Battery capacity increasing system and electric device

Abstract

The utility model discloses a battery capacity-increasing system and an electric device, and the battery capacity-increasing system comprises a first battery string which is electrically connected to a DC bus; a second battery string, the first battery string being connected in parallel with the second battery string, the second battery string being electrically connected to the DC bus via a DC-DC converter; wherein the DCDC converter is used for adjusting the output current of the second battery string into the target output current, so as to balance the residual electric quantity of the first battery string and the residual electric quantity of the second battery string. According to the battery capacity increasing system and the electric device provided by the utility model, the first battery string is directly and electrically connected to the DC bus, the second battery string is electrically connected to the DC bus through the DC-DC converter, and the DC-DC converter is used for adjusting the output current of the second battery string into the target output current. Therefore, the residual electric quantity of the first battery string and the residual electric quantity of the second battery string are balanced, and the battery capacity increasing effect is achieved.

Description

Technical Field

[0001] The utility model relates to the technical field of batteries, in particular to a battery capacity increasing system and an electric device. Background Art

[0002] A battery pack usually includes multiple batteries. Due to differences in individual battery capacity, battery internal resistance and other factors, the SOC (State of Charge, also known as remaining power) of different batteries varies. In addition, the operating environment temperature of each battery cannot be kept completely consistent, resulting in an inevitable SOC mismatch problem when multiple batteries are connected in parallel. Utility Model Content

[0003] A series of simplified concepts are introduced in the utility model content section, which will be further described in detail in the detailed implementation section. The utility model content section of the utility model does not mean to attempt to define the key features and essential technical features of the technical solution claimed for protection, nor does it mean to attempt to determine the scope of protection of the technical solution claimed for protection.

[0004] The utility model provides a battery capacity expansion system, comprising:

[0005] a first battery string, the first battery string being electrically connected to a DC bus;

[0006] a second battery string, the first battery string and the second battery string being connected in parallel, the second battery string being electrically connected to the DC bus via a DC-DC converter;

[0007] The DCDC converter is used to adjust the output current of the second battery string to a target output current so as to balance the remaining power of the first battery string with the remaining power of the second battery string.

[0008] Exemplarily, the battery capacity expansion system further includes:

[0009] A controller is communicatively connected with the first battery string, the second battery string and the DC bus, and is used to obtain the target output current.

[0010] Exemplarily, the DC-DC converter is a four-switch buck-boost converter, and the DC-DC converter comprises at least a first bridge arm with a fixed duty cycle and a second bridge arm with an adjustable duty cycle.

[0011] Exemplarily, the controller is further configured to start the DC-DC converter of the second battery string when a voltage difference between the voltage of the second battery string and the voltage of the DC bus is less than a preset threshold.

[0012] Exemplarily, the controller is used to obtain the target output current of the second battery string, including:

[0013] obtaining a current of the first battery string and a current of the second battery string to determine a bus current;

[0014] Obtaining a ratio of a remaining power of a target battery string to a sum of a remaining power of the first battery string and a remaining power of the second battery string, the target battery string being the second battery string;

[0015] A target output current of the target battery string is obtained based on the bus current and the ratio.

[0016] Exemplarily, when the DC-DC converter of the target battery string is started, the DC-DC converter operates in a constant current mode, and the DC-DC converter is used to transmit a target output power to the target battery string, and the target output power can make the output current of the target battery string reach a target output current, and the target output power is obtained based on the target output current.

[0017] Exemplarily, the controller is further configured to:

[0018] Based on the difference between the input current and the target output current, obtaining the inductor target current;

[0019] Obtaining a target output power based on a difference between a current of the inductor and a target current of the inductor, an input voltage, an output voltage, and a duty cycle of the first bridge arm;

[0020] An output pulse width modulation wave is obtained based on the target output power to drive the first bridge arm and the second bridge arm to open and close.

[0021] Exemplarily, the first battery string and the second battery string have different remaining capacities, the first battery string includes an old battery string, and the second battery string includes a new battery string.

[0022] Exemplarily, the battery capacity expansion system further includes an energy storage inverter, which is electrically connected to the DC bus, and is used to invert the DC current output by the DC bus into AC current.

[0023] The utility model also includes an electrical device, which includes any of the battery capacity expansion systems described above.

