Energy storage system and control method thereof

Abstract

The present application provides an energy storage system and a control method thereof. When the energy storage system is in an off-grid working mode, it is determined whether the grid connection conditions are met based on the electrical parameters of the power grid. When the grid connection conditions are met, the energy storage system is controlled to enter the grid connection working mode: the inverter module is amplitude-locked and phase-locked; a first reference voltage value on the high-voltage bus side is set; the grid connection loop of the host is controlled according to the first reference voltage value to obtain the duty cycle of the switch tube of the inverter module; a second reference voltage value on the low-voltage bus side is set, and the grid connection loop of the slave is controlled according to the second reference voltage value to obtain the duty cycle of the switch tube of the DCDC module; the power of the low-voltage bus side is gradually soft-started to the battery demand power, and the power of the high-voltage bus side is soft-started to the preset power according to the first reference voltage value, the voltage value of the high-voltage bus side, and the battery demand power. The above method can improve the stability and safety of the energy storage system during operation.

Description

Technical Field

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

[0002] With the widespread application of renewable energy and the development of intelligent power systems, energy storage systems play a vital role in microgrids, off-grid power supply, and grid-connected operation. During the energy storage system's power supply process, it involves switching between off-grid and grid-connected modes. For example, when the DC-DC module on the DC side and the resonant converter module and inverter module on the inverter side are not connected to the grid, the energy storage system will have two voltage sources charging each other, one on the DC side and the other on the inverter side. Energy from both ends is applied to the capacitors on the low-voltage side of the resonant converter module, which can easily damage the capacitors of the resonant converter module. Therefore, when the energy storage system switches from off-grid mode to grid-connected mode, one of the key challenges in energy storage system control is how to coordinate the control of the high-voltage and low-voltage bus sides, achieve a stable transition, and avoid abnormal bus voltage fluctuations that could damage the internal circuits of the energy storage system. Summary of the Invention

[0003] An embodiment of the present application provides an energy storage system and a control method thereof. When the energy storage system switches from an off-grid operating mode to a grid-connected operating mode, after the master and slave machines enter the grid-connected loop, the power measured on the high-voltage bus side and the low-voltage bus is gradually adjusted to ensure reasonable power distribution, reduce abnormal conditions such as power mutations and bus voltage fluctuations, 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, wherein the host includes a resonant conversion module and an inverter module, and the slave 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. The control method includes: when the energy storage system is in an off-grid working mode, judging whether the grid-connected conditions are met according to the electrical parameters of the power grid; when the grid-connected conditions are met, controlling the energy storage system to enter the grid-connected working mode: locking the amplitude and phase of the inverter module; and controlling the power supply voltage according to the rated electrical parameters of the energy storage system, the electrical parameters of the battery connected to the slave at the current moment, and the electrical parameters of the host at the current moment. The invention relates to a method for controlling a first reference voltage value on the high-voltage bus side; controlling the grid-connected loop of the host according to the first reference voltage value to obtain the duty cycle of the switch tube of the inverter module; setting a second reference voltage value on the low-voltage bus side according to the electrical parameters of the battery connected to the slave at the current moment, and controlling the grid-connected loop of the slave according to the second reference voltage value to obtain the duty cycle of the switch tube of the DCDC module; gradually soft-starting the power of the low-voltage bus side to the battery required 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 required power of the battery; wherein the ratio of the first reference voltage value to the transformer ratio of the resonant conversion module is greater than the second reference voltage value.

[0005] 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, 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 an off-grid working mode, determine whether the grid-connected conditions are met according to the electrical parameters of the power grid, and when the grid-connected conditions are met, control the energy storage system to enter the grid-connected working mode: lock the amplitude and phase of the inverter module; according to the rated electrical parameters of the energy storage system, the electrical parameters of the battery connected to the slave at the current moment, and the electrical parameters of the host at the current moment A first reference voltage value is set on the high-voltage bus side; the grid-connected loop of the host is controlled according to the first reference voltage value to obtain the duty cycle of the switch tube of the inverter module; a second reference voltage value is set on the low-voltage bus side according to the electrical parameters of the battery connected to the slave at the current moment, and the grid-connected loop of the slave is controlled according to the second reference voltage value to obtain the duty cycle of the switch tube of the DCDC module; the power of the low-voltage bus side is gradually soft-started to the battery required power, and the power of the high-voltage bus side is soft-started 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; wherein the ratio of the first reference voltage value to the transformer 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 a control method thereof. When the energy storage system switches from an off-grid operating mode to a grid-connected operating mode, the DCDC module, the inverter module, and the resonant conversion module are controlled to enter the grid-connected mode. This prevents the resonant conversion module from being damaged by charging the low-voltage bus at both ends of the DC side and the inverter side when the DC side and the inverter side enter the grid-connected mode asynchronously. The control method can also reasonably set voltage reference values ​​for the high-voltage bus side and the low-voltage bus side, so that after the energy storage system enters the grid-connected operating mode, it can respond to changes in the power grid and battery in real time, adapt to multiple operating conditions, and improve the flexibility of the control method. After the master and slave devices enter the grid-connected loop, the power measured 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 high-voltage bus undervoltage or loss of control, and improve the stability and safety of the energy storage system during operation. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0008] Figure 1 A structural block diagram of an energy storage system provided in an embodiment of the present application;

[0009] Figure 2 A circuit structure diagram of a DCDC module provided in an embodiment of the present application;

[0010] Figure 3 A circuit structure diagram of a resonant conversion module provided in an embodiment of the present application;

[0011] Figure 4 A circuit structure diagram of an inverter module provided in an embodiment of the present application;

[0012] Figure 5 A flow chart of a control method for an energy storage system provided in an embodiment of the present application;

[0013] Figure 6 A schematic diagram of a phase-locked loop provided in an embodiment of the present application;

[0014] Figure 7 A schematic diagram of an off-network loop of a host provided in an embodiment of the present application;

[0015] Figure 8 A schematic diagram of a network-connected loop of a host provided in an embodiment of the present application;

[0016] Figure 9 A Bode diagram provided in an embodiment of the present application;

[0017] Figure 10 A schematic diagram of a grid-connected loop of a slave device is provided for an embodiment of the present application;

[0018] Figure 11 A schematic diagram of a calculation loop for a power compensation value provided in an embodiment of the present application;

[0019] Figure 12 A schematic diagram of a startup loop of a DCDC module provided in an embodiment of the present application;

[0020] Figure 13 A schematic diagram of the waveforms of a pulse width modulation signal and a resonant current of a primary-side switching tube provided in an embodiment of the present application;

[0021] Figure 14 A schematic diagram of the waveforms of the pulse width modulation signal and resonant current of another primary-side switching tube provided in an embodiment of the present application;

[0022] Figure 15 A schematic diagram of a voltage waveform on the high-voltage bus side provided in an embodiment of the present application;

[0023] Figure 16A structural block diagram of another energy storage system provided in an embodiment of the present application;

[0024] Figure 17 A structural diagram of a signal generator provided in an embodiment of the present application. DETAILED DESCRIPTION

[0025] In order to facilitate the understanding of the present application, the present application is described in more detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that when an element is described as being "fixed to" another element, it can be directly on the other element, or there can be one or more centered elements therebetween. When an element is described as being "electrically connected" to another element, it can be directly connected to the other element, or there can be one or more centered elements therebetween. The terms "upper", "lower", "inner", "outer", "bottom" and the like used in this specification indicate an orientation or positional relationship based on the orientation or positional relationship shown in the accompanying 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 therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second", "third" and the like are used for descriptive purposes only and cannot be understood as indicating or implying relative importance.

[0026] Unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used in this specification are for the purpose of describing specific embodiments only and are not intended to limit this 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 the different embodiments of this application described below may be combined with each other as long as they do not conflict with each other.

[0027] The present application provides an energy storage system. Figure 1 The energy storage system includes a master 10 and a slave 20. The master 10 includes a resonant conversion module 11 and an inverter module 12, and the slave 20 includes a DC / DC module 21. The resonant conversion module 11 is used to connect the DC / DC module 21 and the inverter module 12. The connection point between the resonant conversion module 11 and the inverter module 12 is on the high-voltage bus side, and the connection point between the resonant conversion module 11 and the DC / DC module 21 is on the low-voltage bus side.

[0028] The DCDC module 21 is 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 multiple cells connected in parallel, series or hybrid, and is used to store and provide electrical energy. Hybrid includes series and parallel. The operating voltage range of the battery 40 can be 20V to 40V. In some embodiments, see Figure 2 The DCDC module 21 is a two-way buck-boost circuit interleaved in parallel. 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, switches Q1, Q2, Q3, and Q4. The buck-boost inductor L1, the buck-boost capacitor C1, the switches Q1, Q2, Q3, and Q4 form one buck-boost loop, and the buck-boost inductor L2, the buck-boost capacitor C2, the switches Q3, and Q4 form another buck-boost loop. Figure 2 In FIG, the connection point A1 and the connection point A2 are the connection points of the resonant conversion module 11 and the DCDC module 21, and the sampling voltage between the connection point A1 and the connection point A2 is the sampling voltage on the low-voltage bus side.

