Battery charging method and device in energy storage system and storage medium

Abstract

The application relates to a battery charging method and device in an energy storage system and a storage medium, and belongs to the technical field of energy storage. The method comprises the following steps: in response to the energy storage system meeting preset charging conditions, controlling the energy storage system to perform an action of connecting to a power grid; acquiring a battery voltage of a battery assembly; based on the battery voltage and a peak value of a grid voltage of the power grid, determining a target duty cycle of a high-voltage side switch tube in an LLC circuit, so that a bus voltage of the high-voltage side in the LLC circuit matches the peak value of the grid voltage; after the action of connecting to the power grid is performed, controlling the high-voltage side switch tube in the LLC circuit to work according to the target duty cycle, and controlling an inverter circuit to work, so that the power grid charges the battery assembly under the condition that an input current is a desired current without a sharp peak; the method can solve the problem that a sharp current exists in the case of under-voltage of the battery assembly when a traditional energy storage system charges the battery assembly; the sharp current is eliminated, and the safety of devices in the energy storage system is ensured.

Description

TECHNICAL FIELD

[0001] The present application relates to a battery charging method, device and storage medium in an energy storage system, and belongs to the technical field of energy storage. BACKGROUND

[0002] With the gradual increase of the demand for reducing carbon emissions, the use of energy storage systems is becoming more and more widespread. The energy storage system is a device that converts electrical energy into other forms of storage and reconverts it into electrical energy for release when needed.

[0003] A typical energy storage system is implemented by using an LLC circuit plus an inverter circuit scheme. That is, the energy storage system includes a battery assembly, an LLC circuit connected to the battery assembly, an inverter circuit connected to the LLC circuit, and a power grid connected to the inverter circuit. For large energy storage systems, the most commonly used control method for the LLC circuit is variable frequency control. In cost-sensitive energy storage applications, a fixed frequency open loop control strategy is more preferred. Since there is no need for frequency adjustment, the control chip requirements are relatively relaxed, the selection range is wider, and the advantages of low cost and simple control are combined, so it is adopted by many manufacturers. For the fixed frequency open loop control strategy, after the energy storage system is connected to the power grid, the LLC circuit controls the low voltage side and high voltage side switch tubes in the LLC circuit at a fixed frequency and a fixed duty cycle (such as 50%).

[0004] Although the energy storage system based on the LLC circuit plus the inverter circuit has simple control and low cost, since the frequency and duty cycle of the high voltage side switch tube in the LLC circuit are fixed, the gain of the LLC circuit is fixed. At this time, when the battery voltage is too low, the bus voltage of the high voltage side of the LLC circuit will be much lower than the peak value of the power grid voltage, so that the inverter circuit cannot control the input current of the power grid during the charging process of the battery assembly connected to the power grid, there is a large current spike in the input current, which may eventually cause damage to internal devices. SUMMARY

[0005] The present application provides a battery charging method, device and storage medium in an energy storage system, which can solve the problem of sharp current in the process of charging the battery assembly by the traditional energy storage system under the condition of low voltage of the battery assembly. The present application provides the following technical solutions:

[0006] In a first aspect, a battery charging method in an energy storage system is provided, the energy storage system including a battery assembly, an LLC circuit connected to the battery assembly, an inverter circuit connected to the LLC circuit, and a power grid connected to the inverter circuit, the method comprising:

[0007] In response to the energy storage system meeting a predetermined charging condition, controlling the energy storage system to perform a power grid connection action;

[0008] acquiring a battery voltage of the battery assembly;

[0009] determining a target duty cycle of a high-voltage side switch tube in the LLC circuit based on the battery voltage and a peak value of a grid voltage of the grid, so that a bus voltage of the high-voltage side in the LLC circuit matches the peak value of the grid voltage;

[0010] after performing the grid access action, controlling the high-voltage side switch tube in the LLC circuit to work according to the target duty cycle, and controlling the inverter circuit to work, so that the grid charges the battery assembly with a desired current without a spike in input current.

[0011] Optionally, the determining of the target duty cycle of the high-voltage side switch tube in the LLC circuit based on the battery voltage and the grid voltage comprises:

[0012] acquiring a primary-secondary winding ratio of a transformer in the LLC circuit and a preset gain when the high-voltage side switch tube in the LLC circuit works at a preset duty cycle;

[0013] determining the target duty cycle based on the battery voltage, the peak value of the grid voltage, the primary-secondary winding ratio and the preset gain.

[0014] Optionally, the target duty cycle is represented by the following formula:

[0015] .

[0016] wherein G represents the preset gain; N represents the primary-secondary winding ratio; Vbat represents the battery voltage; and Vgrid represents the grid voltage.

[0017] Optionally, the method further comprises:

[0018] in a case where the battery voltage is less than a voltage threshold of the current without a spike, triggering the step of determining the target duty cycle of the high-voltage side switch tube in the LLC circuit based on the battery voltage and the peak value of the grid voltage of the grid, and the steps thereafter.

[0019] Optionally, the method further comprises:

[0020] in a case where the battery voltage is greater than or equal to the voltage threshold, controlling the high-voltage side switch tube in the LLC circuit to work at a preset duty cycle, and controlling the inverter circuit to work.

[0021] Optionally, the voltage threshold is determined based on a ratio of the peak value of the grid voltage of the grid to the primary-secondary winding ratio of the transformer in the LLC circuit.

