DC / DC converter, energy storage system and optical storage system

Abstract

The invention provides a DC / DC converter, an energy storage system and an optical storage system, and belongs to the technical field of power electronics. The first power conversion circuit in the DC / DC converter provided by the invention can work in a straight-through mode when the voltages at the two ends of the first power conversion circuit are relatively close. Therefore, on the premise that the power conversion performance of the first power conversion circuit is not affected, the switching loss of the first power conversion circuit can be effectively reduced. Moreover, when the first power conversion circuit works in the straight-through mode, the first controller can carry out closed-loop control on the power of the first end of the second power conversion circuit based on the reference power of the first end (namely the bus side) of the first power conversion circuit. Therefore, power control over the first end (namely, the bus side) of the first power conversion circuit is achieved, and device damage caused by uncontrollable power is avoided.

Description

Technical Field

[0001] The present application relates to the field of power electronics technology, and in particular to a DC / DC converter, an energy storage system, and a photovoltaic storage system. Background Art

[0002] Energy storage systems typically include 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 converts the DC power from the energy storage battery into a voltage-converting power source before outputting it to the DC bus, discharging the energy storage battery. The DC / DC converter also converts the DC power on the DC bus into a voltage-converting power source before outputting it to the energy storage battery, thereby charging the battery.

[0003] A DC / DC converter typically includes a buck-boost circuit. When the energy storage battery is discharging, the buck-boost circuit operates in boost mode; when the energy storage battery is charging, the buck-boost circuit operates in buck mode. When the voltages across the buck-boost circuit are close, the buck-boost circuit can operate in pass-through mode.

[0004] In pass-through mode, the two ends of the buck-boost circuit are directly connected, and the switching state of the buck-boost circuit's switches is no longer switched, effectively reducing switching losses. However, pass-through mode causes uncontrollable power on the end of the buck-boost circuit connected to the DC bus (i.e., the bus side), potentially causing excessive power on the bus side and damaging components. Summary of the Invention

[0005] The present application provides a DC / DC converter, an energy storage system, and a photovoltaic storage system, which can solve the technical problem of uncontrollable bus-side power when the buck-boost circuit in the DC / DC converter operates in direct-through mode.

[0006] In a first aspect, a DC / DC converter is provided, which includes: a first power conversion circuit, a second power conversion circuit, and a first controller. The first end of the first power conversion circuit is used to connect to a DC bus, the second end of the first power conversion circuit is connected to the first end of the second power conversion circuit, and the second end of the second power conversion circuit is used to connect to a DC power supply. When the difference between the voltage at the first end of the first power conversion circuit and the voltage at the second end of the first power conversion circuit is less than a threshold value, the first power conversion circuit operates in a pass-through mode. The first controller is used to 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 of the first power conversion circuit when the first power conversion circuit operates in the pass-through mode.

[0007] It can be understood that in the pass-through mode, the first end of the first power conversion circuit is directly connected to the second end, and the on-off state of the switch tube in the first power conversion circuit is no longer switched. When the first power conversion circuit operates in the pass-through mode, the first controller performs closed-loop control on the power of the first end of the second power conversion circuit based on the reference power of the first end of the first power conversion circuit, so that the actual power of the first end of the first power conversion circuit (i.e., the bus side) reaches or approaches the reference power. In this way, power control of the first end of the first power conversion circuit (i.e., the bus side) is achieved to avoid device damage caused by uncontrollable power on the bus side of the first power conversion circuit in the pass-through mode.

[0008] Optionally, the first controller is used to adjust the duty cycle of a pulse width modulation (PWM) signal output to the switch tube in the second power conversion circuit based on the difference between the reference power of the first end of the first power conversion circuit and the feedback power of the first end of the first power conversion circuit when the first power conversion circuit operates in the pass-through mode, thereby achieving closed-loop control of the power of the first end of the second power conversion circuit.

[0009] In the present application, the first controller can directly adjust the duty cycle of the PWM signal output to the switch tube in the second power conversion circuit based on the difference between the reference power and the feedback power (i.e., actual power) at the first end of the first power conversion circuit. This achieves closed-loop control of the power at the first end of the second power conversion circuit, thereby ensuring that the feedback power (i.e., actual power) at the first end of the first power conversion circuit reaches or approaches the reference power.

[0010] Optionally, the first controller is configured to adjust the duty cycle of a PWM signal output to a switch in the second power conversion circuit based on a difference between a reference power at the first end of the second power conversion circuit and a feedback power at the first end of the second power conversion circuit when the first power conversion circuit operates in a pass-through mode, thereby achieving closed-loop control of the power at the first end of the second power conversion circuit. The reference power at the first end of the second power conversion circuit is determined based on a difference between the reference power at the first end of the first power conversion circuit and a power loss value of the first power conversion circuit.

[0011] It is understandable that the first power conversion circuit will also generate certain losses when transmitting power in the direct mode. The first controller can detect the power loss value of the first power conversion circuit in the direct mode, and determine the reference power of the first end of the second power conversion circuit based on the difference between the reference power of the first end of the first power conversion circuit and the power loss value. Accordingly, after the first controller performs closed-loop control on the feedback power (i.e., actual power) of the first end of the second power conversion circuit based on the reference power of the first end of the second power conversion circuit, the feedback power (i.e., actual power) of the first end of the second power conversion circuit can reach or approach the reference power of the first end of the second power conversion circuit. Furthermore, it can ensure that the feedback power (i.e., actual power) of the first end of the first power conversion circuit reaches or approaches the reference power of the first end of the first power conversion circuit.

[0012] Optionally, the DC / DC converter also includes a second controller, which is used to perform closed-loop control of the voltage at the first end of the first power conversion circuit according to the reference voltage of the first end of the first power conversion circuit when the difference between the voltage at the first end of the first power conversion circuit and the voltage at the second end of the first power conversion circuit is greater than or equal to a threshold.

[0013] The closed-loop control process may be as follows: the second controller adjusts the duty cycle of the PWM signal output to the switch tube in the first power conversion circuit based on the difference between the reference voltage of the first end of the first power conversion circuit and the feedback voltage (i.e., the actual voltage) of the first end of the first power conversion circuit, so that the feedback voltage (i.e., the actual voltage) of the first end of the first power conversion circuit reaches or approaches the reference voltage of the first end of the first power conversion circuit.

[0014] Optionally, the second controller is also used to perform closed-loop control of the power of the first end of the first power conversion circuit based on the reference power of the first end of the first power conversion circuit when the difference between the voltage at the first end of the first power conversion circuit and the voltage at the second end of the first power conversion circuit is greater than or equal to a threshold.

[0015] The closed-loop control process may be as follows: the second controller adjusts the duty cycle of the PWM signal output to the switch tube in the first power conversion circuit based on the difference between the reference power of the first end of the first power conversion circuit and the feedback power (i.e., actual power) of the first end of the first power conversion circuit, so that the feedback power (i.e., actual power) of the first end of the first power conversion circuit reaches or approaches the reference power of the first end of the first power conversion circuit.

[0016] Optionally, the first power conversion circuit is a buck-boost circuit. The buck-boost circuit can also operate in boost mode or buck mode, and has high operating flexibility to meet the needs of different application scenarios. For example, in an energy storage system, the DC power supply can be an energy storage battery. When the energy storage battery needs to be charged, the buck-boost circuit can operate in buck mode; when the energy storage battery needs to be discharged, the buck-boost circuit can operate in boost mode.

[0017] Optionally, for a scenario where the first power conversion circuit is a buck-boost circuit, the first power conversion circuit includes a first switching tube, a second switching tube, and an inductor. The first electrode of the first switching tube is connected to the positive electrode of the DC bus as the positive electrode of the first end of the first power conversion circuit, and the second electrode of the first switching tube is connected to the first electrode of the second switching tube and one end of the first inductor, respectively. The second electrode of the second switching tube is connected to the negative electrode of the DC bus as the negative electrode of the first end of the first power conversion circuit, and is connected to the negative electrode of the first end of the second power conversion circuit as the negative electrode of the second end of the first power conversion circuit. The other end of the first inductor is connected to the positive electrode of the first end of the second power conversion circuit as the positive electrode of the second end of the first power conversion circuit. The first power conversion circuit operates in a pass-through mode, including: the first switching tube is turned on, and the second switching tube is turned off.

