Charging system

Abstract

To provide a charging system capable of suppressing repetition of a charging operation state and a standby state at low temperature.SOLUTION: A charging system 1 includes: a storage battery 11; a BMS 12; a charging unit (DC / DC conversion unit 22), and a control unit 23. The BMS 12 includes a state detection unit for detecting a fully charged state of the storage battery 11 and a processing unit for transmitting a maximum charging current value (a MCCV) to the control unit 23. The control unit 23 performs charging current control for controlling charging operation so that a current value of a charging current I1 becomes the MCCV and performs, when preset charging end conditions are satisfied during charge current control, charging end control for ending the charging current control. The charging end conditions are a condition that the MCCV of zero ampere is received for a plurality of times after the MCCV of non-zero ampere is received.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a charging system.

Background Art

[0002] Conventionally, as an example of a charging system, an electricity storage system including an electricity storage unit and a power conditioner is known. Some electricity storage systems include a photovoltaic power generation function using solar cells, and others include, in addition to the photovoltaic power generation function, a charging and discharging function for electric vehicles by a V2H (Vehicle to Home) device (see, for example, Patent Document 1).

[0003] The electricity storage unit includes a storage battery and a Battery Management System (BMS) that manages the storage battery. The power conditioner includes a charging unit that performs a charging operation to supply charging current to the storage battery, and a control unit that controls the charging operation of the charging unit. The charging unit is constituted by, for example, an AC / DC converter and a DC / DC converter.

[0004] The BMS determines a maximum charging current value (MCCV: Max Charging Current Value), which is the maximum value of charging current that can be supplied to the storage battery, based on the cell temperature and cell voltage of the secondary batteries (lithium-ion secondary batteries) constituting the storage battery. The MCCV is uniquely determined by the cell temperature and the cell voltage. For example, even if the cell temperature is the same, if the cell voltage is different, the MCCV will be a different value.

[0005] In addition, the BMS calculates the state of charge (SOC: State Of Charge) of the storage battery and detects a fully charged state of the storage battery (e.g., 100% SOC). The control unit of the power conditioner communicates with the BMS and performs charging current control to match the current value of the charging current to the MCCV. This charging current control is continuously performed until the BMS detects the fully charged state of the storage battery.

[0006] However, due to the characteristics of lithium-ion secondary batteries, if the energy storage unit is installed outdoors or in a cold climate, it may not be possible to charge the battery to 100% SOC at low temperatures. For this reason, the BMS limits the MCCV to 0 amperes at low temperatures before detecting that the battery is fully charged. When the MCCV is limited to 0 amperes, the control unit controls the charging current to 0 amperes. As a result, the supply of charging current to the battery stops, and the power conditioner enters standby mode.

[0007] During charging, the cell voltage rise of a lithium-ion secondary battery is due to both the voltage rise caused by electrical energy storage and the voltage rise caused by the charging current and the internal resistance of the cell. Therefore, when the charging current becomes 0 amperes, the voltage rise caused by the internal resistance of the cell disappears (becomes 0 volts), resulting in a characteristic drop in cell voltage. When the cell voltage drops to a predetermined threshold, the BMS releases the 0-ampere restriction on the MCCV and sends a non-0-ampere MCCV to the control unit. Upon receiving a non-0-ampere MCCV, the control unit increases the charging current value to resume supplying charging current to the battery, and the power conditioner enters a charging operation state. However, when the cell voltage rises due to electrical energy storage in the cell and the internal resistance of the cell and reaches a predetermined threshold, the BMS again restricts the MCCV to 0 amperes, and the power conditioner returns to standby mode.

[0008] Thus, in conventional energy storage systems, at low temperatures, the system repeatedly switches between charging and standby states, resulting in unstable operation. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Publication No. 2021-87271 [Overview of the project] [Problems that the invention aims to solve]

[0010] The present invention has been made in view of the above circumstances, and its object is to provide a charging system that can suppress the repeated switching between a charging operation state and a standby state at low temperatures. [Means for solving the problem]