[0029] The resonant conversion module 11 is a high-efficiency DC-DC converter using resonant soft switching technology, which can achieve isolated conversion of high and low voltage DC power. Figure 3 The resonant conversion module 11 is an LLC resonant converter, which includes a low-voltage bus capacitor CLbus, a primary switch tube Q5, a primary switch tube Q6, a primary switch tube Q7, a primary switch tube Q8, a transformer T1, an excitation inductor Lm, a resonant inductor Lr, a resonant capacitor Cr, a secondary switch tube Q9, a secondary switch tube Q10, a secondary switch tube Q11, a secondary switch tube Q12, and a high-voltage bus capacitor CHbus. Figure 3 In FIG, the connection point A3 and the connection point A4 are the connection points of the resonant conversion module 11 and the inverter module 12, and the sampling voltage between the connection point A3 and the connection point A4 is the sampling voltage on the high-voltage bus side.

[0030] The inverter module 12 is an electronic power device that can convert DC power into AC power and vice versa. In the grid-connected working mode, the inverter module 12 can convert the AC power of the grid 30 into DC power on the high-voltage bus side. In the off-grid working mode, the inverter module 12 can convert DC power into AC power to power the load 50. In some embodiments, refer to Figure 4The inverter module 12 includes an inverter high-frequency transistor Q13, an inverter high-frequency transistor Q15, an inverter power-frequency transistor Q14, an inverter power-frequency transistor Q16, an inverter inductor L3, an inverter capacitor C3, a relay RY1, and a relay RY2. Relay RY1 establishes a connection between the inverter module 12 and the power grid 30 when it is turned on, or disconnects the connection between the inverter module 12 and the power grid 30 when it is turned off. Relay RY2 establishes a connection between the inverter module 12 and the load 50 when it is turned on, or disconnects the connection between the inverter module 12 and the load 50 when it is turned off.

[0031] 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 the off-grid operating mode enters the grid-connected operating mode, when the inverter module of the host and the DCDC module and resonant conversion module of the slave have not all entered the grid-connected operating mode, that is, when the slave 20 is in the off-grid loop and the host 10 is in the grid-connected loop, a high-voltage side voltage source and a low-voltage side voltage source will be formed inside the energy storage system, causing all energy to accumulate on the low-voltage bus capacitor CLbus of the resonant conversion module 11, which can easily cause overvoltage damage to the buck-boost capacitor C1 and the buck-boost capacitor C2.

[0032] To improve the above-mentioned problems, an embodiment of the present application provides an energy storage system and a control method thereof. When the energy storage system switches from an off-grid operating mode to a grid-connected operating mode, a smooth transition of the mode switching is achieved by dynamically coordinating the reference voltage and power distribution of the master and slave machines. The low-voltage bus side power is gradually increased to the battery demand value, and the high-voltage bus side power is synchronously soft-started to the target value. Power adjustment is only started after both the master and slave machines confirm that they have entered the grid-connected loop, thereby reducing mode conflicts and improving the stability and safety of the energy storage system during operation.

[0033] The present application provides a control method for an energy storage system, which is applied to the energy storage system as described above. Figure 5 , the control method includes steps S10 to S15.

[0034] Step S10: When the energy storage system is in the off-grid working mode, it is determined whether the grid connection conditions are met according to the electrical parameters of the power grid 30. When the grid connection conditions are met, the energy storage system is controlled to enter the grid connection working mode.

[0035] Off-grid operation occurs when the energy storage system is completely disconnected from the grid 30 and operates independently to power local loads 50. During this operation, relay RY2 is closed and relay RY1 is open, allowing energy to flow from the battery to the loads. In this state, the energy storage system functions as an isolated microgrid, autonomously maintaining stable voltage and frequency without relying on the external grid.

[0036] The electrical parameters of the grid 30 include the frequency and amplitude of the input power to the grid 30. Specifically, the host 10 may first detect the grid 30 to determine whether it has input power. If so, it may determine whether the frequency and amplitude of the grid 30 meet the grid connection conditions. If so, the energy storage system may be controlled to enter the grid-connected mode; if not, the energy storage system may continue to operate in the off-grid mode.

[0037] For details, see Figure 4 The host 10 determines whether the grid 30 has input power by detecting the effective value of the voltage between the input port GRIDL1 and the input port GRIDN1 of the grid 30.

[0038] For example, the effective value of voltage is calculated using the following formula:

[0039] ;

[0040] in, is the effective value of 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.

[0041] After obtaining the effective value of the power grid, it is compared with a 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 the power grid 30 has input power. When the effective value of the power grid is less than the first preset voltage value, it is determined that the power grid 30 has no input power. The first preset voltage value can be 50% of the rated voltage of the power grid 30 under normal working conditions.

[0042] Next, after determining that the grid 30 has input power, the host 10 can calculate the frequency of the input power through a generalized second-order integrator. For example, first set the central angular frequency ωn of the generalized second-order integrator (e.g., 2π×50rad / s) and initialize the state variable and , in each sampling period In the code, the state variables are updated by the following formula:

[0043] ;

[0044] ;

[0045] is the kth instantaneous sampling value of the voltage of the grid 30, and the orthogonal component is calculated by the following formula and :

[0046] ;

[0047] ;

[0048] After obtaining the orthogonal components, the frequency offset is calculated using the following formula: :

[0049] ;

[0050] In practical applications, the following formula can be used to approximate the difference calculation: and :

[0051] ;

[0052] ;

[0053] After obtaining the frequency offset, the actual angular frequency is calculated using the following formula: :

[0054] ;

[0055] And the angular frequency is converted into the frequency of the input current through the following formula :

[0056] ;

[0057] If the frequency of the input power is within the preset operating frequency, the host 10 obtains the instantaneous deviation voltage of the input power. If the instantaneous deviation voltage of the input power is greater than or equal to a second preset voltage value, and the duration of the instantaneous deviation voltage of the input power being greater than or equal to the second preset voltage value is greater than or equal to a first preset time, it indicates that the frequency and amplitude of the input power of the power grid 30 are both within the operating range supported by the energy storage system, and the host determines that the electrical parameters of the power grid 30 meet the grid connection conditions. If the instantaneous deviation voltage of the input power is less than the second preset voltage value, or the duration of the instantaneous deviation voltage of the input power being 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. The instantaneous deviation voltage of the input power is the difference between the actual instantaneous voltage of the input power and the rated peak voltage of the power grid 30; the preset operating frequency is the standard frequency range of the power grid 30 supported by 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 energy storage system, and the rated peak voltage is the product of the rated voltage of the power grid 30 supported by the energy storage system and 1.414. The first preset time may be 3ms. In practical applications, the preset operating frequency, the second preset voltage value, and the first preset time may be set according to actual needs and are not limited here.

[0058] Controlling the energy storage system to enter the grid-connected working mode includes the following steps S11 to S15.

[0059] Step S11: performing amplitude and phase locking on the inverter module 12.

[0060] Amplitude and phase locking refers to the process in which the host 10 adjusts the amplitude and phase of the AC power from the inverter module 12 to match those of the input power from the grid 30. This ensures that there is no inrush current at the moment of grid connection (when relay RY1 closes). The AC power from the inverter module 12 is also the AC power across filter capacitor C3.

[0061] For example, the host 10 separates the quadrature components (i.e., the in-phase component and the quadrature component) from the AC power of the inverter module 12 through a generalized second-order integrator. The separation formula is as follows:

[0062] ;

[0063] ;

[0064] in,

[0065] ;

[0066] Then, the phase angle is calculated by the following formula:

[0067] ;

[0068] So:

[0069] ;

[0070] By using trigonometric identities we get:

[0071] ;

[0072] in, is the amplitude of the AC power of the inverter module 12, is the actual phase angle of the AC power of the inverter module 12, is the angular frequency of the alternating current of the inverter module 12, is the frequency of the AC power of the inverter module 12.

[0073] The actual phase angle of the AC power of the inverter module 12 is obtained based on the generalized second-order integrator Then, the phase angle between it and the input power of the grid 30 is Compare and Figure 6 The PI control loop shown is adjusted so that the phase angle of the AC output of the inverter module 12 is The phase angle of the input power from the grid 30 Run until the difference between the two is less than 10°, and phase lock is completed, even if:

[0074] ;

[0075] In addition, the off-grid reference voltage of the inverter module 12 is adjusted to the current voltage of the grid 30, and the voltage amplitude of the AC power of the inverter module 12 is adjusted to follow the voltage amplitude of the current grid 30 until the difference between the two is less than a third preset voltage value, thereby completing the amplitude locking. The third preset voltage value can be 10% of the voltage amplitude of the current grid 30, that is:

[0076] ;

[0077] in, is the voltage amplitude of the AC power of the inverter module 12, is the current voltage amplitude of the power grid 30.

