Abstract:
A storage battery equipment includes a converter, a system interconnection inverter, and a controller. The converter extracts direct current power from a storage battery, then converts a voltage of the direct current power and outputs the direct current power. The system interconnection inverter converts the direct current power outputted from the converter into an alternating current power. The controller controls the system interconnection inverter such that an amount of power output from the system interconnection inverter to a load matches a preset target discharge amount.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    The present application is based on Japanese Patent Application No. 2014-208778 filed on Oct. 10, 2014, disclosure of which is incorporated herein by reference. 
       TECHNICAL FIELD 
       [0002]    The present disclosure relates to a storage battery equipment that supplies electric power, which is stored in a storage battery, to a building. 
       BACKGROUND 
       [0003]    Electrical power supplied from an electric power system (e.g., a power grid) to a building fluctuates greatly depending on the operating status of machinery that use electric power (i.e., a load). In this regard, for buildings that consume a large amount of electric power such as factories, a storage battery equipment is often used to level, or reducing the peak of, the electric power supplied from the electric power system (e.g., refer to JP 2014-128063 A). 
         [0004]    This type of storage battery equipment stores electric power in a storage battery during relatively low power consumption time bands (e.g., during the night), and supplies power from the storage battery during relatively high power consumption time bands. By using the storage battery equipment, a peak value of the electric power supplied from the electric power system may be kept low, and thus electricity fees paid to power companies may be reduced. 
         [0005]    In order to interconnect the power supplied from storage battery equipment with the power supplied from the electric power system, an inverter is included in the storage battery equipment. Specifically, the inverter converts direct current (DC) power extracted from the storage battery into alternating current (AC) power. Further, a converter is included between the storage battery and the inverter. Here, the converter extracts the DC power from the storage battery and converts the voltage of the DC power. 
         [0006]    The storage battery equipment includes a controller that controls the overall operation of the storage battery equipment. The controller periodically sets a target value (i.e., an electric power amount) for the electric power that should be supplied from the storage battery equipment to the building, such that the electric power supplied from the electric power system is efficiently leveled. Further, in some cases, this controller may be in the form of a high level controller that is separate from the storage battery equipment. 
         [0007]    In a conventional storage battery equipment, the controller controls the converter such that the amount of electric power actually extracted from the storage battery (or if there are multiple storage batteries, the total amount of electric power extracted from each battery) matches the above described target value. 
       SUMMARY 
       [0008]    It is understood that in power converters such as the inverter and the converter, the input power and output power are not precisely matched. Instead, conversion losses occur as a result of power conversion. In other words, if “conversion efficiency” is defined as the output power divided by the input power, it is understood that the conversion efficiency of power converters is a value lower than 1. 
         [0009]    In this regard, even when controlling the converter such that the amount of power extracted from the storage battery matches the target value, the actual amount of power supplied to the building is less than the target value, Specifically, the actual amount of power supplied to the building is obtained by multiplying the target value with the conversion efficiency of the converter and then with the conversion efficiency of the inverter. 
         [0010]    As a countermeasure to this point, it is contemplated that the amount of power needed for electric power leveling (i.e., the conventional target value) may be divided by each of the conversion efficiencies, and the resulting value, which is greater than the conversional target value, may be set as the target value for the amount of power output from the storage battery. 
         [0011]    However, the conversion efficiency of power converters is not a fixed value, and varies based on factors such as the magnitude of the power being output by the power converter (e.g., a load factor), the environment of the power converter (e.g., temperature). For this reason, it is difficult to predict the conversion efficiency in advance and suitably set the target value for the amount of power extracted from the storage battery based on the predicted value. Specifically, there is a concern that if the predicted conversion efficiency deviates from the actual conversion efficiency, the storage battery may deteriorate from excess discharging. 
         [0012]    Further, the same problem may occur in the case of charging the storage battery. In order to charge the storage battery with surplus power from the building, a target value for the amount of power that should be charged is set. However, in this case, the amount of power drawn by the storage battery equipment from the building may exceed the surplus power. In other words, although the actual amount of power charged to the storage battery is matched with the target value, the amount of power drawn by the storage battery equipment from the building passes through the inverter and the converter. Thus, the target value is divided by the conversion efficiency of the inverter (i.e., &lt;1) and then divided by the conversion efficiency of the converter (i.e., &lt;1), and the resulting value is greater than the set target value. 
