CN115411808A

CN115411808A - DC/DC converter, output voltage control method thereof and energy storage system

Info

Publication number: CN115411808A
Application number: CN202210968684.9A
Authority: CN
Inventors: 孔洁; 彭昱; 黑畅; 余士江; 朱军卫
Original assignee: Huawei Digital Power Technologies Co Ltd
Current assignee: Huawei Digital Power Technologies Co Ltd
Priority date: 2022-08-12
Filing date: 2022-08-12
Publication date: 2022-11-29
Also published as: WO2024032463A1

Abstract

The application provides a DC/DC converter, an output voltage control method thereof and an energy storage system. The input end of the first direct current conversion circuit is connected with a direct current power supply, and the first output end and the second output end are respectively connected with the first input end of the DC/DC converter and the first input end of the second direct current conversion circuit. And a second input end of the second direct current conversion circuit is connected with a second input end of the DC/DC converter, and an output end of the second direct current conversion circuit is connected with an output end of the DC/DC converter. The controller controls the output voltage of the first direct current conversion circuit according to a voltage difference value between the battery voltage of the battery cluster and the bus voltage of the direct current bus. By adopting the method and the device, the high efficiency of the DC/DC converter in the full-range voltage difference can be realized.

Description

DC/DC converter, output voltage control method thereof and energy storage system

Technical Field

The application relates to the technical field of power supplies, in particular to a DC/DC converter, an output voltage control method thereof and an energy storage system.

Background

In an application scenario of an energy storage system, a plurality of battery clusters (formed by a plurality of battery cells connected in series and in parallel) are generally connected in parallel through a combiner box, and then are connected to a direct current side of a centralized inverter, and an alternating current side of the centralized inverter is connected to a load. Due to battery differences (for example, the battery capacities and the battery capacity attenuation degrees of different manufacturers and even the same manufacturer are different in different degrees), the voltages of a plurality of battery clusters are different, and therefore the circulation problem when the plurality of battery clusters are connected in parallel is caused.

To address the circulating current problem, an energy storage system as shown in fig. 1 is currently provided. As shown in fig. 1, each of the n battery clusters is connected in series with an output terminal of a corresponding DC/DC converter and then connected to a DC bus, and the DC bus is connected to a load through a centralized inverter. And the input ends of the n DC/DC converters corresponding to the n battery clusters are all connected with a power supply. The energy storage system compensates the voltage difference between the battery clusters and the direct current bus through the n DC/DC converters, so that the voltage output to the direct current bus after each battery cluster is connected with the corresponding DC/DC converter in series is the same, and the circulation generated when the plurality of battery clusters are connected in parallel is restrained. However, the DC/DC converter has a wide voltage adjustment range, and some operating points may have low efficiency when compensating for a voltage difference, and thus high efficiency of a full-range voltage difference cannot be achieved.

Disclosure of Invention

The application provides a DC/DC converter, an output voltage control method thereof and an energy storage system, which can realize the high efficiency of the DC/DC converter in the full-range voltage difference.

In a first aspect, the present application provides a DC/DC converter, a first input terminal and a second input terminal of which are connected to a battery cluster, an output terminal of the DC/DC converter is connected to a DC bus, and the DC/DC converter includes a first DC conversion circuit, a second DC conversion circuit, and a controller. Wherein: the input end of the first direct current conversion circuit is connected with a direct current power supply, the first output end and the second output end of the first direct current conversion circuit are respectively connected with the first input end of the DC/DC converter and the first input end of the second direct current conversion circuit, and the first direct current conversion circuit is used for converting the voltage input by the direct current power supply into direct current and outputting the direct current voltage to the second direct current conversion circuit. The second input end of the second direct current conversion circuit is connected with the second input end of the DC/DC converter, the output end of the second direct current conversion circuit is connected with the output end of the DC/DC converter, and the second direct current conversion circuit is used for performing direct current conversion on input voltage and then outputting the converted input voltage. After the DC/DC converter works, the controller obtains a voltage difference value between the battery voltage of the battery cluster and the bus voltage of the direct current bus, and controls the output voltage of the first direct current conversion circuit according to the voltage difference value so as to enable the output voltage of the DC/DC converter to be the bus voltage. It can be understood that the DC/DC converter can dynamically adjust the output voltage of the first DC conversion circuit based on the voltage difference, and further dynamically adjust the input voltage of the second DC conversion circuit, so that the efficiency of the DC/DC converter reaches the preset efficiency when the output voltage reaches the bus voltage through the cooperation of the first DC conversion circuit and the second DC conversion circuit, and the high efficiency of the DC/DC converter at the full range of voltage difference is realized.

With reference to the first aspect, in a first possible implementation manner, when the voltage difference is smaller than a first preset threshold, that is, when the voltage difference is smaller, the controller controls the output voltage of the first dc-to-dc conversion circuit to be the voltage difference. It can be understood that, when the voltage difference is small, the first DC converter circuit only needs to compensate the voltage difference, and only the differential-mode power passes through the first DC converter circuit, so that the loss is small, and therefore, the high efficiency of the DC/DC converter when the voltage difference is within the range smaller than the first preset threshold can be realized.

With reference to the first possible implementation manner of the first aspect, in a second possible implementation manner, when the output voltage of the first dc conversion circuit is a voltage difference value, the controller further controls the first input terminal and the second input terminal of the second dc conversion circuit to be directly connected to the output terminal. It can be understood that when the output voltage of the first DC conversion circuit is the voltage difference, the DC/DC converter can ensure that the output voltage of the DC/DC converter is the bus voltage by controlling the second DC conversion circuit to be in the through mode. When the second direct current conversion circuit is in the through mode, power does not need to pass through the second direct current conversion circuit, and loss is basically avoided, so that the efficiency of the DC/DC converter can be effectively improved. In addition, the embodiment does not need to add extra devices, and the cost of the DC/DC converter can be effectively reduced.

With reference to the first possible implementation manner of the first aspect, in a third possible implementation manner, the DC/DC converter further includes a first switch, the output terminal of the second DC conversion circuit includes a first output terminal, and the first switch is connected between the first input terminal and the first output terminal of the second DC conversion circuit. When the output voltage of the first direct current conversion circuit is a voltage difference value, the controller also controls the first switch to be conducted. It can be understood that, in the case that some DC conversion circuits do not support the through mode, the same function in the through mode can be achieved by adding the first switch in parallel with the DC conversion circuit, thereby improving the applicability of the DC/DC converter.

With reference to the first aspect, in a fourth possible implementation manner, when the voltage difference is greater than or equal to a second preset threshold, that is, when the voltage difference is large, the controller controls the output voltage of the first dc conversion circuit to be 0. It can be understood that, when the voltage difference is large, that is, when the bus voltage of the DC bus is small, since the output voltage of the first DC conversion circuit is 0, that is, the first DC conversion circuit stops operating, it is possible to obtain that only the second DC conversion circuit in the DC/DC converter operates. Because the bus voltage which is required to be output to the direct current bus by the second direct current conversion circuit is smaller, the power which is required to be processed by the second direct current conversion circuit is smaller, the loss of the DC/DC converter is smaller, and the high efficiency of the DC/DC converter in the range that the voltage difference value is larger than or equal to the second preset threshold value can be realized.