[0018] The topology of the first power conversion circuit is relatively simple, which can avoid increasing the structural complexity of the DC / DC converter and avoid increasing the cost. Of course, the first power conversion circuit can also adopt other types of topologies, such as a four-switch buck boost (FSBB) converter.

[0019] Optionally, the second power conversion circuit is an isolated power conversion circuit. The isolated power conversion circuit may refer to a power conversion circuit including a transformer, which can achieve a large-scale voltage conversion to ensure that the operating voltage range required by the system (such as the energy storage system) can be met.

[0020] 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 end of the second power conversion circuit and is connected to the second end of the first power conversion circuit, and the other end of the switching circuit is respectively connected to one end of the first LLC power conversion circuit and one end of the second LLC power conversion circuit. The other end of the first LLC power conversion circuit and the other end of the second LLC power conversion circuit serve as the second end of the second power conversion circuit and are used to connect a DC power supply. The first controller is also used 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 end 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 end of the first power conversion circuit.

[0021] Since the switching circuit can realize series-parallel switching of the two LLC power conversion circuits, it can effectively increase the operating voltage range of the first end of the second power conversion circuit (i.e., the second end of the first power conversion circuit), thereby improving the application flexibility of the DC / DC converter.

[0022] In a second aspect, an energy storage system is provided, comprising: an energy storage battery; and a DC / DC converter as provided in the first aspect. 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 configured to receive a reference power from an inverter at the first terminal of the first power conversion circuit.

[0023] In a third aspect, a photovoltaic energy storage system is provided, comprising an inverter and the energy storage system provided in the second aspect. The inverter is connected to a DC / DC converter in the energy storage system via a DC bus and is configured to transmit a reference power at a first end of a first power conversion circuit to the DC / DC converter.

[0024] In a fourth aspect, another photovoltaic storage system is provided, which includes: an inverter, an energy storage battery and a DC / DC converter. The DC / DC converter includes a first power conversion circuit. The first end of the first power conversion circuit is connected to the DC end of the inverter through a DC bus, and the second end of the first power conversion circuit is connected to the energy storage battery. When the difference between the voltage at the first end of the first power conversion circuit and the voltage at the second end of the first power conversion circuit is less than a threshold value, the first power conversion circuit operates in a pass-through mode. The inverter is used to perform closed-loop control of the power at its DC end based on the reference power at the first end of the first power conversion circuit and the reference power at the DC end of the inverter when the first power conversion circuit operates in the pass-through mode.

[0025] As previously described, when the voltages at both ends of the first power conversion circuit are relatively close, the first power conversion circuit operates in a pass-through mode, effectively reducing the switching losses of the first power conversion circuit without affecting the power conversion performance of the first power conversion circuit. Furthermore, when the first power conversion circuit operates in the pass-through mode, the inverter performs closed-loop control of the power at its DC end based on the reference power at the first end of the first power conversion circuit and the reference power at the DC end of the inverter. This prevents component damage caused by uncontrollable DC bus power in the pass-through mode.

[0026] In summary, the present application provides a DC / DC converter, an energy storage system, and a photovoltaic storage system. The first power conversion circuit in the DC / DC converter provided by the present application can operate in a pass-through mode when the voltages at its two ends are relatively close. As a result, 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. Moreover, when the first power conversion circuit operates in the pass-through mode, the second controller can also perform closed-loop control of the power of the first end of the second power conversion circuit based on the reference power of the first end (i.e., the bus side) of the first power conversion circuit. As a result, the actual power of the first end (i.e., the bus side) of the first power conversion circuit can reach or approach the reference power, thereby achieving power control of the first end (i.e., the bus side) of the first power conversion circuit to avoid damage to the device caused by uncontrollable power.

[0027] In addition, it can be understood that by providing two cascaded power conversion circuits in the DC / DC converter, two-stage power conversion can be achieved, thereby effectively improving the power conversion range of the DC / DC converter and further improving the application flexibility of the DC / DC converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic diagram of the structure of an energy storage system provided in an embodiment of the present application;

[0029] Figure 2 This is a schematic structural diagram of a solar storage system provided in an embodiment of the present application;

[0030] Figure 3 This is a schematic structural diagram of a DC / DC converter provided in an embodiment of the present application;

[0031] Figure 4 is a structural diagram of another DC / DC converter provided in an embodiment of the present application;

[0032] Figure 5 This is a schematic structural diagram of a power conversion circuit in a DC / DC converter provided in an embodiment of the present application;

[0033] Figure 6 is a structural diagram of a first power conversion circuit provided in an embodiment of the present application;

[0034] Figure 7 is a structural diagram of another first power conversion circuit provided in an embodiment of the present application;

[0035] Figure 8 is a structural diagram of another DC / DC converter provided in an embodiment of the present application;

[0036] Figure 9 This is a structural diagram of another optical storage system provided in an embodiment of the present application. DETAILED DESCRIPTION

[0037] The following describes in detail the DC / DC converter, energy storage system and photovoltaic storage system provided by the embodiments of the present application in conjunction with the accompanying drawings. First, the key terms involved in the embodiments of the present application are introduced.

[0038] Pass-through mode: In the field of power electronics, it refers to the operating mode in which the input and output of the power conversion circuit are directly connected under the specific switching state of the switching tube.

[0039] 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. Energy optimizers typically include a DC / DC converter.

[0040] Switching loss: energy consumption caused by the switching of the switch tube.

[0041] Soft switching: refers to the use of control circuits or external auxiliary circuits to turn on or off the switch under zero voltage and zero current conditions, thereby reducing switching losses.

[0042] Proportional integral (PI) control loop: This loop compares collected system data with a reference value, generating a difference. This difference is then subjected to proportional (P) and integral (I) control to produce a calculated value. This calculated value is then fed back into the system through a feedback loop to ensure that the system data reaches or remains at the reference value.

[0043] PWM is a technology that modulates the width of pulses, that is, by modulating the width of a series of pulses to equivalently obtain the required waveform (including shape and amplitude).

[0044] Open-loop control: Open-loop control means giving the system controller an expected value (i.e., reference value). The controller only controls the output of the system according to the expected value, but it is possible that the system output deviates from the expected value.

[0045] Closed-loop control: also called feedback control system, there is a feedback path to compare the measured value of the system output with the expected value, generate a deviation signal and feed it back to the input of the controller for adjustment and control, so that the system output is as close to the expected value as possible.

[0046] Figure 1 This is a schematic diagram of the structure of an energy storage system provided in an embodiment of the present application. Figure 1 As shown, the energy storage system may include: an energy storage battery 00 and a DC / DC converter 10. For example, Figure 1 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 by the energy storage battery 00 into a 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 a voltage and output it to the energy storage battery 00, thereby charging the energy storage battery 00.

[0047] Figure 2 This is a schematic diagram of the structure of a solar storage system provided in an embodiment of the present application. Figure 2 As shown, the solar storage system may include Figure 1 The energy storage system shown 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 end of the DC / AC converter 302 is connected to the DC bus, and the AC end is connected to the power grid 40 and the load 50. The load 50 may be a household load. The DC / DC converter 301 is used to convert the DC power output by the photovoltaic panel 20 into voltage and output it to the DC bus. The DC / AC converter 302 is used to convert the DC power on the DC bus into AC power and output it to the power grid 40 and the load 50.

