Patent Publication Number: US-2015073616-A1

Title: Power supply device, power supply system, and electronic device

Description:
BACKGROUND 
     1. Field 
     The present disclosure relates to a power supply device, a power supply system, and an electronic device. 
     2. Description of the Related Art 
     To supply power, a method of using a centralized generator and a method of using a distributed generator are available. In the case of using a centralized generator, power that has been generated using a large power generation unit is transmitted via a power network and is then used by individual consumers. Thus, if part of the power network breaks down, for example, the consumers may become unable to use the power (power failure). 
     On the other hand, in the case of using a distributed generator, power that has been generated using small power generation units provided near individual consumers is used by the consumers without via a power network. Thus, even if a power failure occurs, the individual consumers are able to use the power generated by the distributed generator. 
     When power supplied from the power network is available, the distributed generator operates such that the frequency and phase thereof are the same as those of the power network (grid connected operation). However, when a power failure occurs, the distributed generator operates independently of the power network (autonomous operation). 
     In the distributed generator, such as small power generation units, the amount of power to be generated is limited, and thus the power to be supplied to a load may be insufficient. 
     Japanese Unexamined Patent Application Publication No. 2008-125295 suggests a device that monitors power consumption of a load, such as an electronic device, and selectively disconnects the load on the basis of the relationship between the power consumption and the power that can be supplied to the load (achieves a balance between supplied power and consumed power). However, installation of such a device may involve an increase in cost. 
     SUMMARY 
     Accordingly, an embodiment of the present disclosure provides a power supply device, such as a distributed generator, and an electronic device that are capable of achieving a balance between supplied power and consumed power without monitoring power consumption in a load. 
     According to an aspect of the present disclosure, there is provided a power supply device including a power inverter, an operation mode switching unit, and an output information control unit. The power inverter is configured to receive a DC power supplied from a DC power source and output an AC power. The operation mode switching unit is configured to switch between grid connected operation and autonomous operation that are performed by the power supply device. The grid connected operation is operation in which power is supplied from an AC power network and a DC power source to a load. The autonomous operation is operation in which the power supply device is disconnected from the AC power network and power is supplied from the DC power source to the load. The output information control unit is configured to control output information about the AC power output from the power inverter. 
     According to another aspect of the present disclosure, there is provided a power supply system including a first power supply device and a second power supply device. The first power supply device is configured to perform grid connected operation and autonomous operation. The grid connected operation is operation in which power is supplied from an AC power network and a DC power source to a load. The autonomous operation is operation in which the first power supply device is disconnected from the AC power network and power is supplied from the DC power source to the load. The first power supply device includes a first power inverter, an operation mode switching unit, and an output information control unit. The first power inverter is configured to receive a DC power supplied from the DC power source and output an AC power. The operation mode switching unit is configured to switch between the grid connected operation and the autonomous operation. The output information control unit is configured to control output information about the AC power output from the first power inverter. The output information control unit changes the output information from setting information that is preset during the grid connected operation, before the grid connected operation is switched to the autonomous operation, or when the grid connected operation is switched to the autonomous operation, or after the grid connected operation is switched to the autonomous operation. The second power supply device adjusts an amount of power to be supplied to the load in accordance with the output information. 
     According to another aspect of the present disclosure, there is provided an electronic device including a monitoring unit and a power consumption adjusting unit. The monitoring unit is configured to monitor output information about an AC power supplied to the electronic device. The power consumption adjusting unit is configured to adjust power consumption in accordance with the output information monitored by the monitoring unit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating a schematic configuration of a power supply device according to an embodiment of the present disclosure; 
         FIG. 2  is a diagram illustrating a detailed configuration of a power conditioner; 
         FIG. 3  is a diagram illustrating a detailed configuration of an electronic device; 
         FIG. 4  is a flowchart illustrating a process executed by the power conditioner; 
         FIG. 5  is a flowchart illustrating a process executed by the electronic device; 
         FIG. 6  is a flowchart illustrating a process executed by the power conditioner during autonomous operation; 
         FIG. 7  is a flowchart illustrating a process executed by the electronic device during autonomous operation; 
         FIG. 8  is a diagram illustrating a schematic configuration of a power supply device; 
         FIG. 9  is a diagram illustrating a detailed configuration of an AC-input-type power storage device; 
         FIG. 10  is a flowchart illustrating another process executed by the power conditioner during autonomous operation; 
         FIG. 11  is a flowchart illustrating a process executed by the AC-input-type power storage device during autonomous operation; 
         FIG. 12  is a diagram illustrating a schematic configuration of a power supply device; 
         FIG. 13  is a flowchart illustrating a process executed by a distribution board; 
         FIG. 14  is a diagram illustrating a schematic configuration of a power supply device; 
         FIG. 15  is a flowchart illustrating a process executed by a power conditioner; 
         FIG. 16  is a flowchart illustrating a process executed by the power conditioner in the case of cancelling frequency control; 
         FIG. 17  is a flowchart illustrating a process executed by an electronic device in the case of cancelling adjustment of power consumption; 
         FIG. 18  is a diagram illustrating a schematic configuration of a power supply system; 
         FIG. 19  is a flowchart illustrating a process executed by a fuel-cell-mounted power supply device; and 
         FIG. 20  is a flowchart illustrating a process executed by a power-storage-device-mounted power supply device during autonomous operation. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, embodiments of the present disclosure will be described in detail with reference to the attached drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and the description thereof is not repeated. 
     First Embodiment 
       FIG. 1  is a diagram illustrating a schematic configuration of a power supply device  100  according to an embodiment of the present disclosure. 
     The power supply device  100  includes a solar battery  130 , a power conditioner  110 , and a remote controller  120 . The power conditioner  110  serves as a power inverter that converts a direct current (DC) power generated by the solar battery  130  to an alternating current (AC) power and outputs the AC power. The remote controller  120  is used by a user to transmit information to or receive information from the power conditioner  110 . 
     The power conditioner  110  includes two output terminals: a first output terminal  111  and a second output terminal  112 . 
     The first output terminal  111  is connected to a commercial power network  300 . The commercial power network  300  is an AC power network. Here, a certain voltage and a certain frequency of the AC power supplied from the AC power network are AC 100 V and 60 Hz, or may be AC 200 V and 50 Hz. The power conditioner  110  operates in conjunction with the commercial power network  300  (grid connected operation). During grid connected operation, the frequency and phase output from the commercial power network  300  are equal to those outputs from the power conditioner  110 . 
     During grid connected operation, an electronic device  200  serving as a load that consumes power is connected to the first output terminal  111  (and the commercial power network  300 ), and uses the power supplied therefrom. The electronic device  200  is connected to the second output terminal  112  if necessary. 
