A photovoltaic charging system based on MPPT buck-boost and isolated full-bridge

Abstract

This invention relates to the field of power electronic converter technology, specifically to a photovoltaic charging system based on MPPT buck-boost and isolated full-bridge converters. The system includes: an MPPT buck-boost converter with its input connected to a photovoltaic panel; an intermediate energy storage unit with its first input connected to the output of the MPPT buck-boost converter and its second input connected to an energy storage element; an isolated full-bridge converter with its input connected to the output of the intermediate energy storage unit and its output connected to a high-voltage battery pack; and a controller connected to the MPPT buck-boost converter, the intermediate energy storage unit, and the isolated full-bridge converter. This invention integrates MPPT buck-boost, intermediate energy storage, and an isolated full-bridge converter, and utilizes a controller for coordinated control to achieve photovoltaic maximum power point tracking and direct charging of the high-voltage battery pack, avoiding multiple energy conversion losses and improving efficiency and integration. Simultaneously, the energy storage element smooths out power fluctuations, ensuring system stability and high energy utilization.

Description

Technical Field

[0001] This invention relates to the field of power electronic converter technology, specifically to a photovoltaic charging system based on MPPT buck-boost and isolated full-bridge converters. Background Technology

[0002] Photovoltaic charging technology has broad application prospects in the field of auxiliary energy supply for new energy vehicles. Traditional solar charging systems typically consist of photovoltaic panels, a maximum power point tracking (MPPT) controller, and an energy storage battery. The MPPT controller improves the utilization efficiency of photovoltaic energy by tracking the maximum power point of the photovoltaic panels in real time.

[0003] In automotive applications, to charge high-voltage power battery packs, a common practice is to set up the photovoltaic MPPT charger and the on-board charger (OBC) as independent devices. The photovoltaic energy is converted into low-voltage electrical energy by the MPPT controller, and then charged to the high-voltage power battery through an independent boost or isolation converter.

[0004] However, existing technologies have the following significant drawbacks: 1) The photovoltaic MPPT charger and the on-board charger work in series as independent devices. The photovoltaic energy needs to go through two energy conversion processes: MPPT step-down conversion and independent step-up isolation. Multiple conversions reduce the overall efficiency of the system and increase the size and manufacturing cost of the equipment.

[0005] 2) Conventional MPPT controllers output low voltage levels, which cannot be directly adapted to the charging requirements of high-voltage power batteries. Additional boost or isolation circuits are required, which increases the complexity and integration difficulty of the system.

[0006] 3) Existing solutions lack intermediate energy storage buffers. When there are fluctuations in sunlight intensity or sudden changes in vehicle electrical load, the system cannot operate stably, and photovoltaic energy cannot be fully utilized, resulting in energy waste.

[0007] The above reasons together make it difficult for existing photovoltaic charging systems to meet the requirements of high efficiency, high integration, and high stability for vehicle applications. Summary of the Invention

[0008] To address the above technical problems, this invention provides a technical solution for a photovoltaic charging system based on MPPT buck-boost and isolated full-bridge.

[0009] The technical problem solved by this invention can be achieved by the following technical solutions: A photovoltaic charging system based on MPPT buck-boost and isolated full-bridge voltage conversion includes: The MPPT buck-boost converter has its input terminal connected to a photovoltaic panel. It is used to buck-boost the DC voltage output by the photovoltaic panel and track the maximum power point of the photovoltaic panel. An intermediate energy storage unit has a first input terminal connected to the output terminal of the MPPT buck-boost converter and a second input terminal connected to an energy storage element. The intermediate energy storage unit is used to store the electrical energy output by the MPPT buck-boost converter and to smooth out power fluctuations through the energy storage element. An isolated full-bridge converter is provided, wherein the input terminal of the isolated full-bridge converter is connected to the output terminal of the intermediate energy storage unit, and the output terminal of the isolated full-bridge converter is connected to the high-voltage battery pack. The converter is used to isolate and boost the DC voltage output by the intermediate energy storage unit to charge the high-voltage battery pack. The controller is connected to the MPPT buck-boost converter, the intermediate energy storage unit, and the isolated full-bridge converter, respectively, and is used to control the operating status of the MPPT buck-boost converter, the intermediate energy storage unit, and the isolated full-bridge converter.

[0010] Preferably, the MPPT buck-boost converter is connected to the photovoltaic panel via a photovoltaic input port, the photovoltaic input port having a first positive terminal and a first negative terminal, the first negative terminal being connected to analog ground; The MPPT buck-boost converter is a four-switch Buck-Boost topology, including: The first switching transistor has its drain connected to the first positive terminal and its gate connected to the first upper transistor drive signal terminal of the controller. The second switching transistor has its drain connected to the source of the first switching transistor, the source connected to the analog ground, and its gate connected to the first lower-side drive signal terminal of the controller. The third switching transistor has its drain connected to the intermediate energy storage unit as the output terminal of the MPPT buck-boost converter, and its gate connected to the second upper transistor drive signal terminal of the controller. The fourth switch has its drain connected to the source of the third switch, the source connected to reference ground, and its gate connected to the second lower drive signal terminal of the controller. A first inductor, wherein a first end of the first inductor is connected between the first switch and the second switch, and a second end is connected between the third switch and the fourth switch.

[0011] Preferably, the MPPT buck-boost converter further includes: The first fuse is connected between the first positive terminal of the photovoltaic input port and the drain of the first switching transistor; A first capacitor, the first end of which is connected to the connection node between the drain of the first switching transistor and the first fuse, and the second end of which is connected to the analog ground; The first resistor is connected between the drains of the second and fourth switching transistors.

[0012] Preferably, the intermediate energy storage unit includes: An intermediate energy storage port has a second positive terminal and a second negative terminal. The second positive terminal serves as the second input terminal of the intermediate energy storage unit and is connected to the energy storage element. The second negative terminal is connected to a reference ground. The internal bus node connects the output of the MPPT buck-boost converter and the input of the isolated full-bridge converter. The second fuse is connected between the internal bus node and the second positive terminal of the intermediate energy storage port; The second capacitor has a first end connected to the internal bus node and a second end connected to the reference ground. The third capacitor has its first end connected to the internal bus node and its second end connected to the reference ground.

[0013] Preferably, the energy storage element is an energy storage battery pack or a supercapacitor module.

[0014] Preferably, the isolated full-bridge converter includes: A full-bridge inverter circuit, wherein the input terminal of the full-bridge inverter circuit is connected to the output terminal of the intermediate energy storage unit; An isolation transformer, the primary side of which is connected to the output terminal of the full-bridge inverter circuit; A rectifier circuit, wherein the input terminal of the rectifier circuit is connected to the secondary side of the isolation transformer; An output filter circuit is provided, the input of which is connected to the output of the rectifier circuit. The output of the output filter circuit serves as the output of the isolated full-bridge converter and is connected to the high-voltage battery pack via the high-voltage power battery port.

