Discharge control device and storage battery system

Abstract

This electric discharge control device comprises: a capacitor connected in series to a storage battery; and a control circuit for controlling, on the basis of information indicating an electric discharge command and information indicating a command value with respect to a current value outputted from the storage battery, a voltage value across both ends of the capacitor such that the current value outputted from the storage battery is equal to or lower than the command value.

Description

[Technical Field]

[0001] The present invention relates to a discharge control device and a storage battery system. [Background technology]

[0002] There is a growing need for storage battery systems. For example, storage batteries are being used for a variety of purposes, such as the efficient use of electrical energy and backup of facilities and equipment. Storage batteries are also expected to be used to stabilize (level) the output of variable power sources whose output fluctuates with the weather, such as renewable energy sources (solar power generation, wind power generation, etc.), which have become widespread in recent years.

[0003] Furthermore, in recent years, high-performance batteries such as lithium-ion batteries have become increasingly popular. However, there are issues from a materials perspective. In particular, lithium-ion batteries contain rare metals such as nickel, cobalt, and lithium, which are also considered conflict materials. Therefore, in systemization, it is ideal to use lithium-ion batteries in appropriate amounts rather than adopting them for every purpose. In recent years, the supply of lithium has been tight due to geopolitical issues in Eastern Europe, and development of lithium-free batteries such as sodium-ion batteries is also progressing.

[0004] A storage battery system generally combines single-cell storage batteries in series to obtain a constant output voltage. Furthermore, to match the output power of the storage battery system to the voltage of the power supply circuit, a power conditioning system (PCS) consisting of a DC / DC converter is connected to the input and output to control the voltage and current during charging and discharging. Because the PCS is a device that boosts the entire output voltage of the storage batteries, high-voltage DC / DC converter components are used to maintain the circuit's voltage resistance. For this reason, PCSs are known to be large in size, difficult to miniaturize, and difficult to keep costs down (e.g., Non-Patent Document 1, Non-Patent Document 2). [Prior art documents]

Non-Patent Literature

[0005]

Non-Patent Literature 1

Non-Patent Literature 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] A typical PCS connects the battery output and DC / DC converter in parallel, boosting the entire battery output power. This results in high voltage or high current for the internal circuits or components, making miniaturization difficult. For example, the discharge current flows entirely through the DC / DC converter without being shunted, making it difficult to reduce the circuit size and cost when used in high-voltage, high-power power supply equipment. Furthermore, if the battery system is connected directly to the main circuit without a PCS in order to simplify the battery system, it is impossible to mix different batteries in parallel. Furthermore, even if a charge pump circuit is used to add voltage, it can boost the voltage but cannot control the output current value. Therefore, when different batteries or DC power sources are connected in parallel, the current burden is concentrated only on the power source or battery with the higher voltage, preventing the desired output current distribution.

[0007] The disclosed technology aims to reduce the size and cost of a storage battery system that uses a mixture of different batteries. [Means for solving the problem]

[0008] The disclosed technology is a discharge control device that includes a capacitor connected in series to a storage battery, and a control circuit that controls the voltage value across the capacitor based on information indicating a discharge command and information indicating a command value for the current value output from the storage battery so that the current value output from the storage battery is the command value or less. [Effects of the Invention]

[0009] According to the disclosed technology, it is possible to reduce the size of a storage battery system that uses a mixture of different batteries. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram illustrating an example of the configuration of a conventional storage battery system. [Figure 2] 1 is a diagram illustrating an example of a configuration of a storage battery system according to an embodiment of the present invention. [Figure 3]1 is a diagram illustrating an example of a configuration of a storage battery system according to Example 1 of an embodiment of the present invention. [Figure 4] FIG. 10 is a diagram illustrating an example of the configuration of a storage battery system according to Example 2 of an embodiment of the present invention. [Figure 5] FIG. 2 is a diagram illustrating an example of an internal circuit of a discharge control device. [Figure 6] FIG. 2 is a diagram illustrating an example of a control circuit included in an internal circuit of the discharge control device. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an embodiment of the present invention (the present embodiment) will be described with reference to the drawings. The embodiment described below is merely an example, and the embodiment to which the present invention is applied is not limited to the following embodiment.

[0012] (Previous problems) First, let us explain the problems with the conventional system. There is a growing need for storage battery systems. For example, storage batteries are used for a variety of purposes, such as the efficient use of electric energy and as backup for facilities or equipment. In addition, there are expectations for the use of storage batteries in stabilizing (leveling) the output power of variable power sources whose output fluctuates with the weather, such as renewable energy sources (solar power generation, wind power generation, etc.), which have become widespread in recent years.

