Direct current / direct current converter, energy storage system, and photovoltaic energy storage system

Abstract

The present application relates to the technical field of power electronics, and provides a DC / DC converter, an energy storage system, and a photovoltaic energy storage system. When voltages at two ends of a first power conversion circuit in the DC / DC converter provided by the present application are relatively close, the first power conversion circuit can operate in a pass-through mode. Therefore, the switching loss of the first power conversion circuit can be effectively reduced without affecting the power conversion performance of the first power conversion circuit. In addition, when the first power conversion circuit operates in the pass-through mode, on the basis of a reference power at a first end (i.e., a bus side) of the first power conversion circuit, a first controller can further perform closed-loop control on the power at a first end of a second power conversion circuit. Therefore, power control on the first end (i.e., the bus side) of the first power conversion circuit is implemented, thereby avoiding device damage caused by uncontrollable power.

Description

DC / DC converters, energy storage systems, and photovoltaic-energy storage systems

[0001] This application claims priority to Chinese Patent Application No. 202411711941.6, filed on November 26, 2024, entitled "DC / DC Converter, Energy Storage System and Photovoltaic-Storage System", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of power electronics technology, and in particular to a DC / DC converter, an energy storage system, and a photovoltaic-energy storage system. Background Technology

[0003] Energy storage systems typically consist of energy storage batteries and a direct current / direct current (DC / DC) converter. One end of the DC / DC converter is connected to the energy storage battery, and the other end is connected to the DC bus. The DC / DC converter can convert the DC power output from the energy storage battery into voltage and then output it to the DC bus to discharge the energy storage battery. The DC / DC converter can also convert the DC power on the DC bus into voltage and then output it to the energy storage battery to charge it.

[0004] DC / DC converters typically include buck-boost circuits. When the battery is discharging, the buck-boost circuit operates in boost mode; when the battery is charging, it operates in buck mode. When the voltages across the buck-boost circuit are relatively close, it can operate in shoot-through mode.

[0005] In shoot-through mode, the two ends of the buck-boost circuit are directly connected, and the on / off state of the switching transistors in the buck-boost circuit no longer switches, which can effectively reduce switching losses. However, shoot-through mode can cause the power of the buck-boost circuit connected to the DC bus (i.e., the bus side) to become uncontrollable, which may result in excessive power on the bus side and damage to the devices. Summary of the Invention

[0006] This application provides a DC / DC converter, an energy storage system, and a photovoltaic energy storage system, which can solve the technical problem of uncontrollable power on the bus side when the buck-boost circuit in the DC / DC converter operates in shoot-through mode.

[0007] In a first aspect, a DC / DC converter is provided, comprising: a first power conversion circuit, a second power conversion circuit, and a first controller. A first terminal of the first power conversion circuit is connected to a DC bus, and a second terminal of the first power conversion circuit is connected to the first terminal of the second power conversion circuit, the second terminal of the second power conversion circuit being connected to a DC power supply. When the voltage difference between the first terminal and the second terminal of the first power conversion circuit is less than a threshold value, the first power conversion circuit operates in shoot-through mode. The first controller is used to perform closed-loop control of the power at the first terminal of the second power conversion circuit based on a reference power at the first terminal of the first power conversion circuit when the first power conversion circuit operates in shoot-through mode.

[0008] Understandably, in shoot-through mode, the first and second terminals of the first power conversion circuit are directly connected, and the on / off state of the switching transistors in the first power conversion circuit no longer switches. When the first power conversion circuit operates in shoot-through mode, the first controller performs closed-loop control on the power of the first terminal of the second power conversion circuit based on the reference power of the first terminal of the first power conversion circuit. This ensures that the actual power of the first terminal (i.e., the bus side) of the first power conversion circuit reaches or approaches the reference power. Thus, power control of the first terminal (i.e., the bus side) of the first power conversion circuit is achieved, preventing device damage caused by uncontrollable power on the bus side of the first power conversion circuit in shoot-through mode.

[0009] Optionally, the first controller is used to adjust the duty cycle of the pulse width modulation (PWM) signal output to the switching transistor in the second power conversion circuit based on the difference between the reference power at the first terminal of the first power conversion circuit and the feedback power at the first terminal of the first power conversion circuit when the first power conversion circuit is operating in the pass-through mode, thereby realizing closed-loop control of the power at the first terminal of the second power conversion circuit.

[0010] In this application, the first controller can directly adjust the duty cycle of the PWM signal output to the switching transistor in the second power conversion circuit based on the difference between the reference power and the feedback power (i.e., the actual power) at the first terminal of the first power conversion circuit. This enables closed-loop control of the power at the first terminal of the second power conversion circuit, thereby ensuring that the feedback power (i.e., the actual power) at the first terminal of the first power conversion circuit reaches or approaches the reference power.

[0011] Optionally, the first controller is configured to, when the first power conversion circuit operates in shoot-through mode, adjust the duty cycle of the PWM signal output to the switching transistor in the second power conversion circuit based on the difference between the reference power at the first terminal of the second power conversion circuit and the feedback power at the first terminal of the second power conversion circuit, thereby achieving closed-loop control of the power at the first terminal of the second power conversion circuit. The reference power at the first terminal of the second power conversion circuit is determined based on the difference between the reference power at the first terminal of the first power conversion circuit and the power loss value of the first power conversion circuit.

[0012] Understandably, the first power conversion circuit also incurs some power loss during power transmission in shoot-through mode. The first controller can detect the power loss value of the first power conversion circuit in shoot-through mode and determine the reference power of the first terminal of the second power conversion circuit based on the difference between the reference power of the first terminal of the first power conversion circuit and the power loss value. Correspondingly, after the first controller performs closed-loop control on the feedback power (i.e., actual power) of the first terminal of the second power conversion circuit based on the reference power of the first terminal, the feedback power (i.e., actual power) of the first terminal of the second power conversion circuit can reach or approach the reference power of the first terminal of the second power conversion circuit. Therefore, it can be ensured that the feedback power (i.e., actual power) of the first terminal of the first power conversion circuit reaches or approaches the reference power of the first terminal of the first power conversion circuit.

[0013] Optionally, the DC / DC converter further includes a second controller, which is used to perform closed-loop control on the voltage of the first terminal of the first power conversion circuit based on the reference voltage of the first terminal of the first power conversion circuit when the difference between the voltage of the first terminal of the first power conversion circuit and the voltage of the second terminal of the first power conversion circuit is greater than or equal to a threshold.

[0014] The closed-loop control process can be as follows: the second controller adjusts the duty cycle of the PWM signal output to the switching transistor in the first power conversion circuit based on the difference between the reference voltage at the first terminal of the first power conversion circuit and the feedback voltage (i.e., the actual voltage) at the first terminal of the first power conversion circuit, so that the feedback voltage (i.e., the actual voltage) at the first terminal of the first power conversion circuit reaches or approaches the reference voltage at the first terminal of the first power conversion circuit.

[0015] Optionally, the second controller is further configured to perform closed-loop control on the power of the first terminal of the first power conversion circuit based on the reference power of the first terminal of the first power conversion circuit when the difference between the voltage at the first terminal of the first power conversion circuit and the voltage at the second terminal of the first power conversion circuit is greater than or equal to a threshold.

[0016] The closed-loop control process can be as follows: the second controller adjusts the duty cycle of the PWM signal output to the switching transistor in the first power conversion circuit based on the difference between the reference power at the first terminal of the first power conversion circuit and the feedback power (i.e., the actual power) at the first terminal of the first power conversion circuit, so that the feedback power (i.e., the actual power) at the first terminal of the first power conversion circuit reaches or approaches the reference power at the first terminal of the first power conversion circuit.

[0017] Optionally, the first power conversion circuit is a buck-boost circuit. This buck-boost circuit can also operate in boost mode or buck mode, offering high operational flexibility to meet the needs of different application scenarios. For example, in an energy storage system, the aforementioned DC power supply can be an energy storage battery. When charging the energy storage battery, the buck-boost circuit can operate in buck mode; when discharging the energy storage battery, the buck-boost circuit can operate in boost mode.

[0018] Optionally, in the scenario where the first power conversion circuit is a buck-boost circuit, the first power conversion circuit includes a first switching transistor, a second switching transistor, and an inductor. The first terminal of the first switching transistor serves as the positive terminal of the first power conversion circuit and is connected to the positive terminal of the DC bus. The second terminal of the first switching transistor is connected to both the first terminal of the second switching transistor and one end of the first inductor. The second terminal of the second switching transistor serves as the negative terminal of the first power conversion circuit and is connected to the negative terminal of the DC bus, and also serves as the negative terminal of the second power conversion circuit and is connected to the negative terminal of the first power conversion circuit. The other end of the first inductor serves as the positive terminal of the second power conversion circuit and is connected to the positive terminal of the first power conversion circuit. The first power conversion circuit operates in a shoot-through mode, including: the first switching transistor is turned on, and the second switching transistor is turned off.

[0019] The topology of the first power conversion circuit described above is relatively simple, which avoids increasing the structural complexity of the DC / DC converter and thus avoiding increased costs. Of course, this first power conversion circuit can also adopt other types of topologies, such as a four-switch buck-boost (FSBB) converter.