[0048] It is understandable that Figure 2The overall energy scheduling in the illustrated solar-to-energy storage system can be achieved by inverter 30, that is, inverter 30 serves as the energy scheduling controller for the solar-to-energy storage system. The energy storage system's operating modes are primarily divided into charging mode and discharging mode. Switching between charging and discharging modes can be achieved by inverter 30 sending different reference voltages to the DC / DC converter 10 in the energy storage system. For example, when charging the energy storage battery 00 in the energy storage system, inverter 30 can control the DC bus to a certain voltage V and send a reference voltage V–ΔV to the DC / DC converter 10 in the energy storage system. Based on this reference voltage V–ΔV, the DC / DC converter 10 can control the voltage on the port connected to the DC bus (i.e., the bus-side voltage) to V–ΔV. At this point, the bus-side voltage V–ΔV of the DC / DC converter 10 is lower than the DC bus voltage V, allowing energy to flow into the energy storage battery 00, thereby charging the energy storage battery 00. When the energy storage battery 00 in the energy storage system needs to be discharged, the inverter 302 can control the DC bus to 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 discharge of the energy storage battery 00.

[0049] It is also understood that the DC / DC converter 10 in the energy storage system generally includes a buck-boost circuit, which can operate in a buck mode or a boost mode. Figure 2 In the solar-to-energy storage system shown, the buck-boost circuit operates in buck mode when the energy storage battery is charging; it operates in boost mode when the energy storage battery is discharging. In both buck and boost modes, the switches in the buck-boost circuit need to continuously switch on and off under the control of a 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.

[0050] 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, while the voltage of the DC bus is lower. 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.

[0051] In some embodiments, the switching losses of a buck-boost circuit can be reduced by adjusting device selection and optimizing parameters. For example, an inductor or switch with better parameters and lower on-resistance can be selected to reduce switching losses. However, this approach relies on technological developments in surrounding areas (such as power device materials) and has limited application flexibility. Furthermore, selecting devices with better parameters can significantly increase device costs.

[0052] In other embodiments, switching losses in buck-boost circuits are reduced by optimizing control strategies. For example, switching losses are reduced by varying the switching frequency under varying load conditions and employing soft switching techniques. However, this approach is limited by chip memory and processor computing power, resulting in limited application flexibility and potential difficulties in practical implementation.

[0053] The present invention provides a DC / DC converter, which can be used in Figure 1 or Figure 2 In the application scenario shown, the switching loss of the DC / DC converter is small, which can reduce the impact on the charging and discharging efficiency of the energy storage system. Figure 3 As shown, the DC / DC converter 10 includes: a first power conversion circuit 101 , a second power conversion circuit 102 and a first controller 103 .

[0054] The first end of the first power conversion circuit 101 is used to connect to the DC bus (BUS+, BUS-), the second end of the first power conversion circuit 101 is connected to the first end of the second power conversion circuit 102, and the second end of the second power conversion circuit 102 is used to connect 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 end of the first power conversion circuit 101 and the first end of the second power conversion circuit 102 are also referred to as the bus side or high-voltage side, and the second end of the first power conversion circuit 101 and the second end of the second power conversion circuit 102 are also referred to as the battery side or low-voltage side.

[0055] When the difference between the voltage at the first end of the first power conversion circuit 101 and the voltage at the second end of the first power conversion circuit 101 is smaller than a threshold, the first power conversion circuit 101 operates in the pass-through mode.

[0056] The first power conversion circuit 101 operating in the pass-through mode may mean that the first terminal of the first power conversion circuit 101 is directly connected to the second terminal by controlling the on / off state of the switch in the first power conversion circuit 101. Furthermore, in the pass-through mode, the switch in the first power conversion circuit 101 can remain in the on or off state, that is, the on / off state of the switch does not switch.

[0057] The first controller 103 is configured to perform closed-loop control on the power at the first end of the second power conversion circuit 102 based on the reference power at the first end of the first power conversion circuit 101 when the first power conversion circuit 101 operates in the pass-through mode.

[0058] The reference power may be issued by a dispatching controller of the system where the DC / DC converter is located (e.g., an inverter in a photovoltaic storage system), and the reference power may be determined based on the charge and discharge capacity of the DC power source (e.g., an energy storage battery). The first controller 103 performs closed-loop control on the power of the first end of the second power conversion circuit 102 based on the reference power of the first end of the first power conversion circuit 101, which may mean that the first controller 103 adjusts the duty cycle of the PWM signal output to the switch tube in the second power conversion circuit 102 based on the reference power of the first end of the first power conversion circuit 101 to achieve closed-loop control of the power of the first end of the second power conversion circuit 102, thereby achieving closed-loop control of the power of the first end of the first power conversion circuit 101. Furthermore, since the reference power of the closed-loop control is the reference power of the first end of the first power conversion circuit 101, the actual power of the first end of the first power conversion circuit 101 can be made to reach or approach the reference power of the first end of the first power conversion circuit 101.

[0059] It can be understood that when the difference between the voltage at the first end of the first power conversion circuit 101 and the voltage at the second end of the first power conversion circuit 101 is less than the threshold value, that is, when the voltages at both ends of the first power conversion circuit 101 are close, the power conversion function (such as the boost function or the buck function) of the first power conversion circuit 101 is not very effective. Alternatively, it can be understood that when the voltages at both ends of the first power conversion circuit 101 are close, the power conversion function of the first power conversion circuit 101 has little effect on the voltages at both ends. Moreover, when the first power conversion circuit 101 performs power conversion, that is, when it operates in the non-through mode, the switch tube in the first power conversion circuit 101 needs to continuously switch the on-off state under the control of the PWM signal, which will cause the switching loss of the first power conversion circuit 101 to be large, thereby affecting the efficiency of the system (such as the energy storage system). Among them, the non-through mode can include one or more of the following modes: buck mode, boost mode, and buck-boost mode.

[0060] Based on the above analysis, it can be seen that in the embodiment of the present application, when the voltages at both ends of the first power conversion circuit 101 are close, the first power conversion circuit 101 operates in the pass-through mode, which can effectively reduce the switching loss of the first power conversion circuit 101 without affecting the power conversion performance of the DC / DC converter 10.

[0061] It can also be understood that after the first power conversion circuit 101 operates in the direct-through mode, since the on-off state of the switch tube in the first power conversion circuit 101 is no longer switched, the current of the first end (i.e., the bus side) of the first power conversion circuit 101 will be uncontrollable, thereby causing the power on the bus side to be uncontrollable. Accordingly, in an embodiment of the present application, after the first power conversion circuit 101 operates in the direct-through mode, the first controller 103 can also perform closed-loop control on the power of the first end of the second power conversion circuit 102 based on the reference power of the first end of the first power conversion circuit 101, thereby achieving effective control of the power of the first end (i.e., the bus side) of the first power conversion circuit 101. Thus, damage to devices caused by uncontrollable power can be effectively avoided. For example, when the power of the first end of the first power conversion circuit 101 is too large, the devices in the system will be damaged due to overcurrent.

[0062] It is also understood that the DC / DC converter provided in the embodiments of the present application can achieve two-stage power conversion by providing two cascaded power conversion circuits. Thus, on the one hand, the power conversion range of the DC / DC converter can be effectively increased, thereby increasing the application flexibility of the DC / DC converter. On the other hand, the requirements for the power conversion performance of a single power conversion circuit can be effectively reduced, thereby significantly reducing the cost and structural complexity of the power conversion circuit.

[0063] For example, assuming that the voltage of the DC bus to which the DC / DC converter 10 is connected is 800 volts (V), and the voltage of the DC power source (such as an energy storage battery) to which the DC / DC converter 10 is connected is 28 V. Then the first power conversion circuit 101 can be used to achieve voltage conversion between 800 V and 700 V, and the second power conversion circuit 102 can be used to achieve voltage conversion between 700 V and 28 V. Compared to directly using a power conversion circuit to achieve voltage conversion from 800 V to 28 V, the two-stage voltage conversion method can effectively reduce the power conversion range (i.e., the voltage conversion ratio) of a single power conversion circuit, thereby reducing the cost and structural complexity of the power conversion circuit.

[0064] In summary, an embodiment of the present application provides a DC / DC converter, in which the first power conversion circuit in the DC / DC converter can operate in a pass-through mode when the voltages at both ends thereof are relatively close. Thus, 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. Moreover, when the first power conversion circuit operates in the pass-through mode, the first controller can also perform closed-loop control of the power of the first end of the second power conversion circuit based on the reference power of the first end (i.e., the bus side) of the first power conversion circuit. Thus, the actual power of the first end (i.e., the bus side) of the first power conversion circuit can reach or approach the reference power, thereby achieving power control of the first end (i.e., the bus side) of the first power conversion circuit to avoid damage to the device caused by uncontrollable power.