With reference to any one of the first to fourth possible implementation manners of the first aspect, in a fifth possible implementation manner, the DC/DC converter further includes a second switch, and the second switch is connected between the first output terminal and the second output terminal of the first direct current conversion circuit. When the voltage difference value is larger than or equal to a second preset threshold value, the controller also controls the second switch to be conducted. It can be understood that the DC/DC converter can realize that the output voltage of the first DC conversion circuit is 0 by controlling the conduction of the second switch to short-circuit the first DC conversion circuit, the control mode is simple and convenient to realize, and the stability of the DC/DC converter can be improved.

With reference to any one of the first to fifth possible implementation manners of the first aspect, in a sixth possible implementation manner, when the output voltage of the first dc conversion circuit is 0, that is, when the input voltage of the second dc conversion circuit is the battery voltage, the controller further controls the output voltage of the second dc conversion circuit to be the bus voltage. Furthermore, not only can high efficiency of the DC/DC converter be realized when the voltage difference value of the DC/DC converter is within a range larger than or equal to a second preset threshold value, but also under the condition that an energy storage system where the DC/DC converter is located comprises a plurality of DC/DC converters, the output voltage of each DC/DC converter is ensured to be bus voltage in a mode that a second direct current conversion circuit in each DC/DC converter outputs bus voltage, so that the circulation current among battery clusters can be effectively inhibited, and the safety and the stability of the DC/DC converter are improved.

With reference to the first aspect, in a seventh possible implementation manner, the controller determines a first output voltage corresponding to the voltage difference according to the voltage difference and a mapping relationship between the voltage difference and the output voltage, and controls an output voltage of the first dc conversion circuit to be the first output voltage. It can be understood that the DC/DC converter can control the output voltage of the first DC conversion circuit to be the first output voltage when the efficiency of the DC/DC converter reaches the preset efficiency through the mapping relationship between the voltage difference value and the output voltage, so that the efficiency of the DC/DC converter within the full-range voltage difference value can be optimized.

With reference to the seventh possible implementation manner of the first aspect, in an eighth possible implementation manner, when the output voltage of the first dc conversion circuit is the first output voltage, the controller controls the output voltage of the second dc conversion circuit to be the bus voltage. And then after the output voltage of the first direct current conversion circuit is the first output voltage when the efficiency of the DC/DC converter reaches the preset efficiency, the efficiency of the DC/DC converter reaches the preset efficiency while the output voltage of the DC/DC converter is the bus voltage through the cooperation of the second direct current conversion circuit.

In a second aspect, the present application provides an energy storage system, which includes one or more DC/DC converters as provided in any one of the first to eighth possible embodiments of the first aspect, and one or more battery clusters, wherein one DC/DC converter is connected to one battery cluster. It can be understood that each DC/DC converter in the energy storage system can dynamically adjust the output voltage of each first DC conversion circuit based on the respective voltage difference, and then dynamically adjust the input voltage of each second DC conversion circuit, so that the efficiency of each DC/DC converter reaches the preset efficiency when the output voltage reaches the bus voltage, thereby achieving the high efficiency of each DC/DC converter at the voltage difference in the full range, and further improving the efficiency of the energy storage system. In addition, when the number of the battery clusters in the energy storage system is multiple, the output voltage of each DC/DC converter is bus voltage, so that the circulation among the battery clusters can be effectively inhibited, and the safety and the stability of the energy storage system are improved.

With reference to the second aspect, in a first possible implementation manner, the battery cluster includes at least two battery modules, each battery module includes a battery unit, a first battery switch and a second battery switch, and the battery unit and the first battery switch are connected in series at two ends of the second battery switch. The energy storage system also comprises a battery management unit, wherein the battery management unit is used for acquiring the battery module voltage of each battery module in the at least two battery modules; and when the battery module voltage of a first battery module in the at least two battery modules is greater than a fourth preset threshold value or less than a fifth preset threshold value, controlling a first battery switch in the first battery module to be switched off and a second battery switch in the first battery module to be switched on. Furthermore, the energy storage system can avoid the short plate effect among the battery units in the battery clusters by controlling the cut-in and cut-out of the minimum battery unit in each battery cluster, and meanwhile, the utilization rate of the battery units in the battery clusters is improved.

With reference to the second aspect or the first possible implementation manner of the second aspect, in a second possible implementation manner, the energy storage system further includes an inverter, an input end of the inverter is connected to the direct current bus, and an output end of the inverter is connected to the alternating current load.

In a third aspect, the present application provides a method for controlling an output voltage of a DC/DC converter, where a first input terminal and a second input terminal of the DC/DC converter are connected to a battery cluster, an output terminal of the DC/DC converter is connected to a DC bus, and the DC/DC converter includes a first DC conversion circuit and a second DC conversion circuit. Wherein: the input end of the first direct current conversion circuit is connected with a direct current power supply, the first output end and the second output end of the first direct current conversion circuit are respectively connected with the first input end of the DC/DC converter and the first input end of the second direct current conversion circuit, and the first direct current conversion circuit is used for converting the voltage input by the direct current power supply into direct current and outputting the direct current power supply to the second direct current conversion circuit. The second input end of the second direct current conversion circuit is connected with the second input end of the DC/DC converter, the output end of the second direct current conversion circuit is connected with the output end of the DC/DC converter, and the second direct current conversion circuit is used for performing direct current conversion on input voltage and then outputting the converted input voltage. The method comprises the following steps: the DC/DC converter obtains a voltage difference value between the battery voltage of the battery cluster and the bus voltage of the direct current bus, and controls the output voltage of the first direct current conversion circuit according to the voltage difference value.

With reference to the third aspect, in a first possible implementation manner, when the voltage difference is smaller than a first preset threshold, the DC/DC converter controls the output voltage of the first direct current conversion circuit to be the voltage difference.

With reference to the first possible implementation manner of the third aspect, in a second possible implementation manner, when the output voltage of the first direct current conversion circuit is a voltage difference, the DC/DC converter further controls the first input terminal and the second input terminal of the second direct current conversion circuit to be directly communicated with the output terminal.

With reference to the first possible implementation manner of the third aspect, in a third possible implementation manner, the DC/DC converter further includes a first switch, the output terminal of the second DC conversion circuit includes a first output terminal, and the first switch is connected between the first input terminal and the first output terminal of the second DC conversion circuit. When the output voltage of the first direct current conversion circuit is a voltage difference value, the DC/DC converter also controls the first switch to be conducted.

With reference to the third aspect, in a fourth possible embodiment, when the voltage difference is greater than or equal to the second preset threshold, the DC/DC converter controls the output voltage of the first direct current conversion circuit to be 0.

With reference to any one of the third aspect to the fourth possible implementation manner of the first aspect, in a fifth possible implementation manner, the DC/DC converter further includes a second switch, and the second switch is connected between the first output terminal and the second output terminal of the first direct current conversion circuit. And when the voltage difference value is greater than or equal to a second preset threshold value, the DC/DC converter also controls the second switch to be conducted.