[0020] Optionally, the second power conversion circuit is an isolated power conversion circuit. This isolated power conversion circuit can refer to a power conversion circuit that includes a transformer. This isolated power conversion circuit can achieve a large proportion of voltage conversion to ensure that the operating voltage range required by the system (such as an energy storage system) can be met.

[0021] Optionally, the second power conversion circuit includes: a switching circuit, a first LLC power conversion circuit, and a second LLC power conversion circuit. One end of the switching circuit serves as the first terminal of the second power conversion circuit and is connected to the second terminal of the first power conversion circuit. The other end of the switching circuit is connected to one terminal of both the first LLC power conversion circuit and the second LLC power conversion circuit. The other terminals of the first and second LLC power conversion circuits serve as the second terminal of the second power conversion circuit and are used to connect to a DC power supply. The first controller is further configured to control the switching circuit to connect the first LLC power conversion circuit and the second LLC power conversion circuit in series to the second terminal of the first power conversion circuit, or to connect the first LLC power conversion circuit and the second LLC power conversion circuit in parallel to the second terminal of the first power conversion circuit.

[0022] Since the switching circuit can realize the series-parallel switching of the two LLC power conversion circuits, it can effectively increase the operating voltage range of the first terminal of the second power conversion circuit (i.e. the second terminal of the first power conversion circuit), thereby improving the application flexibility of the DC / DC converter.

[0023] Secondly, an energy storage system is provided, comprising: an energy storage battery, and a DC / DC converter as described in the first aspect above. A second terminal of a second power conversion circuit in the DC / DC converter is connected to the energy storage battery. The DC / DC converter is used to receive reference power from a first terminal of a first power conversion circuit supplied by an inverter.

[0024] Thirdly, a photovoltaic-energy storage system is provided, comprising: an inverter, and an energy storage system as described in the second aspect above. The inverter is connected to a DC / DC converter in the energy storage system via a DC bus and is used to supply reference power to the first terminal of a first power conversion circuit of the DC / DC converter.

[0025] Fourthly, another photovoltaic-energy storage system is provided, comprising an inverter, an energy storage battery, and a DC / DC converter. The DC / DC converter includes a first power conversion circuit. A first terminal of the first power conversion circuit is connected to the DC terminal of the inverter via a DC bus, and a second terminal of the first power conversion circuit is connected to the energy storage battery. When the voltage difference between the first terminal and the second terminal of the first power conversion circuit is less than a threshold value, the first power conversion circuit operates in shoot-through mode. The inverter is used to perform closed-loop power control on the DC terminal of the first power conversion circuit when it operates in shoot-through mode, based on a reference power at the first terminal of the first power conversion circuit and a reference power at the DC terminal of the inverter.

[0026] As mentioned earlier, when the voltages across the first power conversion circuit are relatively close, the first power conversion circuit operates in shoot-through mode. This effectively reduces the switching losses of the first power conversion circuit without affecting its power conversion performance. Furthermore, when the first power conversion circuit operates in shoot-through mode, the inverter performs closed-loop control of the DC power based on the reference power at the first terminal of the first power conversion circuit and the reference power at the inverter's DC terminal. This avoids device damage caused by uncontrollable DC bus power in shoot-through mode.

[0027] In summary, this application provides a DC / DC converter, an energy storage system, and a photovoltaic-energy storage system. The first power conversion circuit in the DC / DC converter provided by this application can operate in shoot-through mode when the voltages at its two ends are relatively close. Therefore, the switching losses of the first power conversion circuit can be effectively reduced without affecting its power conversion performance. Furthermore, when the first power conversion circuit operates in shoot-through mode, the second controller can also perform closed-loop control of the power at the first end (i.e., the bus side) of the second power conversion circuit based on a reference power at the first end (i.e., the bus side). This allows the actual power at the first end (i.e., the bus side) of the first power conversion circuit to reach or approach the reference power, thereby achieving power control at the first end (i.e., the bus side) of the first power conversion circuit and avoiding device damage caused by uncontrollable power.

[0028] Furthermore, it is understandable that by setting two cascaded power conversion circuits in a DC / DC converter, two-stage power conversion can be achieved, thereby effectively improving the power conversion range of the DC / DC converter and thus enhancing its application flexibility. Attached Figure Description

[0029] Figure 1 is a schematic diagram of an energy storage system provided in an embodiment of this application;

[0030] Figure 2 is a schematic diagram of a photovoltaic energy storage system provided in an embodiment of this application;

[0031] Figure 3 is a schematic diagram of a DC / DC converter provided in an embodiment of this application;

[0032] Figure 4 is a schematic diagram of another DC / DC converter provided in an embodiment of this application;

[0033] Figure 5 is a schematic diagram of the power conversion circuit in a DC / DC converter provided in an embodiment of this application;

[0034] Figure 6 is a schematic diagram of a first power conversion circuit provided in an embodiment of this application;

[0035] Figure 7 is a schematic diagram of another first power conversion circuit provided in an embodiment of this application;

[0036] Figure 8 is a schematic diagram of another DC / DC converter provided in an embodiment of this application;

[0037] Figure 9 is a schematic diagram of another optical energy storage system provided in an embodiment of this application. Detailed Implementation

[0038] The DC / DC converter, energy storage system, and photovoltaic-energy storage system provided in the embodiments of this application are described in detail below with reference to the accompanying drawings. First, the key terms involved in the embodiments of this application are introduced.

[0039] Pass-through mode: In the field of power electronics, this refers to the operating mode of a power conversion circuit in which the input and output are directly connected under a specific switching state of the switching transistor.

[0040] Energy optimizer: An electronic module in a photovoltaic system that manages the output of each solar panel (i.e., photovoltaic panel) to maximize energy production and has monitoring capabilities. An energy optimizer typically includes a DC / DC converter.

[0041] Switching losses: Energy consumption during the turning on and off of a switching transistor.

[0042] Soft switching refers to using control circuits or external auxiliary circuits to turn a switch on or off under zero voltage and zero current conditions, thereby reducing switching losses.

[0043] Proportional-integral (PI) control loop: Data collected in the system is compared to a reference value to obtain a difference. This difference is then subjected to proportional (P) control and integral (I) control to obtain a calculated value. This calculated value is input back into the system through a feedback loop to ensure that the system data reaches or remains at the reference value.

[0044] PWM is a technique that modulates the width of a pulse. It obtains the desired waveform (including shape and amplitude) by modulating the width of a series of pulses.

[0045] Open-loop control: Open-loop control refers to giving the system's controller a desired value (i.e., a reference value), and the controller only controls the system's output according to the desired value. However, there may be situations where the system's output deviates from the desired value.

[0046] Closed-loop control: also called a feedback control system, has a feedback path that compares the measured value of the system's output with the desired value, generates a deviation signal and feeds it back to the input of the controller for adjustment and control, so that the system's output is as close as possible to the desired value.

[0047] Figure 1 is a schematic diagram of an energy storage system provided in an embodiment of this application. As shown in Figure 1, the energy storage system may include an energy storage battery 00 and a DC / DC converter 10. For example, Figure 1 shows multiple energy storage batteries 00 and multiple DC / DC converters 10. One end of each DC / DC converter 10 can be connected to one or more energy storage batteries 00, and the other end of each DC / DC converter 10 is connected to a DC bus (BUS). The DC / DC converter 10 can convert the DC power output from the energy storage battery 00 into voltage and output it to the DC bus, thereby discharging the energy storage battery 00. The DC / DC converter 10 can also convert the DC power on the DC bus into voltage and output it to the energy storage battery 00, thereby charging the energy storage battery 00.

[0048] Figure 2 is a schematic diagram of a photovoltaic-energy storage system provided in an embodiment of this application. As shown in Figure 2, the photovoltaic-energy storage system may include an energy storage system such as that shown in Figure 1, and may also include a photovoltaic (PV) panel 20 and an inverter 30. The inverter 30 includes a DC / DC converter 301 and a direct current / alternating current (DC / AC) converter 302. One end of the DC / DC converter 301 is connected to the photovoltaic panel 20, and the other end is connected to the DC bus. The DC terminal of the DC / AC converter 302 is connected to the DC bus, and the AC terminal is connected to the power grid 40 and a load 50. The load 50 may be a household load. The DC / DC converter 301 converts the DC power output from the photovoltaic panel 20 to AC power and outputs it to the DC bus. The DC / AC converter 302 converts the DC power on the DC bus to AC power and outputs it to the power grid 40 and the load 50.

[0049] It is understandable that the overall energy dispatching in the photovoltaic-storage system shown in Figure 2 can be achieved by the inverter 30, i.e., the inverter 30 acts as the energy dispatch controller in the photovoltaic-storage system. For the energy storage system, its operating modes are mainly divided into charging mode and discharging mode. The switching between charging and discharging modes can be achieved by the inverter 30 issuing different reference voltages to the DC / DC converter 10 in the energy storage system. For example, when it is necessary to charge the energy storage battery 00 in the energy storage system, the inverter 30 can control the DC bus at a certain voltage V and issue a reference voltage V–ΔV to the DC / DC converter 10 of the energy storage system. Based on this reference voltage V–ΔV, the DC / DC converter 10 can control the voltage on its port side connected to the DC bus (i.e., the bus-side voltage) to V–ΔV. At this time, the bus-side voltage V–ΔV of the DC / DC converter 10 is lower than the DC bus voltage V, and energy flows into the energy storage battery 00, thereby charging the energy storage battery 00. When it is necessary to discharge the energy storage battery 00 in the energy storage system, the inverter 302 can control the DC bus at a certain voltage V and send a reference voltage V+ΔV to the DC / DC converter 10 of the energy storage system. Based on this reference voltage V+ΔV, the DC / DC converter 10 can control its bus-side voltage to V+ΔV. At this time, the bus-side voltage V+ΔV of the DC / DC converter 10 is higher than the DC bus voltage V, and energy flows out of the energy storage battery 00, thereby achieving the discharge of the energy storage battery 00.

