Energy storage system and control method

Abstract

This invention provides an energy storage system and control method that can suppress PID phenomena without adding a relay box. [Solution] The energy storage system includes a power conversion unit that supplies power generated by solar panels to a load and the grid, a relay that connects the power conversion unit to the grid, and a control unit that controls the relay. The power conversion unit generates charging power for the storage battery from the power supplied from the grid and supplies the discharge power of the storage battery to the load. The control unit turns off the relay when it is determined that the target value of the charging power or discharge power has remained below a first threshold for a first hour, provided that no surplus power is generated.

Description

Technical Field

[0001] The present disclosure relates to a power storage system and a control method.

Background Art

[0002] A hybrid power storage system including a solar cell, a storage battery, and a power conditioner (i.e., a built-in DC / DC converter or the like) is known. The power conditioner converts DC power generated by the solar cell into AC power and supplies it to a load, and also charges the storage battery with the generated power of the solar power generation. Regarding solar power generation, a PID (Potential Induced Degradation) phenomenon is known in which a solar cell module (solar power generation panel) deteriorates and its output decreases. As the main cause, even at night when the solar cell module is not operating (i.e., generating power), the power conditioner operates to charge the storage battery, and the voltage of the power conditioner is applied to the solar cell module. As a countermeasure against the PID phenomenon, Patent Document 1 below discloses providing a relay box including a plurality of relays for connecting or disconnecting between a plurality of solar cell modules and a power conditioner, and disconnecting them when the solar cell modules are not generating power.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, there is a problem that the relay box provided between the solar cell module and the power conditioner is expensive. In addition, there is also a problem that the number of parts increases and the man-hours in the manufacturing process increase.

[0005] Therefore, the present disclosure aims to provide an energy storage system and control method that can suppress PID phenomena without adding a relay box. [Means for solving the problem]

[0006] A power storage system according to one aspect of the present disclosure includes a power conversion unit that supplies power generated by solar panels to a load and a grid, a relay that connects the power conversion unit to the grid, and a control unit that controls the relay. The power conversion unit generates charging power for a storage battery from the power supplied from the grid and supplies discharging power for the storage battery to a load. The control unit turns off the relay when no surplus power is generated and the target value of the charging power or discharging power has remained below a first threshold for a first hour. [Effects of the Invention]

[0007] According to this disclosure, it is possible to provide an energy storage system and control method that can suppress PID phenomena without adding a relay box. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a block diagram showing the configuration of an energy storage system according to an embodiment of this disclosure. [Figure 2] Figure 2 is a flowchart showing the operation of the energy storage system shown in Figure 1. [Figure 3] Figure 3 is a flowchart showing the interconnection relay off process shown in Figure 2. [Figure 4] Figure 4 is a flowchart showing the interconnection relay ON process shown in Figure 2. [Figure 5] Figure 5 shows the charging and discharging status of the storage battery and the on / off status of the grid connection relay on a day with high solar power generation in the power sales priority mode. [Figure 6] Figure 6 shows the charging and discharging status of the storage battery and the on / off status of the grid connection relay on a day when the amount of solar power generation is low in the power sales priority mode. [Figure 7] Figure 7 shows the charging and discharging status of the storage battery and the on / off status of the grid connection relay on a day with high solar power generation in self-consumption priority mode. [Figure 8] Figure 8 shows the charging and discharging status of the storage battery and the on / off status of the grid connection relay on a day when the amount of solar power generation is low in self-consumption priority mode. [Figure 9] Figure 9 is a flowchart showing the operation of the modified energy storage system. [Figure 10] Figure 10 is a flowchart showing the interconnection relay off process shown in Figure 9. [Modes for carrying out the invention]

[0009] [Description of Embodiments in this Disclosure] The embodiments of this disclosure are listed and described below. At least some of the embodiments described below may be combined in any way.

[0010] (1) The energy storage system according to the first aspect of this disclosure includes a power conversion unit that supplies power generated by solar panels to a load and the grid, a relay that connects the power conversion unit to the grid, and a control unit that controls the relay. The power conversion unit generates charging power for the storage battery from the power supplied from the grid and supplies the discharge power of the storage battery to the load. The control unit turns off the relay when it is determined that the target value of the charging power or discharge power has remained below a first threshold for a first hour, while no surplus power is generated. This suppresses the PID phenomenon. Therefore, it is not necessary to provide a relay box between the solar cell module, including the solar panels, and the power conditioner (energy storage system).