With reference to any one of the third to fifth possible implementation manners of the third aspect, in a sixth possible implementation manner, when the output voltage of the first direct current conversion circuit is 0, the DC/DC converter further controls the output voltage of the second direct current conversion circuit to be the bus voltage.

With reference to the third aspect, in a seventh possible implementation manner, the DC/DC converter determines a first output voltage corresponding to the voltage difference according to the voltage difference and a mapping relation between the voltage difference and the output voltage, and controls the output voltage of the first direct current conversion circuit to be the first output voltage.

With reference to the seventh possible implementation manner of the third aspect, in an eighth possible implementation manner, when the output voltage of the first direct current conversion circuit is the first output voltage, the DC/DC converter controls the output voltage of the second direct current conversion circuit to be the bus voltage.

It should be understood that the implementations and advantages of the various aspects described above in this application are mutually referenced.

Drawings

FIG. 1 is a schematic diagram of a prior art energy storage system;

FIG. 2 is a schematic diagram of an application scenario of a DC/DC converter provided in the present application;

FIG. 3 is a schematic structural diagram of an energy storage system provided herein;

FIG. 4 is another schematic structural diagram of an energy storage system provided herein;

fig. 5 is a schematic structural diagram of a second dc conversion circuit provided in the present application;

FIG. 6 is a schematic diagram of a structure of a battery cluster provided herein;

fig. 7 is a schematic flowchart of an output voltage control method of the DC/DC converter provided in the present application.

Detailed Description

The DC/DC converter provided by the application can be suitable for different application scenes, such as a data center power supply scene (used for supplying power for a load chip), a photovoltaic power supply scene, an energy storage power supply scene, a light storage hybrid power supply scene, a wind storage hybrid power supply scene and the like. The following description will take an energy storage and power supply scenario as an example.

Referring to fig. 2, fig. 2 is a schematic view of an application scenario of the DC/DC converter provided in the present application. As shown in fig. 2, the energy storage system includes a DC/DC converter 11 and its corresponding energy storage battery cluster 21, \8230 \ 8230;, a DC/DC converter 1n and its corresponding energy storage battery cluster 2n, DC buses (i.e., a positive DC BUS + and a negative DC BUS-) and an inverter. Wherein n is a positive integer. Two input ends of the DC/DC converter 11 are connected with the energy storage battery cluster 21, and two output ends are connected with the direct current bus; \8230; two input ends of the DC/DC converter 1n are connected with the energy storage battery cluster 2n, and two output ends are connected with the direct current bus. The direct current bus is connected with an alternating current power grid or alternating current electric equipment through an inverter. In the energy storage and power supply scenario shown in fig. 2, the DC/DC converter provided in this application may be any one of the n DC/DC converters shown in fig. 2. Since the structures and the operation principles of the n DC/DC converters are the same, for convenience of description, the DC/DC converter 11 is taken as an example for the following description. The DC/DC converter 11 includes a DC/DC circuit 1, a DC/DC circuit 2, and a controller (not shown). Two input ends of the DC/DC circuit 1 are connected to a direct current power supply (not shown), a positive output end is connected to the positive input end of the DC/DC circuit 2, and a negative output end is connected to the positive input end of the DC/DC converter 11. The negative input terminal of the DC/DC circuit 2 is connected to the negative input terminal of the DC/DC converter 11, and the two output terminals are connected to the two output terminals of the DC/DC converter 11.

After the DC/DC converter 11 starts to work, the controller obtains the battery voltage of the energy storage battery cluster 21 and the BUS voltage of the DC BUS (i.e. the voltage difference between the positive DC BUS + and the negative DC BUS-), and calculates the difference between the battery voltage of the energy storage battery cluster 21 and the BUS voltage to obtain the voltage difference. Then, the controller controls the output voltage of the DC/DC circuit 1 according to the voltage difference, and controls the output voltage of the DC/DC circuit 2 to be the bus voltage so that the output voltage of the DC/DC converter 11 is the bus voltage, with the sum of the battery voltage of the energy storage battery cluster 21 and the output voltage of the DC/DC circuit 1 being the input voltage of the DC/DC circuit 2. Then, the inverter inverts the bus voltage on the dc bus into ac power, thereby supplying power to an ac load (such as an ac power grid or ac consumer). It can be understood that the DC/DC converter 11 can dynamically adjust the DC/DC circuit 1 and the DC/DC circuit 2 according to the voltage difference, so that the efficiency of the DC/DC converter 11 reaches the preset efficiency when the output voltage reaches the bus voltage, so as to achieve the high efficiency of the DC/DC converter 11 in the full range of voltage difference, and further improve the efficiency of the energy storage system. In addition, when the number of the energy storage battery clusters in the energy storage system is multiple, the output voltage of each DC/DC converter is bus voltage, so that the circulation among the energy storage battery clusters can be effectively inhibited, and the safety of the energy storage system is improved.

The foregoing is merely an example of an application scenario of the DC/DC converter provided in the present application, and is not exhaustive, and the application scenario is not limited in the present application.

The working principle of the energy storage system and the DC/DC converter provided by the present application is illustrated below with reference to fig. 3 to 6.

Referring to fig. 3, fig. 3 is a schematic structural diagram of the energy storage system provided in the present application. As shown in fig. 3, the energy storage system 1 includes a DC/DC converter 11 and its corresponding battery clusters 21, \8230;, a DC/DC converter 1n and its corresponding battery cluster 2n, and DC buses (i.e., a positive DC BUS + and a negative DC BUS). n is a positive integer. The positive input end and the negative input end of the DC/DC converter 11 are connected with the battery pack 21, and the positive output end and the negative output end are respectively connected with a positive direct current BUS BUS + and a negative direct current BUS BUS-; 823060, 8230; the positive input end and the negative input end of the DC/DC converter 1n are connected with a battery cluster 2n, and the positive output end and the negative output end are respectively connected with a positive direct current BUS BUS + and a negative direct current BUS BUS-. The positive direct current BUS BUS + and the negative direct current BUS BUS-are connected with a load. The DC/DC converter 11 includes a first DC conversion circuit 111, a second DC conversion circuit 112, and a controller 113. Two input ends of the first DC-to-DC conversion circuit 111 are connected to the DC power supply 114, a positive output end is connected to the positive input end of the second DC-to-DC conversion circuit 112, and a negative output end is connected to the positive input end of the DC/DC converter 11. The negative input terminal of the second DC converter circuit 112 is connected to the negative input terminal of the DC/DC converter 11, and the positive output terminal and the negative output terminal are connected to the positive output terminal and the negative output terminal of the DC/DC converter 11, respectively. 823060, 8230and its advantages. The DC/DC converter 1n includes a first direct current conversion circuit 1n1, a second direct current conversion circuit 1n2, and a controller 1n3. Two input ends of the first direct current conversion circuit 1n1 are connected to a direct current power supply 1n4, a positive output end is connected to a positive input end of the second direct current conversion circuit 1n2, and a negative output end is connected to a positive input end of the DC/DC converter 1 n. A negative input terminal of the second direct current conversion circuit 1n2 is connected to a negative input terminal of the DC/DC converter 1n, and a positive output terminal and a negative output terminal are connected to a positive output terminal and a negative output terminal of the DC/DC converter 1n, respectively.

