Voltage control apparatus

A voltage control apparatus includes a boost converter configured to convert an input voltage to a voltage equal to or higher than a first voltage in an operative state and directly output the input voltage in an inoperative state, a buck-boost converter coupled with the boost converter in parallel and configured to convert the input voltage to a second voltage lower than the first voltage, a memory, and a processor coupled to the memory and configured to keep the buck-boost converter in the operative state, set the boost converter to the inoperative state when the input voltage is equal to or higher than the first voltage, and change the boost converter to the operative state when the input voltage is lower than the first voltage.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2016-126942, filed on Jun. 27, 2016, the entire contents of which are incorporated herein by reference.

FIELD

The embodiments discussed herein are related to a voltage control apparatus and an information processing apparatus.

BACKGROUND

In a power source circuit that converts an input voltage supplied from a power supply system to a predetermined voltage, the input voltage sometimes drops abruptly due to a change of input voltage sources when a power outage occurs, or the like. In order to prepare such a situation, a power source circuit including a boost converter that boosts the input voltage is provided. Also, there is a problem in that if a boost converter is operated all the time, the transmission efficiency of the power deteriorates, or noise occurs. Accordingly, a proposal has been made of a power source circuit that stops the boost operation of the boost converter if the input voltage is equal to or higher than a predetermined voltage.

Also, as an example of a technique related to a power source circuit, a discharge lamp lighting device including a battery disposed in parallel with a boost converter is provided.

Related-art techniques are disclosed in Japanese Laid-open Patent Publication Nos. 2015-53777 and 2005-108601.

SUMMARY

According to an aspect of the invention, a voltage control apparatus includes a boost converter configured to convert an input voltage to a voltage equal to or higher than a first voltage in an operative state and directly output the input voltage in an inoperative state, a buck-boost converter coupled with the boost converter in parallel and configured to convert the input voltage to a second voltage lower than the first voltage, a memory, and a processor coupled to the memory and configured to keep the buck-boost converter in the operative state, set the boost converter to the inoperative state when the input voltage is equal to or higher than the first voltage, and change the boost converter to the operative state when the input voltage is lower than the first voltage.

DESCRIPTION OF EMBODIMENTS

When an operation start instruction is given to a boost converter in an inoperative state, it takes some time until the boost converter enables the output voltage to be boosted up to a predetermined voltage. Accordingly, if the operation of the boost converter is started in accordance with a drop of the input voltage, there is a possibility that the output voltage temporarily drops significantly before the output voltage of the boost converter is boosted to the predetermined voltage. On the other hand, if the boost converter is operated all the time in preparation for an input voltage drop, there is a problem in that the occurrence of power loss is inevitable, and thus the operation is inefficient.

According to an aspect of the present disclosure, it is desirable to provide a voltage control apparatus and an information processing apparatus that efficiently reduce a drop in the output voltage, which is caused by a drop in the input voltage.

In the following, a description will be given of embodiments of the present disclosure with reference to the drawings.

First Embodiment

FIG. 1is an example of a configuration of a voltage control apparatus according to a first embodiment and an example of operation. A voltage control apparatus10illustrated inFIG. 1includes a boost converter11, a buck-boost converter12, and a control circuit13.

The boost converter11is capable of changing an operative state and an inoperative state in accordance with an instruction from the control circuit13. In the following, when the boost converter11is in an operative state, the boost converter11is referred to be on, and when the boost converter11is in an inoperative state, the boost converter11is referred to be off. When the boost converter11is in the on state, the boost converter11boosts an input voltage Vin to a voltage equal to or higher than a predetermined voltage V1(note that V1>0). On the other hand, when the boost converter11is in an off state, the boost converter11does not perform the boost operation, and directly outputs the input voltage Vin.

The buck-boost converter12is coupled in parallel with the boost converter11. The buck-boost converter12changes the input voltage Vin to a voltage V2lower than the voltage V1(note that V2>0). Also, such operation by the buck-boost converter12is performed under the control of the control circuit13both in the case where the boost converter11is on and in the case where the boost converter11is off.

