Patent Publication Number: US-2022239101-A1

Title: Power management apparatus and power management method

Description:
This nonprovisional application is based on Japanese Patent Application No. 2021-011920 filed on Jan. 28, 2021 with the Japan Patent Office, the entire content of which is hereby incorporated by reference. 
     BACKGROUND 
     Field 
     The present disclosure relates to a power management apparatus and a power management method, and, more particularly, to a power management apparatus and a power management method for managing demand response which requests multiple power adjustment resources electrically connectable to a power network to adjust supply and demand of electric power for the power network. 
     Description of the Background Art 
     For the power management apparatus and power management method as mentioned above, WO 2020/158592 discloses a server device selecting, using information on the reliability of electric power customers, a customer to be requested for a demand response (referred to as “DR” below). As used herein, the information on the reliability of a customer refers to a rate of achievement to a DR request (a percentage of the amount of electric power achieved during a DR request period to a requested amount of electric power) or a stay rate to a DR request (a rate per unit time of a period of time in which the amount of electric power responded to a DR request falls within a predetermined range (for example, plus or minus 20%) of a requested amount of electric power). 
     It is considered to actively use vehicles that have batteries mounted thereon, as power adjustment resources that can participate in DR. When a vehicle, participating in a DR, and a power management apparatus (server), managing the DR, exchange various information over wireless communications, the power management apparatus cannot appropriately obtain the information for use in DR from the vehicle if the communication condition is poor. As a result, appropriate adjustment of supply and demand of electric power may not be performed in response to the DR request. If appropriate adjustment of supply and demand of electric power is not performed in response to the DR request while the vehicle is participating in DR, a customer may suffer from drawbacks, such as being subjected to penalty. 
     SUMMARY 
     The present disclosure is made in view of the problem above, and an object of the present disclosure is to provide a power management apparatus and a power management method that can reduce drawbacks for a customer caused by appropriate adjustment of supply and demand of electric power not being performed in response to a DR request. 
     A power management apparatus according to the present disclosure is a power management apparatus for managing a DR which requests a plurality of power adjustment resources, electrically connectable to a power network, to perform adjustment of supply and demand of electric power for the power network. The plurality of power adjustment resources include a vehicle on which a battery is mounted. The power management apparatus includes: a communication apparatus that wirelessly communicates with the vehicle; an acquisition unit; and a control unit. The acquisition unit obtains, from the vehicle through the communication apparatus, history information indicating that the demand and supply of electric power has been performed for the power network, and information on a state of charge of the battery. The control unit determines priorities of the plurality of power adjustment resources for a request for the DR. When the acquisition unit has not obtained the history information even though the state of charge, obtained by the acquisition unit, has changed, the control unit determines a priority of the vehicle so that the vehicle is less likely to be selected for the request for the DR. 
     A power management method according to the present disclosure is a power management method for managing a DR which requests a plurality of power adjustment resources, electrically connectable to a power network, to perform adjustment of supply and demand of electric power for the power network. The plurality of power adjustment resources include a vehicle on which a battery is mounted. The power management method includes: wirelessly transmitting, from the vehicle to a server, history information indicating that the demand and supply of electric power has been performed for the power network; wirelessly transmitting, from the vehicle to the server, information on a state of charge of the battery; and determining priorities of the plurality of power adjustment resources for a request for the demand response. Determining the priorities includes determining a priority of the vehicle so that the vehicle is less likely to be selected for the request for the DR, when the server has not obtained the history information even though the state of charge of the battery, obtained by the server, has changed. 
     In the power management apparatus and power management method above, if the acquisition unit has not obtained the history information from the vehicle even though the state of charge of the battery has changed, the reliability of wireless communications between the power management apparatus and the vehicle is considered as being degraded, and the priority of the vehicle is determined so that the vehicle is less likely to be selected for a DR request. This can avoid a situation in which, despite the fact that the vehicle is participating in DR, no appropriate adjustment of supply and demand of electric power is performed in response to a DR request due to the degradation of the communication reliability. Therefore, according to the power management apparatus and the power management method, a customer can be prevented from suffering from drawbacks (such as being subjected to penalty) caused by appropriate adjustment of supply and demand of electric power not being performed in response to a DR request. 
     The history information may include information indicating at least one of start and end of changing of the battery from the power network. 
     The history information may include information indicating at least one of start and end of discharging of electric power from the battery to the power network. 
     The history information may include information indicating at least one of electrical connection and electrical disconnection between the power network and the vehicle. 
     If the history information as the above is not obtained from the vehicle, the communication reliability with the vehicle is considered as being degraded. Consequently, even though the state of charge of the battery of the vehicle has changed, the priority of the vehicle is determined so that the vehicle is less likely to be selected for the DR request. Accordingly, a customer can be prevented from suffering from drawbacks caused by appropriate adjustment of supply and demand of electric power not being performed in response to a DR request due to the degradation of the communication reliability. 
     A change in the state of charge of the battery may be a change since deactivation of a travel system of the vehicle until activation of the travel system of the vehicle. 
     The acquisition unit further may obtain location information of the vehicle from the vehicle. A change in the state of charge of the battery may be a change when the location information of the vehicle is constant. 
     The acquisition unit may further obtain a travel distance of the vehicle from the vehicle. A change in the state of charge of the battery may be a change when the travel distance of the vehicle is constant. 
     Such a change in the state of charge of the battery as the above is a change in the state of charge while the vehicle is being parked, and can indicate that the demand and supply of electric power has been performed for the power network. However, if the acquisition unit has not obtained the history information on demand and supply of electric power, the communication reliability is considered as being degraded, and the priority of the vehicle is determined so that the vehicle is less likely to be selected for the DR request the vehicle. Accordingly, a customer can be prevented from suffering from drawbacks caused by appropriate adjustment of supply and demand of electric power not being performed in response to a DR request due to the degradation of the communication reliability. 
     When an amount of change in the state of charge of the battery, obtained by the acquisition unit, exceeds a threshold and the acquisition unit has not obtained the history information, the control unit may determine the priority of the vehicle so that the vehicle is less likely to be selected for the request for the DR. 
