Electric power supplying system

An electric power supplying system includes a plurality of AC output converters connected in parallel to a bus configured to supply power to an AC load. Each of the AC output converters includes: an AC-DC converter; a DC-AC converter; a secondary battery connected in parallel to the DC-AC converter; a first switching circuit provided between the bus and the DC-AC converter; a bypass path, a second switching circuit provided between the bus and the bypass path; a switching control circuit configured to control the first and second switching circuits at the time of power failure and power restoration; and a control power supply circuit configured to receive a supply of the external AC voltage, the AC voltage converted by the DC-AC converter, a bypass voltage of the bypass path, and a voltage of the bus, to generate a control voltage for the switching control circuit.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to an electric power supplying system including a plurality of AC output converters connected in parallel and configured to convert power from direct-current (DC) to alternating-current (AC), for supplying the power to a load.

DESCRIPTION OF THE BACKGROUND ART

There is known an electric power supplying system including a plurality of AC output converters connected in parallel and configured to convert power from DC to AC, for supplying the power to a load.

In this respect, Japanese Patent Laying-Open No. 2017-50933 discloses an electric power supplying system including a plurality of AC output converters such as inverters connected in parallel, which are operated in parallel with respect to a common load.

SUMMARY OF THE INVENTION

While the electric power supplying system in the aforementioned publication is capable of feeding power with a high degree of efficiency by supplying power from the respective AC output converters to the load, the system is configured to switch to a bypass circuit when a power failure occurs, for example.

After a power failure has occurred, however, the respective AC output converters may have different power supplying capacities from a storage battery to the load.

In that case, if some of the AC output converters switch to the bypass circuit while the other AC output converters continue to feed power from the storage battery, there is a risk of backflow. It is thus required to switch to the bypass circuit upon completion of power feeding from all the AC output converters.

However, power supplies of some of the AC output converters do not always operate normally until after the completion of power feeding from the other AC output converters. This may result in difficulty in switching to the bypass circuit.

If the switching to the bypass circuit could not be normally performed, the electric power supplying system may not be restored when the power is restored.

An object of the present invention is to realize an electric power supplying system capable of safely switching to a bypass circuit when a power failure occurs, to solve the problem described above.

An electric power supplying system according to one aspect of the present invention includes a plurality of AC output converters connected in parallel to a bus configured to supply power to an AC load. Each of the AC output converters includes: an AC-DC converter configured to convert an external AC voltage into a DC voltage; a DC-AC converter configured to convert the DC voltage into an AC voltage and supply the AC voltage to the bus; a secondary battery connected in parallel to the DC-AC converter and configured to store the DC voltage; a first switching circuit provided between the bus and the DC-AC converter; a bypass path configured to directly supply the external AC voltage, instead of the AC voltage supplied from the DC-AC converter, to the bus; a second switching circuit provided between the bus and the bypass path; a switching control circuit configured to control the first and second switching circuits at the time of power failure and power restoration; and a control power supply circuit configured to receive a supply of the external AC voltage, the AC voltage converted by the DC-AC converter, a bypass voltage of the bypass path, and a voltage of the bus, to generate a control voltage for the switching control circuit.

Preferably, the switching control circuit of each of the AC output converters is configured to turn the first switching circuit on and turn the second switching circuit off during normal operation.

Preferably, the switching control circuit of each of the AC output converters is connected to the switching control circuits of the other AC output converters, and is configured to receive an input of a signal to stop a voltage to the AC load from the other AC output converters, and to turn the first switching circuit off and turn the second switching circuit on upon receiving the input of the signal to stop the voltage to the AC load for all of the AC output converters.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment is described below based on the drawings. In this example, an uninterruptible power supply (UPS) system is described as an example electric power supplying system.

In this embodiment, the uninterruptible power supply system is described using a parallel configuration of a plurality of AC output converters.

FIG. 1illustrates the configuration of an uninterruptible power supply system1based on the embodiment.