[0065] Furthermore, the DC / DC converter provided in the embodiments of the present application effectively reduces switching losses in the first power conversion circuit without adjusting component selection or optimizing device parameters, offering high application flexibility and low cost. Furthermore, the controller in the DC / DC converter has a relatively simple control strategy, requiring less chip memory and processor computing power, making it easier to implement in practical application scenarios.

[0066] It is understood that, in a scenario where 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 greater than or equal to a threshold value, the first power conversion circuit 101 can operate in a non-through mode, for example, in a buck mode or a boost mode. As described above, when energy flows from the DC bus into the DC power supply (such as a storage battery), the first power conversion circuit 101 can operate in a buck mode. When energy flows from the DC power supply into the DC bus, the first power conversion circuit 101 can operate in a boost mode.

[0067] Furthermore, when the first power conversion circuit 101 operates in the non-shoot-through mode, the first controller 103 can generate a PWM signal for the switch in the second power conversion circuit 102 according to a fixed duty cycle (i.e., a constant duty cycle). That is, the first controller 103 can perform open-loop control of the second power conversion circuit 102 based on the constant duty cycle. Generating a PWM signal refers to providing a PWM signal to the switch.

[0068] Alternatively, as Figure 4As shown, the DC / DC converter may further include a second controller 104. The second controller 104 is configured 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 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 value, the second controller 104 may control the first power conversion circuit 101 to operate in a pass-through mode. 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 greater than or equal to a threshold value, the second controller 104 may control the first power conversion circuit 101 to operate in a non-pass-through mode.

[0069] Optionally, both the first controller 103 and the second controller 104 may be microcontroller units (MCUs). Furthermore, the first controller 103 and the second controller 104 may be two independent devices, or may be integrated, i.e., the first controller 103 and the second controller 104 may be integrated into one controller. Furthermore, the first controller 103 and the second controller 104 may implement closed-loop control of the power conversion circuit via software, or may implement closed-loop control of the power conversion circuit via hardware, which is not limited in the present embodiment.

[0070] 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.

[0071] Figure 5 1 is a schematic diagram of a power conversion circuit in a DC / DC converter provided in an embodiment of the present application. Taking the first power conversion circuit 101 as a buck-boost circuit as an example, Figure 5 As shown, the first power conversion circuit 101 may include a first switch tube S1, a second switch tube S2 and an inductor L1.

[0072] The first electrode of the first switching transistor S1 is connected to the positive electrode BUS+ of the DC bus as the positive electrode of the first end of the first power conversion circuit 101. The second electrode of the first switching transistor S1 is connected to the first electrode of the second switching transistor S2 and one end of the first inductor L1, respectively. The second electrode of the second switching transistor S2 is connected to the negative electrode BUS- of the DC bus as the negative electrode of the first end of the first power conversion circuit 101, and is connected to the negative electrode of the first end of the second power conversion circuit 102 as the negative electrode of the second end of the first power conversion circuit 101. The other end of the first inductor L1 is connected to the positive electrode of the first end of the second power conversion circuit 102 as the positive electrode of the second end of the first power conversion circuit 101.

[0073] It is understood that the first electrode of the switch tube can be one of the source and the drain, and the second electrode can be the other of the source and the drain. For example, the switch tubes in the first power conversion circuit 101 can all be N-type switch tubes, the first electrode of the N-type switch tube can be the drain, and the second electrode can be the source.

[0074] for Figure 5 In the illustrated first power conversion circuit 101, the second controller 104 controlling the first power conversion circuit 101 to operate in direct-pass mode may mean that the second controller 104 controls the first switch S1 to be conductive and the second switch S2 to be off. In other words, 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. In this way, the first terminal and the second terminal of the first power conversion circuit 101 are directly connected.

[0075] Continue to refer Figure 5 , the first power conversion circuit 101 may also include a first capacitor C1, a second capacitor C2 and a diode D1. The first capacitor C2 is connected between the positive pole BUS+ of the DC bus and the negative pole BUS- of the DC bus, that is, connected between the positive pole and the negative pole of the first end of the first power conversion circuit 101. The second capacitor C2 is connected between the positive pole and the negative pole of the second end of the first power conversion circuit 101. The diode D1 is connected in series between the positive pole of the first end and the positive pole of the second end of the first power conversion circuit 101. The first capacitor C1 and the second capacitor C2 can be used for voltage stabilization. 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, so that the first end of the first power conversion circuit 101 is directly connected to the second end.

[0076] It is understandable that for Figure 5 In the first power conversion circuit 101 shown, when the second controller 104 controls the second switch S2 to be normally off and controls the on and off of the first switch S1 via a PWM signal, the first power conversion circuit 101 operates in a buck mode. When the second controller 104 controls the first switch S1 to be normally on and controls the on and off of the second switch S2 via a PWM signal, the first power conversion circuit 101 operates in a boost mode.

[0077] Figure 6 This is a schematic diagram of the structure of a first power conversion circuit provided by an embodiment of the present application. Figure 6As shown, for 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. The FSBB converter is composed of a buck circuit and a boost circuit in cascade, and can achieve higher efficiency over a wide input voltage range.

[0078] refer to Figure 6 As can be seen, the FSBB converter includes an inductor L1 and four switches, S1 to S4. Switches S1 and S2 form the buck leg, while switches S3 and S4 form the boost leg. Inductor L1 is connected between the buck and boost legs. Because all four switches in the FSBB converter are controllable, it offers advantages over traditional buck-boost topologies, such as greater control freedom and the same polarity of the input and output voltages.

[0079] When the second controller 104 controls switch S4 to be normally off, switch S3 to be normally on, and switches S1 and S2 to be alternately turned on, the FSBB converter operates in buck mode. When the second controller 104 controls switch S2 to be normally off, switch S1 to be normally on, and switches S3 and S4 to be alternately turned on, the FSBB converter operates in boost mode. When the second controller 104 controls switches S1 and S4 as a group to be turned on or off simultaneously, and switches S2 and S3 as a complementary group to be turned on or off simultaneously, the FSBB converter operates in buck-boost mode. When the second controller 104 controls switches S1 and S3 to be normally on, and switches S2 and S4 to be normally off, the first terminal of the FSBB converter is directly connected to the second terminal, and the FSBB converter operates in pass-through mode. That is, when the second controller 104 controls the duty cycle of the PWM signal output to the switches S1 and S3 to be 1 and controls the duty cycle of the PWM signal output to the switches S2 and S4 to be 0, the first and second terminals of the FSBB converter are directly connected.

[0080] Figure 7 This is a schematic diagram of the structure of another first power conversion circuit provided by an embodiment of the present application. Figure 7As shown, the first power conversion circuit 101 can also be a step-down (buck) circuit, which includes a switch tube S1, a diode D0, an inductor L1, and capacitors C1 and C2. The first electrode of the switch tube S1 is connected to the positive electrode BUS+ of the DC bus, and the second electrode of the switch tube S1 is connected to the negative electrode of the diode D0 and one end of the inductor L1, respectively. The positive electrode of the diode D0 is connected to the negative electrode BUS- of the DC bus. The capacitor C1 is connected between the positive electrode BUS+ and the negative electrode BUS- of the DC bus, and the capacitor C2 is connected between the other end of the inductor L1 and the negative electrode BUS- of the DC bus.

[0081] for Figure 7 In the first power conversion circuit 101 shown, when the second controller 104 controls the on and off of the switch S1 through the PWM signal, the first power conversion circuit 101 operates in the buck mode. When the second controller 104 controls the switch S1 to be always on, the first power conversion circuit 101 operates in the pass mode. That is, when the duty cycle of the PWM signal output to the switch S1 by the second controller 104 is 1, Figure 7 The first end and the second end of the first power conversion circuit 101 are directly connected.