         [0013]    In view of these points, it is an object of the present disclosure to provide a storage battery equipment that can accurately supply an amount of electric power needed for electric power leveling for a building. 
         [0014]    In view of the above, in one aspect of the present disclosure, there is provided a storage battery equipment for supplying electric power stored in a storage battery to a building, including a converter that extracts direct current power from the storage battery, converts a voltage of the direct current power, and outputs the direct current power, an inverter that converts the direct current power outputted from the converter into an alternating current power, and supplies the alternating current power to the building, and a controller that controls the converter and the inverter. The controller controls the inverter such that an amount of power outputted from the inverter to the building matches a preset target discharge amount. 
         [0015]    In other words, according to the present disclosure, the controller of the storage battery equipment does not control the amount of power extracted by the converter from the storage battery to match the target discharge amount. Instead, the controller controls the amount of power output from the inverter to the building to match the target discharge amount. In this regard, the power output from the inverter to the building is used as a control value, and an amount of power substantially equal to the target discharge amount (i.e., the amount of power necessary for leveling) may be supplied to the building. 
         [0016]    Thus, the present disclosure provides a storage battery equipment that may accurately supply an amount of power needed for electric power leveling for a building. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    The disclosure, together with additional objectives, features and advantages thereof, will be best understood from the following description, the appended claims and the accompanying drawings, in which: 
           [0018]      FIG. 1  is a system view of an entire configuration of a power supply system that includes a storage battery equipment according to an embodiment of the present disclosure; 
           [0019]      FIG. 2  is a control block diagram showing functional blocks of a controller shown in  FIG. 1 ; 
           [0020]      FIG. 3  is a diagram showing a method of updating a target value for an amount of power output from the storage battery equipment; 
           [0021]      FIG. 4  is a block diagram showing a magnitude of the power output from various components of the storage battery equipment during discharging; 
           [0022]      FIG. 5  is a block diagram showing a magnitude of the power output from various components of the storage battery equipment during charging; 
           [0023]      FIG. 6  is a block diagram showing a magnitude of the power output from various components of a storage battery equipment of a reference example during discharging; and 
           [0024]      FIG. 7  is a block diagram showing a magnitude of the power output from various components of a storage battery equipment of a reference example during charging. 
       
    
    
     DETAILED DESCRIPTION 
       [0025]    Hereinafter, embodiments of the present disclosure will be explained with reference to the figures. For easy of understanding, components having the same configuration are denoted with the same reference numerals in each figure where appropriate, and redundant explanations thereof are omitted for brevity. 
         [0026]    First, a storage battery equipment BS according to an embodiment of the present disclosure will be explained with reference to  FIG. 1 . The storage battery equipment BS forms a portion of a power supply system PS for supplying electric power to a factory FC. 
         [0027]    Further, the factory FC receives power supplied from an electric power system CP which is a commercial power supply. The electric power system CP and the factory FC are connected by a power supply line SL 0  which is an AC bus. Specifically, the factory FC is supplied with 3-phase 200V AC power from the electric power system CP through the power supply line SL 0 . Machinery which uses electric power (i.e., a load) is located in the factory FC, and this machinery primarily operates by receiving power supplied from the electric power system CP. Further, in the following explanation, machinery which uses electric power and is located in the factory FC is collectively referred to as a “load LD”. 
         [0028]    The power supply system PS is connected to the middle of the power supply line SL 0  which connects the electric power system CP with the factory FC. The power supply system PS supplies auxiliary power to the load LD through the power supply line SL 0 , and curtails electric power supplied from the electric power system PS to the load LD. Here, the power supply system PS includes a solar power system SS and the storage battery equipment BS. 
         [0029]    The solar power system SS converts sunlight energy into electric power, and supplies this power to the load LD. Specifically. power from the solar power system SS is supplied to the load LD through a power supply line SL 1  and the power supply line SL 0 . The power supply line SL 1  is an AC bus having one terminal connected to the power supply line SL 0 . 
         [0030]    The solar power system SS includes solar panels  41  and inverters  42 . The solar panels  41  generates power by converting sunlight energy into DC power. A plurality of the solar panels  41  is installed on a roof of the factory FC. 