The DC power source connected to the input end of each second DC conversion circuit may be a battery cluster, a DC bus or other power source corresponding to the DC/DC converter where the DC/DC converter is located. The n first direct current conversion circuits may be any one of a BUCK step-down circuit, a BOOST step-up circuit, and a BUCK-BOOST step-up/down circuit, and the n second direct current conversion circuits may be any one of a BUCK step-down circuit, a BOOST step-up circuit, and a BUCK-BOOST step-up/down circuit. The type of the battery connected in series and parallel in each battery cluster is not limited to a lithium battery, and the battery can be other types of electrochemical batteries, such as a lead-acid battery, a lead-carbon battery, a ternary lithium battery, a lithium iron phosphate battery, a lithium titanate battery, and the like. The load may be a dc grid, an inverter, etc.

In an optional embodiment, after the energy storage system 1 is operated, the n DC/DC converters start to obtain the battery voltage of each corresponding battery cluster and the BUS voltage of the DC BUS (i.e. the voltage difference between the positive DC BUS + and the negative DC BUS), and calculate the voltage difference between the battery voltage and the BUS voltage of each corresponding battery cluster. The n DC/DC converters each control the output voltage of the respective first DC conversion circuit based on the respective voltage difference value, so that the input voltage of the respective second DC conversion circuit is the sum of the battery voltage of the respective corresponding battery cluster and the output voltage of the respective first DC conversion circuit. Then, the n DC/DC converters control the respective second DC conversion circuits to DC-convert the input voltages of the respective second DC conversion circuits into the bus voltage so that the output voltages of the n DC/DC converters are all the bus voltage.

In this embodiment, each DC/DC converter in the energy storage system 1 may dynamically adjust the output voltage of each first DC conversion circuit based on the voltage difference value thereof, and then dynamically adjust the input voltage of each second DC conversion circuit, so that the efficiency of each DC/DC converter reaches the preset efficiency when the output voltage reaches the bus voltage, thereby achieving the high efficiency of each DC/DC converter at the voltage difference value in the full range, and further improving the efficiency of the energy storage system 1. In addition, when the number of the battery clusters in the energy storage system 1 is multiple, since the output voltages of the DC/DC converters are the bus voltages, the circulation current between the battery clusters can be effectively suppressed, thereby improving the safety and stability of the energy storage system 1.

Since the structures and operating principles of the DC/DC converters in the energy storage system 1 are the same, for convenience of description, the DC/DC converter 11 is taken as an example and will be described below.

Referring to fig. 4, fig. 4 is another schematic structural diagram of the energy storage system provided in the present application. As shown in fig. 4, the energy storage system 1 includes a DC/DC converter 11 and its corresponding battery cluster 21, \8230 \ 8230;, a DC/DC converter 1n and its corresponding battery cluster 2n, DC buses (i.e., a positive DC BUS + and a negative DC BUS-) and an inverter 31.n is a positive integer. The DC/DC converter comprises a DC/DC converter 11, a positive input end, a negative input end, a positive direct current BUS BUS + and a negative direct current BUS BUS-; \8230; the positive input end and the negative input end of the DC/DC converter 1n are connected with a battery cluster 2n, and the positive output end and the negative output end are respectively connected with a positive direct current BUS BUS + and a negative direct current BUS BUS-. The positive direct current BUS BUS + and the negative direct current BUS BUS-are respectively connected with the positive input end and the negative input end of the inverter 31, and the output end of the inverter 31 is connected with an alternating current power grid. Here, for the specific connection relationship between the circuits included in each of the DC/DC converters 11 to 1n and the internal circuits thereof, please refer to the description of the corresponding parts in the embodiment shown in fig. 3, which is not repeated herein. Optionally, the DC/DC converter 11 further includes a first switch S11 and a second switch S12, the first switch S11 is connected between the positive output end and the positive output end of the second DC conversion circuit 112, and the second switch S12 is connected between the positive output end and the negative output end of the first DC conversion circuit 111; \8230; the DC/DC converter 1n further includes a first switch Sn1 and a second switch Sn2, the first switch Sn1 is connected between the positive output terminal and the positive output terminal of the second DC conversion circuit 1n2, and the second switch Sn2 is connected between the positive output terminal and the negative output terminal of the first DC conversion circuit 1n 1.

Specifically, after the DC/DC converter 11 is operated, the controller 113 starts to obtain the battery voltage of the battery cluster 21 and the bus voltage of the DC bus, and calculates a difference between the battery voltage of the battery cluster 21 and the bus voltage of the DC bus to obtain a voltage difference.

In an optional embodiment, after obtaining the voltage difference, the controller 113 determines a first output voltage corresponding to the voltage difference according to the voltage difference and a mapping relationship between the voltage difference and the output voltage, and controls the output voltage of the first dc converting circuit 111 to be the first output voltage. The mapping relation between the voltage difference values and the output voltage comprises a plurality of voltage difference value intervals and the output voltage of the first direct current conversion circuit when the efficiency of the DC/DC converter corresponding to the voltage difference value intervals reaches the preset efficiency. It should be noted that, if the number of the output voltages of the first DC conversion circuit is multiple when the efficiency of the DC/DC converter reaches the preset efficiency, an output voltage corresponding to the highest efficiency of the DC/DC converter among the multiple output voltages of which the efficiency of the DC/DC converter reaches the preset efficiency may be determined as the output voltage of the first DC conversion circuit corresponding to the voltage difference interval.

Specifically, the controller 113 determines a voltage difference interval in which the voltage difference is located, that is, a first voltage difference interval, according to the voltage difference and a mapping relationship between the voltage difference and the output voltage. And determining a first output voltage corresponding to the first voltage difference interval according to the first voltage difference interval and a mapping relation between the voltage difference and the output voltage, and controlling the output voltage of the first dc conversion circuit 111 to be the first output voltage. When the output voltage of the first DC converter circuit 111 is the first output voltage and the input voltage of the second DC converter circuit 112 is the first output voltage and the battery voltage of the battery cluster 21, the controller 113 controls the second DC converter circuit 112 to DC-convert the input voltage into the bus voltage and output the bus voltage, and the output voltage of the DC/DC converter 11 is the bus voltage at this time.

It can be understood that the DC/DC converter 11 can control the output voltage of the first DC/DC conversion circuit 111 to be the first output voltage when the efficiency of the DC/DC converter 11 reaches the preset efficiency through the mapping relationship between the voltage difference and the output voltage, and further, through the cooperation of the second DC conversion circuit 112, the efficiency reaches the preset efficiency while the output voltage of the DC/DC converter 11 is the bus voltage, so that the efficiency of the DC/DC converter 11 in the full range of voltage difference can be optimized.