[0015] Preferably, the full-bridge inverter circuit includes: The fifth switching transistor has its drain connected to the output terminal of the intermediate energy storage unit and its gate connected to the third upper transistor drive signal terminal of the controller. The sixth switch has its drain connected to the source of the fifth switch, the source connected to reference ground, and its gate connected to the third lower-side drive signal terminal of the controller. The seventh switch is connected to the output terminal of the intermediate energy storage unit by its drain and to the fourth upper switch drive signal terminal of the controller by its gate. The eighth switch has its drain connected to the source of the seventh switch, the source connected to the reference ground, and its gate connected to the fourth lower-side drive signal terminal of the controller. The connection node of the fifth and sixth switching transistors is connected to the first end of the primary side of the isolation transformer, and the connection node of the seventh and eighth switching transistors is connected to the second end of the primary side of the isolation transformer.

[0016] Preferably, the rectifier circuit includes: The first diode has its anode connected to the first terminal of the secondary side of the isolation transformer, and its cathode connected to the input terminal of the output filter circuit. The second diode has its anode connected to the second terminal of the secondary side of the isolation transformer, and its cathode connected to the input terminal of the output filter circuit. A third diode, wherein the anode of the third diode is connected to power ground and the cathode is connected to the anode of the first diode; A fourth diode, the anode of which is connected to the power ground, and the cathode of which is connected to the anode of the second diode.

[0017] Preferably, the controller supports multiple operating modes, specifically including: In the first operating mode, the controller samples the voltage and current of the photovoltaic panel, adjusts the duty cycle of each switching transistor in the MPPT buck-boost converter so that the photovoltaic panel operates at the maximum power point and stores the converted electrical energy in the intermediate energy storage unit. In the second operating mode, the controller samples the voltage and current of the high-voltage battery pack and controls the full-bridge inverter circuit in the isolated full-bridge converter through pulse width modulation to control the rate at which electrical energy is transferred from the intermediate energy storage unit to the high-voltage battery pack. The isolated full-bridge converter transfers the electrical energy of the intermediate energy storage unit to the high-voltage battery pack in a constant current or constant voltage manner according to the charging requirements of the high-voltage battery pack until charging is complete. In the third operating mode, the controller dynamically coordinates the operating states of the MPPT buck-boost converter and the isolated full-bridge converter based on the state of charge of the energy storage element.

[0018] Preferably, in the third operating mode, the controller specifically performs the following operations: When the state of charge of the energy storage element reaches a first preset threshold, the controller starts the isolated full-bridge converter to charge the high-voltage battery pack and controls the MPPT buck-boost converter to synchronously perform photovoltaic maximum power point tracking. When the photovoltaic input power is greater than the output power of the isolated full-bridge converter, the excess electrical energy is stored in the energy storage element; When the photovoltaic input power is less than the output power of the isolated full-bridge converter, electrical energy is released through the energy storage element to make up for the power difference; When the state of charge of the energy storage element drops to a second preset threshold, the controller shuts down the isolated full-bridge converter and controls the MPPT buck-boost converter to charge the energy storage element.

[0019] Beneficial effects: This invention integrates an MPPT buck-boost converter, an intermediate energy storage unit, and an isolated full-bridge converter, and utilizes a controller for coordinated control. This achieves direct tracking of the photovoltaic panel's maximum power point and wide-range buck-boost matching, avoiding the multiple energy conversion losses caused by the independent MPPT controller and on-board charger working in series in traditional solutions. This significantly improves the overall system efficiency and reduces size and cost. At the same time, the energy storage elements of the intermediate energy storage unit smooth out power fluctuations caused by light fluctuations and load changes, ensuring stable operation of the system under dynamic conditions. Furthermore, it enables photovoltaic energy to directly charge the high-voltage battery pack after single-stage isolation boosting, simplifying the system structure and improving integration and energy utilization. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the photovoltaic charging device structure of the present invention; Figure 2 This is a schematic diagram of the front-end circuit of the photovoltaic charging device of the present invention; Figure 3 This is a schematic diagram of the circuit of the photovoltaic charging device of the present invention. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0023] The present invention will be further described below using two parallel drive motors as an example, in conjunction with the accompanying drawings and specific embodiments, but this is not intended to limit the present invention.

[0024] Reference Figure 1This invention provides a photovoltaic charging system based on MPPT buck-boost and isolated full-bridge, comprising: MPPT step-up / step-down converter 1, the input terminal of which is connected to photovoltaic panel 5, is used to step up / down convert the DC voltage output by photovoltaic panel 5 and track the maximum power point of photovoltaic panel 5; Intermediate energy storage unit 2, the first input terminal of the intermediate energy storage unit 2 is connected to the output terminal of the MPPT buck-boost converter 1, and the second input terminal is connected to the energy storage element 10, for storing the electrical energy output by the MPPT buck-boost converter 1, and smoothing power fluctuations through the energy storage element 10; An isolated full-bridge converter 3 is provided, wherein the input terminal of the isolated full-bridge converter 3 is connected to the output terminal of the intermediate energy storage unit 2, and the output terminal of the isolated full-bridge converter 3 is connected to the high-voltage battery pack 6. The converter is used to isolate and boost the DC voltage output by the intermediate energy storage unit 2 to charge the high-voltage battery pack 6. Controller 4 is connected to MPPT buck-boost converter 1, intermediate energy storage unit 2 and isolated full-bridge converter 3 respectively, and is used to control the working status of MPPT buck-boost converter 1, intermediate energy storage unit 2 and isolated full-bridge converter 3.

[0025] Specifically, in this embodiment of the invention, to address the problems of low overall efficiency, poor scenario adaptability, and low energy utilization in existing photovoltaic charging systems due to the separation of front and rear stages and the lack of intermediate energy storage buffers, a highly integrated photovoltaic charging device is constructed by coupling and multiplexing a three-level topology of MPPT buck-boost converter 1, intermediate energy storage unit 2, and isolated full-bridge converter 3. This device utilizes intermediate energy storage unit 2 as the coupling voltage bus between the front and rear stages, and smooths photovoltaic power fluctuations through energy storage element 10. At the same time, a controller 4 is used to dynamically coordinate the working states of the front-end MPPT buck-boost converter 1 and the rear-end isolated full-bridge converter 3 according to the photovoltaic input power and the state of charge of energy storage element 10, so as to achieve dynamic energy balance and global efficiency optimization between the front and rear stages. This effectively avoids the efficiency loss caused by multiple independent conversions in traditional solutions, as well as the photovoltaic energy waste caused by the lack of intermediate buffer links, and achieves high efficiency, high integration, and high stability of the system.

[0026] In practical applications, the MPPT step-up / step-down converter 1 can be connected to a PV photovoltaic panel with a wide input voltage range of 15-100 volts DC, i.e., 15-100Vdc.

[0027] In a preferred embodiment of the present invention, the MPPT buck-boost converter 1 is connected to the photovoltaic panel 5 through the photovoltaic input port 7. The photovoltaic input port 7 has a first positive terminal PV+ and a first negative terminal PV-, and the first negative terminal PV- is connected to the analog ground AGND.