         [0031]    The inverters  42  are power converters that convert the DC power generated by the solar panels  41  into 3-phase 200V AC power, and supplies this power to the power supply line SL 1 . One of the inverters  42  is provided for each of the solar panels  41 . As shown in  FIG. 1 , the present embodiment includes four sets of the solar panels  41  and the inverters  42 , which are connected in parallel to the power supply line SL 1 . However, the number of each the solar panels  41  and the inverters  42  is not limited to four, and may be increased or decreased based on the scale of the factor FC and the performance of the solar panels  41 . 
         [0032]    On clear days, power is supplied from the solar power system SS to the load LD. Accordingly, power supply from the electric power system CP to the load LD is curtailed, and electricity fees paid to power companies may be reduced. 
         [0033]    The storage battery equipment BS temporarily stores whatever power supplied from the solar power system SS or the power supply system CP that could not be consumed by the load LD. During time periods of high power consumption by the load LD, the storage battery equipment BS supplies the stored power to the load LD. In this regard, power supplied from the electric power system CP to the load LD may be curtailed. 
         [0034]    Power from the storage battery equipment BS is supplied to the load LD through a power supply line SL 2  and the power supply line SL 0 . The power supply line SL 2  is a DC bus. Further, the power supply line SL 2  is connected to the power supply line SL 0  and the power supply line SL 1  through a system interconnection inverter (or grid-interconnected inverter)  300  which will be described later. 
         [0035]    The storage battery equipment BS includes a controller  100 , storage battery units  200 , and the system interconnection inverter  300 . 
         [0036]    The controller  100  is a computer system that controls the operation of the entire storage battery equipment BS. The controller  100  includes one high level controller  110  and five low level controllers  120 . As will be explained in detail later, the high level controller  110  is in communication with each of the low level controllers  120  to control the low level controllers  120 , and at the same time controls the operation of the system interconnection inverter  300 . 
         [0037]    Each of the five low level controllers  120  ( 121 ,  122 ,  123 ,  124 ,  125 ) is a system including a CPU, a ROM, a RAM, and an input/output interface. Further, each of the five low level controllers  120  ( 121 ,  122 ,  123 ,  124 ,  125 ) is housed within a housing of a respective one of the storage battery units  200 , and controls the operation of their respective storage battery unit  200  based on instructions from the high level controller  110 . 
         [0038]    The storage battery equipment BS includes five of the storage battery units  200 , which are connected in parallel to the power supply line SL 2 . Each of the storage battery units  200  includes one storage battery  21  and one DC/DC converter  22 , which are housed within a single housing to form a unit. Further, the number of the storage battery units  200  (and the number of the low level controllers  120 ) is not limited to five, and may be increased or decreased based on the scale of the factory FC, the capacity of the storage batteries  21 , and the like. 
         [0039]    The storage batteries  21  are rechargeable batteries such as lithium-ion batteries or nickel-metal hydride batteries. The DC/DC converters  22  are power converters that upscale the voltage of the DC power generated from the storage batteries  21 , and supplies (i.e., discharges) this power to the power supply line SL 2 . Further, the DC/DC converters  22  include a function of downscaling the voltage of the DC power of the power supply line SL 2  and supplying (i.e., charging) this power to the storage batteries  21 . In other words, the DC/DC converters  22  connect the power supply line SL 2  with the storage batteries  21  and regulate the voltage therebetween. 
         [0040]    The system interconnection inverter  300  is a power converter that converts the DC power from the power supply line SL 2  into AC power, and supplies this AC power to the power supply line SL 0 . Further, the system interconnection inverter  300  converts the AC power from the power supply lines SL 0 , SL 1  into DC power, and supplies this DC power to the power supply line SL 2 . In other words, power may be supplied by the system interconnection inverter  300  in either direction between the power supply line SL 2  and the power supply lines SL 0 , SL 1 . The operation of the system interconnection inverter  300  is controlled by the high level controller  110 . 
         [0041]    The specific configuration of the controller  100  will be explained with reference to  FIG. 2 . The five low level controllers  120  include a low level controller  121 . The low level controller  121  is mounted in one of the storage battery units  200  and, naturally, controls the operation of the DC/DC converter  22  mounted in the same storage battery unit  200 . Further, the low level controller  121  also controls the operation of the other low level controllers  122 ,  123 ,  124 ,  125 . It should be noted that only the low level controller  121  communicates with the high level controller  110 . As such, the low level controller  121  functions as a master controller, while the other low level controllers  122 ,  123 ,  124 ,  125  function as slave controllers. 
