power output from a solar cell into AC power and links the solar cell to a commercial power system.

  Conventionally, there is provided a grid interconnection device that converts DC power output from a solar cell whose power generation amount changes according to the amount of solar radiation into AC power and links to a commercial power system via a grid interconnection relay. ing.

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

  By the way, when such a grid interconnection device starts grid interconnection in a state where the amount of power generated by the solar cell is insufficient (the grid interconnection relay is turned on), the inverter circuit increases with an increase in the output current of the inverter circuit. The input voltage decreases, and the voltage required for interconnection cannot be secured, and the grid interconnection relay is turned off. Even if the output voltage of the booster circuit is increased again and grid connection is started, if the amount of power generated by the solar cell is insufficient, the grid connection relay is turned off and the grid connection relay is turned off. Will repeatedly open and close (so-called chattering).

  In order to prevent such chattering, a grid interconnection device that determines whether or not a solar battery can generate the minimum power that can be linked when a solar battery is linked to a commercial power grid has been proposed. (Patent Document 1). In order to make such a determination, the grid interconnection device of Patent Document 1 provides a DC load between the inverter circuit and the booster circuit when the solar cell is linked to the commercial power system. And the grid connection apparatus of patent document 1 operates the booster circuit, adjusts the power supplied to the DC load, monitors the output voltage of the solar battery, and sets the minimum power that can be connected to the solar battery. It is determined whether or not can be supplied.

In addition, the grid interconnection device of Patent Document 1 has a switch circuit for supplying or cutting off power to the DC load, and the switch is turned off during grid connection to supply the DC load. Power to be cut off.
JP-A-10-289026

However, in such a grid interconnection device, it is necessary to boost and adjust the DC power output from the solar cell by a booster circuit, and the boosted voltage is applied to the DC load, and the withstand voltage is reduced. There was a problem that a high expensive load and a switch circuit were required.
The present invention has been made in view of the above-described problems, and it is possible to reduce the withstand voltage of a load or a switch circuit to which power is supplied when determining whether or not a solar cell can supply power that can be connected to the grid. An object of the present invention is to provide a grid interconnection device that can be used at low cost.

  In order to achieve the above object, the present invention provides a pair of terminals to which a solar cell is connected, a reactor and a diode connected in series to one of the terminals, and a connection point between the reactor and the diode, A switching element that opens and closes between the other terminal and a capacitor connected between the diode and the other terminal, and periodically opens and closes the switching element to obtain a predetermined step-up ratio. A booster circuit; an inverter circuit for converting the DC power boosted by the booster circuit into AC power; and connecting the AC power to a commercial power system through an output line; and the output line interposed in the output line A grid interconnection relay that opens and closes, and in the grid interconnection device that links the power generation output of the solar cell to the commercial power grid via the grid interconnection relay, An AC load connected to the inverter circuit side of the output line connecting the grid interconnection relay, to which AC power output from the inverter circuit is supplied, is activated for the grid interconnection device, and the grid After the interconnection relay is opened and the switching element of the booster circuit is opened, the inverter circuit converts the DC power to the AC power so as to gradually increase the output current of the inverter circuit. When the AC power to be converted and supplied to the AC load becomes larger than a predetermined power, the control for switching the grid interconnection relay to the closed state and periodically opening and closing the switching element is started. And

  According to the present invention, after starting the grid interconnection device, the grid interconnection relay is opened, the switching element of the boost circuit is opened, and then the output current of the inverter circuit is gradually increased. The DC power output from the circuit is converted to AC power, and this AC power is supplied to the AC load.

  This eliminates the need for boosting by the booster circuit, and can also reduce the voltage applied to the AC load and the switch circuit connected to the AC load. Therefore, a load or a switch circuit to which power is supplied when determining whether or not the solar cell can supply power that can be interconnected (when switching the grid interconnection relay from the open state to the closed state) Can be used with a low breakdown voltage.

  In the above invention, when switching the grid interconnection relay from the open state to the closed state, the inverter circuit is temporarily stopped, and the output voltage of the booster circuit is boosted to a predetermined voltage threshold value. The operation of the inverter circuit is started, and AC power synchronized with the commercial power system is connected to the system.