[0028] Specifically, in order to achieve a standardized electrical interface between the photovoltaic panel 5 and the MPPT step-up / step-down converter 1, and to ensure the sampling accuracy and anti-interference capability of the control signal, refer to Figure 2 In this embodiment of the invention, a photovoltaic input port 7 is used as the connection hub between the external photovoltaic panel 5 and the internal power circuit. The photovoltaic input port 7 adopts a dual-ended input structure, with its first positive terminal PV+ used to introduce the positive power current of the photovoltaic panel 5 and its first negative terminal PV- used to introduce the negative return current of the photovoltaic panel 5.

[0029] Furthermore, the first negative terminal PV- is directly connected to the analog ground AGND. By shorting the first negative terminal PV- to the analog ground AGND, the power circuit on the photovoltaic input side and the control reference ground of the system are unified at the same potential, avoiding common-mode interference introduced by the separation of power ground and control ground, thereby significantly improving the accuracy of the controller 4 in sampling the voltage and current of the photovoltaic panel.

[0030] Meanwhile, the photovoltaic input port 7 supports a wide input voltage range of 15V-100Vdc, which is compatible with photovoltaic panels 5 of different specifications and output voltage levels, and can effectively enhance the system's adaptability and plug-and-play capability in multi-light scenarios.

[0031] In a preferred embodiment of the present invention, the MPPT buck-boost converter 1 is a four-switch Buck-Boost topology, comprising: The first switching transistor Q1 has its drain connected to the first positive terminal PV+ and its gate connected to the first upper transistor drive signal terminal G1U of the controller 4. The second switch Q2 has its drain connected to the source of the first switch Q1, the source connected to the analog ground AGND, and its gate connected to the first lower drive signal terminal G1L of the controller 4. The third switch Q3, the drain of the third switch Q3 is connected to the intermediate energy storage unit 2 as the output terminal of the MPPT buck-boost converter 1, and the gate is connected to the second upper switch drive signal terminal G2U of the controller 4; The fourth switch Q4 has its drain connected to the source of the third switch Q3, the source connected to reference ground GND, and its gate connected to the second lower drive signal terminal G2L of the controller 4. A first inductor L1 has its first end connected between the first switch Q1 and the second switch Q2, and its second end connected between the third switch Q3 and the fourth switch Q4.

[0032] Specifically, considering that the output voltage of photovoltaic panel 5 fluctuates widely with changes in light intensity and temperature, while the voltage of intermediate energy storage unit 2 is relatively stable, in order to achieve efficient energy transfer whether the photovoltaic voltage is higher or lower than the intermediate energy storage voltage, refer to... Figure 2 In this embodiment of the invention, an MPPT buck-boost converter 1 is constructed using a four-switch Buck-Boost topology. This topology consists of four N-channel MOSFET switches (i.e., metal-oxide-semiconductor field-effect transistors) Q1, Q2, Q3, and Q4, and a first inductor L1. The four PWM drive signals G1U, G1L, G2U, and G2L output by the controller 4 independently control the on and off states of each switch.

[0033] Specifically, controller 4 dynamically adjusts the output state of the four drive signals based on the comparison result between the sampled voltage of photovoltaic panel 5 and the voltage of intermediate energy storage unit 2, thereby switching the working mode of the converter. Specifically: When the output voltage of the photovoltaic panel 5 is higher than the voltage of the intermediate energy storage unit 2, the controller 4 outputs a high level through the second upper transistor drive signal terminal G2U to keep the third switch Q3 constantly on, and outputs a low level through the second lower transistor drive signal terminal G2L to keep the fourth switch Q4 constantly off. At the same time, complementary drive signals are output through the first upper transistor drive signal terminal G1U and the first lower transistor drive signal terminal G1L to control the first switch Q1 and the second switch Q2 to conduct complementaryly. At this time, the circuit is equivalent to a Buck buck topology. Photovoltaic energy is transferred to the output terminal through the first switch Q1, the first inductor L1, and the third switch Q3, and the second switch Q2 provides the freewheeling path. When the output voltage of the photovoltaic panel 5 is lower than the voltage of the intermediate energy storage unit 2, the controller 4 outputs a high level through the first upper transistor drive signal terminal G1U to keep the first switch Q1 constantly on, and outputs a low level through the first lower transistor drive signal terminal G1L to keep the second switch Q2 constantly off. At the same time, it outputs complementary drive signals through the second upper transistor drive signal terminal G2U and the second lower transistor drive signal terminal G2L to control the third switch Q3 and the fourth switch Q4 to conduct complementaryly. At this time, the circuit is equivalent to a Boost topology. Photovoltaic energy is transferred to the output terminal through the first switch Q1, the first inductor L1, and the third switch Q3, and the fourth switch Q4 provides the energy storage path. When the output voltage of the photovoltaic panel 5 fluctuates near the voltage of the intermediate energy storage unit 2, the controller 4 outputs a set of complementary drive signals through the first upper transistor drive signal terminal G1U and the first lower transistor drive signal terminal G1L to control the first switch Q1 and the second switch Q2. At the same time, it outputs another set of complementary drive signals through the second upper transistor drive signal terminal G2U and the second lower transistor drive signal terminal G2L to control the third switch Q3 and the fourth switch Q4, so that the circuit works in Buck-Boost mode. The voltage is smoothly matched by adjusting the duty cycle of the two sets of PWM signals.

[0034] Under the above operating modes, the controller 4 samples the voltage and current of the photovoltaic panel 5 and uses the perturbation observation method or the conductivity increment method to adjust the duty cycle of the four drive signals in real time, so that the photovoltaic panel always works at the maximum power point and efficiently delivers the converted electrical energy to the intermediate energy storage unit 2.

[0035] In a preferred embodiment of the present invention, the MPPT buck-boost converter 1 further includes: The first fuse F1 is connected between the first positive terminal PV+ of the photovoltaic input port 7 and the drain of the first switching transistor Q1; The first capacitor C1 has its first end connected to the connection node between the drain of the first switch Q1 and the first fuse F1, and its second end connected to the analog ground AGND. The first resistor R1 is connected between the drains of the second switch Q2 and the fourth switch Q4.

[0036] Specifically, in order to better improve the reliability and control accuracy of MPPT buck-boost converter 1, refer to Figure 2 In this embodiment of the invention, auxiliary components such as input protection, filtering and current sampling are further integrated into the power circuit.

[0037] Specifically, firstly, a first fuse F1 is connected in series in the positive input path. When a short circuit or overcurrent fault occurs in the circuit, the first fuse F1 blows to cut off the input power supply and protect the subsequent switching transistors and load from damage. Next, a first capacitor C1 is connected in parallel between the back end of the first fuse F1 and the analog ground AGND. This first capacitor C1 serves as an input filter capacitor, which can filter out the high-frequency switching ripple in the DC voltage output by the photovoltaic panel 5, provide a stable input voltage for the MPPT buck-boost converter 1, and reduce the ripple component of the input current, thereby reducing the impact on the photovoltaic panel 5. Furthermore, a first resistor R1 is connected between the source of the second switch Q2 and the source of the fourth switch Q4. This first resistor R1 serves as a current sampling resistor, converting the current flowing through the first inductor L1 into a voltage signal for the controller 4 to acquire. The controller 4 detects the voltage across the first resistor R1 to obtain the amplitude and zero-crossing information of the current in the first inductor L1 in real time, thereby enabling peak current control, overcurrent protection, and judgment of intermittent conduction mode, thus improving the dynamic response speed and stability of MPPT control.