[0078] Specifically, the grid voltage V_GRID between the input terminal GRIDL1 and the input terminal GRIDN1 of the 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 can be obtained first. The grid voltage V_GRID, the inverter voltage V_INV, the inverter current I_INV, and the output current I_LOAD are separated into α and β by a generalized second-order integrator. The separated α and β are subjected to Park transformation to obtain the D-axis component and Q-axis component of the inverter rated voltage VdInvref, the inverter rated voltage Q-axis component VqInvref, the current inverter voltage D-axis component VdInv, the current inverter voltage Q-axis component VqInv, the current output current D-axis component IdOutfeedback, the current output current Q-axis component IqOutfeedback, the current inverter current D-axis component Idinv, and the current inverter current D-axis component Iqinv are obtained. Then, the above components are input to Figure 7 The duty cycle PwmOut is calculated in the loop shown, and the operation of the switch tube in the inverter module 12 is controlled based on the duty cycle PwmOut, thereby adjusting the voltage amplitude of the AC power of the inverter module 12.

[0079] Step S12: setting a first reference voltage value on the high-voltage bus side according to the rated electrical parameters of the energy storage system, the electrical parameters of the battery connected to the slave 20 at the current moment, and the electrical parameters of the master 10 at the current moment.

[0080] 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 peak voltage of the power grid 30 or the rated output voltage peak of the energy storage system.

[0081] The electrical parameters of the battery connected to the slave 20 at the current moment refer to the electrical parameters of the battery 40 connected to the DCDC module at the current moment, such as the voltage value of the battery 40 when the energy storage system enters the grid-connected working mode from the off-grid working mode.

[0082] The electrical parameters of the host 10 at the current moment refer to the electrical parameters of the host 10 at the current moment, such as 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 tube of the inverter module 12 when the energy storage system enters the grid-connected operating mode from the off-grid operating mode, the capacitance value of the inverter capacitor C3 of the inverter module 12, and the transformation ratio of the transformer T1 of the resonant conversion module 11. The transformation 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.

[0083] The first reference voltage value is a target voltage value of the high-voltage bus of the inverter module 12 .

[0084] Step S13: controlling the grid-connected loop of the host 10 according to the first reference voltage value to obtain the duty cycle of the switch tube of the inverter module 12.

[0085] After obtaining the first reference voltage value and controlling relay RY1 to close, the first reference voltage value is input into the grid-connected loop of host 10, and the duty cycle of the switches of inverter module 12 is determined. Based on this duty cycle, the switches of inverter module 12 are controlled to operate so that the target voltage value on the high-voltage bus reaches the first reference voltage value. It will be understood that after relay RY1 is closed, energy flows from grid 30 to battery 40. If relay RY2 is also closed, energy also flows from grid 30 to load 50.

[0086] Step S14: setting a second reference voltage value on the low-voltage bus side according to the electrical parameters of the battery currently connected to the slave 20, and controlling the grid-connected loop of the slave 20 according to the second reference voltage value to obtain the duty cycle of the switch tube of the DCDC module 21.

[0087] Specifically, after the master 10 enters the grid-connected loop, it can notify the slave 20 of its entry into the grid-connected loop via 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, the second reference voltage value is input into the grid-connected loop of the slave 20, and the duty cycle of the switching tube of the inverter module 12 is obtained. Based on this duty cycle, the operation of the switching tube of the inverter module 12 is controlled so that the target voltage value on the low-voltage bus side reaches the first reference voltage value.

[0088] Step S15: Gradually soft-start the power on the low-voltage bus side to the battery required 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 required power, wherein the ratio of the first reference voltage value to the transformer ratio of the resonant conversion module 11 is greater than the second reference voltage value.

[0089] Battery power requirement is Figure 2 The power value that battery 40 expects to receive from the low-voltage bus. It is understood that after the master 10 and slave 20 enter the grid-connected loop, if the input power of the grid 30 (i.e., the power of the AC power between input terminals GRIDL1 and GRIDN1) is less than the battery's required power (corresponding to the required power of the DCDC module 21), this indicates that the power provided by the grid 30 is insufficient to meet the power expected by the battery 40, causing the voltage of the high-voltage bus to drop, resulting in an undervoltage condition. Since the slave 20 utilizes a step-down and voltage-limiting control loop, it cannot stabilize the bus voltage at a specific value. If the input power of the grid 30 is infinite, the bus voltage will be out of control. To avoid this situation, this embodiment performs a soft start operation on the power on the high-voltage bus side and the power on the low-voltage bus side, namely, executing step S15, by gradually increasing the power measured on the low-voltage bus side and the power on the high-voltage bus side until they reach their corresponding target powers.

[0090] In this embodiment, by real-time detection of electrical parameters such as the frequency, amplitude, and phase of the power grid 30 and setting multiple conditional judgments, it is ensured that the energy storage system is controlled to switch to the grid-connected operating mode only when the electrical parameters of the power grid 30 meet the conditions, thereby reducing electrical shock 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 operating mode to the grid-connected operating mode, the voltage reference values ​​on the high-voltage bus side and the low-voltage bus side are dynamically set. After the energy storage system enters the grid-connected operating mode, it can respond to changes in the power grid and battery in real time, adapt to the needs of multiple operating conditions, and improve the flexibility of the control method. After the master and slave devices enter the grid-connected loop, the power measured on the high-voltage bus side and the low-voltage bus is gradually adjusted to ensure reasonable power distribution, reduce abnormal conditions such as undervoltage or loss of control of the high-voltage bus, and improve the stability and safety of the energy storage system during operation.

[0091] In some embodiments, when the energy storage system is controlled from the off-grid working mode to the grid-connected working mode, the first reference voltage value is determined. for:

[0092] ;

[0093] and,

[0094] ;

[0095] ;

[0096] Determine the second reference voltage value for:

[0097] ;

[0098] and,

[0099] ;

[0100] in, is the battery voltage value when the energy storage system switches from off-grid working mode to grid-connected working mode. Set the threshold for the first time, is the voltage peak of the grid 30 or the rated output voltage peak 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, Set the threshold for the second is the voltage peak of the grid 30, is the transformation ratio of the transformer T1 of the resonant conversion module 11.

[0101] When setting the first set threshold and the second set threshold, the settings can be made 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.

[0102] In this embodiment, a first set threshold is introduced into the formula of the first reference voltage value, a redundant calculation of the first reference voltage value is added to the voltage value of the battery, and the bus voltage at the moment of grid connection is ensured to be higher than the sum of the peak voltage of the grid and the voltage ripple value of the inverter capacitor C3, so as to avoid the bus voltage being out of control due to voltage fluctuations and improve the stability of the energy storage system; a second set threshold is introduced into the formula of the second reference voltage value, a 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 ensured to be higher than the sum of the peak voltage of the grid and the voltage ripple value of the inverter capacitor C3, so as to avoid the bus voltage being overvoltage due to load mutation or grid fluctuations after grid connection, and protect key components such as the inverter module 12 from high voltage shocks. Setting It can be achieved by first establishing the inverter voltage and then connecting to the grid, ensuring that when the voltage on the high-voltage bus side reaches the set voltage, the voltage difference between the grid voltage and the inverter voltage is small. In this way, the peak current is small when the relay is closed, and the damage to the relay is small. At the same time, the setting of the first reference voltage value and the second reference voltage value can meet a certain voltage energy on the high-voltage bus side while also avoiding the voltage on the low-voltage bus side from draining the high-voltage bus side.

[0103] In some embodiments, step S13 includes the following steps S131 to S134.

[0104] Step S131: inputting a first reference voltage value and a voltage value on the high-voltage bus side into a bus voltage outer loop to obtain a first reference value of an inverter inductor current inner loop.

[0105] The bus voltage outer loop can use PI control loop. The voltage value of the high voltage bus side is the voltage sampling value of the high voltage bus side. Figure 8 , the first reference voltage value V_BUS_Ref can be first subtracted from the sampled voltage value V_BUS_FB on the high-voltage bus side, and after obtaining the difference between the two, the difference between the two is input into the bus voltage outer loop to obtain the first reference value. If the voltage value V_BUS_FB on the high-voltage bus side sampled during the PI control process is greater than 110% of the first reference voltage value V_BUS_Ref, then at this time, the relay RY1 is kept closed and the battery 40 is discharged. It can supply power to the load 50 through the power grid 30 to avoid the high-voltage bus voltage from being too high and damaging the device. If the voltage value V_BUS_FB on the high-voltage bus side is less than the first reference voltage value V_BUS_Ref, the first reference value is calculated by the following formula:

[0106] ;

[0107] in, is the first reference value, The power required for the battery, is the voltage value of the power grid 30.

[0108] Step S132: Filter the first reference value to obtain a filtered first reference value.

[0109] Then, the first reference value is input into the filter for filtering, thereby obtaining the filtered first reference value. Figure 8 In the illustrated embodiment, the filter may employ a double-power-frequency ripple notch filter to filter the first reference value, thereby filtering out double-power-frequency ripple interference superimposed on the bus voltage and preventing the bus voltage ripple from affecting the inner loop current reference. In practical applications, other suitable filters may be employed to filter the first reference value.