Referring toFIG. 1, uninterruptible power supply system1includes a plurality of (n) AC output converters10-1to10-n. AC output converters10-1to10-n(also collectively referred to as AC output converters10) are connected to an external AC power supply3A and an external bypass AC power supply3B, and are operated in parallel with respect to a common load20. It should be noted that n can be set to any number depending on the load supplied, as long as the number is particularly two or more.

The configuration of each AC output converter10is now described.

AC output converter10includes: a converter5connected to external AC power supply3A and configured to convert an AC voltage from external AC power supply3A into a DC voltage; an inverter7connected to converter5and configured to convert the DC voltage into an AC voltage; and a storage battery6connected to converter5in parallel with inverter7.

AC output converter10further includes: a switching circuit9provided between inverter7and the load; a bypass path provided separately from a path on which converter5and inverter7are supplied, and configured to supply an AC voltage from external bypass AC power supply3B; a switching circuit8provided between the bypass path and the load; a controller4(switching control circuit) configured to control switching circuits8and9; and a control power supply circuit2configured to generate a driving voltage for controller4.

Control power supply circuit2is connected to the input side of converter5, the output side of inverter7, external bypass AC power supply3B, and a bus connected to load20, and is configured to detect their respective AC voltages and receive a supply of the AC voltages to generate the driving voltage for controller4. That is, control power supply circuit2can generate the driving voltage based on the AC voltage supplied from inverter7, even when a power failure occurs in external AC power supply3A.

In accordance with the AC voltage detected on the input side of converter5and the output side of inverter7, control power supply circuit2outputs, to controller4, a signal indicating the detection of a power failure or a reduction in supply voltage from inverter7.

When external AC power supply3A stops supplying the power due to a power failure, power is supplied from storage battery6to the load.

Control power supply circuit2is described as being connected to the input side of converter5, the output side of inverter7, external bypass AC power supply3B, and the bus connected to load20, to generate the necessary driving voltage. However, since the voltages supplied from the input side of converter5, the output side of inverter7, external bypass AC power supply3B, and the bus connected to load20vary in level, a transformer circuit configured to appropriately adjust and supply the voltages is provided, which is not shown.

FIG. 2illustrates voltage supply in uninterruptible power supply system1during normal operation based on the embodiment.

As shown inFIG. 2, a configuration including two AC output converters10-1and10-2is described by way of example.

During normal operation of external AC power supply3A, switching circuit9is turned on to connect load20and inverter7to each other.

Converter5converts an AC voltage from external AC power supply3A into a DC voltage. Inverter7is connected to converter5and converts the DC voltage into an AC voltage. Storage battery6stores the DC voltage converted by converter5.

Power is supplied from inverter7to load20through switching circuit9.

Since the plurality of AC output converters10are configured in parallel, necessary power is supplied from respective AC output converters10to load20.

FIGS. 3A and 3Billustrate voltage supply in uninterruptible power supply system1at the time of conventional power failure.

As shown inFIG. 3A, a configuration including two AC output converters10-1and10-2is described by way of example.

The case in which a power failure has occurred in external AC power supply3A is described. In this case, the voltage supply from converter5decreases. Thus, the power supply to load20is continued from storage battery6through inverter7and switching circuit9. Switching circuit8is OFF in this state.

During normal operation, switching circuit9is turned on to connect load20and inverter7to each other.

Converter5converts an AC voltage from external AC power supply3A into a DC voltage. Inverter7is connected to converter5and converts the DC voltage into an AC voltage. Storage battery6stores the DC voltage converted by converter5.

Power is supplied from inverter7to load20through switching circuit9.

Since the plurality of AC output converters10are configured in parallel, necessary power is supplied from respective AC output converters10to load20.

Next, the case in which storage battery6of AC output converter10-1and storage battery6of AC output converter10-2have different supplying capacities is described.