[0022] Optionally, after controlling the high-voltage side switch in the LLC circuit to operate according to the target duty cycle, the method further includes:

[0023] When the bus voltage is greater than or equal to a preset bus voltage threshold, the target duty cycle is increased so that the high-voltage side switch operates according to the increased target duty cycle.

[0024] And / or,

[0025] When the input current is greater than or equal to a preset input current threshold, the target duty cycle is reduced so that the high-voltage side switch operates at the reduced target duty cycle.

[0026] Optionally, controlling the energy storage system to perform grid connection actions includes:

[0027] At the zero-crossing point of the AC voltage of the power grid, the switching device between the inverter circuit and the power grid is connected to enable conduction between the inverter circuit and the power grid;

[0028] or,

[0029] The low-voltage side switching transistor of the LLC is controlled to operate to increase the bus voltage; after the bus voltage increases, at the zero-crossing point of the AC voltage of the power grid, the switching device between the inverter circuit and the power grid is controlled to connect the inverter circuit and the power grid.

[0030] Optionally, the method further includes:

[0031] If the battery voltage is greater than or equal to the undervoltage protection threshold, the step of triggering the operation of the control LLC low-voltage side switch to increase the bus voltage and subsequent steps are executed.

[0032] In a second aspect, a charging device for a battery in an energy storage system is provided, the device comprising a processor and a memory; the memory stores a program, which is loaded and executed by the processor to implement the charging method for the battery in the energy storage system described in the first aspect.

[0033] Thirdly, a computer-readable storage medium is provided, wherein a program is stored therein, the program being loaded and executed by the processor to implement the battery charging method in the energy storage system described in the first aspect.

[0034] The beneficial effects of this application are as follows: By responding to the energy storage system meeting preset charging conditions, the system is controlled to perform grid connection actions; the battery voltage of the battery module is obtained; based on the peak values ​​of the battery voltage and the grid voltage, the target duty cycle of the high-voltage side switch in the LLC circuit is determined so that the bus voltage on the high-voltage side of the LLC circuit matches the peak value of the grid voltage; after performing grid connection actions, the high-voltage side switch in the LLC circuit is controlled to operate according to the target duty cycle, and the inverter circuit is controlled to operate so that the grid charges the battery module when the input current is the desired current without spikes; this can solve the problem of spike current when the battery module is undervoltage in traditional energy storage systems; since the high-voltage side switch operates with the target duty cycle, the bus voltage matches the peak value of the grid voltage, which can eliminate spike current and ensure the safety of devices in the energy storage system.

[0035] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, the preferred embodiments of this application are described in detail below with reference to the accompanying drawings. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the structure of an energy storage system provided in one embodiment of this application;

[0037] Figure 2 This is a schematic diagram of an LLC circuit provided in one embodiment of this application;

[0038] Figure 3 This is a flowchart of a battery charging method in an energy storage system provided in one embodiment of this application;

[0039] Figure 4 This is a flowchart of a battery charging method in an energy storage system provided in another embodiment of this application;

[0040] Figure 5 This is a block diagram of a battery charging device in an energy storage system provided in one embodiment of this application;

[0041] Figure 6 This is a block diagram of a battery charging device in an energy storage system provided in another embodiment of this application. Detailed Implementation

[0042] The specific embodiments of this application will be described in further detail below with reference to the accompanying drawings and examples. The following examples are used to illustrate this application, but are not intended to limit the scope of this application.

[0043] Figure 1 This is a schematic diagram of the structure of an energy storage system provided in one embodiment of this application, as shown below. Figure 1As shown, the energy storage system includes at least: a battery module 110, an LLC circuit 120, an inverter circuit 130, and a power grid 140.

[0044] Battery assembly 110 is a unit with electrical energy storage function in an energy storage system. Optionally, battery assembly 110 can be a single battery or a battery pack.

[0045] LLC circuit 120 is connected to battery assembly 110, converts the DC power of battery assembly 110 into high-frequency AC power, and steps up or down the voltage through a transformer to meet the input requirements of inverter circuit 130 (i.e., discharge mode); or, converts the high-voltage DC power output by inverter circuit 130 into low-voltage DC power suitable for charging battery assembly 110, and charges battery assembly 110 (i.e., charging mode).

[0046] refer to Figure 2 The schematic diagram of LLC circuit 120 shown includes a low-voltage side connected to battery assembly 110 and a high-voltage side connected to inverter circuit 130. The high-voltage side and the low-voltage side are connected by transformer 200. The transformer includes a primary winding and a secondary winding, and the turns ratio between the primary and secondary windings is N.

[0047] Taking the LLC circuit 120, which implements bidirectional LLC resonant conversion based on a typical LLC full-bridge circuit, as an example, the low-voltage side and the high-voltage side each include 4 switching transistors.

[0048] In this design, MOS1 and MOS3 on the low-voltage side form the upper bridge arm, and MOS2 and MOS4 form the lower bridge arm. The sources of MOS1 and MOS3 are connected to the positive terminal of the battery module 110, and the drains of MOS2 and MOS4 are connected to the negative terminal of the battery module 110. The two ends of the primary winding are connected to the midpoints of the bridge arms of the switching transistors, and the gates of MOS1 to MOS4 are controlled to turn on and off by a driving circuit.

