Patent Publication Number: US-2018041824-A1

Title: Power converting apparatus, distribution board, and operation switching method

Description:
TECHNICAL FIELD 
     The present invention relates to a power converting apparatus by which a DC power is converted to an AC power, a distribution board, and an operation switching method. 
     BACKGROUND ART 
     A power converting apparatus (power conditioner) connected to a distributed power source that outputs a DC (Direct Current) power is known. The power converting apparatus includes a direct current convertor (DC/DC convertor) that converts a voltage of a DC power input from the distributed power source; and an inverter that converts the DC power input from the direct current convertor to an AC (Alternating Current) power (for example, Patent Document 1). 
     PRIOR ART DOCUMENT 
     Patent Document 
     Patent Document 1: Japanese Application Publication No. 2014-171359 
     SUMMARY 
     A aspect is abstracted as a power converting apparatus comprising a communication unit that receives a power instruction message through a communication with an outside; and a controller that changes an operation state from a grid connected state to a self-sustained state when a determination is made that a communication state with the outside is equal to or lower than a predetermined threshold, the grid connected state being a state connected to a power grid and the self-sustained state being a state disconnected from the power grid. 
     A aspect is abstracted as a distribution board comprising a switching unit that connects or disconnects connection between a distributed power source and a power grid, wherein the switching unit switches an operating state from a grid connected state to a self-sustained state when a determination is made that a communication state between a server that transmits a power instruction message and a power converting apparatus that controls the distributed power source is equal to or lower than a predetermined threshold, the grid connected state being a state connected to the power grid and the self-sustained state being a state disconnected from the power grid. 
     A aspect is abstracted as an operation switching method comprising the steps of: receiving, by a power converting apparatus, a power instruction message through a communication with an outside; and changing an operating state from a grid connected state to a self-sustained state when a determination is made that a communication state between the server and the power converting apparatus is equal to or lower than a predetermined threshold, the grid connected state being a state connected to a power grid and the self-sustained state being a state disconnected from the power grid. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating a power management system  1  according to an embodiment. 
         FIG. 2  is a diagram illustrating a PCS  130  according to the embodiment. 
         FIG. 3  is a flowchart illustrating a control method according to the embodiment. 
         FIG. 4  is a flowchart illustrating a control method according to the embodiment. 
         FIG. 5  is a diagram illustrating the power management system  1  according to another embodiment. 
         FIG. 6  is a flowchart illustrating a control method according to another embodiment. 
         FIG. 7  is a flowchart illustrating a control method according to another embodiment. 
         FIG. 8  is a diagram illustrating a PCS  130  according to another embodiment. 
     
    
    
     DESCRIPTION OF THE EMBODIMENT 
     An embodiment is described below by referring to the drawings. In the following description of the drawings, same or similar reference numerals are given to denote same or similar portions. 
     Note that the drawings are merely schematically shown and proportions of sizes and the like are different from actual ones. Thus, specific sizes and the like should be judged by referring to the description below. In addition, there are of course included portions where relationships or ratios of sizes of the drawings are different with respect to one another. 
     Overview of Embodiment 
     A power converting apparatus, which needs to receive from an external server a message instructing suppression of an output of a distributed power source (hereinafter, output suppression message), is assumed to stop the output of the distributed power source when communication between the external server and the power converting apparatus is disconnected. Specifically, the power converting apparatus stops the output of the distributed power source, when communication abnormality between the external server and the power converting apparatus continues over a constant period (five minutes, for example). 
     In the above-described conventional technology, when the communication between the external server and the power converting apparatus is disconnected, the output of the distributed power source must be stopped. However, it is assumed that the output of the distributed power source will not be effectively utilized, when the output of the distributed power source is stopped. 
     Furthermore, in the above-described conventional technology, also known is a power converting apparatus that converts not only a DC power input from the distributed power source but also a DC power input from a storage battery to an AC power. However, it is also assumed that in this type of power converting apparatus, when the operation of the inverter is stopped, the storage battery cannot be charged nor discharged. 