         [0042]    In the following explanation, the storage battery unit  200  in which the low level controller  121  (i.e., the master controller) is mounted in will be referred to as a “storage battery unit  201 ”. Further, the DC/DC converter  22  included in the storage battery unit  201  will be referred to as a “DC/DC converter  221 ”, and the storage battery  21  connected to the DC/DC converter  221  will be referred to as a “storage battery  211 ”. 
         [0043]    Similarly, the storage battery unit  200  in which the low level controller  122  (i.e., one of the slave controllers) is mounted will be referred to as a “storage battery unit  202 ”. Further, the DC/DC converter  22  included in the storage battery unit  202  will be referred to as a “DC/DC converter  222 ”, and the storage battery  21  connected to the DC/DC converter  222  will be referred to as a “storage battery  212 ”. The storage battery units  200  for the other low level controllers  123 ,  124 ,  125 , as well as the DC/DC converters  22  and storage batteries  21  included therein, are referred to in the same manner as above. 
         [0044]    As shown in  FIG. 2 , the high level controller  110  includes a target setting unit  111 , which is a functional control block. The target setting unit  111  sets a target value for the amount of power supplied from the storage battery equipment BS to the load LD, or sets a target value for the amount of power charged to the storage battery equipment BS. 
         [0045]    Each time a predetermined calculation period elapses (e.g., every one hour), the target setting unit  111  determines whether the storage battery equipment BS will supply power or be charged with power for the next calculation period. Along with this determination, the target setting unit  111  also sets one of a target value for the amount of power which should be supplied by the storage battery equipment BS to the load LD (hereinafter referred to as a “target discharge amount”) and a target value for the amount of power which should be drawn by the storage battery equipment BS from the load LD side (hereafter referred to as a “target charge amount”). In this regard, the target setting unit  111  may be regarded as laying out the plan for the operation of the storage battery equipment BS (i.e., to discharge or to charge). 
         [0046]    After the target discharge amount of the target charge amount is set by the target setting unit  111 , the high level controller  110  sets a charge/discharge instruction value based on the target charge amount of the target discharge amount. The charge/discharge instruction value is a target value at which the system interconnection inverter  300  should, at the present time, input or output power. The high level controller  110  then sends the charge/discharge instruction value to the system interconnection inverter  300 . 
         [0047]    The system interconnection inverter  300  includes a power measuring unit  301  and a power control unit  302 , which are functional control blocks. The power measuring unit  301  continuously measures a discharge power or a charge power of the system interconnection inverter  300 . Here, the discharge power is a value of the power being output from the system interconnection inverter  300  to the load LD side. Similarly, the charge power is a value of the power being supplied from the load LD side to the system interconnection inverter  300 . The power measuring unit may be provided by, e.g., an electric power sensor. The discharge power or the charge power measured by the power measuring unit  301  is transmitted to the high level controller  110 . 
         [0048]    When the system interconnection inverter  300  is discharging power, the power control unit  302  controls the operation of the system interconnection inverter  300  such that the instant power being supplied (or discharged) to the load LD matches the charge/discharge instruction value sent from the high level controller  110 . Further, when the system interconnection inverter  300  is charging power, the power control unit  302  controls the operation of the system interconnection inverter  300  such that the instant power being supplied (or charged) to the storage battery equipment BS matches the charge/discharge instruction value sent from the high level controller  110 . 
         [0049]    The low level controller  121  includes an integration unit  130  and a management unit  140 , which are functional control blocks. The management unit  140  of the low level controller  121  is a control block that controls the operation of the DC/DC converter  221 , and manages the input/output power of the storage battery  211 . Specifically, the management unit  140  continuously calculates and stores a state of charge (SOC) of the storage battery  211  based on a voltage between the output terminals of the storage battery  211  and an integrated value of the power discharged and charged by the storage battery  211  (i.e., coulomb counting). Further, the management unit  140  continuously monitors whether the storage battery  211  is operating normally (e.g., whether a portion of the cells are degraded, etc.). 
