Energy storage system based on equalization of different SOC battery stacks and control method thereof

Abstract

The invention relates to the technical field of energy storage systems, and discloses an energy storage system based on different SOC cell stack equalization and a control method thereof.The energy storage system comprises a multi-port converter, an alternating-current busbar and a plurality of cell stacks, and a plurality of direct-current ports and an alternating-current port are formed in the multi-port converter; the multi-port converter is connected with the battery stacks through the direct-current ports, the multi-port converter is connected with the alternating-current busbar through the alternating-current ports, and the multi-port converter can be used for directly transmitting energy among the battery stacks; and the control system is respectively connected with the multi-port converter and the plurality of battery stacks, and the control system is used for respectively monitoring the charge states and the voltages of the plurality of battery stacks and dynamically adjusting the working state of the multi-port converter according to the charge states and the voltage differences of the plurality of battery stacks. According to the invention, the energy among the plurality of cell stacks is directly transmitted through the multi-port converter, so that the system can effectively balance the cell stacks with different SOCs, and the instability of the system is avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of energy storage systems, and in particular to an energy storage system based on balancing of battery stacks with different SOCs and a control method thereof. Background Art

[0002] With the rapid development of renewable energy, the importance of energy storage systems in the power industry has become increasingly prominent, playing a key role in improving grid stability and regulating power supply and demand. However, when energy storage batteries are operated in parallel, they are prone to inconsistent state of charge (SOC) of the battery stacks. The difference in SOC will cause frequency and voltage fluctuations within the energy storage system, which in turn affects the stability of the power system.

[0003] Specifically, batteries with high SOC may trigger a protection mechanism to stop operating due to overcharging, while batteries with low SOC may be damaged due to over-discharge. When the SOC of the energy storage system is too low or too high, its output power capacity is limited, and it is difficult to effectively cope with frequency fluctuations in the power system. If the energy storage system cannot maintain sufficient output voltage, it may cause the grid voltage to drop or even cause instability. In this case, the voltage regulation capability will also be weakened accordingly, further affecting the stability of the power system.

[0004] At present, most control methods mainly use external power sources to balance the charge and discharge of grid-connected energy storage batteries, but there is still a lack of effective solutions for the energy balance problem between two energy storage batteries when they are not working. This limits the flexibility and reliability of energy storage systems and increases the risk of equipment damage and system failure. Summary of the invention

[0005] The object of the present invention is to provide an energy storage system based on balancing of battery stacks with different SOCs and a control method thereof, so as to solve the problem of inconsistent state of charge of battery stacks.

[0006] In order to achieve the above-mentioned objectives, the present invention provides an energy storage system based on balancing of battery stacks with different SOCs, comprising: a multi-port converter, an AC busbar and a plurality of battery stacks, wherein the multi-port converter is formed with a plurality of DC ports and an AC port, the multi-port converter is connected to each of the battery stacks through each of the DC ports, the multi-port converter is connected to the AC busbar through the AC port, and the multi-port converter can be used to directly transfer energy between the plurality of battery stacks to achieve energy balancing; a control system, wherein the control system is respectively connected to the multi-port converter and the plurality of battery stacks, and the control system is used to respectively monitor the state of charge and voltage of the plurality of battery stacks, and dynamically adjust the working state of the multi-port converter according to the state of charge and voltage differences of the plurality of battery stacks to control the direction and rate of energy transmission.

[0007] Furthermore, the multi-port converter includes a plurality of three-phase full-bridge circuits and a plurality of inductors, each of the three-phase full-bridge circuits being formed with a DC port, the DC port being used to access the DC power of the battery stack; and each phase of each of the three-phase full-bridge circuits is connected to the AC busbar through each of the inductors, so that the multi-port converter can perform bidirectional energy flow between the battery stack and the AC busbar.

[0008] Furthermore, the multi-port converter further comprises a plurality of voltage-stabilizing capacitors, and two ends of each of the voltage-stabilizing capacitors are respectively connected to the positive electrode and the negative electrode of the DC port.