[0050] It is also understandable that the DC / DC converter 10 in the energy storage system typically includes a buck-boost circuit, which can operate in either buck or boost mode. For example, in the photovoltaic-energy storage system shown in Figure 2, the buck-boost circuit operates in buck mode when the energy storage battery is charging, and in boost mode when the energy storage battery is discharging. In both buck and boost modes, the switching transistors in the buck-boost circuit need to continuously switch between on and off states under the control of the PWM signal, resulting in significant switching losses in the buck-boost circuit, which in turn affects the charging and discharging efficiency of the energy storage system.

[0051] It is also understandable that in some scenarios, the voltage of the energy storage battery 00 connected to the DC / DC converter 10 may be higher than the voltage of the DC bus. In this case, when the energy storage battery is charging, the buck-boost circuit operates in boost mode; when the energy storage battery is discharging, the buck-boost circuit operates in buck mode.

[0052] In some embodiments, switching losses in buck-boost circuits can be reduced by adjusting device selection and optimizing parameters. For example, selecting inductors or switching transistors with better parameters and lower on-resistance can reduce switching losses. However, this approach relies on technological advancements in related fields (such as power device materials), resulting in limited application flexibility. Furthermore, selecting devices with better parameters significantly increases device costs.

[0053] In other embodiments, switching losses in buck-boost circuits are reduced through optimized control strategies. For example, switching losses can be reduced by varying the switching frequency under different load conditions and by employing soft-switching techniques. However, this approach is limited by chip memory and processor computing power, resulting in poor application flexibility and potential difficulties in practical implementation.

[0054] This application provides a DC / DC converter that can be applied to application scenarios such as those shown in Figure 1 or Figure 2. The DC / DC converter has low switching losses, which can reduce the impact on the charging and discharging efficiency of the energy storage system. As shown in Figure 3, the DC / DC converter 10 includes: a first power conversion circuit 101, a second power conversion circuit 102, and a first controller 103.

[0055] In this circuit, the first terminal of the first power conversion circuit 101 is connected to the DC bus (BUS+, BUS-), and the second terminal of the first power conversion circuit 101 is connected to the first terminal of the second power conversion circuit 102. The second terminal of the second power conversion circuit 102 is connected to a DC power supply. For example, in a scenario where the DC / DC converter 10 is applied to an energy storage system, the DC power supply can be an energy storage battery. The first terminal of the first power conversion circuit 101 and the first terminal of the second power conversion circuit 102 are also referred to as the bus side or high-voltage side, and the second terminal of the first power conversion circuit 101 and the second terminal of the second power conversion circuit 102 are also referred to as the battery side or low-voltage side.

[0056] When the difference between the voltage at the first terminal of the first power conversion circuit 101 and the voltage at the second terminal of the first power conversion circuit 101 is less than a threshold, the first power conversion circuit 101 operates in direct mode.

[0057] The first power conversion circuit 101 operating in direct-through mode can mean that by controlling the on / off state of the switching transistor in the first power conversion circuit 101, the first terminal and the second terminal of the first power conversion circuit 101 are directly connected. Furthermore, in direct-through mode, the switching transistor in the first power conversion circuit 101 can remain in either an on or off state; that is, the on / off state of the switching transistor will not switch.

[0058] The first controller 103 is used to perform closed-loop control on the power of the first terminal of the second power conversion circuit 102 based on the reference power of the first terminal of the first power conversion circuit 101 when the first power conversion circuit 101 is operating in direct mode.

[0059] The reference power can be issued by the scheduling controller of the system where the DC / DC converter is located (e.g., the inverter in a photovoltaic energy storage system), and can be determined based on the charging and discharging capability of the DC power supply (e.g., an energy storage battery). The first controller 103's closed-loop control of the power at the first terminal of the second power conversion circuit 102 based on the reference power at the first terminal of the first power conversion circuit 101 can mean that the first controller 103 adjusts the duty cycle of the PWM signal output to the switching transistor in the second power conversion circuit 102 based on the reference power at the first terminal of the first power conversion circuit 101, thereby achieving closed-loop control of the power at the first terminal of the second power conversion circuit 102, and thus achieving closed-loop control of the power at the first terminal of the first power conversion circuit 101. Furthermore, since the reference power for the above closed-loop control is the reference power at the first terminal of the first power conversion circuit 101, the actual power at the first terminal of the first power conversion circuit 101 can reach or approach the reference power at the first terminal of the first power conversion circuit 101.

[0060] It is understandable that when the difference between the voltage at the first terminal and the voltage at the second terminal of the first power conversion circuit 101 is less than a threshold, i.e., when the voltages at both terminals of the first power conversion circuit 101 are close, the power conversion function (such as boost or buck function) of the first power conversion circuit 101 is not very effective. Alternatively, it can be understood that when the voltages at both terminals of the first power conversion circuit 101 are close, the power conversion function of the first power conversion circuit 101 has a relatively small impact on the voltages at both terminals. Furthermore, when the first power conversion circuit 101 performs power conversion, i.e., operates in non-shoo-through mode, the switching transistors in the first power conversion circuit 101 need to continuously switch between on and off states under the control of the PWM signal. This results in higher switching losses in the first power conversion circuit 101, thereby affecting the efficiency of the system (such as an energy storage system). The non-shoo-through mode can include one or more of the following modes: buck mode, boost mode, and buck-boost, etc.

[0061] Based on the above analysis, it can be seen that in this embodiment of the application, when the voltages across the first power conversion circuit 101 are close, the first power conversion circuit 101 operates in a direct-through mode, which can effectively reduce the switching losses of the first power conversion circuit 101 without affecting the power conversion performance of the DC / DC converter 10.

[0062] It is also understandable that after the first power conversion circuit 101 operates in shoot-through mode, since the on / off state of the switching transistors in the first power conversion circuit 101 no longer switches, the current at the first terminal (i.e., the bus side) of the first power conversion circuit 101 becomes uncontrollable, leading to uncontrollable power on the bus side. Accordingly, in this embodiment, after the first power conversion circuit 101 operates in shoot-through mode, the first controller 103 can also perform closed-loop control of the power at the first terminal of the second power conversion circuit 102 based on the reference power at the first terminal of the first power conversion circuit 101, thereby achieving effective control of the power at the first terminal (i.e., the bus side) of the first power conversion circuit 101. This effectively avoids device damage caused by uncontrollable power. For example, when the power at the first terminal of the first power conversion circuit 101 is too high, it can cause damage to devices in the system due to overcurrent.

[0063] It is also understood that the DC / DC converter provided in this application embodiment can achieve two-stage power conversion by setting two cascaded power conversion circuits. Therefore, on the one hand, it can effectively improve the power conversion range of the DC / DC converter, thereby enhancing its application flexibility. On the other hand, it can effectively reduce the power conversion performance requirements of a single power conversion circuit, thus significantly reducing the cost and structural complexity of the power conversion circuit.

[0064] For example, assuming the voltage of the DC bus connected to DC / DC converter 10 is 800 volts (V), and the voltage of the DC power supply (such as an energy storage battery) connected to DC / DC converter 10 is 28V, then the first power conversion circuit 101 can be used to achieve voltage conversion between 800V and 700V, and the second power conversion circuit 102 can be used to achieve voltage conversion between 700V and 28V. Compared to directly achieving the 800V to 28V voltage conversion with a single power conversion circuit, the two-stage voltage conversion method can effectively reduce the power conversion range (i.e., voltage conversion ratio) of a single power conversion circuit, thereby reducing the cost and structural complexity of the power conversion circuit.

[0065] In summary, this application provides a DC / DC converter in which the first power conversion circuit can operate in shoot-through mode when the voltages at its two ends are relatively close. This effectively reduces the switching losses of the first power conversion circuit without affecting its power conversion performance. Furthermore, when the first power conversion circuit operates in shoot-through mode, the first controller can also perform closed-loop control of the power at the first end of the second power conversion circuit based on a reference power at the first end (i.e., the bus side) of the first power conversion circuit. This ensures that the actual power at the first end (i.e., the bus side) of the first power conversion circuit reaches or approaches the reference power, thereby achieving power control at the first end (i.e., the bus side) of the first power conversion circuit and preventing device damage caused by uncontrollable power.

[0066] Furthermore, the DC / DC converter provided in this application embodiment can effectively reduce the switching losses of the first power conversion circuit without adjusting device selection or optimizing device parameters, offering high application flexibility and low cost. Moreover, the controller strategy in this DC / DC converter is relatively simple, with low requirements for chip memory and processor computing power, making it easy to implement in practical application scenarios.

[0067] Understandably, when the difference between the voltage at the first terminal and the voltage at the second terminal of the first power conversion circuit 101 is greater than or equal to a threshold, the first power conversion circuit 101 can operate in a non-short-through mode, such as buck mode or boost mode. As mentioned earlier, when energy flows from the DC bus into the DC power source (such as an energy storage battery), the first power conversion circuit 101 can operate in buck mode. When energy flows from the DC power source into the DC bus, the first power conversion circuit 101 can operate in boost mode.

