JP5398162B2 - Grid-connected inverter device - Google Patents

Description

  The present invention relates to a grid-connected inverter device in which a plurality of inverters are connected in series.

  As a grid interconnection inverter device linked to a grid, for example, there is one shown in Patent Document 1 below. The grid-connected inverter device disclosed in Patent Document 1 (disclosed as “power conversion device” in this document) converts DC power generated by solar energy into AC power and supplies it to a load or system , The AC side terminals of a plurality of single-phase inverters that receive the DC power supplied by the first to third capacitors are connected in series so that the sum of the voltages generated by the single-phase inverters becomes the output voltage. It is configured.

  In the above configuration, the voltage of the first capacitor is adjusted to a desired voltage via the step-down converter and the step-up chopper, and the voltage of the second and third capacitors is the first voltage. The DC / DC converter connected to the capacitor is adjusted so as to obtain a desired voltage smaller than the voltage of the first capacitor.

JP 2007-166783 A

  By the way, the grid connection inverter apparatus used for a photovoltaic power generation system converts DC power generated by a plurality of solar cell modules into AC power and also connects to a general commercial power source supplied from an electric power company. Thus, the surplus power is regenerated to the grid side, and the shortage power is supplied from the grid side. Therefore, for example, when the amount of solar radiation is small and the generated power from the solar cell module is small, it is necessary to stop the operation of the grid-connected inverter device and put it in a standby state. In this case, the system and the grid-connected inverter device are usually disconnected, for example, via a switch.

  On the other hand, in the configuration having a switch, the life of the relay of the switch may be a problem. For example, when the generated power of the solar cell module is insufficient, power cannot be supplied to the grid side even if the grid-connected inverter device is operated. Therefore, the grid-connected inverter device is set in a standby state, and the grid and grid Usually, the switch is controlled to be turned off in order to disconnect the connection with the interconnection inverter device. That is, in the conventional grid-connected inverter device, each time the start state and the standby state are repeated, on / off switching control of the switch is executed, the number of times of opening and closing of the relay is increased, and the contact life of the relay is shortened. There was a problem.

  On the other hand, if the connection with the system can be maintained regardless of the state of the grid-connected inverter device, the number of on / off times of the switch can be reduced, and the life of the relay can be extended. In addition, for example, if the generated power of the solar cell module is temporarily reduced, the grid-connected inverter device can be used as long as the grid-connected inverter device is allowed to enter a standby state without turning off the switch. It is also possible to lower the threshold for activating. That is, if a configuration that does not require disconnection from the grid when the grid-connected inverter device is in a standby state can be realized, it is possible to extend the life of the relay while improving operating efficiency.

  In the conventional grid-connected inverter device, when the device is in a standby state, it is relatively easy to control it to remain connected without disconnecting from the system. However, in the grid-connected inverter device in which a plurality of inverters are connected in series as shown in Patent Document 1, the first to third capacitors respectively connected in parallel to the input side of the single-phase inverter are included in the system. Therefore, when the device is connected to the system in a standby state, the voltage across each capacitor is determined according to the first to third capacitor capacity ratios, and the breakdown voltage of the component There is a problem that there is a possibility of failure beyond the above.

  The present invention has been made in view of the above, and in a grid-connected inverter device in which a plurality of single-phase inverters are connected in series, the device can be stopped while being connected to the system. It aims at providing the grid connection inverter apparatus which becomes.

  In order to solve the above-described problems and achieve the object, the grid-connected inverter device according to the present invention connects a plurality of AC side terminals of a single-phase inverter that converts DC power into AC power and outputs the series power, In a grid-connected inverter device that includes an inverter unit that supplies a system with an output voltage that is a sum of the generated voltages of the plurality of single-phase inverters, and that controls the output voltage of the inverter unit to link with the system. Capacitor that is connected between a switch for switching whether or not to supply the output of the inverter unit to the system, and a DC bus connected to the DC side terminal of each single-phase inverter, and functions as a DC power source for each single-phase inverter And resistors connected to both ends of each capacitor, and the inverter unit and the system are in a connected state. And when the operation of the inverter unit is stopped, the potential difference generated at both ends of each resistor due to the current flowing from the system does not exceed the withstand voltage of the parts constituting each single-phase inverter. A resistance value of the resistor is set.