  In the above-mentioned invention, the inverter circuit converts the DC power into three-phase AC power, and the AC load is a load balanced with respect to the three-phase AC power. A phase current detector for detecting a current, wherein the operation of the inverter circuit is stopped when a difference between any two of the phase currents is larger than a predetermined current difference threshold value; To do.

  In the above-described invention, the inverter circuit converts the DC power into three-phase AC power, the AC load is a load balanced with respect to the three-phase AC power, and the three-phase AC power line A line voltage detecting unit for detecting a line voltage, and stops the operation of the inverter circuit when a difference between any two line voltages among the line voltages is larger than a predetermined voltage difference threshold value. It is characterized by that.

  According to the present invention, there is provided a system interconnection device that can use a low withstand voltage load or switch circuit to which power is supplied when determining whether or not a solar cell can supply power capable of interconnection operation. Can be provided.

It is a lineblock diagram showing photovoltaic power generation system 100 concerning this embodiment. It is a figure which shows the operation | movement flow until it connects from the state which the grid connection apparatus 2 has stopped. It is a figure which shows the operation | movement flow of the grid connection apparatus 2 in step S14. It is a figure which shows the operation | movement flow of the grid connection apparatus 2 when performing connection start operation | movement (step S18). The operation | movement flow in the case of determining the presence or absence of abnormality of current sensor CT1, CT2 or the voltage sensor 11 is shown.

  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 and a grid interconnection device 2.

  The grid interconnection device 2 includes a booster circuit 4, an inverter circuit 5, a filter circuit 6, a grid interconnection relay 7, a control circuit 8, and an AC load circuit 9. The grid interconnection device 2 links the solar cell 1 to the commercial power grid 30 via the grid interconnection relay 7.

  The booster circuit 4 boosts the output voltage of the solar cell 1. The booster circuit 4 outputs DC power having the boosted output voltage to the inverter circuit 5. As shown in FIG. 1, the booster circuit 4 includes a pair of terminals 46 and 47, a reactor 41, a switch element 42 such as an IGBT (insulated gate bipolar transistor), a diode 43, and capacitors 44a and 44b. A so-called non-insulated booster circuit is used. The solar cell 1 is connected to the pair of terminals 46 and 47, and the reactor 41 and the diode 43 are connected in series to one terminal (plus side) 46 of the terminals 46 and 47. The switch element 42 opens and closes a connection point between the reactor 41 and the diode 43 and the other terminal 47 of the pair of terminals 46 and 47. The capacitors 44 a and 44 b are connected in series, and the capacitors 44 a and 44 b connected in series are connected between the diode 83 and the other terminal 47.

  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. In addition, since the booster circuit 4 is non-insulated, the DC power output from the solar cell 1 is output through the reactor 41 and the diode 43 when the switch element 42 is in the open state.

  The inverter circuit 5 is configured by connecting in parallel a first arm in which switch elements 51 and 52 are connected in series and a second arm in which switch elements 53 and 54 are connected in series (so-called half-bridge type three). Phase inverter circuit). As the switch elements 51 to 54, switch elements such as IGBTs may be used. The operation of the inverter circuit 5 is controlled by the control circuit 8. The inverter circuit 5 opens and closes the switch elements 51 to 54 in accordance with PWM (Pulse Width Modulation) control of the control circuit 8 and converts the DC power output from the booster circuit 4 into three-phase AC power. The three-phase AC power includes the u-phase output line u extending from the connection point between the switch element 53 and the switch element 54, the v-phase output line v extending from the connection point between the capacitor 44a and the capacitor 44b, the switch element 51 and the switch element 52, To the w-phase output line w extending from the connection point.

  The filter circuit 6 includes reactors 61 and 62 and capacitors 63u, 63v, and 63w, and is provided on the output side of the inverter circuit. The filter circuit 6 removes a ripple component of the three-phase alternating current that is generated when the switching elements 51 to 54 of the inverter circuit 5 are PWM-controlled to open and close.