[0011] (2) In (1) above, the control unit may turn on the relay when it is determined that the target value has remained above the second threshold for a second time while the relay is off. This prevents the relay that connects the power conversion unit to the grid (grid-connection relay) from remaining off.

[0012] (3) In the above (1) or (2), when the power conversion unit charges the storage battery at night, it may generate a charging power equal to the rated power. As a result, the storage battery can be charged in a shorter time, the time for turning off the interconnection relay becomes longer, and the PID phenomenon can be further suppressed.

[0013] (4) In any one of the above (1) to (3), the control unit may count the number of times the relay is turned off, and upon receiving that the number has reached or exceeded a third threshold value, even if the target value has been maintained below the first threshold value for a first period of time, or even if the relay has been kept on, the relay may be kept on. As a result, the on-off cycle of the interconnection relay can be reduced, and it is possible to suppress the shortening of the life of the interconnection relay due to an increase in the on-off cycle of the interconnection relay.

[0014] (5) In the above (4), the number may be held for a predetermined period, and may be reset upon receiving that the predetermined period has elapsed. The predetermined period may be one day, one week, one month, or one year. This makes it possible to adjust the trade-off between suppression of the PID phenomenon (maintaining the life of the solar power generation panel) and shortening of the life of the interconnection relay.

[0015] (6) The control method according to the second aspect of the present disclosure is a control method for a power storage system including a power conversion unit that supplies generated power from a solar power generation panel to a load and a power grid, and a relay that connects the power conversion unit to the power grid. The method includes steps of generating, by the power conversion unit, a charging power for the storage battery from the power supplied from the power grid; supplying, by the power conversion unit, a discharging power of the storage battery to the load; and turning off the relay upon receiving that a state where the target value of the charging power or the discharging power is below a first threshold value has been maintained for a first period of time when no surplus power of the generated power is generated. This makes it possible to suppress the PID phenomenon. Therefore, it may not be necessary to provide a relay box between the solar cell module including the solar power generation panel and the power conditioner (power storage system).

[0016] [Details of Embodiments of the Present Disclosure] In the following embodiments, the same parts are given the same reference numerals. Their names and functions are also the same. Therefore, detailed descriptions thereof will not be repeated.

[0017] (System Configuration) Referring to FIG. 1, a power storage system 100 according to an embodiment of the present disclosure includes a DC / DC converter 128 from a DC / DC converter 120, a DC / AC converter 130, a connection relay 132, and an isolation relay 134. The power storage system 100 further includes a control unit 140, a storage unit 142, a timer 144, and a bus 146. The DC / DC converter 120 and the DC / AC converter 130 have functions of converting power bidirectionally. The DC / DC converter 128 from the DC / DC converter 120 is connected in parallel and the DC / AC converter 130 is connected in series. The power storage system 100 is a hybrid power storage system. The power storage system 100 constitutes a power supply system 102 together with PV (Photo Voltage) strings 110 to 116 and a storage battery 118. Note that the power storage system 100 includes an operation unit (not shown) such as a remote controller for a user to input settings of the power storage system 100.

[0018] Each of the PV strings 110 to 116 includes a plurality of PV modules (solar panels). The plurality of PV modules are connected in series with each other. The PV module is, for example, a module in which a plurality of PV cells are connected in series and arranged in a plane and sealed with tempered glass or the like. Each of the PV strings 110 to 116 can be mounted on surfaces with different orientations on a roof.

[0019] The DC power generated by PV strings 110 and 116 is stepped up by DC / DC converters 120 and 126 respectively, input to DC / AC converter 130, converted to AC power by DC / AC converter 130, and output via interconnection relay 132 and independent relay 134. The interconnection relay 132 is connected to the grid 170 via the main breaker 160 and electricity meter 162, and the power generated by PV strings 110 and 116 is output to the grid 170 (sold to the grid). A distribution board 164 is connected between the interconnection relay 132 and the main breaker 160. Power from the grid 170 and power from the energy storage system 100 are supplied to the loads (not shown) of the house where the energy storage system 100 is installed via the distribution board 164. The self-sustaining relay 134 is connected to a specific load (not shown) within the house's loads that receives power through the self-sustaining operation of the energy storage system 100 in the event of a power outage in the grid 170.