  According to the grid-connected inverter device according to the present invention, when the inverter unit and the system are in a connected state and the operation of the inverter unit is stopped, the potential difference generated at both ends of each resistor by the current flowing from the system. Since the resistance value of each resistor is set so that it does not exceed the breakdown voltage of the parts that constitute each single-phase inverter, the grid-connected inverter device can be stopped while being linked to the grid, There is an effect that the life of the relay can be extended.

  Embodiments of a grid-connected inverter device according to the present invention will be described below in detail with reference to the accompanying drawings. In addition, this invention is not limited by embodiment shown below.

(Configuration of solar power generation system)
FIG. 1 is a diagram illustrating an example when the grid-connected inverter device according to the present invention is applied to a photovoltaic power generation system. In the figure, the solar cell module 2 is connected to the input terminal 14 which is the DC input terminal of the grid-connected inverter device 3, and the power supply 50 Hz or 60 Hz is supplied to the output terminal 16 which is the AC output terminal. 12 is connected. In the photovoltaic power generation system 1 configured as described above, the DC power generated by the solar cell module 2 is converted into AC power by the grid interconnection inverter device 3, and surplus power is converted into grid power through interconnection with the grid 12. It is regenerated on the 12 side, and the insufficient power is supplied from the system 12 side. In the configuration shown in the figure, the system 12 shows an embodiment in which a single-phase two-wire power distribution system is connected, but it may be a single-phase three-wire power distribution system. In this case, the neutral line of the system is grounded to the ground GND on the system side, and the remaining two power lines are connected to the output terminal 16 of the system interconnection inverter device 3.

(Configuration of grid-connected inverter device)
Next, the configuration of the grid interconnection inverter device 3 will be described. In FIG. 1, the grid interconnection inverter device 3 includes a converter 4, an inverter unit 5, a control unit 6, an output filter circuit 7, a switch 8, and a DC / DC converter 11.

(Connection configuration and function of grid-connected inverter device)
Next, the connection configuration and function of the grid interconnection inverter device 3 will be described. The converter 4 is connected at its input end to the input end 14 of the grid-connected inverter device 3, and boosts or steps down the DC voltage of the solar cell module 2 supplied through the input end 14, and the inverter unit 5 and the DC / DC converter 11. Output to. The inverter unit 5 includes a plurality of single-phase inverters as will be described later, and a DC voltage supplied from the converter 4 is input to one single-phase inverter among the plurality of single-phase inverters. The remaining single-phase inverters other than the one single-phase inverter are operated by a DC input supplied from the DC / DC converter 11. That is, the inverter unit 5 converts the DC voltage applied from the corresponding supply source into an AC voltage and outputs it. The switch 8 is inserted between the output terminal of the inverter unit 5 and the output terminal 16 that is the output terminal of the grid-connected inverter device 3, and a switching operation for determining whether or not to transmit the output of the inverter unit 5 to the system 12. Execute. The control unit 6 controls the converter 4 and the inverter unit 5, adjusts the voltage output from the converter 4 and the inverter unit 5 to a suitable value, and sets the switch 8 according to the state of the output voltage of the inverter unit 5. Open / close control is performed to control the interconnection operation between the inverter unit 5 and the system 12.

(Detailed configuration of grid-connected inverter device)
Next, a detailed configuration of the grid interconnection inverter device according to the present embodiment will be described with reference to FIG. FIG. 2 is a diagram showing a more detailed configuration of the inverter unit 5 which is a main component of the grid-connected inverter device 3 according to the present embodiment. In the configuration shown in FIG. It is the figure which showed the circuit structure until.

  In FIG. 2, an inverter unit 5 constitutes an inverter unit in which AC side terminals of a plurality (three in the example of the figure) of single-phase inverters 20-1 to 20-3 are connected in series. Each of the single-phase inverters 20-1 to 20-3 includes a plurality of self-extinguishing semiconductor switching elements, for example, IGBTs, in which diodes are connected in antiparallel.

  On the DC terminal side of the single-phase inverter 20-1 that is the first single-phase inverter (inverter in the middle stage in the figure), the capacitor 24-1 that is the first capacitor and the resistor 26 that is the first balance resistor -1 is connected between the DC buses connected to the DC side terminals of the single-phase inverter 20-1. The capacitor 24-1 functions as a first DC power source, and the resistor 26-1 suppresses voltage fluctuations of the DC bus, and a first balance for maintaining a predetermined voltage ratio with other DC buses. Acts as a resistor. On the other hand, in the AC side terminal of the single-phase inverter 20-1, a single-phase inverter 20-2 that is a second single-phase inverter is connected to one of the AC-side terminals, and a third single-phase inverter is connected to the other of the AC-side terminals. Is connected to a single-phase inverter 20-3. In addition, as a short-circuit switch for short-circuiting the AC side terminals of the single-phase inverter 20-1, two self-extinguishing semiconductor switching elements, such as IGBTs, connected in reverse parallel are connected in series with opposite polarities. The switch circuit 22 is provided, and this switch circuit 22 is connected in parallel to the single-phase inverter 20-1.