     Since demand and supply of electric power is not performed for the power network while the vehicle is traveling, no history information is obtained. On the other hand, the state of charge of the battery is changed by the vehicle traveling. Thus, a change in the state of charge while the vehicle is traveling may end up determining the priority of the vehicle so that the vehicle is less likely to be selected for the DR request. Thus, as described above, if a change in state of charge is greater than the threshold, the priority of the vehicle is determined so that the vehicle is less likely to be selected for the DR request, thereby preventing the priority of the vehicle from being unnecessary lowered. It should be noted that, since an average amount of change in state of charge when demand and supply of electric power is performed for the power network is considered as being greater than average amount of change in state of charge while the vehicle is traveling (because electric power is discharged and charged while the vehicle is traveling), the threshold is appropriately set to a value that allows average amounts of change in the SOCs in the above two cases to be distinguishable, for example. 
     The history information may include information indicating that the battery has been charged from the power network. When the acquisition unit has not obtained the history information even though the state of charge, obtained by the acquisition unit, has risen, the control unit may determine the priority of the vehicle so that the vehicle is less likely to be selected for the request for the DR. 
     This can avoid a situation in which, despite the fact that the vehicle is participating in DR, the vehicle does not perform appropriate charging (electric power demand) in response to a DR request due to the degradation of the communication reliability. Accordingly, a customer can be prevented from suffering from drawbacks caused by charging of the battery not being performed in response to a DR request. 
     The foregoing and other objects, features, aspects and advantages of the present disclosure will become more apparent from the following detailed description of the present disclosure when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram showing a configuration of a power management system which includes a power management apparatus according to an embodiment of the present disclosure. 
         FIG. 2  is a detailed block diagram of a vehicle shown in  FIG. 1 . 
         FIG. 3  is a diagram illustrating one example of information transmitted from the vehicle to a server. 
         FIG. 4  is a diagram illustrating one example of information transmitted from the vehicle to the server. 
         FIG. 5  is a diagram illustrating one example of DR information that is managed for each vehicle at the server. 
         FIG. 6  is a diagram illustrating one example of priority information for a DR request. 
         FIG. 7  is a diagram illustrating one example method of determination of priority for a DR request. 
         FIG. 8  is a diagram illustrating one example method of determination of priority for a DR request. 
         FIG. 9  is a flowchart showing one example procedure of a process of updating the priority of a vehicle for a DR request. 
         FIG. 10  is a flowchart illustrating one example procedure of a process of updating the priority of a vehicle for a DR request. 
         FIG. 11  is a flowchart illustrating one example procedure of a process of updating the priority of a vehicle for a DR request, according to Variation 1. 
         FIG. 12  is a flowchart illustrating one example procedure of a process of updating the priority of a vehicle for a DR request, according to Variation 2. 
         FIG. 13  is a flowchart illustrating one example procedure of a process of updating the priority of a vehicle for a DR request, according to Variation 3. 
         FIG. 14  is a flowchart illustrating one example procedure of a process of updating the priority of a vehicle for a DR request, according to Variation 4. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, embodiments according to the present disclosure will be described, with reference to the accompanying drawings. Note that the same reference signs are used to refer to the same or like parts, and the description thereof will not be repeated. 
       FIG. 1  is a diagram showing a configuration of a power management system which includes a power management apparatus according to an embodiment of the present disclosure. Referring to  FIG. 1 , a power management system  1  includes: a power grid PG; a server  30  corresponding to a power management apparatus; an electric vehicle supply equipment (EVSE)  40 ; a vehicle  50 ; and a portable terminal  80 . 
     The vehicle  50  includes an inlet  110 , a charger-discharger  120 , a battery  130 , an electronic control unit (ECU)  150 , and a communication device  180 . The vehicle  50  is configured to transmit/receive electric power to/from the power grid PG through the inlet  110 . In other words, as the vehicle  50  is electrically connected to the EVSE  40  through the inlet  110 , the vehicle  50  can store electric power, which is supplied from the power grid PG, into the battery  130 , or supply the power grid PG with the electric power stored in the battery  130 . Note that, in the following, charging the battery  130  from the power grid PG by the EVSE  40  may be referred to as “external charging” and supplying the power grid PG with electric power stored in the battery  130  by the EVSE  40  may be referred to as “external electric power supply.” 
     The inlet  110  is configured to be electrically connected to a connector  43  of an electric power cable  42  extending from the EVSE  40 . As the connector  43  is connected to the inlet  110 , the vehicle  50  can receive electric power from the power grid PG, or supply electric power to the power grid PG. While  FIG. 1  shows only the inlet  110  (and the charger-discharger  120 ) that supports the powering scheme of the EVSE  40 , it should be noted that the vehicle  50  may include multiple inlets to support multiple types of power supply schemes (for example, an AC (alternate current) power supply scheme and a DC (direct current) power supply scheme). 
     The charger-discharger  120  includes: a relay (not shown) which is provided on a power path between the inlet  110  and the battery  130  and switches electrical connection/disconnection of the power path; and a power converter circuit (not shown). During external charging, the charger-discharger  120  converts the electric power, input from the inlet  110 , into electric power that has the voltage level of the battery  130 , and outputs the electric power to the battery  130 . During external electric power supply, on the other hand, the charger-discharger  120  converts the electric power discharged from the battery  130  into electric power having a voltage level appropriate for the external electric power supply, and outputs the electric power to the inlet  110 . For example, the power converter circuit is configured of a bidirectional converter. 
     The battery  130  includes a secondary battery, such as a lithium-ion secondary battery or a nickel-metal hydride secondary battery. During external charging, the battery  130  is charged with the supply of electric power output from the charger-discharger  120 . During external electric power supply, the battery  130  outputs to the charger-discharger  120  the electric power stored in the battery  130 . In this way, the electric power supplied from the power grid PG (the EVSE  40 ) is stored in the battery  130 , and the electric power stored in the battery  130  is supplied to the power grid PG (the EVSE  40 ), thereby allowing the vehicle  50  to function as a power adjustment resource that can respond to a DR request. The battery  130  is also capable of storing regenerative power generated by a travel motor (not shown) at the time of breaking of the vehicle. 
