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

Abstract

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

Description

Technical Field

[0001] This application relates to the field of power supply technology, and in particular to a DC / DC converter and its output voltage control method, and an energy storage system. Background Technology

[0002] In energy storage system applications, multiple battery clusters (composed of multiple battery cells connected in series and parallel) are typically connected in parallel through a combiner box and then connected to the DC side of a centralized inverter. The AC side of the centralized inverter is connected to the load. Due to differences in batteries (such as differences in capacity and capacity degradation between batteries from different manufacturers or even the same manufacturer), voltage differences can occur among the multiple battery clusters, leading to circulating current problems when multiple battery clusters are connected in parallel.

[0003] To address the circulation problem, the following solutions have been provided. Figure 1 The energy storage system shown. (As shown in the image) Figure 1 As shown, each of the n battery clusters is connected in series with the output of its corresponding DC / DC converter and then connected to a DC bus. The DC bus is connected to the load via a centralized inverter. The inputs of the n DC / DC converters corresponding to the n battery clusters are all connected to a power source. This energy storage system compensates for the voltage difference between each battery cluster and the DC bus using the n DC / DC converters, ensuring that the voltage output to the DC bus from each battery cluster connected in series with its corresponding DC / DC converter is the same, thereby suppressing circulating currents generated when multiple battery clusters are connected in parallel. However, the aforementioned DC / DC converters have a wide voltage regulation range, resulting in lower efficiency at certain operating points during voltage difference compensation, making it impossible to achieve high efficiency across the entire voltage difference range. Summary of the Invention

[0004] This application provides a DC / DC converter and its output voltage control method and energy storage system, which can achieve high efficiency of the DC / DC converter across the entire voltage difference range.

[0005] In a first aspect, this application provides a DC / DC converter. The first and second input terminals of the DC / DC converter are connected to a battery pack, and the output terminal of the DC / DC converter is connected to a DC bus. The DC / DC converter includes a first DC-DC conversion circuit, a second DC-DC conversion circuit, and a controller. Specifically: the input terminal of the first DC-DC conversion circuit is connected to a DC power supply; the first and second output terminals of the first DC-DC conversion circuit are respectively connected to the first input terminal of the DC / DC converter and the first input terminal of the second DC-DC conversion circuit. The first DC-DC conversion circuit converts the input voltage of the DC power supply into a DC-DC converter and outputs it to the second DC-DC conversion circuit. The second input terminal of the second DC-DC conversion circuit is connected to the second input terminal of the DC / DC converter, and the output terminal of the second DC-DC conversion circuit is connected to the output terminal of the DC / DC converter. The second DC-DC conversion circuit converts the input voltage into a DC-DC converter and outputs it. After the DC / DC converter operates, the controller acquires the voltage difference between the battery voltage of the battery pack and the DC bus voltage, and controls the output voltage of the first DC-DC conversion circuit according to the voltage difference, so that the output voltage of the DC / DC converter is the bus voltage. Understandably, a DC / DC converter can dynamically adjust the output voltage of the first DC-DC converter circuit based on the voltage difference, and then dynamically adjust the input voltage of the second DC-DC converter circuit. Thus, through the cooperation of the first and second DC-DC converter circuits, the efficiency of the DC / DC converter reaches the preset efficiency when the output voltage reaches the bus voltage, thereby achieving high efficiency of the DC / DC converter across the entire voltage difference range.

[0006] In conjunction with the first aspect, in a first possible implementation, when the voltage difference is less than a first preset threshold, i.e., when the voltage difference is small, the controller controls the output voltage of the first DC-DC converter to be the voltage difference. It is understood that when the voltage difference is small, the first DC-DC converter only needs to compensate for the voltage difference; the circuit only uses differential-mode power, resulting in low losses. Therefore, the DC / DC converter can achieve high efficiency when the voltage difference is within the range of less than the first preset threshold.

[0007] In conjunction with the first possible implementation of the first aspect, in the second possible implementation, when the output voltage of the first DC-DC converter is a voltage difference, the controller further controls the first and second input terminals of the second DC-DC converter to be directly connected to the output terminal. It is understood that when the output voltage of the first DC-DC converter is a voltage difference, the output voltage of the DC / DC converter can be ensured to be the bus voltage by controlling the second DC-DC converter to be in shoot-through mode. Since the second DC-DC converter does not need to pass power in shoot-through mode and has virtually no losses, the efficiency of the DC / DC converter can be effectively improved. Furthermore, this implementation does not require additional components, effectively reducing the cost of the DC / DC converter.

[0008] In conjunction with the first possible implementation of the first aspect, in a third possible implementation, the DC / DC converter further includes a first switch, the output terminal of the second DC-DC converter 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-DC converter. When the output voltage of the first DC-DC converter is a voltage difference, the controller also controls the first switch to turn on. It is understood that in cases where some DC-DC converters do not support shoot-through mode, the same function in shoot-through mode can be achieved by adding a first switch connected in parallel with the DC-DC converter, thereby improving the applicability of the DC / DC converter.

[0009] In conjunction with the first aspect, in the fourth possible implementation, when the voltage difference is greater than or equal to the second preset threshold, i.e., when the voltage difference is large, the controller controls the output voltage of the first DC-DC converter to be 0. It can be understood that when the voltage difference is large, i.e., when the DC bus voltage is small, since the output voltage of the first DC-DC converter is 0, the first DC-DC converter stops working, and only the second DC-DC converter operates in the DC / DC converter. Since the second DC-DC converter needs to output a smaller bus voltage to the DC bus, the power it needs to process is smaller, thus reducing the losses in the DC / DC converter. This allows the DC / DC converter to achieve high efficiency when the voltage difference is greater than or equal to the second preset threshold.

[0010] In a fifth possible embodiment, in conjunction with any of the first to fourth possible implementations of the first aspect, the DC / DC converter further includes a second switch connected between the first output terminal and the second output terminal of the first DC-DC converter circuit. When the voltage difference is greater than or equal to a second preset threshold, the controller further controls the second switch to turn on. It is understood that the DC / DC converter can achieve a zero output voltage for the first DC-DC converter circuit by controlling the second switch to turn on and short-circuit the first DC-DC converter circuit. This control method is simple, easy to implement, and can improve the stability of the DC / DC converter.