[0068] Furthermore, when the first power conversion circuit 101 operates in non-pass-through mode, the first controller 103 can generate a PWM signal for the switching transistor in the second power conversion circuit 102 according to a fixed duty cycle (i.e., constant duty cycle). In other words, the first controller 103 can perform open-loop control of the second power conversion circuit 102 based on a constant duty cycle. Here, generating a PWM signal refers to providing a PWM signal to the switching transistor.

[0069] Optionally, as shown in FIG4, the DC / DC converter may further include a second controller 104. The second controller 104 is used to control the operating mode of the first power conversion circuit 101. For example, when the second controller 104 detects that the difference between the voltage at the first terminal and the voltage at the second terminal of the first power conversion circuit 101 is less than a threshold, it can control the first power conversion circuit 101 to operate in a shoot-through mode. When the difference between the voltage at the first terminal and the voltage at the second terminal of the first power conversion circuit 101 is greater than or equal to a threshold, the second controller 104 can control the first power conversion circuit 101 to operate in a non-shoot-through mode.

[0070] Optionally, both the first controller 103 and the second controller 104 can be microcontroller units (MCUs). Furthermore, the first controller 103 and the second controller 104 can be two independent devices, or they can be integrated, meaning the first controller 103 and the second controller 104 can be integrated into a single controller. In addition, the first controller 103 and the second controller 104 can implement closed-loop control of the power conversion circuit through software, or they can implement closed-loop control of the power conversion circuit through hardware; this embodiment does not limit the specific implementation.

[0071] Optionally, the first power conversion circuit 101 may be a non-isolated power conversion circuit. For example, the first power conversion circuit 101 may be a buck circuit, a boost circuit, or a buck-boost circuit.

[0072] Figure 5 is a schematic diagram of the power conversion circuit in a DC / DC converter provided in an embodiment of this application. Taking the first power conversion circuit 101 as a buck-boost circuit as an example, as shown in Figure 5, the first power conversion circuit 101 may include a first switch S1, a second switch S2, and an inductor L1.

[0073] In this circuit, the first terminal of the first switching transistor S1 serves as the positive terminal of the first power conversion circuit 101 and is connected to the positive terminal BUS+ of the DC bus. The second terminal of the first switching transistor S1 is connected to both the first terminal of the second switching transistor S2 and one end of the first inductor L1. The second terminal of the second switching transistor S2 serves as the negative terminal of the first power conversion circuit 101 and is connected to the negative terminal BUS- of the DC bus, and also serves as the negative terminal of the second terminal of the first power conversion circuit 101 and is connected to the negative terminal of the first terminal of the second power conversion circuit 102. The other end of the first inductor L1 serves as the positive terminal of the second terminal of the first power conversion circuit 101 and is connected to the positive terminal of the first terminal of the second power conversion circuit 102.

[0074] It is understandable that the first terminal of a switching transistor can be either the source or the drain, and the second terminal can be either the source or the drain. For example, the switching transistors in the first power conversion circuit 101 can all be N-type switching transistors, where the first terminal of the N-type switching transistor can be the drain and the second terminal can be the source.

[0075] For the first power conversion circuit 101 shown in Figure 5, the second controller 104 controlling the first power conversion circuit 101 to operate in direct-on mode means that the second controller 104 controls the first switch S1 to be turned on and controls the second switch S2 to be turned off. That is, the second controller 104 controls the duty cycle of the PWM signal output to the first switch S1 to be 1, so that the first switch S1 is always on, and controls the duty cycle of the PWM signal output to the second switch S2 to be 0, so that the second switch S2 is always off. Thus, the first terminal and the second terminal of the first power conversion circuit 101 are directly connected.

[0076] Referring again to Figure 5, the first power conversion circuit 101 may further include a first capacitor C1, a second capacitor C2, and a diode D1. The first capacitor C2 is connected between the positive terminal BUS+ and the negative terminal BUS- of the DC bus, i.e., between the positive and negative terminals of the first end of the first power conversion circuit 101. The second capacitor C2 is connected between the positive and negative terminals of the second end of the first power conversion circuit 101. The diode D1 is connected in series between the positive terminals of the first and second ends of the first power conversion circuit 101. The first capacitor C1 and the second capacitor C2 can be used for voltage regulation. The diode D1 is used to conduct when the voltage at the second end of the first power conversion circuit 101 is higher than the voltage at the first end, thereby directly connecting the first and second ends of the first power conversion circuit 101.

[0077] It is understandable that, for the first power conversion circuit 101 shown in Figure 5, when the second controller 104 controls the second switch S2 to be normally off and controls the first switch S1 to be turned on and off via a PWM signal, the first power conversion circuit 101 operates in buck mode. When the second controller 104 controls the first switch S1 to be normally on and controls the second switch S2 to be turned on and off via a PWM signal, the first power conversion circuit 101 operates in boost mode.

[0078] Figure 6 is a schematic diagram of a first power conversion circuit provided in an embodiment of this application. As shown in Figure 6, in the scenario where the first power conversion circuit 101 is a buck-boost circuit, the first power conversion circuit 101 can also be a four-switch buck-boost (FSBB) converter, also known as an H-bridge converter or a non-inverting buck-boost converter. This FSBB converter is composed of a buck circuit and a boost circuit cascaded together, and can achieve higher efficiency over a wide input voltage range.

[0079] Referring to Figure 6, the FSBB converter includes an inductor L1 and four switching transistors S1 to S4. Transistors S1 and S2 form the buck bridge arm, and switches S3 and S4 form the boost bridge arm. Inductor L1 is connected between the buck and boost bridge arms. Because all four switching transistors in the FSBB converter are controllable, it offers advantages over traditional buck-boost topologies, such as greater controllability and identical input and output voltage polarity.

[0080] Specifically, when the second controller 104 controls switch S4 to be normally off and switch S3 to be normally on, and controls switches S1 and S2 to be alternately on, the FSBB converter operates in buck mode. When the second controller 104 controls switch S2 to be normally off and switch S1 to be normally on, and controls switches S3 and S4 to be alternately on, the FSBB converter operates in boost mode. When the second controller 104 controls switches S1 and S4 to be simultaneously on or off as a pair of switches, and switches S2 and S3 to be simultaneously on or off as a complementary pair of switches, the FSBB converter operates in buck-boost mode. When the second controller 104 controls switches S1 and S3 to be normally on, and controls switches S2 and S4 to be normally off, the first and second terminals of the FSBB converter are directly connected, and the FSBB converter operates in shoot-through mode. That is, when the second controller 104 controls the duty cycle of the PWM signal output to the switching transistors S1 and S3 to be 1, and controls the duty cycle of the PWM signal output to the switching transistors S2 and S4 to be 0, the first and second terminals of the FSBB converter can be directly connected.

[0081] Figure 7 is a schematic diagram of another first power conversion circuit provided in an embodiment of this application. As shown in Figure 7, the first power conversion circuit 101 can also be a buck circuit, which includes a switching transistor S1, a diode D0, an inductor L1, and capacitors C1 and C2. The first terminal of the switching transistor S1 is connected to the positive terminal BUS+ of the DC bus, and the second terminal of the switching transistor S1 is connected to the negative terminal of the diode D0 and one end of the inductor L1. The positive terminal of the diode D0 is connected to the negative terminal BUS- of the DC bus. Capacitor C1 is connected between the positive terminal BUS+ and the negative terminal BUS- of the DC bus, and capacitor C2 is connected between the other end of the inductor L1 and the negative terminal BUS- of the DC bus.

[0082] For the first power conversion circuit 101 shown in Figure 7, when the second controller 104 controls the switching transistor S1 to turn on and off via a PWM signal, the first power conversion circuit 101 operates in buck mode. When the second controller 104 controls the switching transistor S1 to be normally on, the first power conversion circuit 101 operates in pass-through mode. That is, when the duty cycle of the PWM signal output to the switching transistor S1 by the second controller 104 is 1, the first terminal and the second terminal of the first power conversion circuit 101 shown in Figure 7 are directly connected.

[0083] Optionally, in this embodiment, the topology of the second power conversion circuit 102 in the DC / DC converter 10 can be the same as or different from the topology of the first power conversion circuit 101. For example, the second power conversion circuit 102 can also be a buck-boost circuit, that is, the DC / DC converter 10 can include two cascaded buck-boost circuits. Alternatively, the second power conversion circuit 102 can be an isolated power conversion circuit. An isolated power conversion circuit refers to a power conversion circuit that includes a transformer. By using an isolated power conversion circuit that includes a transformer, on the one hand, a larger voltage conversion ratio can be achieved, which is more flexible in application; on the other hand, high and low voltage isolation can be achieved, which is safer. For example, assuming that the transformer in the isolated power conversion circuit has a turns ratio K = 13, if the voltage range of the DC power supply connected to the second terminal of the isolated power conversion circuit is 16V to 28V, then the voltage range of the first terminal of the isolated power conversion circuit can reach 208V to 728V.

