Inverter device

An inverter device, which has two operation modes including a grid-connected operation mode where the inverter device is interconnected with a commercial power system, and an isolated operation mode where the inverter device is independent of a commercial power system and performs an isolated operation, includes an inverter converting direct-current power received from a direct-current power supply of a solar battery array into alternating-current power, a control unit controlling an action of an inverter device, a plug for outputting the alternating-current power converted by the inverter, and a load-connecting receptacle on a path of a power supply line connecting the inverter and the plug, for outputting the alternating-current power.

This application is the US national phase of international application PCT/JP2005/004622 filed 16 Mar. 2005, which designated the U.S. and claimed priority of JP 2004-087453 filed 24 Mar. 2004, the entire contents of each of which are hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to an inverter device, and particularly to an inverter device converting direct-current power of a direct-current power supply such as a solar battery, a storage battery, or an electric generator into alternating-current power for outputting the same, and having two modes including a grid-connected operation mode where the inverter device is interconnected with a commercial power system or an isolated operation mode where the inverter device is independent of the commercial power system and performs an isolated operation.

BACKGROUND ART

Conventionally, a decentralized power supply grid-connected with a commercial power system by using an inverter device has been developed for practical use. In such a power supply system, an inverter device converts direct-current power of a direct-current power supply such as a solar battery, a storage battery, or an electric generator into alternating-current power, and supplies the converted alternating-current power to each household electrical appliance (household load). If power output from the inverter device is less than power to be consumed by the household load, power is purchased from a power company by allowing power to flow from a commercial power system to cover a shortage of power. In contrast, if power output from the inverter device exceeds power to be consumed by the household load, it is also possible to sell power to the power company by allowing power to flow to the commercial power system. As such, an operation mode of the inverter device in which the inverter device is interconnected with the commercial power system and supplies power to the load is referred to as a “grid-connected operation mode”.

As to the inverter device as described above, when one wishes to use the inverter device as an emergency power supply or an independent power supply in the case where some failure occurs in the commercial power system owing to power outage or the like, some inverter devices can be disconnected from the commercial power system so that only the power output from the inverter devices can be supplied to some load (isolated load) connected to a dedicated receptacle. As such, an operation mode of the inverter device in which the inverter device is independent of the commercial power system and supplies power to the load is referred to as an “isolated operation mode”.

A conventional inverter device in the case where a solar battery is used as a direct-current power source will be described with reference toFIG. 5.

FIG. 5is a functional block diagram showing a configuration of a decentralized power supply system using a conventional inverter device.

An inverter device102includes a converter103, an inverter104, a filter105, a protection relay106, an interconnection relay107, a control unit108, and an isolated relay116. Control unit108is also controlled by a signal from outside, such as from a remote controller109.

A voltage of direct-current power from a solar battery array101is boosted by converter103. The direct-current power, whose voltage is boosted, is converted into alternating-current power in inverter104. A harmonic component of the converted alternating-current power is smoothed in filter105. In the grid-connected operation mode, the alternating-current power converted in inverter device102is supplied to a household load (not shown) in a manner interconnecting with a commercial power system114. At that time, isolated relay116is brought into a non-conduction state, while each of protection relay106and interconnection relay107is brought into a conduction state.

In contrast, in the isolated operation mode, either of protection relay106and interconnection relay107are brought into a non-conduction state, and isolated relay116is brought into a conduction state, so that inverter device102is disconnected from commercial power system114. Accordingly, the alternating-current power converted in inverter device102is supplied from a dedicated, isolated load connecting extension receptacle110to the isolated load.

As described above, in the conventional inverter device102, a power supply line for alternating-current power output from inverter104is provided for each of the grid-connected operation and the isolated operation (see Patent Document 1 and Patent Document 2).

In the conventional inverter device102as described above, interconnection relay107which allows alternating-current power output from inverter104to be in a conduction state/non-conduction state in the grid-connected operation mode, and isolated relay116which allows alternating-current power output from inverter104to be in a conduction state/non-conduction state in the isolated operation mode, are provided in parallel. It was therefore difficult to reduce the dimension of a body of inverter device102.

Furthermore, in Patent Document 1, an output terminal for outputting alternating-current power converted by inverter104in the isolated operation mode is provided at a body surface of inverter device102. Therefore, when one wishes to use a load at a place remote from inverter device102, one inevitably has to connect dedicated, isolated load connecting extension receptacle110thereto.