       FIG. 2  is a diagram illustrating a detailed configuration of the power conditioner  110 . The power conditioner  110  includes a DC/DC converter  113 , a DC/AC inverter  114  (power inverter), a relay  115 , and a control unit  116 . The DC/DC converter  113  efficiently obtains a DC power generated by the solar battery  130  (MPPT control). The DC/AC inverter  114  converts the DC power obtained by the DC/DC converter  113  from the solar battery  130  to an AC power and outputs the AC power. The relay  115  switches between a connection of the DC/AC inverter  114  to the first output terminal  111  and a connection of the DC/AC inverter  114  to the second output terminal  112 . The relay  115  is switched, by an operation mode switching unit  116 A (described below), to the first output terminal  111  side when grid connected operation is performed, and to the second output terminal  112  side when autonomous operation (described below) is performed. 
     The control unit  116  includes the operation mode switching unit  116 A, a frequency control unit  116 B, a voltage monitoring unit  116 C, and a microcomputer  116 D. The operation mode switching unit  116 A switches the operation mode (operation) of the power conditioner  110  to either of grid connected operation and autonomous operation. The frequency control unit  116 B controls the frequency of an AC power (hereinafter it may be simply referred to as a “frequency”) output from the DC/AC inverter  114 . The voltage monitoring unit  116 C monitors the output voltage from the DC/AC inverter  114 . The microcomputer  116 D controls the operation mode switching unit  116 A, the frequency control unit  116 B, and the voltage monitoring unit  116 C. 
     With the above-described configuration, the power supply device  100  is capable of converting a DC power generated by the solar battery  130  to an AC power of a certain frequency, and then outputting the AC power to the first output terminal  111  or the second output terminal  112 . 
       FIG. 3  illustrates a detailed configuration of the electronic device  200 . The electronic device  200  includes a power consuming unit  201 , which consumes an AC power supplied to the electronic device  200 , and a control unit  202 . The control unit  202  includes a power consumption adjusting unit  203 , a frequency monitoring unit  204 , and a microcomputer  205 . The power consumption adjusting unit  203  adjusts the power consumption of the power consuming unit  201 . The frequency monitoring unit  204  monitors the frequency of an AC power supplied to the electronic device  200 . The microcomputer  205  controls the power consumption adjusting unit  203  and the frequency monitoring unit  204 . The power consuming unit  201  may consume a DC power that has been converted from an AC power. Adjustment of power consumption includes stopping of operation of the electronic device  200 . 
     The electronic device  200  may be, for example, a lighting device, a liquid crystal display, or a refrigerator. Alternatively, the electronic device  200  may be an induction motor whose rotation rate changes in proportion to the frequency of the AC power supplied thereto. In that case, the control unit  202  is not necessary. 
     With the above-described configuration, the electronic device  200  is capable of adjusting power consumption (including stopping of operation) in accordance with the frequency of the AC power supplied thereto. 
     Referring back to  FIG. 1 , the electronic device  200  is designed to operate typically using power supplied from the commercial power network  300  (AC 100 V, 60 Hz). Thus, a user can use the electronic device  200  by connecting the electronic device  200  to the first output terminal  111  during grid connected operation. 
     On the other hand, when the power of the commercial power network  300  is not available (when power failure occurs), the power conditioner  110  stops outputting an AC power to the first output terminal  111 . Instead, the power conditioner  110  outputs an AC power to the second output terminal  112 . At this time, the power conditioner  110  operates without being interconnected to the commercial power network  300  (autonomous operation). The user can use the electronic device  200  by connecting the electronic device  200  to the second output terminal  112 . 
     During autonomous operation, the electronic device  200  operates using only the power supplied from the power supply device  100 , but the power is limited to be equal to or smaller than the power generated by the solar battery  130 . Under such a limit, the power consumption of the power consuming unit  201  may be decreased during autonomous operation in order to suppress the occurrence of lack of power supplied to the electronic device  200 . 
     In the power supply device  100 , when grid connected operation is switched to autonomous operation using the frequency control unit  116 B, the frequency of the AC power to be supplied to the electronic device  200  is decreased from a frequency that is preset as setting information when grid connected operation is performed. For example, the setting information is a frequency supplied from the commercial power network  300  (for example, 60 Hz). 
     When grid connected operation is switched to autonomous operation, the frequency control unit  116 B decreases the frequency of the AC power to be supplied to the electronic device  200  from the frequency of the AC power supplied from the commercial power network  300  (for example, from 60 Hz to 59 Hz). In a case where the electronic device  200  is an electronic device whose rotation rate changes in proportion to a frequency, such as an induction motor, the rotation rate decreases as the frequency decreases, and also power consumption decreases. 
     A power conditioner converts a DC power to an AC power (the frequency is the same as that of a commercial power network, for example, 60 Hz) by controlling inner pulses (PWM control) and outputs the AC power. The power conditioner  110  according to the first embodiment of the present disclosure adjusts a frequency parameter of inner pulses, and is thereby capable of converting a DC power generated by the solar battery  130  to an AC power of a frequency that is different from the frequency of the commercial power network (for example, 59 Hz), and outputting the AC power. 
     In a case where the electronic device  200  is a lighting device or the like, the power consumption adjusting unit  203  decreases the power consumption of the power consuming unit  201  as the frequency of the AC power supplied thereto decreases from 60 Hz. Specifically, the power consumption adjusting unit  203  decreases the illuminance of a lighting device or a backlight of a liquid crystal display, or increases the setting temperature of a refrigerator. 
       FIG. 4  is a flowchart illustrating a process executed by the power conditioner  110 . Here, it is assumed that the electronic device  200  is using the power of the commercial power network  300 . 
     Referring to  FIGS. 1 and 4 , the power conditioner  110  is performing grid connected operation (step S 101 ). 
     The power conditioner  110  determines whether or not power failure has occurred (whether or not the power of the commercial power network  300  is not available) (step S 102 ). Whether or not power failure has occurred is determined by, for example, detecting a change in voltage or current in the first output terminal  111 . 
     If power failure has not occurred (NO in step S 102 ), the power conditioner  110  repeats step S 102 . If power failure has occurred (YES in step S 102 ), the power conditioner  110  stops grid connected operation (step S 103 ). 
     After stopping grid connected operation, the power conditioner  110  notifies a user that power failure has occurred via the remote controller  120 . Accordingly, the user recognizes the occurrence of power failure, and connects the electronic device  200  to the second output terminal  112  to use the electronic device  200 . 
     The power conditioner  110  that has stopped grid connected operation sets the frequency of the AC power to be output to the second output terminal  112  to 59 Hz and starts autonomous operation (step S 104 ). An instruction to start autonomous operation may be provided to the power conditioner  110  by the user through an operation of the remote controller  120 . 
     The power conditioner  110  that has started autonomous operation determines whether or not power failure continues (step S 105 ). If power failure continues (YES in step S 105 ), the power conditioner  110  repeats step S 105 . If power failure has ended (NO in step S 105 ), the power conditioner  110  stops autonomous operation and starts grid connected operation (step S 106 ). The user is notified of the recovery from power failure via the remote controller  120 . Accordingly, the user disconnects the electronic device  200  from the second output terminal  112  and connects the electronic device  200  to the first output terminal  111  (commercial power network  300 ). 
     The power conditioner  110  that has started grid connected operation returns to step S 102 . 