[0011] To solve the above problems, the charging system according to the present invention is Storage batteries and A battery management system for managing the aforementioned storage battery, A charging unit that supplies a charging current to the battery and performs a charging operation on the battery, A control unit that controls the charging operation of the charging unit, A charging system equipped with, The aforementioned battery management system A voltage measuring unit for measuring the voltage of the aforementioned storage battery, A temperature measuring unit for measuring the temperature of the storage battery, A state detection unit for detecting the fully charged state of the storage battery, A processing unit that determines the maximum charging current value, which is the maximum value of the charging current, at a predetermined interval based on the temperature measured by the temperature measuring unit and the voltage measured by the voltage measuring unit, and transmits a signal relating to the determined maximum charging current value to the control unit, Equipped with, The control unit, Based on the aforementioned signal, charging current control is performed to control the charging operation so that the current value of the charging current approaches the maximum charging current value. If the charging current control is met when the pre-set charging termination conditions are met, the state detection unit performs charging termination control to terminate the charging current control before detecting the fully charged state. The charging termination condition is characterized in that, after the control unit receives a first signal in which the maximum charging current value is not 0 amperes, the control unit receives a second signal in which the maximum charging current value is 0 amperes multiple times.

[0012] In this configuration, when a charging end condition is satisfied where the control unit receives a plurality of times a second signal having a maximum charging current value of 0 amperes after the control unit receives a first signal having a maximum charging current value not equal to 0 amperes, the control unit terminates said charging current control before the state detection unit detects said fully charged state. Therefore, according to this configuration, repetition between a charging operation state and a standby state at low temperatures can be suppressed.

[0013] In the charging system described above, The charging end condition may be a condition that the control unit receives the second signal a plurality of consecutive times.

[0014] In the charging system described above, The charging end condition may be a condition that a ratio of the second signal received by the control unit within a predetermined period is equal to or higher than a predetermined threshold.

[0015] In the charging system described above, The control unit may be configured to: be configured to perform a counting process of counting the number of said signals starting from a time point when said first signal is received after said second signal is received. Effects of the Invention

[0016] According to the present invention, it is possible to provide a charging system capable of suppressing repetition between a charging operation state and a standby state at low temperatures. Brief Description of the Drawings

[0017] [Figure 1] It is a block diagram of an electricity storage system according to an embodiment of the present invention. [Figure 2] It is a block diagram of an electricity storage unit according to an embodiment of the present invention. [Figure 3] (A) is data showing the relationship between cell voltage and SOC stored in a BMS. (B) is data showing the relationship between cell temperature, cell voltage and MCCV stored in a BMS. [Figure 4]It is a flowchart of charge termination control performed by a power conditioner according to an embodiment of the present invention. [Figure 5] It is a diagram showing the relationship between time and MCCV during counting processing. [Figure 6] It is a diagram showing temporal changes in cell voltage, MCCV, and charging current, in which (A) is a diagram of a comparative example, and (B) is a diagram of the present invention.

Mode for Carrying Out the Invention

[0018] Hereinafter, as an embodiment of the charging system according to the present invention, an electricity storage system will be described as an example.

[0019] FIG. 1 shows an electricity storage system 1 according to an embodiment of the present invention. The electricity storage system 1 includes an electricity storage unit 10, and a power conditioner 20 including a direct current / alternating current conversion unit 21, a direct current / direct current conversion unit 22, a control unit 23, and a system protection relay 24.

[0020] The electricity storage unit 10 includes a storage battery 11, a battery management system (BMS) 12 that manages the storage battery 11, and terminals Ta1 and Ta2. FIG. 2 is a block diagram of the electricity storage unit 10.

[0021] The storage battery 11 is composed of at least one secondary cell 11'. In the present embodiment, the storage battery 11 is composed of a plurality of secondary cells 11' connected in series, and a lithium-ion secondary cell is used as the secondary cell 11'. In the storage battery 11, the positive electrode is connected to the terminal Ta1, and the negative electrode is connected to the terminal Ta2. Note that, although each secondary cell 11' is illustrated as one secondary cell in FIG. 2, it is also possible to modify one secondary cell into a plurality of secondary cells connected in parallel. Furthermore, it is also possible to use a type other than a lithium-ion secondary cell as the secondary cell 11'.

[0022] The BMS12 comprises a voltage measuring unit 13, a temperature measuring unit 14, a current measuring unit 15, a switching means 16, and a management unit 17. The management unit 17 comprises a storage unit 17a, a state detection unit 17b, and a processing unit 17c. The BMS12 also includes a discharge unit (not shown) for equalizing the cell voltage of each secondary battery 11'.