[0110] For the double power frequency ripple notch filter, its transfer function is as follows:

[0111] ;

[0112] in, is the notch width, in rad / s, is the center frequency of the notch, in rad / s.

[0113] Taking double power frequency as an example, , bandwidth frequency is set to 20Hz, , the switching frequency is set to 20KHz, Perform a bilinear transformation and bring in the above data to get:

[0114] ;

[0115] The corresponding Bode diagram is Figure 9 shown.

[0116] Step S133: inputting 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 dual-loop output value and a compensation loop output value.

[0117] The current value of the inverter inductor L3 is the current sampling value flowing through the inverter inductor L3. Figure 8 After obtaining the filtered first reference value I_INV_Ref, the difference is calculated between the first reference value I_INV_Ref and the current value I_INV_FB of the inverter inductor L3. After obtaining the difference, the difference is input into the inverter inductor current inner loop to obtain the dual-loop output value, and the difference is input into the compensation loop to obtain the compensation loop output value.

[0118] The inner loop of the inverter inductor current can use a PI control loop. The compensation loop can use a repetitive controller to reduce the third, fifth, and seventh harmonics of the current. The repetitive controller uses a control algorithm in the existing technology.

[0119] Step S134 : summing the dual-loop output value, the compensation loop output value, and the voltage value of the grid 30 to obtain the duty cycle of the first switch of the inverter module 12 .

[0120] The voltage value of the grid 30 is the voltage sampling value of the grid 30. The first switch of the inverter module 12 includes Figure 4 Inverter high frequency tube Q13, inverter high frequency tube Q15, inverter power frequency tube Q14, inverter power frequency tube Q16. For details, refer to Figure 8 , the dual-loop output value, the compensation loop output value and the voltage value V_Grid of the grid 30 are input into the adder, thereby obtaining the duty cycle INV_PWM of the above-mentioned switch tube of the inverter module 12.

[0121] In this embodiment, the inverter module 12 is controlled by the above-mentioned grid-connected loop so that the high-voltage bus side can reach the first reference voltage value.

[0122] In some embodiments, step S14 : controlling the grid-connected loop of the slave device 20 according to the second reference voltage value to obtain the duty cycle of the switch tube of the DCDC module 21 includes the following steps S141 to S144 .

[0123] Step S141: inputting the second reference voltage value and the voltage value on the low-voltage bus side into the first step-down voltage limiting outer loop to obtain a second reference value of the first step-down inductor current inner loop.

[0124] The first voltage reduction and voltage limiting outer loop can adopt PI control loop. The voltage value of the low voltage bus side is the voltage sampling value of the low voltage bus side. Figure 10 , the second reference voltage value Vbus_ref can be first subtracted from the voltage value Vbus_real_1 on the low-voltage bus side. After obtaining the difference, the difference is input into the first step-down and voltage-limiting outer loop, which outputs the second reference value Iinductor_ref_1. When the voltage value Vbus_real_1 on the low-voltage bus side is greater than the second reference voltage value Vbus_ref, the second reference value Iinductor_ref_1 is the actual demand current. When the voltage value Vbus_real_1 on the low-voltage bus side is less than the second reference voltage value Vbus_ref, the second reference value Iinductor_ref_1 is output using the above method.

[0125] Step S142 : inputting 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 switch tube of one buck loop of the interleaved parallel DCDC module 21 .

[0126] The current value of the first buck inductor is the current sampling value of the buck-boost inductor L1. The inner loop of the first buck inductor current can adopt a PI control loop. Figure 10 , the second reference value Iinductor_ref_1 can be subtracted from the current value Iinductor_real_1 of the first buck inductor, and the difference between the two can be input into the first buck inductor current inner loop. The first buck inductor current inner loop outputs Figure 2 The duty cycle PwmOut_1 of the switch tube Q1 is obtained, and the switch tube Q1 is subsequently controlled to operate based on the duty cycle PwmOut_1.

[0127] Step S143: inputting the second reference voltage value and the voltage value on the low-voltage bus side into the second step-down voltage limiting outer loop to obtain a third reference value of the second step-down inductor current inner loop.

[0128] The second voltage reduction and limiting outer loop can use a PI control loop. Figure 10The second reference voltage value Vbus_ref can be first subtracted from the sampled low-voltage bus voltage value Vbus_real_2 to obtain the difference. This difference is then input into the second voltage reduction and voltage limiting outer loop, which then outputs the second reference value Iinductor_ref_2. The low-voltage bus voltage value Vbus_real_2 and the low-voltage bus voltage value Vbus_real_1 can be the same sampled value.

[0129] Step S144 : inputting 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 switch tube of the other buck loop of the interleaved parallel DCDC module 21 .

[0130] The current value of the second buck inductor is the current sampling value of the buck-boost inductor L2. The inner loop of the second buck inductor current can adopt a PI control loop. Figure 10 , the third reference value Iinductor_ref_2 can be firstly subtracted from the current value Iinductor_real_2 of the second buck inductor, and the difference between the two can be input into the second buck inductor current inner loop. The second buck inductor current inner loop outputs Figure 2 The duty cycle PwmOut_2 of the switch tube Q3 is used, and the switch tube Q3 is subsequently controlled to operate based on the duty cycle PwmOut_2.

[0131] In this embodiment, the DCDC module 21 is controlled by the above-mentioned grid-connected loop so that the low-voltage bus side can reach the second reference voltage value.

[0132] In some embodiments, step S15: soft-starting the power on the high-voltage bus side to a preset power based on the first reference voltage value, the voltage value on the high-voltage bus side, and the required power of the battery, includes the following steps S151 to S153. Step S151: Obtaining the difference between the first reference voltage value and the voltage value on the high-voltage bus side. Step S152: Inputting the difference into an integrator to obtain a power compensation value. Step S153: Summing the required power of the battery and the power compensation value to obtain a preset power, and soft-starting the power on the high-voltage bus side to the preset power.

[0133] It's worth noting that, for example, the inverter input only allows 1A of energy to flow in. However, every topology has inefficiencies. If only 1A of energy is allowed to flow in, the bus voltage cannot be maintained. Therefore, a reasonable power compensation is required to maintain bus voltage stability while ensuring that the battery can receive 1A of energy. During step S15, it is necessary to ensure that the high-voltage side is not drained by the low-voltage side and that the high-voltage side does not overvoltage.

[0134] The voltage value on the high-voltage bus side is the voltage sampling value on the high-voltage bus side. Figure 11 , the first reference voltage value V_BUS_Ref can be subtracted from the voltage value VHbus on the high-voltage bus side to obtain the difference between the two. 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 on the high-voltage bus side is gradually increased with the preset power FinalChargePower as the target.

[0135] In this embodiment, the preset power may be determined in the above manner.

[0136] In some embodiments, the control method of the energy storage system further includes: step S20: when the energy storage system is in a grid-connected working mode, determining whether the grid 30 is powered off based on the electrical parameters of the grid 30; when the grid 30 is powered off, controlling the energy storage system to enter an off-grid working mode.

[0137] 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 .

[0138] Specifically, if the electrical parameters of grid 30 meet any of the following three conditions, grid 30 is determined to be powered off. If the electrical parameters of grid 30 do not meet the following three conditions, grid 30 is determined not to be powered off, and the energy storage system continues to operate in grid-connected mode. Condition one is that the fluctuation amplitude of the instantaneous voltage value of the AC power of grid 30 is greater than or equal to a preset amplitude, and the duration is greater than or equal to a second preset time. The fluctuation amplitude of the instantaneous voltage value of the AC power of grid 30 is the degree of variation of the instantaneous voltage value relative to a standard value (e.g., a rated voltage of 220V). The preset amplitude can be 28%. That is, condition one is that the instantaneous voltage value of the AC power of grid 30 is greater than or equal to 28% of the standard value, and the duration of the instantaneous voltage value of the AC power of 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 two is that the absolute value of the difference between the actual frequency of the AC power of grid 30 and the frequency of the AC power of grid 30 is greater than the preset frequency difference, and the duration is greater than or equal to a third preset time. The preset frequency difference can be 3 Hz, and the third preset time is 1 second. Condition three is that the voltage of the AC power from 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 AC power from grid 30, and the fourth preset time is 1 second.

[0139] When the power grid 30 loses power, the master 10 enters an off-grid operating mode and notifies the slave 20 to enter the off-grid operating mode. The high-voltage side of the resonant conversion module 11 stops outputting pulse-width modulation signals to the secondary-side switch tube, that is, controls the secondary-side switch tube of the resonant conversion module 11 to be turned off, thereby preventing energy from accumulating in the low-voltage side bus and causing overvoltage on the low-voltage side bus. If the low-voltage side bus voltage suddenly rises, the slave 20 controls the DCDC module 21 to stop outputting pulse-width modulation signals to the switch tube in the DCDC module 21, that is, controls the switch tube in the DCDC module 21 to be turned off, thereby preventing the system from being damaged by overvoltage due to energy accumulation.