       FIG. 5  is a flowchart illustrating a process executed by the electronic device  200 . 
     Referring to  FIGS. 3 and 5 , the electronic device  200  monitors the frequency of the AC power supplied thereto (step S 201 ), and determines whether or not the monitored frequency is lower than 60 Hz (step S 202 ). 
     If the frequency is higher than or equal to 60 Hz (NO in step S 202 ), the electronic device  200  operates without decreasing power consumption (normally operates) (step S 203 ). On the other hand, if the frequency is lower than 60 Hz (YES in step S 202 ), the electronic device  200  operates with decreased power consumption (step S 204 ). 
     After step S 203  or S 204 , the electronic device  200  returns to step S 201 . 
     In this way, the frequency of the AC power to be supplied to the electronic device  200  by the power supply device  100  is set to be lower than the frequency of the commercial power network  300  during autonomous operation. Accordingly, the power consumption of the electronic device  200  may be decreased. 
     In the above-described first embodiment, the frequency control unit  116 B controls the frequency of the AC power output from the DC/AC inverter  114 . Alternatively, the frequency control unit  116 B may be replaced by an output information control unit that controls output information other than the AC power output from the DC/AC inverter  114 . 
     The output information may be, for example, the frequency of the AC power output from the DC/AC inverter  114 , or the AC waveform, voltage, or current of the AC power output from the DC/AC inverter  114 . 
     In a case where an AC waveform is used as output information, for example, an AC waveform control unit is used as an output information control unit, instead of the frequency control unit  116 B. An AC waveform may be controlled by, for example, changing the duty ratio of a semiconductor switch included in an inverter circuit that constitutes a DC/AC inverter, or may be controlled by combining the AC waveform of the AC power output from the DC/AC inverter  114  and another waveform to transform the AC waveform. 
     In the above-described first embodiment, the power conditioner  110  decreases the frequency of the AC power to be supplied to the electronic device  200  from 60 Hz during autonomous operation (for example, 59 Hz), but the embodiment is not limited thereto. For example, the power supply device  100  may increase the frequency of the AC power during autonomous operation from 60 Hz (for example, 61 Hz). In this case, in the electronic device  200 , the power consumption adjusting unit  203  decreases the power consumption of the power consuming unit  201  as the frequency of the AC power supplied thereto increases. 
     The setting information is not limited to the frequency that is supplied from the commercial power network  300  during grid connected operation. For example, in a case where an AC waveform control unit is used as an output information control unit, the setting information may be an AC waveform of an AC power supplied from an AC power network during grid connected operation. 
     In the above-described first embodiment, the timing at which the output information control unit changes output information from setting information is the timing at which grid connected operation is switched to autonomous operation, but the embodiment is not limited thereto. The timing at which output information is changed from setting information may be the timing at which the electronic device  200  is notified that grid connected operation is to be switched or has been switched to autonomous operation. Specifically, the timing may be before grid connected operation is switched to autonomous operation or after grid connected operation is switched to autonomous operation. 
     In the above-described first embodiment, the user connects the electronic device  200  to the first output terminal  111  or the second output terminal  112  in accordance with switching of the operation mode of the power conditioner  110 , but the embodiment is not limited thereto. For example, a distribution board may be provided between the commercial power network  300  and the power supply device  100 . In this case, when the power conditioner  110  performs autonomous operation, the commercial power network  300  and the power supply device  100  may be separated (disconnected) from each other by the distribution board. Accordingly, the relay  115 , which switches between a connection of the DC/AC inverter  114  to the first output terminal  111  and a connection of the DC/AC inverter  114  to the second output terminal  112  for grid connected operation and autonomous operation ( FIG. 2 ) becomes unnecessary. That is, the first output terminal  111  and the second output terminal  112  may be combined into a single output terminal. 
     Second Embodiment 
     In the first embodiment, the power consumption of the electronic device  200  is merely decreased during autonomous operation. In contrast, in a second embodiment, a frequency is controlled to achieve a balance between the power supplied from the power supply device  100  and the power consumed by the electronic device  200 . 
     Referring to  FIG. 1 , the electronic device  200  is designed to operate at AC 100 V and 60 Hz. Thus, if the power supplied from the power supply device  100  is substantially equal to the power consumed by the electronic device  200  (if both are balanced), the AC voltage of the supplied power is substantially 100 V. On the other hand, if the balance is lost, the AC voltage increases or decreases from 100 V. Specifically, the electronic device  200  always tries to draw a constant current. Thus, if the power supplied from the power supply device  100  is smaller than the power consumed by the electronic device  200 , overload occurs and the AC voltage decreases. 
     The AC voltage of the power supplied from the power supply device  100  is equal to the voltage monitored by the voltage monitoring unit  116 C. Thus, a frequency is controlled so that the AC voltage monitored by the voltage monitoring unit  116 C becomes close to a certain voltage of AC 100 V, and thereby the balance between supplied power and consumed power may be achieved. The certain voltage is an AC voltage supplied from an AC power network during grid connected operation. A certain voltage of AC 100 V in an actual AC power network, for example, in a commercial power network, includes a certain margin (for example, AC 95 V to AC 105 V). Thus, in a case where the AC voltage is 95 V or higher, for example, it may be considered that the supplied power and the consumed power are substantially balanced. 
     In a case where the AC voltage of the supplied power is lower than 95 V, the power supply device  100  may decrease the frequency. Accordingly, the power supplied from the power supply device  100  may be maximally used without causing lack of supplied power due to overload. 
     On the other hand, the electronic device  200  gradually decreases the power consumption as the frequency decreases to be lower than the certain frequency of 60 Hz. Specifically, the electronic device  200  operates in three modes: power consumption suppression mode 1 to power consumption suppression mode 3. The amount of decrease in power consumption is the largest in the power consumption suppression mode 1, and becomes smaller in the order of the power consumption suppression mode 2 and the power consumption suppression mode 3. The certain frequency is the frequency of the AC power supplied from the AC power network during grid connected operation. 
       FIG. 6  is a flowchart illustrating a process executed by the power conditioner  110  during autonomous operation. 
     Referring to  FIGS. 1 ,  2 , and  6 , the power conditioner  110  sets the frequency to 57 Hz at the start of autonomous operation (step S 301 ). 
     Subsequently, the power conditioner  110  measures an output current (step S 302 ). The output current is measured using, for example, a current sensor (not illustrated) provided in the DC/AC inverter  114 . 
     If there is no output current flowing (NO in step S 302 ), the power conditioner  110  determines that the electronic device  200  (load) is not connected, and repeats step S 302 . 
     If there is an output current flowing (YES in step S 302 ), the power conditioner  110  determines whether or not an output voltage is lower than 95 V (step S 303 ). The output voltage is measured using, for example, a voltage sensor (not illustrated) provided in the DC/AC inverter  114 . 
     If the output voltage is lower than 95 V (YES in step S 303 ), the power conditioner  110  stops operation (step S 304 ). 