The control circuit13continues to keep the buck-boost converter12operating. Together with this, if the input voltage Vin is equal to or higher than the voltage V1, the control circuit13sets the boost converter11off and monitors the input voltage Vin. If the input voltage Vin becomes lower than the voltage V1, the control circuit13changes the boost converter11to on.

In the following, a description will be given of an example of operation of the voltage control apparatus10in accordance with the state of the input voltage Vin.

If the input voltage Vin is equal to or higher than the voltage V1, as illustrated in the upper part inFIG. 1, the control circuit13sets the boost converter11off. In this state, a voltage input from the boost converter11is directly output, and thus the output voltage Vout of the voltage control apparatus10becomes equal to or higher than the voltage V1. In this manner, in a state in which boosting is needless, the boost converter11is set off, and thus excessive power becomes unconsumed. Accordingly, it is possible to reduce the power loss by the entire apparatus. On the other hand, although the buck-boost converter12is set on by the control circuit13, since the input voltage Vin to the boost converter11is lower than the voltage V2, which is output from the buck-boost converter12, and thus the current does not flow through the buck-boost converter12. Accordingly, the power loss by the buck-boost converter12is small.

Next, if the input voltage Vin becomes lower than the voltage V1from the above-described state, as illustrated in the middle part inFIG. 1, the control circuit13changes the boost converter11to on. However, it is not possible for the boost converter11to boost the input voltage to a voltage equal to or higher than the voltage V1immediately upon receipt of a change instruction from the control circuit13. Accordingly, the output voltage of the boost converter11temporarily drops with a drop of the input voltage Vin. On the other hand, the buck-boost converter12coupled in parallel with the boost converter11is kept on. Accordingly, if the input voltage Vin drops, a current flows through the buck-boost converter12. The output voltage Vout of the voltage control apparatus10is kept equal to or higher than the voltage V2by the boost operation of the buck-boost converter12.

After that, the start of the boost converter11is completed, and the output voltage Vout of the voltage control apparatus10is boosted to a voltage equal to or higher than the voltage V1by the boost operation of the boost converter11. In this state, as illustrated by the lower part inFIG. 1, a current does not flow through the buck-boost converter12because the output voltage of the buck-boost converter12is lower than the voltage output from the boost converter11. Accordingly, the power loss by the buck-boost converter12is small.

As described above, in the transient state until the completion of starting the boost converter11, it is possible for the voltage control apparatus10to keep the output voltage Vout of the voltage control apparatus10equal to or higher than the voltage V2, and thus to avoid excessive falling of the output voltage Vout. Also, in the state in which the input voltage Vin is equal to or higher than the voltage V1, it is possible to reduce the power loss of the boost converter11by stopping the boost operation of the boost converter11. Further, in the state in which the input voltage Vin is equal to or higher than the voltage V1, or in the state in which the output voltage Vout is equal to or higher than the voltage V1by the operation of the boost converter11, a current does not flow through the buck-boost converter12, and thus it is possible to reduce a power loss of the buck-boost converter12.

In this manner, in the voltage control apparatus10, in the transient state from when the boost converter11is changed to on to the start of the boost operation, the output voltage is allowed to drop to a certain voltage lower than the steady voltage. Thereby, it is possible to reduce more power loss than in the case of keeping on the boost converter11all the time, which boosts the voltage up to the steady voltage. Accordingly, with the voltage control apparatus10, it is possible to efficiently reduce a drop in the output voltage Vout, which is caused by a drop in the input voltage Vin.

Second Embodiment

Next, a description will be given of an information processing apparatus provided with a power source circuit including the voltage control apparatus10inFIG. 1as a second embodiment. In the following description, first a description will be given of a comparative example of a power supply system that supplies power to an information processing apparatus with reference toFIGS. 2A and 2BandFIGS. 3A and 3B. After that, a description will be given of an information processing apparatus according to the present embodiment.

FIGS. 2A and 2Bare first diagrams of comparative examples of power supply systems.FIG. 2Aillustrates an example of an alternate current (AC) power supply system, andFIG. 2Billustrates an example of a high voltage direct current (HVDC) power supply system.