[0023] The voltage measurement unit 13 is connected to the positive and negative electrodes of each secondary battery 11' that makes up the storage battery 11, measures the terminal voltage (cell voltage) between the positive and negative electrodes of each secondary battery 11', and outputs the measurement result to the management unit 17.

[0024] The temperature measurement unit 14 includes at least one temperature sensor. The one temperature sensor measures the temperature (cell temperature) of one secondary battery 11'. The temperature sensor may be a contact type temperature sensor or a non-contact type temperature sensor. The temperature measurement unit 14 outputs the measurement result to the management unit 17.

[0025] The current measuring unit 15 measures the DC current (charging current I1 or discharge current) flowing through the power line connecting terminal Ta1 and the positive electrode of the storage battery 11, and outputs the measurement result to the control unit 17.

[0026] The switching mechanism 16 is interposed in the power line connecting terminal Ta1 and the positive terminal of the battery 11. The switching mechanism 16 is provided to protect the battery 11 from overcharging, over-discharging, temperature abnormalities, or other abnormalities in the BMS 12, such as abnormalities in the voltage measurement unit 13, and is switched between an open state and a closed state by the control unit 17. In this embodiment, a relay is used as the switching mechanism 16.

[0027] The control unit 17 may be composed of a digital circuit using a microcontroller or DSP, or it may be composed of a circuit combining the digital circuit and an analog circuit. The control unit 17 is configured to communicate with the control unit 23 of the power conditioner 20.

[0028] The memory unit 17a stores control programs for controlling the operation of each part of the BMS 12, and various data related to the storage battery 11 (secondary battery 11'). The various data include, for example, first data showing the relationship between the cell voltage and the state of charge (SOC) of the secondary battery 11', and table data related to the maximum charging current value (MCCV), which is the maximum value of the charging current I1 that can be supplied to the storage battery 11, and second data showing the relationship between MCCV, cell temperature, and cell voltage. The SOC of the secondary battery 11' is defined as 100% for the fully charged state of the secondary battery 11' and 0% for the completely discharged state of the secondary battery 11'.

[0029] Figure 3(A) shows a portion of the first data set. As described above, the first data set shows the relationship between the cell voltage of the secondary battery 11' and the state of charge (SOC). In the first data set, for example, when the cell voltage of the secondary battery 11' is 3.9[V], the SOC of the secondary battery 11' corresponds to 80%, and when the cell voltage is 4.0[V], the SOC corresponds to 93%. Although Figure 3(A) only shows the SOC range of 75% to 100%, the first data set includes data in the SOC range of 0% to 100%.

[0030] In this embodiment, the first data is data showing the relationship between the cell voltage of the secondary battery 11' and the state of charge (SOC), but the first data may also be data showing the relationship between the open-circuit voltage (OCV) of the secondary battery 11' and the SOC. The OCV can be calculated, for example, using the cell voltage, the internal resistance of the secondary battery 11', and the current value of the charging current I1. Furthermore, since the cell voltage of each secondary battery 11' is equalized by a discharge section (not shown), the SOC of the secondary battery 11' and the SOC of the storage battery 11 will be the same value.

[0031] Figure 3(B) shows a portion of the second data set. As described above, the second data set shows the relationship between MCCV and cell temperature and cell voltage. In the second data set, when the cell temperature of secondary battery 11' is below -10[°C], the MCCV is 0[A] when the cell voltage of secondary battery 11' is 3.8[V] or higher. When the cell temperature is between -10[°C] and below 0[°C], the MCCV is 0[A] when the cell voltage is 3.9[V] or higher. When the cell temperature is between 0[°C] and below 10[°C], the MCCV is 0[A] when the cell voltage is 4.0[V] or higher. Thus, in the second data set, at low temperatures below 10[°C], the MCCV is limited to 0[A] before the SOC reaches 100% (cell voltage of 4.06[V]).

[0032] Furthermore, the second data includes a range of 20°C or higher for the cell temperature (for example, 20 to 45°C), a range of cell voltages corresponding to a SOC of 0% to 100%, and the MCCV corresponding to the above cell temperature and cell voltage. In this embodiment, the second data is presented as table data, but the second data may also be data relating to the relationship between the MCCV, cell temperature, and cell voltage.