[0140] When the energy storage system is controlled from the grid-connected working mode to the off-grid working mode, the first reference voltage value is determined. for:

[0141] ;

[0142] Determine the second reference voltage value for:

[0143] ;

[0144] is the battery voltage value when the energy storage system switches from grid-connected working mode to off-grid working mode. Set the threshold for the first time, Set the threshold for the second is the transformation ratio of the transformer T1 of the resonant conversion module 11.

[0145] When setting the first set threshold and the second set threshold, the settings can be made 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.

[0146] 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, determining whether the grid-connected conditions are met based on the electrical parameters of the power grid 30; when the grid-connected conditions are met, starting the host 10 and the slave 20 to control the energy storage system to enter a grid-connected working mode.

[0147] The energy storage system is in a static state, which means that the energy storage system is in a low-power standby mode, that is, the host 10 and the slave 20 are both in a dormant or shut-down state, and only the electrical parameters of the power grid 30 are detected in real time through hardware circuits or low-power software to determine whether the grid connection conditions are met.

[0148] When determining whether grid 30 meets grid-connection conditions, master 10 may first detect grid 30 to determine whether grid 30 is receiving input power. If so, master 10 and slave 20 are activated to control the energy storage system to enter grid-connection mode. If not, the energy storage system is controlled to remain in a static state. The specific determination steps can be found in step S10 and will not be detailed here.

[0149] Wherein, for step S30, starting the host 10 and the slave 20 includes the following steps S31 to S33.

[0150] Among them, step S31: starting the slave: controlling the boost loop of the DCDC module 21 according to the PI loop control principle, adjusting the voltage value on the low-voltage bus side to the third reference voltage value on the low-voltage bus side, so as to complete the startup of the DCDC module 21.

[0151] The voltage value of the low voltage bus side is the voltage sampling value of the low voltage bus side. Figure 12 The reference value Vout1_ref is subtracted from the sampled value Vout1_real to obtain a difference between the two. This difference is input into a first PI controller to obtain a duty cycle PwmOut1 for the switch Q2 in one of the boost loops. The switch Q2 is then controlled based on this duty cycle PwmOut1. Simultaneously, the reference value Vout2_ref is subtracted from the sampled value Vout2_real to obtain a difference between the two. This difference is input into a second PI controller to obtain a duty cycle PwmOut2 for the switch Q4 in another of the boost loops. The switch Q4 is then controlled based on this duty cycle PwmOut2. The reference values ​​Vout1_ref and Vout2_ref are both third reference voltage values; the sampled values ​​Vout1_real and Vout2_real are both voltage values ​​on the low-voltage bus side. The first and second PI controllers are controllers that dynamically adjust the voltage on the low-voltage bus side through a combination of proportional and integral steps.

[0152] The third reference voltage value is determined as follows: Calculate the duty cycle of the switch tube of one of the boost loops of the DCDC modules 21 connected in parallel with each other. The difference between the battery voltage The ratio between the difference and the third reference voltage is determined as the third reference voltage value. , and the product of the third reference voltage value and the transformer ratio of the resonant conversion module 11 is greater than the voltage peak of the power grid 30, or the product of the third reference voltage value and the transformer ratio of the resonant conversion module 11 is greater than the rated output voltage peak of the energy storage system.

[0153] That is:

[0154] ;

[0155] ;

[0156] The duty cycle of the switch tube in one of the boost loops is the duty cycle of the switch tube Q2 or the switch tube Q4.

[0157] Among them, step S32: soft start the resonant conversion module of the host: gradually adjust the duty cycle of the primary side switch tube and the secondary side switch tube 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.

[0158] The rated peak output voltage of the energy storage system is the product of the rated voltage of the energy storage system and 1.414. Specifically, a soft start is first applied to the primary switching transistor of the resonant converter module 11, allowing energy to gradually increase the high-voltage bus voltage through transformer T1 until the voltage of the high-voltage bus is adjusted to the rated peak output voltage of the energy storage system.

[0159] Step S33 : soft-starting the inverter module of the host: gradually adjusting the inverter voltage value of the inverter module 12 to the preset grid voltage value of the grid 30 .

[0160] 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, the inverter module 12 is activated to perform a soft start until the electrical parameters simultaneously meet conditions 4 and 5. Condition 4 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 grid 30 is less than a fourth preset voltage value, which is 10% of the effective value of the voltage of the grid 30; and condition 5 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 grid 30 is less than a fifth preset voltage value, which is 10% of the instantaneous value of the voltage of the grid 30. Next, by adjusting the duty cycle of each switch in the inverter module 12, with the instantaneous voltage of the grid 30 as the target inverter voltage value, a variable step-size soft start is performed in stages. For example, the inverter voltage is first gradually adjusted to half the preset grid voltage value at a slope of 10V per 1ms, and then the inverter voltage across the inverter capacitor C3 is gradually adjusted to the preset grid voltage value at a slope of 20V per 1ms. The inverter voltage refers to the voltage across the inverter capacitor C3 of the inverter module 12 , and the voltage of the grid 30 refers to the voltage between the input port GRIDL1 and the input port GRIDN1 .

[0161] Among them, for step S30, after the soft start of the inverter module 12 is completed, the energy storage system is controlled 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 repeated here.

[0162] In some embodiments, step S32 : gradually adjusting the duty cycle of the primary-side switch of the resonant conversion module 11 includes the following steps S321 to S323 .

[0163] Step S321 : Divide the range from the primary side initial duty cycle to the primary side soft-start target duty cycle into a plurality of primary side duty cycle adjustment stages, and obtain a stage target duty cycle of each primary side duty cycle adjustment stage.

[0164] The primary initial duty cycle refers to the on-duty cycle of the primary switch tube at the initial adjustment moment, which can be the minimum on-duty cycle among the primary switch tubes Q5, Q6, Q7, and Q8.

[0165] The primary side soft start target duty cycle refers to the target conduction duty cycle of the primary side switch tube. The inductance value of the resonant inductor Lr can be determined 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. , the capacitance value of the resonant capacitor Cr and the inductance value of the magnetizing inductance Lm Then, the resonant frequency of the resonant conversion module 11 is calculated according to the following formula: :

[0166] ;

[0167] Then, the switching frequency of the resonant conversion module 11 is The following relationship must be satisfied:

[0168] ;

[0169] in, The maximum supported frequency of each switch in the resonant conversion module 11, that is, the maximum switching frequency allowed by the primary switch Q5, the primary switch Q6, the primary switch Q7, the primary switch Q8, the secondary switch Q9, the secondary switch Q10, the secondary switch Q11 and the secondary switch Q12. Afterwards, the target duty cycle of the primary side soft start can be determined using an oscilloscope. It can be understood that the target duty cycle of the primary side soft start needs to be less than 50% to ensure that there is sufficient dead time between the primary side switches Q5, Q6, Q7, and Q8. The dead time can be adjusted according to the resonant current to ensure that the primary side switch is turned off when the resonant current flowing through the resonant inductor Lr is 0.

[0170] Specifically, such as Figure 13As shown, at time 1, the resonant current flowing through the resonant inductor Lr is 0, but the primary switch Q5 is not turned off at this time. At this time, the deviation between the primary soft start target duty cycle and the current duty cycle of the primary switch Q5 is the duty cycle deviation. , so it is necessary to base it on the duty cycle deviation Obtain the primary side soft start target duty cycle, such as the primary side soft start target duty cycle calculated using the following formula:

[0171] ;

[0172] ;

[0173] in, is the target duty cycle of the primary side soft start, To compensate for the duty cycle, is the switching frequency, is the current duty cycle of the primary switch Q5. When the current duty cycle of the primary switch Q5 reaches the primary soft start target duty cycle, Figure 14 As shown, at time 2, the resonant current flowing through the resonant inductor Lr is 0, and the primary side switch tube Q5 is turned off.

[0174] Similarly, the secondary side soft start target duty cycle is determined according to the above process, the method is the same, and will not be repeated here.

[0175] In a specific embodiment, in step S321, the range from the primary side initial duty cycle to the primary side soft start target duty cycle is divided into multiple primary side duty cycle adjustment stages, including:

[0176] Step S3211: setting the current primary duty cycle to one-quarter of the primary soft-start target duty cycle as the first primary duty cycle adjustment stage; step S3212: setting one-quarter 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; step S3213: setting one-half of the primary soft-start target duty cycle to the first preset duty cycle value as the third primary duty cycle adjustment stage; step S3214: setting the first preset duty cycle value to the primary soft-start target duty cycle as the fourth primary duty cycle adjustment stage, wherein the first preset duty cycle value is the difference between the primary soft-start target duty cycle and the first preset threshold value, the first preset threshold value is greater than 0, and the first preset threshold value is less than one-half of the primary soft-start target duty cycle.

[0177] It can be understood that the target duty cycle of the first primary side duty cycle adjustment stage is It is one quarter of the primary side soft start target duty cycle, and the target duty cycle of the second primary side duty cycle adjustment stage is The target duty cycle of the third primary side duty cycle adjustment stage is half of the target duty cycle of the primary side soft start. is the first preset duty cycle value, and the target duty cycle of the fourth primary side duty cycle adjustment stage is is the target duty cycle of the primary side soft start.