The power supply systems illustrated inFIGS. 2A and 2Bare installed, for example, in a data center. In recent years, various kinds of data are electronized and come to be handled on a computer. Accordingly, the amount of data handled by a business organization is continuing to increase. A data center used by such a business organization has a tendency to be provided with a large number of information and communication technology (ICT) devices, such as servers, storage devices, and the like. Thus, the power for operating the large number of ICT devices and the power for cooling the devices are increasing. Accordingly, power saving becomes a challenge.

Information processing apparatuses40and40aillustrated inFIGS. 2A and 2B, respectively are examples of ICT devices installed in a data center. The AC power supply system illustrated inFIG. 2Ais a power supply system that has been generally used for a long time, and that supplies power supplied from an alternate current power source20to the information processing apparatus40via an alternate current power source system30in AC without change. Also, the alternate current power source system30includes a battery31for continuing to supply power at the time of power outage, or the like. Accordingly, the alternate current power source system30includes an AC/DC converter32that once converts the alternate current power from the alternate current power source20to a direct current power, and a DC/AC converter33that converts the converted direct current power to an alternate current power. The DC/AC converter33converts the direct current power supplied either from the AC/DC converter32or the battery31to an alternate current power and outputs the power.

The information processing apparatus40includes an AC/DC converter41that converts the supplied alternate current power to a direct current power, and a DC/DC converter42that converts the converted direct current power to a predetermined voltage (for example, 12V).

On the other hand, in the HVDC power supply system, the power is supplied to the information processing apparatus in direct current without a change. Thereby, the direct current power does not have to be changed to an alternate current power, and thus it is possible to reduce the power loss. Also, by keeping the direct current power to be transmitted at a high voltage, it is possible to reduce the current at transmission time, and thus to reduce the power loss due to the generation of heat, or the like. By using the HVDC power supply system, for example, it is said that the power loss is allowed to be reduced by a few percent to 20 percent in the entire data center.

In the example inFIG. 2B, the direct current power source system30aincludes the battery31and the AC/DC converter32, but does not include the DC/AC converter33, and outputs a direct current power without change. At this time, the output voltage is a high voltage, for example, 380V. The information processing apparatus40athat is supplied power from the direct current power source system30aincludes a DC/DC converter43that converts the input voltage to a predetermined voltage (for example, 12V), but does not have to include an AC/DC converter.

FIGS. 3A and 3Bare second diagrams of comparative examples of power supply systems. In the HVDC power supply system, the rated voltage for a direct voltage supplied to an ICT device is not unified at present. Currently, roughly speaking, either a relatively high voltage of 350 V to 380 V or a relatively low voltage of 240 V is mainly used. The rated voltages between them differ nearly two times, and thus the configurations of the power supply units (PSUs) that support input of the individual voltages often differ from the viewpoint of efficiency.

FIG. 3Aillustrates an example of the HVDC power supply system including a PSU that supports the input voltage of 350 V to 380 V. A direct current power source system50aincludes an AC/DC converter51aand a battery52a. The AC/DC converter51aor the battery52aoutputs a direct current voltage of 380V, for example. A PSU61in an information processing apparatus60aincludes a DC/DC converter61athat converts the supplied direct current voltage of 380 V to 12 V, for example.

On the other hand,FIG. 3Billustrates an example of the HVDC power supply system including a PSU that supports an input voltage of 240 V. A direct current power source system50bincludes an AC/DC converter51band a battery52b. The AC/DC converter51bor the battery52boutputs a direct current voltage of 240 V.

Also, a PSU62in an information processing apparatus60bincludes the DC/DC converter61athat converts the input voltage to 12 V in the same manner as the PSU61in the information processing apparatus60a. However, if the PSU62uses the input voltage of 240 V without change, the current value is high and thus disadvantages occur, for example, the parts in the PSU62increases in size, energy loss due to heating, or the like becomes large. Accordingly, the PSU62further includes a DC/DC converter (boost converter)62athat boosts the input voltage of 240 V to 410 V, for example. In the PSU62, the DC/DC converter61adecreases the direct current voltage boosted by the DC/DC converter62ato 12 V, and outputs the voltage.

