Power storage system, power storage unit, power supply system, and power storage system control method

Abstract

Each unit (13) constituting this power storage system includes: a storage battery group (30) connected between a high-voltage-side terminal (28A) and a low-voltage-side terminal (28B); a first current-limiting device (36); a first switch (41); and a bypass circuit (48). The first current-limiting device (36) has a function of limiting a current flowing between the high-voltage-side terminal (28A) and the storage battery group (30). The first switch (41) is connected in series with the storage battery group (30) and the first current-limiting device (36). The bypass circuit (48) forms a bypass between the high-voltage-side terminal (28A) and the low-voltage-side terminal (28B). A bypass switch (49) switches the bypass circuit (48) between conduction and non-conduction.

Description

POWER STORAGE SYSTEM, POWER STORAGE UNIT, POWER SUPPLY SYSTEM, AND POWER STORAGE SYSTEM CONTROL METHOD

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

[0002] As renewable energy sources increase in an effort to achieve decarbonization, large-capacity energy storage systems are being used to stabilize the power grid. Relatively large-capacity energy storage systems are also being used in mobile vehicles that run on battery power, such as electric vehicles and battery-powered trains. These energy storage systems achieve large capacities by connecting small-scale battery groups in series and / or parallel.

[0003] For example, the power storage device disclosed in Patent Document 1 (JP 2009-212020 A) has a configuration in which multiple charge / discharge units are connected in parallel. Each charge / discharge unit has a battery string in which unit secondary batteries are connected in series, a resistive element connected in series to the battery string, and a resistive short-circuit switch connected in parallel to the resistive element. Each charge / discharge unit also has an on / off switch connected in series to the battery string.

[0004] Patent Document 2 (WO 2014 / 156041) discloses a power supply system including a plurality of battery units each including a plurality of battery cells connected in series, and a connection unit that connects the plurality of battery units in parallel to an external power source. The connection unit includes a parallel line that connects the plurality of battery units in parallel, and a plurality of connection parts, each of which connects a corresponding battery unit to the parallel line. Each connection part includes a series circuit of a first switch and a second switch connected in series between the parallel line and the corresponding battery unit, a sub-connection circuit connected in parallel with the second switch and including a series circuit of a current-limiting resistor and a third switch, a first rectifier connected in parallel with the first switch and having a rectifying effect in the direction of current flow from the parallel line to the battery unit, and a second rectifier connected in parallel with the second switch and having a rectifying effect in the direction of current flow from the battery unit to the parallel line.

[0005] The power storage system disclosed in Patent Document 3 (JP 2022-141451 A) includes a plurality of storage battery cells connected in series and a plurality of bypass circuits, each provided for a respective storage battery cell. Each bypass circuit includes a bypass line, a first switch, and a second switch. The bypass line bypasses the corresponding storage battery cell. The first switch is provided in the bypass line. The second switch is provided between the positive electrode of the corresponding storage battery cell and one end of the bypass line. When all storage battery cells are to be charged or discharged, each of the first switches is turned off and each of the second switches is turned on.

[0006] The energy storage device disclosed in Patent Document 4 (JP 2020-43653 A) includes a plurality of energy storage units connected in series. Each energy storage unit includes a pair of charge / discharge terminals, a storage unit and a charge switch connected in series between the pair of charge / discharge terminals, and a bypass switch that bypasses the pair of charge / discharge terminals. In a charge mode in which the storage unit is charged, the charge switch is controlled to be on and the bypass switch is controlled to be off. In a bypass mode in which charging of the storage unit is stopped, the charge switch is controlled to be off and the bypass switch is controlled to be on.

[0007] JP 2009-212020 A International Publication No. 2014 / 156041 JP 2022-141451 A JP 2020-43653 A

[0008] If a battery storage system used to stabilize the power grid stops functioning, it may cause the grid to become unstable. Battery storage systems used in conjunction with unstable power sources such as wind power generation must be constantly charged and discharged to stabilize the output of the entire power system. If a battery storage system used in mobile vehicles such as electric vehicles, battery-powered trains, and electric aircraft stops functioning due to a partial failure, it will hinder the safe operation of the mobile vehicles.

[0009] Therefore, even if a malfunction occurs in a part of these battery storage systems, it is necessary to isolate or bypass the malfunctioning part while continuing to operate the entire system. In the battery storage systems disclosed in Patent Documents 1 to 4, if a malfunction occurs in a part of the battery, it is not possible to isolate or bypass the malfunctioning part while continuing to operate the entire battery storage system.

[0010] Specifically, in the case of the energy storage device disclosed in Patent Document 1, the entire battery string can be isolated from the energy storage device by turning off the on / off switch connected in series to the battery string. However, it is not possible to isolate or bypass a faulty unit secondary battery. Similarly, in the case of the power supply system disclosed in Patent Document 2, the entire battery string comprising a battery unit can be isolated from the power supply system by turning off all of the first, second, and third switches comprising the connection section. However, it is not possible to isolate or bypass a faulty battery cell.

[0011] In the case of the energy storage system of Patent Document 3, a bypass circuit is provided for each battery cell, but it is not possible to bypass a battery cell in a short-circuit fault state while the energy storage system remains energized. This is because if the first switch provided in the bypass line is turned on while the second switch connected in series to the battery cell remains on, a short-circuit current will flow between the positive and negative electrodes of the battery cell via the bypass line. The energy storage device disclosed in Patent Document 4 also has a similar problem.

[0012] The present disclosure has been made in consideration of the above-mentioned problems, and one of its objectives is to provide a power storage system that can continue to operate when a failure occurs in part of the power storage system by switching the failed part to a bypass path without interruption.

[0013] In one embodiment, the power storage system includes a plurality of units connected in series. Each of the plurality of units includes a high-voltage side terminal, a low-voltage side terminal, a battery group connected between the high-voltage side terminal and the low-voltage side terminal, a first current limiting device, a first switch, a bypass circuit, and a bypass switch. The first current limiting device is connected between the high-voltage side terminal and the battery group and has a function of limiting a current flowing between the high-voltage side terminal and the battery group in an operating state. The first switch is connected in series with the first current limiting device between the high-voltage side terminal and the battery group. The bypass circuit is connected in parallel with the battery group, the first current limiting device, and the first switch between the high-voltage side terminal and the low-voltage side terminal. The bypass switch switches the bypass circuit between conductive and non-conductive states.

[0014] According to the above embodiment, each unit constituting the power storage system includes a first current limiting device, a first switch, a bypass circuit, and a bypass switch. As a result, when a failure occurs in a part of the power storage system, the power storage system can continue to operate by switching the current path of the failed part to the bypass path without momentary interruption.

[0015] 1. It is an overall circuit diagram of a power supply system including a power storage system according to Embodiment 1. It is an internal circuit diagram of a unit provided in a positive string. It is an internal circuit diagram of a unit provided in a negative string. It is a flowchart showing the operation of the switching controlgear when a faulty unit is isolated without momentary interruption of the energizing current. It is a flowchart showing the operation of the switching controlgear when a faulty unit is isolated by temporarily interrupting the energizing current. It is a flowchart showing the operation of the switching controlgear when a unit is restored without momentary interruption of the energizing current. It is a flowchart showing the operation of the switching controlgear 44 when a unit is restored by temporarily interrupting the energizing current. It is a flowchart showing a modification of FIG. 7. It is a circuit diagram showing an example of the unit converter of FIG. 1. It is a circuit diagram showing an example configuration of a power storage system according to Embodiment 2. It is an enlarged view of a portion corresponding to one positive string in the power storage system of FIG. 10. It is an enlarged view of a portion corresponding to one negative string in the power storage system of FIG. 10. It is an overall circuit diagram of a power supply system including a power storage system according to Embodiment 3. It is a flowchart showing the protective operation of the overall controlgear when a ground fault or short-circuit accident occurs in a busbar of the power storage system. 1 is a flowchart showing a procedure for disconnecting one string and grounding each unit of the string. FIG. 2 is a flowchart showing a procedure for returning a string in a disconnected state to a parallel state. FIG. 3 is an internal circuit diagram of a positive side unit in a power storage system of embodiment 4. FIG. 4 is an internal circuit diagram of a negative side unit in a power storage system of embodiment 4. FIG. 5 is an internal circuit diagram of a modified example of a unit 13P provided in a positive side string 12P in the power storage system of embodiment 1. FIG. 6 is an internal circuit diagram of a modified example of a unit 13N provided in a negative side string 12N in the power storage system of embodiment 1. FIG. 7 is an internal circuit diagram of a modified example of a positive side unit 13P in the power storage system of embodiment 4. FIG. 8 is an internal circuit diagram of a modified example of a negative side unit 13N in the power storage system of embodiment 4.

