Battery system and control method

Abstract

A battery system and control method are provided. The system includes a charging device (200), multiple battery modules (110) to (130) that can be connected in parallel to the charging device (200), and a control device (400). Each of the multiple battery modules has a battery. Upon receiving a charging command, the control device (400) obtains the voltage values ​​of the batteries in each of the multiple battery modules, determines the first battery (E1) with the lowest voltage value and the second battery (E2) with the second lowest voltage value, and begins charging the first battery (E1). After charging the first battery (E1) begins, if the difference between the voltage value of the first battery module (110) and the voltage value (V2) of the second battery (E2) becomes below a first threshold, charging the second battery (E2) begins.

Description

Technical Field

[0001] This disclosure relates to battery systems and control methods. Background Technology

[0002] In recent years, the demand for electrically powered mobile vehicles (such as EVs and ships) has increased. In the battery pack systems (hereinafter referred to as "battery systems") used in such mobile vehicles, a high-capacity structure is employed that connects multiple battery packs (hereinafter simply "batteries") in parallel to enable long-distance travel or navigation. These batteries are charged by a charging device when the mobile vehicle is parked or moored, and discharge to the propulsion system or loads within the mobile vehicle during travel or navigation.

[0003] However, voltage differences sometimes arise between multiple batteries due to variations in the characteristics of the battery cells. When multiple batteries that generate voltage differences are connected in parallel, a phenomenon known as "cross-current" occurs, where current flows from the battery with the higher voltage value to the battery with the lower voltage value.

[0004] Japanese Patent Application Publication No. 2011-182623 discloses a battery system for preventing such cross-current. This battery system performs a process to equalize the voltages of multiple batteries, for example, when charging or discharging multiple batteries. In this battery system, equalization resistors are provided between the batteries. Furthermore, the equalization process is performed by directing current from the battery with the higher voltage value through the equalization resistors to the battery with the lower voltage value. Summary of the Invention

[0005] However, this patent document requires an equalization resistor, which increases the system size. Furthermore, since the current flows through the resistor, the current decreases when the voltage difference is small, increasing the time required for equalization.

[0006] The purpose of this disclosure is to provide a battery system and control method that can perform battery voltage equalization in a short time without increasing the size of the battery system.

[0007] According to one aspect of this disclosure, a battery system includes a charging device, multiple battery modules that can be connected in parallel to the charging device, and a control device. Each of the multiple battery modules has a battery. Upon receiving a charging command, the control device obtains the voltage values ​​of the batteries in each of the multiple battery modules and determines the first battery with the lowest voltage value and the second battery with the second lowest voltage value. First, the control device begins charging the first battery. Next, after starting charging the first battery, if the difference between the voltage value of the first battery module (including the first battery) and the voltage value of the second battery, or the difference between the voltage values ​​of the first battery and the second battery, becomes below a first threshold, the control device begins charging the second battery.

[0008] According to other embodiments of this disclosure, the battery system includes a load, multiple battery modules that can be connected in parallel for the load, and a control device. Each of the multiple battery modules has a battery. Upon receiving a discharge command, the control device obtains the voltage values ​​of the individual batteries in each of the multiple battery modules and determines the first battery with the highest voltage value and the second battery with the second highest voltage value. First, the control device begins discharging the first battery. Next, after starting the discharge of the first battery, if the difference between the voltage value of the first battery module (including the first battery) and the voltage value of the second battery, or the difference between the voltage values ​​of the first battery and the second battery, becomes below a first threshold, the control device begins discharging the second battery.

[0009] According to other embodiments of this disclosure, the control method is a control method for a battery system having a charging device and multiple battery modules that can be connected in parallel for the charging device. Each of the multiple battery modules has a battery. In the control method, upon receiving a charging command, the voltage values ​​of the batteries in each of the multiple battery modules are obtained, and a first battery with the lowest voltage value and a second battery with the second lowest voltage value are determined. First, in the control method, charging of the first battery begins. Next, in the control method, after charging of the first battery begins, if the difference between the voltage value of the first battery module including the first battery and the voltage value of the second battery, or the difference between the voltage values ​​of the first battery and the second battery, becomes below a first threshold, charging of the second battery begins.

[0010] According to other embodiments of this disclosure, the control method is a control method for a battery system having a load and multiple battery modules that can be connected in parallel for the load. Each of the multiple battery modules has a battery. In the control method, upon receiving a discharge command, the voltage values ​​of the individual batteries in each of the multiple battery modules are obtained, and a first battery with the highest voltage value and a second battery with the second highest voltage value are determined. First, in the control method, discharging of the first battery begins. Next, in the control method, after the discharge of the first battery begins, if the difference between the voltage value of the first battery module (including the first battery) and the voltage value of the second battery, or the difference between the voltage values ​​of the first battery and the second battery, becomes below a first threshold, discharging of the second battery begins.

[0011] The above and other objects, features, solutions, and advantages of the invention will become more apparent from the following detailed description of the invention, which is understood in conjunction with the accompanying drawings. Attached Figure Description

[0012] Figure 1 This is a diagram showing an example of battery system installation.

[0013] Figure 2 This is the equivalent circuit diagram of the battery system.

[0014] Figure 3 This is a functional block diagram of the control device in this embodiment.

[0015] Figure 4 This is a flowchart illustrating the charging process of the control device.

[0016] Figure 5 This is a graph showing the experimental results of the comparative example.

[0017] Figure 6 This is a graph showing the experimental results of the battery system according to this embodiment.

[0018] Figure 7 This is a diagram illustrating the implementation of ramp charging control.