Here, as described above, the rated voltage of the HVDC power supply system is not unified at present. Accordingly, it is desirable to develop a PSU that supports a wide range of input voltage from a relatively high voltage (350 V to 380 V) to a relatively low voltage (240 V). However, in order to realize such a PSU, it is desirable to dispose two stages of voltage conversion circuits as the PSU62illustrated inFIG. 3B. With such a configuration, there is a problem in that a power loss occurs due to an increase in the number of conversion stages of voltage, and the efficiency deteriorates. In particular, in a state in which a voltage of 350 V to 380 V is input, in the first voltage conversion circuit, although boosting voltage does not have to be performed, a power loss due to switching operation occurs.

Thus, in an information processing apparatus according to the second embodiment, a PSU including two stages of voltage conversion circuits is provided as the information processing apparatus60binFIG. 3B, and a function of stopping the boost operation of the first stage voltage conversion circuit is added to the PSU. Thereby, a power loss reduction is attempted. In addition to this, in the information processing apparatus according to the second embodiment, the first stage voltage conversion circuit in the PSU is also used as a voltage boosting mechanism when the input voltage is abnormally low.

FIG. 4is a diagram illustrating an example of a configuration of a storage device, which is an example of the information processing apparatus according to the second embodiment. A storage device100illustrated inFIG. 4includes controller modules (CMs)101and102, and a PSU110. Also, a drive enclosure (DE)210and a host device220are coupled to the CMs101and102.

The CMs101and102are storage control devices that control accesses to storage devices mounted in the DE210upon request from the host device220. As storage devices to be access controlled, the DE210is mounted with a plurality of HDDs211,212, and213, for example.

In this regard, the CM101is realized as a computer including, for example, a processor101a, a random access memory (RAM)101b, and the like. The CM102is also realized as a computer including a processor102a, a RAM102b, and the like in the same manner. Also, for example, the CMs101and102may access the storage devices individually by a separate request from the host device. Alternatively, one of the CMs101and102may operate as an operational system, and the other of the CMs101and102may operate as a standby system.

The PSU110supplies power to the CMs101and102based on the power supplied from the outside. The PSU110supports input of a direct current power transmitted in the HVDC power supply system.

FIG. 5is a diagram illustrating an example of a configuration of a power supply system that supplies power to the storage device. The power supply system illustrated inFIG. 5includes an alternate current power source20, a direct current power source system70, an HVDC distribution board80, and a power distribution unit90.

The direct current power source system70includes a rectifier71and a battery72. The rectifier71converts the alternate current power supplied from the alternate current power source20to a direct current power and rectifies the converted direct current power. Also, the rectifier71outputs the rectified direct current power or the direct current power output from the battery72by changing the powers. For example, in a state in which alternate current power is supplied from the alternate current power source20, the rectifier71outputs the direct current power produced by converting this alternate current power and rectifying the current. If the supply level of the alternate current power drops, the rectifier71changes the output power to the power from the battery72. The battery72supplies the direct current power to the rectifier71.

The HVDC distribution board80distributes the power output from the direct current power source system70. Also, the HVDC distribution board80is mounted with safety devices, for example, various breakers, and the like. Various information processing apparatuses100a,100b, . . . , including the storage device100are coupled to the power distribution unit90. Specifically, the respective power source plugs of the information processing apparatuses100a,100b, . . . , are coupled to the power distribution unit90. The power distribution unit90supplies the direct current power supplied from the direct current power source system70via the HVDC distribution board80to the coupled information processing apparatuses100aand100b, . . . .

In this regard, in a power supply system having the above-described configuration, the output voltage from the direct current power source system70may be possible to be a relatively high voltage (350 V to 380 V) and a relatively low voltage (240 V). Also, in the former case, when the output voltage of the rectifier71is changed to the output voltage of the battery72, the output voltage of the rectifier71sometimes becomes a voltage lower than 350 V to 380 V. Further, if the power supplied to the rectifier71from the outside is not a normal alternate current power source20, but the power based on natural energy, such as solar power generation, or the like, the output voltage of the rectifier71sometimes becomes a voltage lower than 350 V to 380 V.

Next, a description will be given of the PSU110of the storage device100.