[0038] With the above-mentioned input protection, filtering and current sampling circuit configuration, the MPPT buck-boost converter 1 can operate reliably and stably over a wide input voltage range, providing the necessary hardware support for precise MPPT control.

[0039] In a preferred embodiment of the present invention, the intermediate energy storage unit 2 includes: The intermediate energy storage port 8 has a second positive terminal LV+ and a second negative terminal LV-. The second positive terminal LV+ is connected to the energy storage element 10 as the second input terminal of the intermediate energy storage unit 2, and the second negative terminal LV- is connected to the reference ground GND. The internal bus node LV_BAT+ connects the output of the MPPT buck-boost converter 1 and the input of the isolated full-bridge converter 3. The second fuse F2 is connected between the internal bus node LV_BAT+ and the second positive terminal LV+ of the intermediate energy storage port 8; The second capacitor C2 has its first end connected to the internal bus node LV_BAT+ and its second end connected to the reference ground GND. The third capacitor C3 has its first end connected to the internal bus node LV_BAT+ and its second end connected to the reference ground GND.

[0040] Specifically, in order to achieve decoupling and buffering of energy between the preceding and following stages, and to construct a stable DC bus voltage, refer to Figure 2 and Figure 3 In this embodiment of the invention, the intermediate energy storage unit 2 is designed with a combination of port access and internal busbar.

[0041] Specifically, firstly, an external energy storage element 10 is connected to the system through an intermediate energy storage port 8. The intermediate energy storage port 8 adopts a double-ended structure with a second positive terminal LV+ and a second negative terminal LV-. The second negative terminal LV- is directly connected to the reference ground GND, forming a current return path with the system ground. The second positive terminal LV+ serves as the positive terminal access point of the energy storage element 10, which is used to connect the energy storage element 10 in parallel to the internal energy bus.

[0042] Next, an internal bus node LV_BAT+ is used as the voltage bus for coupling between the front and rear stages. This internal bus node LV_BAT+ is connected to the output terminal of MPPT buck-boost converter 1 and the input terminal of isolated full-bridge converter 3, respectively. This allows the electrical energy output from the front stage and the electrical energy taken by the rear stage to converge at the same node, thereby directly coupling the front and rear stages electrically and avoiding the energy loss caused by multiple independent buses.

[0043] Furthermore, considering that the energy storage element 10 may generate a large current surge when connected or malfunctioning, a second fuse F2 is connected in series between the internal bus node LV_BAT+ and the second positive terminal LV+ of the intermediate energy storage port 8. This second fuse F2 melts when a short circuit or overcurrent occurs in the energy storage branch, disconnecting the energy storage element 10 from the bus and protecting the main power circuit on the bus side from damage, while not affecting the energy transfer between the MPPT buck-boost converter 1 and the isolated full-bridge converter 3.

[0044] In addition, a second capacitor C2 and a third capacitor C3 are connected in parallel between the internal bus node LV_BAT+ and the reference ground GND. The second capacitor C2 is located near the output terminal of the MPPT buck-boost converter 1 to filter out output voltage ripple generated by the switching action of the preceding stage, stabilizing the preceding stage output. The third capacitor C3 is located near the input terminal of the isolated full-bridge converter 3 to provide transient switching current for the subsequent inverter and suppress the propagation of subsequent stage switching noise to the bus. The two capacitors work together to keep the voltage at the internal bus node LV_BAT+ stable, providing a low-impedance coupling voltage bus between the preceding and following stages.

[0045] Through the above structural design, the intermediate energy storage unit 2 can converge the photovoltaic input, energy storage buffer and the power supply of the subsequent stage onto the same coupling voltage bus, thereby realizing the direct coupling and dynamic balance of energy between the preceding and following stages.

[0046] In a preferred embodiment of the present invention, the energy storage element 10 is an energy storage battery pack or a supercapacitor module.

[0047] Specifically, in order to meet the energy storage needs of different application scenarios, in this embodiment of the invention, the energy storage element 10 can be selected from energy storage devices such as energy storage battery packs or supercapacitor modules.

[0048] Among them, energy storage battery packs (such as 48V DC energy storage batteries) have high energy density and can provide energy buffering for a longer period of time; while supercapacitor modules have high power density and fast response speed, making them more suitable for compensation scenarios with frequent fluctuations or instantaneous high power. Both types of energy storage elements 10 can be connected to the system through the intermediate energy storage port 8, and users can flexibly configure them according to actual application needs.

[0049] In a preferred embodiment of the present invention, the isolated full-bridge converter 3 includes: A full-bridge inverter circuit 31, the input terminal of which is connected to the output terminal of the intermediate energy storage unit 2; Isolation transformer T1, the primary side of which is connected to the output terminal of the full-bridge inverter circuit 31; A rectifier circuit 32, the input terminal of which is connected to the secondary side of the isolation transformer T1; The output filter circuit 33 has its input terminal connected to the output terminal of the rectifier circuit 32. The output terminal of the output filter circuit 33 serves as the output terminal of the isolated full-bridge converter 3 and is connected to the high-voltage battery pack 6 through the high-voltage power battery port 9.

[0050] Specifically, in order to achieve isolated boost conversion from the low-voltage stable voltage (e.g., 48V) of the intermediate energy storage unit 2 to the high-voltage adjustable voltage (e.g., 300-800Vdc) of the high-voltage battery pack 6, refer to Figure 1 In this embodiment of the invention, an isolated full-bridge converter 3 is used as the subsequent energy conversion unit. The isolated full-bridge converter 3 inverts the DC voltage output from the intermediate energy storage unit 2 into a high-frequency square wave through a full-bridge inverter circuit 31, and then uses an isolation transformer T1 to achieve voltage level enhancement and electrical isolation between the primary and secondary sides. The high-frequency square wave is then restored to DC through a rectifier circuit 32, and finally, the high-frequency ripple component is filtered out by an output filter circuit 33 to obtain a smooth and stable DC power, which charges the high-voltage battery pack 6 through the high-voltage power battery port 9.

[0051] Furthermore, in order to establish a standardized high-voltage interface between the isolated full-bridge converter 3 and the external high-voltage battery pack 6, referring to... Figure 3 A high-voltage power battery port 9 is used as the output connector. The high-voltage power battery port 9 has a third positive terminal HV+ and a third negative terminal HV-. The third positive terminal HV+ is connected to the output terminal of the output filter circuit 33, and the third negative terminal HV- is connected to the power ground PGND, which is used to connect to the positive and negative terminals of the high-voltage battery pack 6.