     A power converting apparatus according to an embodiment comprising a communication unit that receives a power instruction message through a communication with an outside; and a controller that changes an operation state from a grid connected state to a self-sustained state when a determination is made that a communication state with the outside is equal to or lower than a predetermined threshold, the grid connected state being a state connected to a power grid and the self-sustained state being a state disconnected from the power grid. 
     In the embodiment, the controller changes the operating state from the grid connected state to the self-sustained state when determination is made that the communication state with the server is equal to or lower than the predetermined threshold, the grid connected state being a state connected to the power grid and the self-sustained state being a state disconnected from the power grid. Therefore, it is possible to avoid stopping the output of the distributed power source, and to effectively utilize the output of the distributed power source. 
     Furthermore, the power converting apparatus according to the embodiment includes: a first direct current convertor that converts a voltage of a DC power input from the distributed power source; a second direct current convertor that converts a voltage of a DC power input from the storage battery; an inverter that converts the DC power input from the first direct current convertor and the DC power input from the second direct current convertor to an AC power; and a controller that changes an operation state of the power converting apparatus from a grid connected state to a self-sustained state, the grid connected state being a state connected to the power grid and the self-sustained state being a state disconnected from the power grid. The power output in the self-sustained state from the inverter may be continuously supplied to a load connected to the inverter in the grid connected state. 
     Such a configuration presupposes that the power output in the self-sustained state from the inverter is supplied to the load connected to the inverter in the grid connected state. Under such a precondition, the controller performs a change from the grid connected state to the self-sustained state. In the self-sustained state, the operation of the inverter may not be necessarily stopped. Therefore, even when in instance where the output of the distributed power source needs to be stopped, it is possible to continue charging and discharging of the storage battery. Furthermore, the output of the distributed power source can also be continued. 
     Embodiment 
     A power management system according to an embodiment will be described, below.  FIG. 1  is a diagram illustrating the power management system  1  according to the embodiment. 
     As illustrated in  FIG. 1 , the power management system  1  includes a consumer&#39;s facility  100 , an external server  400 , and a recording apparatus  500 . The consumer&#39;s facility  100  has an EMS  200 , and the EMS  200  communicates with the external server  400  and the recording apparatus  500  via a network  300 . 
     The consumer&#39;s facility  100  includes a solar cell  110 , a storage battery  120 , a PCS  130 , a distribution board  140 , and a load  150 . Furthermore, the consumer&#39;s facility  100  includes the EMS  200  and a remote controller  210 . 
     The solar cell  110  is an equipment that generates power in response to reception of solar light. The solar cell  110  outputs the generated DC power. An amount of power to be generated by the solar cell  110  varies depending on an amount of the solar radiation entering the solar cell  110 . The solar cell  110  is an example of a distributed power source to operate in accordance with an output suppression message described later. 
     The storage battery  120  is an equipment in which power is accumulated. The storage battery  120  outputs the accumulated DC power. In the embodiment, the storage battery  120  may need not to operate in accordance with the output suppression message described later. 
     The PCS  130  is an example of a power converting apparatus (PCS: Power Conditioning System) that converts a DC power to an AC power. In the embodiment, the PCS  130  is connected to a main power line  10 L (herein, a main power line  10 LA and a main power line  10 LB) connected to a power grid  10 , and connected to both the solar cell  110  and the storage battery  120 . The main power line  10 LA is a power line connecting the power grid  10  and the PCS  130 , and the main power line  10 LB is a power line connecting the PCS  130  and the distribution board  140 . 
     Here, the PCS  130  converts the DC power input from the solar cell  110  to an AC power, and converts the DC power input from the storage battery  120  to an AC power. Furthermore, the PCS  130  converts an AC power supplied from the power grid  10  to a DC power. 