     The ECU  150  includes a processor (such as a central processing unit (CPU)), a random access memory (RAM), a read only memory (ROM), etc. (none of which are shown). The processor deploys programs stored in the ROM into the RAM, etc., and executes the programs. Various control processes performed by the ECU  150  are written in the programs stored in the ROM. 
     The ECU  150  performs various controls on the vehicle  50 . For example, the ECU  150  performs a traveling control on the vehicle  50 . The ECU  150  also performs a charging control and a discharging control on the battery  130 . In particular, in accordance with a DR request received from the server  30  through the communication device  180 , the ECU  150  performs the charging control and/or the discharging control on the battery  130 . The ECU  150  also collects various data, such as the state of charge (SOC) of the battery  130 , the location information of the vehicle  50 , and the remaining EV travel distance based on the SOC, and transmits the collected various data to the server  30  through the communication device  180  at a predetermined timing (at a time of system startup/shutdown, at a time of start/end of charging and discharging, or periodically). The controls performed by the ECU  150  will be described in detail below. 
     The communication device  180  includes a communication interface (I/F) for wireless communications with the server  30 . The ECU  150  can wirelessly communicate with the server  30  through the communication device  180 . The communication device  180  may include a data communication module (DCM) or  5 G enabled communication I/F. 
     The portable terminal  80  corresponds to a terminal carried by a user of the vehicle  50 . The portable terminal  80  is configured to wirelessly communicate with the server  30 . The user of the vehicle  50  can output instructions from the portable terminal  80  to the server  30  so that, for example, the server  30  can obtain the various information (such as the SOC and the remaining travel distance) of the vehicle  50 . In the present embodiment, smartphone which includes a touch panel display is employed as the portable terminal  80 . However, the present disclosure is not limited thereto. Any portable terminal can be employed as the portable terminal  80 . 
     The power grid PG is a power network that is provided by an electric utility (for example, a power company). The power grid PG is electrically connected to multiple EVSEs, including the EVSE  40 , and supplies AC power to the EVSEs. The EVSE  40  includes a power supply circuit  41 , which converts electric power, supplied from the power grid PG, into one that is appropriate for external charging of the vehicle  50 . The power supply circuit  41  may include a sensor for detecting the charging power. 
     As the relay included in the charger-discharger  120  is closed, the battery  130  mounted on the vehicle  50  is electrically connected to the EVSE  40 . During the external charging, electric power is supplied from the power grid PG to the battery  130  via the power supply circuit  41 , the electric power cable  42 , the inlet  110 , and the charger-discharger  120 . During the external electric power supply, electric power is output from the battery  130  to the power grid PG via the charger-discharger  120 , the inlet  110 , the electric power cable  42 , and the power supply circuit  41 . 
     The server  30  includes a communication apparatus  31 , an acquisition unit  32 , a control unit  33 , and a storage unit  34 . The communication apparatus  31  includes a communication I/F for wireless communications with the communication device  180  included in the vehicle  50 . The communication apparatus  31  also includes a communication I/F for wireless communications with the portable terminal  80 . 
     The acquisition unit  32  obtains various information of the vehicle  50  through the communication apparatus  31 . The acquisition unit  32  obtains information, for example, the SOC of the battery  130 , the location information of the vehicle  50 , and the remaining travel distance, etc., and stores in the storage unit  34  the information associated with identification information (ID) for each vehicle. The acquisition unit  32  also obtains, from the vehicle  50  through the communication apparatus  31 , history information indicating that the vehicle  50  has carried out the demand and supply of electric power to the power grid PG, that is, history information indicating that the vehicle  50  has performed external charging or external electric power supply. The history information, for example, indicates start/end of the external charging or the external electric power supply, or that the connector  43  of the electric power cable  42  has been connected/disconnected to/from the inlet  110 . The details of the information obtained by the acquisition unit  32  and when the acquisition unit  32  obtains such information will be described in detail below. 
     The control unit  33  includes a processor (such as a CPU), a memory (a ROM and a RAM), an I/O buffer, etc. (none of which are shown). The processor deploys programs stored in the ROM into the RAM, etc., and executes the programs. Various processes performed by the control unit  33  are written in the programs stored in the ROM. The processes performed by the control unit  33  will be described below. 
     The storage unit  34  is configured to store various information. The information obtained by the acquisition unit  32  from the vehicle  50  is stored in the storage unit  34 , associated with the information (ID) for each vehicle. The storage unit  34  is configured of a hard disk drive (HDD) or a solid state drive (SSD), for example. 
       FIG. 2  is a detailed block diagram of the vehicle  50  shown in  FIG. 1 . Referring to  FIG. 2 , besides the inlet  110 , the charger-discharger  120 , the battery  130 , the ECU  150 , and the communication device  180  described with reference to  FIG. 1 , the vehicle  50  further includes monitoring modules  121 ,  131 , a travel drive unit  160 , and a navigation system (referred to as a “NAVI” below)  170 . 
     The monitoring module  121  includes various sensors for detecting conditions of the charger-discharger  120 , and outputs results of the detections to the ECU  150 . In the present embodiment, the monitoring module  121  is configured to detect voltage and current input to the charger-discharger  120 , and voltage and current output from the charger-discharger  120 . 
     The monitoring module  131  includes various sensors for detecting conditions of the battery  130  (for example, voltage, current, temperature, etc.), and outputs results of the detections to the ECU  150 . The monitoring module  131  may be a battery management system (BMS) that further has an SOC estimation function, a state of health (SOH) estimation function, a cell voltage equalization function, a diagnosis function, etc. for the battery  130 , in addition to the sensor functions above. Based on the outputs of the monitoring module  131 , the ECU  150  can obtain the conditions of the battery  130 . 
     The travel drive unit  160  includes a power control unit (PCU) and a motor generator (MG) (none of which are shown), and generates a travel driving force for the vehicle  50 , using the electric power stored in the battery  130 . The PCU includes, for example, an inverter and a converter (none of which are shown), and is controlled by the ECU  150 . The MG is a three-phase alternating-current (AC) motor generator, for example. The MG is driven by the PCU, and configured to rotate driving wheels W. The PCU drives the MG, using the electric power supplied from the battery  130 . The MG also regenerates electric power upon breaking of the vehicle, and supplies the generated electric power to the battery  130 . 
