Energy storage system and control method thereof

Abstract

The invention provides an energy storage system and a control method thereof, and the method comprises the steps: judging whether a grid-connected condition is met or not according to the electrical parameters of a power grid when the energy storage system is in an off-grid working mode, and controlling the energy storage system to enter a grid-connected working mode when the grid-connected condition is met: carrying out the amplitude locking and phase locking of an inversion module; setting a first reference voltage value on the high-voltage bus side; controlling a grid-connected loop of the host according to the first reference voltage value to obtain the duty ratio of a switching tube of the inversion module; setting a second reference voltage value about the low-voltage bus side, and controlling a grid-connected loop of the slave according to the second reference voltage value to obtain the duty ratio of a switching tube of the DCDC module; and the power of the low-voltage bus side is softly started to the battery required power step by step, and the power of the high-voltage bus side is softly started to the preset power according to the first reference voltage value, the voltage value of the high-voltage bus side and the battery required power. According to the method, the working stability and safety of the energy storage system can be improved.

Description

Technical Field

[0001] The embodiments of the present application relate to the technical field of energy storage, and particularly to an energy storage system and a control method thereof. Background Art

[0002] With the wide application of renewable energy and the development of the intelligentization of power systems, energy storage systems play an important role in microgrids, off-grid power supply, and grid-connected operation. During the energy supply process of the energy storage system, the switching of off-grid and grid-connected modes is involved. For example, when the grid is connected for grid connection, if the DCDC module on the DC side does not switch to the grid-connected state with the resonant conversion module and the inverter module on the inverter side, there will be two voltage sources on the DC side and the inverter side charging each other in the energy storage system at this time, and the energy at both ends is applied to the capacitor on the low-voltage side of the resonant conversion module, which is likely to cause damage to the capacitor of the resonant conversion module. Therefore, during the process of the energy storage system switching from the off-grid mode to the grid-connected mode, how to coordinately control the high-voltage bus side and the low-voltage bus side, achieve a stable transition, and avoid abnormal fluctuations in the bus voltage to prevent damage to the internal circuit of the energy storage system is one of the key challenges in the control of the energy storage system. Summary of the Invention

[0003] The embodiments of the present application provide an energy storage system and a control method thereof. When the energy storage system switches from the off-grid working mode to the grid-connected working mode, after the host and the slave enter the grid-connected loop, the power on the high-voltage bus side and the low-voltage bus side is gradually adjusted to ensure reasonable power distribution, reduce abnormal conditions such as power mutation and bus voltage fluctuation, and improve the stability and safety of the energy storage system during operation.

[0004] In a first aspect, an embodiment of the present application provides a control method for an energy storage system, which is applied to an energy storage system including a host and a slave. The host includes a resonant conversion module and an inverter module, and the slave includes a DCDC module. The connection between the resonant conversion module and the inverter module is the high-voltage bus side, and the connection between the resonant conversion module and the DCDC module is the low-voltage bus side. The control method includes: when the energy storage system is in an off-grid working mode, determining whether the grid connection condition is satisfied according to the electrical parameters of the grid. When the grid connection condition is satisfied, controlling the energy storage system to enter the grid-connected working mode: performing amplitude and phase locking on the inverter module; setting a first reference voltage value for the high-voltage bus side according to the rated electrical parameters of the energy storage system, the electrical parameters of the battery at the current moment connected to the slave, and the electrical parameters of the host at the current moment; controlling the grid-connected loop of the host according to the first reference voltage value to obtain the duty ratio of the switching tube of the inverter module; setting a second reference voltage value for the low-voltage bus side according to the electrical parameters of the battery at the current moment connected to the slave, and controlling the grid-connected loop of the slave according to the second reference voltage value to obtain the duty ratio of the switching tube of the DCDC module; gradually soft-starting the power of the low-voltage bus side to the battery demand power, and soft-starting the power of the high-voltage bus side to a preset power according to the first reference voltage value, the voltage value of the high-voltage bus side, and the battery demand power; wherein, the ratio of the first reference voltage value to the transformer turns ratio of the resonant conversion module is greater than the second reference voltage value.

[0005] Second aspect, an embodiment of the present application provides an energy storage system, which includes a host and a slave; the host includes a resonant conversion module and an inverter module, and the slave includes a DCDC module. Among them, the connection point between the resonant conversion module and the inverter module is the high-voltage bus side, and the connection point between the resonant conversion module and the DCDC module is the low-voltage bus side; the energy storage system is configured to: when the energy storage system is in the off-grid working mode, determine whether the grid connection condition is satisfied according to the electrical parameters of the grid. When the grid connection condition is satisfied, control the energy storage system to enter the grid-connected working mode: perform amplitude and phase locking on the inverter module; set a first reference voltage value for the high-voltage bus side according to the rated electrical parameters of the energy storage system, the electrical parameters of the battery at the current moment connected to the slave, and the electrical parameters of the host at the current moment; control the grid-connected loop of the host according to the first reference voltage value to obtain the duty ratio of the switching tube of the inverter module; set a second reference voltage value for the low-voltage bus side according to the electrical parameters of the battery at the current moment connected to the slave, and control the grid-connected loop of the slave according to the second reference voltage value to obtain the duty ratio of the switching tube of the DCDC module; gradually soft-start the power of the low-voltage bus side to the battery demand power, and soft-start the power of the high-voltage bus side to a preset power according to the first reference voltage value, the voltage value of the high-voltage bus side, and the battery demand power; wherein, the ratio of the first reference voltage value to the transformer turns ratio of the resonant conversion module is greater than the second reference voltage value.

[0006] The beneficial effects of the present application are as follows: An embodiment of the present application provides an energy storage system and its control method. When the energy storage system switches from the off-grid working mode to the grid-connected working mode, it controls the DCDC module, the inverter module, and the resonant conversion module to all enter the grid-connected mode to prevent the phenomenon that the resonant conversion module is damaged due to the charging and discharging of the low-voltage bus at both ends of the DC side and the inverter side when the DC side and the inverter side do not enter the grid-connected mode synchronously. And the control method can reasonably set the voltage reference values of the high-voltage bus side and the low-voltage bus side, so that after the energy storage system enters the grid-connected working mode, it can respond to the changes of the grid and the battery in real time, adapt to the requirements of multiple working conditions, improve the flexibility of the control method, and after the host and the slave enter the grid-connected loop, gradually adjust the power of the high-voltage bus side and the low-voltage bus side to ensure reasonable power distribution, reduce abnormal conditions such as under-voltage or out-of-control of the high-voltage bus, and improve the stability and safety of the energy storage system during operation. Description of the Drawings

[0007] One or more embodiments are exemplarily illustrated by the pictures in the corresponding drawings. These exemplary illustrations do not constitute limitations on the embodiments. Elements with the same reference numerals in the drawings are represented as similar elements, unless otherwise stated, and the drawings in the drawings do not constitute a proportional limitation.

[0008] Figure 1 Block diagram of an energy storage system provided by an embodiment of the present application; Figure 2 Circuit diagram of a DCDC module provided by an embodiment of the present application; Figure 3 Circuit diagram of a resonant conversion module provided by an embodiment of the present application; Figure 4 Circuit diagram of an inverter module provided by an embodiment of the present application; Figure 5 Flow chart of a control method for an energy storage system provided by an embodiment of the present application; Figure 6 Schematic diagram of a phase-locked loop provided by an embodiment of the present application; Figure 7 Schematic diagram of an off-grid loop of a host provided by an embodiment of the present application; Figure 8 Schematic diagram of a grid-connected loop of a host provided by an embodiment of the present application; Figure 9 Bode plot provided by an embodiment of the present application; Figure 10 Schematic diagram of a grid-connected loop of a slave provided by an embodiment of the present application; Figure 11 Schematic diagram of a calculation loop for a power compensation value provided by an embodiment of the present application; Figure 12 Schematic diagram of a start-up loop of a DCDC module provided by an embodiment of the present application; Figure 13 Schematic diagram of waveforms of a pulse width modulation signal of a primary side switching tube and a resonant current provided by an embodiment of the present application; Figure 14 Another schematic diagram of waveforms of a pulse width modulation signal of a primary side switching tube and a resonant current provided by an embodiment of the present application; Figure 15 Schematic diagram of a waveform of a voltage on a high-voltage bus side provided by an embodiment of the present application; Figure 16 Another block diagram of an energy storage system provided by an embodiment of the present application; Figure 17 Structural diagram of a signal generator provided by an embodiment of the present application. Detailed implementation manners

[0009] For the convenience of understanding the present application, the present application will be described in more detail below with reference to the accompanying drawings and specific embodiments. It should be noted that when an element is expressed as "fixed to" another element, it can be directly on the other element, or there can be one or more intermediate elements therebetween. When an element is expressed as "electrically connected to" another element, it can be directly connected to the other element, or there can be one or more intermediate elements therebetween. The terms "upper", "lower", "inner", "outer", "bottom", etc. used in this specification indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus cannot be construed as a limitation to the present application. In addition, the terms "first", "second", "third", etc. are only used for descriptive purposes and cannot be construed as indicating or implying relative importance.

[0010] Unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as commonly understood by those skilled in the technical field to which the present application belongs. The terms used in the specification of the present application are only for the purpose of describing specific embodiments and are not used to limit the present application. The term "and / or" used in this specification includes any and all combinations of one or more of the related listed items. In addition, the technical features involved in different embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0011] An embodiment of the present application provides an energy storage system. Refer to Figure 1 , the energy storage system includes a host 10 and a slave 20. The host 10 includes a resonant conversion module 11 and an inverter module 12, and the slave 20 includes a DCDC module 21. Among them, the resonant conversion module 11 is used to connect the DCDC module 21 and the inverter module 12. The connection between the resonant conversion module 11 and the inverter module 12 is the high-voltage bus side, and the connection between the resonant conversion module 11 and the DCDC module 21 is the low-voltage bus side.