[0020] The storage battery 118 is a rechargeable secondary battery, such as a lithium-ion secondary battery. The storage battery 118 is charged by commercial AC power supplied (purchased) from the grid 170 via the interconnection relay 132, which is converted to DC power by the DC / AC converter 130, and then further converted by the DC / DC converter 128. In addition, the storage battery 118 is charged by DC power generated from the PV string 110 to the PV string 116, which is converted by the DC / DC converter 120, then by the DC / DC converter 126 and DC / DC converter 128.

[0021] The control unit 140 generates and outputs control signals 150 for controlling the operation of the energy storage system 100. Specifically, the control unit 140 generates control signals from the DC / DC converter 120 to cause the DC / DC converter 128 and the DC / AC converter 130 to function as converters, and outputs them to each converter. The control unit 140 also generates control signals to operate (i.e., open and close) the interconnection relay 132 and the independent relay 134, and outputs them to the interconnection relay 132 and the independent relay 134. The control unit 140 is, for example, a CPU (Central Processing Unit). The memory unit 142 is, for example, a rewritable non-volatile semiconductor memory that stores the computer program (hereinafter simply referred to as "program") executed by the control unit 140. The control unit 140 also uses the memory unit 142 as a work memory for executing processing, and stores the results of the executed processing in the memory unit 142 as appropriate. The functions of the energy storage system 100 are realized when the control unit 140 reads and executes a program stored in the memory unit 142.

[0022] The timer 144, upon receiving a request from the control unit 140, outputs information representing the current time (hereinafter also simply referred to as the current time) to the control unit 140. Data transmission between the control unit 140, the storage unit 142, and the timer 144 is performed via the bus 146.

[0023] (operation) The operation of the energy storage system 100 will be explained in detail with reference to Figure 2. The process shown in Figure 2 is realized by the control unit 140 reading a predetermined program stored in the memory unit 142 and executing it. In parallel with this program, the control unit 140 also executes a program that monitors the power generation status of PV strings 110 to 116, the power consumption status of the load, and the status of the battery 118. Specifically, the control unit 140 stores the total power generated by PV strings 110 to 116 and the power consumed by the load in the memory unit 142. The control unit 140 also stores the discharge status and remaining capacity of the battery 118 in the memory unit 142. This operation is repeatedly performed, for example, at predetermined time intervals based on information from the timer 144. The control unit 140 also starts charging the battery 118 with commercial power at night (hereinafter also referred to as nighttime charging) at a predetermined time.

[0024] In step 200, the control unit 140 obtains the current time from the timer 144 and determines whether or not it is the nighttime charging period. The start and end times of nighttime charging are stored in the storage unit 142 in advance, and the control unit 140 determines whether or not the current time falls between these times. If it is determined that it is the nighttime charging period, the control proceeds to step 220. Otherwise, the control proceeds to step 202.

[0025] In step 202, the control unit 140 determines whether there is surplus power obtained by subtracting the self-consumed power from the power generated by PV string 116 from PV string 110. That is, the control unit 140 reads the current power generated and the load power consumed from the storage unit 142 and compares them. If power generated > load power consumed, it determines that there is surplus power. If it is determined that there is surplus power, the control returns to step 200. Otherwise, the control proceeds to step 204.

[0026] In step 204, the control unit 140 determines a target value P for the charging power or discharging power of the battery 118, depending on whether the battery 118 is in a charging state or a discharging state. Specifically, the control unit 140 reads the generated power from PV string 110 to PV string 116 and the load power consumption from the storage unit 142, and determines the target value P according to the difference between them. After that, the control proceeds to step 206. For example, if the system is set to the power sales priority mode (a mode in which surplus power is sold), if the generated power from PV string 110 to PV string 116 is greater than the load power consumption, the battery 118 does not charge or discharge, and the target value P is determined to be 0. If the generated power from PV string 110 to PV string 116 becomes less than the load power consumption, the battery 118 discharges, and the target value P is determined to be power consumption minus generated power. For example, if the system is set to self-consumption priority mode (a mode in which surplus power is charged into the battery for self-consumption and used for that purpose, also known as green mode), then if the power generated by PV string 110 to PV string 116 is greater than the load power consumption, the battery 118 will be charged with that surplus power, and the target value P will be determined to be the surplus power. If the power generated by PV string 110 to PV string 116 becomes less than the load power consumption, the battery 118 will discharge, and the target value P will be determined to be power consumption minus power generation.