FIG. 6is a diagram illustrating an example of an internal configuration of the PSU. In the PSU110, a filter circuit111, a boost converter113, and a DC/DC converter115are coupled in series. Also, a buck-boost converter114is coupled in parallel with the boost converter113. Further, the PSU110includes an inrush current prevention circuit112, a controller116, and switching control circuits117and118. In this regard, the boost converter113, the buck-boost converter114, and the controller116are examples of the boost converter11, the buck-boost converter12, and the control circuit13inFIG. 1, respectively.

The filter circuit111removes dispensable input noise. The inrush current prevention circuit112and a diode D1are coupled in series to a signal line between the filter circuit111and the boost converter113. The inrush current prevention circuit112inhibits the inrush current from the filter circuit111. The diode D1avoids a reverse current flow from the boost converter113to the direction of the inrush current prevention circuit112.

The boost converter113is a chopper-type boost converter and includes a choke coil L1, a switching element M1, a capacitor C1, and a diode D2. The choke coil L1and the diode D2are coupled to the output side of the diode D1in series. The diode D2avoids a reverse current flow to the choke coil L1and the switching element M1.

The switching element M1is an n-channel metal-oxide semiconductor field-effect transistor (MOSFET). The both ends of the capacitor C1are coupled to the both ends of the switching element M1, respectively via the choke coil L1. The drain of the switching element M1is coupled to a connection end of the choke coil L1and the diode D2, and the source of the switching element M1is coupled to the ground side of the capacitor C1. The gate of the switching element M1is coupled to the switching control circuit117. The switching control circuit117controls the voltage input to the gate of the switching element M1under the control of the controller116so as to switch on and off to the switching element M1.

In the boost converter113, when the switching element M1is on, the output voltage is boosted higher than the input voltage by the energy stored in the choke coil L1. The controller116controls the switching interval of the switching element M1via the switching control circuit117so as to keep the output voltage of the boost converter113to be a fixed voltage of 410 V.

The buck-boost converter114is a chopper-type boost converter having the same configuration as that of the boost converter113. The switching control circuit118controls the voltage input to the gate of the switching element (not illustrated inFIG. 6) of the buck-boost converter114under the control of the controller116so as to change on and off of the switching element. The controller116controls the switching interval of the switching element of the buck-boost converter114via the switching control circuit118so as to keep the output voltage of the buck-boost converter114to be a fixed voltage of 330 V.

The output ends of the buck-boost converter114are put together with the output ends of the boost converter113. The DC/DC converter115is coupled to the output side of the boost converter113and the buck-boost converter114in series. The DC/DC converter115includes a transformer115a,and decreases the input voltage to 12 V and outputs the voltage. The input voltage to the DC/DC converter115is smoothed by a capacitor C2. Also, the output voltage from the DC/DC converter115is smoothed by a capacitor C3.

In this regard, the output voltage of the buck-boost converter114is determined to be a value lower than the output voltage (410 V) of the boost converter113, and further that makes the output voltage of the DC/DC converter115not lower than a predetermined value (for example, 12 V).

The controller116further has a function of detecting the input voltage of the boost converter113and the buck-boost converter114and turning on and off the boost operation of the boost converter113based on the detection result. When the controller116turns off the boost operation of the boost converter113, the controller116stops the switching operation of the switching element M1of the boost converter113.

In this regard, the controller116includes, for example, a processor and a memory, and a firmware program stored in the memory is executed by the processor so that the controller116is realized as a microcomputer that performs various kinds of processing.

Next, a description will be given of the details of on-off control of the boost converter113by the controller116. In this regard, “turning on the boost converter113” means starting the boost operation of the boost converter113. Also, “turning off the boost converter113” means stopping the boost operation of the boost converter113. As described above, this is performed by stopping the switching operation of the switching element M1of the boost converter113.

The controller116performs on-off control of the boost converter113so as to handle the following four states based on the detection result of the input voltage of the boost converter113and the buck-boost converter114.

(a) The input voltage is fixed in the range from 350 V to 380 V.

(b) The input voltage is fixed at 240 V.

(c) The input voltage drops from the range from 350 V to 380 V.

(d) The input voltage recovers from the dropped state to the range from 350 V to 380 V.

First, a description will be given of control in the state (a) with reference toFIG. 7.

