Starting method of LLC bidirectional isolation module, controller and energy storage system

Abstract

The invention discloses a starting method of an LLC bidirectional isolation module, a controller and an energy storage system. The starting method of the LLC bidirectional isolation module comprises the following steps: starting the LLC bidirectional isolation module by taking an initial frequency as a current frequency; gradually reducing the current frequency of the LLC bidirectional isolation module according to the frequency change value until the current frequency of the LLC bidirectional isolation module reaches the target frequency; the frequency change value is determined according to the first voltage of the low-voltage connection end and the second voltage of the high-voltage connection end; therefore, along with the change of the first voltage and the second voltage, new frequency change values can be continuously obtained to adjust the current frequency of the LLC bidirectional isolation module, and the starting scene of the LLC bidirectional isolation module does not need to be considered, so that the coordinated starting control of the low-voltage bus equipment and the high-voltage bus equipment of the LLC bidirectional isolation module can be completely separated, and the starting efficiency of the LLC bidirectional isolation module is improved. And the complexity of starting control is effectively reduced.

Description

Technical Field

[0001] The present application relates to the technical field of electronic circuits, and particularly to a starting method, a controller, and an energy storage system for an LLC bidirectional isolation module. Background Art

[0002] The LLC bidirectional isolation boost module can be connected to the low-voltage side DC bus and the high-voltage side DC bus. When the LLC bidirectional isolation boost module is in standby, the voltages of the DC buses on both sides of the LLC are completely determined by other circuits or devices on the DC buses. At the same time, considering the problem of overcurrent during the startup of the LLC bidirectional isolation boost module, generally, the switches at both ends of the LLC are gradually soft-started in a manner of increasing the effective duty cycle.

[0003] In an energy storage system, the LLC bidirectional isolation boost module is commonly used as the front-stage boost module of the energy storage converter, as well as the rear-stage boost and power control module. There are a series of complex startup conditions such as battery activation startup, fast startup after the energy storage system is in standby, and black startup after off-grid shutdown. Under the existing solutions, it is necessary to strongly classify these startup conditions and set corresponding startup strategies according to each startup condition to achieve reliable startup. However, this logic for startup control according to the startup conditions is relatively complex and needs to consider the situation of circuits other than the LLC bidirectional isolation boost module, which is not conducive to reducing the control complexity. Summary of the Invention

[0004] Embodiments of the present application provide a starting method, a controller, and an energy storage system for an LLC bidirectional isolation module, which can achieve decoupled startup and reduce the startup complexity.

[0005] In a first aspect, embodiments of the present application provide a starting method for an LLC bidirectional isolation module. The LLC bidirectional isolation module includes: A low-voltage side connection end connected to a first bridge circuit; A high-voltage side connection end connected to a second bridge circuit; A transformer, the primary side of the transformer is connected to the first bridge circuit, and the secondary side of the transformer is connected to the second bridge circuit; The starting method includes: Starting the LLC bidirectional isolation module with an initial frequency as the current frequency; Gradually reducing the current frequency of the LLC bidirectional isolation module according to a frequency change value until the current frequency of the LLC bidirectional isolation module reaches a target frequency; Wherein, the frequency change value is determined according to a first voltage at the low-voltage connection end and a second voltage at the high-voltage connection end.

[0006] In some embodiments, the frequency change value is obtained through the following steps: Obtain the first voltage and the second voltage; Determine a voltage difference according to the first voltage and the second voltage; Determine the frequency change value according to the voltage difference.

[0007] In some embodiments, the determining the voltage difference according to the first voltage and the second voltage includes: Determine a third voltage according to the turns ratio of the transformer and the first voltage; Determine the voltage difference according to the absolute value of the difference between the third voltage and the second voltage.

[0008] In some embodiments, the frequency change value increases as the voltage difference becomes smaller.

[0009] In some embodiments, the determining the frequency change value according to the voltage difference includes: When starting the LLC bi-directional isolation module at the initial frequency, obtain a first initial voltage of the low-voltage side connection end and a second initial voltage of the high-voltage side connection end; Divide a plurality of voltage intervals according to the difference between the first initial voltage and the second initial voltage, and set a frequency change value corresponding to each voltage interval; Determine the frequency change value for reducing the current frequency according to the corresponding relationship between the voltage difference and the voltage interval.

[0010] In some embodiments, the dividing a plurality of voltage intervals according to the difference between the first initial voltage and the second initial voltage includes: Determine a third initial voltage according to the turns ratio of the transformer and the first initial voltage; Determine a voltage range with the third initial voltage as the lower limit value and the second initial voltage as the upper limit value; Divide the voltage range to obtain a plurality of voltage intervals.