[0024] According to the battery capacity expansion system and power-consuming device provided by the utility model, the first battery string is directly electrically connected to the DC bus, and the second battery string is electrically connected to the DC bus via a DC-DC converter. The DCDC converter is used to adjust the output current of the second battery string to a target output current to balance the remaining power of the first battery string with the remaining power of the second battery string, thereby achieving a battery capacity expansion effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The following drawings of the present invention are used as a part of the present invention for understanding the present invention. The drawings show the embodiments of the present invention and their descriptions, and are used to explain the principle of the present invention.

[0026] In the attached figure:

[0027] Figure 1 It is a structural schematic diagram of a battery capacity expansion system according to an embodiment of the utility model;

[0028] Figure 2 It is a structural schematic diagram of a DC-DC converter according to an embodiment of the utility model;

[0029] Figure 3 is a flowchart of a controller according to an embodiment of the utility model;

[0030] Figure 4 is a control flow chart of a DC-DC converter according to an embodiment of the utility model;

[0031] Figure 5 The figure is a working flow chart of a DC-DC converter according to an embodiment of the utility model.

[0032] Reference numerals

[0033] 11. DC bus 12. Controller

[0034] 13. First battery string 14. Second battery string

[0035] 15. DC-DC converter 21. Energy storage converter

[0036] 31. Power grid DETAILED DESCRIPTION

[0037] In the following description, a large number of specific details are given to provide a more thorough understanding of the utility model. However, it is obvious to those skilled in the art that the utility model can be implemented without one or more of these details. In other examples, in order to avoid confusion with the utility model, some technical features known in the art are not described.

[0038] In order to thoroughly understand the present invention, a detailed description will be provided in the following description to illustrate the battery capacity expansion system and the power device of the present invention. Obviously, the implementation of the present invention is not limited to the specific details familiar to technicians in the field of battery technology. The preferred embodiments of the present invention are described in detail below, but in addition to these detailed descriptions, the present invention can also have other embodiments.

[0039] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the utility model. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should also be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of the features, wholes, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or combinations thereof.

[0040] Now, exemplary embodiments according to the present utility model will be described in more detail with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in a variety of different forms and should not be interpreted as being limited to the embodiments described herein. It should be understood that these embodiments are provided to make the disclosure of the present utility model thorough and complete, and to fully convey the concepts of these exemplary embodiments to those of ordinary skill in the art. In the accompanying drawings, for the sake of clarity, the thickness of layers and regions is exaggerated, and the same reference numerals are used to represent the same elements, and thus their description will be omitted.

[0041] The main methods for solving the SOC mismatch problem at present include: (1) Static balance of battery resistance energy consumption: During charging, if it is detected that the voltage of a battery is too high, the charging time is extended by discharging the high-voltage battery until the low-voltage battery is fully charged. The disadvantage of this method is that it can only perform charging correction, which not only wastes energy but also shortens the battery life. In addition, the correction current needs to be limited during correction to avoid excessive discharge and heat release of the battery in a short period of time. (2) Dynamic balance of battery energy transfer: Inductors, capacitors, etc. are used as energy storage elements. The energy of the high-voltage battery is first transferred to the energy storage element through switching, and then the energy of the energy storage element is converted to the low-voltage battery through switching. The disadvantage of this method is that the energy balancing effect is not obvious when the voltage difference is low, but the number of energy storage elements and switching devices is large, the volume is large, and it is easy to fail. In summary, the above methods will consume the energy of the high-voltage battery, increase the loss of the high-voltage battery, and may cause battery charging and discharging consumption.

[0042] In view of the SOC mismatch problem, the utility model provides a battery capacity expansion system, such as Figure 1 As shown, including:

[0043] A first battery string 13, wherein the first battery string 13 is electrically connected to the DC bus 11;

[0044] A second battery string 14, wherein the first battery string 13 and the second battery string 14 are connected in parallel, and the second battery string 14 is electrically connected to the DC bus 11 via a DC-DC converter 15;

[0045] The DCDC converter 15 is used to adjust the output current of the second battery string 14 to a target output current, so as to balance the remaining power of the first battery string 13 with the remaining power of the second battery string 14 .