     The NAVI  170  includes a processor, a storage device, a touch panel display, and a global positioning system (GPS) module (none of which are shown). The storage device stores map information. For example, the touch panel display receives user input and displays a map and other information, etc. The GPS module is configured to receive a signal (referred to as a “GPS signal” below) from a GPS satellite. The NAVI  170  is capable of locating the position of the vehicle  50 , using the GPS signal. The NAVI  170  is configured to carry out a route search, based on the user input, to find a travel route (for example, a shortest route) from the current location of the vehicle  50  to a destination, and shows the travel route found through the route search on a map. 
     The ECU  150  includes a processor  151 , a RAM  152 , and a storage device  153 . The RAM  152  functions as a working memory temporality storing data processed by the processor  151 . The storage device  153  is configured to save the stored information. The storage device  153  includes, for example, a ROM and a rewritable nonvolatile memory. Besides programs, the storage device  153  stores information (maps, mathematical formulas, various parameters, etc.) which are used in the programs. Various controls at the ECU  150  are performed by the processor  151  executing the programs stored in the storage device  153 . 
     Specifically, the ECU  150  controls the travel drive unit  160 , thereby performing the traveling control on the vehicle  50 . The ECU  150  also controls the charger-discharger  120 , thereby performing the charging control and the discharging control on the battery  130 . The ECU  150  can perform the charging control and/or the discharging control, according to a DR request received from the server  30  through the communication device  180 . 
     The ECU  150  also calculates the SOC of the battery  130  from the voltage and current of the battery  130  which are obtained by the monitoring module  131 , and outputs the SOC to the storage device  153 . The ECU  150  also calculates a remaining travel distance for the vehicle  50  based on the SOC, and outputs the remaining travel distance to the storage device  153 . The ECU  150  also obtains the location information of the vehicle  50  from the NAVI  170  and outputs the location information to the storage device  153 . 
     The ECU  150  then reads the various information above from the storage device  153  at a predetermined timing, and transmits the various information to the server  30  through the communication device  180 . For example, the predetermined timing is at the time of an event, such as at a time of activation/deactivation of the vehicle system (such as at on/off of a start switch, etc.), the start/end of external charging, the start/end of external electric power supply, connection/disconnection between the connector  43  of the electric power cable  42  and the inlet  110 , or at a periodical timing. 
     Note that the various controls at the ECU  150  are not limited to be performed by software, and can be performed by dedicated hardware (electronic circuit). 
       FIGS. 3 and 4  are diagrams illustrating one example of information which is transmitted from the vehicle  50  to the server  30 .  FIG. 3  shows one example of the information that is transmitted from the vehicle  50  to the server  30  at the activation/deactivation of the travel system. Referring to  FIG. 3 , as a driver operates the start switch (not shown) and the travel system of the vehicle  50  is activated, the ECU  150  included in the vehicle  50  reads, from the storage device  153 , “travel start time” indicative of the time when the travel system of the vehicle  50  is activated, and information, such as “GPS location information,” “total travel distance,” and “SOC,” and transmits the “travel start time” and the information to the server  30  through the communication device  180 . Note that the GPS location information is information on the current location of the vehicle  50  obtained by the NAVI  170 . The total travel distance is a total distance traveled by the vehicle  50  up to the present time. The SOC is the current SOC of the battery  130 . 
     As the start switch is operated by the driver and the travel system of the vehicle  50  is deactivated, the ECU  150  reads from the storage device  153  a “travel end time” indicative of the time when the travel system of the vehicle  50  is deactivated, and information, such as the “GPS location information,” the “total travel distance,” the “SOC,” and transmits the “travel end time” and the information to the server  30  through the communication device  180 . 
       FIG. 4  shows one example of the information which is transmitted from the vehicle  50  to the server  30  at the time of an event irrelevant to the vehicle travel. Referring to  FIG. 4 , “event type” indicates an event for which the information is transmitted to the server  30 , indicating that the event is external charging in this example. As the external charging starts, the ECU  150  reads from the storage device  153  the “event type,” and information, such as “time of occurrence” of the event, “GPS location information,” “SOC,” “available time period for external electric power supply,” a “remaining charging time,” “remaining EV travel distance,” and “charger-discharger state information,” and transmits the “event type,” and the information to the server  30  through the communication device  180 . Alternatively, the ECU  150  may collect the information above separately from the “event type.” 
     Note that the available time period for external electric power supply is a time remained during external electric power supply until the battery  130  becomes empty, and calculated based on the SOC and the magnitude of electric power supplied by the vehicle  50 . The remaining charging time is a time remained during external charging until the battery  130  is fully charged, and calculated based on the SOC and the magnitude of the charging power. The remaining EV travel distance is a distance that the vehicle  50  can travel with the electric power stored in the battery  130 , and calculated based on the SOC and the power consumption efficiency of the vehicle  50  (for example, a historic average value, etc.). The charger-discharger state information indicates a state of the charger-discharger  120  (activated/deactivated). 
     Referring, again, to  FIG. 1 , the server  30  carries out DR to the vehicle  50 . Schematically, for example, if a server (not shown) of the power company managing the power grid PG requests the server  30  to adjust supply and demand, the server  30  determines the power capacity that the vehicle  50  can offer. Based on the capacity, the server  30  generates an implementation schedule for the vehicle  50 , and transmits a DR request to the vehicle  50  through the communication apparatus  31 . 
     As the vehicle  50  receives the DR request from the server  30  and is connected to the EVSE  40 , the vehicle  50  can charge the battery  130  (the external charging) with supply of electric power from the EVSE  40  (the power grid PG) or supply the EVSE  40  (the power grid PG) with the electric power stored in the battery  130  (the external electric power supply), according to the DR request. As the external charging or the external electric power supply is performed, the vehicle  50  transmits the information, shown in  FIG. 4 , to the server  30  through the communication device  180  at the occurrence of a respective event (for example, at start/end of external charging). 