     If the output voltage is higher than or equal to 95 V (NO in step S 303 ), the power conditioner  110  determines whether or not the frequency is 60 Hz (step S 305 ). If the frequency is 60 Hz (YES in step S 305 ), the power conditioner  110  continues autonomous operation at the frequency (step S 309 ). On the other hand, if the frequency is not 60 Hz (NO in step S 305 ), the power conditioner  110  increases the frequency by 0.5 Hz (step S 306 ), and determines again whether or not the output voltage is lower than 95 V (step S 307 ). If the output voltage at the time is higher than or equal to 95 V (NO in step S 307 ), the power conditioner  110  returns to step S 305 . If the output voltage at the time is lower than 95 V (YES in step S 307 ), the power conditioner  110  decreases the frequency by 0.5 Hz (step S 308 ), and continues autonomous operation at the frequency (step S 309 ). 
     After step S 309 , the power conditioner  110  determines again whether or not the output voltage is lower than 95 V (step S 310 ). In step S 310 , if the output voltage is lower than 95 V (YES in step S 310 ), the power conditioner  110  proceeds to step S 311 . In step S 311 , the power conditioner  110  determines whether or not the frequency is 57 Hz. If the frequency is 57 Hz (YES in step S 311 ), the power conditioner  110  stops operation (step S 304 ). If the frequency is not 57 Hz (NO in step S 311 ), the power conditioner  110  returns to step S 308  to decrease the frequency. In step S 310 , if the output voltage is higher than or equal to 95 V (NO in step S 310 ), the power conditioner  110  continues autonomous operation for a certain period (At) in that state (step S 312 ). After that, the power conditioner  110  determines whether or not a certain period (Ta) has elapsed from step S 309  (step S 313 ). 
     If the certain period (Ta) has not elapsed (NO in step S 313 ), the power conditioner  110  returns to step S 309 . On the other hand, if the certain period (Ta) has elapsed (YES in step S 313 ), the power conditioner  110  returns to step S 305 . 
       FIG. 7  is a flowchart illustrating a process executed by the electronic device  200  during autonomous operation. 
     Referring to  FIGS. 3 and 7 , the electronic device  200  monitors the frequency of the AC power supplied thereto (step S 401 ), and determines whether or not the frequency is lower than 60 Hz (step S 402 ). 
     If the frequency is higher than or equal to 60 Hz (NO in step S 402 ), the electronic device  200  operates without decreasing power consumption (normally operates) (step S 403 ), and returns to step S 401 . On the other hand, if the frequency is lower than 60 Hz (YES in step S 402 ), the electronic device  200  determines whether or not the frequency is lower than 57 Hz (step S 404 ). 
     If the frequency is lower than 57 Hz (YES in step S 404 ), the electronic device  200  operates in the power consumption suppression mode 1 (step S 405 ). On the other hand, if the frequency is higher than or equal to 57 Hz (NO in step S 404 ), the electronic device  200  determines whether or not the frequency is lower than 58 Hz (step S 406 ). 
     If the frequency is lower than 58 Hz (YES in step S 406 ), the electronic device  200  operates in the power consumption suppression mode 2 (step S 407 ). On the other hand, if the frequency is higher than or equal to 58 Hz (NO in step S 406 ), the electronic device  200  operates in the power consumption suppression mode 3 (step S 408 ). 
     With use of the power supply device  100  and the electronic device  200  in combination, if supplied power lacks and the AC voltage becomes lower than 95 V, the power supply device  100  decreases the frequency and accordingly the electronic device  200  decreases the power consumption. As a result, lack of supplied power is overcome, the AC voltage recovers to be 95 V or higher, and the supplied power and consumed power are balanced. 
     In the above-described second embodiment, the electronic device  200  gradually decreases the power consumption as the frequency decreases from 60 Hz, but the embodiment is not limited thereto. For example, the electronic device  200  may decrease the power consumption as the frequency increases from 60 Hz. For example, in  FIG. 7 , it may be determined in step S 402  whether or not the frequency is higher than 60 Hz, it may be determined in step S 404  whether or not the frequency is higher than 63 Hz, and it may be determined in step S 406  whether or not the frequency is higher than 62 Hz, and power consumption suppression modes corresponding to the individual frequencies may be set. That is, the electronic device  200  decreases the power consumption in a case where the frequency increases or decreases from 60 Hz, and increases the power consumption in a case where the frequency becomes close to 60 Hz. 
     Third Embodiment 
     A third embodiment relates to charging of extra power. 
       FIG. 8  is a diagram illustrating a schematic configuration of a power supply device  100 A. The power supply device  100 A is the same as the power supply device  100  illustrated in  FIG. 1  except that the power supply device  100 A includes an AC-input-type power storage device  140 . 
     The AC-input-type power storage device  140  is connected to the second output terminal  112  of the power conditioner  110 . 
       FIG. 9  is a diagram illustrating a detailed configuration of the AC-input-type power storage device  140 . The AC-input-type power storage device  140  includes a storage battery  141 , a bidirectional DC/AC inverter  142 , and a charge/discharge controller  143 . The storage battery  141  is capable of being charged with or discharging a DC power. The DC/AC inverter  142  converts the DC power of the storage battery  141  to an AC power and outputs the AC power, and also converts the AC power of the power conditioner  110  to a DC power to charge the storage battery  141 . 
     The charge/discharge controller  143  includes a frequency monitoring unit  144 , a charge/discharge control unit  145 , and a microcomputer  146 . The frequency monitoring unit  144  monitors the frequency of an output from the DC/AC inverter  142 . The charge/discharge control unit  145  controls charge and discharge of the storage battery  141  by controlling the DC/AC inverter  142 . The microcomputer  146  controls the frequency monitoring unit  144  and the charge/discharge control unit  145 . 
     With the above-described configuration, the AC-input-type power storage device  140  is capable of performing charge and discharge while monitoring the frequency of the AC power of the power conditioner  110 . 
     In a case where the power generated by the solar battery  130  of the power supply device  100 A is larger than the power consumed by the electronic device  200 , extra power is generated in the power supply device  100 A. 
     Therefore, in the third embodiment, the power supply device  100 A is configured to be capable of setting a frequency to be higher than 60 Hz (60+a Hz), and the AC-input-type power storage device  140  is charged at the frequency. 
       FIG. 10  is a flowchart illustrating another process executed by the power conditioner  110  during autonomous operation. Steps S 501  and S 502  are the same as steps S 301  and S 302  in  FIG. 6 , and thus a description will be given below from step S 503 . 
     Referring to  FIGS. 1 ,  8 , and  10 , if an output voltage is lower than 95 V (YES in step S 503 ), the power conditioner  110  stops operation (step S 504 ). 
