Power converter

Abstract

The present application provides a power converter. By adding an MPPT circuit connected between an input of the power converter and a primary-side circuit, and by controlling the on / off states of switching transistors in the MPPT circuit and the primary-side circuit, when the power converter is connected to two photovoltaic modules connected in series, MPPT can be implemented for individual photovoltaic modules according to requirements. Moreover, when output currents of the two photovoltaic modules connected in series are the same, at least some of the switching transistors in the MPPT circuit can be directly turned off, and by controlling the on / off states of the switching transistors in the primary-side circuit, MPPT can be implemented for the entire connected photovoltaic modules, thereby improving working efficiency. In addition, by controlling the on / off states of the switching transistors in the MPPT circuit and the primary-side circuit, normal operation when an individual photovoltaic module is connected can also be achieved, thus solving the problem of compatibility.

Description

A power converter

[0001] Cross-references to related applications

[0002] This application claims priority to Chinese Patent Application No. 202411048114.3, filed on July 31, 2024, entitled "A Power Converter", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This invention relates to the field of power electronics technology, and more particularly to a power converter. Background Technology

[0004] Currently, with the global shortage of non-renewable energy and the increasing severity of environmental pollution, the application of photovoltaic power generation is becoming more and more widespread. Photovoltaic power generation converts the direct current generated by photovoltaic modules into alternating current through an inverter, and then connects it to the AC power grid or supplies it to loads.

[0005] In the current residential PV market, there are various microinverter solutions. Among these solutions, parallel connection of PV modules is the primary method. Parallel microinverters generally focus on power conversion of multiple PV modules individually, and the circuit topology of a single-stage resonant inverter (cycloconverter), especially with frequency conversion, is difficult to use in scenarios with multiple PV module inputs.

[0006] A single-stage resonant inverter is an isolated DC-AC circuit based on a resonant converter. Its circuit topology contains extremely simple components, achieving very high conversion efficiency, making it suitable for micro-inverter applications with a single photovoltaic module. When pursuing optimal efficiency, the single-stage resonant inverter operates in inverter mode, where its operating frequency is related to the AC voltage and varies non-linearly. This inverter mode is not suitable for scenarios with multiple photovoltaic modules as inputs. Generally, with multiple input ports, the operating frequency needs to be constant and non-resonant for easy control. When the voltage or current of photovoltaic modules is not constant due to illumination and shading conditions, simply connecting several photovoltaic modules in series or parallel with a single-port input makes it difficult to optimize each photovoltaic module. In other words, directly connecting photovoltaic modules in series / parallel cannot guarantee module-level maximum power point tracking (MPPT) for each individual photovoltaic module.

[0007] How to simplify the circuit structure of a single-stage resonant inverter while connecting multiple photovoltaic modules, and precisely control the MPPT of each photovoltaic module to achieve high efficiency and miniaturization of the single-stage resonant inverter has become a key focus for researchers in the industry. Summary of the Invention

[0008] This application provides a power converter for achieving precise control of the MPPT of each photovoltaic module.

[0009] In one aspect, this application provides a power converter, comprising: a transformer, a primary circuit, a secondary circuit, an MPPT circuit, and a controller. The power converter's inputs include a first positive input, a second positive input, a first negative input, and a second negative input. The first negative input and the second positive input are connected. The first positive input and the first negative input are used to connect to a photovoltaic module, and the second positive input and the second negative input are used to connect to another photovoltaic module or a storage battery. The primary circuit is connected between the power converter's inputs and the transformer. The primary circuit includes a first bridge arm and a second bridge arm connected in parallel. Both the first and second bridge arms include an upper bridge arm and a lower bridge arm. The two ends of the first and second bridge arms are respectively connected to the first positive input and the second negative input. The connection point between the upper and lower bridge arms of the first bridge arm is the midpoint of the first bridge arm, and the connection point between the upper and lower bridge arms of the second bridge arm is the midpoint of the second bridge arm. The secondary circuit is connected between the transformer and the power converter's output. The power converter's output is used to connect to the power grid or a load. The power converter is used to convert the direct current output from the photovoltaic module or storage battery into alternating current output to the power grid or load. The MPPT circuit is connected between the input and primary circuit of the power converter. The controller is used to control the MPPT circuit to perform maximum power point tracking on one photovoltaic module or another photovoltaic module.

[0010] The power converter provided in this application, by adding an MPPT circuit connected between the input and primary circuit of the power converter, and combining this with the control of the on / off states of the switching transistors in the MPPT circuit and the primary circuit, can achieve MPPT tracking for a single photovoltaic module when two series-connected photovoltaic modules are connected to the power converter, as needed. Furthermore, when the output currents of the two series-connected photovoltaic modules are the same (i.e., the difference between them is less than a set value), at least some of the switching transistors in the bridge arm of the MPPT circuit can be directly turned off, controlling the on / off state of the switching transistors in the primary circuit, thus achieving MPPT tracking for the entire connected photovoltaic module and improving operating efficiency. In addition, by adding the MPPT circuit and controlling the on / off states of the switching transistors in the MPPT circuit and the primary circuit, normal operation can also be achieved when a single photovoltaic module is connected, solving compatibility issues.

[0011] In some embodiments of this application, the MPPT circuit specifically includes: a third bridge arm and a fourth bridge arm, wherein the third bridge arm is connected between the first negative input and the midpoint of the first bridge arm, and the fourth bridge arm is connected between the second positive input and the midpoint of the second bridge arm; both the third bridge arm and the fourth bridge arm include two switching transistors with opposite freewheeling directions.

[0012] When the difference between the first current and the second current is greater than the set value, it indicates that MPPT tracking needs to be implemented for a single photovoltaic module. The controller then controls the third and fourth bridge arms to be in the working state. The working state is a state in which at least one switch in the bridge arm continuously switches between the on and off states. The first current is the output current of a photovoltaic module connected to the first positive input and the first negative input, and the second current is the output current of another photovoltaic module connected to the second positive input and the second negative input.

[0013] When only the first current is detected, the controller also controls the third and fourth bridge arms to be in the operating state, and controls the switch of the lower bridge arm in the primary circuit to be in the off state. When only the second current is detected, the controller also controls the third and fourth bridge arms to be in the operating state, and controls the switch of the upper bridge arm in the primary circuit to be in the off state. This ensures normal operation when a single photovoltaic module is connected, resolving compatibility issues.

[0014] In some embodiments of this application, the midpoint of the first bridge arm is connected to one end of the primary winding of the transformer, and the midpoint of the second bridge arm is connected to the other end of the primary winding of the transformer. The third and fourth bridge arms each include two switching transistors with opposite freewheeling directions connected in series.

[0015] The above embodiments have the following three operating conditions:

[0016] Under ideal operating conditions, i.e., when the first and second photovoltaic modules are unobstructed, and when the difference between the first and second currents is less than a set value, the controller controls all or part of the switching transistors in the bridge arm of the MPPT circuit to be in the off state. The controller can control the primary circuit to drive according to the complementary drive principle of the full-bridge circuit to achieve MPPT tracking of both the first and second photovoltaic modules.