In another alternative embodiment, after obtaining the voltage difference, the controller 113 controls the output voltage of the first DC converter circuit 111 according to a comparison result between the voltage difference and a preset threshold, so that the output voltage of the DC/DC converter 11 is the bus voltage.

In an alternative embodiment, when the voltage difference is smaller than the first preset threshold, the controller 113 controls the output voltage of the first dc conversion circuit 111 to be the voltage difference. When the output voltage of the first dc conversion circuit 111 is the voltage difference value, and the input voltage of the second dc conversion circuit 112 is the sum of the voltage difference value and the battery voltage of the battery pack 21, that is, the bus voltage, the controller 113 controls the positive input end and the positive output end of the second dc conversion circuit 112 to be directly connected, and controls the negative input end and the negative output end to be directly connected, that is, the second dc conversion circuit 112 is in the through mode. At this time, the output voltage of the second DC converter circuit 112 is the bus voltage, that is, the output voltage of the DC/DC converter 11 is the bus voltage.

For example, when the second dc conversion circuit 112 is a 4-switch symmetric BUCK-BOOST circuit shown in fig. 5, the controller 113 may control the switches S11 and S13 to be turned on and the switches S12 and S14 to be turned off, so that the two input terminals of the second dc conversion circuit 112 are directly connected to the two output terminals, that is, the second dc conversion circuit 112 is in the through mode, at this time, the electric energy at the input terminal of the second dc conversion circuit 112 is directly transmitted to the output terminals, and the second dc conversion circuit 112 has no high-frequency chopping loss of the switch tubes, so that the efficiency of the second dc conversion circuit 112 in the through mode is high.

It can be understood that when the voltage difference is small, the DC/DC converter 11 compensates the voltage difference by controlling the first DC converting circuit 111 and controls the second DC converting circuit 112 to be in the through mode, so that the output voltage of the DC/DC converter 11 reaches the bus voltage. Since the first DC converter circuit 111 only passes the differential mode power, the loss is small, and the efficiency is high when the second DC converter circuit 112 is in the direct mode, the efficiency of the DC/DC converter 11 can reach the preset efficiency when the voltage difference value thereof is smaller than the first preset threshold value, that is, the DC/DC converter 11 can achieve the high efficiency in the range where the voltage difference value thereof is smaller than the first preset threshold value.

In another alternative embodiment, when the voltage difference is smaller than the first preset threshold, the controller 113 controls the output voltage of the first dc converting circuit 111 to be the voltage difference. When the output voltage of the first dc conversion circuit 111 is a voltage difference value, the input voltage of the second dc conversion circuit 112 is the sum of the voltage difference value and the battery voltage of the battery pack 21, i.e. the bus voltage, and the controller 113 controls the first switch S11 to be turned on, at this time, the positive input end of the second dc conversion circuit 112 is directly connected to the positive output end, and the negative input end is directly connected to the negative output end. Therefore, the output voltage of the second DC converter circuit 112 is the bus voltage, that is, the output voltage of the DC/DC converter 11 is the bus voltage.

It can be understood that, in the case that some DC conversion circuits do not support the through mode, the same function in the through mode can be achieved by adding the first switch in parallel with the DC conversion circuit, so that the applicability of the DC/DC converter 11 is improved.

In another alternative embodiment, when the voltage difference is greater than or equal to the second preset threshold, the controller 113 makes the output voltage of the first dc converter circuit 111 be 0 by controlling the duty cycle of the controllable switch in the first dc converter circuit 111 to be 0. When the output voltage of the first DC converter circuit 111 is 0 and the input voltage of the second DC converter circuit 112 is the battery voltage of the battery cluster 21, the controller 113 controls the second DC converter circuit 112 to DC-convert the input voltage into the bus voltage and output the bus voltage, and the output voltage of the DC/DC converter 11 at this time is the bus voltage. The second preset threshold may be equal to the first preset threshold, or may be different from the first preset threshold.

It can be understood that when the voltage difference is large, that is, when the bus voltage of the DC bus is small, the power that needs to be processed by the second DC conversion circuit 112 in the DC/DC converter 11 is also small, and the output voltage of the first DC conversion circuit 111 is 0, that is, the first DC conversion circuit 111 stops operating, so that the loss of the DC/DC converter 11 is small, and therefore, high efficiency of the DC/DC converter 11 in a range where the voltage difference is greater than or equal to the second preset threshold value can be achieved.

In another alternative embodiment, when the voltage difference is greater than or equal to the second preset threshold, the controller 113 controls the second switch S12 to be turned on, so that the output voltage of the first dc converting circuit 111 is 0. When the output voltage of the first DC converter circuit 111 is 0 and the input voltage of the second DC converter circuit 112 is the battery voltage of the battery pack 21, the controller 113 controls the second DC converter circuit 112 to DC-convert the input voltage into the bus voltage and output the bus voltage, and the output voltage of the DC/DC converter 11 at this time is the bus voltage. The second preset threshold may be equal to the first preset threshold, or may not be equal to the first preset threshold.

It can be understood that the DC/DC converter 11 can control the duty ratio of the controllable switch in the first DC conversion circuit 111, and can also control the second switch S12 to be turned on to short-circuit the first DC conversion circuit 111, so that the output voltage of the first DC conversion circuit 111 is 0, and the control method is various and has high flexibility.

In another optional embodiment, when the voltage difference is greater than or equal to the second preset threshold, the controller 113 controls the duty ratio of the controllable switch in the first dc converting circuit 111 to be 0 and controls the second switch S12 to be turned on, so that the output voltage of the first dc converting circuit 111 is 0. When the output voltage of the first DC converter circuit 111 is 0 and the input voltage of the second DC converter circuit 112 is the battery voltage of the battery cluster 21, the controller 113 controls the second DC converter circuit 112 to DC-convert the input voltage into the bus voltage and output the bus voltage, and the output voltage of the DC/DC converter 11 at this time is the bus voltage. The second preset threshold may be equal to the first preset threshold, or may not be equal to the first preset threshold.

It can be understood that, the DC/DC converter 11 realizes that the output voltage of the first DC conversion circuit 111 is 0 by controlling the duty ratio of the controllable switch in the first DC conversion circuit 111 to be 0 and controlling the second switch S12 to be turned on, and can prevent the power supply short circuit problem caused by the second switch S12 being turned on under the condition that the first DC conversion circuit 111 outputs the normal voltage, so that the safety and the stability of the DC/DC converter 11 can be effectively improved.

In another alternative embodiment, when the voltage difference is greater than or equal to the second preset threshold, the controller 113 determines a second output voltage corresponding to the voltage difference according to the voltage difference and a mapping relationship between the voltage difference and the output voltage, and controls the output voltage of the first dc converting circuit 111 to be the second output voltage. The mapping relation between the voltage difference values and the output voltage comprises a plurality of voltage difference value intervals and the output voltage of the first direct current conversion circuit when the efficiency of the DC/DC converter corresponding to the voltage difference value intervals reaches the preset efficiency. It should be noted that, if the number of the output voltages of the first DC conversion circuit is multiple when the efficiency of the DC/DC converter reaches the preset efficiency, an output voltage corresponding to the highest efficiency of the DC/DC converter among the multiple output voltages when the efficiency of the DC/DC converter reaches the preset efficiency may be determined as the output voltage of the first DC conversion circuit corresponding to the voltage difference interval.