[0016] Each embodiment will be described in detail below with reference to the drawings. The same or corresponding parts will be denoted by the same reference characters and description thereof will not be repeated.

[0017] Embodiment 1. [Overall Configuration of Power Supply System and Power Storage System] Fig. 1 is an overall circuit diagram of a power supply system 1 including a power storage system 2 according to embodiment 1. Referring to Fig. 1, power supply system 1 includes power storage system 2, an AC / DC converter 3, a transformer 4, and an AC circuit breaker 5. Power supply system 1 is connected to a general three-phase AC power system, a private power generator, or a motor generator of an electric vehicle, a battery-powered train, an electric aircraft, or other electric mobile object via AC circuit breaker 5 provided in a power feed line.

[0018] The transformer 4 converts the voltage of the general power system. The AC / DC converter 3 is a bidirectional power converter that converts AC to DC and DC to AC. In FIG. 1 , a modular multilevel converter (MMC) is shown as an example of the AC / DC converter 3. An outline of the configuration of the MMC will be described later.

[0019] The energy storage system 2 includes a plurality of strings 12 connected in parallel with each other, a bus 10 connecting the plurality of strings 12 to the AC / DC converter 3, and a disconnector 11 provided between each string 12 and the bus 10. Each string 12 includes a plurality of units 13 connected in series. The units 13 are also referred to as energy storage units. The energy storage system 2 further includes a disconnector 6 provided at a connection point between the bus 10 and the AC / DC converter 3, and a grounding switch 7 for connecting the bus 10 to ground 8.

[0020] The unit 13 is made up of a plurality of storage batteries connected in series and parallel, and serves as a replacement unit when increasing or decreasing the number of storage batteries constituting the power storage system 2, or when replacing or maintaining the storage batteries. The detailed configuration of the unit 13 will be described later with reference to Figures 2 and 3.

[0021] The disconnectors 6 and 11 are devices for opening and closing lines that do not carry load current, and are used manually to ensure the safety of workers during maintenance work. The charging voltage in the section that is disconnected by the disconnectors 6 and 11 is discharged by a grounding switch or the like.

[0022] In the case of the power storage system 2 of FIG. 1 , the above-mentioned components are provided on both the positive electrode side and the negative electrode side. The positive electrode side is on the upper side of the drawing, and the negative electrode side is on the lower side of the drawing. In the present disclosure, components on the positive electrode side are designated by a reference sign suffixed with "P," and components on the negative electrode side are designated by a reference sign suffixed with "N." When it is not necessary to specify the positive electrode side or the negative electrode side, the suffix "P" or "N" is omitted.

[0023] Specifically, the power storage system 2 includes a plurality of positive strings 12P connected in parallel with one another and a plurality of negative strings 12N connected in parallel with one another. A high-voltage end of each of the positive strings 12P is connected to a positive bus 10P via a corresponding positive disconnector 11P. A low-voltage end of each of the positive strings 12P is connected to a common neutral point 15. Similarly, a high-voltage end of each of the negative strings 12N is connected to a negative bus 10N via a corresponding negative disconnector 11N. A low-voltage end of each of the negative strings 12N is connected to the neutral point 15.

[0024] 1, a neutral point 15 connecting the positive electrode string 12P and the negative electrode string 12N is connected to the ground 8. The neutral point 15 does not necessarily have to be connected to the ground 8. In addition, in the present disclosure, in both the positive electrode side and the negative electrode side, a voltage having a large absolute value is referred to as a high voltage, and a voltage having a small absolute value is referred to as a low voltage.

[0025] [Configuration of the Positive Side Unit] Figure 2 is an internal circuit diagram of unit 13P provided in positive side string 12P. In Figure 2, the upper side is the high-voltage side and positive side, and the lower side is the low-voltage side and negative side. Charging current of the storage battery flows from the high-voltage side to the low-voltage side, and discharging current of the storage battery flows from the low-voltage side to the high-voltage side.

[0026] 2 , unit 13P includes high-voltage side terminal 28A, low-voltage side terminal 28B, a storage battery group 30 including a plurality of storage batteries 34, a main switch 41, a current limiting device 36, a current measuring instrument 43, a switching control device 44, a bypass circuit 48, and a metal frame 47. In the present disclosure, main switch 41 is also referred to as a first switch, current limiting device 36 is also referred to as a first current limiting device, and switching control device 44 is also referred to as an individual control device.

[0027] High-voltage side terminal 28A and low-voltage side terminal 28B are terminals for connecting to adjacent units 13P. Main switch 41, current limiting device 36, and storage battery group 30 are connected in series in this order from high-voltage side terminal 28A to low-voltage side terminal 28B.

[0028] Current meter 43 detects the current flowing between high-voltage terminal 28A and low-voltage terminal 28B via main switch 41, current limiting device 36, and storage battery group 30. In the case of Figure 2, current meter 43 detects the current using current sensor 42 provided in the current path between current limiting device 36 and storage battery group 30.

[0029] The battery group 30 includes a plurality of banks 32 connected in parallel between a high-voltage unit bus 31A and a low-voltage unit bus 31B, and switches 33 individually provided between each bank 32 and the unit bus 31A. Each bank 32 includes a plurality of series-connected storage batteries 34 and fuses 35A, 35B connected across both ends of the series combination of the plurality of storage batteries 34. One or both of the fuses 35A and 35B may have a function of interrupting current by melting or breaking an internal conductor in response to an external command, such as a pyro-fuse.

[0030] The fuses 35A and 35B are necessary to cut off the current in the event of a short circuit failure in one of the internal devices of the unit 13, such as one of the storage batteries 34. In such a case, if it is desired to isolate only the bank 32 containing the failed storage battery 34, the contacts of the switch 33 can be opened. Alternatively, if a faster cutoff is required to prevent a short circuit failure in a storage battery 34 in one bank 32 from causing current to flow from other parallel banks 32, a pyroelectric fuse may be used instead of a general fuse. This allows the current to be cut off without waiting for a general fuse to blow. Alternatively, a circuit breaker may be used instead of a general fuse.

[0031] In an operating state, current limiting device 36 has a function of limiting the current flowing between high-voltage side terminal 28A and storage battery group 30. As an example, current limiting device 36 includes switch 37 and a current-limiting element 40 connected in parallel to switch 37. When current limiting device 36 is in an inactive state, switch 37 is in an on state, and current flows through switch 37. When switch 37 is turned off in response to a command from switching control device 44, current is commutated to current-limiting element 40, and current limiting device 36 enters an operating state.

[0032] For example, a resistor is used as the current limiting element 40. The resistor may have a constant resistance, or may have a non-linear resistance by using a varistor or a zinc oxide element as the resistor.

[0033] A general mechanical switch capable of cutting off direct current may be used as the switch 37, or a self-extinguishing semiconductor switching element that can be turned on and off, such as an insulated gate bipolar transistor (IGBT) or a gate commutated turn-off thyristor (GCT), may be used. The semiconductor material may be any of Si, SiC, GaN, or the like.

[0034] When at least one semiconductor element is used as switch 37, the switch 37 may be configured to be able to cut off current in both the charging and discharging directions of the storage battery group 30, or may have a polarity such that only the current in the discharging direction can be turned on and off while the current in the charging direction is always flowing.

[0035] 2 is configured with a semiconductor switching element 38 formed by an IGBT and a diode 39 connected in parallel to this semiconductor switching element 38. The emitter of the IGBT and the anode of diode 39 are provided on the high-voltage side, and the collector of the IGBT and the cathode of diode 39 are provided on the low-voltage side. With this configuration, regardless of whether the IGBT is on or off, current always flows in the direction from high-voltage side terminal 28A to low-voltage side terminal 28B, which is the charging direction of storage battery bank 30. On the other hand, when the IGBT is turned off, current is cut off in the direction from low-voltage side terminal 28B to high-voltage side terminal 28A, which is the discharging direction of storage battery bank 30.

[0036] In order to enable the current to be turned on and off in both the charging and discharging directions using a semiconductor element, switch 37 may be configured by connecting in series, for example, a parallel combination of semiconductor switching element 38 and diode 39 of the polarity shown in FIG. 2 and a parallel combination of semiconductor switching element 38 and diode 39 of the opposite polarity to that in FIG. 2 .