  Single-phase inverter 20-2 (the inverter in the upper part of the figure) that is the second single-phase inverter, and single-phase inverter 20-3 (the inverter in the lower part of the figure) that is the third single-phase inverter The same configuration is also taken on the DC terminal side. More specifically, on the DC terminal side of the single-phase inverter 20-2, the capacitor 24-2 as the second capacitor and the resistor 26-2 as the second balance resistor are connected to the DC-side terminal of the single-phase inverter 20-2. Are connected between the DC buses connected to each other. The capacitor 24-2 functions as a second DC power supply, and the resistor 26-2 suppresses voltage fluctuation of the DC bus, and a second balance for maintaining a predetermined voltage ratio with other DC buses. Acts as a resistor. Similarly, on the DC terminal side of the single-phase inverter 20-3, the capacitor 24-3 as the third capacitor and the resistor 26-3 as the third balance resistor are connected to the DC-side terminal of the single-phase inverter 20-3. Each is connected between DC buses. The capacitor 24-3 functions as a third DC power source, and the resistor 26-3 suppresses voltage fluctuations of the DC bus, and a third balance for maintaining a predetermined voltage ratio with other DC buses. Acts as a resistor.

  On the other hand, each AC side terminal of the single-phase inverter 20-2 and the single-phase inverter 20-3 has the following configuration. First, in the AC side terminal of the single phase inverter 20-2, the single phase inverter 20-1 is connected to one of the AC side terminals, and one of the input side terminals of the output filter circuit 7 is connected to the other of the AC side terminals. . In the AC side terminal of the single phase inverter 20-3, the single phase inverter 20-1 is connected to one of the AC side terminals, and the other of the input side terminals of the output filter circuit 7 is connected to the other of the AC side terminals. .

  As shown also in FIG. 1, the DC power to the capacitor 24-1 serving as the DC power source of the single-phase inverter 20-1 is supplied by the converter 4, and the capacitor 24-- serving as the DC power source of the single-phase inverter 20-2. 2 and each DC power to the capacitor 24-3 serving as a DC power source of the single-phase inverter 20-3 is supplied by the DC / DC converter 11 that receives the DC power supplied from the converter 4.

  Here, the voltage of the capacitor 24-1 that is an input of the single-phase inverter 20-1 is the same as that of the capacitors 24-2 and 24 that are the inputs of the single-phase inverters 20-2 and 20-3 that are other single-phase inverters. Greater than -3 voltage. On the other hand, either the voltage of the capacitor 24-2 or the voltage of the capacitor 24-3 may be large, or both voltages may be equal. Here, for convenience, it is assumed that the voltage of the capacitor 24-2 is approximately equal to the voltage of the capacitor 24-3. That is, when each voltage (equal to the bus voltage of each single-phase inverter) of the capacitors 24-1 to 24-3 when the inverter unit 5 is activated is V1, V2, and V3, There is a relationship of V1> V2 = V3.

  These single-phase inverters 20-1 to 20-3 can generate positive and negative voltages and zero as outputs, and the single-phase inverters 20-1 to 20-3 can be used as a sum total of these generated voltages. Output voltage. This output voltage is smoothed by an output filter circuit 7 as a smoothing filter circuit combining a reactor and a capacitor, for example, and a desired AC voltage is supplied to the system 12. The detailed operation is appropriately disclosed in the above-mentioned publication of Patent Document 1, and detailed description thereof is omitted here.

(Operation of main part of grid-connected inverter device)
Next, the operation of the main part of the grid interconnection inverter device according to the present embodiment will be described with reference to the drawing of FIG. Here, FIG. 3 is a diagram illustrating a current path flowing from the system 12 into the inverter unit 5 when the inverter unit 5 is stopped in a state where the system interconnection is performed.