  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 AC load circuit 9 includes three load relays 91u, 91v, and 91w and three resistors 92u, 92v, and 92w. One end of the resistor 92u is connected to a u-phase output line u connecting the inverter circuit 5 and the grid connection load relay 7 via a load relay 91u. One end of the resistor 92v is connected to a v-phase output line v connecting the inverter circuit 5 and the grid interconnection relay 7 via a load relay 91v. One end of the resistor 92w is connected to a w-phase output line w connecting the inverter circuit 5 and the grid interconnection relay 7 via a load relay 91w. The other ends of the three resistors 92u, 92v, and 92w are connected to each other. The three resistors 92u, 92v, and 92w are connected in this way, thereby forming an AC load to which the three-phase AC power output from the inverter circuit 5 is supplied (hereinafter, the three resistors 92u , 92v, and 92w may be described as an AC load 92). Since the three resistors 92u, 92v, and 92w have the same resistance value, the AC load 92 is a balanced load with respect to the three-phase AC power output from the inverter circuit 5.

  The load relays 91u, 91v, 91w open and close lines connecting the resistors 92u, 92v, 92w and the output lines u, v, w. As the load relays 91u, 91v, 91w, relays that open this line when a signal is input are used. For this reason, this line is closed when the power for control is not supplied to the load relays 91u, 91v, 91w. The load relays 91u, 91v, 91w are supplied with driving power from the solar cell 1.

  The control circuit 8 functions as a phase current detector that detects the phase currents iu and iw of the three-phase AC power output from the inverter circuit 5. Specifically, the control circuit 8 detects the u-phase current iu flowing in the u-phase output line u and the w-phase current iw flowing in the w-phase output line w, respectively, from the two current sensors CT1 and CT2. The phase current iu and the v-phase current iv are detected.

  In addition, the control circuit 8 functions as a line voltage detection unit that detects line voltages vuv and vvw of the three-phase AC power output from the inverter circuit 5. Specifically, the control circuit 8 detects the line voltage vuv applied between the u-phase output line u and the v-phase output line v by the voltage sensor 11 and between the v-phase output line and the w-phase output line w. , Vvw is detected.

  The control circuit 8 controls the booster circuit 4 and the inverter circuit 5 based on the three-phase phase currents iu and iw and the line voltages vuv and vvw thus detected (opening / closing of the switch elements 41 and 51 to 54). Control) and control of relays 91u, 91v, 91w of the AC load circuit 9 described later (control to switch between a closed state and an open state).

(Operation during interconnection)
Next, the operation at the time of interconnection using the configuration described above will be described with reference to the drawings. FIG. 2 shows an operation flow related to the start of the grid interconnection device 2. In this operation flow shown below, since the control circuit 8 mainly controls the grid interconnection device 2, the operation mainly performed by the control circuit 8 is the operation mainly performed by the grid interconnection device 2. Can also be read as

  At the start time, the booster circuit 4 and the inverter circuit 5 are in a stopped state (all the switch elements 41, 51 to 54 are open). Further, the load relays 91u, 91v, 91w are closed because they are not supplied with power from the solar cell (closed state). Further, the grid interconnection relay 7 is in an open state.

  The control circuit 8 detects the open circuit voltage Vpv of the solar cell 1 using the voltage sensor 45 (step S11), and compares whether or not Vpv is larger than the voltage threshold value Vth (step S12). Here, the voltage threshold value Vth is set to a voltage value sufficient to drive the load relays 91u, 91v, 91w.

  In step S11 and step S12, while the control circuit 8 determines that Vpv is not greater than the voltage threshold Vth, the control circuit 8 returns from step 12 to step S11, and repeats step S11 and step S12.

  In step S12, the control circuit 8 starts the operation of the inverter circuit 5 when Vpv becomes larger than the voltage threshold Vth (step S14).

  Here, operation | movement of the grid connection apparatus 2 of step S14 is demonstrated. FIG. 3 is a diagram showing an operation flow of the grid interconnection device 2 in step S14. In step S <b> 14, the booster circuit 4 opens the switch element 42, and outputs DC power output from the solar cell 1 through the reactor 41 and the diode 43 to the inverter circuit 5. The inverter circuit 5 sets the target value it for the output current of the inverter circuit 5 (steps S21 to S25 described later) and sets the inverter circuit 5 so that the target value it for the output current of the inverter circuit 5 is set. (Step S26 described later) is performed. The initial value of the target value it is set to zero.