[0037] The bypass circuit 48 is connected between the high-voltage side terminal 28A and the low-voltage side terminal 28B in parallel with the series combination of the main switch 41, the current limiting device 36, and the storage battery group 30. The bypass circuit 48 is provided with a bypass switch 49. The bypass switch 49 is normally in an open state, so that no current flows through the bypass circuit 48. When the bypass switch 49 is closed by a command from the switching control device 44, current flows through the bypass circuit 48. The bypass switch 49 may be configured as a single switch, or may be configured by connecting two switches in series: a switch that opens and closes DC current, and a closing switch that can close quickly when closed.

[0038] Switching controller 44 controls the opening and closing of switch 37, main switch 41, and bypass switch 49 based on the value of the current measured by current meter 43. Switching controller 44 may be configured based on a computer including a CPU (Central Processing Unit), memory, input / output interface, etc. Alternatively, at least a part of switching controller 44 may be configured by a dedicated integrated circuit such as a PLD (Programmable Logic Device) such as an FPGA (Field Programmable Gate Array) and / or an ASIC (Application Specific Integrated Circuit).

[0039] Furthermore, the switching control device 44 may be configured to control the opening and closing of the switches 33 provided corresponding to each bank 32. Furthermore, if at least one of the fuses 35A, 35B is a pyro-fuse, the current meter 43 may measure the current using a current sensor provided near the pyro-fuse, and the switching control device 44 may be configured to output a pyro-fuse opening signal based on the current measurement result.

[0040] The metal frame 47 is provided to protect the above-mentioned devices. Specifically, the components of the unit 13P other than the bypass circuit 48 and the bypass switch 49 are arranged on or surrounded by the metal frame 47. The metal frame 47 is connected to the low-voltage terminal 28B, thereby establishing a conductive potential with the low-voltage terminal 28B. Arranging the components of the unit 13P as described above has the advantage of facilitating the insulation design of the components of the unit 13P. This is because, while higher voltages are applied to the multiple series-connected units 13P that make up the string 12P, the higher the voltage of the unit 13P, the less consideration is required for the insulation of each device placed inside or on the metal frame 47. The metal frame 47 itself is designed to be insulated to withstand high voltages relative to ground. The metal frame 47 also serves to protect against surges caused by lightning and external disturbances.

[0041] [Configuration example of negative electrode side unit] Figure 3 is an internal circuit diagram of unit 13N provided in negative electrode side string 12N. In Figure 3, the upper side is the low voltage side and positive electrode side, and the lower side is the high voltage side and negative electrode side. Charging current of the storage battery flows from the low voltage side to the high voltage side, and discharging current of the storage battery flows from the high voltage side to the low voltage side.

[0042] Unit 13N in Fig. 3 has a configuration obtained by inverting unit 13P in Fig. 2 upside down, except for the polarities of storage battery 34, semiconductor switching element 38, and diode 39. Therefore, in unit 13N in Fig. 3, parts that are the same as or correspond to those of unit 13P in Fig. 2 are given the same reference numerals, and detailed description thereof will not be repeated.

[0043] The multiple storage batteries 34 that make up the bank 32 are connected in series with their positive electrodes on the low-voltage side (upper side of the figure) and their negative electrodes on the high-voltage side (lower side of the figure). In the current limiting device 36, the emitter of the IGBT serving as the semiconductor switching element 38 and the anode of the diode 39 are located on the low-voltage side (upper side of the figure), while the collector of the IGBT and the cathode of the diode 39 are located on the high-voltage side (lower side of the figure). With this configuration of the switch 37, current always flows from the low-voltage terminal 28B to the high-voltage terminal 28A, which is the charging direction of the storage battery group 30, regardless of whether the semiconductor switching element 38 is on or off. On the other hand, turning off the semiconductor switching element 38 blocks current from the high-voltage terminal 28A to the low-voltage terminal 28B, which is the discharging direction of the storage battery group 30.

[0044] [Unit Disconnection Operation - Uninterrupted Disconnection of Current Flow] Next, a description will be given of the operation when a short circuit occurs between high-voltage side terminal 28A and low-voltage side terminal 28B in units 13P, 13N configured as described above.

[0045] 4 is a flowchart showing the operation of switching controller 44 when disconnecting a faulty unit without momentary interruption of the current. Note that current meter 43 in FIGS. 2 and 3 constantly measures the current and transmits the measured current value data to switching controller 44.

[0046] In the present disclosure, a state of the unit 13 in which the storage battery group 30 can be charged or discharged is referred to as an in-use state, and a state in which the unit 13 is disconnected and the storage battery group 30 cannot be charged or discharged is referred to as a stopped state. When the unit 13 is in the in-use state, the main switch 41 is in a closed state, the current limiting device 36 is in a non-operating state, and the bypass switch 49 is in an open state. When the unit 13 is in a stopped state, the main switch 41 is in an open state, the current limiting device 36 is in an operating state, and the bypass switch 49 is in a closed state. At the start of the flow in FIG. 4 , the unit 13 is in an operating state.

[0047] In step S11, switching controller 44 receives measurement data of the current value from current meter 43. In the next step S12, switching controller 44 determines whether the measured current value exceeds a predetermined threshold, i.e., whether an overcurrent has occurred. Switching controller 44 determines the occurrence of a short-circuit fault by detecting that the measured current value has exceeded the predetermined threshold (step S12).

[0048] Alternatively, units 13P and 13N may be provided with temperature sensors (not shown) that measure the temperatures of the conductors and the storage batteries and / or sensors (not shown) that detect impacts or vibrations caused by earthquakes or collisions of objects. The opening and closing control device 44 may determine the occurrence of an abnormal state in which the detected value of the temperature sensor or the detected value of the impact or vibration sensor exceeds a threshold value (step S12).

[0049] If switching controller 44 detects the above-mentioned overcurrent or abnormal state (YES in step S12), the process proceeds to step S13. If switching controller 44 does not detect either the above-mentioned overcurrent or abnormal state (NO in step S12), the process returns to step S11.

[0050] When switching controller 44 detects an overcurrent or an abnormal state (YES in step S12), it first sends an operation command to current limiting device 36 in step S13. Upon receiving the operation command, current limiting device 36 turns off switch 37, thereby commutating the current to current limiting element 40. This suppresses the current flowing through the unit.

[0051] In the next step S14, the switching control device 44 sends a close command to the bypass switch 49. When the bypass switch 49 closes, the storage battery 34 is short-circuited, but the current is suppressed by the current-limiting element 40 of the current-limiting device 36, so it does not become a large current. For example, when the charging voltage of the bank 32 is 1000 V, if a resistive element of about 2 Ω is used as the current-limiting element 40, the current value will be about 500 A. If the current-limiting device 36 were not present, the short-circuit current might be on the order of kA. Note that even if an arc occurs due to a short circuit between the high-voltage terminal 28A and the low-voltage terminal 28B, the arc will be extinguished when the bypass switch 49 closes because no voltage is applied to the arc.

[0052] In the next step S15, the switching control device 44 sends an opening command to the main switch 41 to open the main switch 41. This completes the process of disconnecting the faulty unit 13, and the faulty unit 13 goes into a stopped state.

[0053] 2 and 3 is operated in the above-described procedure, it is possible to separate the unit 13P or 13N without interrupting the current flow, and continue the operation of the power storage system 2. As described above, if the purpose is to prevent a large current from flowing when the bypass switch 49 is closed, the switch 37 of the current limiting device 36 may be capable of interrupting only the current in the discharge current direction of the storage battery 34.

[0054] Unlike the case where a short circuit accident occurs between the high-voltage side terminal 28A and the low-voltage side terminal 28B of the units 13P, 13N as described above, even if an abnormality or malfunction occurs in the internal circuit of the units 13P, 13N, the operation of the storage system 2 can be continued by disconnecting the units 13P, 13N without any interruption using the method described above.

[0055] In the above procedure, the operating speed of the current limiting device 36 is preferably set so that it operates before the fuses 35A and 35B melt. Even if the storage battery 34 is short-circuited due to the closing of the bypass switch 49, the current can be limited before it reaches a level at which the fuses 35A and 35B melt. This prevents a situation in which the fuses 35A and 35B are melted and operation cannot be continued when the unit 13 is restored after being disconnected.

[0056] [Unit Isolation Operation—Temporarily Shut Off Current Flow] If there is no need to maintain an uninterrupted current flow through the string 12 including the faulty unit 13, there is no need to operate the current limiting device 36. The operation of the switching control device 44 in this case will be described below.

[0057] Figure 5 is a flowchart showing the operation of switching controller 44 when temporarily interrupting the flow of current to isolate a faulty unit. Steps S21 and S22 in Figure 5 are the same as steps S11 and S12 in Figure 4, respectively, and therefore will not be described in detail again. If switching controller 44 does not detect an overcurrent or an abnormal state in step S22 (NO in step S22), it returns to step S21.