[0013] Furthermore, in recent years, high-performance batteries such as lithium-ion batteries have become increasingly popular. However, there are issues from a materials perspective, and lithium-ion batteries in particular contain rare metals such as nickel, cobalt, and lithium, which are also considered conflict materials. Therefore, in systemization, it is ideal to use lithium-ion batteries in appropriate amounts rather than adopting them for every purpose. In recent years, the supply of lithium as a material has been tight due to geopolitical issues, and development of lithium-free batteries such as sodium-ion batteries is also progressing.

[0014] A storage battery system generally combines single-cell storage batteries in series to obtain a constant output voltage. Furthermore, to match the output power of the storage battery system to the voltage of the power supply circuit, a power conditioner (PCS: Power Conditioning System) consisting of a DC / DC converter is connected to the input and output to control the voltage and current during charging and discharging.

[0015] Here, the PCS is a power conversion device that controls the current or voltage during charging or discharging, and is realized by a DC / DC converter, a DC / AC converter, or the like.

[0016] FIG. 1 is a diagram showing an example of the configuration of a conventional storage battery system. Note that protection circuits, control circuits, etc. are omitted in FIG. 1. The battery is an assembled battery in which n single-cell storage batteries with a voltage of A [V] are connected in series, generating a voltage of nA [V]. Hereinafter, the voltage of the entire battery is referred to as V batt The PCS (DC / DC converter) is connected to both the positive (+) and negative (-) terminals of the battery pack, which is made up of single-cell storage batteries connected in series.

[0017] The PCS receives input including a discharge command output from the management device (or built into the PCS) and a current command value or a current upper limit command, and adjusts the output voltage of the battery pack to V batt The boost voltage α [V] is boosted to +α [V] and the boost voltage α [V] is controlled so that it becomes the rated system voltage V1 [V] of the connected power supply system.

[0018] In addition, even if the discharge voltage of the storage battery drops due to discharge, the PCS can boost it to the target voltage and control a stable voltage output.Furthermore, the PCS's output current value can be controlled to prevent the storage battery from over-discharging, preventing strain on the battery and deterioration due to over-discharge.

[0019] However, because the PCS is a device that boosts the entire output voltage of the storage battery, high-voltage DC / DC converter components are used, and it is necessary to maintain the circuit's voltage resistance. For this reason, PCSs are known to be large in size, difficult to miniaturize, and difficult to keep costs down (e.g., Non-Patent Document 1, Non-Patent Document 2).

[0020] There have been many different types of storage batteries in use for a long time, including lithium-ion batteries, lead-acid batteries, nickel-metal hydride batteries, etc. Research and development into batteries made from new materials is also ongoing, and it is expected that the number of types will continue to increase in the future.

[0021] Because storage batteries use an oxidation-reduction reaction, the electromotive force (voltage) varies depending on the material and configuration. As with electromotive force, the characteristics of various storage batteries, such as internal resistance, capacity, and discharge rate (C rate), vary depending on the type. In addition, the characteristics of storage batteries change depending on the usage conditions (SoC, SoH) of the old and new batteries.

[0022] SoC (State of Charge) is an index that shows the charge rate or charging state of a battery, with a fully charged state defined as 100% and a fully discharged state defined as 0%. SoH (State of Health) is an index that shows the health and deterioration state of a storage battery, and is defined as the percentage of the full charge capacity (Ah) at the time of deterioration, when the initial full charge capacity (Ah) is set to 100%.

[0023] For example, almost all characteristics of a battery, such as its electromotive force, internal resistance, and C rate, change depending on the usage conditions of the old and new batteries. As mentioned above, when combining batteries, be sure to match the types and old and new batteries depending on their characteristics. Otherwise, the load on the batteries will increase locally, causing them to deteriorate without being able to perform to their full potential.

[0024] However, there are many cases where mixing different types of batteries would be advantageous in terms of cost. For example, lead-acid batteries are inexpensive and suitable for long-term discharge at low C rates, but they cannot handle frequent charge / discharge or high C rates.

[0025] On the other hand, lithium-ion batteries, although expensive, are smaller, can be set to a higher C-rate, and experience less deterioration during charging and discharging than the lead-acid batteries and nickel-metal hydride batteries that have been used up until now. In a system that requires discharging at various C-rates, it is desirable from a cost perspective to use the cheapest battery type suitable for each mode, if possible.