     The distribution board  140  is connected to the main power line  10 L (herein, the main power line  10 LB). The distribution board  140  divides the main power line  10 LB into a plurality of power lines, and distributes the power to an equipment (herein, the load  150  and the EMS  200 ) connected to the plurality of power lines. Note that the distribution board  140  may be configured to communicate the power information of the amount of electric power passing therethrough (the total electric energy, the electric energy for each branch, etc.) with the EMS  200 . 
     The load  150  is an equipment in which the power supplied via the power line is consumed. Examples of the load  150  include an equipment such as a refrigerator, a lighting, an air conditioner, and a TV. The load  150  may be a single equipment, and may include a plurality of equipments. 
     The EMS  200  is an equipment (EMS: Energy Management System) that manages power information indicating the power supplied to the consumer&#39;s facility  100  from the power grid  10 . The EMS  200  may manage an amount of power to be generated by the solar cell  110 , an amount of power to be stored in the storage battery  120 , and an amount of power to be discharged from the storage battery  120 . 
     In the embodiment, the EMS  200  is connected to the remote controller  210  and the network  300 . For example, the EMS  200  receives the power suppression message described later from the external server  400 , and notifies the remote controller  210  of the power suppression message. Alternatively, the EMS  200  receives a schedule (calendar) described later from the external server  400 , and based on the schedule (calendar), notifies the remote controller  210  of the power suppression message. 
     The PCS  130  has the remote controller  210  provided in connection with the PCS  130 , and the remote controller  210  notifies the PCS  130  of various types of messages to operate the PCS  130 . For example, the remote controller  210  notifies the PCS  130  of the power suppression message received from the EMS  200 . 
     The network  300  is a communication network by which the EMS  200 , the external server  400 , and the recording apparatus  500  are connected. The network  300  may be the Internet. The network  300  may include a mobile communication network. 
     The external server  400  notifies the output suppression message that is a message to instruct suppression of the output of the distributed power source (herein, the solar cell  110 ). Here, the external server  400  may manage a schedule (calendar), as a whole of the power grid  10 , including a date and time for suppressing the output of the distributed power source. The external server  400  notifies the output suppression message, based on such a schedule (calendar). Alternatively, the external server  400  may notify the EMS  200  of such a schedule (calendar). That is, the external server  400  is a server instructing the output suppression of the distributed power supply. 
     Here, the output suppression message and the schedule (calendar) include information indicating a suppression degree (an output suppression power threshold, for example) for the output of the distributed power source (herein, the solar cell  110 ). The suppression degree may be represented by an absolute value (xx kW, for example) of the output of the distributed power source (herein, the solar cell  110 ). Alternatively, the suppression degree may be represented by a relative value (decrease by xx kW, for example) of the output of the distributed power source (herein, the solar cell  110 ). Alternatively, the suppression degree may be represented by a suppression rate (xx%, for example) of the output of the distributed power source (herein, the solar cell  110 ). The suppression rate may be a rate of the distributed power source relative to the output certified, as an output capability of the PCS that controls the distributed power source (hereinafter, facility certified output), when the distributed power source is installed in the consumer&#39;s facility  100 . If the output capability of the distributed power source and that of the PCS differ, either one of a smaller output capability is selected, as the facility certified output. When a plurality of PCSs are installed, the facility certified output is a sum of the output capabilities of the plurality of PCSs. 
     The recording apparatus  500  is an apparatus that records various types of information. Specifically, the recording apparatus  500  records a verification record including whether or not the suppression of the output of the distributed power source is correctly executed according to the output suppression message. The verification record is an amount of power output from the distributed power source after reception of the output suppression message. The amount of power output from the distributed power source may be accumulated in an accumulation period (30 minutes, for example). In such a case, in the verification record accumulated for each accumulation period, the suppression of the output of the distributed power source may be correctly executed. 
     (Power Converting Apparatus) 
     The power converting apparatus according to the embodiment will be described below.  FIG. 2  is a diagram illustrating the PCS  130  according to the embodiment. 