FIG. 7is a diagram illustrating control in the case where an input voltage is a fixed voltage of 350 V to 380 V. In this regard, inFIG. 7, the illustrations of the switching control circuits117and118, the diode D1, and the like are omitted. Also, the input voltage Vin2is the voltage at the output stage of the inrush current prevention circuit112, which is detected by the controller116. This is almost equal to the input voltage Vin1to the PSU110.

Immediately after the PSU110is started, if the input voltage Vin2is equal to or higher than 350 V, the controller116determines that a stable power source voltage of 350 V to 380 V is supplied. In this case, as illustrated inFIG. 7, the controller116turns off the boost converter113. At this time, the boost converter113outputs a voltage equal to or higher than the input 350 V without change. Thereby, the output voltage Vout2is kept equal to or higher than 350 V. In this manner, in a state in which boosting voltage is dispensable, the boost converter113is turned off so that excessive power becomes not consumed, and thus it is possible to reduce the power loss in the PSU110.

Also, the buck-boost converter114is kept on all the time regardless of the on and off of the boost converter113. In the state illustrated inFIG. 7, the input voltage of the buck-boost converter114becomes higher than the output voltage of the buck-boost converter114, and thus a current does not flow through the buck-boost converter114. Accordingly, while the buck-boost converter114is kept in the on state, the power loss by the buck-boost converter114is kept small.

Next, a description will be given of control in the state (b) with reference toFIG. 8.

FIG. 8is a diagram illustrating control in the case where the input voltage is a fixed voltage of 240 V. In this regard, inFIG. 8, the illustrations of the switching control circuits117and118, the diode D1, and the like are omitted in the same manner asFIG. 7.

If the input voltage Vin2is lower than 350 V immediately after the PSU110has been started, the controller116determines that a stable power source voltage of 240 V is supplied. In this case, as illustrated inFIG. 8, the controller116turns on the boost converter113. The boost converter113boosts the input voltage of 240 V to a voltage equal to or higher than 350 V (410 V in the present embodiment) and outputs the voltage. Thereby, the current value output from the boost converter113becomes small so that an increase in the size of the parts of the output side (for example, the capacitor C2and the DC/DC converter115) of the boost converter113, and the occurrence of the power loss by heating from those parts, and the like are inhibited.

Also, while the buck-boost converter114is kept on, in the state illustrated inFIG. 8, the output voltage of the buck-boost converter114becomes lower than the output voltage of the boost converter113so that a current does not flow through the buck-boost converter114. Accordingly, while the buck-boost converter114is in the on state, the power loss by the buck-boost converter114is kept low.

Next, a description will be given of control in the state (c). As described in state (c), a situation in which the input voltage drops from the range of 350 V to 380 V may occur, for example, in the following cases. For example, one case is when the output voltage of the rectifier71is changed to the output voltage of the battery72. Alternatively, another case is when the power supplied to the rectifier71from the outside is not the power from the normal alternate current power source20, but the power based on natural energy, such as solar power generation, or the like.

As illustrated inFIG. 7, if the input voltage Vin2is equal to or higher than 350 V, the boost converter113is kept off. If the input voltage Vin2becomes lower than 350 V from this state, the controller116turns on the boost converter113, and causes the boost converter113to perform boost operation such that the output voltage Vout2does not drop. In this manner, in the present embodiment, the boost converter113disposed for supporting the input voltage of 240 V is also used for coping with a voltage drop at the time of the voltage input of 350 V to 380 V. Thereby, it is possible to effectively use the boost converter113.

However, even if the boost converter113is changed from off to on, it is not possible to start the boost operation until the starting is completed. Accordingly, immediately after the boost converter113is turned on, the output voltage of the boost converter113temporarily drops with a drop in the input voltage.

FIG. 9is a diagram illustrating an example of a voltage change in the case where a buck-boost converter having an output of 330 V is not coupled.FIG. 9illustrates an example of the case where the input voltage Vin2drops from 400 V to 192 V.

As illustrated inFIG. 9, it is assumed that the input voltage Vin2drops from 400 V and becomes lower than 350 V at timing T1. The controller116detects this voltage drop and changes the boost converter113from off to on. However, it is not possible for the boost converter113to the boost operation up to 410 V until the starting is completed. In this regard, the shaded area inFIG. 9indicates a transient state in which starting of the boost converter113is not completed.