[0012] Among them, the DCDC module 21 refers to a device that can adjust the voltage amplitude of direct current and can realize the conversion between direct currents of different voltage levels. The DCDC module 21 is used to connect to the battery 40. The battery 40 includes a plurality of parallel, series, or mixed-connected battery cells for storing and providing electric energy. The mixed connection includes series and parallel. The operating voltage range of the battery 40 can be 20V to 40V. In some embodiments, refer to Figure 2, the DCDC module 21 is two interleaved BUCK - BOOST circuits. Specifically, the DCDC module 21 includes a buck - boost inductor L1, a buck - boost inductor L2, a buck - boost capacitor C1, a buck - boost capacitor C2, a switching transistor Q1, a switching transistor Q2, a switching transistor Q3, and a switching transistor Q4. Among them, the buck - boost inductor L1, the buck - boost capacitor C1, the switching transistor Q1, and the switching transistor Q2 form one BUCK - BOOST loop, and the buck - boost inductor L2, the buck - boost capacitor C2, the switching transistor Q3, and the switching transistor Q4 form another BUCK - BOOST loop. In Figure 2 , the connection points A1 and A2 are the connection points between the resonant conversion module 11 and the DCDC module 21, and the sampled voltage between the connection points A1 and A2 is the sampled voltage on the low - voltage bus side.

[0013] Among them, the resonant conversion module 11 is an efficient DC - to - DC converter using resonant soft - switching technology, which can achieve isolated conversion between high - voltage and low - voltage direct currents. In some embodiments, referring to Figure 3 , the resonant conversion module 11 is an LLC resonant converter, which includes a low - voltage bus capacitor CLbus, primary - side switching transistors Q5, Q6, Q7, Q8, a transformer T1, an exciting inductor Lm, a resonant inductor Lr, a resonant capacitor Cr, secondary - side switching transistors Q9, Q10, Q11, Q12, and a high - voltage bus capacitor CHbus. In Figure 3 , the connection points A3 and A4 are the connection points between the resonant conversion module 11 and the inverter module 12, and the sampled voltage between the connection points A3 and A4 is the sampled voltage on the high - voltage bus side.

[0014] The inverter module 12 is an electronic power device that can convert direct current to alternating current and vice versa. When in the grid - connected working mode, the inverter module 12 can convert the alternating current of the power grid 30 into direct current on the high - voltage bus side. When in the off - grid working mode, the inverter module 12 can convert direct current into alternating current to supply power to the load 50. In some embodiments, referring to Figure 4 , the inverter module 12 includes inverter high - frequency transistors Q13, Q15, inverter power - frequency transistors Q14, Q16, an inverter inductor L3, an inverter capacitor C3, relays RY1, and RY2. Among them, when the relay RY1 is turned on, it establishes the connection between the inverter module 12 and the power grid 30, or when turned off, it disconnects the connection between the inverter module 12 and the power grid 30. When the relay RY2 is turned on, it establishes the connection between the inverter module 12 and the load 50, or when turned off, it disconnects the connection between the inverter module 12 and the load 50.

[0015] In this energy storage system, a first control chip is provided in the host 10 to control the operation of the resonant conversion module 11 and the inverter module 12, and a second control chip is provided in the slave 20 to control the operation of the DCDC module 21. For different operating modes of the energy storage system, the control loop of the control chip includes an off-grid loop and a grid-connected loop. For example, when switching from the off-grid operating mode to the grid-connected operating mode, when the inverter module of the host and the DCDC module and the resonant conversion module of the slave do not all enter the grid-connected operating mode, that is, for example, when the slave 20 is in the off-grid loop and the host 10 is in the grid-connected loop, a charging effect will be formed between the high-voltage side voltage source and the low-voltage side voltage source inside the energy storage system, resulting in all the energy being accumulated on the low-voltage bus capacitor CLbus of the resonant conversion module 11, which easily causes overvoltage damage to the buck-boost capacitor C1 and the buck-boost capacitor C2.

[0016] To improve the above problems, an embodiment of the present application provides an energy storage system and its control method. When the energy storage system switches from the off-grid operating mode to the grid-connected operating mode, by dynamically coordinating the reference voltage and power distribution of the host and the slave, a smooth transition of the mode switch is achieved, gradually increasing the power on the low-voltage bus side to the battery demand value, and synchronously soft-starting the power on the high-voltage bus side to the target value. After both the host and the slave confirm to enter the grid-connected loop, the power adjustment is started, reducing mode conflicts and improving the stability and safety of the energy storage system during operation.

[0017] An embodiment of the present application provides a control method for an energy storage system, which is applied to the energy storage system as described above. Refer to Figure 5 , and the control method includes steps S10 to S15.

[0018] Step S10: When the energy storage system is in the off-grid operating mode, determine whether the grid connection condition is satisfied according to the electrical parameters of the power grid 30. When the grid connection condition is satisfied, control the energy storage system to enter the grid-connected operating mode.

[0019] The off-grid operating mode refers to the operating state where the energy storage system is completely disconnected from the power grid 30 and operates independently to supply power to the local load 50. At this time, the relay RY2 is closed and the relay RY1 is open, and the energy flows from the battery to the load. At this time, the energy storage system is equivalent to an isolated microgrid, autonomously maintaining voltage and frequency stability and not relying on an external power grid.

[0020] The electrical parameters of the power grid 30 include the frequency and amplitude of the input power of the power grid 30. Specifically, the host 10 can first detect the power grid 30 to determine whether there is input power to the power grid 30. When there is input power, determine whether the frequency and amplitude of the power grid 30 meet the grid connection conditions. If so, control the energy storage system to enter the grid-connected operating mode. If not, continue to operate in the off-grid operating mode.

[0021] Specifically, refer to Figure 4, the host 10 determines whether there is input power in the power grid 30 by detecting the effective value of the voltage between the input port GRIDL1 and the input port GRIDN1 of the power grid 30.

[0022] For example, the effective value of the voltage is calculated by the following formula: ; where is the effective value of the voltage, is the total number of sampling points, is the instantaneous voltage value of the input power of the power grid 30 at the th sampling point.

[0023] After obtaining the effective value of the power grid, it is compared with the first preset voltage value. When the effective value of the power grid is greater than or equal to the first preset voltage value, it is determined that there is input power in the power grid 30. When the effective value of the power grid is less than the first preset voltage value, it is determined that there is no input power in the power grid 30. Among them, the first preset voltage value can be 50% of the rated voltage of the power grid 30 under normal working conditions.

[0024] Next, after determining that there is input power in the power grid 30, the host 10 can calculate the frequency of the input power through a generalized second-order integrator. For example, first set the center angular frequency ωn of the generalized second-order integrator (such as 2π×50 rad / s), and initialize the state variables and , and within each sampling period , update the state variables through the following formula: ; ; is the k-th instantaneous sampling value of the voltage of the power grid 30, and the quadrature components and are calculated through the following formula: ; ; After obtaining the quadrature components, calculate the frequency offset through the following formula: ; In practical applications, the and can be approximately calculated by the following formula for difference: ; ; After obtaining the frequency offset, calculate the actual angular frequency through the following formula: ; The angular frequency is converted into the frequency of the input electricity through the following formula : ; If the frequency of the input electricity is within the preset working frequency, the host 10 obtains the instantaneous deviation voltage of the input electricity. When the instantaneous deviation voltage of the input electricity is greater than or equal to the second preset voltage value, and the duration for which the instantaneous deviation voltage of the input electricity is greater than or equal to the second preset voltage value is greater than or equal to the first preset time, it indicates that both the frequency and amplitude of the input electricity of the power grid 30 are within the working range supported by the energy storage system. The host determines that the electrical parameters of the power grid 30 meet the grid connection conditions. When the instantaneous deviation voltage of the input electricity is less than the second preset voltage value, or the duration for which the instantaneous deviation voltage of the input electricity is greater than or equal to the second preset voltage value is less than the first preset time, the host determines that the electrical parameters of the power grid 30 do not meet the grid connection conditions. Among them, the instantaneous deviation voltage of the input electricity is the difference between the actual instantaneous voltage of the input electricity and the rated peak voltage of the power grid 30; the preset working frequency is the standard frequency range of the power grid 30 supported by the design of the energy storage system, such as the rated frequency; the second preset voltage value is 28% of the rated peak voltage of the power grid 30 supported by the design of the energy storage system, and the rated peak voltage is the product of the rated voltage of the power grid 30 supported by the design of the energy storage system and 1.414. The first preset time can be 3 ms. In practical applications, the preset working frequency, the second preset voltage value, and the first preset time can be set according to actual needs and are not limited herein.

[0025] Among them, controlling the energy storage system to enter the grid-connected working mode includes the following steps S11 to S15.

[0026] Step S11: Perform amplitude and phase locking on the inverter module 12.

[0027] Amplitude and phase locking means that the host 10 adjusts the amplitude and phase of the alternating current of the inverter module 12 to match the amplitude and phase of the input electricity of the power grid 30, so as to ensure that there is no impact current at the moment of grid connection (the moment when the relay RY1 is closed). The alternating current of the inverter module 12 is also the alternating current across the filter capacitor C3.

[0028] For example, the host 10 separates the orthogonal components (i.e., the in-phase component and the orthogonal component) from the alternating current of the inverter module 12 through a generalized second-order integrator, and its separation formula is as follows: ; ; Among them, ; Then, the phase angle is calculated through the following formula: ; Then: ; It can be obtained through trigonometric identities that: ; where is the amplitude of the alternating current of the inverter module 12, is the actual phase angle of the alternating current of the inverter module 12, is the angular frequency of the alternating current of the inverter module 12, is the frequency of the alternating current of the inverter module 12.

[0029] After obtaining the actual phase angle of the alternating current of the inverter module 12 based on the generalized second-order integrator, compare it with the phase angle of the input electricity of the power grid 30, and adjust it through the PI control loop as shown in Figure 6 so that the phase angle of the alternating current output by the inverter module 12 follows the phase angle of the input electricity of the power grid 30 until the difference between the two is less than 10°, completing phase locking, that is: ; In addition, adjust the off-grid reference voltage of the inverter module 12 to the current voltage of the power grid 30, and make the voltage amplitude of the alternating current of the inverter module 12 follow the voltage amplitude of the current power grid 30 until the difference between the two is less than the third preset voltage value, completing amplitude locking. The third preset voltage value can be 10% of the voltage amplitude of the current power grid 30, that is: ; where is the voltage amplitude of the alternating current of the inverter module 12, is the voltage amplitude of the current power grid 30.