[0058] On the other hand, if the switching controller 44 detects an overcurrent or an abnormal state in step S22 (YES in step S22), the processing proceeds to step S23. In step S23, the switching controller 44 first sends an opening command to the main switch 41 to open the main switch 41. This interrupts the energizing current flowing through the string 12 including the faulty unit 13.

[0059] In the next step S24, the switching controller 44 sends a close command to the bypass switch 49 to close the bypass switch 49. This completes the isolation of the faulty unit 13.

[0060] [Unit Restoration Operation] Next, a description will be given of a procedure for restoring the disconnected unit 13. The procedure for restoring the unit 13 is basically the reverse of the procedure for disconnecting it.

[0061] 6 is a flowchart showing the operation of the switching control device 44 when the unit is restored without momentary interruption of the current. In the initial state of the isolated unit 13 (step S31), the current limiting device 36 is in current limiting operation (i.e., the switch 37 is off), the main switch 41 is in the open state, and the bypass switch 49 is in the closed state.

[0062] First, in step S32, the switching control device 44 sends a close command to the main switch 41, thereby closing the main switch 41. In the next step S33, the switching control device 44 sends an open command to the bypass switch 49, thereby opening the bypass switch 49. In the next step S34, the switching control device 44 sends a release command (i.e., a command to turn on the switch 37) to the current limiting device 36, thereby placing the current limiting device 36 in a normal conducting state (i.e., a non-operating state) in which current flows via the switch 37. This completes the recovery of the unit 13.

[0063] Fig. 7 is a flowchart showing the operation of the switching control device 44 when the current is temporarily interrupted to restore the unit. The initial state (step S41) of the isolated unit 13 is the same as that in Fig. 6 (step S31). Specifically, the current limiting device 36 is in current limiting operation (i.e., the switch 37 is off), the main switch 41 is in an open state, and the bypass switch 49 is in a closed state.

[0064] First, in step S42, the switching control device 44 sends a command to cancel the current limiting operation (i.e., a command to turn on the switch 37) to the current limiting device 36. This causes the current limiting device 36 to enter a normal energization state in which current flows through the switch 37. In the next step S43, the switching control device 44 sends an opening command to the bypass switch 49, thereby opening the bypass switch 49. As a result, the current flowing through the string 12 including the unit 13 to be restored is interrupted. In the next step S44, the switching control device 44 sends a closing command to the main switch 41, thereby closing the main switch 41. This completes the restoration of the unit 13, and current resumes flowing through the string 12 including that unit 13.

[0065] Fig. 8 is a flowchart showing a modification of Fig. 7. In the flowchart of Fig. 8, steps corresponding to those in Fig. 7 are given the same reference numerals as in Fig. 7. As shown in Fig. 8, the release of the current limiting operation of the current limiting device 36 in step S42 (i.e., turning on the switch 37) may be performed after the opening of the bypass switch 49 in step S43 and the closing of the main switch 41 in step S44 are performed.

[0066] [Configuration Example of AC / DC Converter] A configuration example of the AC / DC converter 3 in Fig. 1 will be briefly described below. In Fig. 1 as an example, the AC / DC converter 3 is configured by a modular multilevel converter including a plurality of cascaded unit converters 23. The unit converters 23 are also referred to as converter cells or submodules. Note that the AC / DC converter 3 is not limited to a modular multilevel converter.

[0067] 1, the AC-DC converter 3 includes a positive DC terminal 20P, a negative DC terminal 20N, AC connection units 22 (22U, 22V, 22W) for each phase, upper arm circuits 21U (21UP, 21VP, 21WP) for each phase, and lower arm circuits 21N (21UN, 21VN, 21WN) for each phase. The upper arm circuit 21U and the lower arm circuit 21N are collectively referred to as arm circuits 21.

[0068] The positive DC terminal 20P is connected to the positive bus 10P of the power storage system 2 via a disconnector 6P. The negative DC terminal 20N is connected to the negative bus 10N of the power storage system 2 via a disconnector 6N. The U-phase AC connecting unit 22U, the V-phase AC connecting unit 22V, and the W-phase AC connecting unit 22W are connected to an AC power system or a motor generator of a mobile object or the like via a transformer 4 and an AC circuit breaker 5.

[0069] The upper arm circuit 21U of each phase is connected between the AC connection unit 22 of the corresponding phase and the positive DC terminal 20P. The lower arm circuit 21N of each phase is connected between the AC connection unit 22 of the corresponding phase and the negative DC terminal 20N. Each arm circuit 21 includes a plurality of cascaded unit converters 23 and a reactor 24. The plurality of unit converters 23 and the reactor 24 are connected in series. The reactor 24 may be inserted at any position in the arm circuit 21.

[0070] Fig. 9 is a circuit diagram showing an example of the unit converter 23 of Fig. 1. The unit converter 23 of Fig. 9 includes an input / output terminal pair P1, P2, a half-bridge circuit 52H, and a storage element 50 (typically a capacitor).

[0071] The input / output terminal pair P1, P2 is provided for connection to adjacent unit converters 23, positive DC terminal 20P, negative DC terminal 20N, AC connecting parts 22U, 22V, 22W, etc. Typically, the input / output terminal P1 is connected to the input / output terminal P2 of the adjacent unit converter 23 on the positive side. The input / output terminal P2 is connected to the input / output terminal P1 of the adjacent unit converter 23 on the negative side.

[0072] The half-bridge circuit 52H includes semiconductor switching elements 53P and 53N and diodes 54P and 54N. The semiconductor switching elements 53P and 53N are self-extinguishing switching elements that can be controlled to turn on and off, such as an insulated gate bipolar transistor (IGBT) or a gate commutated turn-off thyristor (GCT).

[0073] 9, semiconductor switching element 53P is connected between input / output terminal P1 and positive terminal 51P of energy storage element 50. Semiconductor switching element 53N is connected between input / output terminal P1 and input / output terminal P2. Input / output terminal P2 is further connected to negative terminal 51N of energy storage element 50. Diodes 54P and 54N are connected in parallel with and in reverse bias direction to semiconductor switching elements 53P and 53N, respectively.

[0074] According to the above configuration, by controlling the semiconductor switching elements 53P and 53N to be alternately turned on, it is possible to output zero voltage and positive voltage (i.e., the voltage of the storage element 50) between the input / output terminal pair P1 and P2. Note that instead of the half-bridge circuit 52H shown in FIG. 9, a full-bridge circuit may be used, or a sleek full-bridge circuit in which one arm is composed only of a diode may be used. オ A rotor bridge circuit may also be used.

[0075] A control circuit (not shown) that controls the entire AC-DC converter 3 detects the AC voltage and AC current on the AC side, the DC voltage and DC current on the DC side, the current flowing through each arm circuit 21, and the voltage of the storage element 50 of each unit converter 23. Based on these detected values, the control circuit performs bidirectional DC-AC conversion by controlling the semiconductor switching elements 53P, 53N that make up each unit converter 23 using a phase shift PWM (Pulse Width Modulation) method.

[0076] Effect of First Embodiment According to the energy storage system 2 configured as described above, if one of the units 13 constituting the energy storage system 2 experiences a short-circuit fault, the current limiting device 36 provided in the failed unit 13 suppresses the short-circuit current, and then the bypass switch 49 is closed. This allows the current path to be switched from the main circuit of the unit 13 to the bypass circuit 48 without momentary interruption, allowing the energy storage system 2 to continue operating when a fault occurs. Thereafter, the main switch 41 of the failed unit 13 is opened, preventing the short-circuit current from flowing and clearing the fault. Furthermore, even if a current flows from another string 12 connected in parallel to the string 12 including the failed unit 13, the current flows into the bypass circuit 48, and therefore the storage battery 34 is not affected.

[0077] Even if an arc discharge occurs due to a short circuit between high-voltage terminal 28A and low-voltage terminal 28B of one unit 13, the voltage between high-voltage terminal 28A and low-voltage terminal 28B becomes zero when bypass switch 49 is closed, and the arc discharge is extinguished. This allows the short circuit to be quickly cleared.

[0078] Second Embodiment In a power storage system 2 according to a second embodiment, a switch 61 and a current limiting device 62 having the same configuration as the main switch 41 and the current limiting device 36 provided in each unit 13 in the power storage system 2 according to the first embodiment are further provided for each string 12. These will be described in detail below with reference to the drawings. In the present disclosure, the switch 61 is also referred to as a second switch, and the current limiting device 62 is also referred to as a second current limiting device.