[0026] However, as mentioned above, different types of storage batteries cannot be used together, so they are generally not used together. If different types of storage batteries are used in parallel, a PCS (DC / DC converter) is connected in parallel to the output of each battery to control the input / output current and voltage. Therefore, when using a combination of batteries, a PCS (DC / DC converter) is required for each battery system.

[0027] As mentioned above, a typical PCS connects the storage battery output and DC / DC converter in parallel, boosting the entire storage battery output power. This results in high voltage or high current for the internal circuits or components, making miniaturization difficult. For example, since the discharge current flows entirely within the DC / DC converter without being shunted, it is difficult to keep the circuit size and cost down when used in high-voltage, high-power power supply equipment. Furthermore, if the storage battery system is connected directly to the main circuit without using a PCS to simplify the storage battery system, it is not possible to mix and use different batteries in parallel.

[0028] Furthermore, considering that a large amount of used batteries (such as used batteries for electric vehicles) will be generated in the future, the PCS's function of actively controlling the output current according to the battery will become important.

[0029] (Outline of this embodiment) In this embodiment, in order to address the above-mentioned conventional problems, an example will be described in which a capacitor connected in series with a battery is treated as a virtual cell, and the discharge current is actively controlled by the combined voltage of the storage battery and capacitor, thereby achieving an effect equivalent to that of a PCS.

[0030] 2 is a diagram showing an example of the configuration of a storage battery system according to an embodiment of the present invention. The storage battery system 1 includes a discharge control device 10, a management device 20, and a storage battery 30.

[0031] The discharge control device 10 is a device that receives input including a discharge command and a current command value or a current upper limit command from the management device 20, and actively controls the discharge current with the combined voltage of the storage battery and the capacitor, treating the capacitor connected in series with the battery as a virtual cell. The discharge control device 10 performs current control with the output current as a target value, thereby maintaining a discharge current value appropriate for the storage battery and performing parallel operation with multiple storage batteries and DC power sources.

[0032] The management device 20 is, for example, a computer, and transmits information including a discharge command and a current command value or a current upper limit value command to the discharge control device 10 based on a user operation or the like.

[0033] The storage battery 30 includes one or more (n) battery cells. This allows the power supply equipment's main system, inverter, or load to be controlled to a rated system voltage V1 [V]. Here, the voltage of the discharge control device 10 is α [V], and the voltage of the storage battery 30 is nA [V] = V batt [V] (when n battery cells of A[V] are connected in series), V1[V]=V batt +α[V].

[0034] Next, examples 1 and 2 will be described as specific examples of the above-described embodiment.

[0035] Example 1 In this embodiment, an example will be described in which a discharge control device is connected in series to the positive electrode side of a storage battery.

[0036] 3 is a diagram showing an example of the configuration of a storage battery system according to Example 1 of an embodiment of the present invention. A protection circuit is omitted from the illustration. The storage battery system 1 according to this example includes a discharge control device 10, a management device 20, a storage battery 30, and a charging power supply 40. A load 50 and a DC power supply 60 are connected to the storage battery system 1 as examples of a main system, inverter, load, etc. of a power supply facility with a rated system voltage V1 [V].

[0037] The discharge control device 10 includes a control circuit 11 , a power supply 12 , a capacitor 13 , a current sensor 14 , a first voltage sensor 15 , and a second voltage sensor 16 .

[0038] The control circuit 11 calculates the voltage value V of the capacitor 13 based on the command value included in the information received from the management device 20 and the values ​​of each sensor (the current sensor 14, the first voltage sensor 15, and the second voltage sensor 16). C1 and determines the control value of the current value I1.

[0039] The power supply 12 is an isolated step-down DC / DC converter and is connected in parallel with the capacitor 13. The capacitor 13 is connected in series with the storage battery 30. The power supply 12 operates upon receiving a control signal from the control circuit 11.

[0040] The current sensor 14 detects the current value I1 output from the storage battery 30 and transmits a signal indicating the detected current value I1 to the control circuit 11. The first voltage sensor 15 detects the voltage value V across the capacitor 13. C1 Detects the detected voltage value V C1 The second voltage sensor 16 detects the voltage value V across the storage battery 30 and sends a signal indicating the voltage V across the storage battery 30 to the control circuit 11. batt1 Detects the detected voltage value V batt1 The control circuit 11 then transmits a signal indicating this.

[0041] According to the storage battery system 1 of this embodiment, active current control can be performed instead of constant voltage control.

[0042] Furthermore, the charging power supply 40 may be connected in parallel with the storage battery 30 to perform charging in accordance with the characteristics of the storage battery 30. In this way, the discharge control device 10 controls the output current value I1, so there is no need to select a storage battery 30 that is suitable for the storage battery system 1, and any type of storage battery 30 can be used.