[0030] Specifically, first obtain the grid voltage V_GRID between the input terminal GRIDL1 and the input terminal GRIDN1 of the power grid 30, the inverter voltage V_INV across the inverter capacitor C3, the inverter current I_INV flowing through the inverter inductor L3, and the output current I_LOAD flowing through the load 50. Separate α and β from the grid voltage V_GRID, the inverter voltage V_INV, the inverter current I_INV, and the output current I_LOAD through a generalized second-order integrator. After Park transformation of the separated α and β, obtain the D and Q axis components, and get the D axis component VdInvref of the rated inverter voltage, the Q axis component VqInvref of the rated inverter voltage, the D axis component VdInv of the current inverter voltage, the Q axis component VqInv of the current inverter voltage, the D axis component IdOutfeedback of the current output current, the Q axis component IqOutfeedback of the current output current, the D axis component Idinv of the current inverter current, and the D axis component Iqinv of the current inverter current. Then, input the above components into Figure 7 the loop shown in the figure to calculate the duty cycle PwmOut, and control the operation of the switching tubes in the inverter module 12 based on the duty cycle PwmOut, so as to adjust the voltage amplitude of the alternating current of the inverter module 12.

[0031] Step S12: Set a first reference voltage value regarding the high-voltage bus side according to the rated electrical parameters of the energy storage system, the electrical parameters of the battery at the current moment connected to the slave machine 20, and the electrical parameters of the host machine 10 at the current moment.

[0032] The rated electrical parameters of the energy storage system refer to the standard electrical parameters calibrated during the design of the energy storage system. Specifically, the rated electrical parameters of the energy storage system include the voltage peak value of the power grid 30 or the rated output voltage peak value of the energy storage system.

[0033] The electrical parameters of the battery at the current moment connected to the slave machine 20 refer to the electrical parameters of the battery 40 connected to the DCDC module at the current moment, such as including the voltage value of the battery 40 when the energy storage system switches from the off-grid working mode to the grid-connected working mode.

[0034] The electrical parameters of the host machine 10 at the current moment refer to the electrical parameters of the host machine 10 at the current moment, such as including the voltage ripple value of the inverter capacitor C3 of the inverter module 12, the current value of the inverter inductor L3 of the inverter module 12, the period of the switching tubes of the inverter module 12 when the energy storage system switches from the off-grid working mode to the grid-connected working mode, the capacitance value of the inverter capacitor C3 of the inverter module 12, and the turns ratio of the transformer T1 of the resonant conversion module 11. The turns ratio of the transformer T1 of the resonant conversion module 11 is the ratio between the number of turns of the primary winding and the number of turns of the secondary winding.

[0035] The first reference voltage value is the target voltage value of the high-voltage bus of the inverter module 12.

[0036] Step S13: Control the grid-connected loop of the host 10 according to the first reference voltage value to obtain the duty cycle of the switching tubes of the inverter module 12.

[0037] After obtaining the first reference voltage value and closing the control relay RY1, input the first reference voltage value into the grid-connected loop of the host 10, and obtain the duty cycle of the switching tubes of the inverter module 12. Control the switching tubes of the inverter module 12 to operate based on this duty cycle, so that the target voltage value on the high-voltage bus side reaches the first reference voltage value. It can be understood that after the relay RY1 is closed, the energy flows from the power grid 30 to the battery 40. If the relay RY2 is also closed, the energy also flows from the power grid 30 to the load 50.

[0038] Step S14: Set a second reference voltage value regarding the low-voltage bus side according to the electrical parameters of the battery at the current moment when the slave 20 is connected, and control the grid-connected loop of the slave 20 according to the second reference voltage value to obtain the duty cycle of the switching tubes of the DCDC module 21.

[0039] Specifically, after the host 10 enters the grid-connected loop, it can notify the slave 20 to enter the grid-connected loop through the communication bus. The second reference voltage value is the target voltage value on the low-voltage bus side. After obtaining the second reference voltage value, input the second reference voltage value into the grid-connected loop of the slave 20, and obtain the duty cycle of the switching tubes of the inverter module 12. Control the switching tubes of the inverter module 12 to operate based on this duty cycle, so that the target voltage value on the low-voltage bus side reaches the first reference voltage value.

[0040] Step S15: Gradually soft-start the power on the low-voltage bus side to the battery demand power, and soft-start the power on the high-voltage bus side to the preset power according to the first reference voltage value, the voltage value on the high-voltage bus side, and the battery demand power, where the ratio of the first reference voltage value to the transformer turns ratio of the resonant conversion module 11 is greater than the second reference voltage value.

[0041] The battery demand power refers to Figure 2The power value that the medium battery 40 expects to receive from the low-voltage bus side. It can be understood that after the host 10 and the slave 20 enter the grid-connected loop, if the input power of the power grid 30 (i.e., the power of the alternating current between the input terminal GRIDL1 and the input terminal GRIDN1) is less than the battery demand power (corresponding to the demand power of the DCDC module 21), it indicates that the power provided by the power grid 30 is insufficient to meet the power that the battery 40 expects to receive, resulting in the voltage of the high-voltage bus being pulled down and an undervoltage phenomenon occurring; since the slave 20 adopts a buck and voltage-limiting control loop and cannot control the bus voltage to stabilize at a certain specific value, if the input power of the power grid 30 is infinitely large, it will cause the bus voltage to get out of control. To avoid the above situation, in this embodiment, a soft start operation is performed on the power of the high-voltage bus side and the power of the low-voltage bus side, that is, step S15 is executed, and by gradually increasing the power of the low-voltage bus side and the power of the high-voltage bus side, the two respectively reach the corresponding target powers.

[0042] In this embodiment, by detecting electrical parameters such as the frequency, amplitude, and phase of the power grid 30 in real time and setting multiple conditional judgments, it is ensured that the energy storage system is controlled to switch to the grid-connected working mode only when the electrical parameters of the power grid 30 meet the conditions, reducing electrical shocks and improving the safety and stability of the energy storage system during operation. In addition, when the energy storage system switches from the off-grid working mode to the grid-connected working mode, the voltage reference values of the high-voltage bus side and the low-voltage bus side are dynamically set, so that after the energy storage system enters the grid-connected working mode, it can respond to the changes of the power grid and the battery in real time, adapt to the requirements of multiple working conditions, improve the flexibility of the control method, and after the host and the slave enter the grid-connected loop, the power of the high-voltage bus side and the low-voltage bus side is gradually adjusted to ensure reasonable power distribution, reduce abnormal situations such as undervoltage or out-of-control of the high-voltage bus, and improve the stability and safety of the energy storage system during operation.

[0043] In some of these embodiments, when the energy storage system is controlled to enter the grid-connected working mode from the off-grid working mode, a first reference voltage value is determined as: ; And, ; ; A second reference voltage value is determined as: ; And, ; Wherein, is the voltage value of the battery at the moment when the energy storage system enters the grid-connected working mode from the off-grid working mode, is the first set threshold, is the peak voltage of the power grid 30 or the peak rated output voltage of the energy storage system, is the voltage ripple value of the inverter capacitor C3 of the inverter module 12, is the current value of the inverter inductor L3 of the inverter module 12, is the period of the switching tube of the inverter module 12 when the energy storage system enters the grid-connected working mode from the off-grid working mode, is the capacitance value of the inverter capacitor C3 of the inverter module 12, is the second set threshold, is the peak voltage of the power grid 30, is the turns ratio of the transformer T1 of the resonant conversion module 11.

[0044] When setting the first set threshold and the second set threshold, they can be set according to the above relationship. Specifically, the first set threshold can be set to 8V and the second set threshold can be set to 2V.

[0045] In this embodiment, the first set threshold is introduced into the first reference voltage value formula, and redundant calculation of the first reference voltage value is added to the voltage value of the battery, and it is ensured that the bus voltage at the moment of grid connection is higher than the sum of the peak voltage of the power grid and the voltage ripple value of the inverter capacitor C3, avoiding the out-of-control of the bus voltage caused by voltage fluctuations and improving the working stability of the energy storage system; the second set threshold is introduced into the second reference voltage value formula, and redundant calculation of the second reference voltage value is added to the voltage value of the battery, and the bus voltage after grid connection is higher than to avoid overvoltage of the bus voltage after grid connection due to load mutation or power grid fluctuation, protecting key devices such as the inverter module 12 from high-voltage impact. Set can achieve: first establish the inverter voltage and then connect to the power grid, ensure that the voltage on the high-voltage bus side reaches the set voltage, and ensure that the voltage difference between the power grid voltage and the inverter voltage is small. In this way, the peak current is small when closing the relay, and the damage to the relay is small. At the same time, for the setting of the first reference voltage value and the second reference voltage value, it can meet a certain voltage energy on the high-voltage bus side and also avoid the low-voltage bus side from pumping out the high-voltage bus side.

[0046] In some of these embodiments, step S13 includes the following steps S131 to S134.

[0047] Step S131: Input the first reference voltage value and the voltage value of the high-voltage bus side into the bus voltage outer loop to obtain the first reference value of the inverter inductor current inner loop.

[0048] The bus voltage outer loop can adopt a PI control loop. The voltage value of the high-voltage bus side is the voltage sampling value of the high-voltage bus side. Specifically, refer to Figure 8, the difference between the first reference voltage value \(V_{BUS\_Ref}\) and the sampled voltage value \(V_{BUS\_FB}\) of the high-voltage bus side can be calculated first. After obtaining the difference between the two, the difference is input to the outer loop of the bus voltage to obtain the first reference value. If the sampled voltage value \(V_{BUS\_FB}\) of the high-voltage bus side during the PI control process is greater than 110% of the first reference voltage value \(V_{BUS\_Ref}\), then the relay RY1 remains closed at this time, and the battery 40 discharges. It can supply power to the load 50 through the power grid 30 to avoid damage to the device due to excessive high-voltage bus voltage. If the voltage value \(V_{BUS\_FB}\) of the high-voltage bus side is less than the first reference voltage value \(V_{BUS\_Ref}\), the first reference value is calculated through the following formula: ; where, is the first reference value, is the battery demand power, is the voltage value of the power grid 30.

[0049] Step S132: Filter the first reference value to obtain the filtered first reference value.

[0050] Then, the first reference value is input to the filter for filtering to obtain the filtered first reference value. In the Figure 8 illustrated embodiment, the filter can use a double-frequency power ripple notch filter to filter the first reference value, thereby filtering out the double-frequency power ripple interference superimposed on the bus voltage and avoiding the influence of the bus voltage ripple on the inner loop current reference. In practical applications, other suitable filters can be used to filter the first reference value.