[0019] Figure 8 This is a flowchart illustrating the discharge process of the control device. Detailed Implementation

[0020] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. Furthermore, the same or equivalent parts will be referred to by the same symbols in the drawings without repeated descriptions.

[0021] <Example of a battery system structure>

[0022] Figure 1This diagram illustrates an example of the installation of the battery system 100. The battery system 100 is installed on a mobile body 10. The mobile body 10 is a ship or electric vehicle powered by a high-capacity battery. The mobile body 10 includes the battery system 100, a charging device 200, a load 300 (e.g., an inverter), and a control device 400. The load 300 may also be, for example, a propulsion unit.

[0023] The battery system 100, charging device 200, and load 300 are connected in the same circuit. The load 300 (e.g., an inverter) converts the direct current supplied from the battery system 100 into alternating current, and supplies the alternating current as power to a motor (not shown). The charging device 200 supplies power to the battery system 100 to charge the battery system 100, which functions as a secondary battery.

[0024] The control device 400 is connected to the battery system 100, the charging device 200, and the load 300. The control device 400 controls the charging of the battery system 100 by controlling the charging device 200. Additionally, the control device 400 controls the discharge current to the load 300 by controlling the load 300.

[0025] The battery system 100 has N individual battery modules. However, N is an integer greater than or equal to 2. In this embodiment, N = 3. That is, the battery system 100 has 3 battery modules. The battery system 100 includes battery module 110, battery module 120, battery module 130, and an overall BMS (Battery Management System) 101. Battery modules 110, 120, and 130 are each connected in parallel to the charging device 200 and the load 300. Hereinafter, each module of battery modules 110, 120, and 130 will sometimes be referred to as each battery module 110 to 130. Hereinafter, battery module 110 will be mainly described, but battery modules 120 and 130 have the same structure as battery module 110.

[0026] Battery module 110 includes battery E1, bus B1, fuse H1, relay SW1, voltage sensor 111, current sensor 113, and BMS 114. Battery module 120 includes battery E2, bus B2, fuse H2, relay SW2, voltage sensor 121, current sensor 123, and BMS 124. Battery module 130 includes battery E3, bus B3, fuse H3, relay SW3, voltage sensor 131, current sensor 133, and BMS 134. Furthermore, the relay is also referred to as a "connecting element".

[0027] Battery E1 is a battery pack formed by connecting multiple individual cells in series. For example, 80 to 100 individual cells are connected in series in battery E1. Each individual cell is a rechargeable battery. For example, a single cell can be a lithium-ion rechargeable battery or a nickel-metal hydride rechargeable battery.

[0028] Busbar B1 is a conductive component used to connect battery E1, fuse H1, and relay SW1. Busbar B1 can also be installed inside battery E1 to connect multiple single-cell batteries.

[0029] Fuse H1 prevents overcurrent from flowing through battery module 110. The battery system 100 is configured such that if a current higher than the allowable current value flows through it, the over-discharge protection of fuses H1 to H3, etc., will activate, and the use of each battery module 110 to 130 will be interrupted.

[0030] A voltage sensor detects the voltage value of the battery corresponding to it and outputs the detected voltage value to the corresponding BMS. For example, voltage sensor 111 detects the voltage value V1 of battery E1 corresponding to it. Voltage sensor 121 detects the voltage value V2 of battery E2 corresponding to it. Voltage sensor 131 detects the voltage value V3 of battery E3 corresponding to it.

[0031] Additionally, a current sensor detects the current flowing through the battery module corresponding to that current sensor and outputs the detected current value to the corresponding BMS. For example, current sensor 113 detects the current value I1 flowing through battery module 110. Current sensor 123 detects the current value I2 flowing through battery module 120. Current sensor 133 detects the current value I3 flowing through battery module 130.

[0032] BMS114 controls the ON or OFF state of relay SW1. When relay SW1 is ON, charging is performed via charging device 200. When relay SW1 is ON, discharging to load 300 is performed. When relay SW1 is OFF, neither charging via charging device 200 nor discharging to load 300 is performed.

[0033] Additionally, BMS114 acquires the voltage value V1 from voltage sensor 111 and the current value I1 from current sensor 113. Furthermore, BMS114 can obtain, for example, the SOC (State of Charge) of battery E1 and the resistance value of the battery module (resistance value r1, etc., described later) through predetermined calculations.

[0034] The battery module includes a battery and corresponding components. In this embodiment, the corresponding components are a busbar, a fuse, and a relay.

[0035] The overall voltage sensor 150 detects the overall voltage value Vc of the battery modules connected in parallel. The overall voltage sensor 150 outputs the detected overall voltage value Vc to the overall BMS 101. The overall BMS 101 acquires parameters (voltage values, etc.) from each BMS 114, 124, and 134, as well as the overall voltage value Vc from the overall voltage sensor 150. The overall voltage sensor 150 can be installed as a standalone circuit or as part of the functionality of each BMS 114, 124, 134, or the overall BMS 101. Furthermore, the overall BMS 101 controls each battery module 110 to 130.

[0036] exist Figure 1 The example described above illustrates an example where each battery module 110-130 is equipped with a BMS114-134. However, the battery system 100 may also be structured without BMS114-134. For example, the voltage and current sensors of each battery module 110-130 may be directly connected to the overall BMS101. Alternatively, the battery system 100 may also be structured without an overall BMS101. For example, BMS114 may perform the processes described below that are performed by the overall BMS101.

[0037] BMS114, 124, 134, control unit 400, and the overall BMS101 are the main computing units that execute various programs. The control unit 400 and the overall BMS101 are composed of, for example, a CPU (Central Processing Unit), an FPGA (Field-Programmable Gate Array), and a GPU (Graphics Processing Unit).