[0009] Furthermore, each of the three-phase full-bridge circuits includes three bridge arms, and both ends of each of the inductors are respectively connected to the midpoints of each of the bridge arms of the two three-phase full-bridge circuits to achieve connection between the two three-phase full-bridge circuits.

[0010] Furthermore, each of the bridge arms includes two power electronic power switches connected in series, and the control system is connected to each of the power electronic power switches so that each of the power electronic power switches is used to control the magnitude, direction and phase of the output voltage and current.

[0011] Furthermore, it also includes a plurality of circuit breakers and a plurality of cables, and the multi-port converter is connected to the AC busbar or each battery stack through each of the cables; and a circuit breaker is arranged on each of the cables.

[0012] The present invention also proposes an energy storage control method based on balancing of battery stacks with different SOCs, and adopts the above-mentioned energy storage system based on balancing of battery stacks with different SOCs, comprising the following steps:

[0013] S1: the control system detects the state of charge of each battery stack, determines the energy difference between the battery stacks, and proceeds to the next step when the energy difference exceeds a set threshold;

[0014] S2: acquiring a target voltage vector according to the energy difference between the battery stacks, wherein the target voltage vector is used to indicate the direction and magnitude of energy transmission;

[0015] S3: selecting a suitable switch state and time in the voltage space vector diagram according to the direction and magnitude of the target voltage vector;

[0016] S4: The control system controls the opening and closing of each of the power electronic power switches, and continuously adjusts the switch state and time to control the direction and rate of energy transmission, so that the charge states of different battery stacks tend to be consistent, thereby achieving energy balance.

[0017] Furthermore, the step S2 specifically includes the following sub-steps:

[0018] S21: Analyze the energy value and direction to be transmitted according to the energy difference determined in step S1;

[0019] S22: Calculate the direction and magnitude of the target voltage vector according to the energy value and direction to be transmitted.

[0020] Furthermore, the S3 step specifically includes the following sub-steps:

[0021] S31: Obtaining instantaneous values ​​of three-phase voltages of each of the three-phase full-bridge circuits, and synthesizing corresponding voltage vectors on a three-phase coordinate system;

[0022] S32: According to the equal amplitude transformation principle, the voltage vector in the three-phase coordinate system is transformed into the stationary two-phase coordinate system;

[0023] S33: In the two-phase coordinate system, a voltage space vector diagram is drawn according to the transformed voltage vector; the voltage space vector diagram is used to display all possible voltage vectors of each of the power electronic power switches and their corresponding switch states;

[0024] S34: selecting a suitable voltage vector or voltage vector combination in the voltage space vector diagram according to the direction and magnitude of the target voltage vector, and determining a corresponding switch state;

[0025] S35: Based on the volt-second balance principle, calculate the action time required for each switch state.

[0026] Furthermore, the S4 step includes the following sub-steps:

[0027] S41: converting the calculated switch state and time into a control signal;

[0028] S42: the control system sends a control signal to each of the power electronic power switches;

[0029] S43: Each of the power electronic power switches is controlled to be turned on and off according to the control signal.

[0030] Beneficial effects achieved by the present invention:

[0031] 1. The present invention directly transfers energy between multiple battery stacks through a multi-port converter, so that the system of the present invention can quickly and effectively balance battery stacks with different SOCs, avoiding system instability and battery performance degradation caused by SOC differences, reducing the intermediate links of energy conversion, and improving the efficiency of energy balancing.

[0032] 2. The control system in the present invention monitors the charge state and voltage of the battery stack in real time, and dynamically adjusts the working state of the multi-port converter according to the difference, so as to accurately control the direction and rate of energy transmission, ensure that the energy storage system can quickly respond to frequency and voltage fluctuations in the power system, and enhance the overall stability of the system.