[0051] For the double-frequency power ripple notch filter, its transfer function is as follows: ; where, is the notch width, with the unit of rad / s, is the notch center frequency, with the unit of rad / s.

[0052] Taking the double-frequency power as an example, , the bandwidth frequency is set to 20 Hz, , the switching frequency is set to 20 kHz, and substituting into the above data through bilinear transformation can obtain: ; Its corresponding Bode plot is Figure 9 as shown.

[0053] Step S133: Input the current value of the inverter inductor and the filtered first reference value into the inner loop of the inverter inductor current and the compensation loop to obtain the double-loop output value and the compensation loop output value.

[0054] The current value of the inverter inductor L3 is the current sampling value flowing through the inverter inductor L3. Refer to Figure 8 , after obtaining the filtered first reference value I_INV_Ref, subtract it from the current value I_INV_FB of the inverter inductor L3. After obtaining the difference, input the difference into the inner loop of the inverter inductor current to obtain the double-loop output value, and input the difference into the compensation loop to obtain the compensation loop output value.

[0055] The inner loop of the inverter inductor current can adopt a PI control loop. The compensation loop can adopt a repetitive controller for reducing the 3rd harmonic, 5th harmonic, and 7th harmonic of the current. The repetitive controller adopts the control algorithm in the prior art.

[0056] Step S134: Sum the double-loop output value, the compensation loop output value, and the voltage value of the power grid 30 to obtain the duty cycle of the first switch of the inverter module 12.

[0057] The voltage value of the power grid 30 is the voltage sampling value of the power grid 30. The first switch of the inverter module 12 includes Figure 4 the inverter high-frequency transistors Q13 and Q15, and the inverter power-frequency transistors Q14 and Q16 in Figure 8 , input the double-loop output value, the compensation loop output value, and the voltage value V_Grid of the power grid 30 into an adder, so as to obtain the duty cycle INV_PWM of the above-mentioned switching transistors of the inverter module 12.

[0058] In this embodiment, by controlling the inverter module 12 through the above grid connection loop, the high-voltage bus side can reach the first reference voltage value.

[0059] In some of these embodiments, step S14: Control the grid connection loop of the slave machine 20 according to the second reference voltage value to obtain the duty cycle of the switching transistors of the DCDC module 21, including the following steps S141 to S144.

[0060] Step S141: Input the second reference voltage value and the voltage value of the low-voltage bus side into the first buck voltage-limiting outer loop to obtain the second reference value of the inner loop of the first buck inductor current.

[0061] The first buck voltage-limiting outer loop can adopt a PI control loop. The voltage value of the low-voltage bus side is the voltage sampling value of the low-voltage bus side. Specifically, refer to Figure 10, the second reference voltage value Vbus_ref can be subtracted from the voltage value Vbus_real_1 on the low-voltage bus side. After obtaining the difference between the two, the difference is input to the first buck voltage-limiting outer loop, and the first buck voltage-limiting outer loop outputs the second reference value Iinductor_ref_1. When the voltage value Vbus_real_1 on the low-voltage side bus is greater than the second reference voltage value Vbus_ref, the second reference value Iinductor_ref_1 is the actual required current. When the voltage value Vbus_real_1 on the low-voltage side bus is less than the second reference voltage value Vbus_ref, the second reference value Iinductor_ref_1 is output through the above method.

[0062] Step S142: Input the current value of the first buck inductor and the second reference value into the first buck inductor current inner loop to obtain the duty cycle of the switching tube of one of the buck loops of the interleaved parallel DCDC module 21.

[0063] The current value of the first buck inductor is the current sampling value of the buck-boost inductor L1. The first buck inductor current inner loop can adopt a PI control loop. Refer to Figure 10 , the second reference value Iinductor_ref_1 can be subtracted from the current value Iinductor_real_1 of the first buck inductor. After obtaining the difference between the two, the difference is input to the first buck inductor current inner loop, and the first buck inductor current inner loop outputs Figure 2 the duty cycle PwmOut_1 of the switching tube Q1 in

[0064] Step S143: Input the second reference voltage value and the voltage value on the low-voltage bus side into the second buck voltage-limiting outer loop to obtain the third reference value of the second buck inductor current inner loop.

[0065] The second buck voltage-limiting outer loop can adopt a PI control loop. Specifically, refer to Figure 10 , the second reference voltage value Vbus_ref can be subtracted from the sampled voltage value Vbus_real_2 on the low-voltage bus side. After obtaining the difference between the two, the difference is input to the second buck voltage-limiting outer loop, and the second buck voltage-limiting outer loop outputs the second reference value Iinductor_ref_2. The voltage value Vbus_real_2 on the low-voltage bus side and the voltage value Vbus_real_1 on the low-voltage bus side can be the same sampling value.

[0066] Step S144: Input the current value of the second buck inductor and the third reference value into the second buck inductor current inner loop to obtain the duty cycle of the switching tube of the other buck loop of the interleaved parallel DCDC module 21.

[0067] The current value of the second buck inductor is the current sampling value of the buck-boost inductor L2. The second buck inductor current inner loop can adopt a PI control loop. Refer to Figure 10 , first, the difference between the third reference value Iinductor_ref_2 and the current value Iinductor_real_2 of the second buck inductor can be obtained. After getting the difference between the two, the difference between the two is input into the second buck inductor current inner loop, and the second buck inductor current inner loop outputs Figure 2 the duty cycle PwmOut_2 of the switching transistor Q3 in

[0068] In this embodiment, by controlling the DCDC module 21 through the above grid-connected loop, the low-voltage bus side can reach the second reference voltage value.

[0069] In some of these embodiments, step S15: Soft-start the power of the high-voltage bus side to a preset power according to the first reference voltage value, the voltage value of the high-voltage bus side, and the required power of the battery, including the following steps S151 to step S153. Step S151: Obtain the difference between the first reference voltage value and the voltage value of the high-voltage bus side. Step S152: Input the difference into an integrator to obtain a power compensation value. Step S153: Sum the required power of the battery and the power compensation value to obtain the preset power, and soft-start the power of the high-voltage bus side to the preset power.

[0070] It should be noted that, for example, only the energy corresponding to 1A is allowed to flow into the inverter input. However, there is an efficiency difference in each topology. If only 1A of energy is allowed to flow in, it is impossible to maintain the bus voltage at this time. Therefore, a reasonable power needs to be compensated to maintain the stability of the bus voltage and ensure that the battery can obtain 1A of energy. During the implementation of step S15, it is necessary to ensure that the high-voltage side will not be emptied by the low-voltage side and that the high-voltage side will not be overvoltage.

[0071] The voltage value of the high-voltage bus side is the voltage sampling value of the high-voltage bus side. Refer to Figure 11 , the difference between the first reference voltage value V_BUS_Ref and the voltage value VHbus of the high-voltage bus side can be obtained. Then, the difference is input into the integrator of the PI controller to obtain the power compensation value ChargePowerComp; then, the power compensation value ChargePowerComp and the required power ChargePower of the battery are summed to obtain the preset power FinalChargePower, and the power of the high-voltage bus side is gradually increased with the preset power FinalChargePower as the target.

[0072] In this embodiment, the preset power can be determined in the above manner.

[0073] In some of these embodiments, the control method of the energy storage system further includes: Step S20: When the energy storage system is in the grid-connected operation mode, determine whether the power grid 30 loses power according to the electrical parameters of the power grid 30. When the power grid 30 loses power, control the energy storage system to enter the off-grid operation mode.

[0074] The electrical parameters of the power grid 30 include the instantaneous voltage value of the alternating current of the power grid 30, the actual frequency of the alternating current of the power grid 30, and the voltage of the alternating current of the power grid 30.

[0075] Specifically, if the electrical parameters of the power grid 30 meet any one of the following three conditions, it is determined that the power grid 30 loses power; if the electrical parameters of the power grid 30 do not meet the following three conditions, it is determined that the power grid 30 does not lose power, and continue to control the energy storage system to be in the grid-connected operation mode. Condition 1 is that the fluctuation amplitude of the instantaneous voltage value of the alternating current of the power grid 30 is greater than or equal to a preset amplitude and the duration is greater than or equal to a second preset time. Among them, the fluctuation amplitude of the instantaneous voltage value of the alternating current of the power grid 30 is the degree of change of the instantaneous voltage value relative to the standard value (such as the rated voltage of 220V), and the preset amplitude can be 28%, that is, Condition 1 is that the instantaneous voltage value of the alternating current of the power grid 30 is greater than or equal to 28% of the standard value, and the duration of the instantaneous voltage value of the alternating current of the power grid 30 being greater than or equal to 28% of the standard value is greater than or equal to the second preset time; the second preset time can be 3ms. Condition 2 is that the absolute value of the difference between the actual frequency of the alternating current of the power grid 30 and the frequency of the alternating current of the power grid 30 is greater than a preset frequency difference and the duration is greater than or equal to a third preset time. Among them, the preset frequency difference can be 3Hz and the third preset time is 1s. Condition 3 is that the voltage of the alternating current of the power grid 30 is greater than or equal to a preset range and the duration is greater than or equal to a fourth preset time. The preset range can be the rated voltage range of the alternating current of the power grid 30, and the fourth preset time is 1s.

[0076] When the power grid 30 loses power, the host 10 enters the off-grid operation mode, and notifies the slave 20 to enter the off-grid operation mode. The high-voltage side of the resonant conversion module 11 stops outputting the pulse width modulation signal to the secondary side switching tube, that is, controls the secondary side switching tube of the resonant conversion module 11 to turn off, to avoid energy accumulation on the low-voltage side bus, resulting in overvoltage of the low-voltage side bus. If the voltage of the low-voltage side bus suddenly rises, the slave 20 controls the DCDC module 21 to stop outputting the pulse width modulation signal to the switching tube in the DCDC module 21, that is, controls the switching tube in the DCDC module 21 to turn off, to prevent the system from being damaged by overvoltage due to energy accumulation.

[0077] Among them, when the energy storage system is controlled to enter the off-grid operation mode from the grid-connected operation mode, determine the first reference voltage value as: ; Determine the second reference voltage value is: ; is the voltage value of the battery when the energy storage system enters the off-grid working mode from the grid-connected working mode, is the first set threshold, is the second set threshold, is the turns ratio of the transformer T1 of the resonant conversion module 11.