[0011] In conjunction with any of the first to fifth possible embodiments of the first aspect, in the sixth possible embodiment, when the output voltage of the first DC-DC converter is 0, i.e., when the input voltage of the second DC-DC converter is the battery voltage, the controller further controls the output voltage of the second DC-DC converter to be the bus voltage. This not only achieves high efficiency for the DC / DC converter when its voltage difference is greater than or equal to a second preset threshold, but also ensures that the output voltage of each DC / DC converter is the bus voltage when the energy storage system containing the DC / DC converter includes multiple DC / DC converters, by having the second DC-DC converter in each DC / DC converter output the bus voltage. This effectively suppresses circulating currents between battery clusters, thereby improving the safety and stability of the DC / DC converter.

[0012] In conjunction with the first aspect, in the seventh possible implementation, the controller determines the first output voltage corresponding to the voltage difference based on the voltage difference and the mapping relationship between the voltage difference and the output voltage, and controls the output voltage of the first DC-DC converter circuit to be the first output voltage. It is understood that the DC / DC converter can control the output voltage of the first DC-DC converter circuit to be the first output voltage at which the efficiency of the DC / DC converter reaches a preset efficiency through the mapping relationship between the voltage difference and the output voltage, thereby achieving optimal efficiency of the DC / DC converter across the entire range of voltage differences.

[0013] In conjunction with the seventh possible implementation of the first aspect, in the eighth possible implementation, when the output voltage of the first DC-DC converter is the first output voltage, the controller controls the output voltage of the second DC-DC converter to be the bus voltage. Furthermore, after the output voltage of the first DC-DC converter reaches the first output voltage at which the efficiency of the DC / DC converter reaches a preset efficiency, the second DC-DC converter, in cooperation with the second DC-DC converter, ensures that the output voltage of the DC / DC converter is the bus voltage while the efficiency of the DC / DC converter reaches the preset efficiency.

[0014] Secondly, this application provides an energy storage system comprising one or more DC / DC converters as provided in any of the first to eighth possible embodiments, and one or more battery clusters, wherein one DC / DC converter is connected to one battery cluster. It is understood that each DC / DC converter in the energy storage system can dynamically adjust the output voltage of its first DC-DC converter circuit based on its respective voltage difference, and thus dynamically adjust the input voltage of its respective second DC-DC converter circuit. This allows each DC / DC converter to achieve a preset efficiency when its output voltage reaches the bus voltage, thereby achieving high efficiency across the entire voltage difference range and improving the efficiency of the energy storage system. Furthermore, when there are multiple battery clusters in the energy storage system, since the output voltage of each DC / DC converter is the bus voltage, circulating currents between battery clusters can be effectively suppressed, thereby improving the safety and stability of the energy storage system.

[0015] In conjunction with the second aspect, in a first possible implementation, the battery cluster includes at least two battery modules. Each battery module includes a battery cell, a first battery switch, and a second battery switch. The battery cell and the first battery switch are connected in series across the second battery switch. The energy storage system also includes a battery management unit, which is used to acquire the battery module voltage of each of the at least two battery modules. When the battery module voltage of the first battery module is greater than a fourth preset threshold or less than a fifth preset threshold, the battery management unit controls the first battery switch in the first battery module to turn off and the second battery switch to turn on. Furthermore, the energy storage system can avoid the bottleneck effect between battery cells within the battery cluster by controlling the entry and exit of the smallest battery cell in each battery cluster, while simultaneously improving the utilization rate of the battery cells in the battery cluster.

[0016] In conjunction with the second aspect or the first possible implementation of the second aspect, in the second possible implementation, the energy storage system further includes an inverter, the input of which is connected to a DC bus, and the output of which is connected to an AC load.

[0017] Thirdly, this application provides an output voltage control method for a DC / DC converter. The DC / DC converter has a first input terminal and a second input terminal connected to a battery pack, and an output terminal connected to a DC bus. The DC / DC converter includes a first DC-DC conversion circuit and a second DC-DC conversion circuit. Specifically, the input terminal of the first DC-DC conversion circuit is connected to a DC power supply, and its first and second output terminals are respectively connected to the first input terminal of the DC / DC converter and the first input terminal of the second DC-DC conversion circuit. The first DC-DC conversion circuit converts the input voltage of the DC power supply into a DC-DC converter and outputs it to the second DC-DC conversion circuit. The second input terminal of the second DC-DC conversion circuit is connected to the second input terminal of the DC / DC converter, and its output terminal is connected to the output terminal of the DC / DC converter. The second DC-DC conversion circuit converts the input voltage into a DC-DC converter and outputs it. The method includes: the DC / DC converter acquiring the voltage difference between the battery voltage of the battery pack and the bus voltage of the DC bus, and controlling the output voltage of the first DC-DC conversion circuit based on the voltage difference.

[0018] In conjunction with the third aspect, in a first possible implementation, when the voltage difference is less than a first preset threshold, the DC / DC converter controls the output voltage of the first DC-DC converter circuit to be the voltage difference.

[0019] In conjunction with the first possible implementation of the third aspect, in the second possible implementation, when the output voltage of the first DC-DC converter is a voltage difference, the DC / DC converter also controls the first input terminal and the second input terminal of the second DC-DC converter to be directly connected to the output terminal.

[0020] In conjunction with the first possible implementation of the third aspect, in the third possible implementation, the DC / DC converter further includes a first switch, the output terminal of the second DC-DC converter 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-DC converter. When the output voltage of the first DC-DC converter is a voltage difference, the DC / DC converter also controls the first switch to be turned on.

[0021] In conjunction with the third aspect, in a fourth possible implementation, when the voltage difference is greater than or equal to a second preset threshold, the DC / DC converter controls the output voltage of the first DC-DC converter circuit to be 0.

[0022] In a fifth possible embodiment, in conjunction with any of the third to fourth possible implementations of the first aspect, the DC / DC converter further includes a second switch connected between the first and second output terminals of the first DC-DC converter circuit. When the voltage difference is greater than or equal to a second preset threshold, the DC / DC converter also controls the second switch to turn on.

[0023] In conjunction with any of the third to fifth possible implementations of the third aspect, in the sixth possible implementation, when the output voltage of the first DC-DC converter is 0, the DC / DC converter further controls the output voltage of the second DC-DC converter to be the bus voltage.

[0024] In conjunction with the third aspect, in the seventh possible implementation, the DC / DC converter determines the first output voltage corresponding to the voltage difference based on the voltage difference and the mapping relationship between the voltage difference and the output voltage, and controls the output voltage of the first DC-DC converter circuit to be the first output voltage.

[0025] In conjunction with the seventh possible implementation of the third aspect, in the eighth possible implementation, when the output voltage of the first DC-DC converter is the first output voltage, the DC / DC converter controls the output voltage of the second DC-DC converter to be the bus voltage.