[0178] In a specific embodiment, the first preset threshold is 10, and the duty cycle is adjusted with the primary side initial duty cycle as the initial value.

[0179] It is worth noting that the purpose of performing duty cycle soft start in stages is that the magnetic inductance of the resonant cavity and other magnetic devices are affected by temperature, the current size (DC bias) passing through the magnetic devices, etc., which may cause the actual inductance to decrease, thereby increasing the impedance of the resonant cavity. Reducing the current peak that causes the resonant inductance of the resonant cavity to be too large instantly, which will lead to problems such as damage to the switching tube of the switching tube and oversaturation of the inductor, can achieve the purpose of gradually increasing the current of the magnetic inductance or the current passing through the switching tube by gradually adjusting the duty cycle in stages, so as to reduce the risk of damage to circuit components.

[0180] Step S322: setting the duty cycle step size of each primary side duty cycle adjustment stage according to the maximum resonant current peak of the resonant conversion module, the set voltage effective value of the low voltage bus side for soft start, and the stage target duty cycle of each primary side duty cycle adjustment stage.

[0181] Among them, the resonant cavity impedance of the resonant conversion module 11 is It can be calculated according to the following formula:

[0182] ;

[0183] ;

[0184] in, 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.

[0185] Among them, The peak current of the primary switch tube during the primary duty cycle adjustment stage Calculated by the following formula:

[0186] ;

[0187] ;

[0188] in, Representative The primary side duty cycle adjustment stage, is the voltage effective value of the low voltage bus side set for soft start, For the The target duty cycle of the primary side duty cycle adjustment stage, For the The voltage value across the resonant inductor of the resonant cavity at the beginning of the primary side duty cycle adjustment stage, For the The peak on-state current of the primary side switch tube during the primary side duty cycle adjustment stage.

[0189] Among them, for the The step size of the primary side duty cycle adjustment stage for:

[0190] .

[0191] Understandably, The maximum step length of each primary duty cycle adjustment stage is .

[0192] It is worth noting that during the primary side duty cycle soft start process, the primary side charges the high voltage bus side capacitor CHbus of the secondary side, so the voltage on the high voltage bus side will gradually increase. The change of the high voltage bus side voltage is generally as follows: Figure 15 As shown in the figure, in the early stage of duty cycle adjustment, the voltage change slope of the high-voltage bus side is large, that is, the voltage growth of the high-voltage bus side is relatively large, so the duty cycle adjustment step cannot be too large to prevent the resonant inductor current from being too large; in the later stage of duty cycle adjustment, the voltage change of the high-voltage bus side is slow, that is, the voltage growth of the high-voltage bus side is relatively small, and the adjustment step can be larger than the early stage. For the primary side duty cycle adjustment stage, there are some The maximum value, the maximum value Determined by; Due to the multiple primary side duty cycle adjustment process is constantly increasing, then It gradually increases, and then Gradually increasing, so the latter stage will be better than the previous stage , so the next stage The maximum value will be higher than the previous stage The larger the maximum value of , the larger the step size will be.

[0193] Step S323: Complete the duty cycle soft start of each adjustment stage according to the duty cycle step size and the preset duty cycle accumulation time of each primary side duty cycle adjustment stage, until the duty cycle of the primary side switch reaches the primary side soft start target duty cycle.

[0194] According to step S322, it can be known that the above-mentioned design The limited step size takes into account the protection of the circuit components of the resonant module, and in multiple primary side duty cycle adjustment stages, the maximum value of the duty cycle adjustment step size is larger in the later stages, in order to speed up the soft start process of the duty cycle and improve efficiency. The maximum value of each primary duty cycle adjustment stage is limited to protect the circuit components, and the duty cycle step size of the next primary duty cycle adjustment stage can be set. Greater than the duty cycle step size of the previous primary side duty cycle adjustment stage , to speed up the duty cycle adjustment.

[0195] For example, the first preset threshold is 10, and the duty cycle is adjusted with the initial duty cycle of the primary side as the initial value. In the first primary side duty cycle adjustment stage, the step length is The initial primary duty cycle is adjusted to the target duty cycle of the stage by setting the accumulated time to 2ms. That is, in the first primary duty cycle adjustment stage, the duty cycle is adjusted in increments of 1 every 2ms until the primary duty cycle is adjusted to the stage target duty cycle. ; In the second primary side duty cycle adjustment stage, the step size The preset cumulative duration is 1ms, which sets the target duty cycle of the stage Adjust to the target duty cycle of the stage That is, in the second primary side duty cycle adjustment stage, the duty cycle is adjusted in increments of 2 within each 1ms interval until the target duty cycle is reached. Adjust to the target duty cycle of the stage ; In the third primary side duty cycle adjustment stage, the step length The preset cumulative time is 1ms, which sets the target duty cycle of the stage Adjust to the target duty cycle of the stage That is, in the third primary side duty cycle adjustment stage, the duty cycle is adjusted in increments of 5 at every 1ms interval until the target duty cycle is reached. Adjust to the target duty cycle of the stage ; In the fourth primary side duty cycle adjustment stage, the step length It needs to be set to a value less than the first preset threshold value, and the stage target duty cycle Adjust to the primary side soft start target duty cycle.

[0196] Compared with the scheme of using a fixed step size to soft-start the duty cycle of the primary side switch tube, the soft-start efficiency is slow, and if the fixed step size is set too large, the duty cycle of the switch tube changes too much, causing the inductor current of the resonant network of the resonant conversion module to be out of control, thereby causing damage to the switch tube, inductor oversaturation and other problems. In this embodiment, the duty cycle step size is dynamically adjusted in stages, and the step size and adjustment interval are differentiated in each primary side duty cycle adjustment stage to reduce the soft-start time and improve the soft-start efficiency. In addition, by setting the step size by multiple parameters, the inductor current of the resonant network can be avoided from being out of control, thereby improving the safety of the energy storage system.

[0197] In some embodiments, step S32 : gradually adjusting the duty cycle of the secondary-side switch of the resonant conversion module 11 includes the following steps S324 to S326 .

[0198] Step S324 : Divide the range from the secondary side initial duty cycle to the secondary side soft start target duty cycle into a plurality of secondary side duty cycle adjustment stages, and obtain a stage target duty cycle of each secondary side duty cycle adjustment stage.

[0199] The secondary initial duty cycle refers to the duty cycle of the secondary switch tube at the initial adjustment moment, which can be the minimum conduction duty cycle among the secondary switch tubes Q9, Q10, Q11, and Q12.

[0200] The secondary side soft-start target duty cycle refers to the target conduction duty cycle of the secondary side switch. The specific determination process can be found in the Determination of the Secondary Side Soft-Start Target Duty Cycle and will not be further described here.

[0201] In a specific embodiment, in step S321, the range from the secondary side initial duty cycle to the secondary side soft start target duty cycle is divided into multiple secondary side duty cycle adjustment stages, including:

[0202] Step S3211: setting the current secondary side duty cycle to one quarter of the secondary side soft start target duty cycle as the first secondary side duty cycle adjustment stage; step S3212: setting one quarter 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: setting one half of the secondary side soft start target duty cycle to the second preset duty cycle value as the third secondary side duty cycle adjustment stage; step S3214: setting the second preset duty cycle value to the secondary side soft start target duty cycle as the fourth secondary side duty cycle adjustment stage, wherein the second preset duty cycle value is the difference between the secondary side soft start target duty cycle and the second preset threshold value, the second preset threshold value is greater than 0, and the second preset threshold value is less than one half of the secondary side soft start target duty cycle.

[0203] It can be understood that the stage target duty cycle of the first secondary side duty cycle adjustment stage is one quarter 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 cycle 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.

[0204] In a specific embodiment, the first preset threshold is 10, and the duty cycle is adjusted with the initial duty cycle of the secondary side as the initial value.

[0205] It is worth noting that the purpose of performing duty cycle soft start in stages is that the magnetic inductor and other magnetic components of the resonant cavity may be affected by temperature, the current size (DC bias) passing through the magnetic components, etc., which may cause the actual inductance to decrease, thereby reducing the impedance of the resonant cavity and causing the current peak of the resonant inductor of the resonant cavity to be too large instantly, which may cause damage to the switching tube of the switching tube, inductance oversaturation and other problems. Therefore, by gradually adjusting the duty cycle in stages, the purpose of gradually increasing the current of the magnetic inductor or the current passing through the switching tube can be achieved, so as to reduce the risk of damage to circuit components.

[0206] Step S325: setting the duty cycle step size of each secondary side duty cycle adjustment stage according to the maximum resonant current peak of the resonant conversion module, the set voltage effective value of the high voltage bus side for soft start, and the stage target duty cycle of each secondary side duty cycle adjustment stage.

[0207] Among them, the resonant cavity impedance of the resonant conversion module 11 is It can be calculated according to the following formula:

[0208] ;

[0209] ;

[0210] in, 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.