Specifically, when the voltage difference is greater than or equal to the second preset threshold, the controller 113 determines a voltage difference interval in which the voltage difference is located, that is, a second voltage difference interval, according to the voltage difference and a mapping relationship between the voltage difference and the output voltage. And determining a second output voltage corresponding to the second voltage difference interval according to the second voltage difference interval and the mapping relationship between the voltage difference and the output voltage, and controlling the output voltage of the first dc conversion circuit 111 to be the second output voltage. When the output voltage of the first DC conversion circuit 111 is the second output voltage and the input voltage of the second DC conversion circuit 112 is the second output voltage and the battery voltage of the battery pack 21, the controller 113 controls the second DC conversion circuit 112 to DC-convert the input voltage into the bus voltage and output the bus voltage, and the output voltage of the DC/DC converter 11 is the bus voltage at this time. The second preset threshold may be equal to the first preset threshold, or may be different from the first preset threshold. When the second voltage difference interval is the same as the first voltage difference interval, the second output voltage is the same as the first output voltage.

It can be understood that the DC/DC converter 11 can control the output voltage of the first DC/DC converter circuit 111 to be the second output voltage when the efficiency of the DC/DC converter 11 reaches the preset efficiency through the mapping relationship between the voltage difference and the output voltage, and further through the cooperation of the second DC converter circuit 112, the efficiency of the DC/DC converter 11 reaches the preset efficiency while the output voltage of the DC/DC converter 11 is the bus voltage, so that the efficiency of the DC/DC converter 11 is optimal when the voltage difference is within a range greater than or equal to the second preset threshold.

In yet another optional embodiment, when the voltage difference is greater than the first preset threshold and smaller than the second preset threshold, the controller 113 determines a third output voltage corresponding to the voltage difference according to the voltage difference and a mapping relationship between the voltage difference and the output voltage, and controls the output voltage of the first dc converting circuit 111 to be the third output voltage. The mapping relation between the voltage difference values and the output voltage comprises a plurality of voltage difference value intervals and the output voltage of the first direct current conversion circuit when the efficiency of the DC/DC converter corresponding to the voltage difference value intervals reaches the preset efficiency. It should be noted that, if the number of the output voltages of the first DC conversion circuit is multiple when the efficiency of the DC/DC converter reaches the preset efficiency, an output voltage corresponding to the highest efficiency of the DC/DC converter among the multiple output voltages when the efficiency of the DC/DC converter reaches the preset efficiency may be determined as the output voltage of the first DC conversion circuit corresponding to the voltage difference interval.

Specifically, when the voltage difference is greater than or equal to the second preset threshold, the controller 113 determines a voltage difference interval in which the voltage difference is located, that is, a third voltage difference interval, according to the voltage difference and a mapping relationship between the voltage difference and the output voltage. And determining a third output voltage corresponding to the third voltage difference interval according to the third voltage difference interval and the mapping relationship between the voltage difference and the output voltage, and controlling the output voltage of the first dc conversion circuit 111 to be the third output voltage. When the output voltage of the first DC conversion circuit 111 is the third output voltage and the input voltage of the second DC conversion circuit 112 is the third output voltage and the battery voltage of the battery pack 21, the controller 113 controls the second DC conversion circuit 112 to DC-convert the input voltage into the bus voltage and output the bus voltage, and the output voltage of the DC/DC converter 11 is the bus voltage at this time. And when the third voltage difference interval is the same as the first voltage difference interval, the third output voltage is equal to the first output voltage.

It can be understood that the DC/DC converter 11 may control the output voltage of the first DC/DC converter circuit 111 to be a third output voltage when the efficiency of the DC/DC converter 11 reaches the preset efficiency through a mapping relationship between the voltage difference and the output voltage, and further through the cooperation of the second DC converter circuit 112, the efficiency of the DC/DC converter 11 reaches the preset efficiency while the output voltage of the DC/DC converter 11 is the bus voltage, so that the efficiency of the DC/DC converter 11 is optimal when the voltage difference is within a range greater than the first preset threshold and smaller than the second preset threshold.

In summary, the DC/DC converter 11 may divide the range of all the values of the voltage difference into a plurality of intervals (for example, two intervals or three intervals), and the high efficiency of the DC/DC converter 11 in the voltage difference of the full range is realized by ensuring that the efficiency of the DC/DC converter 11 reaches the preset efficiency when the voltage difference of the DC/DC converter 11 is located in each of the plurality of intervals.

The energy storage system 1 not only can realize high efficiency of voltage difference values of all DC/DC converters in a full range, but also can avoid the situation that a battery cluster directly exits from operation due to the occurrence of a fault battery unit (for example, a battery unit with a battery voltage not within a battery operation voltage range) in the battery cluster through the management of all battery clusters, namely, the short plate effect among the battery units in the battery cluster is avoided.

Referring to fig. 6, fig. 6 is a schematic view of the structure of a battery cluster provided herein. As shown in fig. 6, the battery cluster 21 includes m battery modules, i.e., battery modules 211, \8230; \ battery modules 21m. Wherein m is a positive integer greater than 1. The battery module 211 includes a battery cell Bat1, a first battery switch Q11, and a second battery switch Q12; 823060, 8230; the battery module 21m includes a battery cell Batm, a first battery switch Qm1, and a second battery switch Qm2. The first battery switch and the second battery switch may be power electronic devices such as Metal Oxide Semiconductor Field Effect Transistors (MOSFETs), insulated Gate Bipolar Transistors (IGBTs), or Gallium Nitride (GaN) transistors. In the embodiment of the present application, the first battery switch and the second battery switch are described by taking MOSFETs as an example. The battery unit Bat1 and the first battery switch Q11 are connected in series across the second battery switch Q12. Specifically, the positive electrode of the battery unit Bat1 is connected with the drain electrode of the first battery switch Q11, the source electrode of the first battery switch Q11 is connected with the drain electrode of the second battery switch Q12 to form the positive electrode of the battery cluster 21, and the source electrode of the second battery switch Q12 is connected with the negative electrode of the battery unit Bat 1; \8230; the battery cell Batm is connected in series with the first battery switch Qm1 at both ends of the second battery switch Qm2. Specifically, the positive electrode of the battery cell Batm is connected to the drain of the first battery switch Qm1, the source of the first battery switch Qm1 is connected to the drain of the second battery switch Qm2, and the source of the second battery switch Q12 is connected to the negative electrode of the battery cell Batm to form the negative electrode of the battery cluster 21.

The energy storage system 1 further includes a battery management unit, which may be independent of the n DC/DC converters in the energy storage system 1, or may be integrated on a controller in each DC/DC converter. When the battery management unit is integrated with the controller of each DC/DC converter, the controller of each DC/DC converter controls the battery cluster corresponding to each DC/DC converter.