[0026] It should be understood that the implementations and beneficial effects of the above-mentioned aspects of this application can be referenced from each other. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the structure of an energy storage system provided by existing technology;

[0028] Figure 2 This is a schematic diagram illustrating the application scenario of the DC / DC converter provided in this application;

[0029] Figure 3 This is a structural schematic diagram of the energy storage system provided in this application;

[0030] Figure 4 This is another structural schematic diagram of the energy storage system provided in this application;

[0031] Figure 5 This is a schematic diagram of the structure of the second DC-DC converter circuit provided in this application;

[0032] Figure 6 This is a schematic diagram of the battery cluster structure provided in this application;

[0033] Figure 7 This is a flowchart illustrating the output voltage control method of the DC / DC converter provided in this application. Detailed Implementation

[0034] The DC / DC converter provided in this application is applicable to various application scenarios, such as data center power supply scenarios (for powering load chips), photovoltaic power supply scenarios, energy storage power supply scenarios, photovoltaic-energy storage hybrid power supply scenarios, and wind-energy storage hybrid power supply scenarios. The following explanation uses the energy storage power supply scenario as an example.

[0035] See Figure 2 , Figure 2 This is a schematic diagram illustrating an application scenario of the DC / DC converter provided in this application. For example... Figure 2 As shown, the energy storage system includes a DC / DC converter 11 and its corresponding energy storage battery cluster 21, ..., a DC / DC converter 1n and its corresponding energy storage battery cluster 2n, a DC bus (i.e., the positive DC bus BUS+ and the negative DC bus BUS-), and an inverter. Here, n is a positive integer. The two input terminals of DC / DC converter 11 are connected to energy storage battery cluster 21, and the two output terminals are connected to the DC bus; ...; the two input terminals of DC / DC converter 1n are connected to energy storage battery cluster 2n, and the two output terminals are connected to the DC bus. The DC bus is connected to the AC power grid or AC electrical equipment through the inverter. Figure 2 In the energy storage power supply scenario shown, the DC / DC converter provided in this application can be Figure 2 This refers to any one of the n DC / DC converters shown. Since the structures and operating principles of these n DC / DC converters are identical, for ease of description, DC / DC converter 11 will be used as an example below. DC / DC converter 11 includes DC / DC circuit 1, DC / DC circuit 2, and a controller (not shown). The two input terminals of DC / DC circuit 1 are connected to a DC power supply (not shown), its positive output terminal is connected to the positive input terminal of DC / DC circuit 2, and its negative output terminal is connected to the positive input terminal of DC / DC converter 11. The negative input terminal of DC / DC circuit 2 is connected to the negative input terminal of DC / DC converter 11, and its two output terminals are connected to the two output terminals of DC / DC converter 11.

[0036] After the DC / DC converter 11 starts working, the controller acquires 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 BUS+ and the negative DC bus BUS-) in real time, and calculates the voltage difference between the battery voltage of the energy storage battery cluster 21 and the bus voltage. Then, the controller controls the output voltage of the DC / DC circuit 1 based on the voltage difference, and uses the sum of the battery voltage of the energy storage battery cluster 21 and the output voltage of the DC / DC circuit 1 as the input voltage of the DC / DC circuit 2, controlling 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. Afterwards, the inverter converts the bus voltage on the DC bus into AC power, thereby supplying power to AC loads (such as AC power grids or AC electrical equipment). Understandably, the DC / DC converter 11 can dynamically adjust the DC / DC circuit 1 and 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, thereby achieving high efficiency of the DC / DC converter 11 across the entire voltage difference range and improving the efficiency of the energy storage system. Furthermore, when there are multiple energy storage battery clusters in the energy storage system, since the output voltage of each DC / DC converter is the bus voltage, circulating currents between energy storage battery clusters can be effectively suppressed, thereby improving the safety of the energy storage system.

[0037] The above are merely examples of application scenarios for the DC / DC converter provided in this application, and are not exhaustive. This application does not limit the application scenarios.

[0038] The following is combined Figures 3 to 6 The working principle of the energy storage system and DC / DC converter provided in this application is illustrated by examples.

[0039] See Figure 3 , Figure 3 This is a structural schematic diagram of the energy storage system provided in this application. Figure 3As shown, the energy storage system 1 includes a DC / DC converter 11 and its corresponding battery clusters 21, ..., a DC / DC converter 1n and its corresponding battery clusters 2n, and DC buses (i.e., positive DC bus BUS+ and negative DC bus BUS-). n is a positive integer. The positive and negative input terminals of the DC / DC converter 11 are connected to the battery clusters 21, and the positive and negative output terminals are connected to the positive DC bus BUS+ and the negative DC bus BUS-, respectively; ...; the positive and negative input terminals of the DC / DC converter 1n are connected to the battery clusters 2n, and the positive and negative output terminals are connected to the positive DC bus BUS+ and the negative DC bus BUS-, respectively. The positive DC bus BUS+ and the negative DC bus BUS- are connected to the load. The DC / DC converter 11 includes a first DC-DC converter circuit 111, a second DC-DC converter circuit 112, and a controller 113. The two input terminals of the first DC-DC converter 111 are connected to the DC power supply 114, the positive output terminal is connected to the positive input terminal of the second DC-DC converter 112, and the negative output terminal is connected to the positive input terminal of the DC / DC converter 11. The negative input terminal of the second DC-DC converter 112 is connected to the negative input terminal of the DC / DC converter 11, and the positive and negative output terminals are respectively connected to the positive and negative output terminals of the DC / DC converter 11. ... The DC / DC converter 1n includes a first DC-DC converter 1n1, a second DC-DC converter 1n2, and a controller 1n3. The two input terminals of the first DC-DC converter 1n1 are connected to the DC power supply 1n4, the positive output terminal is connected to the positive input terminal of the second DC-DC converter 1n2, and the negative output terminal is connected to the positive input terminal of the DC / DC converter 1n. The negative input terminal of the second DC-DC converter 1n2 is connected to the negative input terminal of the DC / DC converter 1n, and the positive and negative output terminals are respectively connected to the positive and negative output terminals of the DC / DC converter 1n.