     As illustrated in  FIG. 2 , the PCS  130  is connected to a power line  11 L connected to the main power line  10 LA, and a power line  12 L connected to the main power line  10 LB. Furthermore, a power line  13 L connecting the power line  11 L and the power line  12 L is provided. The power line  13 L is connected closer to the power line  11 L at the main power line  10 LA side than a switch  11 SW, and connected closer to the power line  12 L at the main power line  10 LB than a switch  12 SW. 
     The power line  11 L is a power line connecting the power grid  10  and an inverter  133 . The power line  11 L may be a power line configuring a part of the main power line  10 LA, and may be a power line divided from the main power line  10 LA. The power line  12 L is a power line connecting the inverter  133  and the distribution board  140  (load  150 ). The power line  12 L may be a power line configuring a part of the main power line  10 LB, and may be a power line divided from the main power line  10 LB. 
     The PCS  130  includes the switch  11 SW (first relay switch) provided on the power line  11 L, the switch  12 SW (second relay switch) provided on the power line  12 L, and a switch  13 SW (third relay switch) provided on the power line  13 L. 
     The switch  11 SW is controlled to be in a closed state in a grid connected state in which the PCS  130  is connected to the power grid  10 . On the other hand, the switch  11 SW is controlled to be in an opened state in a self-sustained state in which the PCS  130  parallels off the power grid  10 . 
     The switch  12 SW is controlled to be in an opened state in a grid connected state in which the PCS  130  is connected to the power grid  10 . On the other hand, the switch  11 SW is controlled to be in a closed state in a self-sustained state in which the PCS  130  is disconnected from the power grid  10 . 
     The switch  13 SW is controlled to be in a closed state in a grid connected state in which the distribution board  140  (load  150 ) is connected to the power grid  10 . Likewise, the switch  13 SW is controlled to be in a closed state in a grid connected state in which the PCS  130  is connected to the power grid  10 . On the other hand, the switch  13 SW is controlled to be in an opened state in a self-sustained state in which the distribution board  140  (load  150 ) is disconnected from the power grid  10 . Likewise, the switch  13 SW is controlled to be in an opened state in a self-sustained state in which the PCS  130  is disconnected from the power grid  10 . 
     Generally, in the grid connected state in which the consumer&#39;s facility  100  is connected to the power grid  10 , both the PCS  130  and the distribution board  140  (load  150 ) are connected to the power grid  10 . Therefore, in such a grid connected state, the switch  11 SW and the switch  13 SW are controlled to be in a closed state, and the switch  12 SW is controlled to be in an opened state. On the other hand, generally, in the self-sustained state in which the consumer&#39;s facility  100  is disconnected from the power grid  10 , both the PCS  130  and the distribution board  140  (load  150 ) are not connected to the power grid  10 . Therefore, in such a self-sustained state, the switch  11 SW and the switch  13 SW are controlled to be in an opened state, and the switch  12 SW is controlled to be in a closed state. 
     As illustrated in  FIG. 2 , the PCS  130  includes a DC/DC convertor  131 , a DC/DC convertor  132 , the inverter  133 , a controller  134 , and a communication unit  135 . 
     The DC/DC convertor  131  is a first direct current convertor that converts a voltage of a DC power input from the solar cell  110 . The DC/DC convertor  131  may upconvert the voltage of the DC power and downconvert the voltage of the DC power. 
     The DC/DC convertor  132  is a second direct current convertor that converts a voltage of a DC power input from the storage battery  120 . Furthermore, the DC/DC convertor  132  converts a voltage of the DC power input from the inverter  133 . The DC/DC convertor  132  may upconvert the voltage of the DC power and may downconvert the voltage of the DC power. 
     An operation of outputting the DC power from the storage battery  120  to the DC/DC convertor  132  is discharge from the storage battery  120 . The operation of outputting the DC power from the DC/DC convertor  132  to the storage battery  120  is charge into the storage battery  120 . 