After the energy storage system 1 is operated, the battery management unit controls the first battery switch of each battery module of the m battery modules to be turned on, and at this time, the battery cluster 21 starts to output electric energy to the DC/DC converter 11. Then, the battery management unit starts to acquire the battery voltages of the battery cells of each of the m battery modules, and determines the battery voltages of the battery cells of each battery module as the battery module voltages of each battery module, thereby obtaining m battery module voltages. When a first battery module with a battery module voltage larger than a fourth preset threshold or smaller than a fifth preset threshold exists in the m battery modules, that is, when the battery module voltage of the first battery module is not within the battery operation range, the battery management unit controls the first battery switch in the first battery module to be turned off and the second battery switch to be turned on, at this time, the battery unit in the first battery module is short-circuited by the second battery switch in the first battery module, so that the battery unit in the first battery module is directly cut out from the plurality of battery modules connected in series when the battery unit fails, thereby not affecting the normal operation of other battery modules except the first battery module in the battery cluster 21, further avoiding the short plate effect among the battery units in the battery cluster, and simultaneously improving the utilization rate of the battery units in the battery cluster. In addition, the switching-in and switching-over of the minimum battery unit can be realized by controlling the first battery switch and the second battery switch in each battery module, so that the flexible control of the battery voltage of the battery cluster 21 can be realized.

Here, please refer to the control manner of the battery management unit for the battery cluster 21 for the specific control manner of the battery management unit for the other (n-1) battery clusters, which is not described herein again.

In this embodiment, each DC/DC converter in the energy storage system 1 may dynamically adjust the output voltage of each first DC conversion circuit based on the voltage difference value thereof, and then dynamically adjust the input voltage of each second DC conversion circuit, so that the efficiency of each DC/DC converter reaches the preset efficiency when the output voltage reaches the bus voltage, thereby achieving the high efficiency of each DC/DC converter at the voltage difference value in the full range, and further improving the efficiency of the energy storage system 1. In addition, when the number of the battery clusters in the energy storage system 1 is multiple, since the output voltages of the DC/DC converters are the bus voltages, the circulation current between the battery clusters can be effectively suppressed, thereby improving the safety and stability of the energy storage system 1. Furthermore, the energy storage system 1 can avoid the short plate effect among the battery units in the battery clusters by controlling the switching-in and switching-out of the minimum battery unit in each battery cluster, and simultaneously improves the utilization rate of the battery units in the battery clusters. Finally, because two direct current conversion circuits in each DC/DC converter in the energy storage system 1 have a voltage regulation function, the energy storage system 1 can give consideration to the application of the power grid in high-low penetration occasions, prevents the over-distribution of batteries caused by high-low penetration, and has strong applicability.

Referring to fig. 7, fig. 7 is a schematic flowchart of an output voltage control method of the DC/DC converter provided in the present application. The output voltage control method of the DC/DC converter provided in the embodiment of the present application is applicable to any DC/DC converter in the energy storage system 1 shown in fig. 3 and 4. The output voltage control method of the DC/DC converter may include the steps of:

s101, acquiring a voltage difference value between the battery voltage of the battery cluster and the bus voltage of the direct current bus.

In an optional embodiment, after the DC/DC converter operates, it starts to obtain a battery voltage of a corresponding battery cluster and a bus voltage of the DC bus, and calculates a difference between the battery voltage and the bus voltage of the DC bus to obtain a voltage difference.

And S102, controlling the output voltage of the first direct current conversion circuit according to the voltage difference.

In an optional embodiment, the DC/DC converter determines a first output voltage corresponding to the voltage difference according to the voltage difference and a mapping relationship between the voltage difference and the output voltage, and controls the output voltage of the first DC conversion circuit to be the first output voltage. When the output voltage of the first direct current conversion circuit is the first output voltage, the input voltage of the second direct current conversion circuit is the first output voltage and the battery voltage of the battery cluster corresponding to the DC/DC converter, and then the DC/DC converter controls the second direct current conversion circuit to output the bus voltage.

In another alternative embodiment, when the voltage difference is smaller than the first preset threshold, the DC/DC converter controls the output voltage of the first DC conversion circuit to be the voltage difference. When the output voltage of the first direct current conversion circuit is the first output voltage, the input voltage of the second direct current conversion circuit is the bus voltage, and then the DC/DC converter controls the first input end and the second input end of the second direct current conversion circuit to be directly communicated with the output end, or controls a first switch between the first input end and the first output end of the second direct current conversion circuit to be conducted.

In another alternative embodiment, when the voltage difference is greater than or equal to the second preset threshold, the DC/DC converter controls the duty ratio of the controllable switch in the first DC conversion circuit to be 0 and/or controls the second switch between the first output terminal and the second output terminal of the first DC conversion circuit to be turned on, so that the output voltage of the first DC conversion circuit is 0. When the output voltage of the first direct current conversion circuit is 0, the input voltage of the second direct current conversion circuit is the battery voltage of the battery cluster corresponding to the DC/DC converter, and the DC/DC converter controls the second direct current conversion circuit to output the bus voltage. The second preset threshold may be the same as or different from the first preset threshold.

In another optional embodiment, when the voltage difference is greater than or equal to a second preset threshold, the DC/DC converter determines a second output voltage corresponding to the voltage difference according to the voltage difference and a mapping relationship between the voltage difference and the output voltage, and controls the output voltage of the first DC conversion circuit to be the second output voltage. When the output voltage of the first direct current conversion circuit is the second output voltage, the input voltage of the second direct current conversion circuit is the second output voltage and the battery voltage of the battery cluster corresponding to the DC/DC converter, and then the DC/DC converter controls the second direct current conversion circuit to output the bus voltage. The second preset threshold may be the same as or different from the first preset threshold.

In yet another optional implementation, when the voltage difference is greater than the first preset threshold and smaller than the second preset threshold, the DC/DC converter determines a third output voltage corresponding to the voltage difference according to the voltage difference and a mapping relationship between the voltage difference and the output voltage, and controls the output voltage of the first DC conversion circuit to be the third output voltage. When the output voltage of the first direct current conversion circuit is the third output voltage, the input voltage of the second direct current conversion circuit is the third output voltage and the battery voltage of the battery cluster corresponding to the DC/DC converter, and then the DC/DC converter controls the second direct current conversion circuit to output the bus voltage.

In a specific implementation, more operations performed by the DC/DC converter in the output voltage control method of the DC/DC converter provided by the present application can refer to the implementation manner performed by the DC/DC converter 11 shown in fig. 3 and fig. 4, and are not described herein again.

In the embodiment of the application, the DC/DC converter can dynamically adjust the output voltage of the first DC conversion circuit based on the voltage difference, and further dynamically adjust the input voltage of the second DC conversion circuit, so that the efficiency of the DC/DC converter reaches the preset efficiency when the output voltage reaches the bus voltage, and the high efficiency of the DC/DC converter in the full range of voltage difference is realized.