[0011] In some embodiments, the first bridge circuit includes a first bridge arm and a second bridge arm. The first bridge arm includes a first switching tube and a second switching tube connected in series. The second bridge arm includes a third switching tube and a fourth switching tube connected in series. The midpoint of the first bridge arm and the midpoint of the second bridge arm are connected to the primary side of the transformer; the second bridge circuit includes a third bridge arm and a fourth bridge arm. The third bridge arm includes a fifth switching tube and a sixth switching tube connected in series. The fourth bridge arm includes a seventh switching tube and an eighth switching tube connected in series. The midpoint of the third bridge arm and the midpoint of the fourth bridge arm are connected to the secondary side of the transformer.

[0012] In some embodiments, the current frequency is used to control the opening and closing of the first switch tube, the fourth switch tube, the fifth switch tube, and the eighth switch tube, and the inverted frequency of the current frequency is used for the second switch tube, the third switch tube, the sixth switch tube, and the seventh switch tube.

[0013] In a second aspect, an embodiment of the present application provides a controller, including at least one processor and a memory communicatively connected to the at least one processor; the memory stores instructions executable by the at least one processor, and the instructions are executed by the at least one processor to enable the at least one processor to execute the starting method as described in the first aspect.

[0014] In a third aspect, an embodiment of the present application provides an energy storage system, including an LLC bidirectional isolation module and the controller of the second aspect.

[0015] The starting method, controller, and energy storage system of the LLC bidirectional isolation module in the embodiments of the present application at least have the following beneficial effects: The starting method of the LLC bidirectional isolation module in the embodiments of the present application depends on the first voltage on the low-voltage side and the second voltage on the high-voltage side, determines the frequency change value according to the first voltage and the second voltage, and reduces the current frequency of the LLC bidirectional isolation module according to the frequency change value. In this way, as the first voltage and the second voltage change, new frequency change values can be continuously obtained to adjust the current frequency of the LLC bidirectional isolation module, without considering the starting scenario of the LLC bidirectional isolation module. Therefore, it can completely break away from the coordinated starting control of the low-voltage bus equipment and the high-voltage bus equipment of the LLC bidirectional isolation module, effectively reducing the complexity of the starting control.

[0016] Other features and advantages of the present application will be described in the subsequent specification, and, in part, will be obvious from the specification, or will be understood by implementing the present application. The objectives and other advantages of the present application can be achieved and obtained through the structures specifically pointed out in the specification, the claims, and the drawings. Description of the Drawings

[0017] Figure 1 is a circuit diagram of an LLC bidirectional isolation module provided by an embodiment of the present application; Figure 2 is a frequency waveform diagram of the switch tubes for controlling the LLC bidirectional isolation module provided by an embodiment of the present application; Figure 3 is an overall flowchart of a starting method of an LLC bidirectional isolation module provided by an embodiment of the present application; Figure 4 is a flowchart of determining the frequency change value according to the first voltage and the second voltage provided by an embodiment of the present application; Figure 5It is a flowchart for determining the voltage difference in combination with the turns ratio provided by an embodiment of the present application; Figure 6 It is a flowchart for starting control by dividing the voltage range and setting the frequency change value provided by an embodiment of the present application; Figure 7 It is a flowchart for dividing the voltage range provided by an embodiment of the present application; Figure 8 It is a flowchart for the starting method of the LLC bidirectional isolation module provided by an example of the present application; Figure 9 It is a schematic diagram of the relationship between the voltage range and the frequency change value provided by an example of the present application. Detailed implementation manners

[0018] In order to make the objectives, technical solutions and advantages of the present application more clear and understandable, the present application will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application. Additionally, the features, operations or characteristics described in the specification can be combined in any suitable manner to form various embodiments. At the same time, the steps or actions in the method description can also be reordered or adjusted in an obvious manner by those skilled in the art. Therefore, the various sequences in the specification and drawings are only for clearly describing a certain embodiment and do not mean that they are the necessary sequences, unless it is stated that a certain sequence must be followed.

[0019] In the description of the present application, the meaning of several is one or more, the meaning of multiple is more than two, understandings such as greater than, less than, exceeding, etc. do not include the present number, and understandings such as above, below, within, etc. include the present number. If there is a description of first and second, it is only for the purpose of distinguishing technical features and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features or implicitly indicating the sequence of the indicated technical features.