[0033] 3. The present invention avoids damage to the battery stack due to overcharging or over-discharging through precise energy balancing, thereby extending the battery life. At the same time, balanced SOC also helps to reduce performance differences between batteries and improve the overall performance of the energy storage system. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a schematic diagram of the system structure of Embodiment 1 of the present invention;

[0035] Figure 2 It is a schematic diagram of the structure of a three-port converter according to the first embodiment of the present invention;

[0036] Figure 3 This is a schematic diagram of a method flow of Embodiment 2 of the present invention;

[0037] Figure 4 This is a schematic diagram of the sub-step flow of step S2 of embodiment 2 of the present invention;

[0038] Figure 5 This is a schematic diagram of the sub-steps of step S3 of embodiment 2 of the present invention;

[0039] Figure 6 This is a schematic diagram of the sub-steps of step S4 of embodiment 2 of the present invention;

[0040] Figure 7 It is a schematic diagram of a three-phase voltage synthesis voltage vector according to a second embodiment of the present invention;

[0041] Figure 8 It is a schematic diagram of the projected synthetic vector in the α-β coordinate system of the second embodiment of the present invention;

[0042] Fig. 9 64 switch state voltage vector diagrams of the second embodiment of the present invention;

[0043] Fig.10 The α-β coordinate system and its rotating coordinate system of the second embodiment of the present invention are synthesized into a voltage vector diagram;

[0044] Fig.11 A voltage space vector diagram of energy transmission between a single DC system and an AC system according to the second embodiment of the present invention;

[0045] Fig.12 It is a schematic diagram of a vector triangle in sector area I according to the second embodiment of the present invention.

[0046] The drawings are only used for illustrative purposes and should not be construed as limitations on this patent. In order to better illustrate this embodiment, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of the actual product. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted. The same or similar numbers correspond to the same or similar parts. The terms describing the positional relationship in the drawings are only used for illustrative purposes and should not be construed as limitations on this patent. DETAILED DESCRIPTION

[0047] It should be noted that, in the absence of conflict, the embodiments and technical features in the embodiments of the present application can be combined with each other, and the detailed description in the specific embodiments should be understood as an explanation of the purpose of the present application and should not be regarded as an improper limitation on the present application.

[0048] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the specific technical scheme of the present application will be further described in detail below in conjunction with the drawings in the embodiments of the present application. The following embodiments are used to illustrate the present application, but are not used to limit the scope of the present application.

[0049] In the embodiments of the present application, the terms "include", "comprises" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "comprises a ..." does not exclude the presence of other identical elements in the process, method, article or device including the element.

[0050] The technical solution of the present invention is described in detail below in conjunction with the specific drawings.

[0051] Embodiment 1

[0052] like Figure 1 and Figure 2 As shown, an energy storage system based on balancing battery stacks with different SOCs includes: a multi-port converter, an AC busbar and multiple battery stacks, wherein multiple DC ports and one AC port are formed on the multi-port converter, the multi-port converter is connected to each battery stack through each DC port, and the multi-port converter is connected to the AC busbar through the AC port, and the multi-port converter can be used to directly transfer energy between multiple battery stacks to achieve energy balancing; a control system, wherein the control system is respectively connected to the multi-port converter and the multiple battery stacks, and the control system is used to respectively monitor the charge state and voltage of the multiple battery stacks, and dynamically adjust the working state of the multi-port converter according to the charge state and voltage difference of the multiple battery stacks to control the energy transmission direction and rate.

[0053] This embodiment is described by taking a three-port converter as an example. The specific working process of the above energy storage system is as follows:

[0054] 1) Initialization and monitoring: When the energy storage system is started, the control system first initializes to ensure that all components (including the three-port converter, battery stack and AC busbar) are in normal working condition. The control system starts to monitor the state of charge (SOC) and voltage of the two battery stacks in real time through sensors connected to the two battery stacks.

[0055] 2) Data analysis and judgment: The control system collects and analyzes the SOC and voltage data of the two battery stacks to identify the SOC difference between them. According to the preset balancing strategy, the control system determines whether to start the energy balancing process and determines the direction and rate of energy transmission.