[0046] In one embodiment, Figure 1 As shown, the first battery string 13 and the second battery string 14 have different remaining charges (SOC), the first battery string 13 includes an old battery string, and the second battery string 14 includes a new battery string. The capacity of the old battery string is different from that of the new battery string, and the capacity of the old battery string is usually smaller than that of the new battery string. The number of the first battery strings 13 includes one or more, and each first battery string 13 may include one or more first-type batteries. When there are multiple first battery strings 13, they are all arranged in parallel, and each first battery string 13 is directly electrically connected to the DC bus 11. The number of the second battery strings 14 includes one or more, and each second battery string 14 may include one or more second-type batteries. When there are multiple second battery strings 14, they are all arranged in parallel, and each second battery string 14 is electrically connected to its own DC-DC converter 15, and each DC-DC converter 15 is further electrically connected to the DC bus 11.

[0047] By connecting the DC-DC converter only to the new battery string instead of connecting each battery string to the DC-DC converter, the cost of the battery capacity expansion system provided by the utility model is greatly reduced.

[0048] Exemplarily, the DC-DC converter includes at least a first bridge arm with a fixed duty cycle and a second bridge arm with an adjustable duty cycle.

[0049] In one embodiment, Figure 2As shown, the DC-DC converter is a four-switch buck-boost (Four Switch Buck-Boost, FSBB) converter, and the DC-DC converter includes: a first bridge arm, the first bridge arm includes a first switch tube Q1 and a second switch tube Q2 connected in series, and a first connection point is set between the first switch tube Q1 and the second switch tube Q2; a second bridge arm, the second bridge arm includes a third switch tube Q3 and a fourth switch tube Q4 connected in series, and a second connection point is set between the third switch tube Q3 and the fourth switch tube Q4; an inductor L1, the inductor connects the first connection point and the second connection point. In addition, the DC-DC converter also includes a first capacitor C1 and a second capacitor C2 connected in parallel with the first bridge arm and the second bridge arm, wherein the first capacitor and the second capacitor are respectively arranged on the outside of the first bridge arm and the second bridge arm.

[0050] In one embodiment, the conventional boost converter can only work normally when the input voltage is lower than the output voltage by a certain difference △U; the conventional buck converter can only work normally when the input voltage is higher than the output voltage by a certain difference -△U. When the voltage difference between the input voltage and the output voltage is between -△U and +△U, the DC-DC converter cannot work normally because the voltage difference cannot meet the actual working conditions, that is, the voltage rise and fall cannot be controlled by the DC-DC converter. The DC-DC converter based on the FSBB topology provided by the utility model includes a buck bridge arm and a boost bridge arm, one of which has a fixed duty cycle, and the other bridge arm performs output regulation. By fixing the duty cycle of one side of the bridge arm, the DC-DC converter can work between the voltage difference of -△U and +△U, solving the voltage difference problem caused by using a boost (Boost) or buck (Buck) circuit alone, so that the DC-DC converter can work under different voltage differences and can be applied in more working conditions.

[0051] The battery capacity expansion system of the present invention further includes a controller 12 , which is communicatively connected with the first battery string 13 , the second battery string 14 and the DC bus 11 , and is used to obtain a target output current of the second battery string 14 .

[0052] In one embodiment, the communication connection between the controller 12 and the first battery string 13, the second battery string 14 and the DC bus 11 can be wireless communication or wired communication. The controller 12 is used to: obtain the current of the first battery string and the current of the second battery string to determine the bus current; obtain the ratio of the remaining power of the target battery string to the sum of the remaining power of the first battery string and the remaining power of the second battery string, the target battery string being one of the second battery strings; and obtain the target output current of the target battery string based on the bus current and the ratio.

[0053] In one embodiment, the controller 12 is connected to the first battery string 13, the second battery string 14 and the DC bus 11 through a CAN bus to obtain information such as the voltage U, current I and remaining power SOC of the first battery string 13, the second battery string 14 and the DC bus 11.