[0040] The DC power supply connected to the input terminals of each of the aforementioned second DC-DC converter circuits can be the battery cluster, DC bus, or other power source corresponding to its respective DC / DC converter. The aforementioned n first DC-DC converter circuits can be any of the following: buck converter, boost converter, and buck-boost converter. Similarly, the aforementioned n second DC-DC converter circuits can be any of the following: buck converter, boost converter, and buck-boost converter. The types of batteries connected in series and parallel within the aforementioned battery clusters are not limited to lithium batteries; other types of electrochemical batteries can also be used, such as lead-acid batteries, lead-carbon batteries, ternary lithium batteries, lithium iron phosphate batteries, and lithium titanate batteries. The load can be a DC power grid, an inverter, etc.

[0041] In an optional embodiment, after the energy storage system 1 starts operating, each of the n DC / DC converters begins to acquire the battery voltage and the bus voltage of the DC bus (i.e., the voltage difference between the positive DC bus BUS+ and the negative DC bus BUS-) of its corresponding battery cluster, and calculates the voltage difference between the battery voltage and the bus voltage of its corresponding battery cluster. Each of the n DC / DC converters controls the output voltage of its first DC-DC converter circuit based on its respective voltage difference, thereby ensuring that the input voltage of its second DC-DC converter circuit is the sum of the battery voltage of its corresponding battery cluster and the output voltage of its first DC-DC converter circuit. Subsequently, the n DC / DC converters control their respective second DC-DC converter circuits to convert the input voltage of their second DC-DC converter circuits into the bus voltage, so that the output voltage of each of the n DC / DC converters is the bus voltage.

[0042] In this embodiment, each DC / DC converter in the energy storage system 1 can dynamically adjust the output voltage of its first DC-DC converter circuit based on its voltage difference, and then dynamically adjust the input voltage of its second DC-DC converter circuit. This ensures that each DC / DC converter achieves a preset efficiency when its output voltage reaches the bus voltage, thereby achieving high efficiency across the entire voltage difference range and improving the efficiency of the energy storage system 1. Furthermore, when there are multiple battery clusters in the energy storage system 1, since the output voltage of each DC / DC converter is the bus voltage, circulating currents between battery clusters can be effectively suppressed, thus improving the safety and stability of the energy storage system 1.

[0043] Since the structure and working principle of each DC / DC converter in the energy storage system 1 are the same, for ease of description, the following description will take DC / DC converter 11 as an example.

[0044] See Figure 4 , Figure 4 This is another structural schematic diagram of the energy storage system provided in this application. For example... Figure 4As shown, the energy storage system 1 includes a DC / DC converter 11 and its corresponding battery clusters 21, ..., a DC / DC converter 1n and its corresponding battery clusters 2n, DC buses (i.e., positive DC bus BUS+ and negative DC bus BUS-), and an inverter 31. n is a positive integer. The positive and negative input terminals of DC / DC converter 11 are connected to battery clusters 21, and its positive and negative output terminals are connected to the positive DC bus BUS+ and negative DC bus BUS-, respectively; ...; the positive and negative input terminals of DC / DC converter 1n are connected to battery clusters 2n, and its positive and negative output terminals are connected to the positive DC bus BUS+ and negative DC bus BUS-, respectively. The positive DC bus BUS+ and negative DC bus BUS- are connected to the positive and negative input terminals of inverter 31, respectively, and the output terminal of inverter 31 is connected to the AC power grid. For the specific connections of the circuits and internal circuits of each DC / DC converter from DC / DC converter 11 to DC / DC converter 1n, please refer to [link to relevant documentation]. Figure 3 The descriptions of the corresponding parts in the illustrated embodiments will not be repeated here. 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 terminal and the positive output terminal of the second DC-DC converter 112, and the second switch S12 is connected between the positive output terminal and the negative output terminal of the first DC-DC converter 111; ...; 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-DC converter 1n2, and the second switch Sn2 is connected between the positive output terminal and the negative output terminal of the first DC-DC converter 1n1.

[0045] Specifically, after the DC / DC converter 11 starts working, the controller 113 begins to acquire the battery voltage of the battery cluster 21 and the bus voltage of the DC bus, and calculates the voltage difference between the battery voltage of the battery cluster 21 and the bus voltage of the DC bus.

[0046] In an optional embodiment, after obtaining the voltage difference, the controller 113 determines the first output voltage corresponding to the voltage difference based on the voltage difference and the mapping relationship between the voltage difference and the output voltage, and controls the output voltage of the first DC-DC converter 111 to be the first output voltage. The mapping relationship between the voltage difference and the output voltage includes multiple voltage difference intervals and the output voltage of the first DC-DC converter when the efficiency of the DC / DC converter corresponding to each of the multiple voltage difference intervals reaches a preset efficiency. It should be noted that if there are multiple output voltages of the first DC-DC converter when the efficiency of the DC / DC converter reaches the preset efficiency, the output voltage corresponding to the highest efficiency of the DC / DC converter among the multiple output voltages where the efficiency of the DC / DC converter reaches the preset efficiency can be determined as the output voltage of the first DC-DC converter corresponding to the voltage difference interval.

[0047] Specifically, the controller 113 determines the voltage difference range, i.e., the first voltage difference range, based on the aforementioned voltage difference and the mapping relationship between the voltage difference and the output voltage. Then, based on the first voltage difference range and the mapping relationship between the voltage difference and the output voltage, it determines the first output voltage corresponding to the first voltage difference range and controls the output voltage of the first DC-DC converter 111 to be the first output voltage. When the output voltage of the first DC-DC converter 111 is the first output voltage, the input voltage of the second DC-DC converter 112 is the first output voltage and the battery voltage of the battery cluster 21. The controller 113 then controls the second DC-DC converter 112 to convert its input voltage DC-DC to the bus voltage and output it. At this time, the output voltage of the DC / DC converter 11 is the bus voltage.

[0048] Understandably, the DC / DC converter 11 can control the output voltage of the first DC-DC converter 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. Then, with the cooperation of the second DC-DC converter circuit 112, the output voltage of the DC / DC converter 11 is the bus voltage while the efficiency reaches the preset efficiency, thereby achieving the optimal efficiency of the DC / DC converter 11 across the entire range of voltage differences.

[0049] In another alternative embodiment, after obtaining the voltage difference, the controller 113 controls the output voltage of the first DC-DC converter 111 based on the 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.

[0050] In an optional embodiment, when the voltage difference is less than a first preset threshold, the controller 113 controls the output voltage of the first DC-DC converter 111 to be the voltage difference. When the output voltage of the first DC-DC converter 111 is the voltage difference, the input voltage of the second DC-DC converter 112 is the sum of the voltage difference and the battery voltage of the battery cluster 21, i.e., the bus voltage. The controller 113 then controls the positive input terminal and positive output terminal of the second DC-DC converter 112 to be directly connected, and the negative input terminal and negative output terminal to be directly connected, i.e., the second DC-DC converter 112 is in a direct-through mode. At this time, the output voltage of the second DC-DC converter 112 is the bus voltage, which is also the output voltage of the DC / DC converter 11.