[0038] BMS114, 124, 134, control device 400, and overall BMS101 include a memory (not shown). The memory provides a storage area for temporarily storing program code and working memory when the overall BMS101 executes any control program. The memory may be composed of volatile memory devices (RAM) such as DRAM (Dynamic Random Access Memory) or SRAM (Static Random Access Memory).

[0039] BMS114, 124, 134, control unit 400, and overall BMS101 include storage devices such as ROM (Read Only Memory) not shown. ROM and similar storage devices provide storage areas for various programs and data required for computation and processing. In addition to conventional non-writable memory, ROM and similar storage devices can also be composed of non-volatile memory devices such as SSDs (Solid State Drives).

[0040] Additionally, the control program for at least one of BMS114, 124, 134, control device 400, and the overall BMS101 can also be provided by an information provider as a program product downloadable via, for example, the Internet. Alternatively, the control program can be provided by storing it on a storage medium. The storage medium stores the program non-temporarily. Examples of storage media include DVD (Digital Versatile Disc)-ROM and CD (Compact Disc)-ROM.

[0041] Figure 2 yes Figure 1 The equivalent circuit diagram of the battery system is shown. Figure 2 In the example, the combined resistance is described as "the resistance of the corresponding component contained in the battery module" and "the internal resistance of the battery contained in the battery module". For example, in Figure 2 The document describes a combined resistor R1 that combines the resistance of the corresponding component contained in the battery module 110 and the internal resistance of the battery E1 contained in the battery module. Figure 2 Similarly, the combined resistors R2 and R3 are also recorded. The combined resistance value is, for example, the sum of the internal resistance value of battery E1 and the resistance values ​​of bus B1, fuse H1, and relay SW1.

[0042] The resistance values ​​of resistors R1, R2, and R3 are set as r1, r2, and r3, respectively. These resistance values ​​are detected by BMS114, 124, and 134, respectively. Additionally, voltage values ​​V1, V2, and V3 are detected by voltage sensors 111, 121, and 131, respectively. Voltage value Vc is detected by the overall voltage sensor 150. Current values ​​I1, I2, and I3 are detected by current sensors 113, 123, and 133, respectively. The current value Ic is the value of the charging current provided by the charging device 200.

[0043] [Charging Processing]

[0044] Next, the charging process will be explained. Figure 3 This is a functional block diagram of the control device 400 according to this embodiment. The control device 400 includes an acquisition unit 402, a processing unit 404, a control unit 406, and a storage unit 408.

[0045] When the control device 400 receives a charging instruction (charging instruction signal), it starts the charging process. The charging instruction signal is a signal indicating the start of charging using the charging device 200. The charging instruction is sent to the control device 400, for example, from a device different from the control device 400 (not shown). In addition, when the control device 400 receives a discharging instruction (discharging instruction signal), it starts the discharging process. The discharging instruction signal is a signal indicating the start of discharging to the load 300. The discharging instruction is sent to the control device 400, for example, from a device different from the control device 400 (not shown).

[0046] The acquisition unit 402 acquires a plurality of parameters from the battery system 100 (or the overall BMS 101). The plurality of parameters are, for example, voltage values V1, V2, V3, Vc, current values I1, I2, I3, and resistance values r1, r2, r3, etc. The acquisition unit 402 outputs the plurality of parameters to the processing unit 404.

[0047] The processing unit 404 compares the voltage values V1, V2, V3 and determines the order of the voltage values. Then, the processing unit 404 determines the battery with the lowest voltage value (hereinafter also referred to as the "first battery"), the battery with the second lowest voltage value (hereinafter also referred to as the "second battery"), and the battery with the third lowest voltage value (i.e., the battery with the highest voltage value, also referred to as the "third battery"). In addition, the battery module including the first battery is called the first battery module (i.e., the battery module 110), the battery module including the second battery is called the second battery module (i.e., the battery module 120), and the battery module including the third battery is called the third battery module (i.e., the battery module 130). In the present embodiment, the first battery is set as the battery E1, the second battery is set as the battery E2, and the third battery is set as the battery E3. That is, V1 < V2 < V3. The processing unit 404 outputs the determination result to the control unit 406.

[0048] The control unit 406 starts charging the battery E1 with the lowest voltage value. Specifically, the control device 400 turns on the relay SW1 corresponding to the battery E1. And the control device 400 makes the charging device 200 start outputting the charging current.

[0049] Thereby, the voltage value V1 and the voltage value Vc gradually increase. The relationship between Vc and V1 is expressed by the following formula (1).

[0050] Vc = V1 + I1 × r1 (1)

[0051] Furthermore, if the difference between voltage values ​​Vc and V2 falls below the first threshold, charging of battery E1 continues, and charging of battery E2 begins. Specifically, control device 400 turns the relay SW2 corresponding to battery E2 to the ON state. The first threshold can be either zero or a real number greater than zero. The first threshold is stored in storage unit 408. The first threshold will be described later.

[0052] After charging of battery E2 begins, the voltage values ​​V1, V2, and Vc gradually increase. Additionally, when relay SW2 is ON, the charging current Ic is split into currents I1 and I2. However, battery E2 has a higher state of charge (SOC) than battery E1, so more charging current flows to battery E1. Therefore, the SOC of battery E1 eventually catches up with the SOC of battery E2.

[0053] Furthermore, if the difference between voltage value Vc and voltage value V3 falls below the second threshold, charging of batteries E1 and E2 continues, and charging of battery E3 begins. Specifically, the control device 400 turns the relay SW3 corresponding to battery E3 to the ON state. Then, when charging of all batteries E1 to E3 is completed, the control device 400 terminates the charging process. The termination of battery charging refers to, for example, the battery being fully charged. The control device 400 determines that charging of all batteries E1 to E3 is complete, for example, when the SOC of each battery E1 to E3 reaches the target value (batteries E1 to E3 are each fully charged). Furthermore, the first threshold and the second threshold can be the same or different. In this embodiment, the second threshold and the first threshold are the same.