An aspect of the present invention is made to solve such a problem above. An object of the present invention is to provide an inverter device performing a grid-connected operation with an output plug inserted into a household receptacle, the inverter device allowing the output plug and a load-connecting receptacle for the isolated operation to be used with a simple configuration.

SUMMARY

An inverter device according to an aspect of the present invention is an inverter device having two operation modes including a grid-connected operation mode where the inverter device is interconnected with a commercial power system, and an isolated operation mode where the inverter device is independent of the commercial power system and performs an isolated operation, includes: an inverter unit converting direct-current power received from a direct-current power supply into alternating-current power; a control unit controlling an action of the inverter device; a grid-connected output terminal for outputting the alternating-current power converted by the inverter unit; and an isolated operation output terminal provided on a path of a power supply line connecting the inverter unit and the grid-connected output terminal, for outputting the alternating-current power. The grid-connected output terminal is a plug connectable to a commercial receptacle, commercial power from the commercial power system being supplied to the commercial receptacle. The isolated operation output terminal is a receptacle a load is connectable to, the load being supplied with the alternating-current power.

Preferably, the inverter device further includes a switch unit provided between the isolated operation output terminal and the grid-connected output terminal on the path of the power supply line. The control unit brings the switch unit into a non-conduction state when the grid-connected operation mode is terminated.

Preferably, the inverter device further includes a manipulation unit capable of transmitting to the control unit a signal for instructing a start of an operation of the inverter unit. In a case where the control unit receives the signal from the manipulation unit in the isolated operation mode, when the switch unit is in the non-conduction state, the control unit permits the operation of the inverter unit.

Preferably, the inverter device further includes a current detecting unit provided between the inverter unit and the isolated operation output terminal on the path of the power supply line, for detecting whether or not a current flows therebetween. The control unit operates the inverter unit for a prescribed period of time when the control unit brings the switch unit into the non-conduction state, and the control unit continues an operation of the inverter unit when the current detecting unit detects that the current flows for the prescribed period of time.

Preferably, the inverter device further includes a housing having the grid-connected output terminal and the isolated operation output terminal integrally provided therein. The housing includes a plug accommodating unit capable of accommodating the grid-connected output terminal.

Preferably, the inverter device further includes a manipulation unit capable of transmitting to the control unit a signal for instructing a start of an operation of the inverter unit. The plug accommodating unit has a plug accommodation detecting unit detecting whether or not the grid-connected output terminal is accommodated in the plug accommodating unit. In a case where the control unit receives the signal from the manipulation unit in the isolated operation mode, when the plug accommodation detecting unit detects that the grid-connected output terminal is accommodated in the plug accommodating unit, the control unit permits the operation of the inverter unit.

Preferably, the inverter device further includes a current detecting unit provided between the inverter unit and the isolated operation output terminal on the path of the power supply line, for detecting whether or not a current flows therebetween. The control unit operates the inverter unit for a prescribed period of time when the plug accommodation detecting unit detects that the grid-connected output terminal is accommodated in the plug accommodating unit, and the control unit continues the operation of the inverter unit when the current detecting unit detects that the current flows for the prescribed period of time.

According to an embodiment of the present invention, a grid-connected output terminal and an isolated operation output terminal are both provided at a common power supply line, and hence the configuration of the inverter device becomes simple, which makes it possible to downsize the body of the inverter device. Furthermore, in the inverter device according to an embodiment of the present invention, the isolated operation output terminal is a receptacle to which the load is connectable, which makes it possible to improve usability.

DESCRIPTION OF THE REFERENCE SIGNS

DETAILED DESCRIPTION

The embodiments of the present invention will hereinafter be described in detail with reference to the drawings. The same or corresponding portions in the drawings are denoted by the same reference characters, and the description thereof will not be repeated.

First Embodiment

FIG. 1is a functional block diagram showing a configuration of a decentralized power supply system using an inverter device according to a first embodiment of the present invention.

An inverter device2in the first embodiment has two operation modes including a grid-connected operation mode where the inverter device is interconnected with a commercial power system14, or an isolated operation mode where the inverter device is independent of commercial power system14and performs an isolated operation.

Referring toFIG. 1, inverter device2in the first embodiment includes a converter3, an inverter4, a filter5, a protection relay6, an interconnection relay7, a control unit8, a load-connecting receptacle10, and a plug11. In inverter device2, converter3, inverter4, filter5, protection relay6, and control unit8are collectively referred to as a power converting unit2a.