[0027] In step 206, the control unit 140 reads the first threshold value Th1 which is previously stored in the storage unit 142, and determines whether the target value P determined in step 204 is less than or equal to the first threshold value Th1. If P ≤ Th1, the control proceeds to step 208. Otherwise, the control proceeds to step 212. The first threshold value Th1 is set to a value smaller than the rated power of the battery 118 for charging and discharging. For example, the first threshold value Th1 is set to a value of about 5% of the rated power.

[0028] In step 208, the control unit 140 executes a process to turn off the interconnection relay 132 (hereinafter referred to as the interconnection relay off process). Specifically, the control unit 140 executes the flowchart shown in Figure 3.

[0029] Referring to Figure 3, in step 300, the control unit 140 sets the start time. Specifically, the control unit 140 obtains the current time from the timer 144 and stores it as the start time in the storage unit 142. After that, the control proceeds to step 302.

[0030] In step 302, the control unit 140 determines whether or not the first hour has elapsed from the start time set in step 300. If it is determined that the hour has elapsed, the control proceeds to step 308. Otherwise, the control proceeds to step 304. The first hour can be stored in the storage unit 142 in advance. The first hour is arbitrary and can be a relatively short period of time, such as about 5 minutes, or a relatively long period of time, such as about 30 minutes.

[0031] In step 304, the control unit 140 determines a target value P for the charging or discharging power of the battery 118, similar to step 204. The control then proceeds to step 306.

[0032] In step 306, the control unit 140, similar to step 206, determines whether the target value P determined in step 304 is less than or equal to the first threshold Th1. If P ≤ Th1, control returns to step 302. Otherwise, control proceeds to step 310.

[0033] If the result of step 302 is YES, in step 308, the control unit 140 turns off the grid connection relay 132. After that, the control proceeds to step 310. Note that even if the grid connection relay 132 is turned off, power is still supplied to the load from the grid 170.

[0034] In step 310, the control unit 140 clears the start time stored in the memory unit 142. Then, the control returns to the flowchart in Figure 2 and proceeds to step 210.

[0035] As a result, if the state P ≤ Th1 persists for 1 hour (the result of the judgment in step 302 is YES), when it is not a nighttime charging period (the result of the judgment in step 200 is NO) and there is no surplus power from solar power generation (the result of the judgment in step 202 is NO), the grid connection relay 132 will be turned off. If the state P ≤ Th1 does not persist for 1 hour (the result of the judgment in step 306 is NO), the grid connection relay 132 will remain on.

[0036] In step 210, the control unit 140 determines whether or not it has received a termination instruction. If it determines that it has received a termination instruction, the program terminates. Otherwise, control returns to step 200, and the above process is repeated. The termination instruction is given, for example, by turning off the power to the energy storage system 100.

[0037] If the result of the determination in step 206 is NO, in step 212 the control unit 140 determines whether the interconnection relay 132 is off or not. If it is determined that the interconnection relay 132 is off, the control proceeds to step 214. Otherwise, the control proceeds to step 210.

[0038] In step 214, the control unit 140 determines a target value P for the charging or discharging power of the battery 118, similar to step 204. The control then proceeds to step 216.

[0039] In step 216, the control unit 140 reads the second threshold Th2 which is previously stored in the storage unit 142 and determines whether the target value P determined in step 214 is greater than or equal to the second threshold Th2. If P ≥ Th2, the control proceeds to step 218. Otherwise, the control proceeds to step 210. The second threshold Th2 is, for example, greater than the first threshold Th1 and less than the rated power of the battery 118 for charging and discharging. The second threshold Th2 is set to a value of, for example, about 5% of the rated power. Note that the second threshold Th2 may be the same value as the first threshold Th1.

[0040] In step 218, the control unit 140 performs a process to turn on the interconnection relay 132 (hereinafter referred to as the interconnection relay on process). Specifically, the control unit 140 executes the flowchart shown in Figure 4.

[0041] Referring to Figure 4, in step 320, the control unit 140 sets the start time in the same manner as in step 300. After that, the control proceeds to step 322.

[0042] In step 322, the control unit 140 determines whether a second time has elapsed from the start time set in step 320. If it is determined that a second time has elapsed, the control proceeds to step 328. Otherwise, the control proceeds to step 324. The second time can be stored in the storage unit 142 in advance. The second time is arbitrary and can be a relatively short period of time, such as 5 minutes, or a relatively long period of time, such as 30 minutes.