[0020] The serial numbers assigned to the components herein, such as "first", "second", etc., are only used to distinguish the described objects and do not have any sequential or technical meaning. And the "connection" and "coupling" mentioned in the present application, unless otherwise specified, both include direct and indirect connection (coupling).

[0021] The LLC converter, or the LLC bidirectional isolation module, the LLC bidirectional isolation boost module, is to utilize the resonance characteristic to perform voltage conversion so as to output the required voltage waveform, and make the LLC bidirectional isolation module maintain high efficiency at high power through the resonance characteristic, be able to achieve the soft-switching function, and reduce the switching loss.

[0022] LLC bidirectional isolation boost module is usually used as a fixed boost module at one stage in occasions where a large boost gain is required, or is used to connect two DC buses in AC-DC microgrids. Therefore, when the LLC bidirectional isolation boost module is in standby, the voltages of the DC buses on both sides of the LLC are completely determined by other circuits or devices on the DC buses. At the same time, considering the problem of overcurrent during the startup of the LLC bidirectional isolation boost module, generally, the effective duty cycles of the primary switch and the secondary switch of the LLC bidirectional isolation boost module are gradually increased for soft startup. Typical methods include: variable frequency startup, variable dead zone startup, variable phase difference startup, etc. To meet different startup time and starting current requirements, the operating states of other devices or circuits on the high-voltage side and low-voltage side buses often need to be considered, and the system startup logic is relatively complex.

[0023] If the LLC bidirectional isolation boost module is applied to an energy storage system, due to the need to achieve electrical isolation and perform high-gain boosting on low-voltage batteries, the LLC bidirectional isolation boost module is commonly used as the front-stage boost module, rear-stage boost, and power control of the energy storage converter. There are a series of complex startup conditions such as battery activation startup, fast startup after energy storage standby, and black startup after off-grid shutdown. To ensure reliable system startup, during the startup process of the LLC bidirectional isolation boost module, on the premise that the current is within a reasonable range, it is necessary to meet the startup speed requirements under different startup methods. Therefore, after forcibly classifying the startup conditions, the startup of different conditions is achieved by controlling the startup timing and startup speed between the front-stage boost module and the rear-stage boost module. Specifically, there are several startup conditions: Battery activation startup: It is necessary to start the front-stage boost module first, and then start the LLC boost module. And to prevent overcurrent during the startup of the LLC, the LLC boost module needs to perform soft startup at a slow speed; Fast startup after energy storage standby: It is necessary to start both boost modules quickly to meet the function of the energy storage system to quickly respond to power; Black startup after off-grid shutdown requires starting the front-stage LLC boost module slowly first, and then starting the rear-stage boost module.

[0024] Therefore, it can be seen that the startup logic of the front-stage LLC boost module is highly coupled with that of the rear-stage boost module. It is necessary to distinguish different conditions to schedule the startup timing and startup speed of the front-stage and rear-stage boost modules. For the control unit of the energy storage system, the control logic is relatively complex, and control problems are likely to occur during the startup process. Therefore, it is necessary to simplify the control complexity.

[0025] Based on this, the embodiments of the present application provide a startup method, controller, and energy storage system for an LLC bidirectional isolation module. The low-voltage side connection end is connected to the high-voltage side connection end through a transformer. When it is necessary to start the LLC bidirectional isolation module, it starts at the initial frequency and according to the first voltage of the low-voltage side connection end Determine the real-time frequency change value of the second voltage at the high-voltage side connection terminal, and then adjust the current frequency of the LLC bidirectional isolation module in real time according to the frequency change value until the frequency of the LLC bidirectional isolation module reaches the target frequency, thereby completing the startup. During this startup process, the LLC bidirectional isolation module does not need to consider the operating states of other circuits or devices in the system, and relies on the voltages at the low-voltage side and the high-voltage side to complete independent startup, realizing the decoupled startup of the LLC bidirectional isolation module, simplifying the control complexity, and avoiding the problem of excessive current at the initial stage of startup.

[0026] The startup method, controller, and energy storage system of the LLC bidirectional isolation module will be described below with reference to the accompanying drawings.