  When entering step S14, the control circuit 8 detects the phase currents iu and iw of the three phases using the current sensors CT1 and CT2 (step S21). When the control circuit 8 detects the phase currents iu and iw of the three-phase phases, the control circuit 8 calculates the effective values iue and iwe of the phase currents using the detected phase currents iu and iw (step S22). In step S22, the control circuit 8 calculates the average value iave of the effective values iue and iwe of the three phases, and in step S23, the difference between the average value iave and the target value it of the output current of the inverter is calculated. It is determined whether or not it is smaller than the current threshold ith.

  In step S23, 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 inverter circuit 5 is not smaller than the current threshold value isth, the control circuit 8 changes the target value it of the output current of the inverter circuit 5. Without proceeding to step S26. In step S23, 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 inverter circuit 5 is smaller than the current threshold value isth, the target value it is greater than the maximum value itmax of the target value it. It is determined whether it is small (step S24).

  The maximum value itmax of the target value it is set to be larger than the current value when power of a power threshold value Pth described later is supplied to the AC load 92. As a result, AC power PL larger than the power threshold Pth can be supplied to the AC load 92.

  In step S24, when the control circuit 8 determines that the target value it is not smaller than the maximum value itmax of the target value, the control circuit 8 proceeds to step S26 without changing the target value it of the output current of the inverter circuit 5. In step S24, when the control circuit 8 determines that the target value it is smaller than the maximum value itmax of the target value, the control circuit 8 sets a value obtained by adding a predetermined amount iα to the target value it of the output current of the inverter circuit 5. Then, as the target value it of the output current of the new inverter circuit 5 (step S25), the process proceeds to step S26.

  In step S26, the control circuit 8 determines that the difference between the target value it of the output current of the inverter circuit 5 and the effective value iue of the phase currents iu and iw and the average value iave of the phase currents 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 inverter circuit 5 and the average value vave of the vvwe and the target value vt of the voltage becomes zero. The inverter circuit 5 is controlled. When the operation of step S26 is completed, the control circuit 8 proceeds to step S15.

  In step S15, the control circuit 8 detects the line voltages vuv and vvw using the voltage sensor 11, and proceeds to step S16. In step S16, the control circuit 8 calculates the integrated values Piu and Piw of the phase currents iu and iw and the line voltages vuv and vvw corresponding to the phase currents iu and iw for each detected phase current iu and iw. To do. Then, the AC power PL supplied to the AC load is calculated by adding the integrated values Piu and Piw. The phase powers Piu and Piw are obtained by using the effective values iue and iwe of the phase currents obtained from the phase currents iu and iw, and the effective values vve and vvwe of the line voltages obtained from the line voltages vuv and vvw. Piu = iue × vvwe, Piw = iwe × vvwe. The AC power PL supplied to the AC load can be obtained from PL = Piu + Piw.

  Next, in step S <b> 17, the control circuit 8 determines whether or not the AC power PL supplied to the AC load 92 is larger than the power threshold value Pth, so that the solar cell supplies the minimum power that can be connected to the grid. Determine if you can. This can be determined because the output power of the solar cell and the AC power PL supplied to the AC load 92 are substantially equal.

  In step S17, if the AC power PL supplied to the AC load 92 is not greater than the power threshold value Pth, the control circuit 8 determines that the solar cell cannot supply the minimum power that can be interconnected and proceeds to step S14. Transition. In step S17, if the AC power PL supplied to the AC load 92 is greater than the power threshold value Pth, the control circuit 8 determines that the solar cell can supply the minimum power that can be interconnected and proceeds to step S18. Transition. Based on the determination in step S17, the control circuit 8 repeats steps S14 to S17 until the AC power PL becomes larger than the power threshold value Pth.

  By setting the initial value of the target value it of the inverter circuit 5 to zero and repeating steps S14 to S17, the target value it gradually increases. Thereby, the inverter circuit 5 converts the DC power output from the booster circuit 4 into AC power so that the output current of the inverter circuit 5 gradually increases (the operation of the inverter circuit 5 is controlled by the control circuit 8). Controlled). By doing in this way, since an inrush current does not flow into the AC load circuit 9, the AC load 92 and the load relay 91 can be protected.