[0054] In this embodiment, the control device 400 performs constant current charging until any battery is fully charged. Then, when any battery is fully charged, it switches from constant current charging to constant voltage charging.

[0055] Next, the first threshold will be explained. The first threshold is a value set such that even when a cross-current occurs while the relay is controlled to be in the ON state, there is absolutely no or almost no adverse effect on the battery system 100. The first threshold is typically calculated based on the resistance value of the battery module and the maximum current value Ix that is allowed to flow in the battery system 100. The maximum current value Ix is, for example, a value determined in advance through experiments, etc. The first threshold is calculated, for example, by the following equation (2).

[0056] First threshold = Resistance value × Maximum current value Ix (2)

[0057] For example, if the resistance values ​​r1, r2, and r3 of each battery module are 0.05Ω and the maximum current value Ix is 100A, then the first threshold becomes 5V (=100×0.05) using the above equation (2). Furthermore, the method for determining the first threshold is only one example; other values ​​are also possible. Additionally, the first threshold can be a value less than the value calculated using the right side of equation (2). Furthermore, the first threshold can be calculated when the control device 400 receives a charging command. Additionally, the first threshold can be a fixed value. Furthermore, the second threshold can be determined either using the same method as the first threshold or using a different method.

[0058] For example, in the structural example (hereinafter referred to as the "comparative example") described in Japanese Patent Application Publication No. 2011-182623, an equalization resistor is provided to prevent cross-current. However, when such a resistor is provided, the size of the battery system increases.

[0059] Therefore, the control device 400 of the battery system 100 in this embodiment acquires the voltage values ​​of multiple batteries and determines the first battery E1 with the lowest voltage value and the second battery E2 with the second lowest voltage value. Then, the control device 400 starts charging the first battery E1 by controlling the relay SW1 corresponding to the first battery E1 to the ON state. After starting charging the first battery E1, it is determined whether the difference between the voltage value Vc of the first battery module 110 including the first battery E1 and the voltage value V2 of the second battery E2 is below a first threshold. Then, if the difference is below the first threshold, charging the second battery E2 is started by controlling the relay SW2 corresponding to the second battery E2 to the ON state. Therefore, the battery system 100 of this embodiment can charge both the first battery E1 and the second battery E2 even without an equalization resistor.

[0060] Furthermore, when relay SW2 is controlled to the ON state, overcurrent sometimes occurs. However, when relay SW2 is controlled to the ON state, the differential value becomes below the first threshold. Therefore, even if overcurrent occurs in the battery system 100, there is almost no adverse effect on the battery system 100. Therefore, battery voltage equalization can be achieved without the need for an equalization resistor and without increasing the size of the battery system 100. As a result, battery charging can be appropriately performed in the battery system 100. In addition, in the comparative example, the current is used through the equalization resistor, so there is a problem that the current becomes smaller when the voltage difference is small, and the time required for equalization becomes longer. In contrast, in the battery system 100 of this embodiment, there is no such equalization resistor, so the time required for equalization can be shortened. In addition, in the comparative example, there is a problem that the current flowing through the equalization resistor becomes larger when the voltage difference between the batteries is large, and the heat generated by the equalization resistor becomes larger. In contrast, the battery system 100 of this embodiment does not have such an equalization resistor, so such a problem can be prevented.

[0061] Additionally, for example, a first threshold is calculated based on the resistance value of the first battery module and the maximum allowable current value Ix between the first battery module and the second battery module including the second battery (refer to equation (2) above). Therefore, a suitable first threshold is calculated based on the resistance value and the allowable current value.

[0062] Furthermore, the resistance value of the first battery module is, for example, a combined value of the internal resistance value of the first battery E1 and the resistance value of the corresponding component of the first battery E1 (included in the corresponding component of the first battery module). Therefore, the battery system 100 can determine a first threshold reflecting the internal resistance value of the first battery E1 and the resistance value of the corresponding component of the first battery E1.

[0063] [Flowchart of charging process]

[0064] Figure 4 This is a flowchart illustrating the charging process of the control device 400. In step S2, the control device 400 determines whether a charging command has been received. The control device 400 waits until a charging command is received ("No" in step S2). If the control device 400 receives a charging command ("Yes" in step S2), the process proceeds to step S4.

[0065] In step S4, the control device 400 obtains the voltage values ​​V1, V2, and V3 of each battery (in this embodiment, batteries E1, E2, and E3). Next, in step S6, the control device 400 calculates the number of batteries to be charged. Here, the batteries to be charged are those that are not fully charged, for example, batteries with voltage values ​​lower than an upper limit value. The upper limit value is a predetermined value. Furthermore, the batteries to be charged can also be determined by other parameters (such as SOC).

[0066] The control device 400 determines whether the number of batteries to be charged is less than or equal to a predetermined value. For example, as described in this embodiment, when the number of batteries is 3, the predetermined number is determined to be 1. If the number of batteries to be charged is greater than the predetermined number ("No" in step S6), the process proceeds to step S10.

[0067] On the other hand, if the number of batteries determined to be to be charged is less than a predetermined number ("Yes" in step S6), in step S8, the control device 400 limits the maximum charging current value. The maximum charging current value not limited by the charging device 200 is set to "Am", and the maximum charging current value limited in step S8 is set to "Am1". Am1 becomes a value less than Am. For example, the control device 400 sends a limit signal to the charging device 200. Upon receiving the limit signal, the charging device 200 changes the maximum charging current value from Am to Am1 based on the limit signal. After the processing in step S8 is completed, the process proceeds to step S10.