[0082] Optionally, in an embodiment of the present application, the topology type of the second power conversion circuit 102 in the DC / DC converter 10 may be the same as or different from the topology type of the first power conversion circuit 101. For example, the second power conversion circuit 102 may also be a buck-boost circuit, that is, the DC / DC converter 10 may include a cascaded two-stage buck-boost circuit. Alternatively, the second power conversion circuit 102 may be an isolated power conversion circuit. An isolated power conversion circuit refers to a power conversion circuit that includes a transformer. By adopting an isolated power conversion circuit that includes a transformer, on the one hand, a larger proportion of voltage conversion can be achieved, which has greater application flexibility, and on the other hand, isolation between high and low voltages can be achieved, which has better safety. For example, assuming that the transformer in the isolated power conversion circuit has a transformation ratio K = 13, if the voltage range of the DC power supply connected to the second end of the isolated power conversion circuit is 16V to 28V, then the voltage range of the first end of the isolated power conversion circuit can reach 208V to 728V.

[0083] Example, reference Figure 5 , the second power conversion circuit 102 may be an LLC power conversion circuit. Wherein, L refers to inductance, and C refers to capacitance. Figure 5 It can be seen that the LLC power conversion circuit may include a transformer T0, switch tubes Q1 and Q2 located on the primary side of the transformer T0, capacitors C3, C4 and C5, and an inductor L2, switch tubes Q3 to Q6 located on the secondary side of the transformer, and a capacitor C6.

[0084] The switches Q1 and Q2 are connected in series between the positive and negative electrodes of the first terminal of the second power conversion circuit 102. The capacitors C3 and C4 are also connected in series between the positive and negative electrodes of the first terminal of the second power conversion circuit 102. The capacitor C5 is connected between the positive and negative electrodes of the first terminal of the second power conversion circuit 102. The series node between the switches Q1 and Q2 is connected to one end of the inductor L2. The other end of the inductor L2 is connected to one end of the primary side of the transformer T0. The series node between the capacitors C3 and C4 is connected to the other end of the primary side of the transformer T0.

[0085] Switches Q3 and Q4 are connected in series between the positive and negative electrodes of the second terminal of the second power conversion circuit 102. Switches Q5 and Q6 are also connected in series between the positive and negative electrodes of the second terminal of the second power conversion circuit 102. Capacitor C6 is connected between the positive and negative electrodes of the second terminal of the second power conversion circuit 102. The series node between switches Q3 and Q4 is connected to one end of the secondary side of transformer T0, and the series node between switches Q5 and Q6 is connected to the other end of the secondary side of transformer T0.

[0086] It is understandable that the second power conversion circuit 102 can also adopt other isolated power conversion topologies besides LLC, for example, it can also adopt CLLC power conversion topology or dual active bridge (DAB) power conversion topology, etc. The embodiment of the present application does not limit the topology type of the second power conversion circuit 102.

[0087] Figure 8 This is a schematic diagram of the structure of another DC / DC converter provided in an embodiment of the present application. Figure 8 As shown, the second power conversion circuit 102 may include: a switch circuit 1021 , a first LLC power conversion circuit 1022 and a second LLC power conversion circuit 1023 .

[0088] One end of the switch 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 switch circuit 1021 is respectively connected to one end of the first LLC power conversion circuit 1022 and one end of the second LLC power conversion circuit 1023. The other end of the first LLC power conversion circuit 1022 and the other end of 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.

[0089] The first controller 103 is also used to control the switch circuit 1021 to connect the first LLC power conversion circuit 1022 and the second LLC power conversion circuit 1023 in series to the second end 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 end of the first power conversion circuit 101.

[0090] from Figure 8 It can be seen that the topologies 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 a storage battery.

[0091] Optionally, continue to refer to Figure 8 The switch circuit 1021 may include a switch K1, a switch K2, and a switch K3. When the switch K1 is closed and the switches K2 and K3 are both open, the first LLC power conversion circuit 1022 and the second LLC power conversion circuit 1023 are connected in series to the second end of the first power conversion circuit 101. When the switch K1 is open and the switches K2 and K3 are both closed, the first LLC power conversion circuit 1022 and the second LLC power conversion circuit 1023 are connected in parallel to the second end of the first power conversion circuit 101.

[0092] The switches K1, K2, and K3 can be independent switches. Alternatively, the switches K1, K2, and K3 can be integrated into a single relay, also known as a series-parallel relay. Because the switch circuit 1021 can implement series-parallel switching of the two LLC power conversion circuits, a wider operating voltage range can be achieved, thereby ensuring that the required voltage range for different application scenarios is met.

[0093] refer to Figure 8 , assuming that the voltage range of the DC bus is approximately 350V to 980V, and the voltage range of the energy storage battery is approximately 16V to 28V. If the transformation ratio of the transformer of each LLC power conversion circuit in the second power conversion circuit 102 is K, then the voltage range of the second end of the first power conversion circuit 101 is 16V×K to 28V×2K. Assuming K=13, the voltage range of the second end of the first power conversion circuit 101 is 208V to 728V. This voltage range overlaps with the voltage range of the DC bus 350V to 980V, that is, the voltage range of the first end of the first power conversion circuit 101 overlaps with the voltage range of the second end. Therefore, in an embodiment of the present application, 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 pass-through mode to effectively reduce the switching loss of the first power conversion circuit 101.

[0094] Figure 8 The example in which the second power conversion circuit 102 includes two LLC power conversion circuits is used for illustration. It is understood that the second power conversion circuit 102 may also include two power conversion circuits of other topologies. Alternatively, the number n of power conversion circuits included in the second power conversion circuit 102 may also be greater than 2. Accordingly, the switch circuit 1021 may implement series-parallel switching of the n power conversion circuits.

[0095] Optionally, the switching transistors in the first power conversion circuit 101 and the second power conversion circuit 102 may be metal-oxide-semiconductor field-effect transistors (MOSFETs), or MOS transistors for short. Furthermore, the switching transistors may be N-type MOS transistors, i.e., NMOS transistors.

[0096] The following describes the closed-loop control process of the second power conversion circuit 102. As a first optional implementation, when the first power conversion circuit 101 operates in the pass-through mode, the first controller 103 can be used to adjust the duty cycle of the PWM signal output to the switch tube in the second power conversion circuit 102 based on the difference between the reference power at the first end of the first power conversion circuit 101 and the feedback power at the first end of the first power conversion circuit 101, so as to achieve closed-loop control of the power at the first end of the second power conversion circuit 102.

[0097] In this first implementation, the first controller 103 can detect the feedback power of the first end of the first power conversion circuit 101, that is, the actual power of the first end of the first power conversion circuit 101. The actual power is also called the actual value of the bus-side power of the first power conversion circuit 101. In addition, the first controller 103 can obtain a first difference by subtracting the reference power (also called the bus-side given power) of the first end of the first power conversion circuit 101 from the actual power, and adjust the duty cycle of the PWM signal output to the switch tube in the second power conversion circuit 102 based on the first difference to achieve closed-loop control of the second power conversion circuit 102, thereby making the actual power of the first end of the first power conversion circuit 101 reach or approach the reference power.

[0098] Example, reference Figure 8The first controller 103 can process the first difference using a PI controller and adjust the duty cycle of the PWM signal output to the switch 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 to adjust the duty cycle of the PWM signal. For example, other types of closed-loop controllers can be proportional (P) controllers, integral (I) controllers, or proportional-integral-derivative (PID) controllers.

[0099] As a second optional implementation, when the first power conversion circuit 101 operates in the pass-through mode, the first controller 103 may adjust the duty cycle of the PWM signal output to the switch tube in the second power conversion circuit 102 based on the difference between the reference power at the first end of the second power conversion circuit 102 and the feedback power at the first end of the second power conversion circuit 102, so as to achieve closed-loop control of the second power conversion circuit 102. The reference power at the first end of the second power conversion circuit 102 may be determined based on the difference between the reference power at the first end of the first power conversion circuit 101 and the power loss value of the first power conversion circuit 101.