     If the output voltage is higher than or equal to 95 V (NO in step S 503 ), the power conditioner  110  determines whether or not the frequency is 60+a Hz (step S 505 ). If the frequency is 60+a Hz (YES in step S 505 ), the power conditioner  110  continues autonomous operation at the frequency (step S 509 ). On the other hand, if the frequency is not 60+a Hz (NO in step S 505 ), the power conditioner  110  increases the frequency by 0.5 Hz (step S 506 ), and determines again whether or not the output voltage is lower than 95 V (step S 507 ). If the output voltage at the time is higher than or equal to 95 V (NO in step S 507 ), the power conditioner  110  returns to step S 505 . If the output voltage at the time is lower than 95 V (YES in step S 507 ), the power conditioner  110  decreases the frequency by 0.5 Hz (step S 508 ), and continues autonomous operation at the frequency (step S 509 ). 
     After step S 509 , the power conditioner  110  determines again whether or not the output voltage is lower than 95 V (step S 510 ). In step S 510 , if the output voltage is lower than 95 V (YES in step S 510 ), the power conditioner  110  proceeds to step S 511 . In step S 511 , the power conditioner  110  determines whether or not the frequency is 57 Hz. If the frequency is 57 Hz (YES in step S 511 ), the power conditioner stops operation (step S 504 ). If the frequency is not 57 Hz (NO in step S 511 ), the power conditioner  110  continues autonomous operation for a certain period (Δt) in that state (step S 512 ). After that, the power conditioner  110  determines whether or not a certain period (Ta) has elapsed from step S 509  (step S 513 ). 
     If the certain period (Ta) has not elapsed (NO in step S 513 ), the power conditioner  110  returns to step S 509 . On the other hand, if the certain period (Ta) has elapsed (YES in step S 513 ), the power conditioner  110  returns to step S 505 . 
       FIG. 11  is a flowchart illustrating a process executed by the AC-input-type power storage device  140  during autonomous operation. 
     Referring to  FIGS. 9 and 11 , the AC-input-type power storage device  140  monitors the frequency of the AC power supplied thereto (step S 601 ), and determines whether or not the frequency is higher than 57 Hz and is lower than 60+α Hz (step S 602 ). 
     If the frequency is higher than 57 Hz and is lower than 60+α Hz (YES in step S 602 ), the AC-input-type power storage device  140  does not perform charge (step S 603 ), and returns to step S 601 . 
     On the other hand, if the frequency is lower than or equal to 57 Hz or is higher than or equal to 60+α Hz (NO in step S 602 ), the AC-input-type power storage device  140  determines whether or not the frequency is higher than 60+α Hz (step S 604 ). If the frequency is higher than 60+α Hz (YES in step S 604 ), the AC-input-type power storage device  140  starts charge (step S 605 ). If the frequency is lower than or equal to 60+α Hz (NO in step S 604 ), the AC-input-type power storage device  140  starts discharge (step S 606 ). 
     After step S 605  or S 606 , the AC-input-type power storage device  140  returns to step S 601 . 
     Accordingly, extra power of the power supply device  100 A is used to charge the AC-input-type power storage device  140 , and thus the power generated by the solar battery  130  may be maximally used in an effective manner. 
     In the above-described third embodiment, the AC-input-type power storage device  140  starts charge when the frequency increases from 60 Hz, but the embodiment is not limited thereto. For example, the AC-input-type power storage device  140  may start charge when the frequency decreases from 60 Hz (for example, 60−α Hz). That is, the AC-input-type power storage device  140  performs charge when the frequency increases or decreases from 60 Hz. 
     Fourth Embodiment 
     A fourth embodiment relates to control of a connection state between a power conditioner and an electronic device. 
       FIG. 12  is a diagram illustrating a schematic configuration of a power supply device  100 B. The power supply device  100 B is the same as the power supply device  100  illustrated in  FIG. 1  except that the power supply device  100 B includes a distribution board  150 . The electronic device  200 A illustrated in  FIG. 12  includes a plurality of electronic devices (electronic devices  200 A_ 1  to  200 A_ 5 ). 
     The distribution board  150  is provided between (the second output terminal  112  of) the power conditioner  110  and the electronic device  200 A. The distribution board  150  includes relays  151  to  155 , which are provided between the power conditioner  110  and the electronic devices  200 A_ 1  to  200 A_ 5 , and a control unit  156 . The control unit  156  includes a frequency monitoring unit  157 , a relay switching unit  158 , and a microcomputer  159 . The frequency monitoring unit  157  monitors the frequency of the AC power supplied from the power conditioner  110 . The relay switching unit  158  switches between open and close states (on and off states) of the relays  151  to  155 . The microcomputer  159  controls the frequency monitoring unit  157  and the relay switching unit  158 . 
     With the above-described configuration, the distribution board  150  is capable of controlling the connection state between the power conditioner  110  and the electronic device  200 A in accordance with a frequency. Here, the connection state means a combination of some of the electronic devices  200 A_ 1  to  200 A_ 5  connected to the power conditioner  110 . 
     The distribution board  150  assigns the priority order (1 to 5) to the electronic devices  200 A_ 1  to  200 A_ 5 . Also, the distribution board  150  switches the relays  151  to  155  so that the electronic device of the highest priority is connected to the power conditioner  110  at a frequency of 58 Hz or higher, the electronic device of the second highest priority is connected to the power conditioner  110  at a frequency of 58.5 Hz or higher, the electronic device of the third highest priority is connected to the power conditioner  110  at a frequency of 59 Hz or higher, the electronic device of the fourth highest priority is connected to the power conditioner  110  at a frequency of 59.5 Hz or higher, and the electronic device of the fifth highest priority is connected to the power conditioner  110  at a frequency of 60 Hz or higher. 
       FIG. 13  is a flowchart illustrating a process executed by the distribution board  150 . 
     Referring to  FIGS. 12 and 13 , the distribution board  150  monitors the frequency of the AC power output from the power conditioner  110  (step S 701 ), and determines whether or not the frequency is lower than 60 Hz (step S 702 ). 
     If the frequency is higher than or equal to 60 Hz (NO in step S 702 ), the distribution board  150  performs control so that all the relays  151  to  155  are turned on (step S 703 ). On the other hand, if the frequency is lower than 60 Hz (YES in step S 702 ), the distribution board  150  determines whether or not the frequency is lower than 59.5 Hz (step S 704 ). 
     If the frequency is higher than or equal to 59.5 Hz (NO in step S 704 ), the distribution board  150  performs control so that only the relay  155  is turned off (step S 705 ). On the other hand, if the frequency is lower than 59.5 Hz (YES in step S 704 ), the distribution board  150  determines whether or not the frequency is lower than 59 Hz (step S 706 ). 
     If the frequency is higher than or equal to 59 Hz (NO in step S 706 ), the distribution board  150  performs control so that only the relays  154  and  155  are turned off (step S 707 ). On the other hand, if the frequency is lower than 59 Hz (YES in step S 706 ), the distribution board  150  determines whether or not the frequency is lower than 58.5 Hz (step S 708 ). 
     If the frequency is higher than or equal to 58.5 Hz (NO in step S 708 ), the distribution board  150  performs control so that only the relays  153 ,  154 , and  155  are turned off (step S 709 ). On the other hand, if the frequency is lower than 58.5 Hz (YES in step S 708 ), the distribution board  150  determines whether or not the frequency is lower than 58 Hz (step S 710 ). 