[0068] In step S10, the control device 400 refers to all acquired voltage values ​​and detects the lowest voltage value (the voltage value of the battery E1 mentioned above). Then, the control device 400 determines whether there is a voltage value whose difference from the lowest voltage value is below a first threshold. If there is a voltage value whose difference from the lowest voltage value is below the first threshold ("Yes" in step S10), the process proceeds to step S12.

[0069] If a voltage value exists that is below the first threshold value ("Yes" in step S10), the process proceeds to step S12. In step S12, the control device 400 simultaneously begins charging the battery with the lowest voltage value and the battery with a voltage value below the first threshold value that is below the lowest voltage value. Here, "simultaneously" also includes "approximately simultaneously." For example, in Figure 2 In the example described, upon receiving a charging command, if the difference between the first battery E1 and the second battery E2 is already below the first threshold, charging of both the first battery E1 and the second battery E2 begins simultaneously. After the processing in step S12 is completed, the process proceeds to step S22.

[0070] Furthermore, if the determination in step S10 is "No", in step S14, the control device 400 determines whether the difference between the lowest voltage value and the second lowest voltage value is below a third threshold. The third threshold is a value larger than both the first and second thresholds, and is a predetermined value. If the difference between the lowest voltage value and the second lowest voltage value is below the third threshold ("Yes" in step S14), the process proceeds to step S16. In step S16, the control device 400 stores a ramp control flag. The ramp control flag indicates that ramp charging control is being performed. Ramp charging control refers to, for example, gradually increasing the charging current of the charging device 200, causing the voltage value of the first battery module or the voltage value of the first battery to increase linearly (as a linear function) with respect to time. Through this control, charging of the first battery E1 can begin in a manner that prevents the voltage value of the first battery module (overall voltage value Vc) from the initial start of charging from exceeding the voltage value V2 of the second battery E2. In other words, through this control, charging of the first battery E1 can begin in such a way that the voltage value (overall voltage value Vc) of the first battery module does not reach the voltage value V2 of the second battery E2 from the time the charging command is received until a predetermined period has elapsed. The ramp charging control will be described later. After the processing in step S16 is completed, and if the determination in step S14 is "no", the process proceeds to step S18.

[0071] In step S18, the control device 400 begins charging the battery with the lowest voltage value (e.g., the first battery E1). Furthermore, if no ramp control flag is stored, in step S18, the control device 400 charges the battery with the lowest voltage value using normal control (described later). On the other hand, if a ramp charging control flag is stored in step S16, in step S18, the control device 400 uses ramp charging control to start charging the battery with the lowest voltage value from a low charging current.

[0072] Next, in step S20, the control device 400 determines whether the difference between the overall voltage value Vc and the next lower voltage value (e.g., the voltage value V2 of the second battery E2) falls below the first threshold. As the first battery E1 is charged, its voltage value V1 increases, and the overall voltage value Vc also increases. Then, in step S20, the control device 400 waits until the difference between the overall voltage value Vc and the voltage value V2 falls below the first threshold (in step S20, "No").

[0073] If the determination in step S20 is "yes", in step S21, the control device 400 begins charging at the next lower voltage value (e.g., the voltage value V2 of the second battery E2). Next, in step S22, the control device 400 determines whether charging of all batteries is complete. If charging of all batteries is complete, the charging process ends. On the other hand, if the determination in step S22 is "no", the process returns to step S20. Thereafter, the processes of step S20 and step S21 are repeated until charging of all batteries is complete (until the determination in step S22 is "yes").

[0074] As described above, by repeatedly performing steps S20, S21, and S22, the control device 400 can appropriately perform charging of all batteries (battery E1 to battery E3) even without an equalization resistor.

[0075] Furthermore, upon receiving a charging command ("Yes" in step S2), and if the differential value is already below the first threshold ("Yes" in step S10), the control device 400 begins charging the first battery E1 and the second battery E2 (step S12). With this structure, the control device 400 can shorten the charging time.

[0076] Furthermore, when the number of batteries among the multiple batteries (N batteries) that are to be charged by the charging device 200 is less than a predetermined number ("Yes" in step S6), the control device 400 limits the charging current using the control device 400 (step S8). Assuming that the number of batteries to be charged is small, charging a battery with a large charging current may sometimes exceed the battery's allowable current. Therefore, in this embodiment, when the number of batteries to be charged is small, the control device 400 limits the charging current. Thus, the allowable current of the batteries to be charged is not exceeded.

[0077] [Experimental Results of Charging Processing]

[0078] Next, the experimental results of the charging process of the battery system 100 of this embodiment will be explained. Figure 5 This is a graph showing the experimental results for the comparative examples. Additionally, Figure 6 This is a diagram showing the experimental results of the battery system 100 of this embodiment. Figure 5 as well as Figure 6 The circuit structures are all Figure 2 For example, in the comparative example, when the battery system's control device receives a charging command, charging of batteries E1 to E3 begins simultaneously.

[0079] Figure 5 (A)~ Figure 5 (C) and Figure 6 (A)~ Figure 6 (C) The horizontal axis represents the time axis. Figure 5 as well as Figure 6 In the graph, the curves related to battery E1 are represented by dashed lines, those related to battery E2 by single-dotted lines, those related to battery E3 by double-dotted lines, and the curves related to the overall voltage value Vc by solid lines. Additionally, in... Figure 5 (A) and Figure 6 (A) shows the voltage value. Figure 5 In (A), voltage values ​​V2, V3 and the overall voltage value Vc are shown, but voltage value V1 is not shown. Figure 5 (B) and Figure 6 (B) shows the SOC of each battery. Figure 5 (C) and Figure 6 (C) is a graph showing the current values ​​flowing through the wiring within the battery system.