Here, it is thought that the buck-boost converter114having the output of 330 V is not coupled tentatively. In this case, until the boost operation of the boost converter113is started, the output voltage Vout2drops. For example, if it is assumed that the input voltage that makes it difficult for the DC/DC converter115to output the 12 V voltage is 310 V, the output voltage Vout2drops lower than or equal to 310 V at timing T2, and the output voltage Vouti from the PSU110starts to drop. In this manner, even if the boost converter113is changed to on, there is a possibility that the output voltage Vout1of the PSU110is temporarily not kept at the rated voltage of 12 V.

On the other hand, in the present embodiment, the buck-boost converter114, which is on all the time, is coupled to the boost converter113in parallel so that the occurrence of the situation in which the output voltage Vout1drops as described above is avoided.

FIG. 10is a diagram illustrating control in the case where an input voltage has dropped. The upper part inFIG. 10illustrates the case where the input voltage has dropped from the state (a) in which the input voltage is changed from the range of 350 V to 380 V to a voltage lower than 350 V. If the controller116detects that the input voltage Vin2becomes lower than 350 V, the controller116changes the boost converter113from off to on. However, in the transient state up until the boost operation of the boost converter113is started, the output voltage Vout2drops.

On the other hand, if the input voltage Vin2has become lower than 330 V and the output voltage of the buck-boost converter114is going to be lower than 330 V, the buck-boost converter114that has been kept on starts the boost operation under the control of the controller116. At this time, a current flows through the buck-boost converter114, and thus the buck-boost converter114boosts the input voltage Vin2to 330 V. Thereby, the output voltage Vout2is kept equal to or higher than 330 V, and an excessive drop of the output voltage Vout1of the PSU110is avoided.

After that, when the starting of the boost converter113is completed, and the boost converter113has boosted the input voltage Vin2to a voltage higher than 330 V, a current flows through the boost converter113and a current does not flow through the buck-boost converter114as illustrated in the lower part inFIG. 10. The output voltage Vout2is kept a voltage equal to or higher than 350 V by the boost operation of the boost converter113.

FIG. 11is a diagram illustrating an example of a voltage change in the case where the input voltage dropped in the second embodiment.FIG. 11illustrates an example of the case where the input voltage Vin2drops from 400 V to 192 V in the same manner as inFIG. 9.

As illustrated inFIG. 11, it is assumed that the input voltage Vin2has dropped from 400 V and has become a voltage lower than 350 V at timing T11. The controller116detects this voltage drop and changes the boost converter113from off to on. It is not possible for the boost converter113to start boost operation up to 410 V until the starting is completed. However, the buck-boost converter114that is coupled in parallel with the boost converter113is kept on, and if the input voltage Vin2becomes lower than 330 V, the input voltage Vin2is boosted up to 330 V by the buck-boost converter114. As a result, the output voltage Vout1of the PSU110is kept at 12 V.

With the above-described control illustrated inFIG. 10andFIG. 11, even if the input voltage Vin2becomes lower than 350 V, it is possible to keep the output voltage Vout2at a voltage equal to or higher than 330 V. Thereby, it is possible to avoid a drop of the output voltage Vout1of the PSU110, and thus to avoid malfunction in a load circuit to which the power is supplied from the PSU110.

In this regard, although not illustrated in the figure, in the case where the input voltage further drops by a change to the battery72, or the like from the state (b), the controller116keeps the boost converter113on, and causes the boost converter113to continue to perform the boost operation. Thereby, it is possible to avoid a drop in the output voltage Vout1.

Next, a description will be given of the control by the PSU110with reference to a flowchart.

First,FIG. 12is a flowchart illustrating an example of a control procedure at the time of starting the PSU.

Step S11: The PSU110starts in accordance with the connection of the input cable to the storage device100, or the turning on the distribution board80and the turning on the breaker of the power distribution unit90. The controller116operates in the initial mode, which is an operation mode immediately after the start.