[0056] 3) Energy balancing process: If energy balancing needs to be started, the control system sends instructions to the three-port converter to adjust its working state to start energy transmission. According to the instructions of the control system, the three-port converter transfers energy from the battery stack with higher SOC to the battery stack with lower SOC through its DC port, or connects to the AC busbar through the AC port to achieve more complex energy scheduling.

[0057] During the transmission process, the control system continuously monitors the SOC and voltage of the battery stack and dynamically adjusts the operating parameters of the three-port converter (such as voltage level, current size, etc.) to ensure the efficiency and safety of energy transmission.

[0058] 4) Balance completion and monitoring continues: When the SOC difference between the battery stacks reaches the preset balance target, the control system instructs the three-port converter to stop energy transmission. The control system continues to monitor the SOC and voltage of the battery stack to prevent new imbalances caused by system changes (such as load fluctuations, battery aging, etc.).

[0059] This embodiment directly transfers energy between two battery stacks through a three-port converter, so that the system of this embodiment can quickly and effectively balance battery stacks with different SOCs, avoiding system instability and battery performance degradation caused by SOC differences, reducing intermediate links in energy conversion, and improving the efficiency of energy balancing.

[0060] The control system in this embodiment monitors the charge state and voltage of the battery stack in real time, and dynamically adjusts the working state of the three-port converter according to the difference, thereby accurately controlling the direction and rate of energy transmission, ensuring that the energy storage system can quickly respond to frequency and voltage fluctuations in the power system and enhance the overall stability of the system.

[0061] This embodiment avoids damage to the battery stack due to overcharging or over-discharging through precise energy balancing, thereby extending the battery life. At the same time, balanced SOC also helps to reduce performance differences between batteries and improve the overall performance of the energy storage system.

[0062] like Figure 2 As shown, the multi-port converter includes multiple three-phase full-bridge circuits and multiple inductors. A DC port is formed on each three-phase full-bridge circuit, and the DC port is used to access the DC power of the battery stack; and each phase of each three-phase full-bridge circuit is connected to the AC bus through each inductor, so that the multi-port converter can perform bidirectional energy flow between the battery stack and the AC bus.

[0063] In this embodiment, there are two three-phase full-bridge circuits, which are symmetrically arranged in the three-port converter. There are six inductors, and each phase of each three-phase full-bridge circuit is connected to the AC busbar through an inductor. Each phase of the two three-phase full-bridge circuits is connected through two inductors connected in series.

[0064] In this embodiment, each three-phase full-bridge circuit has the function of bidirectional energy transmission. It is connected to the AC busbar through inductance, thereby realizing bidirectional energy flow between the battery stack and the AC busbar. It not only supports energy balance between battery stacks, but also allows the battery stack to exchange energy with the power grid or other energy storage devices, thereby improving the flexibility and adaptability of the system.

[0065] Preferably, in this embodiment, by optimizing the control strategy and parameter design of the three-phase full-bridge circuit, the loss during energy transmission can be further reduced and the overall efficiency of the system can be improved.

[0066] like Figure 2 As shown, the multi-port converter further includes a plurality of voltage stabilizing capacitors, and two ends of each voltage stabilizing capacitor are respectively connected to the positive electrode and the negative electrode of the DC port.

[0067] In this embodiment, the voltage stabilizing capacitor can store electrical energy and play a role in smoothing the DC voltage in the circuit. When the voltage of the DC port fluctuates, the capacitor can release or absorb electrical energy, thereby stabilizing the DC voltage and ensuring the stable operation of the system. At the same time, in the system, when a large instantaneous current is required, the capacitor can quickly release the stored electrical energy and provide the required instantaneous current, which helps to ensure the response speed and stability of the system when facing sudden power demand.

[0068] like Figure 2 As shown, each three-phase full-bridge circuit includes three bridge arms, and both ends of each inductor are respectively connected to the midpoint of each bridge arm of the two three-phase full-bridge circuits to achieve the connection of the two three-phase full-bridge circuits.