[0211] Among them, The peak conduction current of the secondary side switch tube in the secondary side duty cycle adjustment stage Calculated by the following formula:

[0212] ;

[0213] ;

[0214] in, Representative Secondary side duty cycle adjustment stage, is the effective value of the voltage on the high-voltage bus side set for soft start, For the The target duty cycle of each secondary side duty cycle adjustment stage, For the The voltage value across the resonant inductor of the resonant cavity at the beginning of the secondary side duty cycle adjustment stage, For the The peak on-state current of the secondary side switch tube during the secondary side duty cycle adjustment stage.

[0215] Among them, for the The step size of each secondary side duty cycle adjustment stage for:

[0216] .

[0217] Understandably, The maximum step length of each secondary side duty cycle adjustment stage is .

[0218] It is worth noting that during the secondary duty cycle soft start process, the secondary side charges the low voltage bus side capacitor CLbus of the primary side, so the voltage of the low voltage bus side will gradually increase. The change of the low voltage bus side voltage is generally consistent with the Figure 15 The changes in the voltage on the medium and high voltage bus side are similar. In the early stage of duty cycle adjustment, the voltage change slope on the low voltage bus side is large, that is, the voltage growth on the low voltage bus side is large, so the duty cycle adjustment step cannot be too large to prevent the resonant inductor current from being too large; in the later stage of duty cycle adjustment, the voltage change on the low voltage bus side is slow, that is, the voltage growth on the low voltage bus side is small, and the adjustment step can be larger than in the early stage. For the secondary side duty cycle adjustment stage, there are some targeted The maximum value of OK; because in the process of adjusting multiple secondary duty cycles is constantly increasing, then It gradually increases, and then Gradually increasing, so the latter stage It will be better than the previous stage Big, so the next stage The maximum value will be higher than that of the previous stage. The maximum value is larger, that is, in each secondary side duty cycle adjustment stage, the step size selection will become larger and larger.

[0219] Step S326 : completing the duty cycle soft start of each adjustment stage according to the duty cycle step size and the preset duty cycle accumulation time of each secondary side duty cycle adjustment stage, until the duty cycle of the secondary side switch reaches the secondary side soft start target duty cycle.

[0220] According to step S322, it can be known that the above-mentioned design The limited step size takes into account the protection of the circuit components of the resonant module, and in the multiple secondary side duty cycle adjustment stages, the maximum value of the duty cycle adjustment step size is larger in the later stages, in order to speed up the soft start process of the duty cycle and improve efficiency. The maximum value of each secondary duty cycle adjustment stage is limited to protect the circuit components, and the duty cycle step size of the next secondary duty cycle adjustment stage can be set. The duty cycle step size is greater than the previous secondary duty cycle adjustment stage , to speed up the duty cycle adjustment.

[0221] For example, the first preset threshold is 10, and the duty cycle is adjusted with the initial duty cycle of the secondary side as the initial value. In the first secondary side duty cycle adjustment stage, the step size is The default cumulative time is 2ms, and the initial secondary duty cycle is adjusted to the stage target duty cycle. That is, in the first secondary side duty cycle adjustment stage, the duty cycle is adjusted in increments of 1 every 2ms until the secondary side duty cycle is adjusted to the stage target duty cycle. ; In the second secondary side duty cycle adjustment phase, the step size The preset cumulative duration is 1ms, which sets the target duty cycle of the stage Adjust to the target duty cycle of the stage That is, in the first secondary side duty cycle adjustment stage, the duty cycle is adjusted in increments of 2 within each 1ms interval until the target duty cycle is reached. Adjust to the target duty cycle of the stage ; In the third secondary side duty cycle adjustment stage, the step length The preset cumulative time is 1ms, which sets the target duty cycle of the stage Adjust to the target duty cycle of the stage That is, in the third secondary side duty cycle adjustment stage, the duty cycle is adjusted in increments of 5 at every 1ms interval until the target duty cycle is reached. Adjust to the target duty cycle of the stage ; In the fourth secondary side duty cycle adjustment stage, It needs to be set to a value less than the first preset threshold value, and the stage target duty cycle Adjust to the secondary side soft start target duty cycle.

[0222] Compared with the scheme of using a fixed step size to soft-start the duty cycle of the secondary side switch tube, the soft-start efficiency is slow, and if the fixed step size is set too large, the duty cycle of the switch tube changes too much, causing the inductor current of the resonant network of the resonant conversion module to be out of control, thereby causing damage to the switch tube, inductor oversaturation and other problems. In this embodiment, the duty cycle step size is dynamically adjusted in stages, and the step size and adjustment interval are differentiated in each secondary side duty cycle adjustment stage to reduce the soft-start time and improve the soft-start efficiency. In addition, by setting the step size by multiple parameters, the inductor current of the resonant network can be avoided from being out of control, thereby improving the safety of the energy storage system.

[0223] In some embodiments, the host 10 and the slave 20 may be communicatively connected via a CAN communication bus, a serial port, or an IO port.

[0224] See Figure 16 The host 10 includes an input pin ARM_I and an output pin ARM_O, and 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 via a digital isolator 60, and the input pin DSP_I can be electrically connected to the output pin ARM_O via a digital isolator 60. When the power supply of the host 10 and the slave 20 is inconsistent, the digital isolator 60 can isolate the high and low voltages between the host 10 and the slave 20. In actual applications, if the power supply of the host 10 and the slave 20 is the same, the digital isolator 60 can be omitted.

[0225] When the host 10 is in off-grid operation mode or in a static state, a first level signal (e.g., a low level signal) is sent to the input pin DSP_I via the output pin ARM_O. When the host 10 is in grid-connected operation mode, a second level signal (e.g., a high level signal) is sent to the input pin DSP_I via the output pin ARM_O. Then, based on the level change of the input pin DSP_I, the slave 20 can generate a pulse signal through a signal generator, and use the pulse signal as a loop switching flag to switch the working loop of the slave. For details, see Figure 17The signal generator 210 includes an edge-triggered circuit 201, an OR gate U1, and a pulse generator 203. The input of the OR gate U1 is also used to receive the interrupt trigger event signal SIGNAL. The edge-triggered 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 logic signal to the pulse generator 203. The pulse generator 203 emits a pulse signal with a fixed width based on the logic signal. If the current level change has triggered the pulse generator 203 to emit a pulse signal, the interrupt trigger event signal SIGNAL blocks repeated triggering of the same transition (for example, through a state machine or a flag bit), ensuring the uniqueness of the pulse. The specific structure of the signal generator 210 can be referred to the existing technology and is not limited here.

[0226] The response time of the above communication process is close to the clock frequency of the chip system, meeting the real-time requirements, thereby solving the loop synchronization problem of multiple chips during loop switching. It also supports the high-frequency switching requirements of the power electronic system and realizes switching control at the switching frequency level, greatly reducing the probability of abnormal conditions such as oscillation and mutation during the loop switching process.

[0227] 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, 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 an off-grid working mode, determine whether the grid-connected conditions are met based on the electrical parameters of the power grid, and when the grid-connected conditions are met, control the energy storage system to enter the grid-connected working mode: lock the amplitude and phase of the inverter module; set the first parameter on the high-voltage bus side based on the rated electrical parameters of the energy storage system, the electrical parameters of the battery connected to the slave at the current moment, and the electrical parameters of the host at the current moment. Reference voltage value; controlling the grid-connected loop of the host according to the first reference voltage value to obtain the duty cycle of the switch tube of the inverter module; setting a second reference voltage value on the low-voltage bus side according to the electrical parameters of the battery connected to the slave at the current moment, and controlling the grid-connected loop of the slave according to the second reference voltage value to obtain the duty cycle of the switch tube of the DCDC module; gradually soft-starting the power of the low-voltage bus side to the battery required power, and soft-starting the power of the high-voltage bus side 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; wherein, the ratio of the first reference voltage value to the transformer ratio of the resonant conversion module is greater than the second reference voltage value.

[0228] In this energy storage system, when the energy storage system switches from off-grid working mode to grid-connected working mode, a smooth transition of mode switching is achieved by dynamically coordinating the reference voltage and power distribution of the master and slave machines, 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. Power adjustment is only started after both the master and slave machines confirm entering the grid-connected loop, reducing mode conflicts and improving the stability and safety of the energy storage system during operation.

[0229] It should be noted that the device embodiments described above are merely illustrative, wherein the units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of the modules may be selected based on actual needs to achieve the objectives of this embodiment.