         [0050]    Further, the management unit  140  of the low level controller  121  includes a maximum setting unit  141 . The maximum setting unit  141  is a control block that stores a maximum (or upper limit) value for the power discharged or charged through the DC/DC converter  221 . Typically, this maximum value is set as the highest value (i.e., rated value) of power that may be output by the storage battery  211 , and is stored in the maximum setting unit  141 . 
         [0051]    If the SOC of the storage battery  211  is near 0% during a discharge operation, the maximum value is set to zero and stored in the maximum setting unit  141 . Further, if the SOC of the storage battery  211  is near 100% (i.e., fully charged) during a charge operation, the maximum value is set to zero and stored in the maximum setting unit  141 . 
         [0052]    The management unit  140  controls the operation of the DC/DC converter  221  such that the value of the power passing through the DC/DC converter  221  settles below the maximum value stored in the maximum setting unit  141 . However, in the present embodiment, the magnitude of the power passing through the DC/DC inverter  221  is not controlled to match a predetermined target value. Instead, as will be explained later, the management unit  140  merely controls the direction of the power passing through the DC/DC converter  221  (i.e., charging or discharging). 
         [0053]    The integration unit  130  is a control block that communicates with, and controls the operation of, the management units  140  of each of the low level controllers  121 ,  122 ,  123 ,  124 ,  125 . Further, the integration unit  130  includes a directing unit  131  and an SOC memory unit  132 , which will be explained later. 
         [0054]    The low level controller  122  does not include an integration unit  130  as described above, and instead only includes a management unit  140  (as well as a maximum setting unit  141 ) which is a functional control block. The management unit  140  of the low level controller  122  functions in the same manner as that of the low level controller  121 , and controls the operation of the DC/DC converter  222  and manages the input/output levels of the storage battery  212 . The other low level controllers  123 ,  124 ,  125  are configured in the same manner, and include respective management units  140  and maximum setting units  141 , which are also functional control blocks. 
         [0055]    The control process of the controller  100  will be explained with reference to  FIGS. 1 to 3 . As explained previously, each time the calculation period (e.g., one hour) elapses, the controller  100  determines whether charging or discharging will be performed during the next calculation period. In addition, the controller  100  sets the target discharge amount or the target charge amount for use during the next calculation period. 
         [0056]      FIG. 3  shows a case where a calculation period TM 1  (of one hour) is defined between a time t 0  and a time t 1 , a calculation period TM 2  (of one hour) is defined between the time t 1  and a time t 2 , and a calculation period TM 3  (of one hour) is defined between the time t 2  and a time t 3 . In this case, at the time t 1 , which is when the calculation period TM 1  ends, the target setting unit  111  of the high level controller  110  determines whether charging or discharging will be performed during the next calculation period TM 2 . 
         [0057]    For this determination, the power supplied from the electric power system CP to the load LD is leveled as much as possible based on changes in the power consumed by the load LD during the period up to the time t 1 , the time band of the calculation period TM 2  (e.g., night, noon, etc.), and an estimated amount of power to be consumed by the load LD during the calculation period TM 2 . 
         [0058]    After the target setting unit  111  performs this determination, the target setting unit  111  communicates to the integration unit  130  of the low level controller  121  whether discharging or charging will be performed during the calculation period TM 2 . The low level controller  121  then stores this determination result in the directing unit  131 . For example, if discharging will be performed during the calculation period TM 2 , a “0”, which indicates discharging, is stored in the directing unit  131 . If charging will be performed during the calculation period TM 2 , a “1”, which indicates charging, is stored in the directing unit  131 . 
         [0059]    Further, at the time t 1 , the target setting unit  111  of the high level controller  110  determines the target discharge amount or the target charge amount for the next calculation period TM 2 . Specifically, this determination is performed based on the total amount of power stored in each of the storage batteries  21 , or the total amount of power that may be charged to each of the storage batteries  21 . 
         [0060]    Further, the integration unit  130  continuously communicates with each of the management units  140 , and thus is aware of the situation of each of the storage batteries  21 . Specifically, the amount of power stored in each of the storage batteries  21  is communicated to the integration unit  130 , and the total value thereof is stored in the SOC memory unit  132 . Similarly, the amount of power that may be charged to each of the storage batteries  21  is communicated to the integration unit  130 , and the total value thereof is stored in the SOC memory unit  132 . The information stored in the SOC memory unit  132  is transmitted to the high level controller  110 , and this information is used for the above described determination of the target discharge amount or the target charge amount. 