[0079] [Configuration of Power Storage System] Fig. 10 is a circuit diagram showing a configuration example of a power storage system 2 according to embodiment 2. The power storage system 2 of Fig. 10 differs from the power storage system 2 of Fig. 1 in that it further includes a plurality of positive-side switches 61P, a plurality of positive-side current limiting devices 62P, a plurality of negative-side switches 61N, and a plurality of negative-side current limiting devices 62.

[0080] Each positive side switch 61P and each positive side current limiting device 62P are connected in series between the high voltage side of a corresponding string 12P among the plurality of positive side strings 12P and a corresponding disconnector 11P among the plurality of positive side disconnectors 11P. Similarly, each negative side switch 61N and each negative side current limiting device 62N are connected in series between the high voltage side of a corresponding string 12N among the plurality of negative side strings 12N and a corresponding disconnector 11N among the plurality of negative side disconnectors 11N.

[0081] In the following description, the positive side switch 61P and the negative side switch 61N will be collectively referred to as switch 61, and the positive side current limiting device 62P and the negative side current limiting device 62N will be collectively referred to as current limiting device 62. Since the other configurations in Fig. 10 are similar to the configurations of the power storage system 2 in Fig. 1, the same or corresponding parts will be designated by the same reference numerals and description thereof will not be repeated.

[0082] Fig. 11 is an enlarged view of a portion corresponding to one positive-side string 12P in the power storage system 2 of Fig. 10. In Fig. 11, the upper side is the high-voltage side and the positive side, and the lower side is the low-voltage side and the negative side. The charging current of the storage battery 34 constituting each unit 13P flows from the high-voltage side to the low-voltage side, and the discharging current of the storage battery 34 flows from the low-voltage side to the high-voltage side.

[0083] As shown in FIG. 11 , the power storage system 2 further includes a current meter 68 and a switching control device 69 in addition to the disconnector 11P, the switch 61P, and the current limiting device 62P of FIG. 10 as a configuration corresponding to each positive electrode side string 12P.

[0084] The switch 61P has a function of interrupting DC current of approximately the rated current. The current limiting device 62 has a function of limiting current, similar to the current limiting device 36 provided in each unit 13. As an example, the current limiting device 62 includes a switch 63 and a current limiting element 66 (e.g., a resistor) connected in parallel to the switch 63. Under normal circumstances, the switch 63 is in an on state, and current flows through the switch 63. When the switch 63 is turned off in response to a command from the switching control device 69, current is commutated to the current limiting element 66.

[0085] The switch 63 may be a mechanical switch or a semiconductor switch. When a semiconductor switch is used, the polarity may be such that only the current in the charging direction of the storage battery (i.e., from the positive bus 10P to the neutral point 15) can be turned on and off, and the current in the discharging direction is always conducted. For example, as shown in FIG. 11 , the switch 63 includes a semiconductor switching element 64 formed by an IGBT and a diode 65 connected in parallel therewith. The collector of the IGBT and the cathode of the diode 65 are connected to the positive side (high voltage side), and the emitter of the IGBT and the anode of the diode 65 are connected to the neutral point side (low voltage side).

[0086] The current meter 68 detects the current flowing from the positive bus 10P to the corresponding string 12P. In the case of Fig. 11, the current meter 68 detects the current using a current sensor 67 provided in the current path between the current limiting device 62P and the positive string 12P.

[0087] Switching control device 69 controls the opening and closing of switch 63 and switch 61P based on the value of the current measured by current meter 68. For example, when current meter 68 detects an overcurrent exceeding a threshold, switching control device 69 turns off switch 63 and also opens switch 61P.

[0088] The switching control device 69 may be configured based on a computer including a CPU, memory, an input / output interface, etc. Alternatively, at least a part of the switching control device 69 may be configured by a dedicated circuit such as a PLD such as an FPGA and / or an ASIC.

[0089] Although the disconnector 11P is basically operated manually, it may be configured so that it can be remotely operated from the switching control device 69.

[0090] Fig. 12 is an enlarged view of a portion of the power storage system 2 of Fig. 10 corresponding to one string 12N on the negative side. In Fig. 12, the upper side is the low-voltage side and the positive side, and the lower side is the high-voltage side and the negative side. A charging current for the storage battery 34 constituting each unit 13N flows from the low-voltage side to the high-voltage side, and a discharging current for the storage battery 34 flows from the high-voltage side to the low-voltage side. As shown in Fig. 12, the power storage system 2 further includes a current meter 68 and a switching control device 69 as components corresponding to each string 12N on the negative side, in addition to the disconnector 11N, switch 61P, and current limiting device 62N of Fig. 10.

[0091] The negative electrode side configuration shown in Fig. 12 has a configuration obtained by inverting the positive electrode side configuration shown in Fig. 11 upside down, except for the polarities of the storage battery 34, semiconductor switching element 64, and diode 65. Therefore, in the negative electrode side configuration in Fig. 12, parts that are the same as or correspond to those in the positive electrode side configuration in Fig. 11 are given the same or similar reference numerals (i.e., the suffix P and N are swapped), and detailed descriptions thereof will not be repeated.

[0092] 12 includes a semiconductor switching element 64 formed by an IGBT and a diode 65 connected in parallel therewith. The collector of the IGBT and the cathode of the diode 65 are connected to the neutral point side (low voltage side), and the emitter of the IGBT and the anode of the diode 65 are connected to the negative side (high voltage side). Therefore, only the current in the charging direction of the storage battery (i.e., the direction from the neutral point 15 to the negative side bus 10N) can be turned on and off, and the current in the discharging direction is always conducted.

[0093] [Effects of Second Embodiment] As described above, according to the energy storage system 2 of the second embodiment, the current limiting device 62 is provided in series with each string 12. This makes it possible to prevent a large current from occurring when a short circuit or the like occurs in one of the units 13 in the string 12 and the unit 13 is bypassed. In this case, not only is it possible to prevent a current from flowing in from the AC-DC converter 3, but it is also possible to prevent a current from flowing in from other healthy strings 12 connected in parallel to the string 12 including the faulty unit 13. As a result, it is possible to prevent the healthy strings 12 from being damaged.

[0094] Embodiment 3 [Overall Configuration of Power Supply System and Power Storage System] Fig. 13 is an overall circuit diagram of a power supply system 1 including a power storage system 2 according to embodiment 3. The power storage system 2 in Fig. 13 differs from the power storage systems 2 in Figs. 1 and 10 in that it further includes an overall control device 70.

[0095] The overall control device 70 controls the opening and closing of each unit 13 (13P, 13N), the string switches 61 (61P, 61N), and the string current limiting devices 62 (62P, 62N). Furthermore, the overall control device 70 controls the opening and closing of the AC circuit breaker 5.

[0096] Here, the overall control device 70 may have the function of directly controlling the main switch 41, current limiting device 36, switch 33, and fuses 35A and 35B when configured as pyrofuses that constitute each unit 13. Alternatively, these switching devices may be directly controlled by a switching control device 44 provided in each unit 13, and the overall control device 70 may control each unit 13 in an integrated manner by outputting a control command to the switching control device 44.

[0097] Similarly, the overall controller 70 may have a function to directly control the switches 61 and current limiting devices 62 corresponding to each string 12. Alternatively, these switching devices may be directly controlled by the switching control devices 69 provided corresponding to each string 12, and the overall controller 70 may output a control command to the switching control devices 69 to comprehensively control these switching devices.

[0098] The overall control device 70 may be configured based on a computer including a CPU, memory, an input / output interface, etc. Alternatively, at least a part of the overall control device 70 may be configured by a dedicated circuit such as a PLD such as an FPGA and / or an ASIC.

[0099] Furthermore, although the disconnectors 6 and 11 and the earth switch 7 are basically operated manually, they may be configured to be remotely controllable from the overall control device 70 .

[0100] [Short Circuit or Ground Fault on Bus Bar 10 of Power Storage System 2] By using the functions of the overall control device 70 described above, when a ground fault or a short circuit fault occurs on the bus bar 10 of the power storage system 2, for example, the ground fault or the short circuit fault can be eliminated by control from the overall control device 70. Hereinafter, a specific description will be given with reference to the flowchart of FIG.

[0101] 14 is a flowchart showing the protective operation of the overall control device 70 when a ground fault or short-circuit fault occurs on the bus bar 10 of the power storage system 2. In step S51 of FIG. 14 , the overall control device 70 detects that a ground fault or short-circuit fault has occurred on the bus bar 10 based on the detection result of a protective relay (not shown) provided on the bus bar 10 of the power storage system 2.