[0049] In this bridge, MOS5 and MOS7 on the high-voltage side form the upper bridge arm, and MOS6 and MOS8 form the lower bridge arm. The sources of MOS5 and MOS7 are connected to the positive terminal of the high-voltage bus Vbus, and the drains of MOS6 and MOS8 are connected to the negative terminal of the high-voltage bus Vbus. The two ends of the secondary winding are connected to the midpoints of the bridge arms of the switching transistors. The gates of MOS5 to MOS8 are controlled to turn on and off by a drive circuit.

[0050] In the operation of a full-bridge converter, the switches in the upper and lower bridge arms are complementary in conduction. In other words, when the upper bridge arm switch is on, the lower bridge arm switch is off, and vice versa. During the operation of LLC circuit 120, the duty cycle of the switches in the upper and lower bridge arms can be adjusted using a pulse width modulation (PWM) control strategy. The duty cycle is the ratio of the duration each switch is on within a switching cycle to the duration of that switching cycle. The switching cycle is the total duration required for each switch to complete a full switching cycle (including on and off).

[0051] The high-voltage side of the LLC circuit 120 also includes a resonant network. For example, refer to... Figure 2 The resonant network includes a resonant inductor Lr and a resonant capacitor Cr located on the high-voltage side. The resonant inductor Lr and the resonant capacitor Cr are connected in series to one end of the secondary winding, and together they determine the resonant frequency of the resonant network.

[0052] The low-voltage side and / or high-voltage side of the LLC circuit 120 also includes a magnetizing inductor Lm, which is connected across the two ends of the secondary winding and represents the excitation inductance of the transformer.

[0053] It should be added that the reference Figure 2 The implementation of LLC circuit 120 shown is only illustrative. In actual implementation, LLC circuit 120 can also be implemented as a symmetrical half-bridge, an asymmetrical half-bridge, an asymmetrical full-bridge, etc. This embodiment does not limit the implementation of LLC circuit 120.

[0054] Inverter circuit 130 is used to convert the DC power output from LLC circuit 120 into AC power (usually power frequency AC power) compatible with grid 140 and feed it back to the load (i.e., discharge mode); or, to convert the AC power from grid 140 into DC power (i.e., charging mode).

[0055] Inverter circuit 130 is connected to LLC circuit 120. Specifically, inverter circuit 130 is connected across LLC circuit 120. Figure 2 The two ends of the high-voltage bus Vbus in the LLC circuit 120 shown. Optionally, the inverter circuit 130 can be a full-bridge inverter, a half-bridge inverter, etc., and this embodiment does not limit the implementation of the inverter circuit 130.

[0056] The power grid 140 and the inverter circuit 130 are connected on and off via a switching device, so that the connection is made when the battery assembly 110 is charged through the power grid 140 or when the power grid supplies power to the load, and disconnected when the battery assembly 110 supplies power to the load. Exemplarily, the switching device can be implemented as a relay; of course, it can also be implemented in other ways, and this embodiment does not limit the implementation of the switching device. The power grid 140 is a facility for transmitting and distributing electrical energy. In charging mode, the power grid 140 is used to output alternating current to the inverter circuit 130.

[0057] Assuming the turns ratio of the transformer's primary and secondary sides in LLC circuit 120 is N, the battery voltage of battery module 110 is Vbat, the bus voltage is Vbus, the grid voltage is Vgrid, the bus capacitance on the high-voltage side of the transformer is Cbus, and the maximum input current of grid 140 is Imax, then when the energy storage system executes a fixed-frequency open-loop LLC operation, the relationship between the bus voltage Vbus and the battery voltage Vbat of battery module 110 is as follows:

[0058] ;

[0059] The formula for calculating the maximum input current is as follows:

[0060] Imax=Cbus× = Cbus× .

[0061] This represents one switching cycle of the high-voltage side switch of the transformer. According to the above formula, the bus voltage Vbus and the battery voltage Vbat are positively correlated. Therefore, when the battery voltage Vbat is too low, the bus voltage Vbus cannot reach the peak value of the grid voltage Vgrid (140V), resulting in a spike in the maximum input current (i.e., peak current). The smaller the bus voltage Vbus, the larger the peak current. Furthermore, when the switch in inverter circuit 130 is turned off, the inductor in inverter circuit 130 will prevent current flow to maintain current continuity. At this time, energy will be injected into the bus through the body diode of the switch in inverter circuit 130. Therefore, inverter circuit 130 cannot control the peak current input from grid 140. Excessive peak current will affect the normal operation of the system and may even damage components.

[0062] Based on the above-mentioned technical problems, this application provides a charging method for batteries in an energy storage system. This method improves the software control of the energy storage system and, compared with conventional inverter control methods, does not require any additional hardware circuits. It can achieve normal grid connection and charging of battery components under low voltage conditions, thereby improving charging reliability, safety and charging adaptability.

[0063] The following describes the battery charging method in the energy storage system provided in this application.

[0064] Figure 3 This is a flowchart of a battery charging method in an energy storage system according to an embodiment of this application. This embodiment uses the method in an electronic device controlling the energy storage system as an example for illustration. The energy storage system includes... Figure 1 The energy storage system shown includes a battery module, an LLC circuit connected to the battery module, an inverter circuit connected to the LLC circuit, and a power grid connected to the inverter circuit.