[0017] If the first or second photovoltaic module deviates from its maximum power output state due to changes in environmental conditions or other factors, the MPPT circuit needs to activate to bring it back to its maximum power output state. For example, if the second photovoltaic module is shaded, its output current (the second current) decreases. If the second current is less than the first current and the difference between the two currents is greater than a set value, it indicates that the second photovoltaic module has deviated from its maximum power output state. In this case, the MPPT circuit needs to switch the bridge arm from the off state to the on state, meaning at least one switch in the bridge arm continuously switches between on and off states for MPPT tracking. Specifically, the upper bridge arm of the first and second bridge arms can be controlled to conduct complementaryly. When the upper bridge arm of the first bridge arm is on, the lower bridge arm of the fourth and second bridge arms can also be controlled to conduct complementaryly. Similarly, when the upper bridge arm of the second bridge arm is on, the lower bridge arm of the first bridge arm can be controlled to conduct complementaryly. By controlling the working state of the bridge arm in the MPPT circuit, the first photovoltaic module with a larger output current can be kept in the state of output current for a whole control cycle, while the second photovoltaic module with a smaller output current only outputs current for part of the time. The output current duration of the first photovoltaic module is longer than that of the second photovoltaic module, so as to reduce the difference in output current between the first and second photovoltaic modules.

[0018] Similarly, when the first photovoltaic module is shaded, its output current (i.e., the first current) decreases. This means that when the first current is less than the second current and the difference between the first and second currents is greater than a set value, it indicates that the first photovoltaic module has deviated from its maximum power output state. In this case, the MPPT circuit needs to switch its bridge arm from the off state to the operating state, meaning at least one switch in the bridge arm continuously switches between on and off states for MPPT tracking. Specifically, the lower bridge arm of the first bridge arm and the lower bridge arm of the second bridge arm can be controlled to conduct complementaryly. When the lower bridge arm of the first bridge arm is in the on state, the fourth bridge arm and the upper bridge arm of the second bridge arm can be controlled to conduct complementaryly. When the lower bridge arm of the second bridge arm is in the on state, the third bridge arm and the upper bridge arm of the first bridge arm can be controlled to conduct complementaryly.

[0019] Furthermore, the proportion of the time period during which only the first or second photovoltaic module outputs current within a control cycle can be adjusted based on the difference between the first and second currents. For example, when the second photovoltaic module is heavily shaded, the difference between the first and second currents is larger. In this case, the conduction time of the third and fourth bridge arms should be increased, i.e., the duty cycle of the switching transistors of the third and fourth bridge arms should be increased to increase the output current duration of the first photovoltaic module. Therefore, it can be considered that the conduction time of the switching transistors of the bridge arms in the MPPT circuit is positively correlated with the difference between the first and second currents.

[0020] If the power converter's input is connected to only one photovoltaic module, i.e., only the second current is detected, the upper bridge arm of the primary circuit can be controlled to be in the off state. Alternatively, if only the first current is detected, the lower bridge arm of the primary circuit can be controlled to be in the off state. Furthermore, the MPPT circuit's bridge arm is controlled to be in the active state. The active switch in the MPPT circuit's bridge arm can replace the off switch in the primary circuit, forming a full-bridge circuit with the active switch in the primary circuit. Driven according to the complementary drive principle, MPPT tracking of a single photovoltaic module is achieved.

[0021] Specifically, when only the first current is detected, the controller can control the lower arm of the first bridge arm and the lower arm of the second bridge arm to be in the off state, control the third bridge arm to be complementary to the upper arm of the first bridge arm, and control the fourth bridge arm to be complementary to the upper arm of the second bridge arm.

[0022] Specifically, when only the second current is detected, the controller can control the upper arm of the first bridge arm and the upper arm of the second bridge arm to be in the off state, control the third bridge arm to be complementary to the lower arm of the first bridge arm, and control the fourth bridge arm to be complementary to the lower arm of the second bridge arm.

[0023] In the embodiments of this application, the switching transistor that forms a current loop with the primary winding of the transformer and the DC power supply can also be phase-shifted and turned on.

[0024] In other embodiments of this application, both the third and fourth bridge arms include two sub-bridge arms connected in parallel. Each of the two parallel sub-bridge arms includes two switching transistors connected in series with opposite freewheeling directions. The connection point of the two switching transistors connected in series with opposite freewheeling directions is the midpoint of the corresponding sub-bridge arm. The two sub-bridge arms of the third bridge arm are connected in parallel between the first negative input and one end of the primary winding of the transformer. The midpoint of one sub-bridge arm of the third bridge arm is connected to the upper bridge arm of the first bridge arm, and the midpoint of the other sub-bridge arm of the third bridge arm is connected to the lower bridge arm of the first bridge arm. The two sub-bridge arms of the fourth bridge arm are connected in parallel between the second positive input and the other end of the primary winding of the transformer. The midpoint of one sub-bridge arm of the fourth bridge arm is connected to the upper bridge arm of the second bridge arm, and the midpoint of the other sub-bridge arm of the fourth bridge arm is connected to the lower bridge arm of the second bridge arm.

[0025] The above embodiments have the following three operating conditions:

[0026] Under ideal operating conditions, i.e., when the first and second photovoltaic modules are unobstructed, the difference between the first and second currents is less than a set value. Since the first and second photovoltaic modules are already at maximum power output, one switch in the sub-bridge arm of the MPPT circuit connected to the input of the power converter is turned off. The other switch in the sub-bridge arm, together with the switches in the primary circuit, can be driven and controlled according to the complementary drive principle of the full-bridge circuit to achieve MPPT tracking of both the first and second photovoltaic modules.

[0027] Specifically, when the difference between the first current and the second current is less than a set value, the switch in the third bridge arm connected between the upper bridge arm and the primary winding of the first bridge arm is controlled to conduct complementaryly with the lower bridge arm of the second bridge arm; the switch in the third bridge arm connected between the lower bridge arm and the primary winding of the first bridge arm is controlled to conduct complementaryly with the upper bridge arm of the second bridge arm; the switch in the fourth bridge arm connected between the upper bridge arm and the primary winding of the second bridge arm is controlled to conduct complementaryly with the lower bridge arm of the first bridge arm; and the switch in the fourth bridge arm connected between the lower bridge arm and the primary winding of the second bridge arm is controlled to conduct complementaryly with the upper bridge arm of the first bridge arm.

[0028] If the first photovoltaic (PV) module deviates from its maximum power output state due to changes in environmental conditions or other factors, the MPPT circuit needs to activate to bring it back to its maximum power output state. For example, if the second PV module is shaded, its output current (the second current) decreases. When the difference between the first and second currents exceeds a set value, it indicates that the second PV module has deviated from its maximum power output state. In this case, it's necessary to control one switch in the third arm of the MPPT circuit connected to the power converter input to be off, and another switch in the fourth arm connected to the power converter input to be off. Additionally, some switches in the MPPT circuit should be switched from off to active to perform MPPT tracking. At this time, the output voltages of the first PV module PV1 and the second PV2 can be the same or different. By controlling the operating state of each switching transistor in the MPPT circuit, the first photovoltaic module with a larger output current can be kept in the state of output current for a whole control cycle, while the second photovoltaic module with a smaller output current only outputs current for a part of the time. The output current duration of the first photovoltaic module is longer than that of the second photovoltaic module, so as to reduce the difference in output current between the first and second photovoltaic modules.

[0029] Similarly, when the first photovoltaic module is shaded, its output current, i.e., the first current, decreases. When the first current is less than the second current and the difference between the first current and the second current is greater than a set value, it indicates that the first photovoltaic module has deviated from its maximum power output state. It is necessary to control one switch in the third arm of the MPPT circuit connected to the input of the power converter to be turned off, control one switch in the fourth arm connected to the input of the power converter to be turned off, and enable some switches in the MPPT circuit to switch from the off state to the working state for MPPT tracking.