[0051] For example, in the second DC-DC converter circuit 112, Figure 5In the 4-switch symmetrical BUCK-BOOST circuit shown, the controller 113 can directly connect the two input terminals and two output terminals of the second DC-DC converter 112 by controlling both switches S11 and S13 to be on and both switches S12 and S14 to be off. That is, the second DC-DC converter 112 is in the pass-through mode. At this time, the electrical energy at the input terminal of the second DC-DC converter 112 is directly transferred to the output terminal. The second DC-DC converter 112 does not have the high-frequency chopping loss of the switching transistors. Therefore, the efficiency of the second DC-DC converter 112 is high in the pass-through mode.

[0052] Understandably, when the voltage difference is small, the DC / DC converter 11 compensates for the voltage difference by controlling the first DC-DC converter circuit 111 and controls the second DC-DC converter circuit 112 to be in shoot-through mode, so that the output voltage of the DC / DC converter 11 reaches the bus voltage. Since the first DC-DC converter circuit 111 only uses differential mode power, its losses are small, and the second DC-DC converter circuit 112 has high efficiency when it is in shoot-through mode, the efficiency of the DC / DC converter 11 can reach a preset efficiency when its voltage difference is less than a first preset threshold. That is, the DC / DC converter 11 achieves high efficiency when its voltage difference is within the range of less than the first preset threshold.

[0053] In another optional embodiment, when the voltage difference is less than a first preset threshold, the controller 113 controls the output voltage of the first DC-DC converter 111 to be the voltage difference. When the output voltage of the first DC-DC converter 111 is the voltage difference, the input voltage of the second DC-DC converter 112 is the sum of the voltage difference and the battery voltage of the battery cluster 21, i.e., the bus voltage. The controller 113 then controls the first switch S11 to turn on. At this time, the positive input terminal and positive output terminal of the second DC-DC converter 112 are directly connected, as are the negative input terminal and negative output terminal. Therefore, the output voltage of the second DC-DC converter 112 is the bus voltage, which also means the output voltage of the DC / DC converter 11 is the bus voltage.

[0054] Understandably, in cases where some DC-DC converter circuits do not support shoot-through mode, the same function in shoot-through mode can be achieved by adding a first switch connected in parallel with the DC-DC converter circuit, thereby improving the applicability of the DC / DC converter 11.

[0055] In another optional embodiment, when the voltage difference is greater than or equal to the second preset threshold, the controller 113 controls the duty cycle of the controllable switch in the first DC-DC converter 111 to be 0, thereby making the output voltage of the first DC-DC converter 111 0. When the output voltage of the first DC-DC converter 111 is 0, the input voltage of the second DC-DC converter 112 is the battery voltage of the battery cluster 21. The controller 113 then controls the second DC-DC converter 112 to convert its input voltage into a bus voltage and output it. At this time, the output voltage of the DC / DC converter 11 is the bus voltage. The second preset threshold may be equal to or different from the first preset threshold.

[0056] Understandably, when the voltage difference is large, that is, when the DC bus voltage is small, the power that the second DC converter circuit 112 in the DC / DC converter 11 needs to process is also small, and the output voltage of the first DC converter circuit 111 is 0, that is, the first DC converter circuit 111 stops working. Therefore, the loss of the DC / DC converter 11 is small, thereby achieving high efficiency of the DC / DC converter 11 when its voltage difference is greater than or equal to the second preset threshold.

[0057] In another optional embodiment, when the voltage difference is greater than or equal to the second preset threshold, the controller 113 controls the second switch S12 to turn on, so that the output voltage of the first DC-DC converter 111 is 0. When the output voltage of the first DC-DC converter 111 is 0, the input voltage of the second DC-DC converter 112 is the battery voltage of the battery cluster 21. Then, the controller 113 controls the second DC-DC converter 112 to convert its input voltage into a bus voltage and output it. At this time, the output voltage of the DC / DC converter 11 is the bus voltage. The second preset threshold may be equal to or different from the first preset threshold.

[0058] Understandably, in addition to controlling the duty cycle of the controllable switch in the first DC-DC converter 111, the DC / DC converter 11 can also achieve a zero output voltage by controlling the second switch S12 to short-circuit the first DC-DC converter 111. This provides a variety of control methods and high flexibility.

[0059] In another optional embodiment, when the voltage difference is greater than or equal to the second preset threshold, the controller 113 controls the duty cycle of the controllable switch in the first DC-DC converter 111 to be 0 and controls the second switch S12 to be turned on, so that the output voltage of the first DC-DC converter 111 is 0. When the output voltage of the first DC-DC converter 111 is 0, the input voltage of the second DC-DC converter 112 is the battery voltage of the battery cluster 21. Then, the controller 113 controls the second DC-DC converter 112 to convert its input voltage DC-DC to the bus voltage and output it. At this time, the output voltage of the DC / DC converter 11 is the bus voltage. The second preset threshold may be equal to or different from the first preset threshold.

[0060] Understandably, by controlling the duty cycle of the controllable switch in the first DC-DC converter 111 to be 0 and controlling the second switch S12 to be turned on, the DC / DC converter 11 achieves an output voltage of 0 for the first DC-DC converter 111. This prevents a power short circuit caused by the second switch S12 being turned on when the first DC-DC converter 111 is operating at normal output voltage, thereby effectively improving the safety and stability of the DC / DC converter 11.

[0061] In another optional embodiment, when the voltage difference is greater than or equal to a second preset threshold, the controller 113 determines the second output voltage corresponding to the voltage difference based on the voltage difference and the mapping relationship between the voltage difference and the output voltage, and controls the output voltage of the first DC-DC converter 111 to be the second output voltage. The mapping relationship between the voltage difference and the output voltage includes multiple voltage difference intervals and the output voltage of the first DC-DC converter when the efficiency of the DC / DC converter corresponding to each of the multiple voltage difference intervals reaches a preset efficiency. It should be noted that if there are multiple output voltages of the first DC-DC converter when the efficiency of the DC / DC converter reaches the preset efficiency, the output voltage corresponding to the highest efficiency of the DC / DC converter among the multiple output voltages where the efficiency of the DC / DC converter reaches the preset efficiency can be determined as the output voltage of the first DC-DC converter corresponding to the voltage difference interval.