     The inverter  133  converts the DC power input from the DC/DC convertor  131  and the DC power input from the DC/DC convertor  132 , to an AC power. Furthermore, the inverter  133  converts the AC power supplied from the power grid  10  to a DC power. 
     The controller  134  controls the PCS  130 . Firstly, the controller  134  controls an amount of power generated by the solar cell  110 . In particular, the controller  134  controls the amount of power generated by the solar cell  110  by MPPT (Maximum Power Point Tracking) method. As a result, an operation point (point determined by an operation-point voltage value and power value, or a point determined by an operation-point voltage value and electric current value) of the solar cell  110  is optimized. Secondly, the controller  134  controls the charge amount and the discharge amount in the storage battery  120 . 
     Here, the controller  134  suppresses the output of the solar cell  110  according to the output suppression message or the schedule (calendar). As described above, the suppression degree may be represented by an absolute value (xx kW, for example) of the output of the solar cell  110 . Alternatively, the suppression degree may be represented by a relative value (decrease by xx kW, for example) of the output of the solar cell  110 . Alternatively, the suppression degree may be represented with a suppression rate (xx%, for example) of the output of the solar cell  110 . 
     In the embodiment, the controller  134  changes, when the communication between the external server  400  and the PCS  130  is disconnected, the operation state of the PCS  130  from the grid connected state to the self-sustained state. The power output in the self-sustained state from the inverter  133  may be continuously supplied to the load  150  connected to the inverter  133  in the grid connected state. In addition, even during a change period from the grid connected state to the self-sustained state, the power output from the inverter  133  may be continuously supplied to the load  150 . 
     Specifically, “even during the change period from the grid connected state to the self-sustained state, the power output from the inverter  133  is continuously supplied to the load  150 ” means that, for example, the power is required to be continuously supplied to the load  150  at the time of change. That is, at the time of change, the power is required to be supplied without any interruption to the load  150  that is connected in the grid connected state. It is noted that it is required that the operation of the load  150  will not be interpreted due to the failure in supplying the power at the time of change; therefore, the power may be reduced due to, for example, the instantaneous reduction of the voltage. For example, when the load  150  is a fluorescent light, the illumination may be temporarily decreased due to the temporary reduction of the voltage at the time of change. 
     Specifically, when changing the operation state of the PCS  130  from the grid connected state to the self-sustained state, the controller  134  switches the switch  11 SW from a closed state to an opened state and switches the switch  12 SW from an opened state to a closed state while keeping the switch  13 SW in a closed state, after which the controller  134  switches the switch  13 SW from a closed state to an opened state. 
     As described above, the change from the grid connected state to the self-sustained state is performed while keeping the switch  13 SW in a closed state. Thus, even during such a change period, the power output from the inverter  133  is supplied to the load  150  without any interruption. 
     Here, the controller  134  may perform the change from the grid connected state to the self-sustained state without stopping operations of the DC/DC convertor  131 , the DC/DC convertor  132 , and the inverter  133 . Furthermore, the controller  134  may perform the change from the grid connected state to the self-sustained state when the power consumption of the load  150  can be covered with the power outputtable from the inverter  133 . The power outputtable from the inverter  133  is the sum of the generated power of the solar cell  110  and the charge amount of the storage battery  120 . 
     In the embodiment, the controller  134 , may automatically change, when the communication between the external server  400  and the PCS  130  is recovered, the operation state of the PCS  130  from the self-sustained state to the grid connected state. 
     Specifically, when changing the operation state of the PCS  130  from the self-sustained state to the grid connected state, the controller  134  switches the switch  13 SW from an opened state to a closed state, after which the controller  134  switches the switch  12 SW from a closed state to an opened state and switches the switch  11 SW from an opened state to a closed state. 