[0100] It is understandable that the first power conversion circuit 101 will also generate certain losses when transmitting power in the direct-through mode, and the first controller 103 can detect the power loss value of the first power conversion circuit 101. For example, the first controller 103 can determine the power loss value of the first power conversion circuit 101 by detecting the difference in power between the two ends of the first power conversion circuit 101 when the first power conversion circuit 101 operates in the direct-through mode. In addition, 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 at 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.

[0101] Furthermore, in this second implementation, the first controller 103 can detect the feedback power of the first end of the second power conversion circuit 102, that is, the actual power of the first end of the second power conversion circuit 102. Thereafter, the first controller 103 can perform a subtraction between the reference power of the first end of the second power conversion circuit 102 and the feedback power (that is, the actual power) of the first end of the second power conversion circuit 102 to obtain a second difference, and adjust the duty cycle of the PWM signal output to the switch tube in the second power conversion circuit 102 based on the second difference to achieve closed-loop control of the second power conversion circuit 102. In this way, the actual power of the second power conversion circuit 102 can reach or approach the reference power of the first end of the second power conversion circuit 102, thereby making the actual power of the first end of the first power conversion circuit 101 reach or approach the reference power.

[0102] As described above, when the first power conversion circuit 101 operates in a non-through mode, such as in a buck mode or a boost mode, the first controller 103 can generate a pulse for the switch tube in the second power conversion circuit 102 according to a constant duty cycle. In an embodiment of the present application, when the first power conversion circuit 101 operates in a non-through mode, the closed-loop control parameters of the first controller 103 (such as the control parameters of the 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 difference or the second difference) can be greater than the constant duty cycle. At this time, the first controller 103 can perform open-loop control on the switch tube in the second power conversion circuit 102 according to a smaller duty cycle (i.e., a constant duty cycle).

[0103] When the first power conversion circuit 101 operates in the pass-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) is less than the constant duty cycle. For example, when the first power conversion circuit 101 operates in the pass-through mode and the feedback power (such as the feedback power of the first end 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 on the switch tube in the second power conversion circuit 102 according to the smaller duty cycle (i.e., the duty cycle determined based on the first difference or the second difference). Or it can be understood that the first controller 103 can take over the power control of the first end of the first power conversion circuit 101.

[0104] For example, it is assumed that the output out of the first controller 103 is the pulse width of the PWM signal (referred to as pulse width for short), and the output out satisfies: out = kp × err(t) + ki × ∑(err(t)). Wherein, err(t) is the difference between the reference power and the feedback power at time t (such as the first difference or the 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 circumstances, assuming that the energy storage system is in a charging condition, 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 above-mentioned constant duty cycle. For example, if the pulse width corresponding to the above-mentioned constant duty cycle is 0.5, then the output out of the first controller 103 is greater than 0.5. Accordingly, the pulse width (ie, 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. MIN represents a smaller value.

[0105] When the first power conversion circuit 101 operates in the pass-through mode, the current in the first power conversion circuit 101 is in an uncontrollable state, resulting in the feedback power fdb being 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., a value 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 bus side power of the first power conversion circuit 101. It can be understood that since the feedback power fdb is small at this time, it will not cause damage to the components in the system.

[0106] 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 less than or equal to 0.5. Accordingly, the first controller 103 can output a PWM signal to the switch in the second power conversion circuit 102 based on its calculated output out, thereby controlling the bus-side power of the first power conversion circuit 101. For example, the first controller 103 can first quickly lower the output out to a level less than or equal to 0.5 by adjusting kp×err(t). Then, through the integral ki×∑(err(t)), the PWM signal corresponding to the output out can control the bus-side power of the first power conversion circuit 101 to 3510W. This effectively prevents damage to the components of the first power conversion circuit 101 caused by excessive bus-side power.

[0107] Optionally, in the second implementation, the reference power P1 at the first end of the second power conversion circuit 102 determined by the first controller 103 may satisfy the following equation: P1 = P2 - P0 + ΔP. P2 is the reference power at the first end of the first power conversion circuit 101, P0 is the power loss value of the first power conversion circuit 101, and ΔP is a power margin. This power margin ΔP may be a fixed value pre-stored in the first controller 103. For example, this power margin ΔP may be an empirical value, and the value of this power margin ΔP may be positive.

[0108] By superimposing the power margin ΔP to obtain the reference power P1 at the first end of the second power conversion circuit 102, it is possible to prevent the reference power P1 at the first end of the second power conversion circuit 102 from being too small, which would result in a 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 the difference will be small, which may cause the power loop of the first controller 103 to erroneously take over, and the bus-side specified power of the first power conversion circuit 101 may not be achieved.

[0109] Optionally, the second controller 104 can also be used to perform closed-loop control of the voltage at the first end of the first power conversion circuit 101 according to the reference voltage at the first end of the first power conversion circuit 101 (i.e., the bus-side reference voltage) when the difference between the voltage at the first end of the first power conversion circuit 101 and the voltage at the second end of the first power conversion circuit 101 is greater than or equal to a threshold, or to perform closed-loop control of the power at the first end of the first power conversion circuit 101 according to the reference power at the first end of the first power conversion circuit 101 (i.e., the bus-side reference power).

[0110] Among them, reference Figure 8The second controller 104 performs closed-loop control on the voltage at the first end of the first power conversion circuit 101, which may mean that the second controller 104 adjusts the duty cycle of the PWM signal output to the switching tube in the first power conversion circuit 101 according to the difference between the reference voltage at the first end of the first power conversion circuit 101 (i.e., the bus-side reference voltage) and the actual voltage (i.e., the bus-side feedback voltage), so that the actual voltage at the first end of the first power conversion circuit 101 reaches or is close to the reference voltage at the first end of the first power conversion circuit 101.

[0111] Continue to refer Figure 8 The second controller 104 performs closed-loop control on the power of the first end of the first power conversion circuit 101, which may mean that the second controller 104 adjusts the duty cycle of the PWM signal output to the switch tube in the first power conversion circuit 101 according to the difference between the reference power of the first end of the first power conversion circuit 101 (i.e., the bus-side reference power) and the actual power (i.e., the bus-side feedback power), so that the actual power of the first end of the first power conversion circuit 101 (i.e., the bus-side feedback power) reaches or approaches the reference power of the first end of the first power conversion circuit 101.

[0112] Alternatively, as Figure 8 As shown, the second controller 104 can perform closed-loop control on the voltage of the first end of the first power conversion circuit 101 through the PI controller, and can perform closed-loop control on the power of the first end of the first power conversion circuit 101 through the PI controller.

[0113] Example, reference Figure 8 The first controller 103 may include two subtractors and two PI controllers. The first subtractor A1 is used to calculate the voltage difference between the bus-side reference voltage and the bus-side feedback voltage. The first PI controller PI_1 is used to determine the duty cycle of the PWM signal output to the switch in the first power conversion circuit 101 based on the voltage difference. The second subtractor A2 is used to calculate the power difference between the bus-side reference power and the bus-side feedback power. The second PI controller PI_2 is used to determine the duty cycle of the PWM signal output to the switch in the first power conversion circuit 101 based on the 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.

[0114] Furthermore, the two PI controllers (i.e., two PI control loops) can determine the duty cycle of the PWM signal ultimately output to the switch tube in the first power conversion circuit 101 by means of competition. The competition between the two PI controllers can mean that the larger or smaller value of the output values ​​of the two PI controllers (e.g., the duty cycle of the PWM signal) is used as the final output. For example, Figure 8As shown, the second controller 104 further includes a multiplexer MUX connected to the two PI controllers PI_1 and PI_2. The multiplexer MUX can output the output values ​​of the two PI controllers by taking the larger or smaller value.