[0062] Specifically, when the voltage difference is greater than or equal to the second preset threshold, the controller 113 determines the voltage difference interval, i.e., the second voltage difference interval, based on the voltage difference and the mapping relationship between the voltage difference and the output voltage. Then, based on the second voltage difference interval and the mapping relationship between the voltage difference and the output voltage, it determines the second output voltage corresponding to the second voltage difference interval and controls the output voltage of the first DC-DC converter 111 to be the second output voltage. When the output voltage of the first DC-DC converter 111 is the second output voltage, the input voltage of the second DC-DC converter 112 is the second output voltage and the battery voltage of the battery cluster 21. The controller 113 then controls the second DC-DC converter 112 to convert its input voltage DC-DC to the bus voltage and output it. At this time, the output voltage of the DC / DC converter 11 is the bus voltage. The second preset threshold can be equal to or 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 equal to the first output voltage.

[0063] Understandably, 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 a preset efficiency by means of the mapping relationship between the voltage difference and the output voltage. Then, with the cooperation of the second DC-DC converter circuit 112, the output voltage of the DC / DC converter 11 is equal to the bus voltage while the efficiency reaches the preset efficiency, so that the efficiency of the DC / DC converter 11 can be optimized when its voltage difference is greater than or equal to the second preset threshold.

[0064] In another optional embodiment, when the voltage difference is greater than a first preset threshold and less than a second preset threshold, the controller 113 determines the third output voltage corresponding to the voltage difference based on the voltage difference and the mapping relationship between the voltage difference and the output voltage, and controls the output voltage of the first DC-DC converter 111 to be the third output voltage. The mapping relationship between the voltage difference and the output voltage includes multiple voltage difference intervals and the output voltage of the first DC-DC converter when the efficiency of the DC / DC converter corresponding to each of the multiple voltage difference intervals reaches a preset efficiency. It should be noted that if there are multiple output voltages of the first DC-DC converter when the efficiency of the DC / DC converter reaches the preset efficiency, the output voltage corresponding to the highest efficiency of the DC / DC converter among the multiple output voltages where the efficiency of the DC / DC converter reaches the preset efficiency can be determined as the output voltage of the first DC-DC converter corresponding to the voltage difference interval.

[0065] Specifically, when the voltage difference is greater than or equal to the second preset threshold, the controller 113 determines the voltage difference interval, i.e., the third voltage difference interval, based on the voltage difference and the mapping relationship between the voltage difference and the output voltage. Then, based on the third voltage difference interval and the mapping relationship between the voltage difference and the output voltage, it determines the third output voltage corresponding to the third voltage difference interval and controls the output voltage of the first DC-DC converter 111 to be the third output voltage. When the output voltage of the first DC-DC converter 111 is the third output voltage, the input voltage of the second DC-DC converter 112 is the third output voltage and the battery voltage of the battery cluster 21. The controller 113 then controls the second DC-DC converter 112 to convert its input voltage DC-DC to the bus voltage and output it. At this time, the output voltage of the DC / DC converter 11 is the bus voltage. Where 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.

[0066] Understandably, the DC / DC converter 11 can control the output voltage of the first DC-DC converter circuit 111 to be the third output voltage when the efficiency of the DC / DC converter 11 reaches a preset efficiency by mapping the voltage difference to the output voltage. Then, with the cooperation of the second DC-DC converter circuit 112, the output voltage of the DC / DC converter 11 is the bus voltage while the efficiency reaches the preset efficiency, thereby achieving the optimal efficiency of the DC / DC converter 11 when its voltage difference is within the range of being greater than the first preset threshold and less than the second preset threshold.

[0067] In summary, the DC / DC converter 11 can divide the entire range of voltage difference values ​​into multiple intervals (such as two or three intervals). By ensuring that the efficiency of the DC / DC converter 11 reaches a preset efficiency when the voltage difference is located in each of the above intervals, the DC / DC converter 11 achieves high efficiency across the entire range of voltage difference values.

[0068] In addition to achieving high efficiency of each DC / DC converter across the full range of voltage differences, the energy storage system 1 can also prevent the battery cluster from directly shutting down due to faulty battery cells (such as battery cells whose voltage is not within the battery's operating voltage range) by managing each battery cluster, thus avoiding the bottleneck effect between battery cells within the battery cluster.

[0069] See Figure 6 , Figure 6 This is a schematic diagram of the battery cluster provided in this application. Figure 6As shown, battery cluster 21 includes m battery modules, namely battery module 211, ..., battery module 21m, where m is a positive integer greater than 1. Battery module 211 includes battery cell Bat1, first battery switch Q11, and second battery switch Q12; ...; battery module 21m includes battery cell Batm, first battery switch Qm1, and second battery switch Qm2. The first and second battery switches can be power electronic devices such as metal oxide semiconductor field-effect transistors (MOSFETs), insulated gate bipolar transistors (IGBTs), or gallium nitride (GaN) transistors. In this embodiment, a MOSFET is used as an example to illustrate the first and second battery switches. Battery cell Bat1 and first battery switch Q11 are connected in series across the second battery switch Q12. Specifically, the positive terminal of battery cell Bat1 is connected to the drain of the first battery switch Q11. The source of the first battery switch Q11 is connected to the drain of the second battery switch Q12 to form the positive terminal of battery cluster 21. The source of the second battery switch Q12 is connected to the negative terminal of battery cell Bat1; ...; battery cell Batm and the first battery switch Qm1 are connected in series across the two ends of the second battery switch Qm2. Specifically, the positive terminal of 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. The source of the second battery switch Q12 is connected to the negative terminal of battery cell Batm to form the negative terminal of battery cluster 21.

[0070] The energy storage system 1 also includes a battery management unit. This battery management unit can be independent of the n DC / DC converters in the energy storage system 1, or it can be integrated into the controller of each DC / DC converter. It should be noted that when the battery management unit is integrated into the controller of each DC / DC converter, the controller of each DC / DC converter controls the corresponding battery cluster of that DC / DC converter.

[0071] After the energy storage system 1 starts operating, the battery management unit controls the first battery switch of each of the m battery modules to be turned on. At this time, the battery cluster 21 begins to output electrical energy to the DC / DC converter 11. Then, the battery management unit begins to acquire the battery voltage of each battery cell in the m battery modules and determines the battery cell voltage of each battery module as the battery module voltage, thus obtaining the voltages of the m battery modules. When there is a first battery module among the m battery modules whose voltage is greater than a fourth preset threshold or less than a fifth preset threshold (i.e., the battery module voltage of the first battery module is outside the battery operating 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 cell in the first battery module is short-circuited by the second battery switch in the first battery module, so that when the battery cell in the first battery module fails, it is directly disconnected from the multiple series-connected battery modules, thus not affecting the normal operation of other battery modules in the battery cluster 21 except for the first battery module. This avoids the bottleneck effect between battery cells within the battery cluster and improves the utilization rate of the battery cells in the battery cluster. In addition, by controlling the first battery switch and the second battery switch in each battery module, the minimum battery cell can be switched in and out, thereby enabling flexible control of the battery voltage of the battery cluster 21.