[0102] In the next step S52, the overall control device 70 sends an opening command to the AC circuit breaker 5 to open the AC circuit breaker 5. As a result, the power storage system 2 is disconnected from the external AC circuit.

[0103] In the next step S53, the overall controller 70 sends a command to close the bypass switches 49 to the switching controllers 44 of all the units 13. In response to this command, the switching controllers 44 (i) operate the current limiting devices 36, (ii) close the bypass switches 49, and (iii) open the main switch 41, as described in steps S13 to S15 of Fig. 4. This allows the ground fault location on the busbar 10 to be grounded, thereby stopping the flow of current from the string 12 to the ground fault location. As a result, the arc is extinguished and the fault can be cleared.

[0104] In step S53, the overall control device 70 may directly control (i) the operation of the current limiting device 36, (ii) the closing of the bypass switch 49, and (iii) the opening of the main switch 41 in each unit 13. Steps S52 and S53 may also be executed simultaneously.

[0105] [String Disconnection and Grounding] When the neutral point 15 of the power storage system 2 is connected to the ground 8 as shown in FIG. 13 , to ground a certain string 12 (12P or 12N), the bypass switches 49 of all the units 13 included in the string 12 are closed. As described with reference to FIGS. 2 and 3 , the high-voltage side terminal 28A and the low-voltage side terminal 28B of each unit 13 are connected via a bypass circuit 48, and the metal frame 47 is connected to the low-voltage side terminal 28B. Therefore, by closing the bypass switches 49 of all the units 13 constituting the string 12, the main circuits and the metal frames 47 of all the units 13 are connected to the ground 8. In order to reduce voltage fluctuations and reduce surges when connected to the ground 8, the bypass switches 49 of each unit 13 are closed in the order from the high-voltage side unit 13's bypass switch 49 to the low-voltage side unit 13's bypass switch 49.

[0106] 15 is a flowchart showing a procedure for disconnecting one string 12 and grounding each unit 13 of the string 12. In this case, the other strings 12 connected in parallel to the disconnected string 12 can be used as a power storage system.

[0107] First, in step S61 of FIG. 15, the overall control device 70 opens the switch 61 either directly or based on a control command from the overall control device 70, via the switching control device 69 corresponding to the string 12, by sending an opening command to the switch 61.

[0108] In the next step S62, the switching control devices 44 of each unit 13 close the bypass switches 49 of each unit 13 in order from the high-voltage side to the low-voltage side, either directly by the overall control device 70 or based on a control command from the overall control device 70. Note that the main switches 41 of each unit 13 are in a closed state, and the switches 37 of the current limiting devices 36 of each unit 13 are in an on state. Through the above procedure, the string 12 is disconnected, and each unit 13 of the string 12 is grounded.

[0109] In the present disclosure, as described above, when the switch 61 corresponding to a certain string 12 is open and the bypass switches 49 of all the units 13 in the string 12 are in a closed state, the string 12 is said to be in a disconnected state. On the other hand, when the switch 61 corresponding to a certain string 12 is closed and the bypass switches 49 of all the units 13 constituting the string 12 are in an open state, the string 12 is said to be in a parallel state.

[0110] 16 is a flowchart showing the procedure for restoring a disconnected string 12 to a parallel state. First, in step S71 of FIG. 16, the switching control devices 44 of each unit 13 open the bypass switches 49 of each unit 13 in sequence from the high-voltage side to the low-voltage side, either directly by the overall control device 70 or based on a control command from the overall control device 70. The main switches 41 of each unit 13 are in a closed state, and the switches 37 of the current limiting devices 36 of each unit 13 are in an on state.

[0111] In the next step S72, the overall control device 70 directly or the switching control device 69 corresponding to the string 12 in question closes the switch 61 by sending a close command to the switch 61 based on a control command from the overall control device 70. Through the above procedure, the string 12 in question returns to a conducting state.

[0112] Fourth Embodiment In a fourth embodiment, a means for grounding a single unit 13 after closing the bypass switch 49 of the unit 13 will be described.

[0113] [Unit Configuration] Fig. 17 is an internal circuit diagram of the positive electrode side unit 13P in the power storage system of embodiment 4. In Fig. 17, the upper side is the high voltage side and the positive electrode side, and the lower side is the low voltage side and the negative electrode side.

[0114] The unit 13P shown in FIG. 17 differs from the unit 13P shown in FIG. 2 in that it further includes first and second high-voltage disconnectors 75A and 75B and a grounding switch 76. Specifically, in FIG. 17, a metal frame 47 is connected to a node 77 on a current path between a low-voltage side terminal 28B and a unit bus 31B on the low-voltage side of the storage battery group 30. The first high-voltage disconnector 75A is connected between the high-voltage side terminal 28A and the trunk switch 41 (i.e., at a position closer to the high-voltage side terminal 28A than the trunk switch 41 and the current limiting device 36). The second high-voltage disconnector 75B is connected between the low-voltage side terminal 28B and the node 77 to which the metal frame 47 is connected. The bypass circuit 48 is connected between the high-voltage side terminal 28A and the low-voltage side terminal 28B so as to be in parallel with the high-voltage disconnectors 75A and 75B. In this disclosure, the first high-voltage disconnector 75A is also referred to as a first disconnector, and the second high-voltage disconnector 75B is also referred to as a second disconnector.

[0115] Grounding switch 76 is connected between the current path between high-voltage disconnecting switch 75B and node 77 and ground 8. That is, the current path between low-voltage side terminal 28B and storage battery group 30 is fastened to metal frame 47 between the connection point of grounding switch 76 and storage battery group 30. As a result, metal frame 47 has the same potential as the main circuit of unit 13P.

[0116] Fig. 18 is an internal circuit diagram of a negative electrode unit 13N in the power storage system of embodiment 4. In Fig. 18, the upper side is the low voltage side and the positive electrode side, and the lower side is the high voltage side and the negative electrode side.

[0117] Similar to the case of FIG. 17 , unit 13N shown in FIG. 18 differs from unit 13N of FIG. 3 in that it further includes first and second high-voltage disconnectors 75A, 75B and a grounding switch 76. Specifically, first high-voltage disconnector 75A is connected between high-voltage side terminal 28A and main switch 41. Metal frame 47 is connected to node 77 on the current path between low-voltage side terminal 28B and storage battery group 30. Second high-voltage disconnector 75B is connected between low-voltage side terminal 28B and node 77. Bypass circuit 48 is connected between high-voltage side terminal 28A and low-voltage side terminal 28B so as to be in parallel with these high-voltage disconnectors 75A, 75B.

[0118] Grounding switch 76 is connected to the current path between high-voltage disconnecting switch 75B and node 77. That is, the current path between low-voltage side terminal 28B and storage battery group 30 is fastened to metal frame 47 between the connection point of grounding switch 76 and storage battery group 30. As a result, metal frame 47 has the same potential as the main circuit of unit 13P.

[0119] [Disconnection and Grounding of a Single Unit] Next, a procedure for disconnecting the unit 13 (13P, 13N) having the above-described configuration and then grounding it independently will be described.

[0120] First, the bypass switch 49 of the unit 13 to be disconnected is closed according to the procedure of steps S13 to S15 in Fig. 4 or the procedure of steps S23 and S24 in Fig. 5. After that, the high-voltage disconnectors 75A and 75B provided in this unit 13 are opened, and then the grounding switch 76 is closed.

[0121] As a result, only the main circuit of this unit 13 is grounded, and the other units 13 connected in series to this unit 13 are not grounded. Therefore, it becomes possible to safely perform maintenance on only this unit 13 or remove the storage battery from the main circuit while continuing to operate the entire power storage system 2.

[0122] Although the high-voltage disconnectors 75A, 75B and the earthing switch 76 are basically operated manually, they may be configured to be remotely operable by the switching control device 44 and / or the overall control device 70.

[0123] Fifth Embodiment In a fifth embodiment, a modified configuration of the units 13P and 13N shown in FIGS. 2 and 3 of the first embodiment and a modified configuration of the units 13P and 13N shown in FIGS. 17 and 18 of the fourth embodiment will be described.

[0124] Fig. 19 is an internal circuit diagram of a modified example of the unit 13P provided in the positive-side string 12P in the energy storage system of embodiment 1. In Fig. 19, the upper side is the high-voltage side and the positive side, and the lower side is the low-voltage side and the negative side.