Converter3is a DC-DC converter, and boosts a voltage of direct-current power output from a solar battery array1serving as a direct-current power supply. Because of the fluctuations in a system voltage, converter3is controlled to assuredly provide a direct-current voltage of at least a peak value of the system voltage. For example, if a household receptacle13has a 100 V system voltage, its peak value is approximately 141 V. In this case, converter3is controlled to provide an output voltage of at least 150 V. In the first embodiment, a DC-DC converter is used as a boosting device. However, a boosting chopper or the like may be used. Furthermore, if an output voltage from solar battery array1is always at a value equal to or above a peak value of the system voltage, a boosting device such as converter3may be omitted.

Inverter4converts the direct-current power, whose voltage is boosted by converter3, into alternating-current power through pulse width modulation control. Inverter4has full-bridged four switching elements, and each of the switching elements has a diode connected in inverse-parallel therewith. The configuration of inverter4is not limited thereto, and may be other configurations.

Filter5smoothes a radiofrequency pulse generated through a switching action in inverter4to provide a sinusoidal current. Filter5includes a reactor and a capacitor.

Protection relay6is provided in series between filter5and load-connecting receptacle10on a path of the power supply line. Protection relay6is brought into a conduction state/non-conduction state through protective coordinated control by control unit8, which will be described later. When inverter4is operated and protection relay6is in a conduction state, inverter device2outputs alternating-current power. In contrast, even when inverter4is operated, if protection relay6is in a non-conduction state, inverter device2stops outputting alternating-current power.

Interconnection relay7is provided in series between load-connecting receptacle10and plug11on the path of the power supply line. Interconnection relay7is brought into a conduction state/non-conduction state by control unit8, depending on whether the grid-connected operation mode is adopted or not. If the grid-connected operation mode is adopted, interconnection relay7is brought into a conduction state. In contrast, if the isolated operation mode is adopted, interconnection relay7is brought into a non-conduction state.

Control unit8controls a gate pulse width signal to be supplied to a drive circuit for driving a switching element (e.g. an insulated gate bipolar transistor (IGBT), a metal oxide semiconductor field effect transistor (MOS-FET) and the like) in converter3and inverter4, monitors an input voltage, an input current, an output current, and a system voltage, and controls protection relay6and interconnection relay7. Generally, a current control scheme is adopted in the grid-connected operation mode, while a voltage control scheme is adopted in the isolated operation mode. The current control scheme means that an output current of inverter device2is subjected to feedback control such that the output current takes a target current value. The voltage control scheme means that the output voltage of inverter device2is subjected to feedback control such that the output voltage is equal to a voltage reference value.

Control unit8also provides protective coordinated control to inverter device2, to prevent an islanding operation and provide protection against an abnormal event of the system such as an increase/decrease in system voltage, or an increase/decrease in system frequency. The islanding operation means that even in the case of power outage on commercial power system14side, the power outage is not detected, and that inverter device2is still operated in the grid-connected operation mode. Furthermore, control unit8receives from and transmits to a remote controller9various kinds of signals, to manage and control inverter device2.

Remote controller9is a manipulation unit capable of transmitting a signal from outside of inverter device2to control unit8, by being manipulated by a user. For example, remote controller9can select switching to an operation/stop of inverter device2, the grid-connected operation mode/isolated operation mode, and others. A signal selected by the user operating remote controller9is transmitted to control unit8, and control unit8controls inverter device2in accordance with a content indicated by the received signal. The manipulation unit that can be manipulated by the user is not limited to externally-provided one such as remote controller9, and may be one provided at inverter device2.

Load-connecting receptacle10is a receptacle, which is provided between power converting unit2aand interconnection relay7on the path of the power supply line, and to which a load is directly connectable. Load-connecting receptacle10is an isolated operation output terminal that is not interconnected with commercial power system14, and supplies power to the load by exclusively using the alternating-current power converted by power converting unit2a. As such, the load connected to load-connecting receptacle10is referred to as an isolated load.

Plug11is a plug connectable to household receptacle13to which commercial power is supplied from commercial power system14. Plug11is a grid-connected output terminal for supplying power through plug11to a household load and/or commercial power system14. The household load refers to household electrical appliances collectively, and is activated by receiving alternating-current power from the decentralized power supply composed of solar battery array1and inverter device2. When power to be consumed exceeds power supplied from the decentralized power supply, the household load is also supplied with alternating-current power from commercial power system14.

Control of inverter device2in the grid-connected operation mode will be described with reference toFIG. 1.