The operation (adjustment) so as to gradually increase the output current of the inverter circuit 5 means that the AC power PL supplied to the AC load 92 is gradually increased from the relationship of PL = I ² R. It can be said that it is operating (adjusting) to increase. Here, I is a current supplied to the AC load 92, and R is a resistance value of the AC load 92. Furthermore, since the output power of the solar cell 1 and the AC power PL supplied to the AC load 92 are substantially equal, the operation (adjustment) of the output current of the inverter circuit 5 is gradually increased. It can also be said that the operation (adjustment) is performed so that the output power of 1 gradually increases.

  Next, in step S <b> 18, the control circuit 8 executes an operation (interconnection start operation) for starting interconnection using the booster circuit 4, the inverter circuit 5, and the grid interconnection relay 7. FIG. 4 is a diagram showing an operation flow of the grid interconnection device 2 when the interconnection start operation is performed (step S18).

  In step S18, the control circuit 8 opens the switch elements 51 to 54, temporarily stops the inverter circuit 5 (step S31), opens the contact of the load relay 91 (step S32), and the booster circuit 4 The ON duty ratio is adjusted so that the output voltage becomes a predetermined voltage value, and the switch element 42 is periodically opened and closed by this ON duty ratio (step S33).

  Next, the control circuit 8 detects the boosted voltage Vb with the voltage sensor 45 (step S34), and determines whether or not the output voltage Vb of the booster circuit 4 is greater than a predetermined voltage threshold Vth2 (step S35). . Here, the voltage threshold Vth <b> 2 is a voltage value sufficiently large to generate a three-phase AC voltage synchronized with the commercial power system 30. For example, when the commercial power system 30 is a 200V (running value) three-phase AC distribution system, the booster circuit 4 boosts the voltage to 600V (operates with the voltage threshold Vth2 being 600V).

  In step S35, when the output voltage Vb of the booster circuit 4 is not greater than the predetermined voltage threshold Vth2, the control circuit 8 has a voltage sufficiently large to generate a three-phase AC voltage synchronized with the commercial power system 30. Is not obtained from the booster circuit 4, and the process proceeds to step S33.

  In step S35, when the output voltage Vb of the booster circuit 4 is larger than the predetermined voltage threshold Vth2, a voltage sufficiently large to generate a three-phase AC voltage synchronized with the commercial power system 30 is increased. The control circuit 8 determines that it has been obtained from step S36, and proceeds to step S36.

  In step S36, the inverter circuit 5 starts operating. At this time, the inverter circuit 5 detects the three-phase AC voltage of the commercial power system 30 from a voltage sensor (not shown) and feeds back, so that the DC power boosted by the booster circuit 4 is synchronized with the commercial power system 30. Convert to

  When the AC power output from the inverter circuit 5 and the AC power from the commercial power system 30 are synchronized, the control circuit 8 uses the grid connection relay 7 to connect the contacts of the output lines u, v, and w. (Step S37), the step-up circuit 4 and the inverter circuit 5 are caused to operate at the time of interconnection (Step S19).

By operating as described above, when switching the grid interconnection relay 7 from the open state to the closed state, when the AC power PL supplied from the inverter circuit 5 to the AC load 92 is greater than the power threshold value Pth, The inverter circuit 5 is temporarily stopped. Thereafter, the booster circuit 4 adjusts the ON duty ratio so that the output voltage of the booster circuit 4 is equal to or higher than a predetermined voltage threshold value Vth2, and periodically opens and closes the switch element 42 according to the ON duty ratio. When the voltage boosted by the booster circuit 4 becomes equal to or higher than the voltage threshold Vth2, the inverter circuit 5 starts its operation. At this time, the inverter circuit 5 converts the DC power boosted by the booster circuit 4 into AC power synchronized with the commercial power system 30, and the control circuit 8 uses the grid interconnection relay 7 to output lines u, v, Close w. As a result, the grid interconnection device 2 links AC power synchronized with the commercial power grid 30 to the commercial power grid.