[0078] When setting the first set threshold and the second set threshold, they can be set according to the above relationship. Specifically, , the first set threshold can be set to 8V and the second set threshold can be set to 2V.

[0079] In some embodiments, the control method of the energy storage system further includes step S30: when the energy storage system is in a static state, judge whether the grid connection condition is satisfied according to the electrical parameters of the power grid 30. When the grid connection condition is satisfied, start the host 10 and the slave 20, and control the energy storage system to enter the grid-connected working mode.

[0080] The energy storage system being in a static state means that the energy storage system is in a low-power standby mode, that is, both the host 10 and the slave 20 are in a sleep or shutdown state, and only the electrical parameters of the power grid 30 are detected in real time through the hardware circuit or low-power software, and it is judged whether the grid connection condition is satisfied.

[0081] When judging whether the power grid 30 meets the grid connection condition, the host 10 can first detect the power grid 30 to determine whether there is input power to the power grid 30. When there is input power, determine whether the frequency and amplitude of the power grid 30 meet the grid connection condition. If so, start the host 10 and the slave 20, and control the energy storage system to enter the grid-connected working mode. If not, continue to control the energy storage system to be in a static state. The specific judgment steps can refer to step S10 and will not be elaborated here.

[0082] Among them, for step S30, starting the host 10 and the slave 20 includes the following steps S31 to S33.

[0083] Among them, step S31: Start the slave: Control the boost loop of the DCDC module 21 according to the PI loop control principle, and adjust the voltage value on the low-voltage bus side to the third reference voltage value on the low-voltage bus side to complete the startup of the DCDC module 21.

[0084] The voltage value on the low-voltage bus side is the voltage sampling value on the low-voltage bus side. Specifically, refer to Figure 12, the reference value Vout1_ref is subtracted from the sampled value Vout1_real to obtain the difference between the two. The difference is input into the first PI controller to obtain the duty cycle PwmOut1 of the switching transistor Q2 in one of the boost loops, and the switching transistor Q2 is controlled to operate based on this duty cycle PwmOut1. At the same time, the reference value Vout2_ref is subtracted from the sampled value Vout2_real to obtain the difference between the two. The difference is input into the second PI controller to obtain the duty cycle PwmOut2 of the switching transistor Q4 in the other boost loop, and the switching transistor Q4 is controlled to operate based on this duty cycle PwmOut2. Among them, both the reference value Vout1_ref and the reference value Vout2_ref are the third reference voltage values; both the sampled value Vout1_real and the sampled value Vout2_real are the voltage values on the low-voltage bus side; the first PI controller and the second PI controller refer to the controllers that achieve the dynamic regulation of the voltage on the low-voltage bus side through the combination of the proportional and integral links.

[0085] Among them, the third reference voltage value is determined as follows: Calculate the difference between the duty cycle of the switching transistor in one of the boost loops of the interleaved parallel DCDC module 21 and take the ratio between the voltage of the battery and the difference as the third reference voltage value , and make the product of the third reference voltage value and the transformer turns ratio of the resonant conversion module 11 greater than the voltage peak of the power grid 30, or make the product of the third reference voltage value and the transformer turns ratio of the resonant conversion module 11 greater than the rated output voltage peak of the energy storage system.

[0086] That is: ; ; The duty cycle of the switching transistor in one of the boost loops is the duty cycle of the switching transistor Q2 or the switching transistor Q4.

[0087] Among them, step S32: Soft-start the resonant conversion module of the host: Gradually adjust the duty cycles of the primary switching transistor and the secondary switching transistor of the resonant conversion module 11 to adjust the voltage value on the high-voltage bus side to the rated output voltage peak of the energy storage system.

[0088] The rated output voltage peak of the energy storage system is the product of the rated voltage of the energy storage system and 1.414. Specifically, first soft-start the wave to the primary switching transistor of the resonant conversion module 11, so that the energy gradually increases the high-voltage side bus voltage through the transformer T1 until the voltage value on the high-voltage side bus is adjusted to the rated output voltage peak of the energy storage system.

[0089] Step S33: Soft-start the inverter module of the host: Gradually adjust the inverter voltage value of the inverter module 12 to the preset grid voltage value of the power grid 30.

[0090] The preset grid voltage value refers to the target voltage value of the inverter module of the energy storage system during the soft start process. Specifically, start the soft start operation of the inverter module 12 until the electrical parameters simultaneously meet Condition Four and Condition Five. Condition Four is that the absolute value of the difference between the effective value of the inverter voltage and the effective value of the voltage of the power grid 30 is less than the fourth preset voltage value, and the fourth preset voltage value is 10% of the effective value of the voltage of the power grid 30; Condition Five is that the absolute value of the difference between the instantaneous value of the inverter voltage and the instantaneous value of the voltage of the power grid 30 is less than the fifth preset voltage value, and the fifth preset voltage value is 10% of the instantaneous value of the voltage of the power grid 30. Then, by adjusting the duty cycle of each switching tube in the inverter module 12, with the instantaneous voltage value of the power grid 30 as the target inverter voltage value, variable step soft start is carried out in sub-adjustment stages. For example, first adjust the inverter voltage to reach half of the preset grid voltage value at a slope of increasing by 10V per 1ms, and then adjust the inverter voltage across the inverter capacitor C3 to reach the preset grid voltage value at a slope of increasing by 20V per 1ms. Among them, the inverter voltage refers to the voltage across the inverter capacitor C3 of the inverter module 12, and the voltage of the power grid 30 refers to the voltage between the input port GRIDL1 and the input port GRIDN1.

[0091] Among them, for step S30, after the soft start of the inverter module 12 is completed, control the energy storage system to enter the grid-connected working mode. The process of entering the grid-connected working mode is the same as the aforementioned steps S11 to S15, and will not be elaborated here.

[0092] In some of the embodiments, for step S32: Gradually adjust the duty cycle of the primary side switching tube of the resonant conversion module 11, including the following steps S321 to S323.

[0093] Step S321: Divide the range from the primary side initial duty cycle to the primary side soft start target duty cycle into multiple primary side duty cycle adjustment stages, and obtain the stage target duty cycle of each primary side duty cycle adjustment stage.

[0094] The primary side initial duty cycle refers to the conduction duty cycle of the primary side switching tube at the initial moment of adjustment, which can be the minimum conduction duty cycle among the primary side switching tube Q5, the primary side switching tube Q6, the primary side switching tube Q7, and the primary side switching tube Q8.

[0095] The primary side soft start target duty cycle refers to the target conduction duty cycle of the primary side switching tube. First, based on the voltage on the low-voltage bus side, the voltage on the high-voltage bus side, and the output power of the resonant conversion module, confirm the inductance value of the resonant inductor Lr 、the capacitance value of the resonant capacitor Cr and the inductance value of the exciting inductor Lm , then, calculate the resonant frequency of the resonant conversion module 11 according to the following formula : ; Then, the switching frequency of the resonant conversion module 11 needs to satisfy the following relational expression: ; Wherein, is the maximum supported frequency of each switching tube in the resonant conversion module 11, that is, the maximum switching frequency allowed for the primary switching tube Q5, the primary switching tube Q6, the primary switching tube Q7, the primary switching tube Q8, the secondary switching tube Q9, the secondary switching tube Q10, the secondary switching tube Q11 and the secondary switching tube Q12. After determining the switching frequency , an oscilloscope can be used to determine the primary soft-start target duty cycle. It can be understood that the primary soft-start target duty cycle needs to be ensured to be less than 50% to ensure that there is sufficient dead time between the primary switching tubes Q5, Q6, Q7, and Q8. It can be adjusted according to the resonant current to ensure that the primary switching tube is turned off when the resonant current flowing through the resonant inductor Lr is 0.

[0096] Specifically, as Figure 13 shown, at time1, the resonant current flowing through the resonant inductor Lr is 0, but at this time the primary switching tube Q5 is not turned off. At this time, the deviation between the primary soft-start target duty cycle and the current duty cycle of the primary switching tube Q5 is the duty cycle deviation , so it is necessary to obtain the primary soft-start target duty cycle based on the duty cycle deviation , such as calculating the primary soft-start target duty cycle through the following formula: ; ; Wherein, is the primary soft-start target duty cycle, is the compensation duty cycle, is the switching frequency, is the current duty cycle of the primary switching tube Q5. When the current duty cycle of the primary switching tube Q5 reaches the primary soft-start target duty cycle, as Figure 14 shown, at time2, the resonant current flowing through the resonant inductor Lr is 0, and the primary switching tube Q5 has been turned off.

[0097] Similarly, the secondary soft-start target duty cycle is also determined according to the above process, and the method is the same, so it will not be elaborated here.

[0098] In a specific embodiment, for step S321, the original edge initial duty ratio to the original edge soft start target duty ratio range is divided into multiple original edge duty ratio adjustment stages, including: Step S3211: Set the current original edge duty ratio to one-fourth of the original edge soft start target duty ratio as the first original edge duty ratio adjustment stage; Step S3212: Set one-fourth of the original edge soft start target duty ratio to one-half of the original edge soft start target duty ratio as the second original edge duty ratio adjustment stage; Step S3213: Set one-half of the original edge soft start target duty ratio to the first preset duty ratio value as the third original edge duty ratio adjustment stage; Step S3214: Set the first preset duty ratio value to the original edge soft start target duty ratio as the fourth original edge duty ratio adjustment stage, where the first preset duty ratio value is the difference between the original edge soft start target duty ratio and the first preset threshold, the first preset threshold is greater than 0, and the first preset threshold is less than one-half of the original edge soft start target duty ratio.

[0099] Understandably, the stage target duty ratio of the first original edge duty ratio adjustment stage is one-fourth of the original edge soft start target duty ratio, and the stage target duty ratio of the second original edge duty ratio adjustment stage is one-half of the original edge soft start target duty ratio, and the stage target duty ratio of the third original edge duty ratio adjustment stage is the first preset duty ratio value, and the stage target duty ratio of the fourth original edge duty ratio adjustment stage is the original edge soft start target duty ratio.

[0100] In a specific embodiment, the first preset threshold is 10, and the duty ratio is adjusted with the original edge initial duty ratio as the initial value.