         [0061]    If discharging is performed during the calculation period TM 2 , the high level controller  110  sends the charge/discharge instruction value to the system interconnection inverter  300  such that the amount of power supplied from the system interconnection inverter  300  to the load LD matches the target discharge amount set by the target setting unit  111 . Here, the charge/discharge instruction value may be, for example, a value (of power, in Watts) obtained by dividing the target discharge amount by the length of the calculation period TM 2 . Then, the system interconnection inverter  300  operates so that the discharge power measured by the power measuring unit  301  matches the charge/discharge instruction value. In this case, the system interconnection inverter  300  draws power from the power supply line SL 2  so as to output a power equal to the charge/discharge instruction value to the load LD side. 
         [0062]    Due to the system interconnection inverter  300  drawing power, the voltage of the power supply line SL 2  decreases. As a result, the power supplied by each of the DC/DC converter  22  to the power supply line SL 2  is increased. As explained previously, the management units  140  do not control the magnitude of the power output by the DC/DC converters  22 . 
         [0063]    Instead, the management units  140  only control the directionality of the power passing through the DC/DC converters  22  to match the direction stored in the directing unit  131 , while ensuring that the magnitude of this power does not exceed the maximum value. In practice, the magnitude of the power supplied from the DC/DC converters  22  to the power supply line SL 2  varies according to the voltage of the power supply line SL 2 , i.e., as the operation of system interconnection inverter  300  progresses. 
         [0064]    The same applies if charging is performed during the calculation period TM 2 . In this case, the high level controller  110  controls the operation of the system interconnection inverter  300  such that the amount of power supplied from the load LD side (i.e., from the power supply system CP or the solar power system SS) to the system interconnection inverter  300  matches the target charge amount set by the target setting unit  111 . Here, the charge/discharge instruction value may be, for example, a value (of power, in Watts) obtained by dividing the target charge amount by the length of the calculation period TM 2 , and is sent from the high level controller  110  to the system interconnection inverter  300 . Then, the system interconnection inverter  300  operates so that the charge power measured by the power measuring unit  301  matches the charge/discharge instruction value. In this case, the system interconnection inverter  300  draws power equal to the charge/discharge instruction value from the load LD side so as to output a power to the power supply line SL 2 . 
         [0065]    Due to the system interconnection inverter  300  supplying power, the voltage of the power supply line SL 2  increases. As a result, the power output by each of the DC/DC converters  22  to the storage batteries  21  increases. In this case as well, the management units  140  only control the directionality of the power passing through the DC/DC converters  22  to match the direction stored in the directing unit  131 , while ensuring that the magnitude of this power does not exceed the maximum value. In practice, the magnitude of the power drawn by the DC/DC converters  22  from the power supply line SL 2  varies according to the voltage of the power supply line SL 2 , i.e., as the operation of the system interconnection inverter  300  progresses. 
         [0066]    The magnitude of the power output from the various components of the storage battery equipment BS (such as the DC/DC converters  22 ) during discharging will be explained with reference to  FIG. 4 . In the following explanation, a target value obtained from dividing the target discharge amount by the length of the calculation period is referred to as a “target power P T1 ”. The high level controller  110  sends the target power P T1  (i.e., the charge/discharge instruction value) to the system interconnection inverter  300 . The power control unit  302  of the system interconnection inverter  300  controls the operation of the system interconnection inverter  300  such that the power output from the system interconnection inverter  300  to the load LD matches the target power P T1 . 
         [0067]    In this case, the power drawn from the power supply line SL 2  to the system interconnection inverter  300  (i.e., the total power supplied from each of the DC/DC converters  22  to the system interconnection inverter  300 ) does not match the target power P T1 . A conversion efficiency η a  of the system interconnection inverter  300  is less than 1. Accordingly, the total power drawn from the power supply line SL 2  to the system interconnection inverter  300  is a value greater than P T1 , i.e., P T1 /η a . 
         [0068]    Further, the total power output by each of the storage batteries  21  to the DC/DC converters  22  does not match P T1 /η a . A conversion efficiency η b  of the DC/DC converters  22  is less than 1. Accordingly, the total power output by each of the storage batteries  21  to the DC/DC converters  22  is a value even greater than P T1 /η a , i.e., P T1 /η a η b . 