     If the frequency is higher than or equal to 58 Hz (NO in step S 710 ), the distribution board  150  performs control so that only the relays  152 ,  153 ,  154 , and  155  are turned off (step S 711 ). On the other hand, if the frequency is lower than 58 Hz (YES in step S 710 ), the distribution board  150  performs control so that all the relays  151  to  155  are turned off (step S 712 ). 
     Here, an electronic device having a relatively great necessity, such as a lighting device, may be assigned as an electronic device of high priority (the highest priority or approximate thereto). Accordingly, such an electronic device may be preferentially used over another electronic device (for example, a liquid crystal display). 
     In the above-described fourth embodiment, the distribution board  150  appropriately controls the connection state between the power conditioner  110  and the electronic device  200 A when the frequency is lower than or equal to 60 Hz, but the embodiment is not limited thereto. For example, the distribution board  150  may appropriately control the connection state between the power conditioner  110  and the electronic device  200 A when the frequency is higher than 60 Hz. For example, the distribution board  150  may switch the relays  151  to  155  so that the electronic device of the highest priority is connected to the power conditioner  110  at a frequency of 62 Hz or lower, the electronic device of the second highest priority is connected to the power conditioner  110  at a frequency of 61.5 Hz or lower, the electronic device of the third highest priority is connected to the power conditioner  110  at a frequency of 61 Hz or lower, the electronic device of the fourth highest priority is connected to the power conditioner  110  at a frequency of 60.5 Hz or lower, and the electronic device of the fifth highest priority is connected to the power conditioner  110  at a frequency of 60 Hz or lower, among the electronic devices  200 A_ 1  to  200 A_ 5 . 
     Fifth Embodiment 
     A fifth embodiment relates to mounting of a power storage device. 
       FIG. 14  illustrates a schematic configuration of a power supply device  100 C. The power supply device  100 C is the same as the power supply device  100  illustrated in FIG.  1  except that the power supply device  100 C includes a power storage device  160  and a power conditioner  110 A corresponding to the power storage device  160 . 
     The power storage device  160  is capable of being charged with power of the solar battery  130  or the commercial power network  300  obtained via the power conditioner  110 A. Also, the power conditioner  110 A is capable of outputting the power stored in the power storage device  160  as AC power. Further, the power conditioner  110 A and the power storage device  160  are capable of communicating with each other, and the power conditioner  110 A is capable of obtaining information about residual capacity (state of charge (SOC)) of the power storage device  160 . 
     With the above-described configuration, the power supply device  100 C is capable of supplying not only the power generated by the solar battery  130  but also the power stored in the power storage device  160 , which is an AC power, to the electronic device  200 . 
     The amount of power that the power supply device  100 C is capable of supplying to the electronic device  200  also depends on the SOC of the power storage device  160 . Thus, the power consumption of the electronic device  200  may be adjusted in accordance with the SOC of the power storage device  160 . 
     Thus, for example, the frequency may be set to 59 Hz in a case where the SOC is 90% or more, and the frequency may be decreased as the SOC decreases (the frequency may be set to 57 Hz in a case where the SOC is 10% or less). Accordingly, the power consumption of the electronic device  200  may be adjusted in accordance with the SOC. Also, information about the SOC of the power storage device  160  may be obtained only by detecting the frequency of the output power of the power conditioner  110 A, and the information may be displayed on a display (SOC monitor  121 ). 
       FIG. 15  is a flowchart illustrating a process executed by the power conditioner  110 A. Steps S 801  to S 803  are the same as steps S 101  to S 103  in  FIG. 4 , and thus the description is not repeated here. Hereinafter, a description will be given from step S 804 . 
     Referring to  FIGS. 14 and 15 , the power conditioner  110 A checks the SOC of the power storage device  160  at the start of autonomous operation (step S 804 ), and further determines whether or not power failure continues (step S 805 ). 
     If power failure has ended (NO in step S 805 ), the power conditioner  110 A stops autonomous operation and starts grid connected operation (step S 806 ). After that, the power conditioner  110 A returns to step S 802 . On the other hand, if power failure continues (YES in step S 805 ), the power conditioner  110 A determines whether or not the SOC is 90% or more (step S 807 ). 
     If the SOC is 90% or more (YES in step S 807 ), the power conditioner  110 A performs control so that the frequency becomes 59 Hz (step S 808 ). On the other hand, if the SOC is less than 90% (NO in step S 807 ), the power conditioner  110 A determines whether or not the SOC is 75% or more (step S 809 ). 
     If the SOC is 75% or more (YES in step S 809 ), the power conditioner  110 A performs control so that the frequency becomes 58.5 Hz (step S 810 ). On the other hand, if the SOC is less than 75% (NO in step S 809 ), the power conditioner  110 A determines whether or not the SOC is 50% or more (step S 811 ). 
     If the SOC is 50% or more (YES in step S 811 ), the power conditioner  110 A performs control so that the frequency becomes 58 Hz (step S 812 ). On the other hand, if the SOC is less than 50% (NO in step S 811 ), the power conditioner  110 A determines whether or not the SOC is 25% or more (step S 813 ). 
     If the SOC is 25% or more (YES in step S 813 ), the power conditioner  110 A performs control so that the frequency becomes 57.5 Hz (step S 814 ). On the other hand, if the SOC is less than 25% (NO in step S 813 ), the power conditioner  110 A determines whether or not the SOC is 10% or more (step S 815 ). 
     If the SOC is 10% or more (YES in step S 815 ), the power conditioner  110 A performs control so that the frequency becomes 57 Hz (step S 816 ). On the other hand, if the SOC is less than 10% (NO in step S 815 ), the power conditioner  110 A stops autonomous operation (step S 817 ) and returns to step S 805 . 
     Accordingly, the power consumption of the electronic device  200  may be adjusted in accordance with the SOC. Also, information about the SOC of the power storage device  160  may be obtained only by detecting the frequency of the output power of the power conditioner  110 A, and the information may be displayed on a display (SOC monitor  121 ). 
     In the above-described fifth embodiment, the power conditioner  110 A performs control to decrease the frequency from 60 Hz in accordance with the state of the SOC, but the embodiment is not limited thereto. For example, the power conditioner  110 A may perform control to increase the frequency from 60 Hz in accordance with the state of the SOC. For example, the frequency may be set to 61 Hz in a case where the SOC is 90% or more, and the frequency may be increased as the SOC decreases (the frequency may be set to 63 Hz in a case where the SOC is 10% or less). 
     Sixth Embodiment 
     A sixth embodiment relates to cancellation of frequency control. 
     For example, in a lighting device such as a fluorescent lamp, the illuminance may vary or flicker may occur depending on the frequency of an AC power. To suppress such flicker, the frequency of the AC power may be set to be constant (for example, 60 Hz). 
     Therefore, the power supply devices  100 ,  100 A,  100 B, and  100 C illustrated in  FIGS. 1 ,  8 ,  12 , and  14  may perform control so that the frequency is 60 Hz during autonomous operation as well as during grid connected operation (have a function of cancelling frequency control). 