[0230] 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. Based on the concept of the present application, the technical features in the above embodiments or different embodiments can also be combined, 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 simplicity, they are not provided in detail. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A control method for an energy storage system, applied to an energy storage system comprising a master and a slave, wherein the master comprises a resonant conversion module and an inverter module, and the slave comprises a DC / DC module, wherein the connection between the resonant conversion module and the inverter module is on the high-voltage bus side, and the connection between the resonant conversion module and the DC / DC module is on the low-voltage bus side, characterized in that: The control method includes: When the energy storage system is in an off-grid working mode, it is determined whether the grid connection conditions are met according to the electrical parameters of the power grid. When the grid connection conditions are met, the energy storage system is controlled to enter a grid connection working mode: Performing amplitude and phase locking on the inverter module; Setting a first reference voltage value on the high-voltage bus side according to rated electrical parameters of the energy storage system, electrical parameters of a battery currently connected to the slave, and electrical parameters of the master at the current moment; Controlling the grid-connected loop of the host according to the first reference voltage value to obtain a duty cycle of the switch tube of the inverter module; Setting a second reference voltage value on the low-voltage bus side according to electrical parameters of the battery currently connected to the slave device, and controlling the grid-connected loop of the slave device according to the second reference voltage value to obtain a duty cycle of the switch tube of the DCDC module; gradually soft-starting the power on the low-voltage bus side to the battery demand power, obtaining a difference between the first reference voltage value and the voltage value on the high-voltage bus side, inputting the difference into an integrator to obtain a power compensation value, summing the demand power and the power compensation value to obtain a preset power, and soft-starting the power on the high-voltage bus side to the preset power; The ratio of the first reference voltage value to the transformer transformation ratio of the resonant conversion module is greater than the second reference voltage value.

2. The control method according to claim 1, characterized in that: When the energy storage system is controlled from the off-grid working mode to the grid-connected working mode, a first reference voltage value is determined. for: ； and, ； ； Determine the second reference voltage value for: ； and, ； in, is the voltage value of the battery when the energy storage system switches from an off-grid working mode to a grid-connected working mode, Set the threshold for the first time, is the peak voltage of the power grid or the rated output voltage peak 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 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, Set the threshold for the second is the peak voltage of the grid, is the transformation ratio of the transformer of the resonant conversion module.

3. The control method according to claim 1, wherein: Controlling the grid-connected loop of the host according to the first reference voltage value to obtain a duty cycle of the switch tube of the inverter module includes: Inputting 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; filtering the first reference value to obtain a filtered first reference value; Inputting 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 dual-loop output value and a compensation loop output value; The dual-loop output value, the compensation loop output value, and the voltage value of the grid are summed to obtain a duty cycle of the first switch of the inverter module.

4. The control method according to claim 1, wherein: Controlling the grid-connected loop of the slave device according to the second reference voltage value to obtain a duty cycle of the switch tube of the DCDC module includes: Inputting the second reference voltage value and the voltage value of the low-voltage bus side into the first step-down voltage limiting outer loop to obtain a second reference value of the first step-down inductor current inner loop; Inputting 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 switch tube of one of the buck loops of the DCDC modules connected in parallel; Inputting the second reference voltage value and the voltage value on the low-voltage bus side into the second step-down voltage limiting outer loop to obtain a third reference value of the second step-down inductor current inner loop; The current value of the second buck inductor and the third reference value are input into the second buck inductor current inner loop to obtain the duty cycle of the switch tube of the other buck loop of the DCDC module connected in parallel.

5. The control method according to claim 1, characterized in that: The control method includes: When the energy storage system is in a grid-connected working mode, determining whether the grid is powered off based on electrical parameters of the grid, and when the grid is powered off, controlling the energy storage system to enter an off-grid working mode; When the energy storage system is controlled from the grid-connected working mode to the off-grid working mode, Determine the first reference voltage value for: ； Determine the second reference voltage value for: ； is the voltage value of the battery when the energy storage system switches from the grid-connected working mode to the off-grid working mode, Set the threshold for the first time, Set the threshold for the second is the transformation ratio of the transformer of the resonant conversion module.

6. 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, determining whether a grid connection condition is met according to electrical parameters of the power grid, and when the grid connection condition is met, starting the master and the slave to control the energy storage system to enter a grid connection working mode; Wherein, starting the host and the slave includes: The boost loop of the DCDC module is controlled according to a PI loop control principle, and the voltage value on the low-voltage bus side is adjusted to a third reference voltage value on the low-voltage bus side to complete startup of the DCDC module. The third reference voltage value is determined as follows: a difference between the duty cycles of the switching tubes of the boost loops of one of the DCDC modules connected in parallel is calculated, and the ratio between the battery voltage and the difference is determined as the third reference voltage value. The product of the third reference voltage value and the transformer ratio of the resonant conversion module is set to be greater than the peak voltage of the power grid, or the product of the third reference voltage value and the transformer ratio of the resonant conversion module is set to be greater than the rated output voltage peak of the energy storage system. Gradually adjusting the duty cycle of the primary side switch tube and the secondary side switch tube of the resonant conversion module so that the voltage value of the high-voltage bus side is adjusted to the rated output voltage peak of the energy storage system; The inverter voltage value of the inverter module is gradually adjusted to a preset grid voltage value of the grid.

7. The control method according to claim 6, characterized in that: Gradually adjusting the duty cycle of the primary side switch tube of the resonant conversion module, including: Dividing 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 obtaining the stage target duty cycle of each primary side duty cycle adjustment stage; Setting the duty cycle step size of each primary side duty cycle adjustment stage according to the maximum resonant current peak value of the resonant conversion module, the set voltage effective value of the low voltage bus side for soft start, and the stage target duty cycle of each primary side duty cycle adjustment stage; According to the duty cycle step size and the preset duty cycle accumulation time of each primary side duty cycle adjustment stage, the duty cycle soft start of each adjustment stage is completed until the duty cycle of the primary side switch tube reaches the primary side soft start target duty cycle.

8. The control method according to claim 7, characterized in that: The range from the primary side initial duty cycle to the primary side soft start target duty cycle is divided into multiple primary side duty cycle adjustment stages, including: Setting the current primary side duty cycle to one quarter of the primary side soft start target duty cycle is the first primary side duty cycle adjustment stage; Setting a range from one quarter of the primary side soft start target duty cycle to one half of the primary side soft start target duty cycle as a second primary side duty cycle adjustment stage; Setting the value from half of the primary side soft start target duty cycle to the first preset duty cycle value as the third primary side duty cycle adjustment stage; Setting the first preset duty cycle value to the primary side soft start target duty cycle is a fourth primary side duty cycle adjustment stage; The first preset duty cycle value is a difference between the primary side soft start target duty cycle and a first preset threshold value, the first preset threshold value is greater than 0, and the first preset threshold value is less than half of the primary side soft start target duty cycle.

9. The control method according to claim 6, characterized in that: Gradually adjusting the duty cycle of the secondary side switch of the resonant conversion module, including: Divide the range from the secondary side initial duty cycle to the secondary side soft start target duty cycle into multiple secondary side duty cycle adjustment stages, and obtain the stage target duty cycle of each secondary side duty cycle adjustment stage; Setting 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 voltage effective value of the high-voltage bus side for soft start, and the stage target duty cycle of each secondary side duty cycle adjustment stage; According to the duty cycle step size and the preset duty cycle accumulation time of each secondary side duty cycle adjustment stage, the duty cycle soft start of each adjustment stage is completed until the duty cycle of the secondary side switch tube reaches the secondary side soft start target duty cycle.

10. The control method according to claim 9, characterized in that: The range from the secondary side initial duty cycle to the secondary side soft start target duty cycle is divided into multiple secondary side duty cycle adjustment stages, including: Setting the current secondary side duty cycle to one quarter of the secondary side soft start target duty cycle is the first secondary side duty cycle adjustment stage; Setting a second secondary side duty cycle adjustment stage from one quarter of the secondary side soft start target duty cycle to one half of the secondary side soft start target duty cycle; Setting a value from half of the secondary side soft start target duty cycle to a second preset duty cycle value as a third secondary side duty cycle adjustment stage; Setting the second preset duty cycle value to the secondary side soft start target duty cycle is a fourth secondary side duty cycle adjustment stage; The second preset duty cycle value is a difference between the secondary side soft start target duty cycle and a second preset threshold value, the second preset threshold value is greater than 0, and the second preset threshold value is less than half of the secondary side soft start target duty cycle.

11. An energy storage system, characterized in that: Including master and slave; The master includes a resonant conversion module and an inverter module, and the slave includes a DCDC module, wherein 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 as follows: When the energy storage system is in an off-grid working mode, it is determined whether the grid connection conditions are met according to the electrical parameters of the power grid. When the grid connection conditions are met, the energy storage system is controlled to enter a grid connection working mode: Performing amplitude and phase locking on the inverter module; Setting a first reference voltage value on the high-voltage bus side according to rated electrical parameters of the energy storage system, electrical parameters of a battery currently connected to the slave, and electrical parameters of the master at the current moment; Controlling the grid-connected loop of the host according to the first reference voltage value to obtain a duty cycle of the switch tube of the inverter module; Setting a second reference voltage value on the low-voltage bus side according to electrical parameters of the battery currently connected to the slave device, and controlling the grid-connected loop of the slave device according to the second reference voltage value to obtain a duty cycle of the switch tube of the DCDC module; gradually soft-starting the power on the low-voltage bus side to the battery demand power, obtaining a difference between the first reference voltage value and the voltage value on the high-voltage bus side, inputting the difference into an integrator to obtain a power compensation value, summing the demand power and the power compensation value to obtain a preset power, and soft-starting the power on the high-voltage bus side to the preset power; The ratio of the first reference voltage value to the transformer transformation ratio of the resonant conversion module is greater than the second reference voltage value.

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