[0069] This embodiment connects the midpoints of the bridge arms of two three-phase full-bridge circuits through inductance, which can form a more direct and efficient energy transmission path, reduce energy loss during conversion and transmission, and improve the overall efficiency of the system. At the same time, as an energy storage element, the inductor can generate an electromotive force when the current changes, thereby helping the control system to better regulate the current. By accurately controlling the charging and discharging process of the inductor, accurate control of the current can be achieved, improving the stability and response speed of the system.

[0070] like Figure 2 As shown, each bridge arm includes two power electronic switches connected in series, and the control system is connected to each power electronic switch so that each power electronic switch is used to control the magnitude, direction and phase of the output voltage and current.

[0071] This embodiment can achieve high-precision control of output voltage and current by accurately controlling the opening and closing of the power electronic power switch. The bidirectional conduction characteristics of the power electronic power switch enable the bridge arm to support bidirectional transmission of energy. This means that the multi-port converter can not only transmit energy between battery stacks, but also realize bidirectional energy flow between the battery stack and the AC busbar, improving the flexibility and adaptability of the system.

[0072] At the same time, the power electronic power switches have fast turn-on and turn-off times, which enables the multi-port converter to respond quickly to system changes, such as load fluctuations or rapid changes in the battery stack SOC, helping to maintain system stability and reliability.

[0073] like Figure 1 As shown, it also includes multiple circuit breakers and multiple cables. The multi-port converter is connected to the AC busbar or each battery stack through each cable; a circuit breaker is arranged on each cable.

[0074] Embodiment 2

[0075] This embodiment adopts the energy storage system in the first embodiment, and the same contents can be found in the first embodiment.

[0076] like Figure 3 As shown, the energy storage control method based on balancing of battery stacks with different SOCs adopts the above-mentioned energy storage system based on balancing of battery stacks with different SOCs, and includes the following steps:

[0077] S1: The control system detects the state of charge of each battery stack and determines the energy difference between the battery stacks. When the energy difference exceeds a set threshold, the next step is entered;

[0078] S2: obtaining a target voltage vector according to the energy difference between the battery stacks, where the target voltage vector is used to indicate the direction and magnitude of energy transmission;

[0079] S3: Select appropriate switch state and time in the voltage space vector diagram according to the direction and magnitude of the target voltage vector;

[0080] S4: The control system controls the opening and closing of each power electronic power switch, and continuously adjusts the switch state and time to control the direction and rate of energy transmission, so that the charge state between different battery stacks tends to be consistent, thereby achieving energy balance.

[0081] This embodiment can accurately identify the battery stack that needs to be balanced and the direction and size of the balance by monitoring the state of charge (SOC) of each battery stack in real time and accurately calculating the energy difference between them. Combined with the determination of the target voltage vector, the most appropriate switch state and time can be selected in the voltage space vector diagram, thereby achieving accurate energy transmission control and making the SOC of each battery stack tend to be consistent.

[0082] This embodiment can reduce the loss in the energy conversion process and improve the overall efficiency of the system by optimizing the control strategy and parameter design of the power electronic power switch. At the same time, since the energy transmission direction and rate can be adjusted in real time, energy can be reasonably allocated and utilized according to actual needs, avoiding energy waste and unnecessary loss.

[0083] like Figure 4 As shown, step S2 specifically includes the following sub-steps:

[0084] S21: Analyze the energy value and direction to be transmitted according to the energy difference determined in step S1;

[0085] S22: Calculate the direction and magnitude of the target voltage vector according to the energy value and direction to be transmitted.

[0086] like Figure 5 As shown, step S3 specifically includes the following sub-steps:

[0087] S31: Obtain the instantaneous value of the three-phase voltage of each three-phase full-bridge circuit, and synthesize the corresponding voltage vector on the three-phase coordinate system;

[0088] S32: According to the equal amplitude transformation principle, the voltage vector in the three-phase coordinate system is transformed into the stationary two-phase coordinate system;

[0089] S33: in the two-phase coordinate system, drawing a voltage space vector diagram according to the transformed voltage vector; the voltage space vector diagram is used to display all possible voltage vectors of each power electronic power switch and their corresponding switch states;

[0090] S34: selecting a suitable voltage vector or voltage vector combination in the voltage space vector diagram according to the direction and magnitude of the target voltage vector, and determining a corresponding switch state;

[0091] S35: Based on the volt-second balance principle, calculate the action time required for each switch state.