[0027] Refer to Figure 1 As shown in Figure 1 FIG. 11 is a circuit diagram of the LLC bidirectional isolation module provided by an embodiment of the present application. The LLC bidirectional isolation module includes: A low-voltage side connection terminal, connected to the first bridge circuit; A high-voltage side connection terminal, connected to the second bridge circuit; A transformer T, the primary side of the transformer T is connected to the first bridge circuit, and the secondary side of the transformer T is connected to the second bridge circuit; The voltage at the low-voltage side connection terminal is the first voltage , and the voltage at the high-voltage side connection terminal is the second voltage . The first voltage and the second voltage are transformed through the transformer T. Among them, the primary side of the transformer T is connected to the low-voltage side connection terminal through the first bridge circuit, and the secondary side of the transformer T is connected to the low-voltage side connection terminal through the second bridge circuit. By controlling the actions of the switching tubes in the first bridge circuit and the second bridge circuit, LLC soft-switching startup can be achieved. The high voltage and low voltage in the embodiments of the present application are relative, that is, it means that the second voltage is greater than the first voltage .

[0028] Among them, the first bridge circuit includes a first bridge arm and a second bridge arm. The first bridge arm includes a first switching tube S1 and a second switching tube S2 connected in series. The second bridge arm includes a third switching tube S3 and a fourth switching tube S4 connected in series. The midpoint of the first bridge arm and the midpoint of the second bridge arm are connected to the primary side of the transformer T; the second bridge circuit includes a third bridge arm and a fourth bridge arm. The third bridge arm includes a fifth switching tube S5 and a sixth switching tube S6 connected in series. The fourth bridge arm includes a seventh switching tube S7 and an eighth switching tube S8 connected in series. The midpoint of the third bridge arm and the midpoint of the fourth bridge arm are connected to the secondary side of the transformer T.

[0029] Refer to Figure 1The first and second bridge arms shown, the positive connection terminal of the low-voltage side connection terminal is connected to the negative connection terminal of the low-voltage side connection terminal through the first bridge arm, that is, the positive connection terminal of the low-voltage side connection terminal is connected to the negative connection terminal of the low-voltage side connection terminal through the first switch tube S1 and the second switch tube S2. Similarly, the positive connection terminal of the low-voltage side connection terminal is connected to the negative connection terminal of the low-voltage side connection terminal through the second bridge arm, that is, the positive connection terminal of the low-voltage side connection terminal is connected to the negative connection terminal of the low-voltage side connection terminal through the third switch tube S3 and the fourth switch tube S4. The connection point of the first switch tube S1 and the second switch tube S2 is the midpoint of the first bridge arm and is connected to one end of the primary side of the transformer T. The connection point of the third switch tube S3 and the fourth switch tube S4 is the midpoint of the second bridge arm and is connected to the other end of the primary side of the transformer T.

[0030] Referring to Figure 1 The third and fourth bridge arms shown, the positive connection terminal of the high-voltage side connection terminal is connected to the negative connection terminal of the high-voltage side connection terminal through the third bridge arm, that is, the positive connection terminal of the high-voltage side connection terminal is connected to the negative connection terminal of the high-voltage side connection terminal through the fifth switch tube S5 and the sixth switch tube S6. Similarly, the positive connection terminal of the high-voltage side connection terminal is connected to the negative connection terminal of the high-voltage side connection terminal through the fourth bridge arm, that is, the positive connection terminal of the high-voltage side connection terminal is connected to the negative connection terminal of the high-voltage side connection terminal through the seventh switch tube S7 and the eighth switch tube S8. The connection point of the fifth switch tube S5 and the sixth switch tube S6 is the midpoint of the third bridge arm and is connected to one end of the secondary side of the transformer T. The connection point of the seventh switch tube S7 and the eighth switch tube S8 is the midpoint of the fourth bridge arm and is connected to the other end of the secondary side of the transformer T.

[0031] In addition, a first capacitor C1 is also connected between the positive connection terminal and the negative connection terminal of the low-voltage side connection terminal, and the first capacitor C1 is connected in parallel with both the first bridge arm and the second bridge arm. A second capacitor C2 is also connected between the positive connection terminal and the negative connection terminal of the high-voltage side connection terminal, and the second capacitor C2 is connected in parallel with both the third bridge arm and the fourth bridge arm.

[0032] It can be understood that the control pins of these switch tubes such as the first switch tube S1, the second switch tube S2, the third switch tube S3, the fourth switch tube S4, the fifth switch tube S5, the sixth switch tube S6, the seventh switch tube S7, and the eighth switch tube S8 are all connected to the controller, and the controller controls the on and off of the switch tubes. During the starting process of this embodiment, the current frequency output by the controller is used to control the opening and closing of the first switch tube S1, the fourth switch tube S4, the fifth switch tube S5, and the eighth switch tube S8. The current frequency output by the controller The inverted phase frequency is used for the second switch tube S2, the third switch tube S3, the sixth switch tube S6, and the seventh switch tube S7. That is to say, the switching actions of the first switch tube S1, the fourth switch tube S4, the fifth switch tube S5, and the eighth switch tube S8 are opposite to those of the second switch tube S2, the third switch tube S3, the sixth switch tube S6, and the seventh switch tube S7, and the duty cycle is 0.5. Refer to Figure 2 as shown.