         [0069]    In this regard, the amount of power extracted from the storage batteries  21  over the calculation period is greater than the target discharge amount. As a result, the discharging process may attempt to extract more power than the amount stored in the storage batteries  21 , i.e., so-called “excess discharging”. 
         [0070]    However, the target discharge amount set at the beginning of the calculation period (i.e., t 1  of TM 2 ) may be set based on the actual stored amount of power at that time (i.e., the value stored in the SOC memory unit  132 ), with a margin such that excess discharging does not occur. As a result, excess discharging may be reliably prevented. 
         [0071]    The magnitude of the power output from the various components of the storage battery equipment BS (such as the DC/DC converters  22 ) during charging will be explained with reference to  FIG. 5 . In the following explanation, a target value obtained from dividing the target charge amount by the length of the calculation period is referred to as a “target power P T2 ”. The high level controller  110  sends the target power P T2  (i.e., the charge/discharge instruction value) to the system interconnection inverter  300 . The power control unit  302  of the system interconnection inverter  300  controls the operation of the system interconnection inverter  300  such that the power supplied from the load LD side (i.e., the power supply system CP or the solar system SS) to the system interconnection inverter  300  matches the target power P T2 . 
         [0072]    In this case, the power output to the power supply line SL 2  from the system interconnection inverter  300  (i.e., the total power supplied from the system interconnection inverter  300  to each of the DC/DC converters  22 ) does not match the target power P T2 . The conversion efficiency η a  of the system interconnection inverter  300  is less than 1. Accordingly, the power output to the power supply line SL 2  from the system interconnection inverter  300  is a value smaller than P T2 , i.e., P T2 *η a . 
         [0073]    Further, the total power output by each of the DC/DC converters  22  to the storage batteries  21  does not match P T2 *η a . The conversion efficiency η b  of the DC/DC converters  22  is less than 1. Accordingly, the total power output by each of the DC/DC converters  22  to the storage batteries  21  is a value even smaller than P T2 *η a , i.e., P T2 *η a η b . 
         [0074]    As described above, according to the storage battery equipment BS of the present embodiment, the total amount of power extracted from the storage batteries by the DC/DC converters  22  is not matched to the target discharge amount. Instead, the amount of power output from the system interconnection inverter  300  to the load LD side is matched to the target discharge amount. By using the power output from the system interconnection inverter  300  to the load LD side as the control value, the effects of the conversion efficiencies η a , η b  are avoided, and a power that is substantially equal to the target discharge amount (i.e., the amount of power necessary for leveling) may be supplied to the load LD. 
         [0075]    The same applies to charging. According to the storage battery equipment BS, the total amount of power supplied from the DC/DC converter  22  to the storage batteries  21  is not matched to the target charge amount. Instead, the amount of power supplied from the load LD side to the system interconnection inverter  300  is matched to the target charge amount. By using the power output from the load LD side to the system interconnection inverter  300  as the control value, the effects of the conversion efficiencies η a , η b  are avoided, and a power that is substantially equal to the target charge amount (i.e., the amount of power necessary for electric power leveling) may be supplied from the load LD side to the storage battery equipment BS. 
         [0076]    As a comparative example to the present disclosure, the magnitude of the power output from the various components of a reference example storage battery equipment during discharging will be explained with reference to  FIG. 6 . According to the storage battery equipment of the reference example, the total amount of power extracted by each of the DC/DC converters  22  from the storage batteries  21  is used by the controller  100  as the control value. In other words, each of the DC/DC converters  22  is controlled such that the total amount of power extracted by the DC/DC converters  22  from the storage batteries  21  matches the target power P T1 . 
         [0077]    In this case, the power drawn from the power supply line SL 2  to the system interconnection inverter  300  (i.e., the total power supplied from each of the DC/DC converters  22  to the system interconnection inverter  300 ) does not match the target power P T1 . The conversion efficiency η b  of the DC/DC converters  22  is less than 1. Accordingly, the total power drawn from the power supply line SL 2  to the system interconnection inverter  300  is a value smaller than P T1 , i.e., P T1 *η b . 