(Linked state-operation when no balance resistance exists)
First, consider the case where the grid-connected inverter device 3 is connected to the grid 12 (that is, the switch 8 is closed) and the inverter unit 5 is stopped. Consider the case where there are no resistors 26-1 to 26-3 connected in parallel to 24-3. When the inverter unit 5 is stopped, each semiconductor switching element of the inverter unit 5 is controlled to be turned off. However, since there is a current path passing through a diode connected in parallel to each semiconductor switching element, the voltage of the system 12 is The single-phase inverters are connected in parallel, and the entire capacitor is applied to capacitors 24-1 to 24-3 connected in series.

  Here, as shown in FIG. 3, the capacitance values of the capacitors 24-1 to 24-3 are C1, C2, and C3, and the voltage of the system 12 is Vk. Further, the voltages of the capacitors 24-1 to 24-3 after the voltage of the system 12 is applied are assumed to be V1 ', V2', and V3 '.

First, the following equation is established while the inverter unit 5 is activated.
V1> V2 = V3 (1)
As typical values of V1, V2, and V3, V1 = 210 [V] and V2 = V3 = 70 [V] are assumed.

On the other hand, when the inverter unit 5 is stopped, the voltage Vk of the system 12 is applied to both ends of the capacitors 24-1 to 24-3 connected in series, so that the following equation is established.
V1 ′ + V2 ′ + V3 ′ = Vk (2)
C1 * V1 ′ = C2 * V2 ′ = C3 * V3 ′ = Ct * Vk = Q (3)
However, Ct = (C1 * C2 * C3) / (C1 * C2 + C2 * C3 + C3 * C1) (4)
Q is the amount of charge accumulated in each capacitor when the voltage Vk of the system 12 is applied.

From the above equation (3),
V1 ′: V2 ′: V3 ′ = (1 / C1): (1 / C2): (1 / C3) (5)
Holds.

Here, if C1 * C2 + C2 * C3 + C3 * C1 = Cp, then from the relationship of the above formulas (3), (4), and (5),
V1 ′ = (Ct / C1) * Vk = (C2 * C3) / Cp * Vk (6)
V2 ′ = (Ct / C2) * Vk = (C3 * C1) / Cp * Vk (7)
V3 ′ = (Ct / C3) * Vk = (C1 * C2) / Cp * Vk (8)
It becomes.

Among C1, C2, and C3, the capacitance value (C1) of the capacitor 24-1 having the largest terminal voltage is the largest, and the capacitance values (C2, C3) of the capacitors 24-2 and 24-3 are capacitance values. Are substantially equal and smaller than C1, the above equations (6) to (8)
V1 ′ <V2 ′ = V3 ′ (9)
The relationship is obtained.

Further, assuming that the capacitance values of C1, C2, and C3 are substantially equal, according to the above equations (6) to (8),
V1 ′ = V2 ′ = V3 ′ (10)
The relationship is obtained.

  If the voltage of the system 12 is about 280 [V] (peak voltage of AC 200 [V]), V1 ′ = V2 ′ = V3′≈93 [V] even in the case of the above equation (10). . That is, the voltages of the capacitors 24-2 and 24-3 rise from 70 [V] to 93 [V]. At this time, if the breakdown voltage of the parts of the inverter units 20-2 and 20-3 is 70 [V], the breakdown voltage may exceed the breakdown voltage of the parts. In addition, when this capacitor is comprised with the electrolytic capacitor, a capacity | capacitance changes with aging and the influence increases.

  Therefore, if the device is connected to the system when it is in a standby state, the voltage across each capacitor is determined according to the first to third capacitor capacity ratios, which may cause breakdown beyond the breakdown voltage of the component. .

(Linked state-operation when balance resistance exists)
Next, as shown in FIG. 3, a case where resistors 26-1 to 26-3 are present will be considered. In this case, since the voltage of the system 12 is applied to each single-phase inverter of the inverter unit 5 in the same manner as described above, the current from the system 12 is supplied from the capacitors 24-1 to 24-3 and the resistors 26-1 to 26-3. Will flow into each parallel circuit section having.

Here, if the potential differences appearing at both ends of each resistor caused by the current from the system 12 flowing through the resistors 26-1 to 26-3 are V4, V5, and V6, respectively, the following relationship is established.
V4 + V5 + V6 = Vk (11)

  At this time, the resistance values R1, R2, and R3 can be determined so that the magnitudes of V4, V5, and V6 do not exceed the breakdown voltage of the circuit components set for each single-phase inverter. For example, the ratio of the resistance values R1, R2, and R3 of the resistors 26-1 to 26-3 is set to be the same as the ratio of the bus voltage V1, V2, and V3 of each single-phase inverter.