     As described above, the switch  13 SW is first switched from an opened state to a closed state, and then the change from the self-sustained state to the grid connected state is performed. Thus, even during such a change period, the power output from the inverter  133  is supplied to the load  150  without any interruption. 
     Meanwhile, the controller  134  may not automatically change, when the communication between the external server  400  and the PCS  130  is recovered, the operation state of the PCS  130  from the self-sustained state to the grid connected state. In other words, the controller  134  will continue the self-sustained operation even after the communication is recovered. In such a case, the operation state of the PCS  130  is changed from the self-sustained state to the grid connected state by a manual operation of a user. The user may configure in advance whether or not to automatically perform the change from the self-sustained state to the grid connected state when the communication is recovered, or may determine which is better, depending on the situation of the self-sustained operation (for example, the storage capacity of the storage battery, the power generation amount of the solar cell, and the power consumption of the load). 
     A factor of disconnecting the communication between the external server  400  and the PCS  130  may be disconnection of the communication between the external server  400  and the EMS  200  and disconnection of the communication between the EMS  200  and the remote controller  210 . Alternatively, a factor of disconnecting the communication between the external server  400  and the PCS  130  may be disconnection of the communication between the remote controller  210  and the communication unit  135 . 
     For example, the controller  134  detects the disconnection of the communication, upon reception of the message indicating the disconnection of the communication from the EMS  200  when the disconnection of the communication between the external server  400  and the EMS  200  is detected by the EMS  200 . Alternatively, the controller  134  may detect the disconnection of the communication upon reception of the message indicating the disconnection of the communication from the remote controller  210  when the disconnection of the communication between the EMS  200  and the remote controller  210  is detected by the remote controller  210 . In such a case, the message indicating the disconnection of the communication may be replaced by a message instructing an operation stop of the solar cell  110  (hereinafter, operation stop instruction). 
     The disconnection of the communication may not include an instantaneous communication disconnection. Specifically, the controller  134  my detect the disconnection of the communication when a state where the communication is disconnected continues over a constant period (five minutes, for example). It is noted that the disconnection of the communication is an aspect where the communication state between the external server  400  and the PCS  130  is equal to or less than a predetermined threshold. The communication state is determined by a magnitude of a predetermined threshold such as RSSI (Received Signal Strength Indication), SNR (Signal to Noise Ratio), or SIR (Signal to Interference Ratio), for example. More specifically, in the communication between the external server  400  and the EMS  200 , for example, when a value of the RSSI of the communication is equal to or less than a predetermined threshold, “determination of the communication state being equal to or less than a predetermined threshold” is made. 
     The controller  134  outputs a verification record for verifying whether or not the suppression of the output of the solar cell  110  is correctly executed according to the output suppression message or the schedule (calendar). As described above, the verification record is an amount of power output from the solar cell  110  after the output suppression message is received. The controller  134  outputs zero as the verification record when the change from the grid connected state to the self-sustained state is performed. 
     The communication unit  135  communicates with the remote controller  210 . For example, the communication unit  135  receives the output suppression message notified from the external server  400 . The communication unit  135  transmits to the recording apparatus  500  the verification record output from the controller  134 . 
     Furthermore, the communication unit  135  receives, when it is detected by the EMS  200  or the remote controller  210  that the communication is disconnected, a message indicating the disconnection of communication from the EMS  200  or the remote controller  210 . In such a case, the message indicating the disconnection of the communication may be replaced by a message instructing an operation stop of the solar cell  110  (operation stop instruction). In the embodiment, the communication unit  135  receives an operation stop instruction from the EMS  200  or the remote controller  210 . 
     A control method according to the embodiment will be described below.  FIG. 3  and  FIG. 4  are flowcharts showing the control method according to the embodiment. 
     Firstly, a case of stopping the output of the solar cell  110  will be explained with reference to  FIG. 3 . 