[0054] In one embodiment, the controller 12 first obtains the current of each first battery string and the current of each second battery string respectively, and adds them together to obtain the total current I of the DC bus. total :

[0055] I total =∑(I 1 +I 2 +…I i ) Equation 1

[0056] Then, according to the obtained SOC of each first battery string and the SOC of each second battery string, the ratio Per of the SOC of the target battery string in the total SOC of each battery string is calculated. i (i.e., duty cycle):

[0057]

[0058] Next, according to the total current I total , current direction, SOC duty cycle of the target battery string, and calculate the target output current I i-target :

[0059] I i-target =Per i *I total (Discharge) Equation 3

[0060] I i-target =(1-Per i )*I total (Charging) Equation 4

[0061] The target battery string is one of the second battery strings. At this point, the target output current of the target battery string is obtained, and the target output current is sent to the DC-DC converter 15 connected to the target battery string.

[0062] Exemplarily, the controller 12 is also used to: obtain the voltage of the second battery string and the voltage of the DC bus; when the voltage difference between the voltage of the second battery string and the voltage of the DC bus is less than a preset threshold, start the DC-DC converter of the target battery string.

[0063] In one embodiment, Figure 3 and Figure 4 As shown, the controller 12 first obtains the voltage of the new battery string (i.e., the target battery string), and then determines whether there is an old battery string in the battery capacity expansion system. When there is no old battery string, the DC-DC converter is not started (i.e., skipped). When there is an old battery string, the average voltage of the old battery string is used as the bus voltage, and the voltage of the new battery string is compared with the bus voltage. When the difference between the voltage of the new battery string and the bus voltage is greater than or equal to △U, the DC-DC converter is not started (i.e., skipped) and a fault alarm is issued. When the difference between the voltage of the new battery string and the bus voltage is less than △U, it is further detected whether the output side voltage of the DC-DC converter has reached the target value. When the target value is reached, the DC-DC converter of the new battery string is successfully started.

[0064] Exemplarily, when the DC-DC converter of the target battery string is started, the DC-DC converter operates in a constant current mode, and the DC-DC converter is used to: receive the target output current, and obtain a target output power based on the target output current; and send the target output power to the target battery string so that the input current reaches the target output current.

[0065] Exemplarily, the DC-DC converter is also used to: obtain an inductor target current based on a difference between an input current and the target output current; obtain a target output power based on a difference between the inductor current and the inductor target current, an input voltage, an output voltage, and a duty cycle of the first bridge arm; and obtain an output pulse width modulation wave based on the target output power to drive the first bridge arm and the second bridge arm to open and close.

[0066] In one embodiment, Figure 4 and Figure 5As shown, when the DC-DC converter of the target battery string is started, the target output current of the receiving controller 12 is received, and the DC-DC converter operates in constant current mode, and the target output power obtained based on the target output current is sent to the target battery string to obtain the target output current. Specifically, the DC-DC converter is controlled by dual-loop PI, and the current outer loop calculates the difference between the input current Iin (that is, the actual output current of the target battery string) and the target output current Iobj, and obtains the inductor target current ILobj through PI control. The current inner loop calculates the difference between the inductor target current ILobj and the inductor current IL (that is, the actual current of the inductor), and obtains the target output power PIout through PI control. Based on the input voltage Uin, the output voltage Uout and the fixed duty cycle buck_duty of the first bridge arm, the target value is obtained through feedforward control, and is added to PIout to obtain the target output power. The target output power is controlled through coupling and limiting to obtain an output pulse width modulation (PWM) wave, which drives the two bridge arms of the DC-DC converter to open or close, so that the input current Iin is equal to the target output current Iobj.

[0067] The SOC between different battery strings is balanced by the DC-DC converter, that is, the SOC of the new and old batteries is balanced by controlling the battery output current. In this way, the SOC values ​​of different batteries can be reduced to 0 at the same time when they are discharged, reducing the problem that a battery string with the lowest SOC in the battery pack is discharged first, reaching the discharge cut-off voltage in advance, and then the entire battery pack exits operation and cannot be discharged at full power according to the designed time. This ensures that the battery pack can discharge at full power for a longer period of time, greatly improving the capacity of the energy storage system and solving the problem of small effective capacity and poor performance of the battery pack caused by the voltage imbalance of each battery string in the battery pack. In addition, the control of the battery output current by the DC-DC converter does not require the help of an external power supply, saving energy, and fully realizing the SOC balance between different battery strings, effectively improving the performance of the battery pack, making the battery capacity of the battery pack larger and the performance more superior.