[0092] like Figure 6 As shown, step S4 includes the following sub-steps:

[0093] S41: converting the calculated switch state and time into a control signal;

[0094] S42: The control system sends a control signal to each power electronic power switch;

[0095] S43: Each power electronic power switch is controlled to be turned on and off according to the control signal.

[0096] In summary, the step S3 is described in detail by taking a three-port converter as an example.

[0097] Assume the three-phase voltage is:

[0098]

[0099] Among them, u a 、u b 、u c Corresponding to the phase voltages of phases A, B, and C respectively; U m represents the voltage amplitude; ω represents the angular frequency; t represents the time.

[0100] The corresponding voltage vector is synthesized in the three-phase coordinate system, such as Figure 7 As shown in the figure, U A , U B , U C is a fixed three-phase coordinate system, in which sinusoidal quantities are distributed. As the sinusoidal quantities change, the resultant vector V also changes. According to the principle of equal amplitude transformation, U A , U B , U C The fixed three-phase coordinate system can synthesize the following vector expression:

[0101]

[0102] By transformation, the physical quantities in the three-phase coordinate system are converted into the stationary two-phase coordinate system (α-β), and the following is made:

[0103] V=V α +jV β ,

[0104] Where V represents the resultant voltage vector in the α-β coordinate system, which contains the components of the two phases; the real part V α represents the voltage component along the α axis; the imaginary part V β represents the voltage component along the β axis.

[0105] Then we can get:

[0106]

[0107] The corresponding coordinates after transformation are as follows Figure 8 As shown, in a three-phase AC system, if u a 、u b 、u c If the three-phase asymmetric sinusoidal quantity is equal, the amplitude is different, but the phase difference is still 120°. In the case of unequal amplitudes, there is always a three-phase symmetrical voltage u a '、u b '、u c ', so that:

[0108]

[0109] According to the characteristics of symmetrical three-phase electricity:

[0110] u′ a +u′ b +u′ c =0,

[0111] The zero sequence component is derived as:

[0112]

[0113] The present invention will describe a bidirectional energy flow modulation scheme for a dual DC system and an AC system. During energy transmission, two switching devices in the same bridge arm of a power electronic switching device cannot be turned on or off at the same time. By analyzing the voltage vector synthesis problem of energy transmission between a dual DC system and an AC system, it is concluded that the new inter-stack balancing device circuit has 64 switching states in the working mode of bidirectional energy flow between a dual DC system and an AC system. Each switching state will correspond to a different voltage vector, and a voltage space vector diagram in an α-β coordinate system can be obtained. The voltage vector corresponding to each switching state can be obtained by writing the Kirchhoff voltage equation according to the volt-second balance, which is abbreviated as (for example: V 4 +V 6' The 64 voltage vectors synthesized as 46' are shown in Fig. 9 It should be understood that different switching vector composition methods can produce a variety of synthetic vectors, and the present invention only describes a general modulation scheme.

[0114] by Fig. 9 Taking 35'-46'-51'-62'-13'-24' as an example, modulation is performed in the form of 120° space vector decoupling. Assuming that the rotation angle of the hexagon with respect to the α-β coordinate system is θ, we get:

[0115]

[0116] Among them, y 24′ Indicates V 24' The voltage scalar on the β axis based on the α-β coordinate system; x 24′ Indicates V 24' The voltage scalar on the α-axis based on the α-β coordinate system.

[0117] By establishing a rotation matrix and rotating the α-β coordinate system, the 24' point is on the α' axis and divided into 6 sector areas according to the voltage vector, such as Fig.10 shown.