  If the phase of the three-phase AC voltage output from the inverter circuit 5 is shifted in order to form a waveform synchronized with the commercial power system 30 with the inverter circuit 5 operated, a load is applied to the switch elements 51 to 54. The load can be removed by temporarily stopping the inverter circuit 5. For this reason, the lifetime of the switch elements 51-54 of the inverter circuit 5 can be extended.

  As described above, in the present embodiment, the grid interconnection device 2 is activated, the grid interconnection relay 7 is opened, the switching element 42 of the booster circuit 4 is opened, and then the inverter circuit 5 The DC power output from the booster circuit 41 is converted to AC power so that the output current is gradually increased, and this AC power is supplied to the AC load 92. For this reason, it is not necessary to boost the output voltage of the solar cell 1 with a booster circuit (or the boost ratio can be reduced). As a result, the voltage applied to the AC load 92 and the load relay 91 connected to the AC load 92 can also be lowered, and therefore it is determined whether or not the solar cell 1 can supply power capable of interconnection operation. In doing so, the AC load 92 and the load relay 91 to which power is supplied can be used with a low withstand voltage.

  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, in the present embodiment, the control circuit 8 starts up the grid interconnection device 2 and controls the operation of the inverter circuit 5 using the effective values iue and iwe of the three-phase currents iu and iw output from the inverter circuit 5. However, the amplitude or average value of the phase current may be used.

  Further, for example, in this embodiment, the control circuit 8 performs control based on the three-phase currents iu and iw output from the inverter circuit 5 according to the start of the grid interconnection device 2, but the three-phase currents iu, Three-phase to two-phase conversion may be performed on iw and control may be performed using a current vector.

  For example, although the load relay 7 is connected to the AC load 92, a switch element such as an IGBT or FET may be used as long as the switch circuit can cut off the power supply from the inverter circuit 5. .

  For example, although the inverter circuit 5 that outputs three-phase AC power is used in the present embodiment, the present invention can also be applied to the inverter circuit 5 that outputs single-phase AC power.

  Further, for example, in the present embodiment, when supplying power to the AC load, the operation flow shown in steps S14 to S17 in FIG. 2 is executed in order to gradually increase the output current of the inverter circuit 5. Alternatively, the voltage of the AC power output from the inverter circuit 5 may be increased (the voltage target value vt is gradually increased). This is because only the simple resistors 92u, 92v, and 92w are provided as the AC load 92, and the fact that the output current of the inverter circuit 5 is proportional to the output voltage of the inverter circuit 5 is used.

  Further, for example, it is possible to determine whether or not there is an abnormality in the current sensors CT1 and CT2 and the voltage sensor 11 using the phase currents iu and iw and the line voltages vuv and vvw.

  This utilizes the fact that, in this embodiment, when the AC load 92 is balanced with respect to the three-phase AC power output from the inverter circuit 5, the phase current of each phase and the line voltage are equal. That is, when the difference between any two phase currents of each phase current is larger than a predetermined current difference threshold Isth, it can be considered that the current sensors CT1 and CT2 are abnormal and the balance is lost. . As for the line voltage, when the difference between any two line voltages among the line voltages is larger than a predetermined line voltage difference threshold Vsth, the voltage sensor 11 is abnormal and the balance is lost. Can be considered. Note that the phase current and the line voltage here are not instantaneous values but feature values that determine the magnitude of the waveform such as effective value, average value, or amplitude.

  If it is determined that there is an abnormality in the current sensors CT1, CT2 or the voltage sensor 11, the operation of the inverter circuit 5 is stopped, an indication that there is an abnormality on a display unit (not shown), an alarm sound, etc. Inform the user.

  When such an operation is executed, the operation flow shown in FIG. 5 is added between step S16 and step S17 in FIG. In the operation flow of FIG. 5, effective values are used for the phase current and the line voltage. The process proceeds from step S16 to step S41, and the control circuit 8 determines whether or not the difference between the effective value iue of the u-phase current and the effective value iwe of the w-phase current is greater than a predetermined current difference threshold Isth. In step S41, when the difference between the effective value iue of the u-phase current and the effective value iwe of the w-phase current is not larger than the predetermined current difference threshold Isth, the control circuit 8 has no abnormality in the current sensors CT1 and CT2. Therefore, the process proceeds to step S42. Further, when the difference between the effective value iue of the u-phase current and the effective value iwe of the w-phase current is larger than the predetermined current difference threshold Isth, the control circuit 8 can determine that the current sensors CT1 and CT2 are abnormal. The process proceeds to step S43.