[0033] Based on the circuit diagram of the above LLC bidirectional isolation module, refer to Figure 3 as shown, a starting method for an LLC bidirectional isolation module provided by an embodiment of the present application includes but is not limited to the following steps: Step S100, start the LLC bidirectional isolation module with the initial frequency as the current frequency ;

[0034] Step S200, gradually reduce the current frequency of the LLC bidirectional isolation module according to the frequency change value , until the current frequency of the LLC bidirectional isolation module reaches the target frequency ;

[0035] Among them, the frequency change value is determined according to the first voltage at the low-voltage connection end and the second voltage at the high-voltage connection end.

[0036] The initial frequency corresponds to the initial starting current of the LLC bidirectional isolation module. The initial frequency gradually becomes smaller during the starting process. By the frequency change value , the initial frequency is reduced, the voltage division ratio of the primary side and the secondary side of the transformer T is changed, and finally it is reduced to the target frequency to reach the state of stable voltage output, and the starting process is completed. Among them, the target frequency is related to the parameters of the equivalent capacitance and equivalent inductance of the LLC bidirectional isolation module. At this time, the LLC bidirectional isolation module works in the resonant state, and the switching losses of each switch tube in the first bridge circuit and the second bridge circuit can be eliminated, so as to realize soft-switching control.

[0037] The above starting process requires gradually reducing the frequency based on the initial frequency , until the current frequency reaches the target frequency . The frequency change value is determined according to the first voltage at the low-voltage connection end and the second voltage Determined. During the starting process, due to the first voltage and the second voltage varying with time, therefore, according to the first voltage and the second voltage the determined frequency change value also varies with time. For example, each time the current frequency is adjusted by reducing the frequency change value , the first voltage at the low-voltage connection terminal is collected once and the second voltage at the high-voltage connection terminal , to determine a new frequency change value , and then this new frequency change value is used to continue reducing the current frequency , and so on; or for another example, according to the magnitude relationship between the first voltage and the second voltage , multiple intervals are divided, and each interval corresponds to a frequency change value , so that during the starting process, according to the first voltage in the current state and the second voltage a frequency change value can be determined to reduce the current frequency . It is also possible to determine the frequency change value according to the first voltage and the second voltage in other ways, and no further examples will be given here. Through the above methods, the situation of other circuits and devices connected to the LLC bidirectional isolation module can be not considered, and only the voltages on both sides of the LLC bidirectional isolation module are considered to complete the starting, thereby reducing the control complexity of the starting process of the LLC bidirectional isolation module.

[0038] It can be understood that in order to meet the requirements of the starting current, the initial frequency is relatively high compared to the target frequency to achieve a larger starting current. On the premise of meeting the starting current, the embodiments of the present application also need to obtain a faster starting time for the LLC bidirectional isolation module. Therefore, the voltage difference between the first voltage and the second voltage can be used to determine the frequency change value , and it is made that the greater the voltage difference between the first voltage and the second voltage , the smaller the frequency change value . During the starting process, the voltage difference between the first voltage and the second voltage becomes smaller, and thus the frequency change value becomes larger.

[0039] Specifically, with reference to Figure 4 shown, in the embodiments of the present application, the frequency change value is obtained through the following steps:

[0040] Step S101, obtain the first voltage and the second voltage ;

[0041] Step S102, determine the voltage difference according to the first voltage and the second voltage ;

[0042] Step S103, determine the frequency change value according to the voltage difference .

[0043] During the startup process of the LLC bidirectional isolation module, the first voltage of the low-voltage connection end is periodically collected and the second voltage of the high-voltage connection end , calculate the difference between the first voltage and the second voltage as the voltage difference, and then determine the frequency change value according to the voltage difference . As known before, the frequency change value increases as the voltage difference becomes smaller. On the premise of satisfying the startup current, the step size of frequency adjustment is increased subsequently, that is, the frequency change value increases with time subsequently, so as to shorten the process of changing from the initial frequency to the target frequency , and accelerate the startup speed. Among them, the initial frequency can be determined according to the maximum voltage difference between the low-voltage side connection end and the high-voltage side connection end and the maximum current of the LLC bidirectional isolation module, and the target frequency is the frequency corresponding to the stable resonance state of the LLC bidirectional isolation module.