[0118]

[0119] Where r represents a two-dimensional rotation matrix; θ represents the rotation angle of the α-β coordinate system rotating counterclockwise around the origin to the α'-β' coordinate system; cosθ and sinθ are the cosine and sine values ​​of the rotation angle θ, respectively.

[0120]

[0121] Suppose the synthetic vector required at this time is:

[0122]

[0123] The desired synthesized voltage vector is projected onto the rotated α'-β' coordinate system through the rotation matrix. r 'for:

[0124]

[0125] Among them, V′ r represents the two-dimensional voltage vector in the α'-β' coordinate system after rotation; θ represents the rotation angle of the α'-β' coordinate system from the origin to the α'-β' coordinate system counterclockwise; cosθ and sinθ are the cosine and sine values ​​of the rotation angle, respectively; V α represents the voltage component along the α axis; V β represents the voltage component along the β axis; V α_r represents the voltage component of the α' axis in the α'-β' coordinate system after rotation; V β_r represents the β'-axis voltage component in the α'-β' coordinate system after rotation.

[0126] The voltage space vector diagram of energy transmission between a single DC system and an AC system is shown in the figure below. Fig.11 As shown, the V marked in the figure 1 、V 2 、V 3 、V 4 、V 5 、V 6The six basic voltage vectors representing the output are located at the six vertices of the regular hexagon, and they correspond to different switch states. By connecting the six vertices to the origin, six sector areas can be divided. It should be noted that in the working mode of energy transmission between the dual DC system and the AC system, the basis for judging the division of the sector area is the same as the principle of the above voltage space vector diagram.

[0127] In the working mode based on energy transmission between dual DC system and AC system, according to the following formula, V r 'Perform sector judgment:

[0128]

[0129] Among them, Ι, ΙΙ, ΙΙΙ, ΙV, V, and VI represent the numbers of 6 sectors; V α_r represents the voltage component of the α' axis in the α'-β' coordinate system after rotation; V β_r represents the β'-axis voltage component in the α'-β' coordinate system after rotation.

[0130] By judging different sector areas according to the above formula, the corresponding target vector can be synthesized to achieve output voltage modulation.

[0131] Sector area I vector triangle Fig.12 As shown. According to the above sector area judgment, the corresponding voltage vector can be selected to synthesize the target vector. Taking sector 1 as an example to calculate the working time of the voltage vector, it should be noted that the described sector area 1 is only a part of the modulation method of the present invention, and the calculation method of the working time of the remaining sector areas is similar to that of area 1. Assuming the switching period is T C , the working time of the voltage vector 24' is T 1 , the working time of voltage vector 35' is T 2 , V 0 、V 7 represents the zero voltage vector, and the action time is recorded as T 0 , T 7 (Since it is a zero voltage vector, T 0 =T 7 ),but:

[0132]

[0133] According to the vector triangle formed by the voltage vector V', the voltage vector 24' and the voltage vector 35', assuming that the angle between the voltage vector V' and the α' axis is γ, according to the sine theorem, we can get:

[0134]

[0135] The solution is:

[0136]

[0137] The serial numbers of the embodiments of the present application are only for description and do not represent the advantages and disadvantages of the embodiments. The above are only preferred embodiments of the present application, and do not limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made by using the contents of the present application specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. An energy storage system based on balancing of battery stacks with different SOCs, characterized in that: include: A multi-port converter, an AC busbar and a plurality of battery stacks, wherein the multi-port converter is formed with a plurality of DC ports and an AC port, the multi-port converter is connected to each of the battery stacks through each of the DC ports, the multi-port converter is connected to the AC busbar through the AC port, and the multi-port converter can be used to directly transfer energy between the plurality of battery stacks to achieve energy balance; A control system, wherein the control system is connected to the multi-port converter and the plurality of battery stacks, respectively, and is used to monitor the charge state and voltage of the plurality of battery stacks, respectively, and dynamically adjust the working state of the multi-port converter according to the charge state and voltage differences of the plurality of battery stacks, so as to control the direction and rate of energy transmission.