       FIG. 16  is a flowchart illustrating a process executed by the power conditioner  110 A of the power supply device  100 C ( FIG. 14 ) in the case of cancelling frequency control. The flowchart illustrated in  FIG. 16  is the same as that illustrated in  FIG. 15  except that steps S 907  and S 908  are added, and thus a description will be given of the part different from  FIG. 15 . 
     Referring to  FIGS. 14 and 16 , the power conditioner  110 A determines in step S 907  whether or not frequency control is to be cancelled. Whether or not frequency control is to be cancelled may be set, for example, by providing an instruction to the power conditioner  110 A via the remote controller  120  by a user. 
     If frequency control is to be cancelled (YES in step S 907 ), the power conditioner  110 A performs control so that the frequency becomes 60 Hz (step S 908 ). On the other hand, if frequency control is not to be cancelled (NO in step S 907 ), the power conditioner  110 A proceeds to step S 909 . 
     At the time of the above-described operation of cancelling frequency control, the power consumption of an electronic device is not decreased, and thus some restrictions may be imposed on the operation of the electronic device. For example, the operation of cancelling frequency control may be stopped when a certain period has elapsed since the start of the cancellation operation, when the SOC becomes a certain value or less, or when the power consumption in the electronic device  200  exceeds the power that can be supplied from the power supply device  100  or the like. 
     Also, the electronic device  200  (and  200 A) may be capable of cancelling adjustment of power consumption in accordance with a frequency. 
       FIG. 17  is a flowchart illustrating a process executed by the electronic device  200  in the case of cancelling adjustment of power consumption. The flowchart illustrated in  FIG. 17  is the same as that illustrated in  FIG. 7  except that steps S 1004  and S 1005  are added, and thus a description will be given of the part different from FIG.  7 . 
     In step S 1004 , the electronic device  200  determines whether or not adjustment of power consumption is to be cancelled. Whether or not adjustment of power consumption is to be cancelled is set by, for example, a user operation. 
     If adjustment of power consumption is to be cancelled (YES in step S 1004 ), the electronic device  200  operates without decreasing power consumption (normal operation) (step S 1005 ). On the other hand, if adjustment of power consumption is not to be cancelled (NO in step S 1004 ), the electronic device  200  proceeds to step S 1006 . 
     Accordingly, the user may cancel frequency control if necessary, and use an electronic device with a constant frequency of AC power. 
     Alternatively, restrictions may be imposed to stop the cancellation operation when a certain period has elapsed from the start of the operation of cancelling adjustment of power consumption. 
     Seventh Embodiment 
     A seventh embodiment relates to a power supply system. 
     As a power supply device, a device that uses a power generation device operated using a fuel cell or the like may be used, as well as a device that uses a solar battery or a power storage device. These power supply devices may be combined together to constitute a power supply system that performs frequency control. 
     The power supply system according to this embodiment is applicable to a mass housing, an office building, a factory, a housing complex, and the like that are provided with a fuel cell or a storage battery as well as a solar battery. 
       FIG. 18  illustrates a schematic configuration of a power supply system  400 . The power supply system  400  includes the power supply device  100  illustrated in  FIG. 1  serving a first power supply device, a fuel-cell-mounted power supply device  170  serving as a second power supply device, and a power-storage-device-mounted power supply device  180  serving as s third power supply device. 
     The fuel-cell-mounted power supply device  170  includes a fuel cell  171  serving as a power generator and a power conditioner  172  serving as a second power inverter. The power-storage-device-mounted power supply device  180  includes a power storage device  181  and a power conditioner  182  serving as a third power inverter. Instead of the fuel cell  171 , a battery other than a storage battery, a solar battery, or a rectifier generator may be used as a power generator. The power storage device  181  may be a general storage battery or an electric double-layer capacitor. Here, examples of the storage battery include a lithium-ion battery, a lead storage battery, or a nickel-cadmium storage battery. 
     The power supply system according to an embodiment of the present disclosure may include either or both of the fuel-cell-mounted power supply device  170  and the power-storage-device-mounted power supply device  180 . 
     In the power supply system according to an embodiment of the present disclosure, the number of fuel-cell-mounted power supply devices  170  and the number of power-storage-device-mounted power supply devices  180  are not particularly limited, and a plurality of fuel-cell-mounted power supply devices  170  or a plurality of power-storage-device-mounted power supply devices  180  may be provided. 
     It is necessary that the power supply device  100 , the fuel-cell-mounted power supply device  170 , and the power-storage-device-mounted power supply device  180  operate in conjunction with one another. Thus, one of these devices is set as a master, and the others are set as slaves. For example, in a case where the power supply device  100  is set as a master, the fuel-cell-mounted power supply device  170  and the power-storage-device-mounted power supply device  180  are set as slaves. In this case, in accordance with the frequency of the AC power supplied from the power supply device  100  serving as a master (hereinafter referred to as a “system frequency”), the fuel-cell-mounted power supply device  170  generates power, and the power-storage-device-mounted power supply device  180  performs charge or discharge. In a case where the power supply device  100  is set as a slave, the power supply device  100  outputs an AC power of the system frequency. 
     Here, in the case of being set as a slave, the fuel-cell-mounted power supply device  170  generates (supplies) power only in a case where the system frequency is higher than or equal to 57 Hz and is lower than 58 Hz. In the case of being set as a slave, the power-storage-device-mounted power supply device  180  performs discharge only in a case where the system frequency is lower than 57 Hz, and performs charge in a case where the system frequency higher than or equal to 60 Hz. 
       FIG. 19  is a flowchart illustrating a process executed by the fuel-cell-mounted power supply device  170 . 
     Referring to  FIGS. 18 and 19 , the fuel-cell-mounted power supply device  170  determines whether or not the fuel-cell-mounted power supply device  170  is a master (step S 1101 ). Whether or not the fuel-cell-mounted power supply device  170  is a master is set by, for example, a user operation. 
     If the fuel-cell-mounted power supply device  170  is a master (YES in step S 1101 ), the fuel-cell-mounted power supply device  170  controls a system frequency (step S 1102 ). Specifically, the power conditioner  172  executes a process similar to the process executed by the power conditioner  110  illustrated in  FIG. 6 . 
     On the other hand, if the fuel-cell-mounted power supply device  170  is not a master (NO in step S 1101 ), the fuel-cell-mounted power supply device  170  operates as a slave (step S 1103 ). 
     The fuel-cell-mounted power supply device  170  operating as a slave determines whether or not the system frequency is higher than 58 Hz (step S 1104 ). 
     If the system frequency is higher than 58 Hz (YES in step S 1104 ), the fuel-cell-mounted power supply device  170  stops power generation (step S 1105 ). On the other hand, if the system frequency is lower than or equal to 58 Hz (NO in step S 1104 ), the fuel-cell-mounted power supply device  170  outputs an AC power at the system frequency (step S 1106 ). 
     After step S 1105  or S 1106 , the fuel-cell-mounted power supply device  170  returns to step S 1104 . 