[0072] For details on the specific control methods of the battery management unit for the other (n-1) battery clusters, please refer to the control methods of the battery management unit for battery cluster 21, which will not be repeated here.

[0073] In this embodiment, each DC / DC converter in the energy storage system 1 can dynamically adjust the output voltage of its first DC-DC converter circuit based on its voltage difference, and then dynamically adjust the input voltage of its second DC-DC converter circuit. This ensures that each DC / DC converter achieves a preset efficiency when its output voltage reaches the bus voltage, thereby achieving high efficiency across the entire voltage difference range and improving the efficiency of the energy storage system 1. Furthermore, when there are multiple battery clusters in the energy storage system 1, since the output voltage of each DC / DC converter is the bus voltage, circulating currents between battery clusters can be effectively suppressed, thus improving the safety and stability of the energy storage system 1. Moreover, the energy storage system 1 can avoid the bottleneck effect between battery cells within a battery cluster by controlling the entry and exit of the smallest battery cell in each battery cluster, while simultaneously improving the utilization rate of the battery cells in the battery cluster. Finally, since both DC-DC converter circuits in each DC / DC converter in the energy storage system 1 have voltage regulation functions, the energy storage system 1 can also be used in high-voltage and low-voltage grid connection scenarios, preventing battery over-matching caused by high-voltage and low-voltage connections, thus demonstrating strong applicability.

[0074] See Figure 7 , Figure 7This is a flowchart illustrating the output voltage control method for the DC / DC converter provided in this application. The output voltage control method for the DC / DC converter provided in this application is applicable to… Figure 3 and Figure 4 Any DC / DC converter in the energy storage system 1 shown. The output voltage control method of the DC / DC converter may include the following steps:

[0075] S101, obtain the voltage difference between the battery voltage of the battery cluster and the bus voltage of the DC bus.

[0076] In one alternative implementation, after the DC / DC converter starts operating, it begins to acquire the battery voltage of its corresponding battery cluster and the bus voltage of the DC bus, and calculates the difference between the battery voltage and the bus voltage of the DC bus to obtain the voltage difference value.

[0077] S102 controls the output voltage of the first DC-DC converter circuit based on the voltage difference.

[0078] In one optional embodiment, the DC / DC converter determines the first output voltage corresponding to the voltage difference based on the voltage difference and the mapping relationship between the voltage difference and the output voltage, and controls the output voltage of the first DC-DC converter circuit to be the first output voltage. When the output voltage of the first DC-DC converter circuit is the first output voltage, the input voltage of the second DC-DC converter circuit is the first output voltage and the battery voltage of the battery cluster corresponding to the DC / DC converter, then the DC / DC converter controls the output bus voltage of the second DC-DC converter circuit.

[0079] In another optional embodiment, when the voltage difference is less than a first preset threshold, the DC / DC converter controls the output voltage of the first DC-DC converter circuit to be the voltage difference. When the output voltage of the first DC-DC converter circuit is the first output voltage, and the input voltage of the second DC-DC converter circuit is the bus voltage, the DC / DC converter controls the first and second input terminals of the second DC-DC converter circuit to be directly connected to the output terminal, or controls the first switch located between the first input terminal and the first output terminal of the second DC-DC converter circuit to be turned on.

[0080] In another optional embodiment, when the voltage difference is greater than or equal to a second preset threshold, the DC / DC converter controls the duty cycle of the controllable switch in the first DC-DC converter circuit to be 0 and / or controls the second switch located between the first output terminal and the second output terminal of the first DC-DC converter circuit to be turned on, so that the output voltage of the first DC-DC converter circuit is 0. When the output voltage of the first DC-DC converter circuit is 0, the input voltage of the second DC-DC converter circuit is the battery voltage of the battery cluster corresponding to the DC / DC converter, and then the DC / DC converter controls the output bus voltage of the second DC-DC converter circuit. The second preset threshold and the first preset threshold may be the same or different.

[0081] In another optional embodiment, when the voltage difference is greater than or equal to a second preset threshold, the DC / DC converter determines the second output voltage corresponding to the voltage difference based on the voltage difference and the mapping relationship between the voltage difference and the output voltage, and controls the output voltage of the first DC-DC converter circuit to be the second output voltage. When the output voltage of the first DC-DC converter circuit is the second output voltage, the input voltage of the second DC-DC converter circuit is the second output voltage and the battery voltage of the corresponding battery cluster of the DC / DC converter, then the DC / DC converter controls the output bus voltage of the second DC-DC converter circuit. The second preset threshold and the first preset threshold may be the same or different.

[0082] In another optional embodiment, when the voltage difference is greater than a first preset threshold and less than a second preset threshold, the DC / DC converter determines a third output voltage corresponding to the voltage difference based on the voltage difference and the mapping relationship between the voltage difference and the output voltage, and controls the output voltage of the first DC-DC converter circuit to be the third output voltage. When the output voltage of the first DC-DC converter circuit is the third output voltage, the input voltage of the second DC-DC converter circuit is the third output voltage and the battery voltage of the corresponding battery cluster of the DC / DC converter, then the DC / DC converter controls the output bus voltage of the second DC-DC converter circuit.

[0083] In specific implementation, further details of the operations performed by the DC / DC converter in the output voltage control method of the DC / DC converter provided in this application can be found in [reference needed]. Figure 3 and Figure 4 The implementation method of the DC / DC converter 11 shown will not be described in detail here.

[0084] In this embodiment, the DC / DC converter can dynamically adjust the output voltage of the first DC-DC converter circuit based on the voltage difference, and then dynamically adjust the input voltage of the second DC-DC converter circuit, so that the DC / DC converter achieves a preset efficiency when the output voltage reaches the bus voltage, thereby realizing high efficiency of the DC / DC converter across the entire range of voltage differences.