         [0078]    Further, the total power output by the system interconnection inverter  300  to the load LD does not match P T1 /η b . The conversion efficiency η a  of the system interconnection inverter  300  is less than 1. Accordingly, the total power output by the system interconnection inverter  300  to the load LD is a value even less than P T1 *η b , i.e., P T1 *n a η b . 
         [0079]    For this reason, the amount of power supplied from the storage battery equipment to the load LD during the calculation period is smaller than the target discharge amount. As a result, the power supplied from the power supply system CP to the load LD is not sufficiently leveled. In contrast, according to the storage battery equipment BS of the present embodiment, the amount of power supplied to the load LD is substantially equal to the target discharge amount as explained above. Accordingly, the power supplied from the power supply system CP to the load LD is sufficiently leveled as initially planned. 
         [0080]    In addition to discharge, the same applies to charging. The magnitude of the power output from the various components of the reference example storage battery equipment during charging will be explained with reference to  FIG. 7 . According to the storage battery equipment of the reference example, the total amount of power supplied from each of the DC/DC converters  22  to the storage batteries  21  is used by the controller  100  as the control value. In other words, each of the DC/DC converters  22  is controlled such that the total amount of power supplied from the DC/DC converters  22  to the storage batteries  21  matches the target power P T2 . 
         [0081]    In this case, the power supplied from the system interconnection inverter  300  to the power supply line SL 2  (i.e., the total power supplied from the system interconnection inverter  300  to each of the DC/DC converters  22 ) does not match the target power P T2 . The conversion efficiency η b  of the DC/DC converters  22  is less than 1. Accordingly, the total power supplied from the system interconnection inverter  300  to the power supply line SL 2  is a value greater than P T2 , i.e., P T2 /η b . 
         [0082]    Further, the power supplied from the load LD side (i.e., from the power supply system CP or the solar power system SS) to the system interconnection inverter  300  does not match P T2 /η b . The conversion efficiency η a  of the system interconnection inverter  300  is less than 1. Accordingly, the power supplied from the load LD side to the system interconnection inverter  300  is a value even greater than P T2 /η b , i.e., P T2 /η a η b . 
         [0083]    For this reason, the amount of power drawn by the storage battery equipment from the load LD side during the calculation period is greater than the target charge amount. As a result, the power supplied from the power supply system CP to the load LD is not sufficiently leveled. In contrast, according to the storage battery equipment BS of the present embodiment, the amount of power drawn by the storage battery equipment BS from the load LD side is substantially equal to the target charge amount as explained above. Accordingly, the power supplied from the power supply system CP to the load LD is sufficiently leveled as initially planned. 
         [0084]    Further, in the present embodiment, a plurality of the storage battery units  200  are included. In other words, an example is provided where a plurality of sets of the storage batteries  21  and the DC/DC converters  22  are included. However, the present embodiment of the present disclosure is not limited to such a configuration. Instead, even if only one storage battery unit  200  is provided, the present disclosure may still be applied. 
         [0085]    However, by including a plurality of the storage battery units  200  as in the present embodiment, the number of storage battery units  200  may be increased or decreased according to the scale of the factory FC (i.e., the power usage amount of the load LD). In other words, the storage battery equipment BS of the present disclosure is highly scalable and may be applied to a variety of scales of buildings without needing to prepare storage batteries having different storage capacities beforehand. 
         [0086]    Further, in the present embodiment, the controller  100  is divided into the high level controller  110  and the low level controllers  120 . Further, the storage batteries  21  and the DC/DC converters  22  are controlled by only the low level controllers  120 . 
         [0087]    In other words, control of power outputted to the load LD or drawn from the load LD is exclusively performed by the high level controller  110 , and detailed control based on the status of each of the storage batteries  21  (by considering the stored amount of power, any deteriorated cells, etc.) is performed by the low level controllers  120 . As a result, the two types of controls may easily coexist and avoid difficulties caused by intertwining the two types of controls. 
         [0088]    Embodiments of the present disclosure are explained with reference to specific examples above. However, the present disclosure is not limited to these specific examples. In other words, a skilled artisan may suitable alter these specific examples without departing from the gist of the present disclosure. For example, the arrangement, material, requirements, sizes, shapes, etc. of the components of the each specific example may be suitable altered by a skilled artisan. Moreover, the components of each embodiment may be combined in any technically feasible manner that does not depart from the gist of the present disclosure.