[0065] The electronic device can be a control component in the energy storage system, or a device that is communicatively connected to the control component but independent of the energy storage system. This embodiment does not limit the implementation method of the electronic device. Figure 3 As shown, the method includes at least:

[0066] Step 301: In response to the energy storage system meeting the preset charging conditions, control the energy storage system to perform the grid connection action.

[0067] For example, the charging conditions include: receiving a charging command and the amplitude-frequency characteristics of the power grid meeting the grid connection characteristics.

[0068] The charging command is used to instruct the battery module to be charged. Methods for obtaining the charging command include, but are not limited to: receiving a charging command from another device; or, generating a charging command when the battery voltage of the battery module is below a certain threshold. This embodiment does not limit the method of obtaining the charging command.

[0069] Optionally, the amplitude-frequency characteristics of the power grid include the voltage amplitude and voltage frequency. Accordingly, the amplitude-frequency characteristics satisfy the grid connection characteristics, including: the voltage amplitude is greater than a preset lower amplitude threshold and less than a preset upper amplitude threshold; and the voltage frequency is greater than a preset lower frequency threshold and less than a preset upper frequency threshold. In actual implementation, the amplitude-frequency characteristics may also include other types of parameters, and correspondingly, the grid connection characteristics may also include thresholds corresponding to these parameters. This embodiment does not limit the implementation method of the amplitude-frequency characteristics satisfying the grid connection characteristics.

[0070] In one example, controlling the energy storage system to perform grid connection actions includes: controlling the connection of switching devices between the inverter circuit and the grid at the zero-crossing point of the AC voltage of the grid, so as to enable conduction between the inverter circuit and the grid.

[0071] For example, if the inverter circuit and the power grid are connected on and off via a relay, then when the energy storage system is controlled to perform the grid connection action, the connection between the inverter circuit and the power grid can be achieved by activating the relay.

[0072] Since the bus voltage is initialized to 0, directly connecting the inverter circuit to the grid at the zero-crossing point of the grid's AC voltage would result in a large current surge when energy flows from the grid to the bus. Based on this, in another example, controlling the energy storage system to perform grid connection actions includes: controlling the low-voltage side switch of the LLC to operate, thereby increasing the bus voltage; and after the bus voltage has increased, controlling the switching devices between the inverter circuit and the grid at the zero-crossing point of the grid's AC voltage to connect the inverter circuit to the grid.

[0073] In the example above, increasing the bus voltage before connecting the inverter circuit to the grid can reduce current surges. However, since controlling the operation of the low-voltage side switch of the LLC involves outputting energy from the battery module to the bus to raise the bus voltage, this can exacerbate the undervoltage situation of the battery module.

[0074] To avoid triggering the undervoltage protection of the battery management system when the bus voltage rises, the following steps can be taken: first, when the battery voltage is greater than or equal to the undervoltage protection threshold, the low-voltage side switch of the control LLC can be activated to raise the bus voltage. If the battery voltage is greater than the undervoltage protection threshold, the connection of the switching devices between the inverter circuit and the grid can be directly controlled at the AC voltage zero-crossing point.

[0075] The undervoltage protection threshold is the critical voltage value of the battery component that triggers the battery management system to perform undervoltage protection. The undervoltage protection threshold is preset in the electronic device, and this embodiment does not limit the value of the undervoltage protection threshold.

[0076] Step 302: Obtain the battery voltage of the battery assembly.

[0077] Electronic devices sample the battery voltage of battery modules, or acquire battery voltages sent by other devices.

[0078] Step 303: Based on the peak values ​​of the battery voltage and the grid voltage, determine the target duty cycle of the high-voltage side switch in the LLC circuit so that the bus voltage on the high-voltage side of the LLC circuit matches the peak value of the grid voltage.

[0079] Optionally, matching the peak values ​​of the bus voltage and the grid voltage means that the peak values ​​of the bus voltage and the grid voltage are equal, or that the peak values ​​of the bus voltage and the grid voltage are basically consistent, that is, the difference between the peak values ​​of the bus voltage and the grid voltage is within a preset allowable error range.

[0080] According to the fundamental equivalent analysis method, the formula for calculating the Fourier series of the high-voltage side voltage of an LLC circuit can be expressed by the following equation:

[0081] ;

[0082] ;

[0083] ;

[0084] ;

[0085] Where n represents the harmonic order, Vbus represents the angular frequency of the fundamental voltage, D represents the bus voltage, D represents the duty cycle of the high-voltage side switch in the LLC circuit, and T represents the switching period of the high-voltage side switch.

[0086] Based on the above representation of the high-voltage side Fourier series, the equivalent fundamental frequency of the high-voltage side voltage of the LLC circuit is:

[0087] ;

[0088] The voltage amplitude is:

[0089] .

[0090] According to the above formula, the voltage amplitude of the equivalent fundamental voltage of the high-voltage side of the LLC circuit can be determined by the duty cycle D of the high-voltage side switch of the LLC circuit. Specifically, the duty cycle D is directly proportional to the voltage amplitude of the equivalent fundamental voltage. Based on this, the voltage amplitude of the equivalent fundamental voltage of the LLC circuit can be controlled by controlling the duty cycle D of the high-voltage side switch of the LLC circuit.