[0030] Furthermore, the proportion of the time period during which only the first photovoltaic module outputs current within a control cycle can be adjusted based on the difference between the first and second currents. For example, when the second photovoltaic module is heavily shaded, the difference between the first and second currents is larger. In this case, the on-time of the switching transistors in the third and fourth bridge arms should be increased, i.e., the duty cycle of the switching transistors in the third and fourth bridge arms should be increased to increase the output current duration of the first photovoltaic module. Therefore, it can be considered that the on-time of the switching transistors in the bridge arms of the MPPT circuit is positively correlated with the difference between the first and second currents.

[0031] If the power converter's input is connected to only one photovoltaic module, i.e., only the second current is detected, the upper bridge arm of the primary circuit can be controlled to be turned off. Alternatively, if only the first current is detected, the lower bridge arm of the primary circuit can be controlled to be turned off. Furthermore, the switch connected to the power converter's input in the third bridge arm of the MPPT circuit and the switch connected to the power converter's input in the fourth bridge arm can be controlled to be turned off. The other switches in the bridge arms can be either on or active. The active switch in the MPPT circuit can replace the upper or lower bridge arm in the primary circuit that is off, forming a full-bridge circuit with the active switch in the primary circuit. Driven according to the complementary drive principle, this achieves MPPT tracking of a single photovoltaic module.

[0032] In the embodiments of this application, the switching transistor that forms a current loop with the primary winding of the transformer and the DC power supply can also be phase-shifted and turned on.

[0033] In other embodiments of this application, in order to avoid the problem of short circuit in photovoltaic modules caused by incorrect terminal connection, a first switching transistor can be connected between the first negative input and the second positive input. The freewheeling direction of the first switching transistor is from the first negative input to the second positive input. It has the function of blocking the flow of current from the second positive input to the first negative input, which can effectively prevent the formation of short circuit current between the second positive input and the first negative input, and effectively avoid the risk of photovoltaic module fire caused by short circuit.

[0034] In this application, the first switching transistor also serves to improve safety when the power converter is powered off. Generally, the output voltage of a single photovoltaic module is relatively safe for users. However, when the output voltages of two photovoltaic modules are superimposed, the total output voltage is high, posing a certain threat to user safety. Specifically, in a circuit topology without the first switching transistor, when the power converter stops working, the user may be exposed to a high output voltage from one of the photovoltaic modules, which is the sum of the output voltages of the first and second photovoltaic modules. This could pose a safety threat to the user. However, in a circuit topology with the first switching transistor, by actively turning off the first switching transistor, the user can only be exposed to the output voltage of one of the first or second photovoltaic modules at most, greatly reducing the safety threat posed by excessive voltage.

[0035] In some embodiments of this application, one end of the first switch is connected to the first negative input, and the other end of the first switch is connected to the second positive input. One end of the third bridge arm is connected to the first negative input, and one end of the fourth bridge arm is connected to the second positive input; or, one end of the third bridge arm and one end of the fourth bridge arm are both connected to the first negative input; or, one end of the third bridge arm and one end of the fourth bridge arm are both connected to the second positive input.

[0036] In other embodiments of this application, a second switch may also be included, with the first and second switches connected in series between the first negative input and the second positive input; one end of the third bridge arm and one end of the fourth bridge arm are both connected to the connection point of the first and second switches.

[0037] In other embodiments of this application, the primary-side circuit may further include a first capacitor as a DC blocking capacitor. The first circuit is connected between the midpoint of the first bridge arm or the midpoint of the second bridge arm and the transformer. The first capacitor can reduce signal interference between the primary-side circuit and the transformer.

[0038] In other embodiments of this application, the power converter may further include an inductive device, with the secondary circuit connected in series with the inductive device and then connected to the transformer.

[0039] In other embodiments of this application, the secondary circuit includes a fifth bridge arm, which comprises an upper bridge arm and a lower bridge arm. The upper bridge arm includes two switching transistors with opposite freewheeling directions, and the lower bridge arm includes two switching transistors with opposite freewheeling directions. The connection point of the upper and lower bridge arms is connected in series with an inductive device and then connected to one end of the secondary winding of the transformer, or the connection point of the upper and lower bridge arms is connected to one end of the secondary winding of the transformer. The secondary circuit may also include a second capacitor and a third capacitor, which are connected in series and then in parallel with the fifth bridge arm. The connection point of the second and third capacitors is connected to the other end of the secondary winding of the transformer.

[0040] In other embodiments of this application, the secondary circuit may include a fifth bridge arm, which comprises an upper bridge arm and a lower bridge arm. The upper bridge arm includes two switching transistors with opposite freewheeling directions, and the lower bridge arm includes two switching transistors with opposite freewheeling directions. The connection point of the upper and lower bridge arms is connected in series with an inductive device and then connected to one end of the secondary winding of the transformer, or the connection point of the upper and lower bridge arms is connected to one end of the secondary winding of the transformer. The secondary circuit may also include a fifth capacitor, which is connected between the upper or lower bridge arm and the other end of the secondary winding of the transformer.

[0041] In other embodiments of this application, the secondary circuit includes a fifth and a sixth bridge arm connected in parallel. Each fifth and sixth bridge arm includes an upper half-bridge arm and a lower half-bridge arm. The upper half-bridge arm includes two switching transistors with opposite freewheeling directions, and the lower half-bridge arm includes two switching transistors with opposite freewheeling directions. The connection point of the upper and lower half-bridge arms of the fifth bridge arm is connected to one end of the secondary winding of the transformer after a series inductive device; alternatively, the connection point of the upper and lower half-bridge arms of the fifth bridge arm is connected to one end of the secondary winding of the transformer. The connection point of the upper and lower half-bridge arms of the sixth bridge arm is connected to the other end of the secondary winding of the transformer.

[0042] In other embodiments of this application, the secondary circuit includes a fifth, sixth, and seventh bridge arm connected in parallel. One end of each of the fifth, sixth, and seventh bridge arms is connected in series with an inductive device and then connected to one end of the secondary winding of the transformer; alternatively, one end of each of the fifth, sixth, and seventh bridge arms is connected to one end of the secondary winding of the transformer. The other end of each of the fifth, sixth, and seventh bridge arms is connected to the other end of the secondary winding of the transformer. Each of the fifth, sixth, and seventh bridge arms includes an upper half-bridge arm and a lower half-bridge arm. The upper half-bridge arm includes two switching transistors with opposite freewheeling directions, and the lower half-bridge arm includes a second capacitor. The connection points of the upper and lower half-bridge arms in the fifth, sixth, and seventh bridge arms are respectively connected to the output of the power converter. Attached Figure Description

[0043] Figure 1 is a schematic diagram of a photovoltaic system;

[0044] Figure 2 is a schematic diagram of a power converter provided in an embodiment of this application;

[0045] Figure 3a is the drive timing diagram of the power converter provided in Figure 2 under one operating condition;

[0046] Figure 3b is the drive timing diagram of the power converter provided in Figure 2 under another operating condition;

[0047] Figure 3c is the drive timing diagram of the power converter provided in Figure 2 under another operating condition;

[0048] Figure 4 is a schematic diagram of another structure of the power converter provided in an embodiment of this application;

[0049] Figure 5a is the drive timing diagram of the power converter provided in Figure 4 under one operating condition;

[0050] Figure 5b is the drive timing diagram of the power converter provided in Figure 4 under another operating condition;

[0051] Figure 5c is the drive timing diagram of the power converter provided in Figure 4 under another operating condition;