     At this time, if the wireless communication between the vehicle  50  and the server  30  is poor, the server  30  is unable to appropriately obtain from the vehicle  50  the information for use in the DR. As a result, appropriate adjustment of supply and demand of electric power may not be performed in response to the DR request. If appropriate adjustment of supply and demand of electric power is not performed in response to the DR request while the vehicle is participating in DR, the user of the vehicle  50  may suffer from drawbacks, such as being subjected to penalty. 
     Thus, in the present embodiment, if the wireless communication between the vehicle  50  participating in DR and the server  30  is determined to be poor, the priority of the vehicle  50  is lowered among power adjustment resources (referred to as “distributed energy resources (DERs)” below) participating in DR. 
     In other words, while DERs are requested for DR, the priority of each of DERs participating in DR is determined, considering response situations (a time when the DER is available, charging capability/electric power supply capability, etc.). In the present embodiment, despite the fact that the changes in SOC of the vehicle  50  are sensed, if the server  30  has not obtained the history information indicating that the vehicle  50  has performed external charging or external electric power supply from the vehicle  50 , the server  30  determines that the reliability of the communication with the vehicle  50  is degraded, and determines the priority of the vehicle  50  so that the vehicle  50  is less likely to be selected for a DR request. 
     This can avoid a situation in which, despite the fact that the vehicle  50  is participating in DR, no appropriate adjustment of supply and demand of electric power is performed in response to a DR request due to the degradation of the communication reliability. Accordingly, a customer (the user of the vehicle  50 ) can be prevented from suffering from drawbacks (such as being subjected to penalty) caused by appropriate adjustment of supply and demand of electric power not being performed in response to a DR request. 
     In the present embodiment, for each vehicle participating in and registered in DR, the server  30  manages information (referred to as “DR information” below) for determining the priority of the vehicle for DR. Based on the DR information of each vehicle participating in DR, the server  30  determines the priority of the vehicle  50  for a DR request. 
       FIG. 5  is a diagram illustrating one example of the DR information managed for each vehicle by the server  30 . Referring to  FIG. 5 , “UID” is identification information (ID) of the vehicle  50 , which is given to each vehicle when the vehicle is registered in participation in DR. “State of vehicle” indicates whether the vehicle  50  is available for a DR request by being connected to the EVSE  40 . The information is determined based on the activation/deactivation state of the travel system of the vehicle  50  and the location information, which are obtained from the vehicle  50 . The “state of vehicle” changes to available for DR when the travel system of the vehicle  50  is deactivated and the location information of the vehicle  50  indicates a location near the EVSE  40  (for example, home). 
     “SOC” is a most-recent SOC obtained from the vehicle  50 . The DR request includes an increase demand request (also referred to as a “posiwatt DR” below) requesting an increase in electric power demand from an electric power customer (the vehicle  50 ), and a reduce demand request (also referred to as a “negawatt DR” below) requesting a reduction in electric power demand. Note that the negawatt DR is not limited to reduction in electric power demand, and also includes supply of electric power to the power grid PG. The lower the SOC of the vehicle  50  is, the highly available the vehicle  50  is for a posiwatt DR. The higher the SOC is, the highly available the vehicle  50  is for a negawatt DR. Thus, if a DR request is a posiwatt DR, the SOC being low raises the priority of the vehicle  50  for the DR request, and the SOC being high lowers the priority of the vehicle  50  for the DR request. In contrast, if a DR request is a negawatt DR, the SOC being low lowers the priority of the vehicle  50  for the DR request, and the SOC being high raises the priority of the vehicle  50  for the DR request. 
     “Communication reliability” indicates reliability of wireless communication between the vehicle  50  and the server  30 . As mentioned above, as the reliability of communication between the vehicle  50  and the server  30  is degraded, the vehicle  50  may not perform appropriate adjustment of supply and demand of electric power in response to a DR request. Therefore, the degradation of the communication reliability lowers the priority of the vehicle  50  for a DR request. In the present embodiment, the reliability of the communication with the vehicle  50  is determined to be poor if, although the server  30  has sensed changes in SOC of the vehicle  50 , the server  30  has not obtained the history information indicating that the vehicle  50  has performed external charging or external electric power supply from the vehicle  50 . 
       FIG. 6  is a diagram illustrating one example of priority information for a DR request. Referring to  FIG. 6 , the priority information is managed by the server  30 , and indicates a priority of each user participating in DR. “UID-***” indicates a user ID of a user (a customer) corresponding to the priority. The priority information is updated based on the DR information for each vehicle shown in  FIG. 5 . 
       FIGS. 7 and 8  are diagrams each illustrating one example method of determination of the priority of the vehicle  50  for a DR request. Referring to  FIGS. 5 and 7 , X11 to X13 are indices respectively indicating degrees of “state of vehicle,” “SOC,” and “communication reliability” shown in  FIG. 5 . 
     For example, the longer the time period for which the vehicle  50  is available for DR relative to a time period the DR request, a point farther away from the center X0 (outer side), the “state of vehicle” indicated by X11 is plotted to. This example shows that the vehicle  50  is available for DR for an entire period of time for which a DR request is made. 
     When the DR request is a posiwatt DR, the lower the SOC is, the outer side of the chart the “SOC” indicated by X12 is plotted to. When the DR request is a negawatt DR, the higher the SOC is, the outer side of the chart the “SOC” indicated by X12 is plotted to. The higher the reliability of the communication between the server  30  and the vehicle  50  is determined to be, the outer side of the chart the “communication reliability” indicated by X13 is plotted to. Stated differently, the “communication reliability” indicated by X13 is plotted to the inner side of the chart if the reliability of communication between the server  30  and the vehicle  50  is determined to be low. 
     Then, in this example, based on the area of the hatched region defined by the plots of X11 to X13, the priority of the vehicle  50  is determined. In other words, as compared to other vehicles, the greater the area of the hatched region, the higher the priority the vehicle  50  has, while the smaller the area of the hatched region, the lower the priority the vehicle  50  has. 