[0084] For example, referring to Figure 5, the second power conversion circuit 102 can be an LLC power conversion circuit. Here, L refers to inductance, and C refers to capacitance. Referring to Figure 5, this LLC power conversion circuit can include a transformer T0, switching transistors Q1 and Q2 on the primary side of transformer T0, capacitors C3, C4, and C5, an inductor L2, switching transistors Q3 to Q6 on the secondary side of the transformer, and capacitor C6.

[0085] In this circuit, switching transistors Q1 and Q2 are connected in series between the positive and negative terminals of the first terminal of the second power conversion circuit 102. Capacitors C3 and C4 are also connected in series between the positive and negative terminals of the first terminal of the second power conversion circuit 102. Capacitor C5 is connected between the positive and negative terminals of the first terminal of the second power conversion circuit 102. The series connection point between switching transistors Q1 and Q2 is connected to one end of inductor L2, and the other end of inductor L2 is connected to one end of the primary winding of transformer T0. The series connection point between capacitors C3 and C4 is connected to the other end of the primary winding of transformer T0.

[0086] Switches Q3 and Q4 are connected in series between the positive and negative terminals of the second power conversion circuit 102. Switches Q5 and Q6 are also connected in series between the positive and negative terminals of the second power conversion circuit 102. Capacitor C6 is connected between the positive and negative terminals of the second power conversion circuit 102. The series connection point between switches Q3 and Q4 is connected to one end of the secondary winding of transformer T0, and the series connection point between switches Q5 and Q6 is connected to the other end of the secondary winding of transformer T0.

[0087] It is understood that the second power conversion circuit 102 may also adopt other isolated power conversion topologies besides LLC, such as CLLC power conversion topology or dual active bridge (DAB) power conversion topology. The embodiments of this application do not limit the topology type of the second power conversion circuit 102.

[0088] Figure 8 is a schematic diagram of another DC / DC converter provided in an embodiment of this application. As shown in Figure 8, the second power conversion circuit 102 may include: a switching circuit 1021, a first LLC power conversion circuit 1022, and a second LLC power conversion circuit 1023.

[0089] In this circuit, one end of the switching circuit 1021 serves as the first end of the second power conversion circuit 102 and is connected to the second end of the first power conversion circuit 101. The other end of the switching circuit 1021 is connected to one end of the first LLC power conversion circuit 1022 and one end of the second LLC power conversion circuit 1023, respectively. The other ends of the first LLC power conversion circuit 1022 and the second LLC power conversion circuit 1023 serve as the second end of the second power conversion circuit 102 and are connected to a DC power supply.

[0090] The first controller 103 is also used to control the switching circuit 1021 to connect the first LLC power conversion circuit 1022 and the second LLC power conversion circuit 1023 in series to the second terminal of the first power conversion circuit 101, or to connect the first LLC power conversion circuit 1022 and the second LLC power conversion circuit 1023 in parallel to the second terminal of the first power conversion circuit 101.

[0091] As can be seen from Figure 8, the topology of the first LLC power conversion circuit 1022 and the second LLC power conversion circuit 1023 can be the same, and the other end of the first LLC power conversion circuit 1022 and the other end of the second LLC power conversion circuit 1023 can be connected in parallel to a DC power supply, such as an energy storage battery.

[0092] Optionally, continuing to refer to Figure 8, the switching circuit 1021 may include switches K1, K2, and K3. When switch K1 is closed and both switches K2 and K3 are open, the first LLC power conversion circuit 1022 and the second LLC power conversion circuit 1023 are connected in series to the second terminal of the first power conversion circuit 101. When switch K1 is open and both switches K2 and K3 are closed, the first LLC power conversion circuit 1022 and the second LLC power conversion circuit 1023 are connected in parallel to the second terminal of the first power conversion circuit 101.

[0093] The switches K1, K2, and K3 mentioned above can be independent switches. Alternatively, they can be integrated into a single relay, also known as a series-parallel relay. Because the switching circuit 1021 can achieve series-parallel switching between two LLC power conversion circuits, a wider operating voltage range can be achieved, thus ensuring that the required voltage range for different application scenarios is met.

[0094] Referring to Figure 8, assuming the DC bus voltage range is approximately 350V to 980V, and the energy storage battery voltage range is approximately 16V to 28V. If the transformer ratio of each LLC power conversion circuit in the second power conversion circuit 102 is K, then the voltage range at the second terminal of the first power conversion circuit 101 is 16V×K to 28V×2K. Assuming K = 13, the voltage range at the second terminal of the first power conversion circuit 101 is 208V to 728V. This voltage range overlaps with the DC bus voltage range of 350V to 980V, meaning the voltage range at the first terminal of the first power conversion circuit 101 overlaps with the voltage range at the second terminal. Therefore, in this embodiment, when the voltages at both ends of the first power conversion circuit 101 are close, the first power conversion circuit 101 can be controlled to operate in a shoot-through mode to effectively reduce the switching losses of the first power conversion circuit 101.

[0095] Figure 8 is a schematic diagram using the second power conversion circuit 102, which includes two LLC power conversion circuits, as an example. It can be understood that the second power conversion circuit 102 may also include two power conversion circuits with other topologies. Alternatively, the number n of power conversion circuits included in the second power conversion circuit 102 may be greater than 2, and correspondingly, the switching circuit 1021 can realize the series-parallel switching of n power conversion circuits.

[0096] Optionally, the switching transistors in the first power conversion circuit 101 and the second power conversion circuit 102 can both be metal-oxide-semiconductor field-effect transistors (MOSFETs), abbreviated as MOS transistors. Furthermore, the aforementioned switching transistors can both be N-type MOS transistors, i.e., NMOS.

[0097] The closed-loop control process of the second power conversion circuit 102 is described below. As a first optional implementation, when the first power conversion circuit 101 operates in direct mode, the first controller 103 can adjust the duty cycle of the PWM signal output to the switching transistor in the second power conversion circuit 102 based on the difference between the reference power at the first terminal of the first power conversion circuit 101 and the feedback power at the first terminal of the first power conversion circuit 101, so as to realize closed-loop control of the power at the first terminal of the second power conversion circuit 102.

[0098] In this first implementation, the first controller 103 can detect the feedback power at the first terminal of the first power conversion circuit 101, i.e., the actual power at the first terminal of the first power conversion circuit 101. This actual power is also referred to as the actual value of the bus-side power of the first power conversion circuit 101. Furthermore, the first controller 103 can obtain a first difference value by subtracting the reference power (also referred to as the bus-side given power) at the first terminal of the first power conversion circuit 101 from the actual power, and adjust the duty cycle of the PWM signal output to the switching transistor in the second power conversion circuit 102 based on the first difference value to achieve closed-loop control of the second power conversion circuit 102, thereby making the actual power at the first terminal of the first power conversion circuit 101 reach or approach the reference power.

[0099] For example, referring to Figure 8, the first controller 103 can process the first difference using a PI controller and adjust the duty cycle of the PWM signal output to the switching transistor in the second power conversion circuit 102. Of course, the first controller 103 can also use other types of closed-loop controllers to process the first difference and adjust the duty cycle of the PWM signal. For example, other types of closed-loop controllers could be proportional (P) controllers, integral (I) controllers, or proportional-integral-derivative (PID) controllers, etc.

[0100] As a second optional implementation, when the first power conversion circuit 101 operates in direct mode, the first controller 103 can adjust the duty cycle of the PWM signal output to the switching transistor in the second power conversion circuit 102 based on the difference between the reference power at the first terminal of the second power conversion circuit 102 and the feedback power at the first terminal of the second power conversion circuit 102, thereby achieving closed-loop control of the second power conversion circuit 102. The reference power at the first terminal of the second power conversion circuit 102 can be determined based on the difference between the reference power at the first terminal of the first power conversion circuit 101 and the power loss value of the first power conversion circuit 101.

[0101] It is understandable that the first power conversion circuit 101 will also experience some power loss when transmitting power in direct mode, and the first controller 103 can detect the power loss value of the first power conversion circuit 101. For example, when the first power conversion circuit 101 is operating in direct mode, the first controller 103 can determine the power loss value of the first power conversion circuit 101 by detecting the power difference between the two ends of the first power conversion circuit 101. Furthermore, the first controller 103 can determine the reference power of the first end of the second power conversion circuit 102 based on the difference between the reference power of the first end of the first power conversion circuit 101 and the power loss value of the first power conversion circuit 101. Therefore, it can be seen that after the reference power of the first end of the second power conversion circuit 102 reaches the DC bus through the first power conversion circuit 101, it can meet the reference power of the first end of the first power conversion circuit 101, that is, meet the given power on the bus side.

[0102] Furthermore, in this second implementation, the first controller 103 can detect the feedback power at the first terminal of the second power conversion circuit 102, i.e., the actual power at the first terminal of the second power conversion circuit 102. Then, the first controller 103 can calculate a second difference by subtracting the reference power at the first terminal of the second power conversion circuit 102 from the feedback power (i.e., the actual power) at the first terminal of the second power conversion circuit 102, and adjust the duty cycle of the PWM signal output to the switching transistor in the second power conversion circuit 102 based on this second difference to achieve closed-loop control of the second power conversion circuit 102. Thus, the actual power of the second power conversion circuit 102 can reach or approach the reference power at the first terminal of the second power conversion circuit 102, thereby making the actual power at the first terminal of the first power conversion circuit 101 reach or approach the reference power.