[0043] In step 324, the control unit 140 determines a target value P for the charging or discharging power of the battery 118, similar to step 204. The control then proceeds to step 326.

[0044] In step 326, the control unit 140, similar to step 216, determines whether the target value P determined in step 324 is greater than or equal to the second threshold Th2. If P ≥ Th2, control returns to step 322. Otherwise, control proceeds to step 330.

[0045] If the result of step 322 is YES, in step 328 the control unit 140 turns on the interconnection relay 132. After that, the control proceeds to step 330.

[0046] In step 330, the control unit 140 clears the start time stored in the memory unit 142. Then, the control returns to the flowchart in Figure 2 and proceeds to step 210.

[0047] As a result, if the state P≧Th2 persists for two hours while the interconnection relay 132 is OFF (the result of the judgment in step 322 is YES), the interconnection relay 132 will be turned ON. If the state P≧Th2 does not persist for two hours (the result of the judgment in step 326 is NO), the interconnection relay 132 will remain OFF.

[0048] (Night charging operation) If the result of step 200 is YES, then in step 220, it is determined whether or not the battery 118 needs to be charged. Specifically, the control unit 140 determines that charging is necessary if the current charge capacity (i.e., remaining capacity) of the battery 118 is less than the target capacity (i.e., remaining capacity at the end of nighttime charging). If it is determined that charging is necessary, the control proceeds to step 222. Otherwise (i.e., the battery is charged to the target capacity), the control proceeds to step 204, and the above-described process is executed.

[0049] In step 222, the control unit 140 controls the DC / AC converter 130 to charge the battery 118 with the rated power of the DC / AC converter 130 for charging and discharging. After that, the control proceeds to step 210.

[0050] Normally, the battery is charged to its target capacity over the entire nighttime charging period (e.g., several hours), so the charging power is much lower than the rated power. In contrast, in step 222, the battery 118 is charged at the rated power. The process returns from step 210 to step 200, and steps 220 and 222 are repeated, allowing the battery 118 to be charged to its target capacity in a relatively short time, and no further charging of the battery 118 is performed for the remainder of the nighttime charging period. Therefore, after the battery 118 has been charged to its target capacity, for the remainder of the nighttime charging period, the result of the determination in step 206 becomes YES, and the interconnection relay 132 is turned off by step 208 (i.e., in Figure 3, the result of the determination in step 302 becomes YES, and by step 308).

[0051] When the nighttime charging period ends and morning arrives, if the power generated by PV string 110 to PV string 116 is less than the load power consumption, a target value P of discharge power greater than threshold Th1 is set in order to supply the discharge power of battery 118 to the load. Therefore, in step 218, the grid connection relay 132 is turned on, the power generated by PV string 110 to PV string 116 is supplied to the load, and any power deficit is supplied by the discharge power of battery 118.

[0052] As a result, the time during which the grid-connection relay 132 is turned off can be extended, thereby suppressing the PID phenomenon. Therefore, it is not necessary to install a relay box between the PV string 110, which includes the solar power generation panels, the PV string 116, and the energy storage system 100.

[0053] As described above, the control unit 140 turns on the grid connection relay 132 when the target value P of the charging or discharging power of the battery 118 remains above the second threshold Th2 for a second time while the grid connection relay 132 is off. This prevents the grid connection relay 132, which connects the DC / AC converter 130 to the grid 170, from remaining off.

[0054] As described above, when the DC / AC converter 130 charges the battery 118 at night, it generates charging power at the rated power to charge the battery 118. This allows the battery 118 to be charged in a shorter time, the time the grid-connection relay 132 is turned off is extended, and the PID phenomenon can be suppressed more effectively.

[0055] Furthermore, this is not limited to charging the battery 118 at its rated power. The goal is to shorten the time spent charging the battery 118 overnight, creating free time during the overnight charging period. Therefore, the battery 118 can be charged overnight with a higher charging power than the power used to charge it during the entire overnight charging period. If free time is created during the overnight charging period, the grid-connection relay 132 can be turned off during that time to suppress PID phenomena.