[0033] The state detection unit 17b is configured to detect the fully charged state of the storage battery 11 at predetermined intervals. When the cell voltage of the secondary battery 11' is input from the voltage measurement unit 13, the state detection unit 17b calculates the state of charge (SOC) of the secondary battery 11' by referring to the first data in the storage unit 17a. By referring to the first data, the state detection unit 17b can uniquely calculate the SOC based on the cell voltage.

[0034] The state detection unit 17b, when the calculated SOC is 100%, detects that the battery 11 is fully charged and outputs a full charge detection signal to the control unit 23 of the power conditioner 20. For example, the state detection unit 17b switches the voltage signal output to the control unit 23 from a low level to a high level. The voltage signal is low when the SOC is not 100% and high when the SOC is 100%.

[0035] The state detection unit 17b may output a signal to the control unit 23 of the power conditioner 20 regarding the numerical value [%] of the State of Charge calculated by referring to the first data. In this case, the signal when the numerical value of the State of Charge is 100% becomes the full charge detection signal. In this embodiment, the state detection unit 17b considers a State of Charge of 100% as the fully charged state of the battery 11, but the conditions for the fully charged state are not limited to this.

[0036] The processing unit 17c is configured to determine the MCCV at a predetermined interval. When the cell voltage of the secondary battery 11' is input from the voltage measurement unit 13 and the cell temperature of the secondary battery 11' is input from the temperature measurement unit 14, the processing unit 17c refers to the second data and determines the MCCV. By referring to the second data, the processing unit 17c can uniquely determine the MCCV based on the cell voltage and cell temperature. The processing unit 17c outputs the determined MCCV to the control unit 23 of the power conditioner 20.

[0037] As shown in Figure 1, the power conditioner 20 includes terminals TL1, TL2, TN1, terminals TL3, TL4, TN2, terminals Tb1, Tb2, a DC / AC converter 21, a DC / DC converter 22, a control unit 23, and a grid protection relay 24. The power conditioner 20 also includes a detection unit (not shown). The detection unit detects voltage and current values ​​necessary for controlling the control unit 23, and is composed of, for example, at least one voltage sensor and at least one current sensor.

[0038] Terminals TL1, TL2, and TN1 are connected to the commercial power grid 2 via single-phase three-wire connections. Specifically, terminal TL1 is connected to the first voltage line of the single-phase three-wire system, terminal TL2 is connected to the second voltage line of the single-phase three-wire system, and terminal TN1 is connected to the neutral line of the single-phase three-wire system. General loads (e.g., household electrical appliances) are connected between each of the single-phase three-wire lines (not shown in the diagram). The DC / AC converter 21 and terminals TL1, TL2, and TN1 are each connected via a grid protection relay 24, and power supply lines capable of supplying discharged power from the battery 11 are branched from between the DC / AC converter 21 and the grid protection relay 24 to terminals TL3, TL4, and TN2, to which the self-sustaining load 3 (critical loads that require power supply from the battery 11 even during a power outage) is connected.

[0039] Power system 2 supplies 200[V] AC system power to a single-phase three-wire system. Specifically, 100[V] AC system power is supplied between the first voltage line and the neutral line (between terminals TL1 and TN1), 100[V] AC system power is supplied between the neutral line and the second voltage line (between terminals TN1 and TL2), and 200[V] AC system power is supplied between the first voltage line and the second voltage line (between terminals TL1 and TL2).

[0040] Terminals Tb1 and Tb2 are connected to the energy storage unit 10. Specifically, terminal Tb1 is connected to terminal Ta1 of the energy storage unit 10 and is connected to the positive terminal of the battery 11. Terminal Tb2 is connected to terminal Ta2 of the energy storage unit 10 and is connected to the negative terminal of the battery 11.

[0041] The power conditioner 20 is configured to charge and discharge the battery 11. During charging, the power conditioner 20 converts the 200V AC grid power supplied between terminals TL1 and TL2 into DC power and supplies this DC power to the battery 11. During discharging, the power conditioner 20 converts the discharge power from the battery 11 supplied between terminals Tb1 and Tb2 into AC power at commercial frequency and supplies this AC power to the loads connected between each of the single-phase three-wire lines. When the grid is energized, the power conditioner 20 closes the grid protection relay 24 and operates in grid-connected mode, while when the grid is down, it opens the grid protection relay 24 and operates in standalone mode.