[0103] As mentioned above, when the first power conversion circuit 101 operates in non-pass-through mode, such as in buck or boost mode, the first controller 103 can generate a waveform for the switching transistors in the second power conversion circuit 102 with a constant duty cycle. In this embodiment, when the first power conversion circuit 101 operates in non-pass-through mode, the closed-loop control parameters of the first controller 103 (e.g., the control parameters of a PI controller) can ensure that the duty cycle of the PWM signal calculated based on the difference between the reference power and the feedback power (such as the first or second difference mentioned above) can be greater than the constant duty cycle. At this time, the first controller 103 can perform open-loop control of the switching transistors in the second power conversion circuit 102 with a smaller duty cycle (i.e., a constant duty cycle).

[0104] When the first power conversion circuit 101 operates in shoot-through mode, the closed-loop control parameters of the first controller 103 can ensure that the duty cycle of the PWM signal calculated based on the difference between the reference power and the feedback power (such as the first difference or the second difference mentioned above) is less than the constant duty cycle. For example, when the first power conversion circuit 101 operates in shoot-through mode and the feedback power (such as the feedback power at the first terminal of the first power conversion circuit 101) is greater than the reference power, the duty cycle of the PWM signal calculated by the first controller 103 can be less than the constant duty cycle. At this time, the first controller 103 can perform closed-loop control of the switching transistor in the second power conversion circuit 102 according to a smaller duty cycle (i.e., the duty cycle determined based on the first difference or the second difference mentioned above). Or it can be understood that the first controller 103 can take over the control of the power at the first terminal of the first power conversion circuit 101.

[0105] For example, assume that the output out of the first controller 103 is the pulse width of the PWM signal, and that the output out satisfies: out = kp × err(t) + ki × ∑(err(t)). Where err(t) is the difference between the reference power and the feedback power at time t (such as the first or second difference mentioned above). kp is the proportional coefficient of the PI controller, and ki is the integral coefficient of the PI controller. Under normal conditions, assuming the energy storage system is in charging mode, the feedback power fdb is 3500W, and the reference power ref is 3510W. The difference err between the reference power ref and the feedback power fdb is: err = ref – fdb = 10W. At this time, the output out calculated by the first controller 103 based on the proportional coefficient kp and the integral coefficient ki (both positive values) is greater than the pulse width corresponding to the constant duty cycle mentioned above. For example, if the pulse width corresponding to the constant duty cycle is 0.5, then the output out of the first controller 103 is > 0.5. Correspondingly, the pulse width (i.e., duty cycle) of the PWM signal output by the second controller 04 to the second power conversion circuit 102 is obtained according to MIN(0.5, out), that is, the first controller 103 outputs the PWM signal according to a constant duty cycle. Here, MIN indicates taking the smaller value.

[0106] When the first power conversion circuit 101 operates in shoot-through mode, the current in the first power conversion circuit 101 is in an uncontrollable state, causing the feedback power fdb to be either less than 3500W or greater than 3500W. When the feedback power fdb is less than 3500W, the output out of the first controller 103 is still a large positive value (e.g., greater than 0.5), and the first controller 103 still outputs a PWM signal according to a constant duty cycle. That is, when the feedback power fdb on the bus side of the first power conversion circuit 101 is less than the reference power ref, the first controller 103 does not need to control the power on the bus side of the first power conversion circuit 101. It is understood that since the feedback power fdb is small at this time, it will not cause damage to the devices in the system.

[0107] When the feedback power fdb = 3520 > 3510 at a certain moment, the difference err between the reference power ref and the feedback power fdb is a negative value. At this time, the output out of the first controller 103 is <= 0.5. Accordingly, the first controller 103 can output a PWM signal to the switching transistor in the second power conversion circuit 102 according to its calculated output out, so as to control the bus-side power of the first power conversion circuit 101. For example, the first controller 103 can first rely on the adjustment of kp × err(t) to quickly pull the output out to a level less than or equal to 0.5, and then adjust it through integral ki × ∑(err(t)) so that the PWM signal corresponding to the output out can control the bus-side power of the first power conversion circuit 101 at the level of 3510W. Thus, the damage to the devices caused by excessive bus-side power of the first power conversion circuit 101 can be effectively avoided.

[0108] Optionally, in the second implementation described above, the reference power P1 at the first terminal of the second power conversion circuit 102 determined by the first controller 103 can satisfy: P1 = P2 - P0 + ΔP. Here, P2 is the reference power at the first terminal of the first power conversion circuit 101, P0 is the power loss value of the first power conversion circuit 101, and ΔP is the power margin. This power margin ΔP can be a fixed value pre-stored in the first controller 103. For example, the power margin ΔP can be an empirical value, and its value can be positive.

[0109] By superimposing a power margin ΔP to obtain the reference power P1 at the first terminal of the second power conversion circuit 102, it is possible to avoid the reference power P1 at the first terminal of the second power conversion circuit 102 being too small, which would result in an excessively small difference between the reference power calculated by the first controller 103 and the feedback power. It is understood that if the difference between the reference power calculated by the first controller 103 and the feedback power is too small, the duty cycle of the PWM signal calculated based on this difference will be small, which may lead to the power loop of the first controller 103 being incorrectly connected, failing to reach the bus-side given power of the first power conversion circuit 101.

[0110] Optionally, the second controller 104 can also be used to perform closed-loop control on the voltage of the first terminal of the first power conversion circuit 101 based on the reference voltage (i.e., bus-side reference voltage) of the first terminal of the first power conversion circuit 101 when the difference between the voltage of the first terminal of the first power conversion circuit 101 and the voltage of the second terminal of the first power conversion circuit 101 is greater than or equal to a threshold, or to perform closed-loop control on the power of the first terminal of the first power conversion circuit 101 based on the reference power (i.e., bus-side reference power) of the first terminal of the first power conversion circuit 101.

[0111] Referring to Figure 8, the closed-loop control of the voltage at the first terminal of the first power conversion circuit 101 by the second controller 104 can be described as follows: the second controller 104 adjusts the duty cycle of the PWM signal output to the switching transistor in the first power conversion circuit 101 based on the difference between the reference voltage (i.e., the bus-side reference voltage) and the actual voltage (i.e., the bus-side feedback voltage) at the first terminal of the first power conversion circuit 101, so that the actual voltage at the first terminal of the first power conversion circuit 101 reaches or approaches the reference voltage at the first terminal of the first power conversion circuit 101.

[0112] Referring again to Figure 8, the closed-loop control of the power at the first terminal of the first power conversion circuit 101 by the second controller 104 can mean that the second controller 104 adjusts the duty cycle of the PWM signal output to the switching transistor in the first power conversion circuit 101 based on the difference between the reference power (i.e., the bus-side reference power) and the actual power (i.e., the bus-side feedback power) at the first terminal of the first power conversion circuit 101, so that the actual power (i.e., the bus-side feedback power) at the first terminal of the first power conversion circuit 101 reaches or approaches the reference power at the first terminal of the first power conversion circuit 101.

[0113] Optionally, as shown in FIG8, the second controller 104 can perform closed-loop control of the voltage at the first terminal of the first power conversion circuit 101 through a PI controller, and can also perform closed-loop control of the power at the first terminal of the first power conversion circuit 101 through a PI controller.

[0114] For example, referring to Figure 8, the first controller 103 may include two subtractors and two PI controllers. The first subtractor A1 calculates the voltage difference between the bus-side reference voltage and the bus-side feedback voltage. The first PI controller PI_1 determines the duty cycle of the PWM signal output to the switching transistor in the first power conversion circuit 101 based on this voltage difference. The second subtractor A2 calculates the power difference between the bus-side reference power and the bus-side feedback power. The second PI controller PI_2 determines the duty cycle of the PWM signal output to the switching transistor in the first power conversion circuit 101 based on this power difference. The first PI controller PI_1 is also called the voltage loop, and the second PI controller PI_2 is also called the power loop.

[0115] Furthermore, the two PI controllers (i.e., two PI control loops) can compete to determine the duty cycle of the PWM signal ultimately output to the switching transistor in the first power conversion circuit 101. This competition between the two PI controllers can mean choosing the larger or smaller value of their outputs (e.g., the duty cycle of the PWM signal) as the final output. For example, as shown in Figure 8, the second controller 104 also includes a multiplexer MUX connected to the two PI controllers PI_1 and PI_2. This multiplexer MUX can select the larger or smaller value from the outputs of the two PI controllers before outputting.

[0116] Optionally, referring to Figure 8, the second controller 104 may also include a third subtractor A3 and a third PI controller PI_3. Furthermore, in this scenario, the output values ​​of both the first PI controller PI_1 and the second PI controller PI_2 can be current values. The multiplexer MUX can take the larger or smaller current value output by the two PI controllers and use it as a reference current output to the third subtractor A3. The third subtractor A3 is used to calculate the current difference between the reference current and the feedback current. The third PI controller PI_3 is used to determine the duty cycle of the PWM signal output to the switching transistor in the first power conversion circuit 101 based on this current difference. The feedback current can refer to the current in the inductor L1 in the first power conversion circuit 101. This third PI controller PI_3 is also called the current loop or the inner current loop.