       FIG. 8  is a diagram illustrating a situation in which the reliability of the communication between the server  30  and the vehicle  50  is degraded. Referring to  FIG. 8 , in this example, since the reliability of the communication between the server  30  and the vehicle  50  is degraded, “communication reliability” indicated by X13 is plotted to the inner side of the chart, as compared to the example of  FIG. 7 . Therefore, the area of the hatched region defined by the plots of X11 to X13 is smaller than the example of  FIG. 7 . In other words, the chart illustrated in  FIG. 8  indicates that the vehicle  50  has a lower priority than the example shown in  FIG. 7 . 
     The respective indices of X11 to X13 may be weighed. For example, the indices may be weighed so that the degradation of the communication reliability has a greater contribution to lowering the priority than the condition of the SOC has. The parameters determining the priority of the vehicle  50  for a DR request are not limited to X11 to X13, and other parameters may be included. 
       FIGS. 9 and 10  are flowcharts each illustrating one example procedure of a process of updating the priority of the vehicle  50  for a DR request. The flowchart of  FIG. 9  shows a procedure when a posiwatt DR is requested. The flowchart of  FIG. 10  shows a procedure when a negawatt DR is requested. The series of process steps illustrated in these flowcharts are performed by the server  30 , and is started once the server  30  obtains the various information ( FIG. 3 ) on the vehicle  50  from the vehicle  50  upon the deactivation of the travel system of the vehicle  50 . 
     Referring to  FIG. 9 , as the travel system of the vehicle  50  is deactivated, the server  30  obtains the information on the SOC (will be referred to as S 1 ) of the battery  130  from the information ( FIG. 3 ) transmitted from the vehicle  50  (step S 10 ). 
     Subsequently, the server  30  determines whether the server  30  has received external charging start event and end event from the vehicle  50  (step S 20 ). Specifically, the server  30  determines whether the server  30  has received the information ( FIG. 4 ) indicating that the event type is start and end of external charging from the vehicle  50 , after the travel system is deactivated. Upon receiving the external charging start event and end event (YES in step S 20 ), the server  30  passes the process to END, without performing the subsequent process steps. 
     While the server  30  has not received at least one of the external charging start event and end event from the vehicle  50  (NO in step S 20 ), the server  30  determines whether the travel system of the vehicle  50  is activated (step S 30 ). Specifically, the server  30  determines whether the server  30  has received the various information ( FIG. 3 ) of the vehicle  50  from the vehicle  50  upon deactivation of the travel system. If the server  30  has not yet received the information and the travel system is being deactivated (NO in step S 30 ), the process returns to step S 20 . 
     If the travel system of the vehicle  50  is determined to be activated in step S 30  (YES in step S 30 ), the server  30  obtains the information on the SOC (will be referred to as S 2 ) of the battery  130  from the information ( FIG. 3 ) transmitted from the vehicle  50  (step S 40 ). 
     Subsequently, the server  30  calculates a difference ΔSOC (=S 2 −S 1 ) between the SOC (S 2 ) obtained in step S 40  and the SOC (S 2 ) obtained in step S 10 , and determines whether ΔSOC is greater than a threshold Sth 1  (step S 50 ). It should be noted that, since an average amount of increase in SOC during external charging is considered as being sufficiently greater than an amount of increase in SOC while the vehicle is traveling (in general, the SOC decreases while the vehicle is traveling), the threshold Sth 1  is appropriately set to a value that allows the SOCs in the above two cases to be distinguishable. 
     Then, if ΔSOC is determined to be greater than the threshold Sth in step S 50  (YES in step S 50 ), the server  30  updates, by lowering, the priority of the vehicle  50  for the DR request (posiwatt DR) (step S 60 ). Specifically, if the server  30  has not received at least one of the external charging start event and end event from the vehicle  50  (NO in step S 20 ) although ASOC is greater than the threshold Sth 1  (YES in step S 50 ), such a situation is determined as the reliability of communication being degraded between the server  30  and the vehicle  50 . Then, the server  30  updates, by lowering, the priority of the vehicle  50  for the DR request (posiwatt DR), based on the area of the hatched region defined by the plots of X11 to X13, as described with respect to  FIGS. 7 and 8 . 
     While, in the above description, the case where the server  30  has not received at least one of the external charging start event and end event from the vehicle  50  is the condition under which the priority of the vehicle  50  is lowered, it should be noted that the condition may be that the server  30  has not received both the external charging start event and end event from the vehicle  50 . 
     The weight on the communication reliability in determination of the priority may be changed, depending on whether the server  30  has not received both the external charging start event and end event or one of both events. 
     Referring to  FIG. 10 , a procedure when a negawatt DR is requested is now described. The process steps S 210 , S 230 , S 240 , and S 260  in the flowchart illustrated in  FIG. 10  are the same as the process steps S 10 , S 30 , S 40 , and S 60 , respectively, illustrated in  FIG. 9 . 
     In the flowchart, if obtained the information on the SOC (S 1 ) of the battery  130  in step S 210 , the server  30  determines whether the server  30  has received external electric power supply start event and end event from the vehicle  50  (step S 220 ). Specifically, after the travel system is deactivated, the server  30  determines whether the server  30  has received from the vehicle  50  the information ( FIG. 4 ) indicating that the event type is start and end of the external electric power supply. Then, if the server  30  receives the external electric power supply start event and end event (YES in step S 220 ), the server  30  passes the process to END, without performing the subsequent process steps. 
     As long as the server  30  has not received at least one of the external electric power supply start event and end event from the vehicle  50  (NO in step S 220 ), the server  30  passes the process to step S 230 . 
     If obtained the information on the SOC (S 2 ) of the battery  130  in step S 240 , the server  30  calculates a difference ΔSOC (=S 1 −S 2 ) between the SOC (S 1 ) obtained in step S 210  and the SOC (S 2 ) obtained in step S 240 , and determines whether ΔSOC is greater than a threshold Sth 2  (step S 250 ). 
     Then, if ΔSOC is determined to be greater than the threshold Sth 2  in step S 250  (YES in step S 250 ), the process is passed to step S 260  in which the priority of the vehicle  50  for the DR request (negawatt DR) is updated by being lowered. Specifically, if the server  30  has not received at least one of the external electric power supply start event and end event from the vehicle  50  (NO in step S 220 ) although ΔSOC is greater than the threshold Sth 2  (YES in step S 250 ), such a situation is determined as the reliability of communication being degraded between the server  30  and the vehicle  50 . Then, the server  30  updates, by lowering, the priority of the vehicle  50  for the DR request (negawatt DR), based on the area of the hatched region defined by the plots of X11 to X13, as described with respect to  FIGS. 7 and 8 . 