[0101] It should be noted that the purpose of performing duty ratio soft start in stages is as follows: Magnetic components such as the magnetic inductance of the resonant cavity may be affected by temperature, the magnitude of the current passing through the magnetic component (DC bias), etc., which may cause the actual inductance to decrease, thereby reducing the impedance of the resonant cavity and resulting in an instantaneous excessive current peak of the resonant inductor of the resonant cavity, that is, it may cause problems such as damage to the switching tube and inductor saturation. Therefore, by gradually adjusting the duty ratio in stages, the purpose of gradually increasing the current of the magnetic inductance or the current passing through the switching tube can be achieved to reduce the risk of damage to circuit components.

[0102] Step S322: According to the maximum resonant current peak of the resonant conversion module, the set effective voltage value of the low-voltage bus side for soft start, and the stage target duty ratio of each original edge duty ratio adjustment stage, set the duty ratio step size of each original edge duty ratio adjustment stage.

[0103] Among them, the impedance of the resonant cavity of the resonant conversion module 11 can be calculated according to the following formula: ; ; Among them, is the inductance value of the resonant inductor Lr, is the capacitance value of the resonant capacitor Cr, is the switching angular frequency, is the switching frequency of the resonant conversion module 11.

[0104] Among them, the peak value of the conduction current of the primary switching tube in the th primary duty ratio adjustment stage is calculated by the following formula: ; ; Among them, represents the th primary duty ratio adjustment stage, is the effective value of the voltage on the low-voltage bus side set for soft start, is the target duty ratio of the th primary duty ratio adjustment stage, is the voltage value across the resonant inductor of the resonant cavity at the start of the th primary duty ratio adjustment stage, is the peak value of the conduction current of the primary switching tube in the th primary duty ratio adjustment stage.

[0105] Among them, for the step size of the th primary duty ratio adjustment stage is:

[0106] It can be understood that the maximum value of the step size of the th primary duty ratio adjustment stage is .

[0107] It should be noted that during the soft start of the primary duty ratio, the high-voltage bus side capacitor CHbus on the secondary side is charged by the primary side, so the voltage on the high-voltage bus side will gradually increase. Generally, the change of the voltage on the high-voltage bus side is as follows Figure 15 shown. In the early stage of duty ratio adjustment, the voltage change slope on the high-voltage bus side is relatively large, that is, the voltage on the high-voltage bus side increases relatively large. Therefore, the step size of duty ratio adjustment cannot be too large to prevent the resonant inductor current from being too large; in the later stage of duty ratio adjustment, the voltage change on the high-voltage bus side is gentle, that is, the voltage on the high-voltage bus side increases relatively small. At this time, the adjustment step size can be larger than that in the early stage. For the primary duty ratio adjustment stage, there is a specific The maximum value, maximum value is determined by; since during the adjustment process of multiple primary duty cycles it is continuously increasing, then is gradually increasing, and then is increasing step by step. Therefore, in the subsequent stage will be larger than that in the previous stage Hence, in the subsequent stage the maximum value of will be larger than that in the previous stage The maximum value of, and the step size selection will become larger and larger.

[0108] Step S323: According to the duty cycle step size and the preset cumulative duration of each primary duty cycle adjustment stage, complete the soft start of the duty cycle for each adjustment stage until the duty cycle of the primary side switch tube reaches the primary side soft start target duty cycle.

[0109] According to step S322, it can be known that the designed The limited step size takes into account the protection of the circuit devices of the resonant module, and in multiple primary duty cycle adjustment stages, the maximum value of the duty cycle adjustment step size in the later stage is larger. In order to accelerate the soft start process of the duty cycle to improve efficiency. Thus, when selecting the duty cycle adjustment step size for each primary duty cycle adjustment stage, Limit the maximum value of each primary duty cycle adjustment stage to protect the circuit devices, and the step size of the duty cycle in the subsequent primary duty cycle adjustment stage can be set to be larger than the step size of the duty cycle in the previous primary duty cycle adjustment stage , so as to accelerate the duty cycle adjustment speed.

[0110] For example, the first preset threshold is 10, and the duty cycle is adjusted with the initial primary duty cycle as the initial value. In the first primary duty cycle adjustment stage, the step size is 1, and the preset cumulative duration is 2 ms to adjust the initial primary duty cycle to the stage target duty cycle , that is, in the first primary duty cycle adjustment stage, the duty cycle is adjusted with an increment of 1 every 2 ms until the primary duty cycle is adjusted to the stage target duty cycle ; in the second primary duty cycle adjustment stage, the step size is 2, and the preset cumulative duration is 1 ms to adjust the stage target duty cycle to the stage target duty cycle , that is, in the second primary duty cycle adjustment stage, the duty cycle is adjusted with an increment of 2 every 1 ms until the stage target duty cycle is adjusted to the stage target duty cycle ; in the third primary duty cycle adjustment stage, the step size is 5, and the preset cumulative duration is 1 ms. The duty ratio of the stage target is adjusted to the duty ratio of the stage target , that is, in the third primary-side duty ratio adjustment stage, the duty ratio is adjusted every 1 ms with an increment of 5 until the duty ratio of the stage target is adjusted to the duty ratio of the stage target ; in the fourth primary-side duty ratio adjustment stage, the step size needs to be set to a value less than the first preset threshold, and the duty ratio of the stage target is adjusted to the primary-side soft-start target duty ratio.

[0111] Compared with the soft-start scheme of the duty ratio of the primary-side switch tube using a fixed step size, the soft-start efficiency is slow, and if the set fixed step size is too large, the large change in the duty ratio of the switch tube will cause the inductor current of the resonant network of the resonant conversion module to get out of control, resulting in problems such as damage to the switch tube and inductor saturation. In this embodiment, by dynamically adjusting the duty ratio step size in stages and differentially designing the step size and adjustment interval in each primary-side duty ratio adjustment stage, the soft-start time is reduced, the soft-start efficiency is improved, and by setting the step size with multiple parameters, the phenomenon of out-of-control inductor current of the resonant network can be avoided, and the working safety of the energy storage system is improved.

[0112] In some embodiments, for step S32: gradually adjust the duty ratio of the secondary-side switch tube of the resonant conversion module 11, including the following steps S324 to S326.

[0113] Step S324: Divide the range from the secondary-side initial duty ratio to the secondary-side soft-start target duty ratio into multiple secondary-side duty ratio adjustment stages, and obtain the stage target duty ratio of each secondary-side duty ratio adjustment stage.

[0114] The secondary-side initial duty ratio refers to the duty ratio of the secondary-side switch tube at the initial moment of adjustment, which can be the minimum conduction duty ratio among the secondary-side switch tube Q9, the secondary-side switch tube Q10, the secondary-side switch tube Q11, and the secondary-side switch tube Q12.

[0115] The secondary-side soft-start target duty ratio refers to the target conduction duty ratio of the secondary-side switch tube. The specific determination process can refer to the determination process of the secondary-side soft-start target duty ratio, which will not be elaborated here.

[0116] In a specific embodiment, for step S321, dividing the range from the secondary-side initial duty ratio to the secondary-side soft-start target duty ratio into multiple secondary-side duty ratio adjustment stages includes: Step S3211: Set the current secondary-side duty cycle to one-fourth of the secondary-side soft-start target duty cycle as the first secondary-side duty cycle adjustment stage; Step S3212: Set the range from one-fourth of the secondary-side soft-start target duty cycle to one-half of the secondary-side soft-start target duty cycle as the second secondary-side duty cycle adjustment stage; Step S3213: Set the range from one-half of the secondary-side soft-start target duty cycle to the second preset duty ratio value as the third secondary-side duty cycle adjustment stage; Step S3214: Set the range from the second preset duty ratio value to the secondary-side soft-start target duty cycle as the fourth secondary-side duty cycle adjustment stage, where the second preset duty ratio value is the difference between the secondary-side soft-start target duty cycle and the second preset threshold, the second preset threshold is greater than 0 and less than one-half of the secondary-side soft-start target duty cycle.

[0117] Understandably, the stage target duty cycle of the first secondary-side duty cycle adjustment stage is one-fourth of the secondary-side soft-start target duty cycle, the stage target duty cycle of the second secondary-side duty cycle adjustment stage is one-half of the secondary-side soft-start target duty cycle, the stage target duty cycle of the third secondary-side duty cycle adjustment stage is the second preset duty ratio value, and the stage target duty cycle of the fourth secondary-side duty cycle adjustment stage is the secondary-side soft-start target duty cycle.

[0118] In a specific embodiment, the first preset threshold is 10, and the duty cycle is adjusted with the secondary-side initial duty cycle as the initial value.

[0119] It should be noted that the purpose of performing duty cycle soft start in stages is as follows: Magnetic components such as the magnetic inductance of the resonant cavity may be affected by temperature, the magnitude of the current passing through the magnetic component (DC bias), etc., which may cause the actual inductance to decrease, thereby reducing the impedance of the resonant cavity and causing the current peak value of the resonant inductor of the resonant cavity to be instantaneously too large. That is, it may cause problems such as damage to the switching tube and inductor saturation. Therefore, by gradually adjusting the duty cycle in stages, the purpose of gradually increasing the current of the magnetic inductance or the current passing through the switching tube can be achieved to reduce the risk of damage to circuit components.

[0120] Step S325: Set the duty cycle step size of each secondary-side duty cycle adjustment stage according to the maximum resonant current peak value of the resonant conversion module, the set effective value of the voltage on the high-voltage bus side for soft start, and the stage target duty cycle of each secondary-side duty cycle adjustment stage.

[0121] Among them, the impedance of the resonant cavity of the resonant conversion module 11 can be calculated according to the following formula: ; ; Among them, is the inductance value of the resonant inductor Lr, is the capacitance value of the resonant capacitor Cr, is the switching angular frequency, is the switching frequency of the resonant conversion module 11.

[0122] Among them, the peak value of the conduction current of the secondary side switching tube in the th secondary side duty ratio adjustment stage is calculated by the following formula: ; ; Among them, represents the th secondary side duty ratio adjustment stage, is the effective value of the voltage on the high-voltage bus side set for soft start, is the target duty ratio of the th secondary side duty ratio adjustment stage, is the voltage value across the resonant inductor of the resonant cavity at the start of the th secondary side duty ratio adjustment stage, is the peak value of the conduction current of the secondary side switching tube in the th secondary side duty ratio adjustment stage.