[0052] Figure 6a is a schematic diagram of another structure of the power converter provided in an embodiment of this application;

[0053] Figure 6b is a schematic diagram of the power converter provided in the embodiment of this application when it is misconnected;

[0054] Figure 7 is a schematic diagram of another structure of the power converter provided in an embodiment of this application;

[0055] Figure 8 is a schematic diagram of another structure of the power converter provided in an embodiment of this application;

[0056] Figure 9 is a schematic diagram of another structure of the power converter provided in the embodiment of this application;

[0057] Figure 10 is a schematic diagram of another structure of the power converter provided in an embodiment of this application;

[0058] Figure 11 is a schematic diagram of another structure of the power converter provided in an embodiment of this application;

[0059] Figure 12 is a schematic diagram of another structure of the power converter provided in an embodiment of this application;

[0060] Figure 13 is a schematic diagram of another structure of the power converter provided in an embodiment of this application;

[0061] Figure 14 is a schematic diagram of another structure of the power converter provided in the embodiment of this application. Detailed Implementation

[0062] To make the objectives, technical solutions, and advantages of this application clearer, a further detailed description of this application will be provided below in conjunction with the accompanying drawings. However, the exemplary embodiments can be implemented in various forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided to make this application more comprehensive and complete, and to fully convey the concept of the exemplary embodiments to those skilled in the art. The same reference numerals in the drawings denote the same or similar structures, and therefore repeated descriptions of them will be omitted. Terms describing position and direction as described in this application are illustrative based on the accompanying drawings, but changes may be made as needed, and all such changes are included within the scope of protection of this application. The accompanying drawings of this application are for illustrating relative positional relationships only and do not represent actual scale.

[0063] It should be noted that specific details are set forth in the following description to provide a full understanding of this application. However, this application can be implemented in many ways other than those described herein, and those skilled in the art can make similar extensions without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below. The following descriptions are preferred embodiments for carrying out this application; however, these descriptions are for the purpose of illustrating the general principles of this application and are not intended to limit the scope of this application. The scope of protection of this application shall be determined by the appended claims.

[0064] To facilitate understanding of the embodiments of this application, the relevant technologies involved in the embodiments of this application will be introduced first below.

[0065] The terminology used in the following embodiments is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. As used in the specification and appended claims of this application, the singular expressions “a,” “an,” and “the” are intended to also include expressions such as “one or more,” unless the context clearly indicates otherwise. It should also be understood that in the following embodiments of this application, “at least one” means one, two, or more.

[0066] References to "one embodiment" and similar terms used in this specification mean that one or more embodiments of this application include a particular feature, structure, or characteristic described in connection with that embodiment. Therefore, phrases such as "in one embodiment," "in some embodiments," and "in other embodiments" appearing in different parts of this specification do not necessarily refer to the same embodiment, but rather mean "one or more, but not all, embodiments," unless otherwise specifically emphasized. The terms "comprising," "having," and variations thereof mean "including, but not limited to," unless otherwise specifically emphasized.

[0067] Referring to Figure 1, a photovoltaic system generally includes photovoltaic modules and a power converter. In the embodiment shown in Figure 1, a micro-inverter is used as the power converter. The input of the micro-inverter is connected to the photovoltaic modules, which serve as a DC power source. The output of the micro-inverter is connected to the power grid / load via a power line. The micro-inverter acts as a power converter to convert the energy provided by the photovoltaic modules into AC power for output to the power grid or load.

[0068] Currently, the single-stage resonant dual active bridge (DAB) topology offers relatively better conversion efficiency, a simpler circuit structure, and requires fewer components. Therefore, the single-stage resonant DAB topology has a broader application prospect compared to other topologies. However, when using a DAB circuit topology in a power converter, directly connecting two photovoltaic modules in series with the converter prevents module-level MPPT optimization, meaning it cannot achieve IV scanning for a single photovoltaic module and is incompatible with operating conditions requiring only one photovoltaic module.

[0069] To address the above issues, this application improves the circuit topology of the power converter by adding an MPPT circuit. While leveraging the advantages of a simple and efficient resonant single-stage power converter circuit topology, it enables module-level MPPT optimization, i.e., IV scanning of a single photovoltaic module. Furthermore, it allows power conversion even when a single photovoltaic module is connected, thus resolving compatibility issues.

[0070] Referring to Figure 2, the power converter provided in this embodiment includes: a transformer T, a primary circuit, a secondary circuit, and an MPPT circuit. The primary circuit is connected between the input of the power converter and the transformer. The input of the power converter is used to connect to a DC power supply. The primary circuit is connected to the input of the power converter, that is, one end of the primary circuit is connected to the DC power supply and used to input DC voltage. The DC power supply can be at least one energy storage battery or at least one photovoltaic module. When the DC power supply is a photovoltaic module, the power converter is an inverter. The other end of the primary circuit is connected to the primary winding of the transformer T. The primary circuit is used to convert the input DC voltage into a high-frequency AC rectangular wave signal. The transformer T is specifically a high-frequency transformer with a turns ratio of 1:n. The transformer T is mainly used to realize voltage transformation and electrical isolation. The transformer T can be designed as a transformer with a secondary leakage inductance equal to Lr, so that the inductive device Lr connected in series with the secondary winding of the transformer T can be the secondary leakage inductance of the transformer T. Alternatively, the power converter can also include an inductive device Lr. That is, the transformer T can be designed as a high-frequency transformer with very low leakage inductance, with a separate inductive device Lr connected in series. The inductive device Lr can act as a resonant inductor and resonant capacitor to form a resonant element, which assists the transformer T in achieving soft-switching control. The secondary circuit is connected between the transformer T and the output of the power converter. The output of the power converter can output AC or DC power and is used to connect to the power grid or load. This power grid can be an AC power grid; the following description uses the connection of the power converter output to an AC power grid as an example. The secondary circuit is connected to the output of the power converter; one end of the secondary circuit outputs AC voltage, and the other end is connected to the secondary winding of the transformer. When an inductive device Lr is present, the other end of the secondary circuit is connected in series with the inductive device Lr. s The secondary winding of the transformer is then connected. The secondary circuit converts high-frequency AC rectangular wave signals into AC voltage outputs. The output of the secondary circuit can be connected to the power grid or a load. The primary circuit, transformer T, and secondary circuit of the power converter work together to convert DC power from a DC power source into AC power.

[0071] Specifically, in this application, the inputs of the power converter include a first positive input IN1+, a second positive input IN2+, a first negative input IN1-, and a second negative input IN2-. The first negative input IN1- and the second positive input IN2+ are connected, and the first positive input IN1+ and the second positive input IN2+ are used to connect to the positive terminal of the DC power supply. The first negative input IN1- and the second negative input IN2- are used to connect to the negative terminal of the DC power supply. The output of the power converter is used to connect to the power grid or a load. In a first application scenario, the power converter can be connected to two photovoltaic modules connected in series. Specifically, the first positive input IN1+ and the first negative input IN1- can be connected to one of the two photovoltaic modules connected in series, which is the first photovoltaic module PV1, and the second positive input IN2+ and the second negative input IN2- can be connected to the other of the two photovoltaic modules connected in series, which is the second photovoltaic module PV2. In the second application scenario, the power converter can be connected to only one photovoltaic (PV) module. For example, the first positive input IN1+ and the first negative input IN1- can be connected to one PV module, namely the first PV module PV1, while the second positive input IN2+ and the second negative input IN2- are idle and no PV module is installed. Alternatively, the first positive input IN1+ and the first negative input IN1- are idle and no PV module is installed, while the second positive input IN2+ and the second negative input IN2- are connected to one PV module, namely the second PV module PV2. Or, the first positive input IN1+ and the second negative input IN2- can be connected to one PV module, namely the first PV module PV1, while the second positive input IN2+ and the first negative input IN1- are idle and no PV module is installed. In other application scenarios, parts of the first PV module PV1 and the second PV module PV2 in the first application scenario are replaced with energy storage batteries. For example, the second positive input IN2+ and the second negative input IN2- are connected to energy storage batteries. For ease of explanation, the following descriptions all use the power converter connected to a PV module as an example.