The above description is only for the specific embodiments of the present application, but the scope of the present application is not limited thereto, and any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present application, and shall be covered by the scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

Claims

1. A DC/DC converter, wherein a first input terminal and a second input terminal of the DC/DC converter are connected to a battery cluster, an output terminal of the DC/DC converter is connected to a DC bus, the DC/DC converter comprising a first DC conversion circuit, a second DC conversion circuit, and a controller, wherein:

the input end of the first direct current conversion circuit is connected with a direct current power supply, the first output end and the second output end of the first direct current conversion circuit are respectively connected with the first input end of the DC/DC converter and the first input end of the second direct current conversion circuit, and the first direct current conversion circuit is used for converting the voltage input by the direct current power supply into direct current and outputting the direct current converted voltage to the second direct current conversion circuit;

a second input end of the second direct current conversion circuit is connected with a second input end of the DC/DC converter, an output end of the second direct current conversion circuit is connected with an output end of the DC/DC converter, and the second direct current conversion circuit is used for performing direct current conversion on input voltage and then outputting the converted input voltage;

the controller is configured to control an output voltage of the first dc conversion circuit according to a voltage difference between a battery voltage of the battery cluster and a bus voltage of the dc bus.

2. The DC/DC converter of claim 1, wherein the controller is configured to control the output voltage of the first DC conversion circuit to be the voltage difference value when the voltage difference value is smaller than a first preset threshold value.

3. The DC/DC converter of claim 2, wherein the controller is further configured to control the first input terminal and the second input terminal of the second DC converter circuit to be directly connected to the output terminal when the output voltage of the first DC converter circuit is the voltage difference.

4. The DC/DC converter of claim 2, further comprising a first switch, wherein the output of the second DC converter circuit comprises a first output, and wherein the first switch is connected between the first input and the first output of the second DC converter circuit;

the controller is further configured to control the first switch to be turned on when the output voltage of the first dc conversion circuit is the voltage difference.

5. The DC/DC converter of claim 1, wherein the controller is configured to control the output voltage of the first DC conversion circuit to be 0 when the voltage difference is greater than or equal to a second predetermined threshold.

6. The DC/DC converter according to any of claims 1 to 5, further comprising a second switch connected between the first output terminal and the second output terminal of the first DC conversion circuit;

the controller is further configured to control the second switch to be turned on when the voltage difference is greater than or equal to a second preset threshold.

7. The DC/DC converter according to any of claims 1 to 6, wherein the controller is further configured to control the output voltage of the second DC conversion circuit to be the bus voltage when the output voltage of the first DC conversion circuit is 0.

8. The DC/DC converter of claim 1, wherein the controller is configured to determine a first output voltage corresponding to the voltage difference according to the voltage difference and a mapping relationship between the voltage difference and the output voltage, and control the output voltage of the first DC conversion circuit to be the first output voltage.

9. The DC/DC converter of claim 8, wherein the controller is further configured to control the output voltage of the second DC conversion circuit to be the bus voltage when the output voltage of the first DC conversion circuit is the first output voltage.

10. An energy storage system, characterized in that the energy storage system comprises one or more DC/DC converters according to any of claims 1-9, and one or more battery clusters, wherein one of the DC/DC converters is connected to one of the battery clusters.

11. The energy storage system of claim 10, wherein the battery cluster comprises at least two battery modules, the battery modules comprising a battery cell, a first battery switch, and a second battery switch, the battery cell and the first battery switch being connected in series across the second battery switch;

the energy storage system further comprises a battery management unit, wherein the battery management unit is used for acquiring the battery module voltage of each battery module in the at least two battery modules; and when the battery module voltage of a first battery module of the at least two battery modules is greater than a fourth preset threshold value or less than a fifth preset threshold value, controlling a first battery switch of the first battery module to be switched off and a second battery switch of the first battery module to be switched on.

12. The energy storage system of claim 10 or 11, further comprising an inverter, wherein an input end of the inverter is connected with a direct current bus, and an output end of the inverter is connected with an alternating current load.

13. An output voltage control method of a DC/DC converter, wherein a first input terminal and a second input terminal of the DC/DC converter are connected with a battery cluster, an output terminal of the DC/DC converter is connected with a direct current bus, the DC/DC converter comprises a first direct current conversion circuit and a second direct current conversion circuit, wherein: the input end of the first direct current conversion circuit is connected with a direct current power supply, the first output end and the second output end of the first direct current conversion circuit are respectively connected with the first input end of the DC/DC converter and the first input end of the second direct current conversion circuit, and the first direct current conversion circuit is used for converting the voltage input by the direct current power supply into direct current and outputting the direct current converted voltage to the second direct current conversion circuit; a second input end of the second direct current conversion circuit is connected with a second input end of the DC/DC converter, an output end of the second direct current conversion circuit is connected with an output end of the DC/DC converter, and the second direct current conversion circuit is used for performing direct current conversion on input voltage and then outputting the converted input voltage;

the method comprises the following steps:

acquiring a voltage difference value between the battery voltage of the battery cluster and the bus voltage of the direct current bus;

and controlling the output voltage of the first direct current conversion circuit according to the voltage difference.

14. The method of claim 13, wherein said controlling the output voltage of the first dc conversion circuit according to the voltage difference comprises:

and when the voltage difference value is smaller than the first preset threshold value, controlling the output voltage of the first direct current conversion circuit to be the voltage difference value.

15. The method of claim 14, further comprising:

and when the output voltage of the first direct current conversion circuit is the voltage difference value, controlling the first input end and the second input end of the second direct current conversion circuit to be directly communicated with the output end.

16. The method of claim 14, wherein the DC/DC converter further comprises a first switch, wherein the output of the second DC converter circuit comprises a first output, and wherein the first switch is connected between the first input and the first output of the second DC converter circuit;

the method further comprises the following steps:

and when the output voltage of the first direct current conversion circuit is the voltage difference value, controlling the first switch to be conducted.

17. The method of claim 13, wherein said controlling the output voltage of the first dc conversion circuit according to the voltage difference comprises:

and when the voltage difference is greater than or equal to a second preset threshold value, controlling the output voltage of the first direct current conversion circuit to be 0.

18. The method of any of claims 13-17, wherein the DC/DC converter further comprises a second switch coupled between the first output terminal and the second output terminal of the first DC conversion circuit;

the method further comprises the following steps:

and when the voltage difference value is greater than or equal to a second preset threshold value, controlling the second switch to be conducted.

19. The method according to any one of claims 13-18, further comprising:

and when the output voltage of the first direct current conversion circuit is 0, controlling the output voltage of the second direct current conversion circuit to be the bus voltage.

20. The method of claim 13, wherein said controlling the output voltage of the first dc conversion circuit according to the voltage difference comprises:

and determining a first output voltage corresponding to the voltage difference value according to the voltage difference value and a mapping relation between the voltage difference value and the output voltage, and controlling the output voltage of the first direct current conversion circuit to be the first output voltage.

21. The method of claim 20, further comprising:

and when the output voltage of the first direct current conversion circuit is the first output voltage, controlling the output voltage of the second direct current conversion circuit to be the bus voltage.