[0115] Optionally, continue to refer to Figure 8 , the second controller 104 may also include a third subtractor A3 and a third PI controller PI_3. Moreover, in this scenario, the output values ​​of the first PI controller PI_1 and the second PI controller PI_2 may both be current values. The multiplexer MUX may take the larger or smaller current value output by the two PI controllers and output it as a reference current to the third subtractor A3. The third subtractor A3 is used to calculate the current difference between the reference current and the feedback current, and the third PI controller PI_3 is used to determine the duty cycle of the PWM signal output to the switch tube in the first power conversion circuit 101 based on the current difference. The feedback current may refer to the current of the inductor L1 in the first power conversion circuit 101. The third PI controller PI_3 is also called a current loop, or a current inner loop.

[0116] from Figure 8 It can be seen that the second controller 104 can also include a fourth subtractor A4 and a threshold comparator. Among them, the fourth subtractor A4 is used to calculate the difference between the feedback voltage of the first end of the first power conversion circuit 101 (that is, the actual value of the bus side voltage) and the feedback voltage of the second end (also called the actual value of the internal bus voltage). The threshold comparator can compare the difference (such as the absolute value of the difference) with the size of the threshold. If the difference is greater than or equal to the threshold, the second controller 104 can provide a PWM signal to the switch tube 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 can force the duty cycle of the PWM signal output to the switch tube in the first power conversion circuit 101 to be the duty cycle in the pass-through mode. For example, for Figure 5 In the first power conversion circuit 101 shown, the second controller 104 can control the duty cycle of the PWM signal output to the first switch tube S1 to be 1, and control the duty cycle of the PWM signal output to the second switch tube S2 to be 0.

[0117] The above description is based on the example that the closed-loop controllers in the second controller 104 are all PI controllers. It is understandable that the closed-loop controller in the second controller 104 can also adopt other types of closed-loop controllers. For example, a proportional (P) controller, an integral (I) controller, or a proportional integral differential (PID) controller can also be used. It is also understandable that the positions of the above-mentioned PI controllers can also be adjusted according to the situation. For example, the position of the third PI controller PI_3 (i.e., the current loop) can be interchanged with the first PI controller PI_1 (i.e., the voltage loop) or the second PI controller PI_2 (power loop). Alternatively, the third PI controller PI_3 can also be connected to the input side of the multiplexer MUX, that is, the multiplexer MUX can take the larger or smaller output value of the three PI controllers and output it.

[0118] In summary, an embodiment of the present application provides a DC / DC converter, in which the first power conversion circuit in the DC / DC converter can operate in a pass-through mode when the voltages at both ends thereof are relatively close. Thus, 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. Moreover, when the first power conversion circuit operates in the pass-through mode, the second controller can also perform closed-loop control of the power of the first end of the second power conversion circuit based on the reference power of the first end (i.e., the bus side) of the first power conversion circuit. Thus, the actual power of the first end (i.e., the bus side) of the first power conversion circuit can reach or approach the reference power, thereby achieving power control of the first end (i.e., the bus side) of the first power conversion circuit to avoid damage to the device caused by uncontrollable power.

[0119] In addition, it can be understood that by providing two cascaded power conversion circuits in the DC / DC converter, two-stage power conversion can be achieved, thereby effectively improving the power conversion range of the DC / DC converter and further improving the application flexibility of the DC / DC converter.

[0120] The present application also provides an energy storage system, such as Figure 1 and Figure 2 As shown, the energy storage system includes: an energy storage battery 00, and a DC / DC converter 10 as provided in the above embodiment. The second end 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 Figure 3 and Figure 5 The second end of the second power conversion circuit 102 is connected to the positive electrode BAT+ and the negative electrode BAT- of the energy storage battery 00. The DC / DC converter 10 is used to receive the reference power of the first end of the first power conversion circuit 101 sent by the inverter.

[0121] The present application also provides a solar storage system, such as Figure 2 As shown, the photovoltaic storage system includes an inverter 30 and an energy storage system as provided in the above embodiment. The inverter 30 is connected to the DC / DC converter 10 in the energy storage system via a DC bus and is configured to transmit a reference power at the first end of the first power conversion circuit 101 to the DC / DC converter 10.

[0122] The present application also provides another optical storage system, such as Figure 2 As shown, the photovoltaic storage system includes: an inverter 30, an energy storage battery 00 and a DC / DC converter 10. Figure 3 , the DC / DC converter 10 includes a first power conversion circuit 101 .

[0123] The first end of the first power conversion circuit 101 is connected to the DC end of the inverter 30 via the DC bus (BUS+, BUS-), and the second end of the first power conversion circuit 101 is connected to the energy storage battery 00. For example, the second end of the first power conversion circuit 101 can be directly connected to the energy storage battery 00. Or, as Figure 3 As shown, the DC / DC converter 10 further includes a second power conversion circuit 102 , and the second end of the first power conversion circuit 101 is connected to the positive electrode BAT+ and the negative electrode BAT− of the energy storage battery 00 through the second power conversion circuit 102 .

[0124] When the difference between the voltage at the first end of the first power conversion circuit 101 and the voltage at the second end of the first power conversion circuit 101 is smaller than a threshold, the first power conversion circuit 101 operates in the pass-through mode.

[0125] The inverter 30 is used to perform closed-loop control on the power at the DC end of the inverter 30 based on the reference power at the first end of the first power conversion circuit 101 and the reference power at the DC end of the inverter 30 when the first power conversion circuit 101 operates in the pass-through mode.

[0126] It is understandable that, in this embodiment, the DC / DC converter 10 may not include the second power conversion circuit 102, or the DC / DC converter 10 includes 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 a closed-loop control function 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 storage system, when the first power conversion circuit 101 operates in the pass-through mode, the inverter 30 can perform closed-loop control of the power at its DC end based on the reference power at the first end of the first power conversion circuit 101 and the reference power at the DC end of the inverter 30.

[0127] For example, reference Figure 2 and Figure 8 The inverter 30 includes a DC / DC converter 301 and a DC / AC converter 302. The DC end of the DC / DC converter 301 is connected to the DC end of the DC / AC converter 302 and to the DC bus. Accordingly, the DC end of the inverter 30 may refer to the DC end of the DC / DC converter 301 and the DC end of the DC / AC converter 302. Furthermore, when the first power conversion circuit 101 operates in direct-flow 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 end based on the reference power at the first end of the first power conversion circuit 101 and the reference power at its DC end. Since the DC / DC converter 301 in the inverter 30 is used to connect to the photovoltaic panel 20 and the DC / AC converter 302 is used to connect to the power grid 40, the above process can also be understood as: when the first power conversion circuit 101 operates in direct-flow mode, the PV side or the grid side takes over control of the power (i.e., current) on the DC bus of the photovoltaic storage system.

[0128] The following is an introduction to the control mode of the DC bus in the photovoltaic storage system. Figure 2 In the illustrated solar-to-energy storage system architecture, the DC / DC converter 301 within 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, the DC bus voltage level (magnitude) can be determined through competition between the photovoltaic panel 20, the energy storage system, and the power grid 40.

[0129] refer to Figure 9 , taking the DC / DC converter 10, DC / DC converter 301 and DC / AC converter 302 all adopting power loop control and voltage loop control as an example, the voltage control mode of the DC bus is explained. The scheduling controller in the inverter 30 can send the corresponding reference power and reference voltage to each of the above converters respectively. 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. Reference Figure 9The duty cycle output by the power control loop and voltage control loop can be increased or decreased by a multiplexer (MUX) and used as the duty cycle of the PWM signal ultimately output to the converter's switches. This allows each converter to achieve closed-loop control of its bus-side voltage and power.

[0130] The final voltage on the DC bus is determined based on the principle of "the stronger (larger capacity) controls the bus." Capacity refers to the charge and discharge capability, i.e., the power that can be output to or received from the DC bus. That is, for DC / DC converter 10, DC / DC converter 301, and DC / AC converter 302, if the target converter has the largest capacity, the DC bus voltage is controlled by the bus-side voltage of that target converter.