[0043] Alternatively, the discharge control device 10 may be connected in series to the negative electrode side of the storage battery 30, or two discharge control devices 10 may be connected to both electrodes of the storage battery 30.

[0044] Example 2 A second embodiment will be described below with reference to the drawings. The second embodiment differs from the first embodiment in that a plurality of storage batteries are connected in parallel, and each output current value (e.g., I1 and I2) is controlled by a plurality of discharge control devices 10. Therefore, the following description of the second embodiment will focus on the differences from the first embodiment, and components having the same functional configuration as the first embodiment will be assigned the same reference numerals as those used in the description of the first embodiment, and their description will be omitted.

[0045] 4 is a diagram showing an example of the configuration of a storage battery system according to Example 2 of an embodiment of the present invention. Protection circuits are omitted from the illustration. The storage battery system 1 according to this example includes a first discharge control device 10A, a second discharge control device 10B, a management device 20, a first storage battery 30A, and a second storage battery 30B.

[0046] The first storage battery 30A and the second storage battery 30B are connected in parallel with each other. The first discharge control device 10A is connected in series with the first storage battery 30A. The second discharge control device 10B is connected in series with the second storage battery 30B.

[0047] The first discharge control device 10A controls the output current value I1 of the first storage battery 30A. The second discharge control device 10B controls the output current value I2 of the second storage battery 30B. A current equivalent to the sum of the current values ​​(I1+I2) flows through the load 50 and the DC power source 60. The management device 20 transmits information including a discharge command and a current command value or a current upper limit command to each of the multiple discharge control devices (the first discharge control device 10A and the second discharge control device 10B).

[0048] According to this embodiment, load sharing can be realized by utilizing a plurality of storage batteries connected in parallel and controlling the output value of each storage battery by a plurality of discharge control devices.

[0049] (Internal circuit of discharge control device) Next, the internal circuitry of the discharge control device 10 according to this embodiment will be described.

[0050] 5 is a diagram showing an example of an internal circuit of a discharge control device. A protection circuit is omitted. The power supply 12 included in the discharge control device 10 according to each of the above-described embodiments includes a transformer 121, a switch 122, a voltage sensor 123, a first rectifier diode 124, a second rectifier diode 125, an inductor 126, and a current sensor 127.

[0051] The power supply 12 is used to control the voltage of the capacitor 13. Any type of power supply 12 may be used, but it is necessary to use a circuit that can insulate the primary side from the secondary side.

[0052] The control circuit 11 controls the voltage value V of the capacitor 13. C1 Based on the detection result of the current value I1, the ON / OFF of the switch 122 (e.g., a power semiconductor) is controlled, and the voltage value applied to the primary side of the transformer 121 is controlled, thereby controlling the voltage value applied to the secondary side of the transformer 121 in accordance with the winding ratio of the transformer 121.

[0053] FIG. 6 is a diagram showing an example of a control circuit included in the internal circuit of the discharge control device. The protection circuit is omitted. The control circuit 11 controls the rated system voltage V of the power supply system. * Based on 1, the target current value I * While correcting with 1, V C1 The control circuit 11 is a circuit that controls V * Battery voltage V from target value 1 batt1 By subtracting C1 The target value V * C1 Furthermore, the control circuit 11 obtains a target voltage V C1 To correct this, the current value I1 and the target current I * The difference between 1 and 2 is converted into a voltage by the virtual impedance of the proportional controller K, and V C1 This voltage control using the virtual impedance functions as a droop control based on the current value I1, while also achieving feedback control characteristics that approach the desired current value. ref The voltage is limited by a protection circuit so that it is within the rated system voltage of the power supply system.

[0054] The control circuit 11 detects the voltage value V C1 and current values ​​I1, I L The target voltage value is determined based on the above, and a PWM signal indicating the determined voltage value is output to the switch 122.

[0055] This control operation reduces the voltage V C1 and the current value I1 are controlled, thereby realizing an active storage battery system 1 that controls the power output at the target current value I1. This allows the discharge control device 10 to achieve the same function as a PCS with a simple circuit.

[0056] In addition, the discharge control device 10 may detect an abnormal state of the storage battery 30 and the connected circuit, and control the voltage value of the capacitor 13, thereby controlling the current value I1 output from the storage battery 30 to 0 A.