[0123] Among them, for the step size of the th secondary side duty ratio adjustment stage is: .

[0124] It can be understood that the maximum value of the step size of the th secondary side duty ratio adjustment stage is .

[0125] It should be noted that during the soft start of the secondary side duty ratio, the low-voltage bus side capacitor CLbus on the secondary side charges the primary side, so the voltage on the low-voltage bus side will gradually increase. The change of the voltage on the low-voltage bus side is generally similar to that of the high-voltage bus side voltage in Figure 15 . In the early stage of duty ratio adjustment, the change slope of the voltage on the low-voltage bus side is large, that is, the voltage on the low-voltage bus side increases relatively large. Therefore, the step size of duty ratio adjustment cannot be too large to prevent the resonant inductor current from being too large; in the later stage of duty ratio adjustment, the change of the voltage on the low-voltage bus side is gentle, that is, the voltage on the low-voltage bus side increases relatively small. At this time, the adjustment step size can be larger than that in the early stage. For the secondary side duty ratio adjustment stage, there is a maximum value for , and the maximum value is determined by ; since is continuously increasing during the adjustment of multiple secondary side duty ratios, then is gradually increasing, and then is gradually increasing. Therefore, the will be larger than that in the previous stage Therefore, the maximum value of the in the subsequent stage will be larger than the maximum value of the in the previous stage, that is, in each sub-secondary duty cycle adjustment stage, the step size selection will become larger and larger.

[0126] Step S326: According to the duty cycle step size and the preset cumulative duration of each sub-secondary duty cycle adjustment stage, complete the soft start of the duty cycle of each adjustment stage until the duty cycle of the sub-secondary switch tube reaches the sub-secondary soft start target duty cycle.

[0127] According to step S322, it can be known that the step size designed as described above limits takes into account the protection of the circuit devices of the resonant module, and in multiple sub-secondary duty cycle adjustment stages, the maximum value of the duty cycle adjustment step size in the later stage is larger. In order to accelerate the soft start process of the duty cycle to improve efficiency. Thus, when selecting the adjustment step size of the duty cycle for each sub-secondary duty cycle adjustment stage, limits the maximum value of each sub-secondary duty cycle adjustment stage to protect the circuit devices, and the step size of the duty cycle of the subsequent sub-secondary duty cycle adjustment stage can be set to be greater than the step size of the duty cycle of the previous sub-secondary duty cycle adjustment stage , so as to accelerate the duty cycle adjustment speed.

[0128] For example, the first preset threshold is 10, and the duty cycle is adjusted with the initial sub-secondary duty cycle as the initial value. In the first sub-secondary duty cycle adjustment stage, the step size is 1, and the preset cumulative duration is 2 ms to adjust the initial sub-secondary duty cycle to the stage target duty cycle , that is, in the first sub-secondary duty cycle adjustment stage, the duty cycle is adjusted with an increment of 1 every 2 ms until the sub-secondary duty cycle is adjusted to the stage target duty cycle ; in the second sub-secondary duty cycle adjustment stage, the step size is 2, and the preset cumulative duration is 1 ms to adjust the stage target duty cycle to the stage target duty cycle , that is, in the first sub-secondary duty cycle adjustment stage, the duty cycle is adjusted with an increment of 2 every 1 ms until the stage target duty cycle is adjusted to the stage target duty cycle ; in the third sub-secondary duty cycle adjustment stage, the step size is 5, and the preset cumulative duration is 1 ms to adjust the stage target duty cycle to the stage target duty cycle , that is, in the third sub-secondary duty cycle adjustment stage, the duty cycle is adjusted with an increment of 5 every 1 ms until the stage target duty cycle Adjust to the duty cycle of the phase target ; within the fourth secondary duty cycle adjustment phase, it is necessary to set a value less than the first preset threshold, and adjust the duty cycle of the phase target to the soft start target duty cycle of the secondary side.

[0129] Compared with the soft start scheme that uses a fixed step size to adjust the duty cycle of the secondary side switch tube, the soft start efficiency is slow, and if the set fixed step size is too large, the change in the duty cycle of the switch tube will cause the inductor current of the resonant network of the resonant conversion module to get out of control, resulting in problems such as switch tube damage and inductor saturation. In this embodiment, by dynamically adjusting the duty cycle step size in stages, the step size and adjustment interval are differentially designed within each secondary duty cycle adjustment phase, reducing the soft start time and improving the soft start efficiency. Moreover, by setting the step size with multiple parameters, the out-of-control phenomenon of the inductor current in the resonant network can be avoided, and the working safety of the energy storage system can be improved.

[0130] In some of these embodiments, the host 10 and the slave 20 can be communicatively connected through a CAN communication bus, a serial port, or an IO port.

[0131] Refer to Figure 16 , the host 10 includes an input pin ARM_I and an output pin ARM_O, the slave 20 includes an output pin DSP_0 and an input pin DSP_I, the output pin DSP_0 can be electrically connected to the input pin ARM_I through a digital isolator 60, and the input pin DSP_I is electrically connected to the output pin ARM_O through the digital isolator 60. When the power supplies of the host 10 and the slave 20 are inconsistent, the digital isolator 60 can isolate the high and low voltages between the host 10 and the slave 20. In practical applications, if the power supplies of the host 10 and the slave 20 are consistent, the digital isolator 60 can be omitted.

[0132] When the host 10 is in the off-grid working mode or the static state, a first level signal (such as a low level signal) is sent from the output pin ARM_O to the input pin DSP_I. When the host 10 is in the grid-connected working mode, a second level signal (such as a high level signal) is sent from the output pin ARM_O to the input pin DSP_I. Then, the slave 20 can generate a pulse signal through a signal generator based on the level change of the input pin DSP_I, and use the pulse signal as a flag for loop switching to enable the slave to switch the working loop. Specifically, refer to Figure 17, the signal generator 210 includes an edge trigger circuit 201, an OR gate U1, and a pulse generator 203. The input terminal of the OR gate U1 is also used to receive an interrupt trigger event signal SIGNAL. The edge trigger circuit 201 detects the level change (rising edge or falling edge) based on the input pin DSP_I and generates a trigger signal to the OR gate U1. The OR gate U1 performs a logical OR operation on the trigger signal and the interrupt trigger event signal SIGNAL and outputs a logical signal to the pulse generator 203. The pulse generator 203 issues a pulse signal with a fixed width based on the logical signal. Among them, if the current level change has triggered the pulse generator 203 to issue a pulse signal, the interrupt trigger event signal SIGNAL masks the repeated trigger of the same jump (for example, implemented through a state machine or a flag bit) to ensure the uniqueness of the pulse. For the specific structure of the signal generator 210, reference can be made to the prior art and will not be limited here.

[0133] The response time of the above communication process is close to the clock frequency of the chip system, meeting the real-time requirement, thus solving the loop synchronization problem of multiple chips during the loop switching process, and supporting the high-frequency switching requirement of the power electronic system, realizing the switching control at the switching frequency level, and greatly reducing the probability of abnormal conditions such as oscillation and mutation during the loop switching process.

[0134] In a second aspect, an embodiment of the present application provides an energy storage system, which includes a host and a slave. The host includes a resonant conversion module and an inverter module, and the slave includes a DCDC module. Among them, the connection between the resonant conversion module and the inverter module is the high-voltage bus side, and the connection between the resonant conversion module and the DCDC module is the low-voltage bus side; the energy storage system is configured to: when the energy storage system is in the off-grid working mode, determine whether the grid electrical parameters meet the grid connection conditions, and when the grid connection conditions are met, control the energy storage system to enter the grid connection working mode: perform amplitude and phase locking on the inverter module; set a first reference voltage value for the high-voltage bus side according to the rated electrical parameters of the energy storage system, the electrical parameters of the battery at the current moment connected to the slave, and the electrical parameters of the host at the current moment; control the grid connection loop of the host according to the first reference voltage value to obtain the duty cycle of the switching tube of the inverter module; set a second reference voltage value for the low-voltage bus side according to the electrical parameters of the battery at the current moment connected to the slave, and control the grid connection loop of the slave according to the second reference voltage value to obtain the duty cycle of the switching tube of the DCDC module; gradually soft-start the power of the low-voltage bus side to the battery demand power, and soft-start the power of the high-voltage bus side to a preset power according to the first reference voltage value, the voltage value of the high-voltage bus side, and the battery demand power; among them, the ratio of the first reference voltage value to the transformer turns ratio of the resonant conversion module is greater than the second reference voltage value.

[0135] In this energy storage system, when the energy storage system switches from the off-grid working mode to the grid-connected working mode, by dynamically coordinating the reference voltages and power distribution of the host and slave units, a smooth transition of the mode switch is achieved. The power on the low-voltage bus side is gradually increased to the battery demand value, and the power on the high-voltage bus side is softly started to the target value synchronously. After both the host and slave units confirm entering the grid-connected loop, the power adjustment is started, reducing mode conflicts and improving the stability and safety of the energy storage system during operation.

[0136] It should be noted that the device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed to multiple network units. Some or all of the modules can be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0137] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them; under the idea of the present application, the technical features in the above embodiments or different embodiments can also be combined, and the steps can be implemented in any order, and there are many other variations in different aspects of the present application as described above. For the sake of brevity, they are not provided in detail; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the various embodiments of the present application.

Claims

1. A control method for an energy storage system, which is applied to an energy storage system including a master machine and a slave machine. The master machine includes a resonant conversion module and an inverter module, and the slave machine includes a DCDC module. The connection point between the resonant conversion module and the inverter module is the high-voltage bus side, and the connection point between the resonant conversion module and the DCDC module is the low-voltage bus side. It is characterized in that, The control method includes: When the energy storage system is in the off-grid working mode, it is judged whether the grid connection condition is satisfied according to the electrical parameters of the grid. When the grid connection condition is satisfied, the energy storage system is controlled to enter the grid-connected working mode: Perform amplitude and phase locking on the inverter module; Set a first reference voltage value regarding the high-voltage bus side according to the rated electrical parameters of the energy storage system, the electrical parameters of the battery at the current moment connecting the slave unit, and the electrical parameters of the master unit at the current moment; Control the grid-connected loop of the master unit according to the first reference voltage value to obtain the duty ratio of the switching tube of the inverter module; Set a second reference voltage value regarding the low-voltage bus side according to the electrical parameters of the battery at the current moment connecting the slave unit, and control the grid-connected loop of the slave unit according to the second reference voltage value to obtain the duty ratio of the switching tube of the DCDC module; Gradually soft-start the power of the low-voltage bus side to the battery demand power, and soft-start the power of the high-voltage bus side to a preset power according to the first reference voltage value, the voltage value of the high-voltage bus side, and the battery demand power; Wherein, the ratio of the first reference voltage value to the transformer turns ratio of the resonant conversion module is greater than the second reference voltage value.