[0042] The DC / AC converter 21 includes AC terminals connected to terminals TL1, TL2, TN1 and terminals TL3, TL4, TN2, and DC terminals connected to the DC / DC converter 22, and performs AC / DC conversion operation to convert AC voltage input to the AC terminals into DC voltage, and DC / AC conversion operation to convert DC voltage input to the DC terminals into AC voltage.

[0043] The DC / AC conversion unit 21 is composed of a switching circuit that performs AC / DC conversion and DC / AC conversion operations. The switching circuit includes, for example, a first leg, a second leg, and a third leg connected in parallel, each leg including an upper arm and a lower arm connected in series, and each arm including a switching element. The switching element can be a power semiconductor switching element capable of switching at high frequencies, such as an IGBT (insulated gate bipolar transistor), a MOSFET (metal-oxide-semiconductor field-effect transistor) using SiC (silicon carbide) or GaN (gallium nitride). The DC / AC conversion unit 21 may also include an LC filter circuit between the switching circuit and the AC terminal.

[0044] The DC / DC conversion unit 22 includes a first DC terminal connected to the DC terminal of the DC / AC conversion unit 21 and a second DC terminal connected to terminals Tb1 and Tb2. It performs DC / DC conversion operations such as boosting or stepping down the DC voltage input to the first DC terminal and outputting it from the second DC terminal, or boosting or stepping down the DC voltage input to the second DC terminal and outputting it from the first DC terminal. In other words, the DC / DC conversion unit 22 performs a charging operation to charge the battery 11 by supplying a charging current I1 to the battery 11, and a discharging operation to discharge the battery 11. The DC / DC conversion unit 22 corresponds to the "charging unit" of the present invention.

[0045] The DC / DC conversion unit 22 is composed of a switching circuit that performs DC / DC conversion, for example, a bidirectional DC / DC converter circuit. The bidirectional DC / DC converter circuit may be, for example, a current-resonant DC / DC converter capable of bidirectional operation, a voltage-current DC / DC converter, or a DC / DC converter such as a phase-shift type or a DAB (Dual Active Bridge) type. The switching elements included in the bidirectional DC / DC converter circuit can be the same as those in the DC / AC conversion unit 21.

[0046] The control unit 23 controls the DC / AC converter 21, the DC / DC converter 22, and the system protection relay 24 while communicating with the management unit 17 of the BMS 12. The control unit 23 may be composed of a digital circuit using a microcontroller or DSP, an analog circuit, or a circuit combining a digital circuit and an analog circuit. In this embodiment, the DC / AC converter 21, the DC / DC converter 22, and the system protection relay 24 are controlled by a single control unit 23. However, the control unit 23 may be divided into a first control unit that controls the DC / AC converter 21, a second control unit that controls the DC / DC converter 22, and a third control unit that controls the system protection relay 24, with at least the first and second control units communicating with each other.

[0047] The control unit 23 controls the switching elements of the DC / AC converter 21 to match the output value (output current value, output voltage value, or output power value) of the DC / AC converter 21 to a predetermined target value (target current value, target voltage value, or target power value). For example, when the DC / AC converter 21 is made to perform AC / DC conversion, the control unit 23 performs PWM control of the switching elements and voltage control to match the output voltage value to a predetermined target voltage value. The control to match the output value to the target value may be feedback control, feedforward control, or both. The target value may be a value preset by the control unit 23, a value determined from the input / output conditions of the DC / AC converter 21, or a value input from an external device. The target value may change moment by moment.

[0048] The control unit 23 controls the switching elements of the DC / DC converter 22 to match the output value (output current value, output voltage value, or output power value) of the DC / DC converter 22 to a predetermined target value (target current value, target voltage value, or target power value). For example, when the DC / DC converter 22 is to perform a charging operation, the control unit 23 performs current control to match the output current value to a predetermined target current value. In this embodiment, as one of the current control methods, the control unit 23 performs charging current control to match the current value of the charging current I1 to the MCCV.

[0049] For controlling the output value to match the target value, known control methods such as feedback control and / or feedforward control can be used. Furthermore, for controlling the switching elements of the DC / DC converter 22 during charging current control, any method can be used depending on the circuit configuration of the DC / DC converter 22, such as PWM control, frequency modulation control, or phase shift control.