If we use the same numerical value as above,
The ratio of the bus voltage of each single-phase inverter is
V1: V2: V3 = 210: 70: 70 = 3: 1: 1 (12)
And the ratio of the resistance values R1, R2, R3 is
R1: R2: R3 = 3: 1: 1 (13)
And set.

When the ratio of the resistance values R1, R2, and R3 is set as in the above equation (13), when the inverter is stopped in a state connected to the system 12 (Vk = 280 [V]), the voltage of the system 12 becomes the resistance If a current flowing at that time is applied to a series circuit of 26-1 to 26-3 and Ik is set as Ik, the following relationship is obtained.
V4 = Ik * R1, V5 = Ik * R2, V6 = Ik * R3 (14)

From the above equations (13) and (14),
V4: V5: V6 = 3: 1: 1 (15)
It becomes.

Further, according to the above equations (11) and (15), V4, V5, and V6 are respectively
V4≈170 [V] <V1
V5≈57 [V] <V2
V6≈57 [V] <V3
Therefore, the voltage across the resistance values R1, R2, and R3 does not exceed the withstand voltage of the circuit components that constitute each single-phase inverter.

(Disconnected state-operation when balance resistance exists)
Next, the operation when the inverter unit 5 is disconnected from the system 12 and the inverter unit 5 is stopped will be described with reference to the drawing of FIG. FIG. 4 is a diagram showing a discharge path of charges accumulated in each capacitor when the inverter unit 5 is stopped in a state of being disconnected from the system 12.

  When the inverter unit 5 is disconnected from the system 12 and the inverter unit 5 is stopped, if there are no resistors 26-1 to 26-3, the electric charges accumulated in the capacitors 24-1 to 24-3 are Remain in the Therefore, for example, when the maintenance of the grid interconnection inverter device 3 is performed, it is necessary to wait until the charge accumulated in each capacitor becomes small.

  On the other hand, in the grid interconnection inverter device 3 according to the present embodiment, since the resistors 26-1 to 26-3 provided as balance resistors exist, these resistors can also be used as discharge resistors. In the state where the inverter unit 5 is disconnected from the system 12, the path through which the electric charge accumulated in the capacitors 24-1 to 24-3 flows is only the path through the resistors 26-1 to 26-3. It is possible to quickly and automatically discharge the charge accumulated in 24-3. As a result, even if maintenance of the grid interconnection inverter device 3 is performed immediately after the grid interconnection inverter device 3 is disconnected from the grid 12, it does not take much time and does not take special measures. Maintenance work can be started.

(Other methods for selecting resistance values)
In the above, as an example of the resistance value selection method, the method of setting the bus voltage ratio (voltage division ratio) of each single-phase inverter has been described. Here, the power consumed by each resistor (power consumption) A method for determining the influence on the power conversion efficiency of the interconnection inverter device 3 to be reduced will be described.

  First, the ratio of R1, R2, and R3 is selected in accordance with the current Ik flowing from the system 12, so that V4, V5, and V6 do not exceed the withstand voltages of the components that constitute each single-phase inverter.

At this time, the electric power P1, P2, and P3 consumed by the discharge resistors R1, R2, and R3 can be expressed by the following equations.
P1 = (V1 ^ 2) / R1 (16)
P2 = (V2 ^ 2) / R2 (17)
P3 = (V3 ^ 2) / R3 (18)

  As is clear from the above equations (16) to (18), when the resistance value decreases, the loss during operation also increases. That is, when the resistance value is small, the charge accumulated in the capacitor can be discharged quickly, but the loss during operation also increases.

Therefore, it is meaningful to determine the resistance value so that the loss in the resistors R1, R2, and R3 does not affect the power conversion efficiency of the inverter unit. For example, in a single-phase inverter with a rated output of 4.0 [kW], assuming that V1 = 210 [V] and R1 = 150 [kΩ], the loss P1 at R1 is P1 = 0. 3 [W]. If the ratio of loss to rated output is defined as “power conversion efficiency influence (η)”, the power conversion efficiency influence η1 in R1 is
η1 = 0.3 / 4000 = 0.0075 [%]
Thus, the power conversion efficiency of the inverter unit is not affected.

If R1 can be determined as described above, R2 and R3 can be determined using, for example, the relationship of the above equation (13). Specifically, using the relationship of equation (13),
R2 = R3 = 50 [kΩ]
Is obtained.