[0125] 19 , the battery bank 30, the current limiting device 36, and the main switch 41 are connected in series in this order from the high-voltage terminal 28A to the low-voltage terminal 28B. That is, the current limiting device 36 is connected between the low-voltage terminal 28B and the battery bank 30, and the main switch 41 is connected in series with the current limiting device 36 between the low-voltage terminal 28B and the battery bank 30. More generally, the main switch 41, the current limiting device 36, and the battery bank 30 connected in series between the high-voltage terminal 28A and the low-voltage terminal 28B may be connected in any order.

[0126] 19, each switch 33 constituting the storage battery group 30 is connected between the corresponding bank 32 and the low-voltage unit bus 31B. More generally, the order in which each switch 33 connected in series between the high-voltage unit bus 31A and the low-voltage unit bus 31B of the storage battery group 30 and the corresponding bank 32 may be any order.

[0127] 2, the same or corresponding parts are designated by the same reference numerals, and description thereof will not be repeated. For example, as in the case of FIG. 2, metal frame 47 is connected to low-voltage side terminal 28B and thereby has the same potential as low-voltage side terminal 28B.

[0128] Figure 20 is an internal circuit diagram of a modified example of unit 13N provided in negative-side string 12N in the energy storage system of embodiment 1. In Figure 20, the upper side is the low-voltage side and positive side, and the lower side is the high-voltage side and negative side. Unit 13N in Figure 20 has a configuration obtained by inverting unit 13P in Figure 19 up and down, except for the polarities of storage battery 34, semiconductor switching element 38, and diode 39. In unit 13N in Figure 20, parts that are the same as or correspond to unit 13P in Figure 19 are designated by the same reference numerals, and description thereof will not be repeated.

[0129] It goes without saying that the configurations of the modified units 13P and 13N shown in FIGS. 19 and 20 also provide the same effects as those of the first embodiment.

[0130] Fig. 21 is an internal circuit diagram of a modified example of the positive-side unit 13P in the power storage system of embodiment 4. In Fig. 21, the upper part is the high-voltage side and the positive side, and the lower part is the low-voltage side and the negative side. Fig. 22 is an internal circuit diagram of a modified example of the negative-side unit 13N in the power storage system of embodiment 4. In Fig. 22, the upper part is the low-voltage side and the positive side, and the lower part is the high-voltage side and the negative side.

[0131] 21 and 22 , first high-voltage disconnector 75A is connected between high-voltage side terminal 28A and high-voltage unit bus 31A of battery group 30. Metal frame 47 is connected to node 77 on the current path between low-voltage side terminal 28B and trunk switch 41. Second high-voltage disconnector 75B is connected between low-voltage side terminal 28B and node 77 to which metal frame 47 is connected. Bypass circuit 48 is connected between high-voltage side terminal 28A and low-voltage side terminal 28B so as to be in parallel with high-voltage disconnectors 75A and 75B. Grounding switch 76 is connected between ground 8 and the current path between second high-voltage disconnector 75B and node 77. Other configurations in FIGS. 21 and 22 are similar to those in FIGS. 19 and 20 , and therefore, the same or corresponding parts are designated by the same reference numerals and description thereof will not be repeated.

[0132] It goes without saying that the configurations of the modified units 13P and 13N shown in FIGS. 21 and 22 also provide the same effects as those of the fourth embodiment.

[0133] The connections of high-voltage disconnectors 75A, 75B, grounding switch 76, and metal frame 47 can be generally described as follows, so as to apply to both the cases of Figures 17 and 18 of embodiment 4 and the above-mentioned Figures 21 and 22. That is, metal frame 47 is connected to node 77 on the current path between low-voltage terminal 28B and the series-connected assembly of storage battery group 30, current limiting device 36, and trunk switch 41. The first high-voltage disconnector 75A is connected between the series-connected assembly of storage battery group 30, current limiting device 36, and trunk switch 41 and high-voltage terminal 28A (i.e., at a position closer to high-voltage terminal 28A than the storage battery group 30, current limiting device 36, and trunk switch 41). The second high-voltage disconnector 75B is connected between node 77 and low-voltage terminal 28B. The earth switch 76 is connected between the current path between the second high voltage disconnect switch 75B and the node 77 and the ground 8.

[0134] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of this application is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims.

[0135] 1 Power supply system, 2 Storage system, 3 AC / DC converter, 4 Transformer, 5 AC circuit breaker, 6, 11 Disconnector, 7, 76 Grounding switch, 8 Grounding, 10 Busbar, 12 String, 13 Unit, 15 Neutral point, 20N Negative DC terminal, 20P Positive DC terminal, 21 Arm circuit, 21N Lower arm circuit, 21U Upper arm circuit, 22U, 22V, 22W AC connection section, 23 Unit converter, 24 Reactor, 28A High voltage side terminal, 28B Low voltage side terminal, 30 Storage battery group, 31A, 31B Unit busbar, 32 Bank, 33, 61 Switch, 34 Storage battery, 35A, 35B Fuse, 36, 62 Current limiting device, 37, 63 Switch, 38, 53, 64 Semiconductor switching element, 39, 54, 65 Diode, 40, 66 Current limiting element, 41 Main switch, 42, 67 Current sensor, 43, 68 Current measuring instrument, 44, 69 Switching control device, 47 Metal frame, 48 Bypass circuit, 49 Bypass switch, 50 Storage element, 51N Negative terminal, 51P Positive terminal, 52H Half-bridge circuit, 70 Overall control device, 75A, 75B High voltage disconnect switch, P1, P2 Input / output terminal.

Claims

1. A power storage system comprising a plurality of units connected in series, each of the plurality of units including: a high-voltage side terminal; a low-voltage side terminal; a battery group connected between the high-voltage side terminal and the low-voltage side terminal; a first current limiting device connected between the high-voltage side terminal and the battery group and having a function of limiting a current flowing between the high-voltage side terminal and the battery group in an operating state; a first switch connected in series with the first current limiting device between the high-voltage side terminal and the battery group; a bypass circuit connected in parallel with the battery group, the first current limiting device, and the first switch between the high-voltage side terminal and the low-voltage side terminal; and a bypass switch for switching the bypass circuit between conductive and non-conductive states.

2. A power storage system comprising a plurality of units connected in series, each of the plurality of units including: a high-voltage side terminal; a low-voltage side terminal; a battery group connected between the high-voltage side terminal and the low-voltage side terminal; a first current limiting device connected between the low-voltage side terminal and the battery group and having a function of limiting a current flowing between the low-voltage side terminal and the battery group in an operating state; a first switch connected in series with the first current limiting device between the low-voltage side terminal and the battery group; a bypass circuit connected in parallel with the battery group, the first current limiting device, and the first switch between the high-voltage side terminal and the low-voltage side terminal; and a bypass switch for switching the bypass circuit between conductive and non-conductive states.

3. The energy storage system according to claim 1 or 2, wherein each of the plurality of units has a usage state in which the storage battery group can be charged and discharged and a stop state in which the storage battery group cannot be charged or discharged, and in the usage state, the first current limiting device is in a non-operating state, the first switch is in a closed state, and the bypass switch is in an open state, and when switching from the usage state to the stop state, first the first current limiting device goes into the operating state, then the bypass switch goes into the closed state, and then the first switch goes into the open state.

4. The energy storage system according to claim 3, wherein in the stopped state, the first current limiting device is in an operating state, the first switch is in an open state, and the bypass switch is in a closed state, and when switching from the stopped state to the used state, first the first switch becomes in a closed state, then the bypass switch becomes in an open state, and then the first current limiting device becomes in a non-operating state.

5. The energy storage system of claim 3 or 4, wherein each of the plurality of units further includes an individual control device, and the individual control device switches the state from the in-use state to the stopped state when a current flowing between the high-voltage side terminal and the storage battery group exceeds a threshold value.

6. The energy storage system according to any one of claims 1 to 5, wherein the first current limiting device includes a first switch and a first current limiting element connected in parallel to the first switch, and when the first current limiting device is in the operating state, the first switch is in an off state.

7. The energy storage system according to claim 6, wherein the first switch is constituted by at least one semiconductor element, and when the first switch is in the off state, the first switch does not conduct current in a discharging direction of the storage battery group but conducts current in a charging direction of the storage battery group.

8. The energy storage system according to any one of claims 1 to 7, comprising: a plurality of strings, each of which is made up of a plurality of units connected in series and connected in parallel with each other; and a bus to which high-voltage ends of the plurality of strings are commonly connected.

9. The energy storage system according to claim 8, further comprising a plurality of second current limiting devices, each of the plurality of second current limiting devices being connected between a corresponding string of the plurality of strings and the bus bar and limiting a current flowing between the corresponding string and the bus bar in an operating state.