     It should be noted that, since an average amount of decrease in SOC during external electric power supply is considered as being greater than an amount of decrease in SOC while the vehicle is traveling (because electric power is discharged and charged while the vehicle is traveling), the threshold Sth 2  is appropriately set to a value that allows average amounts of change in the SOCs in the above two cases to be distinguishable, for example. 
     While, in the example of  FIG. 10 , the case where the server  30  has not received at least one of the external electric power supply start event and end event from the vehicle  50  is the condition under which the priority of the vehicle  50  is lowered, it should be noted that the condition may be that the server  30  has not received both the external electric power supply start event and end event from the vehicle  50 . 
     The weight that is applied to the communication reliability when determining the priority may be changed, depending on whether the server  30  has not received both the external electric power supply start event and end event or one of both events. 
     As described above, in the present embodiment, if the server  30  has not obtained, even though the SOC of the battery  130  of the vehicle  50  has changed, the history information indicating that the vehicle  50  has performed external charging or external electric power supply, the reliability of wireless communications between the server  30  and the vehicle  50  is considered as being degraded, and the priority of the vehicle  50  is determined so that the vehicle  50  is less likely to be selected for a DR request. This can avoid a situation in which, despite the fact that the vehicle  50  is participating in DR, no appropriate adjustment of supply and demand of electric power is performed in response to a DR request due to the degradation of the communication reliability. Therefore, according to the present embodiment, a customer (the user of the vehicle  50 ) can be prevented from suffering from drawbacks (such as being subjected to penalty) caused by appropriate adjustment of supply and demand of electric power not being performed in response to a DR request. 
     [Variation 1] 
     The embodiment above has been described with reference to using the information indicating the start/end of external charging or external electric power supply as the history information indicating that the vehicle  50  has performed demand and supply of electric power for the power grid PG, that is, the history information indicating that the vehicle  50  has performed the external charging or the external electric power supply. Information indicating connection/disconnection between the connector  43  of the electric power cable  42  and the inlet  110  may instead be used as the history information above. 
       FIG. 11  is a flowchart illustrating one example procedure of a process of updating the priority of the vehicle  50  for a DR request, according to Variation 1. The flowchart corresponds to the flowcharts illustrated in  FIGS. 9 and 10 . 
     Referring to  FIG. 11 , the process steps S 310 , S 330 , S 340 , and S 360  illustrated in the flowchart are the same as the process steps S 10 , S 30 , S 40 , S 60 , respectively, illustrated in  FIG. 9 . 
     In the flowchart, if obtained the information on the SOC (S 1 ) of the battery  130  in step S 310 , the server  30  determines whether the server  30  has received from the vehicle  50  a connect event and a disconnect event between the connector  43  of the electric power cable  42  and the inlet  110  (step S 320 ). Specifically, after the travel system is deactivated, the server  30  determines whether the server  30  has received from the vehicle  50  the information ( FIG. 4 ) indicating that the event type is connection and disconnection between the connector  43  and the inlet  110 . Then, upon receiving a connect event and a disconnect event between the connector  43  and the inlet  110  (YES in step S 320 ), the server  30  passes the process to END, without performing the subsequent process steps. 
     If the server  30  has not received at least one of a connect event and a disconnect event between the connector  43  and the inlet  110  from the vehicle  50  (NO in step S 320 ), the server  30  passes the process to step S 330 . 
     If obtained the information on the SOC (S 2 ) of the battery  130  in step S 340 , the server  30  calculates a difference |ΔSOC| between the SOC (S 1 ) obtained in step  310  and the SOC (S 2 ) obtained in step S 340 , and determines whether |ΔSOC| is greater than a threshold Sth (step S 350 ). 
     Then, if |ΔSOC| is determined to be greater than the threshold Sth in step S 350  (YES in step S 350 ), the process is passed to step S 360  in which the priority of the vehicle  50  for the DR request is updated by being lowered. Specifically, if the server  30  has not received at least one of a connect event and a disconnect event between the connector  43  and the inlet  110  from the vehicle  50  (NO in step S 320 ) although |ΔSOC| is greater than the threshold Sth (YES in step S 350 ), such a situation is determined as the reliability of communication being degraded between the server  30  and the vehicle  50 . Then, the server  30  updates, by lowering, the priority of the vehicle  50  for the DR request, based on the area of the hatched region defined by the plots of X11 to X13, as described with respect to  FIGS. 7 and 8 . 
     As described above, Variation 1 yields the same advantages effects as the embodiment above. 
     [Variation 2] 
     While the embodiment above and Variation 1 have been described with reference to using a change in SOC (ΔSOC) since the travel system is deactivated until the travel system is next activated in order to determine the reliability of communication between the server  30  and the vehicle  50 , a change in SOC when the location of the vehicle  50  remains unchanged may instead be used. 
       FIG. 12  is a flowchart illustrating one example procedure of a process of updating the priority of the vehicle  50  for the DR request, according to Variation 2. The flowchart illustrates a procedure when a posiwatt DR is requested. The series of process steps illustrated in the flowchart is repeated at prescribed cycles. 
     Referring to  FIG. 12 , the server  30  obtains the information on the vehicle  50  (the location information, the SOC of the battery  130 , etc.) from the information ( FIG. 4 ) that is periodically transmitted from the vehicle  50  (step S 410 ). The server  30  then determines whether the location information on the vehicle  50 , obtained in step S 410 , has changed from the previous values (step S 420 ). If the location of the vehicle has changed (YES in step S 420 ), the process is passed to RETURN, without the subsequent series of process steps being performed. 
     If the location of the vehicle remains unchanged (NO in step S 420 ), the server  30  determines whether the server  30  has received external charging start event and end event from the vehicle  50  (step S 430 ). If the server  30  has received the external charging start event and end event (YES in step S 430 ), the server  30  passes the process to RETURN, without performing the subsequent process steps. 