[0044] With reference to Figure 5 shown, in some embodiments, in the above step S102, determining the voltage difference according to the first voltage and the second voltage includes:

[0045] Step S104, determine the third voltage according to the turns ratio N of the transformer T and the first voltage ;

[0046] Step S105, determine the voltage difference according to the absolute value of the difference between the third voltage and the second voltage .

[0047] The frequency change value In the actual calculation process, the turns ratio N of the transformer T is considered, and the voltage difference satisfies the following formula:

[0048]

[0049] Wherein, is the voltage difference, which is the absolute value of the difference between the product of the first voltage and the turns ratio N of the transformer T and the second voltage . At the starting moment of the LLC bidirectional isolation module, the product of the first voltage at the low-voltage side connection end and the turns ratio N of the transformer T is lower than the second voltage . After the LLC bidirectional isolation module starts up, the product of the first voltage at the low-voltage side connection end and the turns ratio N of the transformer T is equal to the second voltage . Therefore, before the LLC bidirectional isolation module starts up to the completion of startup, the product of the first voltage at the low-voltage side connection end and the turns ratio N of the transformer T is not equal to the second voltage . By calculating this voltage difference , the frequency change value is determined. Such calculation is suitable for quickly adjusting the current frequency after the LLC bidirectional isolation module starts up, so as to reduce to the target frequency more quickly and shorten the startup time of the LLC bidirectional isolation module.

[0050] The above-mentioned corresponding relationship between the frequency change value and the voltage difference can have various forms. Here is an example to illustrate one of the corresponding relationships. Specifically, referring to Figure 6 shown, determining the frequency change value according to the voltage difference in the above step S102 includes:

[0051] Step S106, when starting up the LLC bidirectional isolation module with the initial frequency , obtain the first initial voltage at the low-voltage side connection end and the second initial voltage at the high-voltage side connection end;

[0052] Step S107, divide several voltage intervals according to the difference between the first initial voltage and the second initial voltage, and set the frequency change value corresponding to each voltage interval;

[0053] Step S108, determine the frequency change value used to reduce the current frequency according to the corresponding relationship between the voltage difference and the voltage interval.

[0054] At the starting moment, determine the voltage difference between the low-voltage side connection terminal and the high-voltage side connection terminal, that is, the voltage difference between the first initial voltage and the second initial voltage. Divide multiple voltage intervals according to this difference, and set that each voltage interval corresponds to a frequency change value , and then during the starting process, determine the first voltage and the second voltage of the voltage difference, and then refer to the corresponding relationship between the voltage interval and the frequency change value to determine a frequency change value to reduce the current frequency .

[0055] It can be understood that in order to facilitate determining which voltage interval the voltage difference falls into, when calculating the voltage difference according to the first initial voltage and the second initial voltage, the turns ratio N of the transformer T can be referred to and calculated according to the above formula (1). It is equivalent to that the voltage difference calculated by the first initial voltage and the second initial voltage at this time is the absolute value of the result obtained by multiplying the first initial voltage by the turns ratio N of the transformer T and then subtracting the second initial voltage. The interval between this value and 0 is divided into several voltage intervals, and each corresponds to a frequency change value . Specifically:

[0056] Referring to Figure 7 as shown, the steps of dividing several voltage intervals according to the difference between the first initial voltage and the second initial voltage in the above step S107 include: Step S109, determine the third initial voltage according to the turns ratio N of the transformer T and the first initial voltage; Step S110, determine the voltage range with the third initial voltage as the lower limit value and the second initial voltage as the upper limit value; Step S111, divide the voltage range to obtain several voltage intervals.

[0057] For example, three voltage intervals can be divided, and the three voltage intervals respectively correspond to three frequency change values . When it is judged during the starting process that the real-time voltage difference falls into the second voltage interval, select the frequency change value corresponding to the second voltage interval to reduce the current frequency . Dividing the voltage intervals can further simplify the control logic and does not require calculating the frequency change value according to the real-time voltage difference , reducing the calculation burden of the controller.

[0058] Through the starting method of the above steps, only relying on the first voltage of the low-voltage side connection terminal and the second voltage Control the starting process of the LLC bidirectional isolation module, so that it is not necessary to consider the operating states of other circuits and devices connected to the LLC bidirectional isolation module, and achieve decoupled starting; in this process, use a relatively high initial frequency to start, meet the starting requirements of large current, and then determine the frequency change value according to the difference between the first voltage and the second voltage , and gradually reduce the initial frequency to the target frequency through the frequency change value . The smaller the difference between the first voltage and the second voltage , the larger the frequency change value , so that the initial frequency can be quickly reduced to the target frequency , accelerate the starting process of the LLC bidirectional isolation module, and shorten the starting time.