[0091] During battery module charging, since the turns ratio of the primary and secondary sides of the transformer in the LLC circuit is a fixed constant N, changing the voltage amplitude of the equivalent fundamental wave at the input terminal (high voltage side) of the LLC transformer will also change the voltage amplitude of the equivalent fundamental wave at the output terminal (low voltage side) of the LLC transformer. The voltage gain of the LLC circuit based on the fundamental wave can be expressed as the ratio of the voltage at the transformer output terminal to the voltage at the transformer input terminal. Therefore, by changing the duty cycle D, the gain of the LLC circuit can be changed.

[0092] As can be seen from the above technical issues, the reason why energy storage systems employing a fixed-frequency open-loop control strategy generate peak currents during charging is due to the fixed gain of the fixed-frequency open-loop LLC circuit, resulting in a significant difference between the bus voltage Vbus and the grid voltage Vgrid. Therefore, when the battery voltage of the battery module is low, the gain of the LLC circuit can be changed to reduce the difference between the bus voltage Vbus and the grid voltage Vgrid, thereby reducing peak currents.

[0093] Specifically, the voltage gain G of the LLC circuit can be expressed by the following formula:

[0094] ;

[0095] in, This represents the equivalent fundamental frequency of the low-side voltage in an LLC circuit. Vbus represents the equivalent fundamental voltage of the high-voltage side of the LLC circuit; Vbus represents the bus voltage; Vbat represents the battery voltage of the battery module; D represents the duty cycle of the high-voltage side switch in the LLC circuit; N represents the primary-to-secondary turns ratio of the transformer in the LLC circuit.

[0096] To eliminate peak currents, it is desirable that the bus voltage Vbus should be at least the peak value of the grid voltage Vgrid when the energy storage system is charging the battery modules (i.e., Vgrid), and maintaining the primary-to-secondary turns ratio relationship between the bus voltage Vbus and the battery voltage Vbat, based on this, let Vbus = in the above voltage gain G formula. Vgrid can be used to obtain the target duty cycle of the high-voltage side switch in an LLC circuit. The calculation formula is as follows:

[0097] .

[0098] Where G is the preset gain of the high-voltage side switch of the LLC circuit when it operates at a preset duty cycle. The preset duty cycle refers to the default duty cycle in the LLC circuit design, for example, the preset duty cycle of a traditional fixed-frequency open-loop LLC is 50% by default.

[0099] As can be seen from the above formula, the target duty cycle of the high-voltage side switch in the LLC circuit is determined based on the battery voltage and the grid voltage. This includes: obtaining the primary and secondary turns ratio of the transformer in the LLC circuit, and the preset gain of the high-voltage side switch in the LLC circuit when it operates with a preset duty cycle; and determining the target duty cycle based on the peak values ​​of the battery voltage and the grid voltage, the primary and secondary turns ratio, and the preset gain.

[0100] Assuming the value of G is 1 (the gain of a fixed-frequency open-loop LLC is typically 1), the target duty cycle of the LLC high-voltage side switch can be obtained. for:

[0101] .

[0102] Optionally, if the current battery voltage is sufficient to match the peak value of the bus voltage with the grid voltage, then there is no need to obtain the target duty cycle; the battery module can be charged directly. Based on this, to save computational resources of the electronic equipment, when the battery voltage is less than the voltage threshold without peak current, the step of determining the target duty cycle of the high-voltage side switch in the LLC circuit based on the peak value of the battery voltage and the grid voltage is triggered, followed by step 303.

[0103] When the battery voltage is greater than or equal to the voltage threshold, the high-voltage side switch in the control LLC circuit operates according to the preset duty cycle, and controls the inverter circuit to operate.

[0104] The voltage threshold is determined based on the ratio of the peak value of the grid voltage to the turns ratio of the primary and secondary windings of the transformer in the LLC circuit. That is, the voltage threshold is expressed by the following formula:

[0105] ;

[0106] Among them, Vbat min Indicates the voltage threshold; Vgrid× Vgrid represents the peak value of the grid voltage; N represents the primary-to-secondary turns ratio.

[0107] Optionally, steps 302 and 303 can be executed before step 301, or after step 301, or synchronously with step 301. This embodiment does not limit the execution order between steps 302-303 and 301.

[0108] Step 304: After performing the grid connection action, control the high-voltage side switch in the LLC circuit to operate according to the target duty cycle, and control the inverter circuit to operate so that the grid charges the battery pack when the input current is the desired current without spikes.

[0109] Controlling the high-voltage side switch in the LLC circuit to operate according to the target duty cycle includes: controlling the high-voltage side switch in the LLC circuit to operate at a preset frequency, and gradually increasing the duty cycle of the high-voltage side switch from 0 until the target duty cycle is reached (i.e., the duty cycle gradually increases from 0 to the target duty cycle through a soft start).

[0110] In this embodiment, by making the high-voltage side switch operate at the target duty cycle, the peak value of the bus voltage is matched with the peak value of the grid voltage, thus eliminating peak current.

[0111] Optionally, after controlling the high-voltage side switch in the LLC circuit to operate according to the target duty cycle, the method further includes: increasing the target duty cycle when the bus voltage is greater than or equal to a preset bus voltage threshold, so that the high-voltage side switch operates according to the increased target duty cycle; and / or decreasing the target duty cycle when the input current is greater than or equal to a preset input current threshold, so that the high-voltage side switch operates according to the decreased target duty cycle.