[0056] Referring to Figures 5 to 8, an example of the state in which the grid-connection relay 132 is turned off is shown. In each of Figures 5 to 8, the upper section shows a graph of the generated power and the power consumed by the load over a day. The horizontal axis represents time, with the center of the horizontal axis being noon. The middle section shows the charge / discharge state of the battery 118 and the on / off state of the grid-connection relay 132 when the conventional control method (hereinafter referred to as control A) is executed, corresponding to the upper section graph. The lower section shows the charge / discharge state of the battery 118 and the on / off state of the grid-connection relay 132 when the control method shown in Figure 2 (hereinafter referred to as control B) is executed, corresponding to the upper section graph.

[0057] Figure 5 shows a scenario where the energy storage system 100 is set to a power sales priority mode, the weather is good, sufficient solar radiation is obtained, and the generated power is large. In control A, the grid connection relay 132 is always kept ON. The surplus power generated by PV strings 110 and 116 is sold to the grid 170. The battery 118 is charged to its target capacity at relatively low power throughout the entire nighttime charging period, and if the generated power is less than the load power consumption, the deficit is supplied by discharge. On the other hand, in control B, nighttime charging of the battery 118 is performed at rated power, so it is completed in a relatively short time (see downward arrow), and there is a gap in the nighttime charging period (see dashed ellipse). Therefore, during that time, the target value P of the charging power is 0 (P ≤ Th1), and the grid connection relay 132 is turned OFF. Thus, the PID phenomenon can be suppressed.

[0058] In Figure 5, with respect to control B, the grid-connection relay 132 is ON during periods other than the idle time during the nighttime charging period. However, near the two points where the graph of generated power and the graph of consumed power intersect, the discharge power of the battery 118 is small, and the target value P of the discharge power of the battery 118 may fall below the first threshold Th1. Therefore, if the first time is set to a relatively short period, the state P≦Th1 can be maintained for the first time, and the grid-connection relay 132 can be turned OFF. Thus, the time during which the grid-connection relay 132 is OFF can be made longer, and the PID phenomenon can be further suppressed. Note that while the grid-connection relay 132 is OFF, the load is not supplied with generated power or the discharge power of the battery 118, and power is supplied from the grid 170.

[0059] Figure 6, like Figure 5, shows the energy storage system 100 set to the power sales priority mode, but unlike Figure 5, it shows a case where the weather is poor and sufficient solar radiation intensity is not obtained, resulting in low power generation. As with Figure 5, Figure 6 also shows the sale of surplus power and the charging and discharging of the battery 118, which are carried out by control A and control B, respectively. With respect to control B, there is idle time during the nighttime charging period (see the dashed-dotted ellipse), and during that time the grid connection relay 132 is turned off. Therefore, the PID phenomenon can be suppressed.

[0060] In Figure 6, as in Figure 5, with respect to control B, the grid connection relay 132 is ON during periods other than the idle time during the nighttime charging period. However, as in Figure 5, near the four points where the power generation graph and the power consumption graph intersect, the discharge power of the battery 118 is small, and the target value P of the discharge power of the battery 118 may be less than or equal to the first threshold Th1. Therefore, if the first time is set to a relatively short period, the state P≦Th1 can be maintained for the first time, and the grid connection relay 132 can be turned OFF. Thus, the time during which the grid connection relay 132 is OFF can be made longer, and the PID phenomenon can be further suppressed.

[0061] Figure 7 shows the case where the energy storage system 100 is set to self-consumption priority mode, the weather is good, sufficient solar radiation is obtained, and the generated power is large. In control A, the grid connection relay 132 is always kept ON. Power generated by PV string 110 and PV string 116 is supplied to the load, and the battery 118 is charged with the surplus power. The battery 118 is charged to the target capacity with relatively low power over the entire nighttime charging period, and if the generated power is less than the power consumed by the load, the deficit is supplied by discharge. On the other hand, in control B, nighttime charging of the battery 118 is performed at rated power, so it is completed in a relatively short time (see downward arrow), and there is idle time during the nighttime charging period (see two ellipses in the dashed line). Therefore, during that time, the target value P of the charging power is 0 (P ≤ Th1), and the grid connection relay 132 is turned OFF. Note that in self-consumption priority mode, the battery 118 is charged with surplus power from the generated power. Therefore, since it is sufficient to charge the battery 118 to a capacity that can supply power to the load the next morning through overnight charging, the charging time of the battery 118 is shorter than in the power sales priority mode. Consequently, the time for which the grid connection relay 132 is turned off in the self-consumption priority mode is longer than in the power sales priority mode, and the PID phenomenon can be suppressed more effectively.