2. The energy storage system based on balancing of different SOC battery stacks according to claim 1 is characterized in that: The multi-port converter includes multiple three-phase full-bridge circuits and multiple inductors, each of which has a DC port for connecting to the DC power of the battery stack; and each phase of each of the three-phase full-bridge circuits is connected to the AC busbar through each of the inductors, so that the multi-port converter can perform bidirectional energy flow between the battery stack and the AC busbar.

3. The energy storage system based on balancing of different SOC battery stacks according to claim 2 is characterized in that: The multi-port converter further includes a plurality of voltage-stabilizing capacitors, and two ends of each of the voltage-stabilizing capacitors are respectively connected to the positive electrode and the negative electrode of the DC port.

4. The energy storage system based on balancing of different SOC battery stacks according to claim 2 is characterized in that: Each of the three-phase full-bridge circuits includes three bridge arms, and both ends of each of the inductors are respectively connected to the midpoints of each of the bridge arms of the two three-phase full-bridge circuits to achieve connection between the two three-phase full-bridge circuits.

5. The energy storage system based on balancing of different SOC battery stacks according to claim 4 is characterized in that: Each of the bridge arms comprises two power electronic switches connected in series, and the control system is connected to each of the power electronic switches so that each of the power electronic switches is used to control the magnitude, direction and phase of the output voltage and current.

6. The energy storage system based on balancing of different SOC battery stacks according to claim 1, characterized in that: It also includes a plurality of circuit breakers and a plurality of cables, and the multi-port converter is connected to the AC busbar or each battery stack through each of the cables; and each of the cables is provided with a circuit breaker.

7. An energy storage control method based on balancing of battery stacks with different SOCs, using an energy storage system based on balancing of battery stacks with different SOCs as claimed in any one of claims 1 to 6, characterized in that: The following steps are involved: S1: the control system detects the state of charge of each battery stack, determines the energy difference between the battery stacks, and proceeds to the next step when the energy difference exceeds a set threshold; S2: acquiring a target voltage vector according to the energy difference between the battery stacks, wherein the target voltage vector is used to indicate the direction and magnitude of energy transmission; S3: selecting a suitable switch state and time in the voltage space vector diagram according to the direction and magnitude of the target voltage vector; S4: The control system controls the opening and closing of each power electronic power switch, and continuously adjusts the switch state and time to control the direction and rate of energy transmission, so that the charge states of different battery stacks tend to be consistent, thereby achieving energy balance.

8. The energy storage control method based on balancing of different SOC battery stacks according to claim 7, characterized in that: The S2 step specifically includes the following sub-steps: S21: Analyze the energy value and direction to be transmitted according to the energy difference determined in step S1; S22: Calculate the direction and magnitude of the target voltage vector according to the energy value and direction to be transmitted.

9. The energy storage control method based on balancing of different SOC battery stacks according to claim 7, characterized in that: The S3 step specifically includes the following sub-steps: S31: Obtain the instantaneous value of the three-phase voltage of each three-phase full-bridge circuit, and synthesize the corresponding voltage vector on the three-phase coordinate system; S32: According to the equal amplitude transformation principle, the voltage vector in the three-phase coordinate system is transformed into the stationary two-phase coordinate system; S33: In the two-phase coordinate system, a voltage space vector diagram is drawn according to the transformed voltage vector; the voltage space vector diagram is used to display all possible voltage vectors of each of the power electronic power switches and their corresponding switch states; S34: selecting a suitable voltage vector or voltage vector combination in the voltage space vector diagram according to the direction and magnitude of the target voltage vector, and determining a corresponding switch state; S35: Based on the volt-second balance principle, calculate the action time required for each switch state.

10. The energy storage control method based on balancing of different SOC battery stacks according to claim 7, characterized in that: The S4 step includes the following sub-steps: S41: converting the calculated switch state and time into a control signal; S42: the control system sends a control signal to each of the power electronic power switches; S43: Each of the power electronic power switches is controlled to be turned on and off according to the control signal.

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