[0052] Specifically, considering that the high-voltage battery pack 6 may experience short circuits, overloads, or other faults during charging, or that internal abnormalities in the battery pack may lead to current runaway, refer to Figure 3 A third fuse F3 is installed between the output terminal of the output filter circuit 33 and the third positive terminal HV+ of the high-voltage power battery port 9. The third fuse F3 is connected in series in the positive output path. When the output current exceeds the set threshold, F3 melts to cut off the charging circuit, protecting the isolated full-bridge converter 3 and the high-voltage battery pack 6 from overcurrent damage, thus improving the safety and reliability of the system.

[0053] The configuration of the high-voltage power battery port 9 and the third fuse F3 achieves a standardized interface and overcurrent protection function on the high-voltage output side, ensuring that the device can safely cut off the output under abnormal conditions and meet the safety specifications of the vehicle high-voltage electrical system.

[0054] In a preferred embodiment of the present invention, the full-bridge inverter circuit 31 includes: The fifth switch Q5 has its drain connected to the output terminal of the intermediate energy storage unit 2 and its gate connected to the third upper switch drive signal terminal G3U of the controller 4. The sixth switch Q6 has its drain connected to the source of the fifth switch Q5, the source connected to reference ground GND, and its gate connected to the third lower drive signal terminal G3L of the controller 4. The seventh switch Q7 has its drain connected to the output terminal of the intermediate energy storage unit 2 and its gate connected to the fourth upper-side drive signal terminal G4U of the controller 4. The eighth switch Q8 has its drain connected to the source of the seventh switch Q7, the source connected to the reference ground GND, and its gate connected to the fourth lower drive signal terminal G4L of the controller 4. The connection node of the fifth switch Q5 and the sixth switch Q6 is connected to the first end of the primary side of the isolation transformer T1, and the connection node of the seventh switch Q7 and the eighth switch Q8 is connected to the second end of the primary side of the isolation transformer T1.

[0055] Specifically, in order to convert the DC voltage output from the intermediate energy storage unit 2 into a high-frequency AC square wave to meet the operating requirements of the isolation transformer T1 and achieve voltage transformation and electrical isolation, refer to Figure 3 In this embodiment of the invention, a full-bridge inverter circuit 31 composed of four N-channel MOSFET switches (Q5, Q6, Q7, Q8) is used to invert DC energy.

[0056] In this structure, the fifth switch Q5 and the sixth switch Q6 form the first bridge arm, and the seventh switch Q7 and the eighth switch Q8 form the second bridge arm. These two bridge arms are connected in parallel between the output terminal of the intermediate energy storage unit 2 and the reference ground GND, forming a full-bridge topology. The gate of each switch receives four drive signals (G3U, G3L, G4U, G4L) output by the controller 4, thereby enabling independent control of the switch's on / off state.

[0057] Accordingly, during normal operation, controller 4 outputs a phase-shifted drive signal, which generates an alternating voltage on the primary side of the transformer through the alternating conduction of diagonal switches. Specifically: When the third upper transistor drive signal terminal G3U and the fourth lower transistor drive signal terminal G4L are at high level, the fifth switch Q5 and the eighth switch Q8 are turned on, and the current flows from the internal bus node LV_BAT+ of the intermediate energy storage unit 2 through the fifth switch Q5, the primary side of the isolation transformer T1, and the eighth switch Q8 back to the reference ground GND. When the fourth upper transistor drive signal terminal G4U and the third lower transistor drive signal terminal G3L are at high levels, the seventh switch Q7 and the sixth switch Q6 are turned on, with current flowing in opposite directions. The current flows from the internal bus node LV_BAT+ of the intermediate energy storage unit 2 through the seventh switch Q7, the primary side (reverse direction) of the isolation transformer T1, and the sixth switch Q6 back to the reference ground GND. Through this alternating conduction of the diagonal switches, a high-frequency square wave voltage with alternating positive and negative values ​​is generated across the primary side of the isolation transformer T1.

[0058] Next, the controller 4 samples the voltage and current of the high-voltage battery pack 6 and adjusts the duty cycle or frequency of the four drive signals in real time to control the amount of energy transferred to the secondary side, thereby realizing constant current or constant voltage charging mode.

[0059] Meanwhile, to prevent short circuits caused by simultaneous conduction of the upper and lower switches on the same bridge arm, the controller 4 sets a dead time between the third upper switch drive signal terminal G3U and the third lower switch drive signal terminal G3L, and between the fourth upper switch drive signal terminal G4U and the fourth lower switch drive signal terminal G4L, to ensure that the other switch is only turned on after one switch is completely turned off.

[0060] Through the design of the full-bridge inverter circuit 31, the DC voltage output by the intermediate energy storage unit 2 is efficiently converted into a high-frequency square wave, which can provide a foundation for the subsequent isolation boost and rectification stages, and at the same time realize the precise control of the charging power of the high-voltage battery pack 6.

[0061] In a preferred embodiment of the present invention, the rectifier circuit 32 includes: The first diode D1 has its anode connected to the first end of the secondary side of the isolation transformer T1, and its cathode connected to the input end of the output filter circuit 33. The second diode D2 has its anode connected to the second terminal of the secondary side of the isolation transformer T1, and its cathode connected to the input terminal of the output filter circuit 33. The third diode D3 has its anode connected to power ground PGND and its cathode connected to the anode of the first diode D1. The fourth diode D4 has its anode connected to the power ground PGND and its cathode connected to the anode of the second diode D2.

[0062] Specifically, in order to convert the high-frequency AC square wave output from the secondary side of isolation transformer T1 into a unidirectional pulsating DC, refer to Figure 3 In this embodiment of the invention, a full-bridge rectifier circuit 32 composed of four diodes D1, D2, D3, and D4 is used to rectify the secondary output of the isolation transformer T1.

[0063] Specifically, the secondary output of isolation transformer T1 is a high-frequency square wave voltage with alternating positive and negative values, as follows: When the voltage at the first terminal of the secondary side is higher than that at the second terminal, current flows out from the first terminal of the secondary side, is forward-biased by the first diode D1, and flows into the input terminal of the output filter circuit 33. After passing through the output filter circuit 33 and the high-voltage battery pack 6, the current flows to the power ground PGND. Then, it is forward-biased by the fourth diode D4 and flows back to the second terminal of the secondary side, forming a complete circuit. At this time, the second diode D2 and the third diode D3 are reverse-biased and turned off.

[0064] When the voltage at the second terminal of the secondary side is higher than that at the first terminal, current flows out from the second terminal of the secondary side, is forward-biased by the second diode D2, and flows into the input terminal of the output filter circuit 33. After passing through the output filter circuit 33 and the high-voltage battery pack 6, the current flows to the power ground PGND. Then, it is forward-biased by the third diode D3 and flows back to the first terminal of the secondary side, forming a complete circuit. At this time, the first diode D1 and the fourth diode D4 are reverse-biased and turned off.

[0065] Through the alternating conduction of the four diodes, a consistently positive pulsating DC voltage is obtained at the input of the output filter circuit 33, with a pulsating frequency twice that of the transformer switching frequency. This unidirectional pulsating DC voltage is then filtered out by the output filter circuit 33 to remove high-frequency ripple components, ultimately resulting in a smooth and stable DC charging voltage across the high-voltage battery pack 6.