2. The control method according to claim 1, wherein When the energy storage system is controlled to enter the grid-connected working mode from the off-grid working mode, determine a first reference voltage value as follows: ； And, ； ； Determine the second reference voltage value It is: ； And, ； Among them, is the voltage value of the battery at the moment when the energy storage system enters the grid-connected working mode from the off-grid working mode, is the first set threshold, is the voltage peak value of the power grid or the rated output voltage peak value of the energy storage system, is the voltage ripple value of the inverter capacitor of the inverter module, is the current value of the inverter inductor of the inverter module, is the period of the switching tube of the inverter module at the moment when the energy storage system enters the grid-connected working mode from the off-grid working mode, is the capacitance value of the inverter capacitor of the inverter module, is the second set threshold, is the voltage peak value of the power grid, is the turns ratio of the transformer of the resonant conversion module.

3. The control method according to claim 1, characterized in that, Controlling the grid-connected loop of the master unit according to the first reference voltage value to obtain the duty ratio of the switching tube of the inverter module includes: Input the first reference voltage value and the voltage value of the high-voltage bus side into the bus voltage outer loop to obtain a first reference value of the inverter inductor current inner loop; Filter the first reference value to obtain a filtered first reference value; Input the current value of the inverter inductor and the filtered first reference value into the inverter inductor current inner loop and the compensation loop to obtain a double-loop output value and a compensation loop output value; Sum the double-loop output value, the compensation loop output value, and the voltage value of the grid to obtain the duty ratio of the first switch of the inverter module.

4. The control method according to claim 1, characterized in that, Controlling the grid-connected loop of the slave unit according to the second reference voltage value to obtain the duty ratio of the switching tube of the DCDC module includes: Input the second reference voltage value and the voltage value of the low-voltage bus side into the first buck-boost voltage limit outer loop to obtain a second reference value of the first buck-boost inductor current inner loop; Input the current value of the first buck-boost inductor and the second reference value into the first buck-boost inductor current inner loop to obtain the duty ratio of the switching tube of one path of the interleaved parallel DCDC module's buck loop; Input the second reference voltage value and the voltage value of the low-voltage bus side into the second buck-boost voltage limit outer loop to obtain a third reference value of the second buck-boost inductor current inner loop; Input the current value of the second buck-boost inductor and the third reference value into the second buck-boost inductor current inner loop to obtain the duty ratio of the switching tube of the other path of the interleaved parallel DCDC module's buck loop.

5. The control method according to claim 1, wherein Soft-starting the power of the high-voltage bus side to a preset power according to the first reference voltage value, the voltage value of the high-voltage bus side, and the battery demand power includes: Obtain the difference between the first reference voltage value and the voltage value of the high-voltage bus side; Input the difference value into an integrator to obtain a power compensation value; Sum the required power and the power compensation value to obtain the preset power, and softly start the power on the high-voltage bus side to the preset power.

6. The control method according to claim 1, wherein The control method includes: When the energy storage system is in the grid-connected operation mode, determine whether the grid is powered off according to the electrical parameters of the grid. When the grid is powered off, control the energy storage system to enter the off-grid operation mode; Wherein, when the energy storage system is controlled to enter the off-grid operation mode from the grid-connected operation mode, Determine the first reference voltage value It is: ； Determine the second reference voltage value It is: ； is the voltage value of the battery when the energy storage system enters the off-grid working mode from the grid-connected working mode, is the first set threshold, is the second set threshold, is the turns ratio of the transformer of the resonant conversion module.

7. The control method according to claim 1, characterized in that, The control method further includes: When the energy storage system is in a static state, determine whether the grid connection conditions are met according to the electrical parameters of the grid. When the grid connection conditions are met, start the host and the slave, and control the energy storage system to enter the grid-connected operation mode; Wherein, starting the host and the slave includes: Controlling the boost loop of the DCDC module according to the PI loop control principle, and adjusting the voltage value on the low-voltage bus side to the third reference voltage value on the low-voltage bus side to complete the start of the DCDC module. The determination method of the third reference voltage value is as follows: calculate the difference between the duty cycle of the switching tube of one path of the boost loop of the interleaved parallel DCDC module, and determine the ratio between the voltage of the battery and the difference as the third reference voltage value, and make the product of the third reference voltage value and the transformer turns ratio of the resonant conversion module greater than the peak voltage of the grid, or make the product of the third reference voltage value and the transformer turns ratio of the resonant conversion module greater than the peak value of the rated output voltage of the energy storage system; Gradually adjust the duty cycles of the primary switch tube and the secondary switch tube of the resonant conversion module to adjust the voltage value on the high-voltage bus side to the peak value of the rated output voltage of the energy storage system; Gradually adjust the inverter voltage value of the inverter module to the preset grid voltage value of the grid.

8. The control method according to claim 7, wherein Gradually adjusting the duty cycle of the primary switch tube of the resonant conversion module includes: Dividing the range from the initial primary duty cycle to the primary soft-start target duty cycle into multiple primary duty cycle adjustment stages, and obtaining the stage target duty cycle of each primary duty cycle adjustment stage; According to the maximum resonant current peak value of the resonant conversion module, the set effective voltage value of the low-voltage bus side for soft start, and the stage target duty cycle of each primary duty cycle adjustment stage, set the duty cycle step length of each primary duty cycle adjustment stage; According to the duty cycle step length and the preset cumulative duration of the duty cycle of each primary duty cycle adjustment stage, complete the soft start of the duty cycle of each adjustment stage until the duty cycle of the primary switch tube reaches the primary soft-start target duty cycle.

9. The control method according to claim 8, wherein, Dividing the range from the initial primary duty cycle to the primary soft-start target duty cycle into multiple primary duty cycle adjustment stages includes: Setting the current primary duty cycle to one-fourth of the primary soft-start target duty cycle as the first primary duty cycle adjustment stage; Setting the range from one-fourth of the primary soft-start target duty cycle to one-half of the primary soft-start target duty cycle as the second primary duty cycle adjustment stage; Set the range from one - half of the original - side soft - start target duty ratio to the first preset duty ratio value as the third original - side duty - ratio adjustment stage; Set the range from the first preset duty ratio value to the original - side soft - start target duty ratio as the fourth original - side duty - ratio adjustment stage; Wherein, the first preset duty ratio value is the difference between the original - side soft - start target duty ratio and the first preset threshold value, the first preset threshold value is greater than 0 and less than one - half of the original - side soft - start target duty ratio.

10. The control method according to claim 7, wherein Gradually adjust the duty ratio of the secondary - side switch tube of the resonant conversion module, including: Divide the range from the secondary - side initial duty ratio to the secondary - side soft - start target duty ratio into multiple secondary - side duty - ratio adjustment stages, and obtain the stage - target duty ratio of each secondary - side duty - ratio adjustment stage; According to the maximum resonant current peak value of the resonant conversion module, the set effective value of the voltage on the high - voltage bus side for soft - start, and the stage - target duty ratio of each secondary - side duty - ratio adjustment stage, set the duty - ratio step size of each secondary - side duty - ratio adjustment stage; According to the duty - ratio step size and the preset cumulative duration of the duty ratio of each secondary - side duty - ratio adjustment stage, complete the soft - start of the duty ratio of each adjustment stage until the duty ratio of the secondary - side switch tube reaches the secondary - side soft - start target duty ratio.

11. The control method according to claim 10, wherein Dividing the range from the secondary - side initial duty ratio to the secondary - side soft - start target duty ratio into multiple secondary - side duty - ratio adjustment stages includes: Set the range from the current secondary - side duty ratio to one - quarter of the secondary - side soft - start target duty ratio as the first secondary - side duty - ratio adjustment stage; Set the range from one - quarter of the secondary - side soft - start target duty ratio to one - half of the secondary - side soft - start target duty ratio as the second secondary - side duty - ratio adjustment stage; Set the range from one - half of the secondary - side soft - start target duty ratio to the second preset duty ratio value as the third secondary - side duty - ratio adjustment stage; Set the range from the second preset duty ratio value to the secondary - side soft - start target duty ratio as the fourth secondary - side duty - ratio adjustment stage; Wherein, the second preset duty ratio value is the difference between the secondary - side soft - start target duty ratio and the second preset threshold value, the second preset threshold value is greater than 0 and less than one - half of the secondary - side soft - start target duty ratio.

12. An energy storage system, characterized in that, It includes a host and a slave; The host includes a resonant conversion module and an inverter module, the slave includes a DCDC module. Wherein, the connection point between the resonant conversion module and the inverter module is the high - voltage bus side, and the connection point between the resonant conversion module and the DCDC module is the low - voltage bus side; The energy storage system is configured to: When the energy storage system is in the off - grid working mode, judge whether it meets the grid - connection conditions according to the electrical parameters of the power grid. When the grid - connection conditions are met, control the energy storage system to enter the grid - connection working mode: Perform amplitude and phase locking on the inverter module; Set the first reference voltage value about the high - voltage bus side according to the rated electrical parameters of the energy storage system, the electrical parameters of the battery at the current moment connected to the slave, and the electrical parameters of the host at the current moment; Control the grid - connection loop of the host according to the first reference voltage value to obtain the duty ratio of the switch tube of the inverter module; Set a second reference voltage value regarding the low-voltage bus side according to the electrical parameters of the battery at the current moment when connecting the slave, and control the grid-connected loop of the slave according to the second reference voltage value to obtain the duty ratio of the switching tube of the DCDC module; Gradually soft-start the power on the low-voltage bus side to the battery demand power, and soft-start the power on the high-voltage bus side to a preset power according to the first reference voltage value, the voltage value on the high-voltage bus side, and the demand power of the battery; Wherein, the ratio of the first reference voltage value to the transformer turns ratio of the resonant conversion module is greater than the second reference voltage value.

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