[0080] In the comparative example, the state of charge (SOC) of batteries E1, E2, and E3 before charging was 20%, 35%, and 50%, respectively. In this embodiment, the SOC of batteries E1, E2, and E3 before charging is 20%, 35%, and 40%, respectively. Furthermore, the resistance values ​​r1 to r3 are set to 0.5Ω, and the charging current using the charging device 200 is 50A.

[0081] First, use Figure 5 This section describes the battery system of the comparative example. In the comparative example, when charging of batteries E1 to E3 begins simultaneously, as follows... Figure 5 As shown in (A), voltage values ​​V1 and V2 gradually increase by the same value. In addition, the overall voltage value Vc gradually increases by a predetermined value that is greater than the same value.

[0082] In addition, Figure 5 In (B), the SOC of batteries E1 through E3 becomes the same value and gradually increases. Additionally, as... Figure 5 As shown in (C), when a charging command is received, the current value I1 becomes a very large current value of approximately 190A. The reason for such a large current value is that a cross-current occurs from batteries E2 and E3 to battery E1.

[0083] Next, use Figure 6 This describes the battery system 100 of this embodiment. Furthermore, in... Figure 6 In the example, the first threshold is set to zero. Figure 6 In (A), at time t1 when the control device 400 receives the charging command, the control device 400 begins charging the battery E1 (see reference). Figure 4Step S18). With this start, the voltage value V1 and the overall voltage value Vc gradually increase. Then, at timing t2 when the overall voltage value Vc reaches the next lower voltage value V2 (in... Figure 4 In step S20, when the timing is determined to be "yes", the control device 400 begins charging of battery E2 (refer to...). Figure 4 Step S21).

[0084] Then, by starting the charging of the second battery E2, not only the voltage value V1, but also the voltage value V2 and the overall voltage value Vc gradually increase. Then, at time t3, when the overall voltage value Vc reaches the next lower voltage value V3... Figure 4 In step S20, if the timing is "yes", the control device 400 begins charging the battery E3 (refer to...). Figure 4 (Step S21). After that, the charging process ends when the SOC of all batteries E1 to E3 reaches the charging end value.

[0085] Next, the explanation is in Figure 4 The slope control signs described in step S16. Control device 400, as... Figure 6 As shown by time t1, the first battery E1 is charged in a manner that executes control (hereinafter referred to as "normal control") to increase the overall voltage value Vc by a predetermined amount at time t1. Figure 4 In this example, the predetermined value is approximately 3V. The control device 400 can shorten the charging time by performing normal control at time t1.

[0086] However, when the difference between the overall voltage value Vc and the voltage value V2 is greater than the first threshold but less than the third threshold (in the case of "No" in step S10 and "Yes" in step S14), when the control device 400 performs normal control, at time t1, the overall voltage value Vc exceeds the voltage value V2, and sometimes it is impossible to "suppress the occurrence of cross-current and connect the battery".

[0087] Therefore, in this embodiment, when the difference between the overall voltage value Vc and the voltage value V2 is greater than the first threshold but less than the third threshold, a ramp control flag is set (step S16). Then, in step S18, the control device 400 performs ramp charging control that gradually increases the charging current. As a result, the voltage value V1 of the first battery E1 gradually increases, thus suppressing the occurrence of cross-current and connecting the battery.

[0088] Figure 7 This is a diagram illustrating the implementation of ramp-charge control. (As shown...) Figure 7As shown, by implementing ramp charging control, the voltage value (or overall voltage value Vc) of the first battery module does not reach the voltage value V2 of the second battery E2 until a predetermined period has elapsed. Furthermore, the predetermined period is a pre-determined period.

[0089] [Discharge Processing]

[0090] Next, the discharge process of the battery system 100 according to this embodiment will be described. As described above, when the control device 400 receives a charging command, the batteries with the lowest voltage values ​​are charged sequentially. In the discharge process, the batteries with the highest voltage values ​​are discharged sequentially to the load 300. As a result, the occurrence of cross-current can be reduced.

[0091] Figure 8 This is a flowchart illustrating the discharge process of the control device 400. In step S102, the control device 400 determines whether a discharge command has been received. The control device 400 waits until a discharge command is received ("No" in step S102). If the control device 400 receives a discharge command ("Yes" in step S102), the process proceeds to step S104.

[0092] In step S104, the control device 400 obtains the voltage values ​​V1, V2, and V3 of each of the batteries (in this embodiment, batteries E1, E2, and E3). Next, in step S106, the control device 400 calculates the number of batteries that can be discharged. Here, the batteries to be discharged are, for example, batteries whose voltage values ​​are greater than the lower limit value for discharge to the load 300. Furthermore, the batteries to be discharged can also be determined by other parameters (such as SOC).

[0093] The control device 400 determines whether the number of batteries to be discharged is less than or equal to a predetermined value. For example, as described in this embodiment, when the number of batteries is 3, the predetermined number is determined to be 1. If the number of batteries to be discharged is greater than the predetermined number ("No" in step S106), the process proceeds to step S110.

[0094] On the other hand, if the number of batteries determined to be subject to discharge is less than a predetermined number ("Yes" in step S106), in step S108, the control device 400 limits the maximum discharge current value. The maximum discharge current value that is not limited by the load 300 is set to "Bm", and the maximum discharge current value limited in step S108 is set to "Bm1". Bm1 becomes a value less than Bm. For example, the control device 400 sends a limit signal to the load 300. Upon receiving the limit signal, the load 300 reduces the current value required by the load 300 according to the limit signal. For example, the load 300 changes the maximum discharge current value from Bm to Bm1. After the processing in step S108 is completed, the process proceeds to step S110.