[0117] As shown in Figure 8, the second controller 104 may further include a fourth subtractor A4 and a threshold comparator. The fourth subtractor A4 calculates the difference between the feedback voltage at the first terminal of the first power conversion circuit 101 (i.e., the actual value of the bus-side voltage) and the feedback voltage at the second terminal (also called the actual value of the internal bus voltage). The threshold comparator compares this difference (e.g., the absolute value of the difference) with a threshold. If the difference is greater than or equal to the threshold, the second controller 104 provides a PWM signal to the switching transistors in the first power conversion circuit 101 according to the duty cycle output by the third PI controller PI_3. If the difference is less than the threshold, the second controller 104 forces the duty cycle of the PWM signal output to the switching transistors in the first power conversion circuit 101 to be the duty cycle of the shoot-through mode. For example, for the first power conversion circuit 101 shown in Figure 5, the second controller 104 can control the duty cycle of the PWM signal output to the first switching transistor S1 to be 1, and control the duty cycle of the PWM signal output to the second switching transistor S2 to be 0.

[0118] The above explanation uses the example of PI controllers as the closed-loop controllers in the second controller 104. It is understood that other types of closed-loop controllers can also be used in the second controller 104. For example, proportional (P) controllers, integral (I) controllers, or proportional-integral-derivative (PID) controllers can also be used. It is also understood that the positions of the PI controllers can be adjusted as needed. For example, the position of the third PI controller PI_3 (i.e., the current loop) can be interchanged with that of the first PI controller PI_1 (i.e., the voltage loop) or the second PI controller PI_2 (the power loop). Alternatively, the third PI controller PI_3 can also be connected to the input side of a multiplexer MUX, meaning the multiplexer MUX can take the larger or smaller output value of the three PI controllers before outputting.

[0119] In summary, this application provides a DC / DC converter in which the first power conversion circuit can operate in shoot-through mode when the voltages at its two ends are relatively close. This effectively reduces the switching losses of the first power conversion circuit without affecting its power conversion performance. Furthermore, when the first power conversion circuit operates in shoot-through mode, the second controller can perform closed-loop control of the power at the first end (i.e., the bus side) of the second power conversion circuit based on a reference power at the first end (i.e., the bus side). This ensures that the actual power at the first end (i.e., the bus side) of the first power conversion circuit reaches or approaches the reference power, thereby achieving power control at the first end (i.e., the bus side) of the first power conversion circuit and preventing device damage due to uncontrollable power.

[0120] Furthermore, it is understandable that by setting two cascaded power conversion circuits in a DC / DC converter, two-stage power conversion can be achieved, thereby effectively improving the power conversion range of the DC / DC converter and thus enhancing its application flexibility.

[0121] This application also provides an energy storage system, as shown in Figures 1 and 2. The energy storage system includes an energy storage battery 00 and a DC / DC converter 10 as provided in the above embodiments. The second terminal of the second power conversion circuit 102 in the DC / DC converter 10 is connected to the energy storage battery 00. For example, referring to Figures 3 and 5, the second terminal of the second power conversion circuit 102 is connected to the positive terminal BAT+ and the negative terminal BAT- of the energy storage battery 00. The DC / DC converter 10 is used to receive reference power from the first terminal of the first power conversion circuit 101 sent by the inverter.

[0122] This application also provides a photovoltaic-energy storage system, as shown in Figure 2. The photovoltaic-energy storage system includes an inverter 30 and an energy storage system as provided in the above embodiments. The inverter 30 is connected to the DC / DC converter 10 in the energy storage system via a DC bus and is used to send the reference power of the first terminal of the first power conversion circuit 101 to the DC / DC converter 10.

[0123] This application also provides another photovoltaic-energy storage system, as shown in FIG2. The photovoltaic-energy storage system includes: an inverter 30, an energy storage battery 00, and a DC / DC converter 10. Referring to FIG3, the DC / DC converter 10 includes a first power conversion circuit 101.

[0124] In this circuit, the first terminal of the first power conversion circuit 101 is connected to the DC terminal of the inverter 30 via a DC bus (BUS+, BUS-), and the second terminal of the first power conversion circuit 101 is connected to the energy storage battery 00. For example, the second terminal of the first power conversion circuit 101 can be directly connected to the energy storage battery 00. Alternatively, as shown in Figure 3, the DC / DC converter 10 further includes a second power conversion circuit 102, and the second terminal of the first power conversion circuit 101 is connected to the positive terminal BAT+ and the negative terminal BAT- of the energy storage battery 00 via the second power conversion circuit 102.

[0125] When the difference between the voltage at the first terminal of the first power conversion circuit 101 and the voltage at the second terminal of the first power conversion circuit 101 is less than a threshold, the first power conversion circuit 101 operates in direct mode.

[0126] The inverter 30 is used to perform closed-loop control of the power at the DC terminal of the inverter 30 based on the reference power at the first terminal of the first power conversion circuit 101 and the reference power at the DC terminal of the inverter 30 when the first power conversion circuit 101 is operating in direct mode.

[0127] It is understood that in this embodiment, the DC / DC converter 10 may not need to include the second power conversion circuit 102, or the DC / DC converter 10 may include the second power conversion circuit 102, but the controller of the second power conversion circuit 102 (i.e., the first controller 103) does not have closed-loop control functionality and can only perform open-loop control on the second power conversion circuit 102. Accordingly, in order to achieve effective control of the current (also known as the load current) on the DC bus of the photovoltaic energy storage system, when the first power conversion circuit 101 operates in shoot-through mode, the inverter 30 can perform closed-loop control on the power of its DC terminal based on the reference power of the first terminal of the first power conversion circuit 101 and the reference power of the DC terminal of the inverter 30.

[0128] For example, referring to Figures 2 and 8, the inverter 30 includes a DC / DC converter 301 and a DC / AC converter 302. The DC terminal of the DC / DC converter 301 is connected to the DC terminal of the DC / AC converter 302 and is connected to the DC bus. Accordingly, the DC terminal of the inverter 30 can refer to both the DC terminal of the DC / DC converter 301 and the DC terminal of the DC / AC converter 302. Furthermore, when the first power conversion circuit 101 operates in shoot-through mode, one of the DC / DC converter 301 and the DC / AC converter 302 can perform closed-loop control of the power at its DC terminal based on the reference power at the first terminal of the first power conversion circuit 101 and the reference power at its DC terminal. Since the DC / DC converter 301 in the inverter 30 is used to connect the photovoltaic panel 20 and the DC / AC converter 302 is used to connect the grid 40, the above process can also be understood as follows: when the first power conversion circuit 101 is working in direct mode, the power (i.e., current) on the DC bus of the photovoltaic-storage system is controlled by the PV side or the grid side.

[0129] The control mode of the DC bus in a photovoltaic-storage system is described below. In the architecture of a photovoltaic-storage system as shown in Figure 2, the DC / DC converter 301 inside the inverter 30 is connected to the photovoltaic panel 20, and the DC / AC converter 302 is connected to the power grid 40. The high-voltage side of the DC / DC converter 10 in the energy storage system is connected to the inverter 30, and can jointly control the DC bus voltage with the DC / DC converter 301 connected to the photovoltaic panel 20 and the DC / AC converter 302 connected to the power grid 40. Alternatively, it can be understood that the voltage level (magnitude) of the DC bus is determined by the photovoltaic panel 20, the energy storage system, and the power grid 40 through a competitive process.

[0130] Referring to Figure 9, taking DC / DC converter 10, DC / DC converter 301, and DC / AC converter 302 as examples where both power loop control and voltage loop control are used, the voltage control mode of the DC bus is explained. The dispatch controller in inverter 30 can send corresponding reference power and reference voltage to each of the aforementioned converters. For each converter, its power control loop can calculate the power difference between the reference power and the actual power, and determine the first duty cycle of the PWM signal based on the power difference. The voltage control loop can calculate the voltage difference between the reference voltage and the actual voltage, and determine the second duty cycle of the PWM signal based on the voltage difference. Referring to Figure 9, the duty cycles output by the power control loop and the voltage control loop can be increased or decreased by a multiplexer (MUX) and used as the duty cycle of the PWM signal finally output to the switching transistors in the converter. Thus, each converter can achieve closed-loop control of its bus-side voltage and closed-loop control of its bus-side power.

[0131] The final voltage on the DC bus is determined based on the fundamental principle of "whoever has the strongest (largest capacity) controls the bus." Capacity refers to charging and discharging capability, i.e., the power that can be output to or received from the DC bus. In other words, for DC / DC converter 10, DC / DC converter 301, and DC / AC converter 302, if the target converter has the largest capacity, then the DC bus voltage is controlled by the bus-side voltage of that target converter.

[0132] For example, assuming no grid connection (40), and the DC / DC converter 301 connected to the photovoltaic panel 20 can output 2000 watts (W) to the DC bus. In this case, if the energy storage system needs to receive the power generated by the photovoltaic panel 20 (i.e., to charge the energy storage battery 00), the inverter 30 can control the DC bus voltage to 850V, and the reference voltage at the first terminal of the first power conversion circuit 101 sent by the dispatch controller in the inverter 30 to the DC / DC converter 10 in the energy storage system can be 835V. If the maximum input power that the energy storage battery 00 can withstand is >3500W, then the reference power at the first terminal of the first power conversion circuit 101 sent by the dispatch controller in the inverter 30 to the DC / DC converter 10 can be 3500W. At this point, since the bus-side power of DC / DC converter 10 can reach 3500W, which is greater than the bus-side power of DC / DC converter 301 (2000W), the charging power of energy storage battery 00 is the bus-side power of DC / DC converter 301, which is 2000W. Furthermore, the DC bus voltage can be controlled to 835V by DC / DC converter 10 in the larger capacity energy storage system.