  In step S42, the control circuit 8 determines the effective value vuve of the line voltage vuv between the u-phase output line u and the v-phase output line v, and the effective value of the line voltage vvw between the v-phase output line v and the w-phase output line w. It is determined whether or not the difference from vve is greater than a predetermined line voltage difference threshold Vsth. The control circuit 8 determines that there is no abnormality in the voltage sensor 11 when the difference between the effective value vve of the line voltage vuv and the effective value vve of the line voltage vvw is not larger than a predetermined line voltage difference threshold Vsth. Therefore, the abnormality confirmation of the current sensors CT1, CT2 and the voltage sensor 11 is terminated, and the process proceeds to step S17. The control circuit 8 determines that the voltage sensor 11 is abnormal when the difference between the effective value vve of the line voltage vuv and the effective value vve of the line voltage vvw is larger than a predetermined line voltage difference threshold Vsth. Since this is possible, the process proceeds to step S43.

  In step S43, the control circuit 8 stops the operation of the inverter circuit 5, notifies the display unit (not shown) that the current sensors CT1, CT2 and the voltage sensor 11 are abnormal (step S43), and relays for system interconnection The process when switching 7 from the open state to the closed state (operation flow in FIG. 2) is abnormally terminated.

By doing so, it is possible to prevent the grid interconnection device 2 from operating while the current sensors CT1, CT2 and the voltage sensor 11 are abnormal.

DESCRIPTION OF SYMBOLS 1 Solar cell 2 Power conditioner 4 Booster circuit 5 Inverter circuit 6 Filter circuit 7 Grid connection relay 9 AC load circuit 11 Voltage sensor 30 Commercial power system 45 Voltage sensor 91 Load relay 92 AC load CT1 Current sensor CT2 Current sensor

Claims (3)

A pair of terminals to which a solar cell is connected, a reactor and a diode connected in series to one terminal of the terminal, and a switch that opens and closes between the connection point of the reactor and the diode and the other terminal of the terminal A booster circuit having an element and a capacitor connected between the diode and the other terminal, and periodically opening and closing the switch element to obtain a predetermined boost ratio;
An inverter circuit that converts the DC power boosted by the booster circuit into AC power, and connects the AC power to a commercial power system via an output line;
A grid interconnection relay that intervenes in the output line and opens and closes the output line; and
In the grid interconnection device that links the power generation output of the solar cell to the commercial power grid via the grid interconnection relay,
An AC load connected between the inverter circuit of the output line and the grid interconnection relay, to which AC power output from the inverter circuit is supplied;
When the grid interconnection device is activated, the grid interconnection relay is in an open state, and the switch element of the booster circuit is in an open state.
The inverter circuit converts the DC power to AC power and supplies the AC load to the AC load so that the output current of the inverter circuit gradually increases.
When the AC power supplied to the AC load becomes larger than a predetermined power, the inverter circuit temporarily stops the conversion operation, and the output voltage of the booster circuit is predetermined by periodically switching the switch element. A grid interconnection apparatus that links the output of the inverter circuit, whose operation has been resumed, to the commercial power system via the grid interconnection relay that is switched to a closed state after being boosted to a voltage threshold value. The inverter circuit converts the DC power into three-phase AC power,
The AC load is a load balanced with respect to the three-phase AC power,
A phase current detector for detecting a phase current of the three-phase AC power;
2. The grid interconnection device according to claim 1, wherein when the difference between any two phase currents among the phase currents is larger than a predetermined current difference threshold, the operation of the inverter circuit is stopped. The inverter circuit converts the DC power into three-phase AC power,
The AC load is a load balanced with respect to the three-phase AC power,
A line voltage detector for detecting a line voltage of the three-phase AC power;
2. The grid interconnection according to claim 1, wherein the operation of the inverter circuit is stopped when a difference between any two of the line voltages is larger than a predetermined voltage difference threshold value. apparatus.