[0072] In this application, the primary-side circuit is connected between the input of the power converter and the transformer T. The primary-side circuit can be a full-bridge circuit, that is, the primary-side circuit includes a first bridge arm M1 and a second bridge arm M2 connected in parallel. One end of the first bridge arm M1 and the second bridge arm M2 are connected to the first positive input IN1+, and the other end of the first bridge arm M1 and the second bridge arm M2 are connected to the second negative input IN2-. The first bridge arm M1 and the second bridge arm M2 can each include an upper bridge arm and a lower bridge arm. The connection point between the upper bridge arm and the lower bridge arm of the first bridge arm M1 is the midpoint of the first bridge arm M1. The midpoint of the first bridge arm M1 can be directly or indirectly connected to one end of the primary winding of the transformer T. The connection point between the upper bridge arm and the lower bridge arm of the second bridge arm M2 is the midpoint of the second bridge arm M2. The midpoint of the second bridge arm M2 can be directly or indirectly connected to the other end of the primary winding of the transformer T. Specifically, both the upper and lower bridge arms may include at least one switching transistor. For example, the first bridge arm M1 may include a first switching transistor S11a and a second switching transistor S12a, and the connection point of the first switching transistor S11a and the second switching transistor S12a may be the midpoint of the first bridge arm M1. The second bridge arm M2 may include a first switching transistor S11b and a second switching transistor S12b, and the connection point of the first switching transistor S11b and the second switching transistor S12b may be the midpoint of the second bridge arm M2.

[0073] In this embodiment, the MPPT circuit is connected between the input and the primary circuit of the power converter, and the MPPT circuit is used to perform maximum power point tracking on the first photovoltaic module or the second photovoltaic module.

[0074] Specifically, the MPPT circuit may include a third bridge arm M3 and a fourth bridge arm M4. The third bridge arm M3 is connected between the first negative input IN1- and the midpoint of the first bridge arm M1, and the fourth bridge arm M4 is connected between the second positive input IN2+ and the midpoint of the second bridge arm M2. Both the third bridge arm M3 and the fourth bridge arm M4 include at least two switching transistors with opposite freewheeling directions.

[0075] The power converter provided in this application, by adding an MPPT circuit connected between the input and primary circuit of the power converter, and combining this with the control of the on / off states of the switching transistors in the MPPT circuit and the primary circuit, can achieve MPPT tracking for a single photovoltaic module when two photovoltaic modules are connected to the power converter, as needed. Furthermore, when the output currents of the two photovoltaic modules are the same (i.e., the difference between them is less than a set value), all or part of the switching transistors in the bridge arm of the MPPT circuit can be directly turned off, controlling the on / off state of the switching transistors in the primary circuit, thus achieving overall MPPT tracking for the connected photovoltaic modules and improving operating efficiency. In addition, by adding the MPPT circuit and controlling the on / off states of the switching transistors in the MPPT circuit and the primary circuit, normal operation can also be achieved when a single photovoltaic module is connected, solving compatibility issues.

[0076] In this application, the switching transistors in the primary circuit and the MPPT circuit are both controlled by a controller, which sends control signals such as pulse width modulation (PWM) signals to each switching transistor in the primary circuit and the MPPT circuit.

[0077] When the difference between the first current and the second current is greater than a set value, the controller controls the third and fourth bridge arms to be in an operating state. The operating state involves at least one switch in the bridge arm continuously switching between on and off states. The first current is the output current of the first photovoltaic module connected to the first positive and first negative inputs, and the second current is the output current of the second photovoltaic module connected to the second positive and second negative inputs.

[0078] When only the first current is detected, the controller also controls the third and fourth bridge arms to be in the operating state, and controls the switch of the lower bridge arm in the primary circuit to be in the off state. When only the second current is detected, the controller also controls the third and fourth bridge arms to be in the operating state, and controls the switch of the upper bridge arm in the primary circuit to be in the off state. This ensures normal operation when a single photovoltaic module is connected, resolving compatibility issues.

[0079] The circuit topology and working principle of the power converter provided in this application are described below with reference to specific embodiments.

[0080] Referring to Figure 2, in some embodiments of this application, the midpoint of the first bridge arm M1 can be directly connected to one end of the primary winding of the transformer T, and the midpoint of the second bridge arm M2 can be directly connected to the other end of the primary winding of the transformer T. The third bridge arm M3 of the MPPT circuit may include a third switch S31a and a fourth switch S32a connected in series with opposite freewheeling directions, and the fourth bridge arm M4 of the MPPT circuit may include a third switch S31b and a fourth switch S32b connected in series with opposite freewheeling directions. Specifically, each switch can be defined as having two ports connected to the bridge arm, namely port 1 and port 2. When the switch is turned on, current can flow into port 1 and out of port 2, or vice versa; when the switch is in freewheeling state, current flows into port 2 and out of port 1. In the third bridge arm M3, port 1 of the third switch S31a can be connected to port 1 of the fourth switch S32a. Port 2 of the third switch S31a is connected to the first negative input IN1-, and port 2 of the fourth switch S32a is connected to the connection point of the first switch S11a and the second switch S12a. Alternatively, port 2 of the third switch S31a can be connected to port 2 of the fourth switch S32a. Port 1 of the third switch S31a is connected to the first negative input IN1-, and port 1 of the fourth switch S32a is connected to the connection point of the first switch S11a and the second switch S12a. Similarly, in the fourth bridge arm M4, port 1 of the third switch S31b can be connected to port 1 of the fourth switch S32b. Port 2 of the third switch S31b is connected to the connection point of the second positive input IN2+, and port 2 of the fourth switch S32b is connected to the connection point of the first switch S11b and the second switch S12b. Alternatively, port 2 of the third switch S31b can be connected to port 2 of the fourth switch S32b, port 1 of the third switch S31b can be connected to the second positive input IN2+, and port 1 of the fourth switch S32b can be connected to the connection point of the first switch S11b and the second switch S12b.

[0081] The working principle of the power converter shown in Figure 2 is described below.

[0082] For ease of explanation of the working principle of this embodiment, the output current of the first photovoltaic module PV1 connected to the first positive input IN1+ and the first negative input IN1- is denoted as the first current I1, the output current of the second photovoltaic module PV1 connected to the second positive input IN2+ and the second negative input IN2- is denoted as the second current I2, and the output voltages of the first photovoltaic module PV1 and the second photovoltaic module PV2 are denoted as U1 and U2, respectively. The first photovoltaic module PV1 and the first photovoltaic module PV2 are considered to have consistent module performance, that is, the first photovoltaic module PV1 and the second photovoltaic module PV2 have the same operating performance under the same environmental conditions.