[0057] The discharge control device 10 actively controls the output current of the storage battery (current control based on voltage control), and therefore, it is possible to incorporate droop characteristics into the control. Therefore, even when multiple discharge control devices 10 are connected in parallel as shown in the second embodiment, they can share current or share the desired current and operate in cooperation as a distributed power source.

[0058] Furthermore, if a switch, capacitor, or the like fails, the voltage will not be boosted, but at least discharging can continue via a rectifier diode, inductor, or the like.

[0059] (Summary of the embodiment) This specification describes at least the discharge control device and storage battery system described in the following sections. (Section 1) a capacitor connected in series with the storage battery; a control circuit that controls a voltage value across the capacitor based on information indicating a discharge command and information indicating a command value for a current value output from the storage battery so that the current value output from the storage battery is the command value or less. Discharge control device. (Section 2) a power supply connected in parallel with the capacitor; a current sensor that detects a current value output from the storage battery and transmits a signal indicating the detected current value to the control circuit; a first voltage sensor that detects a voltage value across the capacitor and transmits a signal indicating the detected voltage value to the control circuit; a second voltage sensor that detects a voltage value across the storage battery and transmits a signal indicating the detected voltage value to the control circuit; the control circuit controls the power supply based on the detection results of the current sensor, the first voltage sensor, and the second voltage sensor, thereby controlling the voltage value across the capacitor, thereby controlling the output current of the storage battery; 2. The discharge control device according to claim 1. (Section 3) The power supply a transformer having a primary side connected to the storage battery and a secondary side connected to the capacitor that is insulated from each other; a switch for controlling a voltage value applied to the primary side of the transformer; 3. The discharge control device according to claim 2. (Section 4) The power supply a rectifier diode connected to the secondary side to which the capacitor is connected; The rectifier diode allows the discharge to continue even if the switch fails. 4. The discharge control device according to claim 3. (Section 5) A storage battery system including a plurality of discharge control devices and a plurality of storage batteries, The plurality of storage batteries are connected in parallel with each other, Each discharge control device included in the plurality of discharge control devices is a capacitor connected in series to each of the plurality of storage batteries; a control circuit that controls a voltage value across the capacitor based on information indicating a discharge command and information indicating a command value for a current value output from each of the plurality of storage batteries, so that the current value output from each of the plurality of storage batteries is the command value or less; Battery storage system.

[0060] Although the present embodiment has been described above, the present invention is not limited to such a specific embodiment, and various modifications and changes are possible within the scope of the gist of the present invention described in the claims. [Explanation of symbols]

[0061] 1. Battery storage system 10 Discharge control device 11 Control circuit 12 Power supply 13 Capacitor 14 Current Sensor 15 First voltage sensor 16 Second voltage sensor 20 Management device 30 Storage battery 40 Charging power supply 50 load 60 DC power supply 121 Transformer 122 Switch 123 Voltage Sensor 124 First rectifier diode 125 Second rectifier diode 126 Inductor 127 Current Sensor

Claims

1. a capacitor connected in series with the storage battery; a control circuit that controls a voltage value across the capacitor based on information indicating a discharge command and information indicating a command value for a current value output from the storage battery so that the current value output from the storage battery is the command value or less. Discharge control device.

2. a power supply connected in parallel with the capacitor; a current sensor that detects a current value output from the storage battery and transmits a signal indicating the detected current value to the control circuit; a first voltage sensor that detects a voltage value across the capacitor and transmits a signal indicating the detected voltage value to the control circuit; a second voltage sensor that detects a voltage value across the storage battery and transmits a signal indicating the detected voltage value to the control circuit; the control circuit controls the power supply based on the detection results of the current sensor, the first voltage sensor, and the second voltage sensor, thereby controlling the voltage value across the capacitor, thereby controlling the output current of the storage battery. The discharge control device according to claim 1 .

3. The power supply a transformer having a primary side connected to the storage battery and a secondary side connected to the capacitor that is insulated from each other; a switch for controlling a voltage value applied to the primary side of the transformer; The discharge control device according to claim 2 .

4. The power supply a rectifier diode connected to the secondary side to which the capacitor is connected; The rectifier diode allows the discharge to continue even if the switch fails. The discharge control device according to claim 3 .

5. A storage battery system including a plurality of discharge control devices and a plurality of storage batteries, The plurality of storage batteries are connected in parallel with each other, Each discharge control device included in the plurality of discharge control devices is a capacitor connected in series to each of the plurality of storage batteries; a control circuit that controls a voltage value across the capacitor based on information indicating a discharge command and information indicating a command value for a current value output from each of the plurality of storage batteries, so that the current value output from each of the plurality of storage batteries is the command value or less; Battery storage system.

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