10. The energy storage system according to claim 9, wherein each of the plurality of second current limiting devices includes a second switch and a second current limiting element connected in parallel to the second switch, and each of the plurality of second current limiting devices has the second switch in an off state when in the operating state.

11. The energy storage system according to claim 10, wherein the second switch is configured by at least one semiconductor element, and when the second switch is in the off state, the second switch does not conduct current in a charging direction of the storage battery group but conducts current in a discharging direction of the storage battery group.

12. The energy storage system according to any one of claims 9 to 11, wherein the low-voltage end of each of the plurality of strings is connected to a common ground.

13. The energy storage system according to claim 12, further comprising a plurality of second switches, each of which is connected in series with a corresponding one of the plurality of second current limiting devices between a corresponding one of the plurality of strings and the bus, each of the plurality of strings having a disconnected state and a parallel state, in which in the disconnected state, a corresponding one of the plurality of second switches is in an open state and the bypass switch of each of the plurality of series-connected units is in a closed state, and in which in the parallel state, the corresponding one of the plurality of second switches is in a closed state and the bypass switch of each of the plurality of series-connected units is in an open state.

14. The energy storage system according to claim 13, wherein, when switching from the parallel state to the parallel-off state, the corresponding second switch is first opened, and then the bypass switch of each unit is closed in the order from the unit on the highest voltage side to the unit on the lowest voltage side among the plurality of units connected in series.

15. The energy storage system according to claim 13 or 14, wherein, when switching from the disconnected state to the parallel state, the bypass switch of each unit first opens in the open state in the order from the unit with the lowest voltage to the unit with the highest voltage among the plurality of units connected in series, and then the corresponding second switch opens in the open state.

16. The energy storage system according to any one of claims 12 to 15, further comprising an overall control device that controls all units constituting the energy storage system, wherein when a ground fault or short circuit fault is detected in the energy storage system, the overall control device sends an opening command to a circuit breaker that cuts off the connection between the energy storage system and an external circuit, and closes the bypass switches of all of the units.

17. The energy storage system according to any one of claims 1 to 16, wherein each of the plurality of units further includes a metal frame arranged to surround the first switch, the first current limiting device, and the group of storage batteries, and the metal frame is connected to the low-voltage side terminal.

18. The energy storage system according to claim 17, wherein the metal frame is connected to a node on a current path between the low-voltage side terminal and the series connection of the storage battery group, the first current limiting device, and the first switch, and each of the plurality of units further includes: a first disconnector connected at a position closer to the high-voltage side terminal than the storage battery group, the first switch, and the first current limiting device; a second disconnector connected between the node connected to the metal frame and the low-voltage side terminal; and a grounding switch for grounding the current path between the node and the second disconnector, and the bypass circuit is also connected in parallel with the first disconnector and the second disconnector.

19. A control method for a power storage system including a plurality of units connected in series, each of the plurality of units including: a high-voltage side terminal; a low-voltage side terminal; a storage battery group connected between the high-voltage side terminal and the low-voltage side terminal; a first current limiting device connected between the high-voltage side terminal and the storage battery group and having a function of limiting a current flowing between the high-voltage side terminal and the storage battery group in an operating state; a first switch connected in series with the first current limiting device between the high-voltage side terminal and the storage battery group; a bypass circuit connected in parallel with the storage battery group, the first current limiting device, and the first switch between the high-voltage side terminal and the low-voltage side terminal; and a bypass switch for switching the bypass circuit between conductive and non-conductive states, the control method comprising the step of: at least one control device switching a first unit of the plurality of units from a usage state in which the storage battery group can be charged and discharged to a stop state in which the storage battery group cannot be charged and discharged, the step of switching the first unit from the usage state to the stop state comprising: A control method for a power storage system, comprising: a first step of switching the first current limiting device of the first unit from a non-operating state to an operating state; a second step of switching the bypass switch of the first unit from an open state to a closed state after the first step; and a third step of opening the first switch after the second step.

20. A control method for a power storage system including a plurality of units connected in series, each of the plurality of units including: a high-voltage side terminal; a low-voltage side terminal; a storage battery group connected between the high-voltage side terminal and the low-voltage side terminal; a first current limiting device connected between the low-voltage side terminal and the storage battery group and having a function of limiting a current flowing between the low-voltage side terminal and the storage battery group in an operating state; a first switch connected in series with the first current limiting device between the low-voltage side terminal and the storage battery group; a bypass circuit connected in parallel with the storage battery group, the first current limiting device, and the first switch between the high-voltage side terminal and the low-voltage side terminal; and a bypass switch for switching the bypass circuit between conductive and non-conductive states, the control method comprising the step of: at least one control device switching a first unit of the plurality of units from a usage state in which the storage battery group can be charged and discharged to a stop state in which the storage battery group cannot be charged and discharged, the step of switching the first unit from the usage state to the stop state comprising: A control method for a power storage system, comprising: a first step of switching the first current limiting device of the first unit from a non-operating state to an operating state; a second step of switching the bypass switch of the first unit from an open state to a closed state after the first step; and a third step of opening the first switch after the second step.

21. The control method for a power storage system according to claim 19 or 20, further comprising a step in which the at least one control device switches the first unit from the stopped state to the used state, the step of switching the first unit from the stopped state to the used state including: a fourth step of switching the first switch from an open state to a closed state; a fifth step of switching the bypass switch from a closed state to an open state after the fourth step; and a sixth step of switching the first current limiting device from an operating state to a non-operating state after the fifth step.

22. A control method for a power storage system according to any one of claims 19 to 21, further comprising a step in which the at least one control device detects a current flowing between the high-voltage side terminal of each of the plurality of units and the storage battery group, and the at least one control device executes a step of switching the first unit from the use state to the stop state when the current flowing between the high-voltage side terminal of the first unit and the storage battery group exceeds a threshold value.

23. The control method for an energy storage system according to any one of claims 19 to 22, wherein the energy storage system includes: a plurality of strings, each of which is composed of a plurality of units connected in series and connected in parallel to one another; a bus to which high-voltage ends of the plurality of strings are commonly connected; and a plurality of second switches, each of which is connected between a corresponding one of the plurality of strings and the bus, and low-voltage ends of the plurality of strings are connected to a common ground, and the control method further includes a step by the at least one control device switching a first string of the plurality of strings from a parallel state to a disconnected state, the step of switching the first string from the parallel state to the disconnected state including: a seventh step of switching the second switch from a closed state to an open state; and an eighth step of switching the bypass switch of each unit from an open state to a closed state in the order from the highest-voltage unit to the lowest-voltage unit of the plurality of series-connected units constituting the first string, after the seventh step.

24. The control method for a power storage system according to claim 23, further comprising a step by at least one control device switching the first string from the disconnected state to the parallel state, wherein the step of switching the first string from the disconnected state to the parallel state includes: a ninth step of switching the bypass switch of each unit from a closed state to an open state in the order from the unit on the lowest voltage side to the unit on the highest voltage side among the plurality of series-connected units constituting the first string; and a tenth step of switching the second switch from an open state to a closed state after the ninth step.

25. A storage unit for constituting a power storage system, the power storage system comprising a plurality of the storage units connected in series and in parallel, the storage unit comprising: a high-voltage side terminal; a low-voltage side terminal; a storage battery group connected between the high-voltage side terminal and the low-voltage side terminal; a first current limiting device connected between the high-voltage side terminal and the storage battery group and limiting a current flowing between the high-voltage side terminal and the storage battery group in an operating state; a first switch connected in series with the first current limiting device between the high-voltage side terminal and the storage battery group; a bypass circuit connected in parallel with the storage battery group, the first current limiting device, and the first switch between the high-voltage side terminal and the low-voltage side terminal; and a bypass switch for controlling the conduction and interruption of the current flowing in the bypass circuit.

26. A storage unit for constituting a power storage system, the power storage system comprising a plurality of the storage units connected in series and in parallel, the storage unit comprising: a high-voltage side terminal; a low-voltage side terminal; a storage battery group connected between the high-voltage side terminal and the low-voltage side terminal; a first current limiting device connected between the low-voltage side terminal and the storage battery group and limiting a current flowing between the low-voltage side terminal and the storage battery group in an operating state; a first switch connected in series with the first current limiting device between the low-voltage side terminal and the storage battery group; a bypass circuit connected in parallel with the storage battery group, the first current limiting device, and the first switch between the high-voltage side terminal and the low-voltage side terminal; and a bypass switch for controlling the conduction and interruption of the current flowing in the bypass circuit.

27. A power supply system comprising: the storage system according to any one of claims 1 to 18; and an AC / DC converter provided between the storage system and an AC circuit.

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