[0083] Under ideal operating conditions, i.e., when the first photovoltaic module PV1 and the second photovoltaic module PV2 are unshaded (for example, when the light intensity and temperature of the first photovoltaic module PV1 and the second photovoltaic module PV2 are the same), the current-voltage characteristic curves (hereinafter referred to as IV curves) of the photovoltaic modules are the same. At this time, the first photovoltaic module PV1 and the second photovoltaic module PV2 have the same output current and output voltage, I1 equals I2, U1 equals U2, and both are in the maximum power output state, that is, the difference between the first current and the second current is less than the set value. Since the first photovoltaic module PV1 and the second photovoltaic module PV2 are already in the maximum power output state, the bridge arm in the MPPT circuit is in the off state, that is, the current cannot flow through the bridge arm. For example, referring to Figure 3a, the third switches S31a and S31b and the fourth switches S32a and S32b can all be in the off state, so that the third bridge arm M3 and the fourth bridge arm M4 are in the off state; or, only the fourth switches S32a and S32b need to be in the off state to ensure that the third bridge arm M3 and the fourth bridge arm M4 are in the off state. The states of the third switches S31a and S31b are not limited. For example, the third switches S31a and S31b can be in the on state or the working state. Specifically, the working state is the state in which the switches continuously switch between on and off. The primary-side circuit can be driven and controlled according to the complementary driving principle of the full-bridge circuit to achieve MPPT tracking of the first photovoltaic module PV1 and the second photovoltaic module PV2. For example, referring to Figure 3a, in the first bridge arm M1 of the primary side circuit, the upper and lower bridge arms, namely the first switch S11a and the second switch S12a, are complementaryly conducting. In the second bridge arm M2, the upper and lower bridge arms, namely the first switch S11b and the second switch S12b, are complementaryly conducting. The first switch S11a and the second switch S12b can be phase-shifted or simultaneously conducting. Complementary conduction of switch A and switch B means that when switch A is in the conducting state, switch B is in the off state, and when switch A is in the off state, switch B is in the conducting state. Furthermore, there can be a certain dead time between the switching states of switch A and switch B. This dead time can be dynamically adjusted according to the input and output voltages and frequencies to achieve optimal results. Phase-shifted conduction of switch A and switch B refers to a certain dead time when switch A and switch B switch switch A switch ...

[0084] If either the first photovoltaic module PV1 or the second photovoltaic module PV2 deviates from its maximum power output state due to changes in environmental conditions or other factors, the MPPT circuit needs to activate to bring either module back to its maximum power output state. The following explanation uses the example of the second photovoltaic module PV2 being shaded for further detail. After the second photovoltaic module PV2 is shaded, its output current, i.e., the second current I2, decreases. When the second current is less than the first current and the difference between the two currents is greater than a set value, it indicates that the second photovoltaic module PV2 has deviated from its maximum power output state. In this case, the MPPT circuit needs to switch its bridge arm from the off state to the active state, meaning the bridge arm continuously switches between on and off currents for MPPT tracking. Specifically, the upper arms of the first bridge arm M1 and the second bridge arm M2 can be controlled to conduct complementaryly. When the upper arm of the first bridge arm M1, i.e., the first switch S11a, is in the conducting state, the lower arms of the fourth bridge arm M4 and the second bridge arm M2, i.e., the second switch S12b, can be controlled to conduct complementaryly. When the upper arm of the second bridge arm M2, i.e., the first switch S11b, is in the conducting state, the third bridge arm M3 and the lower arm of the first bridge arm M1, i.e., the second switch S12a, can be controlled to conduct complementaryly. At this time, the output voltages of the first photovoltaic module PV1 and the second photovoltaic module PV2 can be the same or different.

[0085] For example, taking the signal timing diagram shown in Figure 3b as an example, a control cycle can be divided into four consecutive time periods. In time period t1, the upper arm of the second bridge arm M2, i.e., the first switch S11b, and the lower arm of the first bridge arm M1, i.e., the second switch S12a, are in the on state, while the third bridge arm M3 and the fourth bridge arm M4 are in the off state. The first photovoltaic module PV1 and the second photovoltaic module PV2 connected in series form a current loop with the primary winding of the transformer T, and the first photovoltaic module PV1 and the second photovoltaic module PV2 jointly output current. In time period t2, the upper arm of the second bridge arm M2, i.e., the first switch S11b, and the fourth switch S32a of the third bridge arm M3 are in the on state. The state of the third switch S31a is not limited. For example, the third switch S31a can be in the on state. The current of the first photovoltaic module PV1 forms a current loop with the primary winding of the transformer T, and only the first photovoltaic module PV1 outputs current. During time period t3, the upper arm of the first bridge arm M1 (i.e., the first switch S11a) and the lower arm of the second bridge arm M2 (i.e., the second switch S12b) are in the on state, while the third bridge arm M3 and the fourth bridge arm M4 are in the off state. The first photovoltaic module PV1 and the second photovoltaic module PV2 connected in series form a current loop with the primary winding of the transformer T, and the first photovoltaic module PV1 and the second photovoltaic module PV2 jointly output current. During time period t4, the upper arm of the first bridge arm M1 (i.e., the first switch S11a) and the fourth switch S32b of the fourth bridge arm M4 are in the on state, while the state of the third switch S31b is not limited. For example, the third switch S31b can be in the on state. The current of the first photovoltaic module PV1 forms a current loop with the primary winding of the transformer T, and only the first photovoltaic module PV1 outputs current. It can be seen that within one control cycle, the first photovoltaic module PV1 with a larger output current is always in the state of output current, while the second photovoltaic module PV2 with a smaller output current only outputs current during the time periods t1 and t3. The output current duration of the first photovoltaic module PV1 is longer than that of the second photovoltaic module PV2, so as to reduce the difference in output current between the first photovoltaic module PV1 and the second photovoltaic module PV2.

[0086] Similarly, when the first photovoltaic module PV1 is shaded, its output current, i.e., the first current I1, decreases. This means that when the first current is less than the second current and the difference between the first and second currents is greater than a set value, it indicates that the first photovoltaic module PV1 has deviated from its maximum power output state. Therefore, the MPPT circuit needs to switch its bridge arm from the off state to the working state, i.e., the bridge arm continuously switches between on and off currents for MPPT tracking. Specifically, the lower bridge arm of the first bridge arm M1 and the lower bridge arm of the second bridge arm M2 can be controlled to conduct complementaryly. When the lower bridge arm of the first bridge arm M1, i.e., the second switch S12a, is in the on state, the fourth bridge arm M4 and the upper bridge arm of the second bridge arm M2, i.e., the first switch S11b, can be controlled to conduct complementaryly. When the lower bridge arm of the second bridge arm M2, i.e., the second switch S12b, is in the on state, the third bridge arm M3 and the upper bridge arm of the first bridge arm M1, i.e., the first switch S11a, can be controlled to conduct complementaryly.

[0087] Furthermore, the proportions of time periods t2 and t4 within a control cycle can be adjusted based on the difference between the first and second currents. For example, when the second photovoltaic module PV2 is heavily shaded, the difference between the first and second currents is larger. In this case, the conduction time of the third bridge arm M3 and the fourth bridge arm M4 should be increased, i.e., the duty cycle of the switching transistors of the third bridge arm M3 and the fourth bridge arm M4 should be increased to increase the output current duration of the first photovoltaic module PV1. Therefore, it can be considered that the conduction time of the switching transistors of the bridge arms in the MPPT circuit is positively correlated with the difference between the first and second currents.