Step S12: The controller116turns on both the boost converter113and the buck-boost converter114. Thereby, the boost operation of the boost converter113and the buck-boost converter114is started.

Step S13: The controller116detects the input voltage Vin2of the boost converter113and the buck-boost converter114.

Step S14: The controller116determines whether or not the detected input voltage Vin2is equal to or higher than 350 V. If the input voltage Vin2is equal to or higher than 350 V, the processing of step S15is performed. On the other hand, if the input voltage Vin2is lower than 350 V, the processing of step S17is performed with the boost converter113kept on.

Step S15: The controller116changes the boost converter113to off.

Step S16: The controller116changes the operation mode to the normal mode. Thereby, the operation by the input voltage of 350 V to 380 V is started.

Step S17: The controller116changes the operation mode to the normal mode. Thereby, the operation by the input voltage of 240 V is started.

In this regard, after step S17is performed, the boost converter113is kept on. Thereby, if the input voltage Vin2changes to a voltage lower than 240 V, the boost converter113keeps the output voltage Vout2at a voltage equal to or higher than 350 V, and a drop of the output voltage Vout1of the PSU110is avoided.

Next,FIG. 13andFIG. 14are flowcharts illustrating an example of a control procedure after operation with an input voltage of 350 V to 380 V has been started.

Step S21: The controller116detects the input voltage Vin2of the boost converter113and the buck-boost converter114.

Step S22: The controller116determines whether or not the detected input voltage Vin2is equal to or higher than 350 V. If the input voltage Vin2is equal to or higher than 350 V, the processing of step S21is performed after a certain period of time. Thereby, while the operation is performed with the input voltage of 350 V to 380 V, the controller116monitors the input voltage Vin2at certain time intervals. On the other hand, if the input voltage Vin2is lower than 350 V, the processing of step S23is performed.

Step S23: The controller116changes the boost converter113to on.

Thereby, the boost converter113is started, but until the boost operation by the boost converter113is started with a voltage equal to or higher than 350 V, the boost operation of the buck-boost converter114keeps the output voltage Vout2at a voltage equal to or higher than 330 V. As a result, the output voltage Vout1of the PSU110is kept at 12 V in the steady state. When the starting of the boost converter113is completed, the output voltage Vout2is kept equal to or higher than 350 V by the boost operation of the boost converter113.

Step S31: The controller116detects the input voltage Vin2of the boost converter113and the buck-boost converter114.

Step S32: The controller116determines whether or not the detected input voltage Vin2is equal to or higher than 350 V. If the input voltage Vin2is lower than 350 V, the processing of step S31is performed after a certain period of time. Thereby, after the processing of step S23is performed, the controller116monitors the input voltage Vin2at certain time intervals. On the other hand, if the input voltage Vin2is boosted to equal to or higher than350, that is to say, if the voltage supply of 350 V to 380 V is returned, the processing of step S33is performed.

Step S33: The controller116changes the boost converter113to of. After this, the processing returns to step S21inFIG. 13, and the input voltage Vin2is monitored.

With the PSU110described above, in the state in which the voltage of 240 V is supplied, after the boost converter113boosted the input voltage equal to or higher than 350 V once, the DC/DC converter115converts the voltage to the power source voltage of 12 V. Thereby, it is possible to avoid the occurrence of a power loss due to an increase in the size of the circuit parts in the PSU110and heating, or the like. On the other hand, in the state in which the voltage of 350 V to 380 V is supplied, the boost converter113is turned off. Thereby, it is possible to reduce the power loss by the boost converter113.

Also, both in the state in which the voltage of 240 V is supplied, and in the state in which the voltage of 350 V to 380 V is supplied, a current does not flow through the buck-boost converter114, and thus it is possible to reduce the power loss of the buck-boost converter114that is turned on all the time.

If the input voltage drops from the state in which the voltage of 350 V to 380 V is supplied, the boost converter113is changed to on in order to boost the voltage to 350 V. At this time, until the starting of the boost converter113is completed, the output voltage Vout2is kept equal to or higher than 330 V by the buck-boost converter114that has been kept on before that time. Thereby, it is possible to inhibit a voltage drop in the output voltage Vout1to the extent that the output voltage Vout1of the PSU110does not drop.