[0050] The control unit 23 is characterized by performing the charging termination control shown in Figure 4 when controlling the charging current. When the control unit 23 starts the charging termination control during charging current control, it determines whether or not the storage battery 11 is in a fully charged state (S101).

[0051] The control unit 23 determines that the battery 11 is fully charged (YES in S101) when the state detection unit 17b of the BMS 12 detects a fully charged state, that is, when a fully charged detection signal is input from the state detection unit 17b (for example, when the voltage signal switches from a low level to a high level), or when it detects that the SOC is 100% through communication with the management unit 17. Having determined that the battery 11 is fully charged, the control unit 23 terminates the charging current control and ends the charging termination control.

[0052] The control unit 23 determines that the battery 11 is not in a fully charged state (NO in S101) if the state detection unit 17b of the BMS 12 has not detected a fully charged state, that is, if no fully charged detection signal is input from the state detection unit 17b (for example, if the voltage signal is at a low level), or if it detects through communication with the management unit 17 that the SOC is less than 100%.

[0053] Incidentally, if the energy storage unit 10 is installed outdoors or in a cold region, the battery 11 may become cold (for example, below 10°C). Also, due to the characteristics of lithium-ion secondary batteries, they tend to significantly limit the MCCV at low temperatures, regardless of whether or not a charging current can be supplied to the battery 11. For example, the MCCV may be limited by the actual performance of the battery 11. If the BMS 12 limits the MCCV to 0[A] before the state detection unit 17b detects a fully charged state, the control unit 23 controls the current value of the charging current I1 to 0[A]. As a result, the power conditioner 20 enters a standby state. When the current value of the charging current I1 is controlled to 0[A] and the cell voltage of the secondary battery 11' drops, the BMS 12 releases the 0[A] limit on the MCCV. That is, the MCCV input to the control unit 23 changes from 0[A] to a value other than 0[A].

[0054] For example, as shown in Figure 3(B), when the cell temperature of the secondary battery 11' is between 0°C and 10°C, the MCCV input to the control unit 23 becomes 0A when the battery 11 is charged until the cell voltage of the secondary battery 11' reaches 4.0V (equivalent to a SOC of 93%). Subsequently, when the cell voltage of the secondary battery 11' drops to 3.9V while the cell temperature of the secondary battery 11' remains between 0°C and 10°C, the MCCV input to the control unit 23 changes from 0A to 2A. As a result, the control unit 23 controls the current value of the charging current I1 to 2A, and the supply of the charging current I1 is resumed.

[0055] In step S101 of Figure 4, the control unit 23, having determined that the battery 11 is not fully charged, determines whether the MCCV has changed from 0[A] to X[A] (where X is a value other than 0) (S102). Here, an MCCV of X[A] corresponds to the "first signal" of the present invention, and an MCCV of 0[A] corresponds to the "second signal" of the present invention.

[0056] If MCCV is 0[A], or if MCCV is X[A] without ever becoming 0[A] (if the power conditioner 20 is continuing its charging operation), the control unit 23 determines that MCCV has not changed from 0[A] to X[A] (NO in S102) and proceeds to step S101.

[0057] On the other hand, if the MCCV changes from 0[A] to X[A] (YES in S102), the control unit 23 starts counting (S103). The control unit 23, having started counting, counts the number of MCCVs at X[A] and the number of MCCVs at 0[A] at predetermined time intervals (every 250[ms] in this embodiment) and determines whether or not the charging termination condition set in the control unit 23 is met (S104). If the control unit 23 determines that the charging termination condition is met (YES in S104), it terminates the charging current control and ends the charging termination control.

[0058] In this embodiment, the charging termination condition is that, after the counting process has started, the percentage of 0[A] MCCVs received by the control unit 23 during a predetermined determination period is equal to or greater than a predetermined threshold. In this embodiment, the determination period is set to the most recent 2.5[s], and the threshold is set to 40%. The determination period and / or the threshold can be changed as appropriate.

[0059] Figure 5 shows the relationship between the time during counting and MCCV. In Figure 5, it is assumed that charging current control has been performed since before time t0, and that MCCV became 0[A] for the first time at time t0. Also, in Figure 5, it is assumed that the cell temperature of the secondary battery 11' is between 0[°C] and 10[°C].