     If the server  30  has not received at least one of the external charging start event and end event from the vehicle  50  (NO in step S 430 ), the server  30  calculates a difference ΔSOC (=S 2 −S 1 ) between the current value (will be referred to as S 2 ), obtained in step S 410 , and the previous value (will be referred to as S 1 ) of the SOC, and determines whether ΔSOC is greater than a threshold Sth 1  (step S 440 ). 
     Then, if the ΔSOC is determined to be greater than the threshold Sth 1  in step S 440  (YES in step S 440 ), the server  30  updates, by lowering, the priority of the vehicle  50  for the DR request (posiwatt DR) (step S 450 ). Specifically, if the server  30  has not received at least one of the external charging start event and end event from the vehicle  50  (NO in step S 430 ) although the SOC has changed (ΔSOC&gt;Sth 1 ) (YES in step S 440 ) while the vehicle  50  is being parked (the location information remains unchanged), such a situation is determined as the reliability of communication being degraded between the server  30  and the vehicle  50 . Then, the server  30  updates, by lowering, the priority of the vehicle  50  for the DR request (posiwatt DR), based on the area of the hatched region defined by the plots of X11 to X13, as described with respect to  FIGS. 7 and 8 . 
     Note that, although not shown particularly, for a procedure when a negawatt DR is requested, the priority of the vehicle  50  for the DR request (negawatt DR) is updated by determining whether the server  30  has received external electric power supply start/end events in step S 430 , and determining whether ΔSOC=S 1  (previous value)−S 2  (current value) is greater than the threshold Sth 1  in step S 440 . 
     As described above, Variation 2 also yields the same advantages effects as the embodiment above. 
     [Variation 3] 
     Similarly to Variation 1 of the present embodiment, in Variation 2, information indicating connection/disconnection between the connector  43  of the electric power cable  42  and the inlet  110  may be used as the history information indicating that the vehicle has performed external charging or external electric power supply. 
       FIG. 13  is a flowchart illustrating one example procedure of a process of updating the priority of the vehicle  50  for a DR request, according to Variation 3. The flowchart corresponds to the flowchart illustrated in  FIG. 12 . 
     Referring to  FIG. 13 , the process steps S 510 , S 520 , and S 550  illustrated in the flowchart are the same as the process steps S 410 , S 420 , and S 450 , respectively, illustrated in  FIG. 12 . 
     In the flowchart, if the location of the vehicle remains unchanged (NO in step S 520 ), the server  30  determines whether the server  30  has received from the vehicle  50  a connect event and a disconnect event between the connector  43  of the electric power cable  42  and the inlet  110  (step S 530 ). Specifically, the server  30  determines whether the server  30  has received from the vehicle  50  the information ( FIG. 4 ) indicating that the event type is connection and disconnection between the connector  43  and the inlet  110 . Then, upon receiving a connect event and a disconnect event between the connector  43  and the inlet  110  (YES in step S 530 ), the server  30  passes the process to RETURN, without performing the subsequent process steps. 
     If the server  30  has not received at least one of a connect event and a disconnect event between the connector  43  and the inlet  110  from the vehicle  50  (NO in step S 530 ), the server  30  calculates a difference |ΔSOC| between the current value of the SOC obtained in step S 510  and the previous value, and determines whether |ΔSOC| is greater than a threshold Sth (step S 540 ) 
     Then, if |ΔSOC| is determined to be greater than the threshold Sth in step S 540  (YES in step S 540 ), the process is passed to step S 550 , and the priority of the vehicle  50  for the DR request is updated by being lowered. 
     As described above, Variation 3 also yields the same advantages effects as the embodiment above. 
     [Variation 4] 
     While Variations 2 and 3 have been described, with reference to using changes in SOC (ΔSOC) when the location of the vehicle remains unchanged in order to determine the reliability of communication between the server  30  and the vehicle  50 , a change in travel distance of the vehicle  50  may instead be used. 
       FIG. 14  is a flowchart illustrating one example procedure of a process of updating the priority of the vehicle  50  for a DR request, according to Variation 4. The flowchart illustrates a procedure when a posiwatt DR is requested. The flowchart corresponds to the flowchart illustrated in  FIG. 12 . 
     Referring to  FIG. 14 , the process steps S 610 , S 630  to S 650  illustrated in the flowchart are the same as the process steps S 410 , S 430  to S 450 , respectively, illustrated in  FIG. 12 . 
     In the flowchart, as the server  30 , in step S 610 , obtains the information on the vehicle  50  (including the location information, the SOC, the travel distance, etc.) from the information ( FIG. 4 ) that is periodically transmitted from the vehicle  50 , the server  30  determines whether the travel distance of the vehicle  50  has changed from the previous value (step S 620 ). If the travel distance has changed (YES in step S 620 ), the process is passed to RETURN, without the subsequent series of process steps being performed. 
     If the travel distance remains unchanged (NO in step S 620 ), the server  30  passes the process to step S 630  in which the server  30  determines whether the server  30  has received external charging start event and end event from the vehicle  50 . The subsequent process steps are the same as those illustrated in  FIG. 12 . 
     Note that, although not shown particularly, for a procedure when a negawatt DR is requested, the priority of the vehicle  50  for the DR request (negawatt DR) is updated by determining whether the server  30  has received external electric power supply start/end events in step S 630 , and determining whether ΔSOC=S 1  (previous value)−S 2  (current value) is greater than the threshold Sth 1  in step S 640 . In step S 630 , the server  30  may determine whether the server  30  has received connect/disconnect events between the connector  43  of the electric power cable  42  and the inlet  110 , instead of determining whether the server  30  has received the external charging start/end events. 
     As described above, Variation 4 also yields the same advantages effects as the embodiment above. 
     The presently disclosed embodiment and the variations thereof should be considered in all aspects as illustrative and not restrictive. The technical scope of the present disclosure is indicated by the appended claims, rather than by the embodiments above, and all changes that come within the scope of the claims and the meaning and range of equivalency of the claims are intended to be embraced within their scope. 
     Although the present disclosure has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the scope of the present disclosure being interpreted by the terms of the appended claims.