[0112] At this time, the electronic equipment also needs to obtain the bus voltage and / or the input current of the power grid. The acquisition method can be that the electronic equipment collects the data or that other equipment sends the data. This embodiment does not limit the acquisition method.

[0113] Optionally, the increase and decrease of the target duty cycle may be the same or different, and the magnitude is a preset value. This embodiment does not limit the value of the magnitude.

[0114] Due to factors such as parasitic circuit parameters and component numerical deviations in energy storage systems, the actual duty cycle of the high-voltage side switching transistors may not reach the target duty cycle when the electronic equipment controls the high-voltage side switching transistors to operate according to the target duty cycle; that is, there is a certain deviation between the actual duty cycle and the target duty cycle. When the actual duty cycle is less than the target duty cycle, the grid energy may not be able to be transferred to the battery modules quickly, leading to excessive rise in the bus voltage. Therefore, by increasing the target duty cycle when the bus voltage is detected to be greater than or equal to a preset bus voltage threshold, the bus voltage can be reduced, making the actual duty cycle closer to the target duty cycle. When the actual duty cycle is greater than the target duty cycle, the inverter circuit may not be able to effectively control the input current, leading to the input current exceeding the input current threshold. Therefore, by decreasing the target duty cycle when the input current is detected to be continuously (e.g., continuously for a preset time) greater than the input current threshold, the input current can be reduced, ensuring device safety.

[0115] Optionally, after step 304, the electronic device executes step 302 again every preset detection time until the battery voltage is greater than or equal to the voltage threshold. Then, it controls the high-voltage side switch in the LLC circuit to work according to the preset duty cycle and controls the inverter circuit to work, executing the normal charging logic of the battery assembly.

[0116] In summary, the battery charging method in the energy storage system provided in this embodiment controls the energy storage system to perform grid connection in response to the energy storage system meeting preset charging conditions; obtains the battery voltage of the battery module; determines the target duty cycle of the high-voltage side switch in the LLC circuit based on the peak values ​​of the battery voltage and the grid voltage, so that the bus voltage on the high-voltage side of the LLC circuit matches the peak value of the grid voltage; after performing grid connection, controls the high-voltage side switch in the LLC circuit to operate according to the target duty cycle, and controls the inverter circuit to operate, so that the grid charges the battery module when the input current is the desired current without spikes; this can solve the problem of spike current when the battery module is undervoltage in traditional energy storage systems; since the high-voltage side switch operates at the target duty cycle, the bus voltage matches the peak value of the grid voltage, which can eliminate spike current and ensure the safety of devices in the energy storage system.

[0117] In addition, by calculating the target duty cycle only when the battery voltage is below the voltage threshold without peak current, the battery modules can be charged directly without determining the target duty cycle when the current battery voltage is already sufficient to match the peak value of the bus voltage and the grid voltage, thus saving the computing resources of electronic devices.

[0118] In addition, by controlling the low-voltage side switch of the LLC to operate before the inverter circuit is connected to the power grid, the bus voltage is increased and the difference between the peak values ​​of the bus voltage and the power grid voltage is reduced, which can reduce the current surge generated when the inverter circuit is connected to the power grid and improve device safety.

[0119] In addition, by increasing the bus voltage when the battery voltage is greater than or equal to the undervoltage protection threshold, the problem of triggering the undervoltage protection of the battery management system of the battery module and interrupting charging can be avoided, thus ensuring the charging effect.

[0120] In addition, by controlling the high-voltage side switching transistor to operate according to the target duty cycle, the target duty cycle is dynamically adjusted to make the actual duty cycle as close as possible to the target duty cycle, thereby further ensuring device safety.

[0121] To better understand the battery charging method in the energy storage system provided in this application, an example is given below for illustration. Figure 4 The method includes the following steps:

[0122] Step 41: In response to the command to start charging the battery module, obtain the amplitude-frequency characteristics of the power grid to determine whether the amplitude-frequency characteristics meet the grid connection characteristics; if yes, proceed to step 42; if no, proceed to step 41 again.

[0123] Step 42: Obtain the battery voltage of the battery assembly;

[0124] Step 43: Determine whether the battery voltage is greater than or equal to the voltage threshold without peak current; if yes, proceed to step 44; if no, proceed to step 45.

[0125] Step 44: Control the energy storage system to perform grid connection action; control the high-voltage side switch in the LLC circuit to work according to the preset duty cycle, and control the inverter circuit to work until the charging is finished, and the process ends.

[0126] Step 45: Control the energy storage system to perform grid connection action and determine the target duty cycle of the high-voltage side switch in the LLC circuit;

[0127] Optionally, the grid connection action in step 44 may be the same as or different from the grid connection action in step 45.

[0128] Step 46: Control the high-voltage side switching transistor in the LLC circuit to operate according to the target duty cycle;

[0129] Step 47: Control the inverter circuit to operate;

[0130] Step 48: Based on the bus voltage and input current, dynamically adjust the target duty cycle and execute step 42.

[0131] In summary, the battery charging method in the energy storage system provided in this embodiment can achieve adaptive, spike-current-free charging of the energy storage system under the condition of undervoltage of the battery components without the need for additional hardware, thereby improving the charging reliability of the energy storage system.