In this example, the case in which storage battery6of AC output converter10-1has greater supplying capacity than storage battery6of AC output converter10-2is described.

In this case, even if the supply from storage battery6of AC output converter10-2to load20stops, there is a risk of backflow when continuing the supply from AC output converter10-1to load20. Thus, switching circuit8of AC output converter10-2cannot be turned on.

Therefore, AC output converter10-2needs to wait for a command to switch from switching circuit9to switching circuit8until after the supply from AC output converter10-1to load20ends.

During this waiting period, control power supply circuit2needs to continue to ensure the driving voltage for controller4. If the waiting period is long, however, it may be difficult for control power supply circuit2to continue to ensure the driving voltage for controller4. If control power supply circuit2can no longer ensure the driving voltage for controller4, the command to switch from switching circuit9to switching circuit8cannot be output, causing switching circuit8to be maintained in an OFF state.

FIG. 3Bshows the case in which the power has been restored when switching circuit9of AC output converter10-1is ON and switching circuit8of AC output converter10-2is OFF.

In this case, switching circuit8of AC output converter10-1is ON, and thus power is supplied to load20through the bypass path.

On the other hand, switching circuit8of AC output converter10-2is OFF, and thus power cannot be supplied to load20through the bypass path.

As a result, only AC output converter10-1supplies power to load20, to reach a state of overload. Thus, the supply from AC output converter10-1will also stop.

That is, a conventional uninterruptible power supply system may not be able to perform a normal power restoration process.

FIGS. 4A and 4Billustrate voltage supply in uninterruptible power supply system1at the time of power failure according to the embodiment.

As shown inFIG. 4A, a configuration including two AC output converters10-1and10-2is described by way of example.

The case in which a power failure has occurred in external AC power supply3A is described.

In this case, the voltage supply from converter5decreases. Thus, the power supply to load20is continued from storage battery6through inverter7and switching circuit9. Switching circuit8is OFF in this state.

As described above, the case in which storage battery6of AC output converter10-1and storage battery6of AC output converter10-2have different supplying capacities is described, for example.

In this example, the case in which storage battery6of AC output converter10-1has greater supplying capacity than storage battery6of AC output converter10-2is described.

As described above, even if the supply from storage battery6of AC output converter10-2to load20stops, there is a risk of backflow when continuing the supply from AC output converter10-1to load20. Thus, switching circuit8of AC output converter10-2cannot be turned on.

On the other hand, control power supply circuit2according to the embodiment is connected to the input side of converter5, the output side of inverter7, external bypass AC power supply3B (a bypass voltage of the bypass path), and the bus connected to the load, to generate the necessary driving voltage.

Therefore, even if the supply from storage battery6of AC output converter10-2to load20stops, control power supply circuit2of AC output converter10-2can receive the voltage from the bus connected to load20, for example, to continue to supply the necessary driving voltage to controller4.

Finally, controller4of AC output converter10-1notifies, when the supply from storage battery6to load20stops, controller4of AC output converter10-2of the stop.

Then, when it is detected that the voltage supply from all AC output converters10to load20has stopped, controller4of each AC output converter10turns switching circuit9off and turns switching circuit8on.

FIG. 4Bshows the case in which the power has been restored when switching circuits8of AC output converters10-1and10-2are ON.

In this case, switching circuits8of AC output converters10-1and10-2are ON, and thus power is supplied to load20through the bypass path.

As a result, AC output converters10-1and10-2supply power to load20, and thus an overload state can be suppressed and a restoration process can be normally performed. That is, uninterruptible power supply system1according to the embodiment can perform a normal power restoration process.

While two AC output converters10have been mainly described in this example, the present invention is not particularly limited thereto, and is similarly applicable to three or more AC output converters10.

While the configuration in which external AC power supply3A and external bypass AC power supply3B are provided independently from each other has been described in this example, the present invention is similarly applicable to a configuration in which external bypass AC power supply3B is not provided and the bypass path is also connected to the external AC power supply.