In the grid-connected operation mode, protection relay6and interconnection relay7are brought into a conduction state. By providing such control, alternating-current power converted by power converting unit2ais output from plug11. Furthermore, when a certain load is connected to load-connecting receptacle10provided on a cord of plug11, the alternating-current power is also output from load-connecting receptacle10. The alternating-current power output from plug11is supplied through household receptacle13to the household load (not shown) and commercial power system14.

When the grid-connected operation mode is terminated, control unit8brings interconnection relay7into a non-conduction state. By doing so, it is possible to switch to the isolated operation in a safe manner. Furthermore, it is possible to prevent a user or the like from receiving an electric shock by touching of plug11.

Control of inverter device2in the isolated operation mode will now be described with reference toFIG. 1.

In the isolated operation mode, protection relay6is brought into a conduction state, and interconnection relay7is brought into a non-conduction state. By providing such control, inverter device2is shut off from commercial power system14. Accordingly, the alternating-current power converted by power converting unit2ais not output from plug11, and is output from load-connecting receptacle10. The alternating-current power output from load-connecting receptacle10is supplied to the isolated load (not shown) connected to load-connecting receptacle10.

Even if control unit8receives a signal for starting the isolated operation mode by the user's operation of remote controller9, control unit8never starts outputting the alternating-current power until it senses that interconnection relay7is brought into a non-conduction state.

By doing so, even when the isolated operation mode is selected with plug11inserted into household receptacle13, it is possible to prevent a user from receiving an electric shock by touching of plug11subsequently. Even when plug11is removed from household receptacle13, if interconnection relay7is still in a conduction state, the alternating-current power converted by inverter4is also supplied to plug11. Therefore, by bringing interconnection relay7into a non-conduction state, it is possible to prevent a user from receiving an electric shock by touching of plug11. Furthermore, when power outage occurs for some reason in commercial power system14during a grid-connected operation, an output of alternating-current power from inverter device2is stopped. By providing such control, it is possible to prevent a recovery worker from suffering an electric shock accident owing to system charge. In the case where the isolated operation mode is started with interconnection relay7being in a conduction state, even if the system, in which power outage occurs because of a failure, is recovered, a waveform from the inverter device2is not in synchronization with an actual system voltage waveform, which may cause a failure in inverter device2. However, the above-described control is provided in the present embodiment, and hence such a failure in inverter device2can be prevented.

In the first embodiment, plug11may include a voltage detecting unit using a transformer, an isolation amplifier or the like. Referring toFIG. 1, when plug11is inserted into household receptacle13, the voltage detecting unit detects a system voltage, and transmits the detected signal to control unit8as shown by a dotted line. Control unit8monitors the signal, and thereby brings interconnection relay7into a conduction state if the system voltage is normal, and brings interconnection relay7into a non-conduction state if the system voltage is abnormal. By doing so, it is possible to switch between the grid-connected mode and the isolated operation mode in a safe manner.

Alternatively, interconnection relay7may be controlled by a user's manipulation of remote controller9. For example, interconnection relay7is brought into a non-conduction state if a user selects a stop of the grid-connected operation mode, and interconnection relay7is brought into a conduction state if a user selects a start of the grid-connected operation mode.

FIG. 2is a functional block diagram showing a configuration in which a current detecting unit is provided at the inverter device according to the first embodiment of the present invention.

Referring toFIG. 2, a current detecting unit21is provided between filter5and protection relay6. For current detecting unit21, a shunt resistor or the like is used. Current detecting unit21detects an output current of the alternating-current power converted by inverter4and output through filter5. Control unit8monitors the output current detected by current detecting unit21.

When the grid-connected operation mode is stopped by power outage, a manipulation of remote controller9or the like, control unit8brings interconnection relay7into a non-conduction state, as described above. Subsequently, control unit8operates inverter4for a short period of time (e.g. one second). If isolated load22is connected to load-connecting receptacle10, current detecting unit21detects an extremely small amount of current. Accordingly, if current detecting unit21detects a current, it is recognized that isolated load22is connected, and hence an operation of inverter4is continued. If current detecting unit21does not detect a current, it is recognized that isolated load22is not connected, and hence the operation of inverter4is stopped. With such a configuration, even if power outage occurs in commercial power system14because of some failure, inverter4is automatically operated, and hence power can immediately be supplied to isolated load22.