[0066] In addition, the power ground PGND serves as the current return reference point on the high-voltage side and is electrically isolated from the reference ground GND on the low-voltage side through the isolation transformer T1, thereby ensuring safe isolation between the high-voltage power battery charging circuit and the low-voltage control circuit.

[0067] In addition, synchronous rectification can be used to construct the rectifier circuit 32, that is, four N-channel MOSFETs can replace the four diodes (D1, D2, D3, D4) mentioned above, and the controller 4 can synchronously drive the MOSFETs to turn on and off according to the polarity of the transformer secondary voltage. This synchronous rectification method can significantly reduce the conduction loss of the rectification stage and further improve the efficiency of the subsequent converter, which is especially suitable for high current output scenarios.

[0068] Through the design of the above rectifier circuit 32, the high-frequency AC energy output from the secondary side of the isolation transformer T1 is efficiently converted into DC energy, providing a stable and clean charging power supply for the high-voltage battery pack 6.

[0069] In a preferred embodiment of the present invention, the output filter circuit 33 is a Π-type filter, including a second inductor L2, a fourth capacitor C4, and a fifth capacitor C5, wherein: The first end of the second inductor L2 is connected to the output end of the rectifier circuit 32, and the second end of the second inductor L2 is connected to the high-voltage power battery port 9 as the output end of the isolated full-bridge converter 3. The first terminal of the fourth capacitor C4 is connected to the first terminal of the second inductor L2, and the second terminal of the fourth capacitor C4 is connected to power ground PGND. The first terminal of the fifth capacitor C5 is connected to the second terminal of the second inductor L2, and the second terminal of the fifth capacitor C5 is connected to the power ground PGND.

[0070] Specifically, in order to filter out the high-frequency switching ripple components in the pulsating DC output of the rectifier circuit 32 and provide a smooth and stable charging voltage for the high-voltage battery pack 6, refer to Figure 3 In this embodiment of the invention, a Π-type filter composed of a second inductor L2, a fourth capacitor C4, and a fifth capacitor C5 is used as the output filter circuit 33.

[0071] Specifically, the unidirectional pulsating DC voltage output by the rectifier circuit 32 contains significant ripple components of the switching frequency and its harmonics. This pulsating DC voltage is first filtered by the fifth capacitor C5. The fifth capacitor C5 is connected in parallel between the output terminal of the rectifier circuit 32 and the power ground PGND, providing a low-impedance bypass path for high-frequency ripple and suppressing the propagation of high-frequency noise to subsequent stages.

[0072] Next, the DC voltage that has undergone preliminary filtering passes through the second inductor L2. The second inductor L2 presents high impedance to the changing current, which hinders the sudden change of current, thereby further smoothing the current waveform and reducing the ripple amplitude.

[0073] Then, at the output of the second inductor L2, the fourth capacitor C4 performs a second bypass filter on the residual high-frequency ripple, so that the voltage finally applied across the high-voltage battery pack 6 is close to the ideal DC voltage.

[0074] Through the combined effect of the two-stage capacitor filtering of the above-mentioned Π-type filter and the energy storage smoothing of the first-stage inductor, the pulsating DC output of the rectifier circuit 32 is efficiently filtered out of high-frequency components, and finally a low-ripple, high-stability DC charging voltage is obtained at the high-voltage power battery port 9, thereby meeting the quality requirements of the high-voltage battery pack 6 for the charging power supply, so as to extend the service life of the battery.

[0075] In a preferred embodiment of the present invention, the controller 4 supports multiple operating modes, specifically including: In the first working mode, the controller 4 samples the voltage and current of the photovoltaic panel 5, adjusts the duty cycle of each switching transistor in the MPPT step-up / step-down converter 1 so that the photovoltaic panel 5 operates at the maximum power point, and stores the converted electrical energy in the intermediate energy storage unit 2. In the second operating mode, the controller 4 samples the voltage and current of the high-voltage battery pack 6 and controls the full-bridge inverter circuit 31 in the isolated full-bridge converter 3 through pulse width modulation to control the rate at which electrical energy is transferred from the intermediate energy storage unit 2 to the high-voltage battery pack 6. The isolated full-bridge converter 3 transfers the electrical energy of the intermediate energy storage unit 2 to the high-voltage battery pack 6 in a constant current or constant voltage manner according to the charging requirements of the high-voltage battery pack 6 until charging is complete. In the third operating mode, the controller 4 dynamically coordinates the operating states of the MPPT buck-boost converter 1 and the isolated full-bridge converter 3 according to the state of charge of the energy storage element 10. In the third operating mode, the controller 4 specifically performs the following operations: When the state of charge of the energy storage element 10 reaches the first preset threshold, the controller 4 starts the isolated full-bridge converter 3 to charge the high-voltage battery pack 6, and controls the MPPT buck-boost converter 1 to synchronously perform photovoltaic maximum power point tracking. When the photovoltaic input power is greater than the output power of the isolated full-bridge converter 3, the excess electrical energy is stored in the energy storage element 10; When the photovoltaic input power is less than the output power of the isolated full-bridge converter 3, electrical energy is released through the energy storage element 10 to make up for the power difference. When the state of charge of the energy storage element 10 drops to a second preset threshold, the controller 4 shuts down the isolated full-bridge converter 3 and controls the MPPT buck-boost converter 1 to charge the energy storage element 10.

[0076] Specifically, in order to achieve efficient and stable operation of the system under different lighting conditions and load requirements, in this embodiment of the invention, the controller 4 intelligently switches between the three operating modes by sampling the voltage and current of the photovoltaic panel 5, the voltage and current of the high-voltage battery pack 6, and the state of charge of the energy storage element 10. Specifically: In the first operating mode (i.e., photovoltaic MPPT charging mode), the system is in normal operation. The controller 4 samples the voltage and current of the photovoltaic panel 5 and uses maximum power point tracking algorithms such as perturbation and observation (P&O) or incremental conductance (INC) to adjust the duty cycle of the first switch Q1, the second switch Q2, the third switch Q3 and the fourth switch Q4 in the MPPT buck-boost converter 1 in real time, so that the photovoltaic panel 5 always outputs maximum power and stores all of this energy in the energy storage element 10 of the intermediate energy storage unit 2 to reserve energy for subsequent power replenishment.

[0077] In the second operating mode (i.e., power battery charging mode), when it is necessary to charge the high-voltage battery pack 6, the controller 4 controls the conduction sequence of the fifth switch Q5, the sixth switch Q6, the seventh switch Q7 and the eighth switch Q8 in the full-bridge inverter circuit 31 through the pulse width modulation (PWM) signal according to the sampled battery voltage and current, so as to adjust the energy transmitted to the secondary side of the isolation transformer T1, so that the isolated full-bridge converter 3 charges the high-voltage battery pack 6 in a constant current or constant voltage manner until charging is completed.