[0132] In addition, by adjusting the duty cycle through PWM modulation to achieve charging without peak current, this method is applicable to almost all chips that perform LLC control, thus improving the method's versatility.

[0133] Figure 5 This is a block diagram of a battery charging device in an energy storage system according to an embodiment of this application. The device includes at least the following modules: a grid access module 510, a voltage acquisition module 520, a duty cycle determination module 530, and a charging control module 540.

[0134] The grid access module 510 is used to control the energy storage system to perform grid access operation in response to the energy storage system meeting preset charging conditions;

[0135] Voltage acquisition module 520 is used to acquire the battery voltage of the battery assembly;

[0136] The duty cycle determination module 530 is used to determine the target duty cycle of the high-voltage side switch in the LLC circuit based on the peak values ​​of the battery voltage and the grid voltage of the grid, so that the bus voltage on the high-voltage side of the LLC circuit matches the peak value of the grid voltage.

[0137] The charging control module 540 is used to control the high-voltage side switch in the LLC circuit to operate according to the target duty cycle after performing the grid connection action, and to control the inverter circuit to operate so that the grid charges the battery pack when the input current is the desired current without spikes.

[0138] Optionally, the duty cycle determination module 530 is used for:

[0139] Obtain the primary-to-secondary turns ratio of the transformer in the LLC circuit, and the preset gain of the high-voltage side switch of the LLC circuit when it operates with a preset duty cycle;

[0140] The target duty cycle is determined based on the battery voltage, the peak value of the grid voltage, the primary-to-secondary turns ratio, and the preset gain.

[0141] Optionally, the target duty cycle This can be expressed by the following formula:

[0142] .

[0143] Wherein, G represents the preset gain; N represents the primary-to-secondary turns ratio; Vbat represents the battery voltage; and Vgrid represents the grid voltage.

[0144] Optionally, the duty cycle determination module 530 is further configured to:

[0145] If the battery voltage is less than the voltage threshold at which there is no spike current, the step of determining the target duty cycle of the high-voltage side switch in the LLC circuit based on the peak value of the battery voltage and the grid voltage of the grid is triggered, and subsequent steps are then executed.

[0146] Optionally, the charging control module 540 is further configured to:

[0147] When the battery voltage is greater than or equal to the voltage threshold, the high-voltage side switch in the LLC circuit is controlled to operate according to a preset duty cycle, and the inverter circuit is controlled to operate.

[0148] Optionally, the voltage threshold is determined based on the ratio of the peak value of the grid voltage of the power grid to the ratio of the number of turns on the primary and secondary sides of the transformer in the LLC circuit.

[0149] Optionally, the device further includes: a duty cycle adjustment module, used for:

[0150] After controlling the high-voltage side switch in the LLC circuit to operate according to the target duty cycle, if the bus voltage is greater than or equal to a preset bus voltage threshold, the target duty cycle is increased so that the high-voltage side switch operates according to the increased target duty cycle.

[0151] And / or,

[0152] When the input current is greater than or equal to a preset input current threshold, the target duty cycle is reduced so that the high-voltage side switch operates at the reduced target duty cycle.

[0153] Optionally, the power grid access module 510 is used for:

[0154] At the zero-crossing point of the AC voltage of the power grid, the switching device between the inverter circuit and the power grid is connected to enable conduction between the inverter circuit and the power grid;

[0155] or,

[0156] The low-voltage side switching transistor of the LLC is controlled to operate to increase the bus voltage; after the bus voltage increases, at the zero-crossing point of the AC voltage of the power grid, the switching device between the inverter circuit and the power grid is controlled to connect the inverter circuit and the power grid.

[0157] Optionally, the power grid access module 510 is used for:

[0158] If the battery voltage is greater than or equal to the undervoltage protection threshold, the step of triggering the operation of the control LLC low-voltage side switch to increase the bus voltage and subsequent steps are executed.

[0159] For relevant details, please refer to the above method implementation examples.

[0160] It should be noted that the battery charging device in the energy storage system provided in the above embodiments is only an example of the above functional module division when describing the battery charging method in the energy storage system. In practical applications, the above functions can be assigned to different functional modules as needed, that is, the internal structure of the battery charging device in the energy storage system can be divided into different functional modules to complete all or part of the functions described above. In addition, the battery charging device in the energy storage system and the battery charging method embodiments provided in the above embodiments belong to the same concept, and the specific implementation process is detailed in the method embodiments, which will not be repeated here.

[0161] Figure 6 This is a block diagram of a battery charging device in an energy storage system according to an embodiment of this application. The device is used to control... Figure 1 The energy storage system shown charges the battery pack. The charging device can be a control component within the energy storage system, or it can be a user device, portable terminal, laptop terminal, desktop terminal, control terminal, etc. This embodiment does not limit this. The device includes at least a processor 601 and a memory 602.

[0162] Processor 601 may include one or more processing cores, such as a quad-core processor or a hexa-core processor. Processor 601 may be implemented using at least one hardware form selected from DSP (Digital Signal Processing), FPGA (Field-Programmable Gate Array), and PLA (Programmable Logic Array). Processor 601 may also include a main processor and a coprocessor. The main processor, also known as a CPU (Central Processing Unit), is used to process data in the wake-up state; the coprocessor is a low-power processor used to process data in the standby state. In some embodiments, processor 601 may integrate a GPU (Graphics Processing Unit), which is responsible for rendering and drawing the content to be displayed on the screen. In some embodiments, processor 601 may also include an AI (Artificial Intelligence) processor, which is used to handle computational operations related to machine learning.