[0060] As shown in Figure 5, the control unit 23 starts counting at time t1 when the MCCV changes from 0[A] to 2[A]. After starting the counting process, the control unit 23 counts the number of MCCVs with X[A] and the number of MCCVs with 0[A] at predetermined time intervals (every 250[ms] in Figure 5) and determines whether the charging termination condition is met.

[0061] In this embodiment, the determination period for the charging termination condition is set to the most recent 2.5 seconds. Therefore, the control unit 23 determines whether the first charging termination condition is met at time t10 (the period from t1 to t10) when the count becomes 10 after 2.5 seconds. The charging termination condition in this embodiment is that the proportion of MCCVs with 0 A becomes 40% or more in the most recent 2.5 seconds. However, the proportion in the first instance was 30%, so the charging current control is continued. At time t11, the control unit 23 starts the second counting process, and at time t20 (the period from t11 to t20) when the proportion of MCCVs with 0 A reaches 40%, it determines that the charging termination condition is met and terminates the charging current control.

[0062] In this embodiment, the first counting process is performed during the period from t1 to t10 (the first determination is made at t10), and the second counting process is performed during the period from t11 to t20 (the second determination is made at t20). However, instead, a determination may be made every 250 [ms] (+1 count) from t10 onward to determine whether the charging termination condition is met. In that case, the control unit 23 will, for example, make a second determination at t11 ​​based on the count value during the period from t2 to t11, and in the seventh determination based on the count value during the period from t7 to t16 (the determination at t16 when the proportion of MCCV at 0 [A] reaches 40%), it will determine that the charging termination condition is met and terminate the charging current control.

[0063] The control unit 23, having terminated the charging current control, does not cause the current value of the charging current I1 to follow the MCCV. For example, even if the MCCV output from the processing unit 17c of the BMS12 changes from 0[A] to 2[A] at time t20, the current value of the charging current I1 output from the power conditioner 20 does not increase. The control unit 23 continues to communicate with the BMS12 even after terminating the charging current control (for example, after time t20), but it may terminate communication with the BMS12 (at least communication regarding the MCCV) at the same time as terminating the charging current control.

[0064] Figure 6(A) shows the time evolution of cell voltage, MCCV, and charging current in the comparative example, and Figure 6(B) shows the time evolution of cell voltage, MCCV, and charging current in the case of Figure 5 of this embodiment. The comparative example is the same as this embodiment except that the charging termination control shown in Figure 4 is not performed. That is, in the comparative example, charging current control continues until the BMS state detection unit detects a fully charged state.

[0065] As shown in Figure 6(A), in the comparative example, since no charge termination control is performed, the cell voltage repeatedly rises and falls, the MCCV frequently switches between 0[A] and 2[A], and consequently the charging current repeatedly rises and falls. In other words, the power conditioner in the comparative example repeatedly switches between a charging operation state and a standby state, resulting in unstable operation.

[0066] On the other hand, in this embodiment, the control unit 23 performs charge termination control, so as shown in Figure 6(B), counting is started at time t1 when the MCCV changes from 0[A] to 2[A], and the charging current control is terminated at time t20 when the charge termination condition is met. After that, the charging current converges to 0[A], and the cell voltage converges to 3.85[V]. In other words, in this embodiment, the power conditioner 20 suppresses repeated cycles between the charging operation state and the standby state, resulting in stable operation.

[0067] As described above, in the energy storage system 1 according to this embodiment, at low temperatures, the control unit 23 of the power conditioner 20 performs charging termination control and terminates the charging current control before the state detection unit 17b of the BMS 12 detects a fully charged state. Therefore, according to the energy storage system 1 according to this embodiment, it is possible to suppress the repetition of the charging operation state and the standby state at low temperatures.

[0068] In the energy storage system 1 according to this embodiment, the control unit 23 of the power conditioner 20 defines the fully charged state of the battery 11 at low temperatures. For example, if the power conditioner 20 is equipped with a display unit that displays the status of the battery 11 (for example, an indoor remote control including a touch panel that also serves as a display screen), the control unit 23 may display the status of the battery 11 as fully charged (for example, SOC 100%) on the display unit when it determines that the charging termination condition has been met and terminates the charging current control.

[0069] Although embodiments of the charging system according to the present invention have been described above, the present invention is not limited to the above embodiments.