[0062] In Figure 7, as in Figure 5, the interconnection relay 132 can be turned off near the two points where the graph of generated power and the graph of consumed power intersect. Therefore, the time during which the interconnection relay 132 is turned off can be made longer, and the PID phenomenon can be further suppressed.

[0063] Figure 8 shows the same scenario as Figure 7, where the energy storage system 100 is set to self-consumption priority mode. However, unlike Figure 7, it shows a case where the weather is poor, sufficient solar radiation is not obtained, and the generated power is small. As with Figure 7, Figure 8 also shows the charging of the battery 118 with surplus power and the discharging of the battery 118, which are performed by control A and control B, respectively. With respect to control B, there is idle time during the nighttime charging period (see the two ellipses in the dashed line), during which the grid connection relay 132 is turned off. Therefore, the PID phenomenon can be suppressed.

[0064] In Figure 8, as in Figure 6, the interconnection relay 132 can be turned off near the four points where the graph of generated power and the graph of consumed power intersect. Therefore, the time during which the interconnection relay 132 is turned off can be made longer, and the PID phenomenon can be further suppressed.

[0065] (modified version) The control method of the energy storage system 100 shown in Figure 2 allows for a longer period of the off state of the grid-connection relay 132, thereby suppressing PID phenomena. However, this increases the number of on / off cycles of the grid-connection relay 132, shortening its lifespan. The modified version addresses this issue. The configuration of the energy storage system is the same as that shown in Figure 1. On the other hand, regarding the control method, the process shown in Figure 9 is executed instead of the process shown in Figure 2. The flowchart shown in Figure 9 is the same as the flowchart shown in Figure 2, but with steps 240 and 242 added, and step 208 replaced by step 244. Therefore, in the following, we will refer to the reference numerals in Figure 1 and explain mainly the differences without repeating explanations.

[0066] A counter is provided in the storage unit 142 to record the number of times the interconnection relay 132 has been turned off. In step 240, the control unit 140 determines whether or not to reset the counter. Specifically, the control unit 140 reads the time when the counter was last reset (hereinafter referred to as the reset time) and a predetermined period from the storage unit 142, obtains the current time from the timer 144, and determines whether the current time has elapsed to the time obtained by adding the predetermined period to the reset time. If it is determined that the time has elapsed, the control proceeds to step 242. Otherwise, the control proceeds to step 200.

[0067] In step 242, the control unit 140 resets the counter stored in the memory unit 142, i.e., sets it to its initial value (for example, 0). The control unit 140 also obtains the current time from the timer 144 and stores it in the memory unit 142 as the reset time. The reset time stored in the memory unit 142 is used as described above when step 240 is executed again. After that, the control proceeds to step 200.

[0068] The predetermined period is arbitrary and may be, for example, one day, one week, one month, or one year. For example, if the initial value of the reset time is set to a predetermined time on the day the energy storage system 100 is first put into operation (for example, 6 a.m.), the counter will be reset by step 242 around the predetermined time on the day after the predetermined period has elapsed.

[0069] As described above, steps 200 to 206 are executed, and if the result of step 206 is YES, the interconnection relay off process in step 244 is executed. Specifically, the control unit 140 executes the flowchart shown in Figure 10. The flowchart in Figure 10 is the same as the flowchart in Figure 3, but with steps 340 and 342 added. Below, we will mainly explain the differences without repeating explanations.

[0070] Referring to Figure 10, in step 340, the control unit 140 reads the value recorded in the counter (hereinafter referred to as the counter value) and the threshold Th3 from the storage unit 142, and determines whether the counter value is greater than or equal to the threshold Th3. If it is determined that the counter value ≥ Th3, the control returns to the flowchart in Figure 9 and proceeds to step 210. Otherwise, the control proceeds to step 300. The threshold Th3 should be set to an appropriate value according to a predetermined period, which is the interval at which the counter is reset.

[0071] Steps 300 and 302 are executed, and if the result of step 302 is YES (the first time has elapsed), step 308 turns off the interconnection relay 132. Subsequently, in step 342, the control unit 140 increments the value of the counter stored in the memory unit 142 by 1. After that, the control moves to step 310, and after step 310, the control returns to the flowchart in Figure 9 and moves to step 210.