[0088] When the power converter's input is connected to only one photovoltaic module, i.e., when only the second current is detected, the upper bridge arm switch in the primary circuit can be controlled to be turned off. Similarly, when only the first current is detected, the lower bridge arm switch in the primary circuit can be controlled to be turned off. Furthermore, the MPPT circuit's bridge arm is controlled to be in an active state, meaning at least one switch in the bridge arm continuously switches between on and off states. The active bridge arm in the MPPT circuit can replace the upper or lower bridge arm in the primary circuit that is in an off state, forming a full-bridge circuit with the active upper or lower bridge arm in the primary circuit. Driven according to the complementary drive principle, this achieves MPPT tracking of a single photovoltaic module.

[0089] For example, when the first positive input IN1+ and the first negative input IN1- are in an idle state without any photovoltaic modules installed, only the second photovoltaic module PV2 is connected, meaning only the second current is detected. In the primary-side circuit, the upper arms of the first bridge arm M1 and the second bridge arm M2 are in a turned-off state, meaning the first switches S11a and S11b connected to the first positive input IN1+ are in a turned-off state. In the MPPT circuit, the third bridge arm M3 can replace the first switch S11a and complementarily conduct with the lower bridge arm of the first bridge arm M1, and the fourth bridge arm M4 can replace the first switch S11b and complementarily conduct with the lower bridge arm of the second bridge arm M2. For example, referring to FIG3c, the states of the fourth switches S32a and S32b are not limited. For example, the fourth switches S32a and S32b can be in the on state. The third switch S31a replaces the upper bridge arm of the first bridge arm M1, i.e., the first switch S11a, and is complementary to the lower bridge arm, i.e., the second switch S12a. The third switch S31b replaces the upper bridge arm of the second bridge arm M2, i.e., the first switch S11b, and is complementary to the lower bridge arm, i.e., the second switch S12b. The third switch S31a and the second switch S12b can be phase-shifted or simultaneously turned on.

[0090] Similarly, when the second positive input IN2+ and the second negative input IN2- are idle and no photovoltaic modules are installed, only the first photovoltaic module PV1 is connected, meaning only the first current is detected. In the primary circuit, the lower arm of the first bridge arm M1 and the lower arm of the second bridge arm M2 are in the off state, meaning the second switches S12a and S12b connected to the second negative input IN2- are in the off state. The third bridge arm M3 in the MPPT circuit can replace the second switch S12a and conduct complementaryly with the upper arm of the first bridge arm M1, and the fourth bridge arm M4 can replace the second switch S12b and conduct complementaryly with the upper arm of the second bridge arm M2.

[0091] Figures 3a, 3b, and 3c above are merely examples illustrating the driving timing of each switch in the MPPT circuit and the primary-side circuit under different operating conditions. The actual driving timing of the switch is not limited to the above timing.

[0092] Referring to Figure 4, in some other embodiments of this application, the midpoint of the first bridge arm M1 can be indirectly connected to one end of the primary winding of the transformer T, and the midpoint of the second bridge arm M2 can be indirectly connected to the other end of the primary winding of the transformer T. The third bridge arm M3 and the fourth bridge arm M4 of the MPPT circuit can each include two sub-bridge arms connected in parallel, namely the first sub-bridge arm and the second sub-bridge arm. The two sub-bridge arms of the third bridge arm M3 are connected in parallel between the first negative input IN1- and one end of the primary winding of the transformer T. Specifically, one end of both the first and second sub-bridge arms of the third bridge arm M3 is connected to the first negative input IN1-, and the other end of both the first and second sub-bridge arms of the third bridge arm M3 is connected to one end of the primary winding of the transformer T. The two sub-arms of the fourth bridge arm M4 are connected in parallel between the second positive input IN2+ and the other end of the primary winding of transformer T. Specifically, one end of the first and second sub-arms of the fourth bridge arm M4 is connected to the second positive input IN2+, and the other end of the first and second sub-arms of the fourth bridge arm M4 is connected to the other end of the primary winding of transformer T. Each of the two parallel sub-arms includes two switching transistors connected in series with opposite freewheeling directions. The connection point of the two switching transistors with opposite freewheeling directions is the midpoint of the corresponding sub-arm. The midpoint of one sub-arm of the third bridge arm M3 is connected to the upper bridge arm of the first bridge arm M1, and the midpoint of the other sub-arm of the third bridge arm M3 is connected to the lower bridge arm of the first bridge arm M1. The midpoint of one sub-arm of the fourth bridge arm M4 is connected to the upper bridge arm of the second bridge arm M2, and the midpoint of the other sub-arm of the fourth bridge arm M4 is connected to the lower bridge arm of the second bridge arm M2. Specifically, the first sub-arm of the third bridge arm M3 includes a third switch S31a and a fourth switch S32a connected in series with opposite freewheeling directions. The third switch S31a is connected to the first negative input IN1-, and the fourth switch S32a is connected to one end of the primary winding of the transformer T. The midpoint of the first sub-arm, i.e., the connection point of the third switch S31a and the fourth switch S32a, is connected to the upper bridge arm of the first bridge arm M1, i.e., the first switch S11a. The second sub-arm of the third bridge arm M3 includes a fifth switch S33a and a sixth switch S34a connected in series with opposite freewheeling directions. The fifth switch S33a is connected to the first negative input IN1-, and the sixth switch S34a is connected to the other end of the primary winding of the transformer T. The midpoint of the second sub-arm, i.e., the connection point of the fifth switch S33a and the sixth switch S34a, is connected to the lower bridge arm of the first bridge arm M1, i.e., the second switch S12a. The first sub-bridge arm of the fourth bridge arm M4 includes a third switch S31b and a fourth switch S32b connected in series with opposite freewheeling directions. The third switch S31b is connected to the second positive input IN2+, and the fourth switch S32b is connected to the other end of the primary winding of the transformer T. The midpoint of the first sub-bridge arm, which is the connection point of the third switch S31b and the fourth switch S32b, is connected to the upper bridge arm of the second bridge arm M2, which is the first switch S11b.The second sub-bridge arm of the fourth bridge arm M4 includes a fifth switch S33b and a sixth switch S34b connected in series with opposite freewheeling directions. The fifth switch S33b is connected to the second positive input IN2+, and the sixth switch S34b is connected to the other end of the primary winding of the transformer T. The midpoint of the second sub-bridge arm, which is the connection point of the fifth switch S33b and the sixth switch S34b, is connected to the lower bridge arm of the second bridge arm M2, which is the second switch S12b.

[0093] The working principle of the power converter shown in Figure 4 is described below.

[0094] Under ideal operating conditions, i.e., when the first photovoltaic module PV1 and the second photovoltaic module PV2 are unshaded (for example, when the first photovoltaic module PV1 and the second photovoltaic module PV2 receive the same light intensity and temperature), the current-voltage characteristic curves (hereinafter referred to as IV curves) of the photovoltaic modules are the same. At this time, the first photovoltaic module PV1 and the second photovoltaic module PV2 have the same output current and output voltage, I1 equals I2, U1 equals U2, and both are in the maximum power output state, that is, the difference between the first current and the second current is less than the set value. Since the first photovoltaic module PV1 and the second photovoltaic module PV2 are already in the maximum power output state, one switch in the subbridge arm of the MPPT circuit is in the off state. This switch is the switch connected to the first negative input IN1- or the second positive input IN2+.