According to the configuration in the first embodiment, plug11and load-connecting receptacle10are provided in parallel on the common power supply line, and hence a configuration of inverter device2becomes simple. When compared with the conventional inverter device102(seeFIG. 5), interconnection relay7is configured to serve as interconnection relay107and isolated relay116. It is therefore possible to reduce the number of relays and hence the cost. Furthermore, an output terminal for supplying power to the isolated load in the isolated operation mode corresponds to load-connecting receptacle10to which a load is directly connectable, and hence usability can be improved. Furthermore, load-connecting receptacle10is provided on the path of the power supply line connecting power converting unit2aand plug11, and hence there may be a case where the trouble of using an extension receptacle is eliminated, which can improve usability.

Second Embodiment

FIG. 3is a functional block diagram showing a configuration of a decentralized power supply system using an inverter device according to a second embodiment of the present invention.

Referring toFIG. 3, in the second embodiment, load-connecting receptacle10and plug11are integrated to configure a plug accommodating module12capable of accommodating plug11therein.

When compared with the first embodiment, interconnection relay7does not exist between load-connecting receptacle10and plug11, and an output relay15is provided between protection relay6and load-connecting receptacle10. Output relay15is for controlling an output itself of inverter device2by being brought into a conduction/non-conduction state. Other configurations are similar to those in the first embodiment.

Plug accommodating module12will be described in detail with reference toFIGS. 4A and 4B.

FIG. 4Ais an external view of plug accommodating module12provided at inverter device2in the second embodiment of the present invention.FIG. 4Bis a partial enlarged view of a part shown by30inFIG. 4A.

Referring toFIG. 4A, a housing20of plug accommodating module12has a load-connecting receptacle10at its surface. Plug11is configured such that plug11is rotated and thereby accommodated in a plug accommodating unit33in housing20. Referring toFIG. 4B, a plug rotary shaft31provided at the opposite ends of plug11rotates plug11by sliding groove portion32. As such, plug11can be accommodated in plug accommodating unit33. Reference numeral34inFIG. 4Bdenotes a spring.

Referring toFIG. 4Aagain, a plug accommodation detecting switch35sensing that plug11is accommodated in plug accommodating unit33is provided at the back of plug accommodating unit33. Plug accommodation detecting switch35is turned on when plug11is completely accommodated. When control unit8receives from plug accommodation detecting switch35a signal indicating that plug11is accommodated in plug accommodating unit33, control unit8permits the isolated operation mode.

By providing such control, it is possible to prevent a user from receiving an electric shock by touching of plug11after inverter device2starts the isolated operation mode.

Alternatively, as in the first embodiment, a current detecting unit (seeFIG. 2) may be provided between filter5and protection relay6. When control unit8detects from plug accommodation detecting switch35that plug11is accommodated in plug accommodating unit33, control unit8operates inverter4for a short period of time (e.g. one second). When the isolated load is connected to load-connecting receptacle10, current detecting unit21detects an extremely small amount of current. Accordingly, when current detecting unit21detects a current after the grid-connected operation is stopped, it is recognized that the isolated load is connected, and hence the operation of inverter4is just continued. When current detecting unit21does not detect a current, it is recognized that the isolated load is not connected, and hence the operation of inverter4is stopped. With such a configuration, power can automatically be supplied to the isolated load.

According to the configuration in the second embodiment, load-connecting receptacle10and plug11are integrated, and hence they can be easy to handle. When the grid-connected operation mode is terminated, and there is no need to insert plug11into household receptacle13, for example, plug11, which is not used, is accommodated in plug accommodating unit33so that plug11does not cause an obstruction.

In the second embodiment, plug accommodating module12may have a configuration other than those shown inFIGS. 4A and 4B, and have any configuration allowing plug11to be bent for accommodation. Although plug accommodation detecting switch35is used as a configuration sensing that plug11is detected, the configuration is not limited thereto, as long as it can detects that the sensor or the like is accommodated.

As such, the embodiments of the present invention have been described. However, a configuration of the inverter device is not limited to the configurations shown inFIGS. 1-4.

In the embodiments of the present invention, the direct-current power supply is described as a solar battery. However, the direct-current power supply is not limited to a solar battery, and may be a fuel cell or the like, as long as it is a direct-current power supply.

It should be understood that all the embodiments disclosed here are by way of illustration and examples only and are not to be taken by way of limitation. It is intended that the scope of the present invention is indicated not by the description above, but by the appended claims, and that all the modifications that fall within the meaning and range of equivalents of the claims are embraced.