[0059] The starting method of the LLC bidirectional isolation module of the present application will be described in detail below through a specific example.

[0060] The primary side coil of the transformer T of the LLC bidirectional isolation module is connected to the low-voltage side connection terminal through the first bridge circuit, and the secondary side coil of the transformer T is connected to the high-voltage side connection terminal through the second bridge circuit. Both the first bridge arm and the second bridge arm of the first bridge circuit are composed of two switching tubes connected in series, which are the first switching tube S1, the second switching tube S2, the third switching tube S3, and the fourth switching tube S4 respectively. Both the third bridge arm and the fourth bridge arm of the second bridge circuit are composed of two switching tubes connected in series, which are the fifth switching tube S5, the sixth switching tube S6, the seventh switching tube S7, and the eighth switching tube S8 respectively. These switching tubes are controlled to conduct and turn off by the PWM signal output by the controller, and the PWM signal corresponds to the frequency for controlling the starting of the LLC bidirectional isolation module.

[0061] As shown in Figure 8 , at the moment of starting the LLC bidirectional isolation module, start with the initial frequency , and collect the first voltage at the low-voltage side connection terminal and the second voltage at the high-voltage side connection terminal, and calculate the equivalent voltage difference between the low-voltage side connection terminal and the high-voltage side connection terminal, that is, the voltage difference is:

[0062]

[0063] Query the frequency change value according to the voltage difference , and use the frequency change value to reduce the initial frequency , satisfying the formula:

[0064]

[0065] Wherein, is the frequency after subtracting the frequency change value , which is used as the new current frequency, is the frequency before subtracting the frequency change value , that is, the actual current frequency.

[0066] After that, judge the relationship between the new current frequency and the target frequency . If the new current frequency is less than or equal to the target frequency , the LLC bidirectional isolation module operates at the current frequency , or operates at the target frequency , thus ending the startup process of the LLC bidirectional isolation module.

[0067] Wherein, for the convenience of calculating the frequency change value , as shown in reference to Figure 9 , in this example, the voltage is divided into three voltage intervals from 0 to , namely the first voltage interval , the second voltage interval and the third voltage interval . At this time, the three voltage intervals respectively correspond to three frequency change values , and . Therefore, during the startup process, when the calculated voltage difference falls into the first voltage interval , is used to reduce the current frequency . When the calculated voltage difference falls into the second voltage interval , is used to reduce the current frequency . When the calculated voltage difference falls into the third voltage interval , is used to reduce the current frequency .

[0068] The embodiment of the present application also provides a controller, including at least one processor and a memory for communicating with the at least one processor; the memory stores instructions that can be executed by the at least one processor, and the instructions are executed by the at least one processor so that the at least one processor can execute the startup method of the LLC bidirectional isolation module as described above.

[0069] The embodiment of the present application also provides an energy storage system, including an LLC bidirectional isolation module and the controller in the above embodiment.

[0070] Those of ordinary skill in the art can understand that all or some of the steps and systems disclosed in the above methods can be implemented as software, firmware, hardware, and their appropriate combinations. Some physical components or all physical components can be implemented as software executed by a processor, such as a central processing unit, a digital signal processor, or a microprocessor, or can be implemented as hardware, or can be implemented as an integrated circuit, such as an application-specific integrated circuit. Such software can be distributed on a computer-readable medium, which can include a computer storage medium (or non-transitory medium) and a communication medium (or transitory medium). As is well known to those of ordinary skill in the art, the term computer storage medium includes volatile and non-volatile, removable and non-removable media implemented in any method or technology for storing information, such as computer-readable instructions, data structures, program modules, or other data. Computer storage media includes, but is not limited to, RAM, ROM, EEPROM, flash memory or other memory technologies, CD-ROM, digital versatile disc (DVD) or other optical disc storage, magnetic cassette, tape, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to store the desired information and can be accessed by a computer. In addition, as is well known to those of ordinary skill in the art, a communication medium generally contains computer-readable instructions, data structures, program modules, or other data in a modulated data signal such as a carrier wave or other transmission mechanism, and can include any information delivery medium.