     As illustrated in  FIG. 3 , in step S 10 , the communication between the external server  400  and the PCS  130  is disconnected. Here, the disconnection of the communication between the external server  400  and the PCS  130  is disconnection of the communication between the external server  400  and the EMS  200  and disconnection of the communication between the EMS  200  and the remote controller  210 . 
     In step S 11 , the PCS  130  determines whether or not a message instructing the stop of the operation of the solar cell  110  (operation stop instruction) has been received from the remote controller  210 . If a determination result is YES, the PCS  130  moves to a process of step S 12 . If the determination result is NO, the PCS  130  holds steady. 
     In step S 12 , the PCS  130  performs the change from the grid connected state to the self-sustained state. Specifically, the PCS  130  switches the switch  11 SW from a closed state to an opened state and switches the switch  12 SW from an opened state to a closed state while keeping the switch  13 SW in a closed state, after which the PCS  130  switches the switch  13 SW from a closed state to an opened state. 
     Secondly, a case of resuming the output of the solar cell  110  will be explained with reference to  FIG. 4 . 
     As illustrated in  FIG. 4 , in step S 15 , the communication between the external server  400  and the PCS  130  is recovered. 
     In step S 16 , the PCS  130  determines whether or not a message instructing a release of the operation stop of the solar cell  110  (operation stop release instruction) has been received from the remote controller  210 . If a determination result is YES, the PCS  130  moves to a process of step S 16 . If the determination result is NO, the PCS  130  holds steady. 
     In step S 17 , the PCS  130  performs the change from the self-sustained state to the grid connected state. Specifically, the PCS  130  switches the switch  13 SW from an opened state to a closed state, after which the PCS  130  switches the switch  12 SW from a closed state to an opened state and switches the switch  11 SW from an opened state to a closed state. 
     (Operation and Effect) 
     In the embodiment, it is presupposed that the power output in the self-sustained state from the inverter is supplied to the load  150  connected to the inverter  133  in the grid connected state. Under such a precondition, the PCS  130  performs, upon reception of a message instructing the operation stop of the solar cell  110  (operation stop instruction), the change from the grid connected state to the self-sustained state. In the self-sustained state, the operation of the inverter  133  may not be necessarily stopped even in a state in which the communication between the external server  400  and the PCS  130  is disconnected. Therefore, even when in instance where the output of the solar cell  110  must be stopped, it is possible to continue charging and discharging of the storage battery  120 . Furthermore, power generation of the solar cell  110  can be continued. 
     Another Embodiment 
     Another embodiment will be described, below. A difference from the above-described embodiment will be described, below. 
     In the other embodiment, the consumer&#39;s facility  100  does not include the EMS  200  and the remote controller  210 , as illustrated in  FIG. 5 . The PCS  130  (communication unit  135 ) is directly connected to the network  300 , and communicates with the external server  400  and the recording apparatus  500 . 
     Therefore, the PCS  130  (controller  134 ) detects the disconnection of the communication between the external server  400  and the EMS  200 . For example, the PCS  130  (controller  134 ) may detect the disconnection of the communication depending upon whether or not a beacon signal cyclically transmitted from the external server  400  is successfully received. Alternatively, the PCS  130  (controller  134 ) may detect the disconnection of the communication by monitoring the network  300 . 
     (Control Method) 
     A control method according to another embodiment will be described below.  FIG. 6  and  FIG. 7  are flowcharts showing the control method according to the other embodiment. 
     Firstly, a case of stopping the output of the solar cell  110  will be explained with reference to  FIG. 6 . 
     As illustrated in  FIG. 6 , in step S 20 , the communication between the external server  400  and the PCS  130  is disconnected. 
     In step S 21 , the PCS  130  determines whether or not the communication disconnection has been detected. If a determination result is YES, the PCS  130  moves to a process of step S 22 . If the determination result is NO, the PCS  130  holds steady. 