[0133] Based on the above analysis, it can be seen that both the DC / DC converter 301 and the DC / AC converter 302 in the inverter 30 have the functions of power loop control and voltage loop control. Therefore, when the first power conversion circuit 101 of the DC / DC converter 10 in the energy storage system is working in direct mode, the DC / DC converter 301 or the DC / AC converter 302 can also perform closed-loop control of the power of its DC terminal based on the reference power of the first terminal of the first power conversion circuit 101 and the reference power of its own DC terminal.

[0134] Optionally, the power control loop and voltage control loop in each of the above converters can be PI control loops, or other types of control loops. For example, they can also be proportional (P) control loops, integral (I) control loops, or proportional-integral-derivative (PID) control loops, etc.

[0135] It is also understandable that, as mentioned above, each converter in DC / DC converter 301 and DC / AC converter 302 also receives a reference power at its DC end from the dispatch controller in inverter 30. Accordingly, DC / DC converter 301 and DC / AC converter 302 can perform closed-loop control of their DC-end power based on the smaller of the reference power they receive and the reference power at the first terminal of the first power conversion circuit 101. The reference power at the first terminal of the first power conversion circuit 101 can be determined based on the charging and discharging capacity (also known as power limitation) of the energy storage system. The reference power at the DC end of DC / DC converter 301 can be determined based on the discharge capacity of the photovoltaic panel. The reference power at the DC end of DC / AC converter 302 can be determined based on the charging and discharging capacity of the power grid.

[0136] Alternatively, the reference power sent from the dispatch controller in inverter 30 to DC / DC converter 301 can be determined based on the discharge capacity of the photovoltaic panel and the charging and discharging capacity of the energy storage system. For example, the smaller of the power corresponding to the charging and discharging capacities of the two can be used as the reference power sent to DC / DC converter 301. Furthermore, the reference power sent from the dispatch controller in inverter 30 to DC / AC converter 302 can be determined based on the charging and discharging capacity of the power grid and the charging and discharging capacity of the energy storage system. For example, the smaller of the power corresponding to the charging and discharging capacities of the two can be used as the reference power sent to DC / AC converter 302. This ensures that when the first power conversion circuit 101 in the energy storage system operates in shoot-through mode, DC / DC converter 301 or DC / AC converter 302 can effectively control the power on the DC bus to avoid excessive power and damage to components.

[0137] In summary, this application provides a photovoltaic-storage system, which includes an inverter, a storage battery, and a DC / DC converter. When the voltages across the first power conversion circuit are relatively close, the first controller in the DC / DC converter controls the first power conversion circuit to operate in shoot-through mode. This effectively reduces the switching losses of the first power conversion circuit without affecting its power conversion performance. Furthermore, when the first power conversion circuit operates in shoot-through mode, the inverter performs closed-loop control of the DC power at its DC terminal based on the reference power at the first terminal of the first power conversion circuit and the reference power at the inverter's DC terminal. This avoids device damage caused by uncontrollable DC bus power in shoot-through mode.

[0138] It is understood that the DC / DC converter 10 provided in this application embodiment can be applied not only to the scenarios shown in Figures 1, 2, or 8, but also to other scenarios. For example, it can be applied to an energy storage converter in an energy storage system, also known as a power conversion system (PCS), or to a battery energy optimizer in an energy storage system. Alternatively, it can be applied to an inverter or photovoltaic energy optimizer in the photovoltaic field, where the DC power supply connected to the DC / DC converter 10 can be a photovoltaic panel. Furthermore, it can be applied to an on-board charger (OBC) in an on-board battery management system, where the DC power supply connected to the DC / DC converter 10 can be a power battery. Alternatively, it can be applied to the terminal field or the communication power supply field, etc.

[0139] In the embodiments of this application, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. The term "at least one" refers to one or more, and "multiple" refers to two or more.

[0140] In the embodiments of this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0141] The above description is merely an optional implementation of this application, but the scope of protection of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered 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 DC / DC converter includes: a first power conversion circuit, a second power conversion circuit, and a first controller; The first terminal of the first power conversion circuit is used to connect to the DC bus, the second terminal of the first power conversion circuit is connected to the first terminal of the second power conversion circuit, and the second terminal of the second power conversion circuit is used to connect to the DC power supply. When the difference between the voltage at the first terminal of the first power conversion circuit and the voltage at the second terminal of the first power conversion circuit is less than a threshold, the first power conversion circuit operates in pass-through mode. The first controller is used to perform closed-loop control on the power of the first terminal of the second power conversion circuit based on the reference power of the first terminal of the first power conversion circuit when the first power conversion circuit is operating in direct mode.

2. The DC / DC converter according to claim 1, characterized in that, The first controller is used to adjust the duty cycle of the pulse width modulation (PWM) signal output to the switching transistor in the second power conversion circuit based on the difference between the reference power at the first terminal of the first power conversion circuit and the feedback power at the first terminal of the first power conversion circuit when the first power conversion circuit is operating in pass-through mode, so as to perform closed-loop control of the power at the first terminal of the second power conversion circuit.

3. The DC / DC converter according to claim 1, characterized in that, The first controller is used to adjust the duty cycle of the PWM signal output to the switching transistor in the second power conversion circuit based on the difference between the reference power at the first terminal of the second power conversion circuit and the feedback power at the first terminal of the second power conversion circuit when the first power conversion circuit is operating in the pass-through mode, so as to perform closed-loop control on the power at the first terminal of the second power conversion circuit. The reference power at the first terminal of the second power conversion circuit is determined based on the difference between the reference power at the first terminal of the first power conversion circuit and the power loss value of the first power conversion circuit.

4. The DC / DC converter according to any one of claims 1 to 3, characterized in that, The DC / DC converter further includes a second controller, the second controller being configured to: When the difference between the voltage at the first terminal of the first power conversion circuit and the voltage at the second terminal of the first power conversion circuit is greater than or equal to the threshold, closed-loop control is performed on the voltage at the first terminal of the first power conversion circuit based on the reference voltage at the first terminal of the first power conversion circuit, or closed-loop control is performed on the power at the first terminal of the first power conversion circuit based on the reference power at the first terminal of the first power conversion circuit.

5. The DC / DC converter according to any one of claims 1 to 4, characterized in that, The first power conversion circuit is a step-up / step-down circuit.

6. The DC / DC converter according to claim 5, characterized in that, The first power conversion circuit includes a first switching transistor, a second switching transistor, and an inductor; The first terminal of the first switching transistor is connected to the positive terminal of the DC bus as the positive terminal of the first power conversion circuit, and the second terminal of the first switching transistor is connected to the first terminal of the second switching transistor and one end of the first inductor. The second terminal of the second switching transistor is connected to the negative terminal of the DC bus as the negative terminal of the first terminal of the first power conversion circuit, and is also connected to the negative terminal of the first terminal of the second power conversion circuit as the negative terminal of the second terminal of the first power conversion circuit. The other end of the first inductor is connected to the positive terminal of the first power conversion circuit as the second terminal of the first power conversion circuit. The first power conversion circuit operates in a shoot-through mode, comprising: the first switch being turned on and the second switch being turned off.

7. The DC / DC converter according to any one of claims 1 to 6, characterized in that, The second power conversion circuit is an isolated power conversion circuit.

8. The DC / DC converter according to claim 7, characterized in that, The second power conversion circuit includes: a switching circuit, a first LLC power conversion circuit, and a second LLC power conversion circuit; One end of the switching circuit serves as the first end of the second power conversion circuit and is connected to the second end of the first power conversion circuit. The other end of the switching circuit is connected to one end of the first LLC power conversion circuit and one end of the second LLC power conversion circuit, respectively. The other ends of the first LLC power conversion circuit and the other ends of the second LLC power conversion circuit serve as the second end of the second power conversion circuit and are used to connect to the DC power supply. The first controller is also configured to control the switching circuit to connect the first LLC power conversion circuit and the second LLC power conversion circuit in series to the second terminal of the first power conversion circuit, or to connect the first LLC power conversion circuit and the second LLC power conversion circuit in parallel to the second terminal of the first power conversion circuit.

9. An energy storage system, characterized in that, The energy storage system includes: an energy storage battery, and a DC / DC converter as described in any one of claims 1 to 8, wherein a second terminal of a second power conversion circuit in the DC / DC converter is connected to the energy storage battery; The DC / DC converter is used to receive the reference power from the first terminal of the first power conversion circuit sent by the inverter.

10. A photovoltaic energy storage system, characterized in that, The photovoltaic-storage system includes: an inverter, an energy storage battery, and a DC / DC converter, wherein the DC / DC converter includes a first power conversion circuit; The first terminal of the first power conversion circuit is connected to the DC terminal of the inverter via a DC bus, and the second terminal of the first power conversion circuit is connected to the energy storage battery. When the difference between the voltage at the first terminal of the first power conversion circuit and the voltage at the second terminal of the first power conversion circuit is less than a threshold, the first power conversion circuit operates in pass-through mode. The inverter is used to perform closed-loop control of the power at the DC terminal based on the reference power at the first terminal of the first power conversion circuit and the reference power at the DC terminal of the inverter when the first power conversion circuit is operating in direct mode.

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