[0070] The charging system according to the present invention comprises a storage battery, a battery management system for managing the storage battery, a charging unit that supplies a charging current to the storage battery and performs a charging operation on the storage battery, and a control unit that controls the charging operation of the charging unit, wherein the battery management system comprises a voltage measuring unit for measuring the voltage of the storage battery, a temperature measuring unit for measuring the temperature of the storage battery, a state detection unit for detecting a fully charged state of the storage battery, and a processing unit that determines a maximum charging current value, which is the maximum value of the charging current, at a predetermined interval based on the temperature measured by the temperature measuring unit and the voltage measured by the voltage measuring unit, and transmits a signal related to the determined maximum charging current value to the control unit, wherein the control unit performs charging current control to control the charging operation so that the current value of the charging current approaches the maximum charging current value based on the signal, and when a preset charging termination condition is met during charging current control, it performs charging termination control to terminate the charging current control before the state detection unit detects a fully charged state, and the charging termination condition is characterized in that the control unit receives a first signal in which the maximum charging current value is not 0 amperes, and then receives a second signal in which the maximum charging current value is 0 amperes multiple times.

[0071] For example, in the above embodiment, the charging termination condition may be set to the condition that the control unit 23 receives an MCCV of 0[A] multiple times (for example, two or more times) consecutively. For example, in the case of Figure 5, if the multiple times is set to two, the charging termination condition is met at time t9, and if the multiple times is set to three, the charging termination condition is met at time t10.

[0072] Furthermore, in the above embodiment, the control unit 23 starts the counting process when MCCV changes from 0[A] to X[A] (time t1 in Figure 5), but the timing of starting the counting process can be changed as appropriate. For example, the counting process may start when MCCV first becomes 0[A] (for example, time t0 in Figure 5), or it may start the counting process after a predetermined time (a time predetermined in the control unit 23) has elapsed since MCCV first became 0[A].

[0073] The charging system according to the present invention can also be applied to energy storage systems equipped with solar power generation capabilities, and to energy storage systems equipped with solar power generation capabilities and electric vehicle charging and discharging capabilities.

[0074] Furthermore, the charging system according to the present invention can be applied to systems other than energy storage systems, such as electric vehicle charging systems. In the case of an electric vehicle charging system, for example, the storage battery and battery management system are provided on the electric vehicle side, and the charging unit and control unit are provided on the charging device side (for example, a stationary fast charger). [Explanation of symbols]

[0075] 1. Energy storage system 2 Power system 3. Self-supporting load 10 Energy storage units 11. Storage batteries 11' secondary battery 12. Battery Management System (BMS) 13 Voltage Measurement Section 14 Temperature measurement section 15 Current measurement section 16 Opening and closing means 17 Management Department 17a Storage section 17b State detection unit 17c Processing Unit 20 Power Conditioner 21 AC conversion unit 22 DC conversion section 23 Control Unit 24-channel protection relay

Claims

1. Storage batteries and A battery management system for managing the aforementioned storage battery, A charging unit that supplies a charging current to the battery and performs a charging operation on the battery, A control unit that controls the charging operation of the charging unit, A charging system equipped with, The aforementioned battery management system A voltage measuring unit for measuring the voltage of the aforementioned storage battery, A temperature measuring unit for measuring the temperature of the storage battery, A state detection unit for detecting the fully charged state of the storage battery, A processing unit that determines the maximum charging current value, which is the maximum value of the charging current, at a predetermined interval based on the temperature measured by the temperature measuring unit and the voltage measured by the voltage measuring unit, and transmits a signal relating to the determined maximum charging current value to the control unit, Equipped with, The control unit, Based on the aforementioned signal, charging current control is performed to control the charging operation so that the current value of the charging current approaches the maximum charging current value. If the charging current control is met when the pre-set charging termination conditions are met, the state detection unit performs charging termination control to terminate the charging current control before detecting the fully charged state. The charging termination condition is that, after the control unit receives a first signal in which the maximum charging current value is not 0 amperes, the control unit receives a second signal in which the maximum charging current value is 0 amperes multiple times. A charging system characterized by the following features.

2. The charging termination condition is that the control unit receives the second signal multiple times in a row. The charging system according to claim 1.

3. The charging termination condition is that the proportion of the second signal received by the control unit during a predetermined period exceeds a predetermined threshold. The charging system according to claim 1.

4. The control unit, After receiving the second signal, a counting process is performed to count the number of signals from the time the first signal is received. The charging system according to claim 3.

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