     In step S 22 , the PCS  130  performs the change from the grid connected state to the self-sustained state. Specifically, the PCS  130  switches the switch  11 SW from a closed state to an opened state and switches the switch  12 SW from an opened state to a closed state while keeping the switch  13 SW in a closed state, after which the PCS  130  switches the switch  13 SW from a closed state to an opened state. 
     Secondly, a case of resuming the output of the solar cell  110  will be explained with reference to  FIG. 7 . 
     As illustrated in  FIG. 7 , in step S 25 , the communication between the external server  400  and the PCS  130  is recovered. 
     In step S 26 , the PCS  130  determines whether or not the communication recovery has been detected. If a determination result is YES, the PCS  130  moves to a process of step S 27 . If the determination result is NO, the PCS  130  holds steady. 
     In step S 27 , the PCS  130  performs the change from the self-sustained state to the grid connected state. Specifically, the PCS  130  switches the switch  13 SW from an opened state to a closed state, after which the PCS  130  switches the switch  12 SW from a closed state to an opened state and switches the switch  11 SW from an opened state to a closed state. 
     (Operation and Effect) 
     In another embodiment, it is presupposed that the power output in the self-sustained state from the inverter is supplied to the load  150  connected to the inverter  133  in the grid connected state. Under such a precondition, the PCS  130  performs, upon detection of the disconnection of the communication between the external server  400  and the PCS  130 , the change from the grid connected state to the self-sustained state. In the self-sustained state, the operation of the inverter  133  may not be necessarily stopped even in a state in which the communication between the external server  400  and the PCS  130  is disconnected. Therefore, even when in instance where the output of the solar cell  110  must be stopped, it is possible to continue charging and discharging of the storage battery  120 . Furthermore, power generation of the solar cell  110  can be continued. 
     Another Embodiment 
     Another embodiment will be described, below. A difference from the above-described embodiment will be described, below. 
     In the other embodiment, the PCS  130  includes a recording unit  136 , as illustrated in  FIG. 8 . The recording unit  136  records, in much the same way as the recording apparatus  500  does, the verification record to verify whether or not the suppression of the output of the distributed power source is correctly executed according to the output suppression message. In such a case, the recording unit  136  may record the verification record output from the controller  134 . 
     In the other embodiment, the recording unit  136  that records the verification record is provided in the PCS  130 , and thus, the power management system  1  need not to include the recording apparatus  500 . 
     Other Embodiments 
     The present invention was described in terms of the embodiment set forth above, the invention should not be understood to be limited by the statements and the drawings constituting a part of this disclosure. From this disclosure, various alternative embodiments, examples, and operational technologies will be obvious to those skilled in the art. 
     The embodiments provide an example of the solar cell  110  as the distributed power source to operate in accordance with the output suppression message. However, the distributed power source is not limited thereto. The distributed power source may be an equipment that utilizes a natural energy such as a wind power and a geothermal heat to generate power. Alternatively, the distributed power source may be a fuel cell that utilizes a fuel gas to produce power. 
     In the embodiments, the controller  134  controls the PCS  130 . In such a case, the controller  134  may control the PCS  130  according to an instruction from the EMS  200  or the remote controller  210 . In other words, when the communication between the external server and the power converting apparatus is disconnected, a controller (a function block including a similar function to that of the controller  134 ) that changes the operation state of the power converting apparatus from the grid connected state of being connected to the power grid to the self-sustained state of being disconnected from the power grid may be provided in the EMS  200  or the remote controller  210 . 
     In the other embodiment, the recording unit  136  that records the verification record is provided in the PCS  130 . However, the embodiment is not limited thereto. The recording unit  136  that records the verification record may be provided in the EMS  200  or the remote controller  210 . 
     In the embodiment, the  11 SW, the  12 SW, and the  13 SW are provided in the PCS  130 , however the embodiment is not limited thereto. A switching unit configured to switch the grid connected state and the self-sustained state may be provided in the distribution board  140 . 
     The entire content of Japanese patent application No. 2015-035090 (filed on Feb. 25, 2015) is incorporated herein by reference.