Further, when calculating the power P2, P3 consumed by the resistors R2, R3 and the power conversion efficiency influences η2, η3, respectively,
P2 = P3 = 0.1 [W]
η2 = η3 = 0.1 / 4000 = 0.0025 [%]
Thus, the power consumed by R2 and R3 is also at a level that does not affect the power conversion efficiency of the inverter unit.

  As described above, according to the grid-connected inverter device according to the present embodiment, the current flowing from the grid when the inverter unit and the grid are connected and the operation of the inverter unit is stopped. Because the resistance value of each resistor is set so that the potential difference generated at both ends of each resistor does not exceed the withstand voltage of the components that make up each single-phase inverter, the inverter unit can be stopped in a state linked to the system. In addition, in each inverter unit, it is possible to use a component having a breakdown voltage lower than the system voltage.

  Moreover, according to the grid connection inverter apparatus concerning this Embodiment, since a grid connection inverter apparatus can be stopped in the state linked to the system, deterioration of the relay contact of the switch is suppressed. It is possible to extend the life of the switch.

  Furthermore, according to the grid interconnection inverter device according to the present embodiment, the resistance value of each resistor can be set based on the evaluation value that evaluates the degree of influence on the degree of influence of power conversion efficiency. It is possible to reduce the influence on the power conversion efficiency.

  In this embodiment, the voltage ratio and the resistance ratio are exemplified. However, it is not necessary to match the voltage ratio and the resistance ratio in a strict sense, and a certain amount of error is allowed. is there.

  Further, in the present embodiment, the case where the generated power of the solar cell module is used for interconnection with the grid is shown as an example, but a fuel cell or the like may be used as an energy source for supplying the generated power.

  Further, in the present embodiment, the configuration including three single-phase inverters has been illustrated. However, the present invention is not limited to this aspect, and a configuration including two or four or more single-phase inverters may be used. Absent.

  As described above, the grid-connected inverter device according to the present invention is useful as an invention that can extend the life of a relay.

It is a figure which shows an example at the time of applying the grid connection inverter apparatus concerning this invention to a solar energy power generation system. It is a figure which shows the more detailed structure of the inverter unit 5 which is the main components of the grid connection inverter apparatus 3 concerning this Embodiment. It is a figure which shows the electric current path | route which flows in into the inside of the inverter unit 5 from the system | strain 12 when the inverter unit 5 is stopped in the state which is performing grid connection. It is a figure which shows the discharge path | route of the electric charge accumulate | stored in each capacitor | condenser when the inverter unit 5 is stopped in the state isolate | separated from the system | strain 12.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photovoltaic power generation system 2 Solar cell module 3 Grid connection inverter apparatus 4 Converter 5 Inverter unit 6 Control part 7 Output filter circuit 8 Switch 11 DC / DC converter 12 System 14 Input terminal 16 Output terminal 20-1-20-3 Single-phase inverter 22 Switch circuit 24-1 to 24-3 Capacitor 26-1 to 26-3 Resistance

Claims (3)

An inverter unit that connects a plurality of AC-side terminals of a single-phase inverter that converts DC power to AC power and outputs it in series, and supplies an output voltage to the system by the sum of the generated voltages of the plurality of single-phase inverters In a grid-connected inverter device that controls the output voltage of this inverter unit and links to the system,
A switch for switching whether to supply the output of the inverter unit to the system;
Connected between the DC buses connected to the DC side terminals of the single-phase inverters, connected in parallel to the single-phase inverters, and connected in series as a whole, as a DC power source for the single-phase inverters A functioning capacitor;
Resistors connected to both ends of each capacitor;
With
When the inverter unit and the system are in a connected state and the operation of the inverter unit is stopped, the potential difference generated at both ends of the resistors by the current flowing from the system constitutes each single-phase inverter. A grid-connected inverter device, wherein a resistance value of each of the resistors is set so as not to exceed a withstand voltage of a component to be performed. When the bus voltage of each single-phase inverter when operating the inverter unit is set for each single-phase inverter,
2. The grid-connected inverter device according to claim 1, wherein a resistance ratio between the resistors is set equal to a voltage ratio of the bus voltages.   3. The grid connection according to claim 1, wherein the resistance value of each resistor is set for each single-phase inverter based on an evaluation value related to power conversion efficiency of each single-phase inverter. System inverter device.

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