[0163] The memory 602 may include one or more computer-readable storage media, which may be non-transitory. The memory 602 may also include high-speed random access memory and non-volatile memory, such as one or more disk storage devices or flash memory devices. In some embodiments, the non-transitory computer-readable storage media in the memory 602 are used to store at least one instruction, which is executed by the processor 601 to implement the battery charging method in the energy storage system provided in the method embodiments of this application.

[0164] In some embodiments, the battery charging device in the energy storage system may optionally include: a peripheral device interface and at least one peripheral device. The processor 601, memory 602, and peripheral device interface can be connected via a bus or signal line. Each peripheral device can be connected to the peripheral device interface via a bus, signal line, or circuit board. Indicatively, peripheral devices include, but are not limited to: radio frequency circuits, touch displays, audio circuits, and power supplies.

[0165] Of course, the battery charging device in the energy storage system may include fewer or more components, and this embodiment does not limit this.

[0166] Optionally, this application also provides a computer-readable storage medium storing a program that is loaded and executed by a processor to implement the battery charging method in the energy storage system of the above method embodiments.

[0167] Optionally, this application also provides a computer product including a computer-readable storage medium storing a program that is loaded and executed by a processor to implement the battery charging method in the energy storage system of the above method embodiments.

[0168] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0169] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method of charging a battery in an energy storage system, characterized by, The energy storage system comprises a battery assembly, an LLC circuit connected to the battery assembly, an inverter circuit connected to the LLC circuit, and a power grid connected to the inverter circuit, and the method comprises: In response to the energy storage system meeting a preset charging condition, controlling the energy storage system to perform a grid access action; Obtaining a battery voltage of the battery assembly; Based on the battery voltage and the peak value of the grid voltage of the power grid, determining a target duty cycle of a high-voltage side switch tube in the LLC circuit, so that the bus voltage of the high-voltage side of the LLC circuit matches the peak value of the grid voltage; After performing the grid access action, controlling the high-voltage side switch tube in the LLC circuit to work according to the target duty cycle, and controlling the inverter circuit to work, so that the power grid charges the battery assembly under the condition that the input current is a desired current without spikes; The method further comprises: Obtaining the primary and secondary winding ratio of the transformer in the LLC circuit, and the preset gain when the high-voltage side switch tube in the LLC circuit works at a preset duty cycle; Determine the target duty cycle based on the battery voltage, the peak value of the grid voltage, the primary-secondary turn ratio, and the preset gain, wherein the target duty cycle is expressed by the following formula: Wherein, G represents the preset gain; N represents the primary and secondary winding ratio; Vbat represents the battery voltage; Vgrid represents the grid voltage.

2. The method of claim 1, wherein, The method further comprises: In the case that the battery voltage is less than the voltage threshold of the non-spiked current, triggering the step of determining the target duty cycle of the high-voltage side switch tube in the LLC circuit based on the battery voltage and the peak value of the grid voltage of the power grid, and the subsequent steps.

3. The method of claim 2, wherein, The method further comprises: In the case that the battery voltage is greater than or equal to the voltage threshold, controlling the high-voltage side switch tube in the LLC circuit to work at a preset duty cycle, and controlling the inverter circuit to work.

4. The method of claim 2, wherein, The voltage threshold is determined based on the ratio of the peak value of the grid voltage of the power grid to the primary and secondary winding ratio of the transformer in the LLC circuit.

5. The method according to any one of claims 1 to 4, characterized in that, After controlling the high-voltage side switch tube in the LLC circuit to work at the target duty cycle, the method further comprises: In the case that the bus voltage is greater than or equal to a preset bus voltage threshold, increasing the target duty cycle, so that the high-voltage side switch tube works at the increased target duty cycle; And / or, In the case that the input current is greater than or equal to a preset input current threshold, reducing the target duty cycle, so that the high-voltage side switch tube works at the reduced target duty cycle.

6. The method of any one of claims 1 to 4, wherein The control of the energy storage system to perform the grid access action comprises: At the zero-crossing point of the AC voltage of the power grid, controlling the connection of the switching device between the inverter circuit and the power grid to make the inverter circuit and the power grid conductive; Or, Controlling the LLC low-voltage side switch tube to work to raise the bus voltage; after the bus voltage is raised, at the zero-crossing point of the AC voltage of the power grid, controlling the connection of the switching device between the inverter circuit and the power grid to make the inverter circuit and the power grid conductive.

7. The method of claim 6, wherein, The method further comprises: In the case that the battery voltage is greater than or equal to an under-voltage protection threshold, triggering the step of performing the control of the LLC low-side switch to raise the bus voltage and the subsequent steps.

8. A charging device for a battery in an energy storage system, characterized in that The device comprises a processor and a memory; the memory has stored therein a program, which is loaded and executed by the processor to implement the charging method of the battery in the energy storage system according to any one of claims 1 to 7.

9. A computer-readable storage medium, characterized in that, The storage medium has stored therein a program, which is executed by a processor to implement the charging method of the battery in the energy storage system according to any one of claims 1 to 7.

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