[0071] It should be understood that in the present application, "at least one (item)" means one or more, and "a plurality" means two or more. "And / or" is used to describe the association relationship of associated objects, indicating that three relationships can exist. For example, "A and / or B" can represent: only A exists, only B exists, and both A and B exist at the same time. Among them, A and B can be singular or plural. The character " / " generally represents an "or" relationship between the associated objects before and after. "At least one (one) of the following" or its similar expression refers to any combination of these items, including any combination of single item (one) or plural items (ones). For example, at least one (one) of a, b, or c can represent: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", where a, b, and c can be single or multiple.

[0072] In several embodiments provided by the present application, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative. For example, the division of units is only a logical function division. In actual implementation, there may be other division methods. For example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the displayed or discussed couplings or direct couplings or communication connections between each other can be through some interfaces, indirect couplings or communication connections of apparatuses or units, and can be in electrical, mechanical, or other forms. The units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they can be located in one place or distributed to multiple network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0073] It should also be understood that the various embodiments provided by the embodiments of the present application can be combined arbitrarily to achieve different technical effects.

[0074] The above has specifically described the preferred embodiments of the present application, but the present application is not limited to the above embodiments. Those skilled in the art can also make various equivalent deformations or substitutions without departing from the spirit of the present application, and these equivalent deformations or substitutions are all included within the scope defined by the claims of the present application.

Claims

1. A starting method for an LLC bidirectional isolation module, characterized in that, the LLC bidirectional isolation module includes: a low-voltage side connection terminal connected to a first bridge circuit; a high-voltage side connection terminal connected to a second bridge circuit; a transformer, the primary side of the transformer is connected to the first bridge circuit, and the secondary side of the transformer is connected to the second bridge circuit; the starting method includes: starting the LLC bidirectional isolation module with an initial frequency as the current frequency; gradually reducing the current frequency of the LLC bidirectional isolation module according to a frequency change value until the current frequency of the LLC bidirectional isolation module reaches a target frequency; wherein, the frequency change value is determined according to a first voltage at the low-voltage connection terminal and a second voltage at the high-voltage connection terminal.

2. The starting method according to claim 1, characterized in that, the frequency change value is obtained through the following steps: acquiring the first voltage and the second voltage; determining a voltage difference according to the first voltage and the second voltage; determining the frequency change value according to the voltage difference.

3. The starting method according to claim 2, characterized in that, the determining the voltage difference according to the first voltage and the second voltage includes: determining a third voltage according to the turns ratio of the transformer and the first voltage; determining the voltage difference according to the absolute value of the difference between the third voltage and the second voltage.

4. The starting method according to any one of claims 1 to 3, characterized in that, the frequency change value increases as the voltage difference becomes smaller.

5. The starting method according to claim 2, characterized in that, the determining the frequency change value according to the voltage difference includes: when starting the LLC bidirectional isolation module with the initial frequency, acquiring a first initial voltage at the low-voltage side connection terminal and a second initial voltage at the high-voltage side connection terminal; dividing a plurality of voltage intervals according to the difference between the first initial voltage and the second initial voltage, and setting a frequency change value corresponding to each voltage interval; determining the frequency change value for reducing the current frequency according to the corresponding relationship between the voltage difference and the voltage interval.

6. The starting method according to claim 5, characterized in that, the dividing a plurality of voltage intervals according to the difference between the first initial voltage and the second initial voltage includes: determining a third initial voltage according to the turns ratio of the transformer and the first initial voltage; determining a voltage range with the third initial voltage as the lower limit value and the second initial voltage as the upper limit value; dividing the voltage range to obtain a plurality of voltage intervals.

7. The starting method according to claim 1, characterized in that, The first bridge circuit includes a first arm and a second arm. The first arm includes a first switch and a second switch connected in series, and the second arm includes a third switch and a fourth switch connected in series. The midpoint of the first arm and the midpoint of the second arm are connected to the primary side of the transformer. The second bridge circuit includes a third arm and a fourth arm. The third arm includes a fifth switch and a sixth switch connected in series, and the fourth arm includes a seventh switch and an eighth switch connected in series. The midpoint of the third arm and the midpoint of the fourth arm are connected to the secondary side of the transformer.

8. The starting method according to claim 7, wherein, the current frequency is used to control the opening and closing of the first switch, the fourth switch, the fifth switch, and the eighth switch, and the inverted frequency of the current frequency is used for the second switch, the third switch, the sixth switch, and the seventh switch.

9. A controller, wherein, it includes at least one processor and a memory communicatively connected to the at least one processor; the memory stores instructions executable by the at least one processor, and the instructions are executed by the at least one processor to enable the at least one processor to execute the starting method according to any one of claims 1 to 8.

10. An energy storage system, wherein, it includes an LLC bidirectional isolation module and the controller according to claim 9.

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