[0072] As a result, each time the interconnection relay 132 is turned off by step 308, the counter value is incremented by 1 by step 342. Once the counter value increases from its initial value (e.g., 0) to Th3, the subsequent processing from step 300 onwards in Figure 10 is not executed. That is, step 308 is not executed, the interconnection relay 132 remains on, step 342 is not executed, and the counter maintains its current value. Therefore, the number of times the interconnection relay 132 is turned on and off can be reduced, and the shortening of the interconnection relay 132's lifespan can be suppressed.

[0073] As described above, the number of times the grid connection relay 132 has been turned off (counter value) may be retained for a predetermined period, or it may be reset after the predetermined period has elapsed. The predetermined period may be one day, one week, one month, or one year. This allows for adjustment of the trade-off between suppressing the PID phenomenon (maintaining the lifespan of the solar power generation panels) and shortening the lifespan of the grid connection relay 132.

[0074] The above describes a case where the counter is reset periodically, but it is not limited to this. For example, a threshold Th3 may be set according to the operating period of the energy storage system 100. For example, a threshold Th3 for each predetermined operating period (e.g., one year or one month) may be stored in advance in the storage unit 142. In that case, steps 240 and 242 are deleted in Figure 9, and in step 340 of Figure 10, the control unit 140 reads the threshold Th3 corresponding to the operating period of the energy storage system 100 from the storage unit 142 and compares that threshold Th3 with the counter value. In step 340, if it is determined that the counter value ≥ Th3, the grid connection relay 132 is kept ON. Therefore, the number of times the grid connection relay 132 is turned ON and OFF can be reduced, and the shortening of the lifespan of the grid connection relay 132 can be suppressed.

[0075] Furthermore, the specified operating periods do not have to be at regular intervals. For example, the operating periods may be 1 year, 3 years, 5 years, and 8 years, and a threshold Th3 may be set for each.

[0076] The present disclosure has been described above by describing embodiments, but the embodiments described above are illustrative and the present disclosure is not limited to the embodiments described above. The scope of the present disclosure is as indicated by each claim of the claims, with reference to the description of the detailed description of the invention, and includes all modifications within the meaning and scope equivalent to the wording contained herein. [Explanation of symbols]

[0077] 100 Energy Storage Systems 102 Power supply system 110, 112, 114, 116 PV strings 118 Storage Battery 120, 122, 124, 126, 128 DC / DC converters 130 DC / AC Converter 132 interconnected relays 134 Self-supporting relay 140 Control Unit 142 Storage section 144 timers 146 Bus 150 Control signal 160 Main circuit breaker 162 Electric energy meter 164 Distribution board 170 strains

Claims

1. A power conversion unit that supplies power generated by solar panels to the load and grid, A relay connecting the power conversion unit to the system, Includes a control unit that controls the relay, The power conversion unit is The power supplied from the aforementioned grid is used to generate charging power for the storage battery. The discharge power of the aforementioned battery is supplied to the aforementioned load. The control unit, in a state where no surplus power is generated, turns off the relay when it is determined that the target value of the charging power or the discharging power has remained below a first threshold for a first hour.

2. The energy storage system according to claim 1, wherein the control unit turns on the relay when the relay is turned off and the state in which the target value is equal to or greater than a second threshold has been maintained for a second time.

3. The energy storage system according to claim 1 or 2, wherein the power conversion unit generates the rated power of the charging power when charging the storage battery at night.

4. The control unit, The number of times the relay is turned off is counted, The energy storage system according to claim 1 or 2, wherein, in response to the number of occurrences exceeding a third threshold, the relay remains in the ON state even if the state in which the target value is less than or equal to the first threshold is maintained for a first time.

5. The number of times mentioned above is It is kept for a predetermined period of time. After the predetermined period has elapsed, it is reset. The energy storage system according to claim 4, wherein the predetermined period is one day, one week, one month, or one year.

6. A control method for an energy storage system, which includes a power conversion unit that supplies power generated by solar panels to a load and a grid, and a relay that connects the power conversion unit to the grid, The power conversion unit generates charging power for the storage battery from the power supplied from the grid, The power conversion unit supplies the discharge power of the storage battery to the load, A control method comprising the step of turning off the relay after confirming that, in a state in which no surplus power of the generated power is generated, the target value of the charging power or the discharging power has remained below a first threshold for a first hour.

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