[0095] In step S110, the control device 400 refers to all acquired voltage values ​​and detects the highest voltage value (the voltage value of battery E3 mentioned above). Then, the control device 400 determines whether there is a voltage value whose difference from the highest voltage value is below a first threshold. If there is a voltage value whose difference from the highest voltage value is below the first threshold ("Yes" in step S110), the process proceeds to step S112.

[0096] In step S112, the control device 400 simultaneously begins discharging the battery with the highest voltage value and the battery with a voltage value below a first threshold that differs from the highest voltage value. Here, "simultaneously" also includes "approximately simultaneously." For example, in... Figure 2 In the example described, upon receiving a discharge command, if the difference between the third battery E3 and the second battery E2 is already below the first threshold, the discharge of both the third battery E3 and the second battery E2 begins simultaneously. After the processing in step S112 is completed, the process proceeds to step S122.

[0097] Furthermore, if the determination in step S110 is "No", in step S118, the control device 400 begins discharging the battery with the highest voltage value (e.g., the third battery E3). Next, in step S120, the control device 400 determines whether the difference between the overall voltage value Vc and the next higher voltage value (e.g., the voltage value V2 of the second battery E2) falls below a first threshold. Through the discharge of the third battery E3, the voltage value V3 of the third battery E3 decreases, and the overall voltage value Vc also decreases. Then, in step S120, the control device 400 waits until the difference between the overall voltage value Vc and the voltage value V2 falls below the first threshold ("No" in step S120).

[0098] If the control device 400 determines "yes" in step S120, in step S121, it begins discharging the battery with the next high voltage value determined in step S120. Next, in step S122, the control device 400 determines whether the discharge of all batteries has ended. If the discharge of all batteries has ended ("yes" in step S122), the discharge process ends. On the other hand, if the determination in step S122 is "no", the process returns to step S120. Thereafter, the processes of step S120 and step S121 are repeated until the discharge of all batteries has ended (until the determination in step S122 is "yes"). In this way, the battery system 100 repeatedly performs the processes of steps S120, S121, and S122.

[0099] As described above, even if a cross-current occurs during the discharge process, the battery system 100 can be kept free of any adverse effects or have almost no adverse effects on the battery system 100. Therefore, battery voltage equalization can be achieved without the need for an equalization resistor and without increasing the size of the battery system 100. As a result, battery discharge can be appropriately performed in the battery system 100. Furthermore, in the comparative example, the current flowing through the equalization resistor is used, so there is a problem that the current decreases when the voltage difference is small, and the equalization time becomes longer. In contrast, the battery system 100 of this embodiment does not have such an equalization resistor, so the equalization time can be shortened. Additionally, in the comparative example, there is a problem that the current flowing through the equalization resistor increases when the voltage difference between batteries is large, and the heat generated by the equalization resistor increases. In contrast, the battery system 100 of this embodiment does not have such an equalization resistor, so this problem can be prevented.

[0100] Furthermore, upon receiving a discharge instruction ("Yes" in step S102), and if the differential value is already below the first threshold ("Yes" in step S110), the control device 400 begins discharging the first battery E1 and the second battery E2 (step S112). With this structure, the control device 400 is able to provide a large sum of power to the load 300.

[0101] Furthermore, if the number of batteries in the plurality of batteries (N batteries) that are to be discharged to the load 300 is less than a predetermined number ("Yes" in step S106), the control device 400 limits the discharge current to the load 300 (step S108). Assuming that the number of batteries to be discharged is small, the power supplied to the load 300 becomes insufficient, and sometimes the moving body 10 cannot be properly controlled. Therefore, the control device 400 sends a limiting signal to the load 300. Thus, the load 300 can identify in advance that the power supplied to it is insufficient. Therefore, the load 300 can control the moving body 10 with the insufficient power.

[0102] [Other Implementation Methods]

[0103] (1) In the charging process of the above embodiment, as described in step S20, the difference value is described as the difference between the "overall voltage value Vc" and the "next low voltage value". However, in step S20, the difference value may also be the difference between the lowest voltage value and the next low voltage value (the second lowest voltage value). Alternatively, in step S20, the difference value may be the difference between the "next low voltage value" and the next low voltage value (the third lowest voltage value) of the "next low voltage value". For example, in step S20, the control device 400 may also determine whether the difference between the voltage value V1 of the first battery E1 and the voltage value V2 of the second battery E2 is below the first threshold. In addition, in step S20, the control device 400 may also determine whether the difference between the voltage value V2 of the second battery E2 and the voltage value V3 of the third battery E3 is below the first threshold. Using this structure achieves the same effect as the above-described implementation.

[0104] (2) In the discharge process of the above embodiment, as explained in step S120, the difference value is described as the difference between the "overall voltage value Vc" and the "next high voltage value". However, in step S120, the difference value can also be the difference between the highest voltage value and the next high voltage value (the second high voltage value). Alternatively, in step S120, the difference value can be the difference between the "next high voltage value" and the next high voltage value (the third high voltage value) of that "next high voltage value". For example, in step S120, the control device 400 can also determine whether the difference between the voltage value V3 of the third battery E3 and the voltage value V2 of the second battery E2 is below a first threshold. Furthermore, in step S120, the control device 400 can also determine whether the difference between the voltage value V2 of the second battery E2 and the voltage value V1 of the first battery E1 is below a first threshold. Using such a structure achieves the same effect as the above embodiment.