[0131] For example, assuming that access to the power grid 40 is not considered, and the power that the DC / DC converter 301 connected to the photovoltaic panel 20 can output to the DC bus is 2000 watts (W). At this time, if the energy storage system needs to receive the power generated by the photovoltaic panel 20 (i.e., it needs to charge the energy storage battery 00), the inverter 30 can control the voltage of the DC bus to 850V, and the reference voltage of the first end of the first power conversion circuit 101 sent by the scheduling 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 greater than 3500W, the reference power of the first end of the first power conversion circuit 101 sent by the scheduling controller in the inverter 30 to the DC / DC converter 10 can be 3500W. At this time, 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 2000W of the bus-side power of DC / DC converter 301. In addition, the DC bus voltage can be controlled to 835V by DC / DC converter 10 in the energy storage system with a larger capacity.

[0132] Based on the above analysis, it can be seen that the DC / DC converter 301 and the DC / AC converter 302 in the inverter 30 both have the functions of power loop control and voltage loop control. Therefore, in the energy storage system, when the first power conversion circuit 101 of the DC / DC converter 10 operates in the pass-through mode, the DC / DC converter 301 or the DC / AC converter 302 can also perform closed-loop control of the power at its DC end based on the reference power at the first end of the first power conversion circuit 101 and the reference power at its own DC end.

[0133] Optionally, the power control loop and the voltage control loop in each of the above-mentioned converters may be PI control loops, or other types of control loops, such as a proportional (P) control loop, an integral (I) control loop, or a proportional-integral-derivative (PID) control loop.

[0134] It can also be understood that, as described above, each converter in the DC / DC converter 301 and the DC / AC converter 302 will also receive the reference power of the DC end issued by the scheduling controller in the inverter 30. Accordingly, the DC / DC converter 301 and the DC / AC converter 302 can perform closed-loop control of the power of their DC ends based on the smaller value of the reference power received by themselves and the reference power of the first end of the first power conversion circuit 101. Among them, the reference power of the first end of the first power conversion circuit 101 can be determined based on the charging and discharging capability (also known as power limit) of the energy storage system. The reference power of the DC end of the DC / DC converter 301 can be determined based on the discharge capability of the photovoltaic panel. The reference power of the DC end of the DC / AC converter 302 can be determined based on the charging and discharging capability of the power grid.

[0135] Alternatively, the DC-side reference power sent by the dispatching controller in the inverter 30 to the DC / DC converter 301 can be determined based on the discharge capacity of the photovoltaic panel and the charge / discharge capacity of the energy storage system. For example, the smaller of the powers corresponding to the charge / discharge capacity of the two is taken as the reference power and sent to the DC / DC converter 301. Furthermore, the DC-side reference power sent by the dispatching controller in the inverter 30 to the DC / AC converter 302 can be determined based on the charge / discharge capacity of the power grid and the charge / discharge capacity of the energy storage system. For example, the smaller of the powers corresponding to the charge / discharge capacity of the two is taken as the reference power and sent to the DC / AC converter 302. This ensures that when the first power conversion circuit 101 in the energy storage system operates in the pass-through mode, the DC / DC converter 301 or the DC / AC converter 302 can effectively control the power on the DC bus to avoid damage to components caused by excessive power.

[0136] In summary, an embodiment of the present application provides a photovoltaic storage system, which includes an inverter, an energy storage battery, and a DC / DC converter. When the voltages at both ends of 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 a pass-through mode, which can effectively reduce the switching loss of the first power conversion circuit without affecting the power conversion performance of the first power conversion circuit. Moreover, when the first power conversion circuit operates in the pass-through mode, the inverter performs closed-loop control of the power at its DC end based on the reference power at the first end of the first power conversion circuit and the reference power at the DC end of the inverter, which can avoid device damage caused by uncontrollable DC bus power in the pass-through mode.

[0137] It is understandable that the DC / DC converter 10 provided in the embodiment of the present application can be applied to Figure 1 、 Figure 2 or Figure 8 The scenario shown can also be applied to other scenarios. For example, it can also be applied to energy storage converters in energy storage systems, also known as power conversion systems (PCS), or it can also be applied to battery energy optimizers in energy storage systems. Alternatively, it can also be applied to inverters or photovoltaic energy optimizers in the photovoltaic field, and accordingly, the DC power supply connected to the DC / DC converter 10 can be a photovoltaic panel. Alternatively, it can also be applied to on-board chargers (OBCs) in vehicle-mounted battery management systems, and accordingly, the DC power supply connected to the DC / DC converter 10 can be a power battery. Alternatively, it can also be applied to terminal fields or communication power supply fields, etc.

[0138] In the embodiments of the present application, the terms "first", "second" and "third" are used for descriptive purposes only and should not be understood as indicating or implying relative importance. The term "at least one" means one or more, and "a plurality" means two or more.

[0139] In the embodiments of this application, the term "and / or" is simply a description of the association relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this document generally indicates that the related objects are in an "or" relationship.

[0140] The above are merely optional embodiments of the present application, but the scope of protection of the present 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 such modifications or substitutions should be included in the scope of protection of this application. Therefore, the scope of protection of this application should be based on the scope of protection of the claims.

Claims

1. A DC / DC converter, characterized in that: The DC / DC converter comprises: a first power conversion circuit, a second power conversion circuit and a first controller; The first end of the first power conversion circuit is used to connect to the DC bus, the second end of the first power conversion circuit is connected to the first end of the second power conversion circuit, and the second end of the second power conversion circuit is used to connect to a DC power supply; When the difference between the voltage at the first end of the first power conversion circuit and the voltage at the second end of the first power conversion circuit is less than a threshold, the first power conversion circuit operates in a pass-through mode; The first controller is used to perform closed-loop control of the power of the first end of the second power conversion circuit based on the reference power of the first end of the first power conversion circuit when the first power conversion circuit operates in a pass-through 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 switch tube in the second power conversion circuit based on the difference between the reference power at the first end of the first power conversion circuit and the feedback power at the first end of the first power conversion circuit when the first power conversion circuit operates in the pass-through mode, so as to perform closed-loop control of the power at the first end 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 switch tube in the second power conversion circuit based on the difference between the reference power of the first end of the second power conversion circuit and the feedback power of the first end of the second power conversion circuit when the first power conversion circuit operates in the pass-through mode, so as to perform closed-loop control on the power of the first end of the second power conversion circuit; The reference power of the first end of the second power conversion circuit is determined based on the difference between the reference power of the first end 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, wherein the second controller is configured to: When the difference between the voltage at the first end of the first power conversion circuit and the voltage at the second end of the first power conversion circuit is greater than or equal to the threshold, the voltage at the first end of the first power conversion circuit is closed-loop controlled according to the reference voltage at the first end of the first power conversion circuit, or the power at the first end of the first power conversion circuit is closed-loop controlled according to the reference power at the first end 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 buck-boost circuit.

6. The DC / DC converter according to claim 5, characterized in that: The first power conversion circuit includes a first switch tube, a second switch tube and an inductor; The first electrode of the first switch tube is connected to the positive electrode of the DC bus as the positive electrode of the first end of the first power conversion circuit, and the second electrode of the first switch tube is connected to the first electrode of the second switch tube and one end of the first inductor respectively; The second electrode of the second switch tube is connected to the negative electrode of the DC bus as the negative electrode of the first end of the first power conversion circuit, and is connected to the negative electrode of the first end of the second power conversion circuit as the negative electrode of the second end of the first power conversion circuit; The other end of the first inductor is connected to the positive electrode of the first end of the second power conversion circuit as the positive electrode of the second end of the first power conversion circuit; The first power conversion circuit operates in a pass-through mode, including: the first switch tube is turned on, and the second switch tube is 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 switch circuit, a first LLC power conversion circuit and a second LLC power conversion circuit; One end of the switch 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 switch circuit is respectively connected to one end of the first LLC power conversion circuit and one end of the second LLC power conversion circuit; the other end of the first LLC power conversion circuit and the other end of the second LLC power conversion circuit serve as the second end of the second power conversion circuit and are used to connect the DC power supply; The first controller is also used 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 end 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 end of the first power conversion circuit.

9. An energy storage system, characterized in that: The energy storage system comprises: an energy storage battery, and a DC / DC converter according to any one of claims 1 to 8, wherein the second end of the 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 of the first end of the first power conversion circuit sent by the inverter.

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

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