       FIG. 20  is a flowchart illustrating a process executed by the power-storage-device-mounted power supply device  180  during autonomous operation. 
     Referring to  FIGS. 18 and 20 , the power-storage-device-mounted power supply device  180  determines whether or not the power-storage-device-mounted power supply device  180  is a master (step S 1201 ). Whether or not the power-storage-device-mounted power supply device  180  is a master is set by, for example, a user operation. 
     If the power-storage-device-mounted power supply device  180  is a master (YES in step S 1201 ), the power-storage-device-mounted power supply device  180  controls a system frequency (step S 1202 ). Specifically, the power conditioner  182  executes a process similar to the process executed by the power conditioner  110  illustrated in  FIG. 6 . 
     If the power-storage-device-mounted power supply device  180  is not a master (NO in step S 1201 ), the power-storage-device-mounted power supply device  180  operates as a slave (step S 1203 ). 
     Accordingly, the power supplied from the power supply device  100 , the fuel-cell-mounted power supply device  170 , and the power-storage-device-mounted power supply device  180  is used in this priority order, and thus the power stored in the power-storage-device-mounted power supply device  180  may be preserved. 
     In the above-described seventh embodiment, in the case of being set as a slave, the fuel-cell-mounted power supply device  170  and the power-storage-device-mounted power supply device  180  supply power when the system frequency is lower than 60 Hz, but the embodiment is not limited thereto. For example, the fuel-cell-mounted power supply device  170  may generate (supply) power only in a case where the system frequency is higher than 62 Hz and is lower than or equal to 63 Hz. The power-storage-device-mounted power supply device  180  may perform discharge only in a case where the system frequency is higher than 63 Hz, and may perform charge in a case where the system frequency is lower than 60 Hz. 
     Finally, the embodiments of the present disclosure will be summarized. 
     Referring to  FIGS. 1 and 2 , a power supply device according to an embodiment of the present disclosure includes a power inverter ( 110 ), an operation mode switching unit ( 116 A), and an output information control unit ( 116 B). The power inverter is configured to receive a DC power supplied from a DC power source and output an AC power. The operation mode switching unit is configured to switch between grid connected operation and autonomous operation that are performed by the power supply device. The grid connected operation is operation in which power is supplied from an AC power network ( 300 ) and a DC power supply ( 130 ) to a load ( 200 ,  200 A). The autonomous operation is operation in which the power supply device is disconnected from the AC power network and power is supplied from the DC power source to the load. The output information control unit is configured to control output information about the AC power output from the power inverter. 
     Accordingly, a load side may recognize that the power supply device is performing autonomous operation in accordance with change in the frequency or AC waveform of the power supplied thereto, without performing special communication with the power supply device. The load may adjust, for example, power consumption in accordance with the operation state of the power supply device. 
     The load may be an electronic device configured to adjust power consumption in accordance with a frequency. An adjustment range of the power consumption includes zero consumption (consumption of power by the load is stopped). 
     The power supply device may further include a voltage monitoring unit ( 116 C) configured to monitor a voltage of the AC power. The frequency control unit ( 116 B) controls a frequency so that the voltage monitored by the voltage monitoring unit becomes close to a certain voltage. 
     The electronic device ( 200 ,  200 A) may decrease the power consumption in a case where the frequency increases or decreases from a certain frequency, and may increase the power consumption in a case where the frequency becomes close to the certain frequency. The frequency control unit ( 116 B) causes the power inverter ( 110 ) to increase or decrease the frequency from the certain frequency in a case where the voltage monitored by the voltage monitoring unit ( 116 C) is lower than the certain voltage, and causes the power inverter ( 110 ) to cause the frequency to be close to the certain frequency in a case where the voltage monitored by the voltage monitoring unit ( 116 C) is higher than or equal to the certain voltage. 
     Accordingly, the power supplied from the power supply device and the power consumed by the electronic device are balanced. 
     As illustrated in  FIG. 8 , the power supply device ( 100 A) may further include an AC-input-type power storage device ( 140 ) configured to be charged with the AC power, the AC-input-type power storage device being charged in a case where the frequency increases or decreases from a certain frequency. 
     Accordingly, extra power of the power supply device is used for charging the AC-input-type power storage device, and thus the power generated by the power supply device may be maximally used in an effective manner. 
     As illustrated in  FIG. 12 , the power supply device ( 100 B) may further include a connection state control unit ( 150 ) configured to control a connection state between the power supply device and a load in accordance with a frequency. 
     Accordingly, an electronic device having a relatively great necessity may be preferentially used. 
     As illustrated in  FIG. 14 , the power supply device ( 100 C) may further include a power storage device ( 160 ). The frequency control unit ( 116 B) may control a frequency in accordance with residual capacity of the power storage device. 
     Accordingly, the power consumption of the electronic device may be adjusted in accordance with the residual capacity of the power storage device. 
     The frequency control unit ( 116 B) illustrated in  FIG. 2  may perform control so that the frequency becomes a certain frequency in response to an instruction provided from a user. 
     Accordingly, the user may use the electronic device at the certain frequency. 
     Referring to  FIG. 18 , a power supply system ( 400 ) according to another embodiment of the present disclosure includes any one of the above-described power supply devices ( 100 ,  100 A,  100 B,  100 C), a second power supply device ( 170 ), and a third power supply device ( 180 ). The second power supply device includes a power storage device and is charged with power supplied from the power supply device or supplies power to the load in accordance with a frequency. The third power supply device includes a power generation device and supplies power to the load in accordance with a frequency. 
     Referring to  FIG. 3 , an electronic device ( 200 ) according to another embodiment of the present disclosure uses power of an AC power network ( 300 ) of a certain voltage and a certain frequency, and includes a frequency monitoring unit ( 204 ) and a power consumption adjusting unit ( 203 ). The frequency monitoring unit is configured to monitor the frequency of the AC power supplied to the electronic device. The power consumption adjusting unit is configured to adjust power consumption in accordance with the frequency monitored by the frequency monitoring unit. 
     The power consumption adjusting unit ( 203 ) may decrease the power consumption in a case where the frequency monitored by the frequency monitoring unit ( 204 ) increases or decreases from a certain frequency, and increases the power consumption in a case where the frequency monitored by the frequency monitoring unit ( 204 ) becomes close to the certain frequency. 
     The power consumption adjusting unit ( 203 ) may adjust the power consumption in response to an instruction provided from a user so that the power consumption becomes power consumption in a case where the frequency monitored by the frequency monitoring unit ( 204 ) is equal to a certain frequency. 
     It should be considered that the embodiments disclosed here are examples from every point of view and are not restrictive. The scope of the present disclosure is specified by the scope of the claims, not by the description of the embodiments given above, and includes all the changes within the meaning and scope equivalent to the claims. 
     The present disclosure contains subject matter related to that disclosed in Japanese Priority Patent Application JP 2013-187278 filed in the Japan Patent Office on Sep. 10, 2013, the entire contents of which are hereby incorporated by reference.