[0068] The battery capacity expansion system of the present invention further includes an energy storage inverter 21 , which is electrically connected to the DC bus. The energy storage inverter 21 is used to invert the DC current output by the DC bus 11 into AC current and is electrically connected to the power grid 31 .

[0069] In one embodiment, the DC bus 11 is connected in parallel to the power grid 31 through the DC side of the energy storage converter (PCS) 21 to complete the charging and discharging of the battery string. The controller 12 communicates with the energy storage converter 21 through Ethernet to exchange the collected information of the battery string, so that the battery string can be normally connected in parallel to the power grid 31 to complete the charging and discharging.

[0070] According to the battery capacity expansion system provided by the utility model, the first battery string is directly electrically connected to the DC bus, and the second battery string is electrically connected to the DC bus via a DC-DC converter. The DCDC converter is used to adjust the output current of the second battery string to a target output current to balance the remaining power of the first battery string with the remaining power of the second battery string, thereby achieving a battery capacity expansion effect.

[0071] The utility model also provides an electrical device, comprising the battery capacity expansion system as described above.

[0072] The utility model has been described through the above embodiments, but it should be understood that the above embodiments are only for the purpose of example and description, and are not intended to limit the utility model to the scope of the described embodiments. In addition, it can be understood by those skilled in the art that the utility model is not limited to the above embodiments, and more variations and modifications can be made according to the teachings of the utility model, and these variations and modifications all fall within the scope of protection claimed by the utility model. The protection scope of the utility model is defined by the attached claims and their equivalents.

Claims

1. A battery capacity expansion system, characterized in that: include: a first battery string, the first battery string being electrically connected to a DC bus; a second battery string, the first battery string and the second battery string being connected in parallel, the second battery string being electrically connected to the DC bus via a DC-DC converter; The DC-DC converter is used to adjust the output current of the second battery string to a target output current so as to balance the remaining power of the first battery string with the remaining power of the second battery string.

2. The battery capacity expansion system according to claim 1, characterized in that: Also includes: A controller is communicatively connected with the first battery string, the second battery string and the DC bus, and is used to obtain the target output current.

3. The battery capacity expansion system according to claim 2, characterized in that: The DC-DC converter is a four-switch buck-boost converter, and the DC-DC converter comprises at least a first bridge arm with a fixed duty cycle and a second bridge arm with an adjustable duty cycle.

4. The battery capacity expansion system according to claim 2, characterized in that: The controller is further configured to start the DC-DC converter of the second battery string when a voltage difference between the voltage of the second battery string and the voltage of the DC bus is less than a preset threshold.

5. The battery capacity expansion system according to claim 2, characterized in that: The controller is used to obtain the target output current, comprising: obtaining a current of the first battery string and a current of the second battery string to determine a bus current; Obtaining a ratio of a remaining power of a target battery string to a sum of a remaining power of the first battery string and a remaining power of the second battery string, the target battery string being the second battery string; A target output current of the target battery string is obtained based on the bus current and the ratio.

6. The battery capacity expansion system according to claim 5, characterized in that: When the DC-DC converter of the target battery string is started, the DC-DC converter operates in a constant current mode. The DC-DC converter is used to transmit a target output power to the target battery string. The target output power can make the output current of the target battery string reach a target output current. The target output power is obtained based on the target output current.

7. The battery capacity expansion system according to claim 3, characterized in that: The controller is also used for: Based on the difference between the input current and the target output current, obtaining the inductor target current; Obtaining a target output power based on a difference between a current of the inductor and a target current of the inductor, an input voltage, an output voltage, and a duty cycle of the first bridge arm; An output pulse width modulation wave is obtained based on the target output power to drive the first bridge arm and the second bridge arm to open and close.

8. The battery capacity expansion system according to claim 1, characterized in that: The first battery string and the second battery string have different remaining capacities, the first battery string includes an old battery string, and the second battery string includes a new battery string.

9. The battery capacity expansion system according to claim 1, characterized in that: It also includes an energy storage converter, which is electrically connected to the DC bus and is used to invert the DC current output by the DC bus into AC current.

10. An electrical device, characterized in that: The electrical device comprises the battery capacity expansion system according to any one of claims 1-9.

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