[0078] In the third operating mode (i.e., joint optimization and efficiency optimization mode), when there is sufficient sunlight and the photovoltaic power generation can meet the charging demand, the controller 4 dynamically coordinates the operation of the upstream and downstream stages according to the state of charge of the energy storage element 10. Specifically: The controller 4 monitors the state of charge of the energy storage element 10 in real time. When the state of charge (SOC) of the energy storage element 10 reaches the first preset threshold (e.g., 95%), the controller 4 starts the isolated full-bridge converter 3 to charge the high-voltage battery pack 6, and at the same time controls the MPPT buck-boost converter 1 to continue to perform photovoltaic maximum power point tracking so that the photovoltaic panel 5 always outputs maximum power.

[0079] During the charging process, if the photovoltaic input power is greater than the output power of the isolated full-bridge converter 3, the controller 4 will continue to store the excess electrical energy in the energy storage element 10; if the photovoltaic input power is less than the output power of the isolated full-bridge converter 3, the energy storage element 10 will release electrical energy to make up for the power difference, ensuring that the isolated full-bridge converter 3 can charge the high-voltage battery pack 6 with its maximum output capacity.

[0080] When the state of charge (SOC) of the energy storage element 10 drops to the second preset threshold (e.g., 50%), the controller 4 shuts down the isolated full-bridge converter 3, stops charging the high-voltage battery pack 6, and controls the MPPT buck-boost converter 1 to charge the energy storage element 10 alone until its SOC reaches the first preset threshold again.

[0081] Throughout the entire control process, the state of charge of the energy storage element 10 is always controlled between the first preset threshold and the second preset threshold to avoid overcharging or over-discharging.

[0082] Through the aforementioned multi-mode intelligent control strategy, this invention achieves coordinated operation and dynamic energy balance between the front-end MPPT buck-boost converter 1 and the rear-end isolated full-bridge converter 3. This control strategy assumes that the front-end always operates at the photovoltaic maximum power point, targets the maximum output capacity of the rear-end, and uses the state of charge of the intermediate energy storage element 10 as the basis for regulation. This allows the system to automatically adjust its operating mode when photovoltaic power fluctuates or load changes, achieving global efficiency optimization rather than local optimization. This effectively solves the energy waste problem caused by light fluctuations or sudden load changes in traditional solutions, significantly improving the system's energy utilization and operational stability.

[0083] In summary, this invention constructs a highly integrated photovoltaic charging system through three-stage topology coupling and multiplexing of the MPPT buck-boost converter 1, intermediate energy storage unit 2, and isolated full-bridge converter 3. This system utilizes the intermediate energy storage unit 2 as the coupling voltage bus between the front and rear stages, and the energy storage element 10 smooths photovoltaic power fluctuations to achieve dynamic energy balance. Simultaneously, the controller 4 dynamically coordinates the operating modes of the front and rear stages based on the photovoltaic input power and the state of charge of the energy storage elements, ensuring that the front stage always tracks the photovoltaic maximum power point, and the rear stage efficiently charges the high-voltage battery pack. Therefore, this invention achieves direct coupling and multiplexing between the front and rear stages in its topology structure, rather than simple series connection, thus avoiding energy loss caused by multiple independent conversions.

[0084] Compared with the prior art, the present invention has the following significant effects: High integration and high efficiency: By sharing the same intermediate energy storage bus with the MPPT buck-boost converter 1 and the isolated full-bridge converter 3, three-level energy optimization management is achieved, reducing multiple energy conversion links between independent devices, significantly improving the overall system efficiency, and reducing size and manufacturing cost.

[0085] Strong adaptability to different scenarios: In this invention, the front-end MPPT buck-boost converter 1 adopts a four-switch Buck-Boost topology, supports a wide input voltage range of 15-100Vdc, and can be adapted to photovoltaic panels 5 of different specifications; the rear-end isolated full-bridge converter 3 supports a wide output voltage range of 300-800Vdc, and can directly charge various high-voltage power battery packs without the need for additional boost or isolation stages.

[0086] High energy utilization and stability: By introducing intermediate energy storage unit 2 as an energy buffer, the energy storage element 10 can smooth out the power difference when there are fluctuations in sunlight or sudden changes in load, ensuring that the front-end MPPT does not deviate from the maximum power point, so that photovoltaic energy can be fully utilized, thereby making the system operation more stable and reliable.

[0087] Intelligent control with optimal global efficiency: Controller 4 supports three operating modes and dynamically switches according to the state of charge of the energy storage element. In the joint optimization mode, the front and rear stages work together to make up the power difference through the charging and discharging of the energy storage element 10, effectively achieving optimal global efficiency rather than local efficiency, while ensuring that the energy storage element 10 is not overcharged or over-discharged.

[0088] High safety: The downstream stage adopts an isolated full-bridge converter 3, and the electrical isolation between the primary and secondary sides is achieved through the isolation transformer T1, which meets the safety specifications of the vehicle high-voltage system; at the same time, protective components such as fuses are set at each port to ensure that the system can safely cut off the power supply in abnormal conditions.

[0089] The above description is merely a preferred embodiment of the present invention and does not limit the implementation and protection scope of the present invention. Those skilled in the art should realize that any equivalent substitutions and obvious changes made based on the description and illustrations of the present invention should be included within the protection scope of the present invention.

Claims

1. A photovoltaic charging system based on MPPT buck-boost and isolated full-bridge, characterized in that, include: MPPT step-up converter (1), the input terminal of which is connected to photovoltaic panel (5), is used to step up and down the DC voltage output by photovoltaic panel (5) and track the maximum power point of photovoltaic panel (5); Intermediate energy storage unit (2), the first input terminal of the intermediate energy storage unit (2) is connected to the output terminal of the MPPT buck-boost converter (1), and the second input terminal is connected to the energy storage element (10), used to store the electrical energy output by the MPPT buck-boost converter (1) and smooth out power fluctuations through the energy storage element (10); An isolated full-bridge converter (3) is provided. The input terminal of the isolated full-bridge converter (3) is connected to the output terminal of the intermediate energy storage unit (2), and the output terminal of the isolated full-bridge converter (3) is connected to the high-voltage battery pack (6). The converter is used to isolate and boost the DC voltage output by the intermediate energy storage unit (2) to charge the high-voltage battery pack (6). The controller (4) is connected to the MPPT buck-boost converter (1), the intermediate energy storage unit (2) and the isolated full-bridge converter (3) respectively, and is used to control the working status of the MPPT buck-boost converter (1), the intermediate energy storage unit (2) and the isolated full-bridge converter (3).