[0085] The above are merely specific embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A DC / DC converter, characterized in that, The first and second input terminals of the DC / DC converter are connected to a battery pack, and the output terminal of the DC / DC converter is connected to a DC bus. The DC / DC converter includes a first DC-DC conversion circuit, a second DC-DC conversion circuit, and a controller, wherein: The input terminal of the first DC-DC converter is connected to a DC power supply. The first output terminal and the second output terminal of the first DC-DC converter are respectively connected to the first input terminal of the DC / DC converter and the first input terminal of the second DC-DC converter. The first DC-DC converter is used to convert the voltage input from the DC power supply into a DC power supply and output it to the second DC-DC converter. The second input terminal of the second DC-DC converter is connected to the second input terminal of the DC / DC converter, and the output terminal of the second DC-DC converter is connected to the output terminal of the DC / DC converter. The second DC-DC converter is used to convert the input voltage into DC and output it. The controller is configured to, when the voltage difference between the battery voltage of the battery cluster and the bus voltage of the DC bus is greater than a first preset threshold and less than a second preset threshold, determine a third output voltage corresponding to the voltage difference based on the voltage difference and the mapping relationship between the voltage difference and the output voltage, and control the output voltage of the first DC-DC converter circuit to be the third output voltage, wherein the third output voltage is not equal to 0 and the voltage difference; and when the output voltage of the first DC-DC converter circuit is the third output voltage, control the output voltage of the second DC-DC converter circuit to be the bus voltage.

2. The DC / DC converter according to claim 1, characterized in that, The controller is further configured to control the output voltage of the first DC-DC converter to be the voltage difference when the voltage difference is less than the first preset threshold.

3. The DC / DC converter according to claim 2, characterized in that, The controller is also configured to directly connect the first input terminal and the second input terminal of the second DC-DC converter to the output terminal when the output voltage of the first DC-DC converter is the voltage difference.

4. The DC / DC converter according to claim 2, characterized in that, The DC / DC converter further includes a first switch, and the output terminal of the second DC-DC converter includes a first output terminal. The first switch is connected between the first input terminal and the first output terminal of the second DC-DC converter. The controller is also configured to control the first switch to turn on when the output voltage of the first DC-DC converter is the voltage difference.

5. The DC / DC converter according to claim 1, characterized in that, The controller is also configured to control the output voltage of the first DC-DC converter to be 0 when the voltage difference is greater than or equal to the second preset threshold.

6. The DC / DC converter according to any one of claims 1-5, characterized in that, The DC / DC converter further includes a second switch, which is connected between the first output terminal and the second output terminal of the first DC-DC converter circuit. The controller is also configured to control the second switch to turn on when the voltage difference is greater than or equal to the second preset threshold.

7. The DC / DC converter according to any one of claims 1-6, characterized in that, The controller is also configured to control the output voltage of the second DC-DC converter to be the bus voltage when the output voltage of the first DC-DC converter is 0.

8. An energy storage system, characterized in that, The energy storage system includes one or more DC / DC converters as described in any one of claims 1-7 and one or more battery clusters, wherein one of the DC / DC converters is connected to one of the battery clusters.

9. The energy storage system according to claim 8, characterized in that, The battery cluster includes at least two battery modules. Each battery module includes a battery cell, a first battery switch, and a second battery switch. The battery cell and the first battery switch are connected in series across the two ends of the second battery switch. The energy storage system further includes a battery management unit, which is used to obtain the battery module voltage of each of the at least two battery modules; when the battery module voltage of the first battery module in the at least two battery modules is greater than a fourth preset threshold or less than a fifth preset threshold, the battery management unit controls the first battery switch in the first battery module to turn off and the second battery switch to turn on.

10. The energy storage system according to claim 8 or 9, characterized in that, The energy storage system also includes an inverter, the input of which is connected to a DC bus, and the output of which is connected to an AC load.

11. A method for controlling the output voltage of a DC / DC converter, characterized in that, The first and second input terminals of the DC / DC converter are connected to a battery pack, and the output terminal of the DC / DC converter is connected to a DC bus. The DC / DC converter includes a first DC-DC conversion circuit and a second DC-DC conversion circuit, wherein: the input terminal of the first DC-DC conversion circuit is connected to a DC power supply, and the first and second output terminals of the first DC-DC conversion circuit are respectively connected to the first input terminal of the DC / DC converter and the first input terminal of the second DC-DC conversion circuit. The first DC-DC conversion circuit is used to convert the voltage input from the DC power supply into a DC-DC converter and output it to the second DC-DC conversion circuit; the second input terminal of the second DC-DC conversion circuit is connected to the second input terminal of the DC / DC converter, and the output terminal of the second DC-DC conversion circuit is connected to the output terminal of the DC / DC converter. The second DC-DC conversion circuit is used to convert the input voltage into a DC-DC converter and output it. The method includes: When the voltage difference between the battery voltage of the battery cluster and the bus voltage of the DC bus is greater than a first preset threshold and less than a second preset threshold, a third output voltage corresponding to the voltage difference is determined according to the voltage difference and the mapping relationship between the voltage difference and the output voltage, and the output voltage of the first DC-DC converter is controlled to be the third output voltage, wherein the third output voltage is not equal to 0 and the voltage difference; When the output voltage of the first DC-DC converter is the third output voltage, the output voltage of the second DC-DC converter is controlled to be the bus voltage.

12. The method according to claim 11, characterized in that, The method further includes: When the voltage difference is less than the first preset threshold, the output voltage of the first DC-DC converter is controlled to be the voltage difference.

13. The method according to claim 12, characterized in that, The method further includes: When the output voltage of the first DC-DC converter is the voltage difference, the first input terminal and the second input terminal of the second DC-DC converter are directly connected to the output terminal.

14. The method according to claim 12, characterized in that, The DC / DC converter further includes a first switch, and the output terminal of the second DC-DC converter includes a first output terminal. The first switch is connected between the first input terminal and the first output terminal of the second DC-DC converter. The method further includes: When the output voltage of the first DC-DC converter circuit is the voltage difference, the first switch is controlled to turn on.

15. The method according to claim 11, characterized in that, The method further includes: When the voltage difference is greater than or equal to the second preset threshold, the output voltage of the first DC-DC converter is controlled to be 0.

16. The method according to any one of claims 11-15, characterized in that, The DC / DC converter further includes a second switch, which is connected between the first output terminal and the second output terminal of the first DC-DC converter circuit. The method further includes: When the voltage difference is greater than or equal to a second preset threshold, the second switch is controlled to turn on.

17. The method according to any one of claims 11-16, characterized in that, The method further includes: When the output voltage of the first DC-DC converter is 0, the output voltage of the second DC-DC converter is controlled to be the bus voltage.

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