[0105] In addition to battery packs or battery modules consisting of multiple batteries connected in series, the battery system of this embodiment also includes a single battery or a structure in which batteries are connected in parallel.

[0106] Embodiments of the present invention have been described, but should be considered illustrative in all respects and not restrictive. The scope of the invention is defined by the claims and is intended to include all modifications within the meaning and scope of the claims.

Claims

1. A battery system comprising: Charging device; Multiple battery modules are connected in parallel with the charging device; and Control device, Each of the plurality of battery modules has a battery. The control device: Upon receiving a charging command, the voltage values ​​of each battery in the plurality of battery modules are obtained, and the first battery with the lowest voltage value and the second battery with the second lowest voltage value are determined. Start charging the first battery. After charging of the first battery begins, if the difference between the voltage value of the first battery module (including the first battery) and the voltage value of the second battery, or the difference between the voltage value of the first battery and the voltage value of the second battery, falls below a first threshold, then charging of the second battery begins. Upon receiving the charging command, if the difference value is greater than the first threshold but less than the third threshold, the control device begins charging the first battery in such a way that the voltage value of the first battery module or the voltage value of the first battery increases linearly from the time the charging command is received until a predetermined period has elapsed.

2. The battery system according to claim 1, wherein, The plurality of battery modules includes three battery modules. The control device: Upon receiving the charging command, the third battery with the third lowest voltage value is determined together with the first battery and the second battery. After the charging of the second battery begins, if the difference between the voltage value of the second battery module including the second battery and the voltage value of the third battery, or the difference between the voltage value of the second battery and the voltage value of the third battery, becomes a second threshold, the charging of the third battery begins.

3. The battery system according to claim 1 or 2, wherein, Upon receiving the charging command, if the differential value is below the first threshold, the control device begins charging the first battery and the second battery.

4. The battery system according to claim 1 or 2, wherein, When the number of batteries to be charged by the charging device is less than a predetermined number, the control device limits the charging current using the control device.

5. The battery system according to claim 1, wherein, It also has load capacity. The plurality of battery modules can be connected in parallel with the load. The control device: Upon receiving a discharge command, the voltage values ​​of each battery in the plurality of battery modules are obtained, and the first discharge battery with the highest voltage value and the second discharge battery with the second highest voltage value are determined. The discharge of the first discharge battery begins. After the discharge of the first discharge battery begins, if the difference between the voltage value of the first discharge battery module including the first discharge battery and the voltage value of the second discharge battery, or the difference between the voltage value of the first discharge battery and the voltage value of the second discharge battery, becomes below the first discharge threshold, the discharge of the second discharge battery begins.

6. The battery system according to claim 5, wherein, The plurality of battery modules includes three battery modules. The control device: Upon receiving the discharge command, a third discharge battery with the third highest voltage value is determined together with the first and second discharge batteries. After the discharge of the second discharge battery begins, if the difference between the voltage value of the second discharge battery module including the second discharge battery and the voltage value of the third discharge battery, or the difference between the voltage value of the second discharge battery and the voltage value of the third discharge battery, becomes below the second discharge threshold, the discharge of the third discharge battery begins.

7. The battery system according to claim 5 or 6, wherein, Upon receiving the discharge command, if the differential value is below the first discharge threshold, the control device begins discharging the first discharge battery and the second discharge battery.

8. The battery system according to claim 5 or 6, wherein, When the number of batteries discharging the load is less than a predetermined number, the control device limits the discharge current using the control device.

9. The battery system according to claim 1 or 2, wherein, The first threshold is calculated based on the resistance value of the first battery module and the allowable current value to flow between the first battery module and the second battery module including the second battery.

10. The battery system according to claim 5 or 6, wherein, The first discharge threshold is calculated based on the resistance value of the first discharge battery module and the allowable current value to flow between the first discharge battery module and the second discharge battery module including the second discharge battery.

11. The battery system according to claim 9, wherein, The resistance value is a composite value of the internal resistance value of the first battery and the resistance value of the component corresponding to the first battery.

12. The battery system according to claim 10, wherein, The resistance value is a composite value of the internal resistance value of the first discharge battery and the resistance value of the component corresponding to the first discharge battery.

13. A control method for a battery system, the battery system comprising a charging device and a plurality of battery modules capable of being connected in parallel with the charging device, wherein, Each of the plurality of battery modules has a battery. The control method comprises: Upon receiving a charging command, the voltage values ​​of the batteries in each of the plurality of battery modules are obtained, and the first battery with the lowest voltage value and the second battery with the second lowest voltage value are determined. Start charging the first battery; as well as After charging of the first battery begins, if the difference between the voltage value of the first battery module (including the first battery) and the voltage value of the second battery, or the difference between the voltage value of the first battery and the voltage value of the second battery, falls below a first threshold, then charging of the second battery begins. Upon receiving the charging command, if the difference value is greater than the first threshold but less than the third threshold, the control method starts charging the first battery in such a way that the voltage value of the first battery module or the voltage value of the first battery increases linearly from the time the charging command is received until a predetermined period has elapsed.

14. The control method according to claim 13, wherein, The battery system also includes a load, and the plurality of battery modules can be connected in parallel with the load. The control method comprises: Upon receiving a discharge command, the voltage values ​​of the batteries in each of the plurality of battery modules are obtained, and the first discharge battery with the highest voltage value and the second discharge battery with the second highest voltage value are determined. The discharge of the first discharge battery begins; as well as After the discharge of the first discharge battery begins, if the difference between the voltage value of the first discharge battery module including the first discharge battery and the voltage value of the second discharge battery, or the difference between the voltage value of the first discharge battery and the voltage value of the second discharge battery, becomes below the first discharge threshold, the discharge of the second discharge battery begins.

Images