2. The photovoltaic charging system based on MPPT buck-boost and isolated full-bridge as described in claim 1, characterized in that, The MPPT buck-boost converter (1) is connected to the photovoltaic panel (5) through the photovoltaic input port (7). The photovoltaic input port (7) has a first positive terminal (PV+) and a first negative terminal (PV-). The first negative terminal (PV-) is connected to the analog ground (AGND). The MPPT buck-boost converter (1) is a four-switch Buck-Boost topology, including: The first switch (Q1) has its drain connected to the first positive terminal (PV+) and its gate connected to the first upper drive signal terminal (G1U) of the controller (4). The drain of the second switch (Q2) is connected to the source of the first switch (Q1), the source is connected to the analog ground (AGND), and the gate is connected to the first lower drive signal terminal (G1L) of the controller (4). The third switch (Q3) has its drain connected to the intermediate energy storage unit (2) as the output terminal of the MPPT buck-boost converter (1), and its gate connected to the second upper tube drive signal terminal (G2U) of the controller (4). The fourth switch (Q4) has its drain connected to the source of the third switch (Q3), the source connected to reference ground (GND), and its gate connected to the second lower drive signal terminal (G2L) of the controller (4). The first inductor (L1) has its first end connected between the first switch (Q1) and the second switch (Q2), and its second end connected between the third switch (Q3) and the fourth switch (Q4).

3. A photovoltaic charging system based on MPPT buck-boost and isolated full-bridge as described in claim 2, characterized in that, The MPPT buck-boost converter (1) also includes: The first fuse (F1) is connected between the first positive terminal (PV+) of the photovoltaic input port (7) and the drain of the first switching transistor (Q1); The first capacitor (C1) has its first end connected to the connection node between the drain of the first switch (Q1) and the first fuse (F1), and its second end connected to the analog ground (AGND). The first resistor (R1) is connected between the drains of the second switch (Q2) and the fourth switch (Q4).

4. A photovoltaic charging system based on MPPT buck-boost and isolated full-bridge as described in claim 1, characterized in that, The intermediate energy storage unit (2) includes: The intermediate energy storage port (8) has a second positive terminal (LV+) and a second negative terminal (LV-). The second positive terminal (LV+) is connected to the energy storage element (10) as the second input terminal of the intermediate energy storage unit (2), and the second negative terminal (LV-) is connected to the reference ground (GND). The internal bus node (LV_BAT+) connects the output of the MPPT buck-boost converter (1) and the input of the isolated full-bridge converter (3); The second fuse (F2) is connected between the internal bus node (LV_BAT+) and the second positive terminal (LV+) of the intermediate energy storage port (8); The second capacitor (C2) has its first end connected to the internal bus node (LV_BAT+) and its second end connected to the reference ground (GND). The third capacitor (C3) has its first end connected to the internal bus node (LV_BAT+) and its second end connected to the reference ground (GND).

5. A photovoltaic charging system based on MPPT buck-boost and isolated full-bridge as described in claim 4, characterized in that, The energy storage element (10) is an energy storage battery pack or a supercapacitor module.

6. A photovoltaic charging system based on MPPT buck-boost and isolated full-bridge as described in claim 1, characterized in that, The isolated full-bridge converter (3) includes: A full-bridge inverter circuit (31) is provided, the input of which is connected to the output of the intermediate energy storage unit (2). An isolation transformer (T1) is provided, the primary side of which is connected to the output terminal of the full-bridge inverter circuit (31). A rectifier circuit (32), the input of which is connected to the secondary side of the isolation transformer (T1); The output filter circuit (33) is connected to the output of the rectifier circuit (32) and the output of the output filter circuit (33) serves as the output of the isolated full-bridge converter (3). It is connected to the high-voltage battery pack (6) through the high-voltage power battery port (9).

7. A photovoltaic charging system based on MPPT buck-boost and isolated full-bridge as described in claim 6, characterized in that, The full-bridge inverter circuit (31) includes: The fifth switch (Q5) has its drain connected to the output terminal of the intermediate energy storage unit (2) and its gate connected to the third upper tube drive signal terminal (G3U) of the controller (4). The sixth switch (Q6) has its drain connected to the source of the fifth switch (Q5), the source connected to reference ground (GND), and its gate connected to the third lower drive signal terminal (G3L) of the controller (4). The seventh switch (Q7) has its drain connected to the output terminal of the intermediate energy storage unit (2) and its gate connected to the fourth upper-side drive signal terminal (G4U) of the controller (4). The eighth switch (Q8) has its drain connected to the source of the seventh switch (Q7), the source connected to the reference ground (GND), and its gate connected to the fourth lower drive signal terminal (G4L) of the controller (4). The connection node of the fifth switch (Q5) and the sixth switch (Q6) is connected to the first end of the primary side of the isolation transformer (T1), and the connection node of the seventh switch (Q7) and the eighth switch (Q8) is connected to the second end of the primary side of the isolation transformer (T1).

8. A photovoltaic charging system based on MPPT buck-boost and isolated full-bridge as described in claim 6, characterized in that, The rectifier circuit (32) includes: The anode of the first diode (D1) is connected to the first end of the secondary side of the isolation transformer (T1), and the cathode is connected to the input end of the output filter circuit (33). The anode of the second diode (D2) is connected to the second end of the secondary side of the isolation transformer (T1), and the cathode is connected to the input end of the output filter circuit (33). The third diode (D3) has its anode connected to power ground (PGND) and its cathode connected to the anode of the first diode (D1). The fourth diode (D4) has its anode connected to the power ground (PGND) and its cathode connected to the anode of the second diode (D2).

9. A photovoltaic charging system based on MPPT buck-boost and isolated full-bridge as described in claim 1, characterized in that, The controller (4) supports multiple operating modes, including: In the first working mode, the controller (4) samples the voltage and current of the photovoltaic panel (5), adjusts the duty cycle of each switch in the MPPT step-up / step-down converter (1) so that the photovoltaic panel (5) works at the maximum power point and stores the converted electrical energy in the intermediate energy storage unit (2). In the second working mode, the controller (4) samples the voltage and current of the high-voltage battery pack (6) and controls the full-bridge inverter circuit (31) in the isolated full-bridge converter (3) by pulse width modulation to control the rate at which electrical energy is transferred from the intermediate energy storage unit (2) to the high-voltage battery pack (6). The isolated full-bridge converter (3) transfers the electrical energy of the intermediate energy storage unit (2) to the high-voltage battery pack (6) in a constant current or constant voltage manner according to the charging requirements of the high-voltage battery pack (6) until the charging is completed. In the third working mode, the controller (4) dynamically coordinates the working states of the MPPT buck-boost converter (1) and the isolated full-bridge converter (3) according to the charge state of the energy storage element (10).

10. A photovoltaic charging system based on MPPT buck-boost and isolated full-bridge as described in claim 9, characterized in that, In the third operating mode, the controller (4) specifically performs the following operations: When the state of charge of the energy storage element (10) reaches the first preset threshold, the controller (4) starts the isolated full-bridge converter (3) to charge the high-voltage battery pack (6) and controls the MPPT buck-boost converter (1) to synchronously perform photovoltaic maximum power point tracking. When the photovoltaic input power is greater than the output power of the isolated full-bridge converter (3), the excess electrical energy is stored in the energy storage element (10). When the photovoltaic input power is less than the output power of the isolated full-bridge converter (3), electrical energy is released through the energy storage element (10) to make up for the power difference; When the state of charge of the energy storage element (10) drops to the second preset threshold, the controller (4) shuts down the isolated full-bridge converter (3) and controls the MPPT buck-boost converter (1) to charge the energy storage element (10).

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