[0095] For example, referring to Figure 5a, the third switches S31a and S31b are in the off state, and the fifth switches S33a and S33b are in the off state. The other switch in the sub-bridge arm can be in the working state or in the conducting state, and together with the switches in the primary circuit, they can be driven and controlled according to the complementary driving principle of the full-bridge circuit to achieve MPPT tracking of the first photovoltaic module and the second photovoltaic module. For example, referring to FIG5a, the upper bridge arms of the first bridge arm M1 of the primary side circuit, namely the first switch S11a and the fourth switch S32a, operate in similar states, and the lower bridge arms of the first bridge arm M1, namely the second switch S12a and the sixth switch S34a, operate in similar states. The first switch S11a and the fourth switch S32a are complementary to the second switch S12a and the sixth switch S34a in conducting. The upper bridge arms of the second bridge arm M2, namely the first switch S11b and the fourth switch S32b, operate in similar states, and the lower bridge arms of the second bridge arm M1, namely the second switch S12b and the sixth switch S34b, operate in similar states. The first switch S11b and the fourth switch S32b are complementary to the second switch S12b and the sixth switch S34b in conducting. Furthermore, the first switch S11a and the second switch S12b can be phase-shifted for conduction.

[0096] If the first photovoltaic module PV1 and the second photovoltaic module PV2 deviate from their maximum power output state due to changes in environmental conditions or other factors, the MPPT circuit needs to operate to bring them back to their maximum power output state. The following explanation uses the example of the second photovoltaic module PV2 being shaded for further detail. After the second photovoltaic module PV2 is shaded, its output current, i.e., the second current I2, decreases. That is, when the second current is less than the first current and the difference between the first and second currents is greater than a set value, it indicates that the second photovoltaic module PV2 has deviated from its maximum power output state. Therefore, it is necessary to keep one switch in the third bridge arm M3 connected to the first negative input IN1- in the off state, and one switch in the fourth bridge arm M4 connected to the second positive input IN1+ in the off state. Furthermore, some switches in the MPPT circuit should be switched from the off state to the operating or conducting state for MPPT tracking. Specifically, the third switches S31a and S31b of the third bridge arm M3 and the fourth bridge arm M4 can be controlled to be in the off state. The upper arm of the first bridge arm M1, namely the first switch S11a, the fourth switch S32a of the third bridge arm M3, and the sixth switch S34b of the fourth bridge arm M4, have the same operating state. The upper arm of the second bridge arm M2, namely the first switch S11b, the fourth switch S32b of the fourth bridge arm M4, and the sixth switch S34a of the third bridge arm M3, have the same operating state and are complementary to the above three switches in conduction. When the upper arm of the first bridge arm M1 (i.e., the first switch S11a), the fourth switch of the third bridge arm M3 (S32a), and the sixth switch of the fourth bridge arm M4 (S34b) are simultaneously turned on, the fifth switch of the fourth bridge arm M4 (S33b) and the lower arm of the second bridge arm M2 (S12b) can be controlled to conduct complementaryly. Similarly, when the upper arm of the second bridge arm M2 (i.e., the first switch S11b), the fourth switch of the fourth bridge arm M4 (S32b), and the sixth switch of the third bridge arm M3 (S34a) are simultaneously turned on, the fifth switch of the third bridge arm M3 (S33a) and the lower arm of the first bridge arm M1 (S12a) can be controlled to conduct complementaryly. In this case, the output voltages of the first photovoltaic module PV1 and the second photovoltaic module PV2 can be the same or different.

[0097] For example, taking the signal timing diagram shown in Figure 5b as an example, one control cycle can be divided into four consecutive time periods. During each time period, both the third switch S31a and S31b are in the off state. In time period t1, the first switch S11b, the fourth switch S32b, the sixth switch S34a, and the second switch S12a are in the on state. The first photovoltaic module PV1 and the second photovoltaic module PV2, connected in series, form a current loop with the primary winding of the transformer T, and both photovoltaic modules PV1 and PV2 output current. In time period t2, the first switch S11b, the fourth switch S32b, the sixth switch S34a, and the fifth switch S33a are in the on state. The current of the first photovoltaic module PV1 forms a current loop with the primary winding of the transformer T, and only the first photovoltaic module PV1 outputs current. During time period t3, the first switch S11a, the fourth switch S32a, the sixth switch S34b, and the second switch S12b are in the conducting state. The first photovoltaic module PV1 and the second photovoltaic module PV2, connected in series, form a current loop with the primary winding of the transformer T. The first photovoltaic module PV1 and the second photovoltaic module PV2 jointly output current. During time period t4, the first switch S11a, the fourth switch S32a, the sixth switch S34b, and the fifth switch S33b are in the conducting state. The current of the first photovoltaic module PV1 forms a current loop with the primary winding of the transformer T, and only the first photovoltaic module PV1 outputs current. It can be seen that within one control cycle, the first photovoltaic module PV1, which has a larger output current, is always outputting current, while the second photovoltaic module PV2, which has a smaller output current, only outputs current during time periods t1 and t3. The output current duration of the first photovoltaic module PV1 is longer than that of the second photovoltaic module PV2 to reduce the difference in output current between the first photovoltaic module PV1 and the second photovoltaic module PV2.

[0098] In practical applications, during the time periods t1 and t2, the first switch S11b and the fourth switch S32b can be turned on simultaneously, and are also phase-shifted connected with the sixth switch S34a. During the time periods t3 and t4, the first switch S11a and the fourth switch S32a can be turned on simultaneously, and the sixth switch S34b is also phase-shifted connected.

[0099] Similarly, when the first photovoltaic module PV1 is shaded, its output current, i.e., the first current I1, decreases. That is, when the first current is less than the second current and the difference between the first and second currents is greater than a set value, it indicates that the first photovoltaic module PV1 has deviated from its maximum power output state. Therefore, it is necessary to keep one switch in the third bridge arm M3 connected to the first negative input IN1- in the off state, and one switch in the fourth bridge arm M4 connected to the second positive input IN1+ in the off state. Furthermore, some switches in the MPPT circuit should be switched from the off state to the working or conducting state for MPPT tracking. Specifically, the fifth switches S33a and S33b of the third bridge arm M3 and the fourth bridge arm M4 can be controlled to be in the off state. The lower arms of the first bridge arm M1, namely the second switch S12a, the sixth switch S34a of the third bridge arm M3, and the fourth switch S32b of the fourth bridge arm M4, have the same operating state. The lower arms of the second bridge arm M2, namely the second switch S12b, the sixth switch S34b of the fourth bridge arm M4, and the fourth switch S32a of the third bridge arm M3, have the same operating state and are complementary to the above three switches in conduction. When the lower bridge arm of the first bridge arm M1 (i.e., the second switch S12a), the sixth switch S34a of the third bridge arm M3, and the fourth switch S32b of the fourth bridge arm M4 are simultaneously in the conducting state, the third switch S31b of the fourth bridge arm M4 and the upper bridge arm of the second bridge arm M2 (i.e., the first switch S11b) can be controlled to conduct complementaryly. When the lower bridge arm of the second bridge arm M2 (i.e., the second switch S12b), the sixth switch S34b of the fourth bridge arm M4, and the fourth switch S32a of the third bridge arm M3 are simultaneously in the conducting state, the third switch S31a of the third bridge arm M3 and the upper bridge arm of the first bridge arm M1 (i.e., the first switch S11a) can be controlled to conduct complementaryly.

[0100] Furthermore, the proportions of time periods t2 and t4 within a control cycle can be adjusted based on the difference between the first and second currents. For example, when the second photovoltaic module PV2 is heavily shaded, the difference between the first and second currents is larger. In this case, the conduction time of the third bridge arm M3 and the fourth bridge arm M4 should be increased, i.e., the duty cycle of the switching transistors of the third bridge arm M3 and the fourth bridge arm M4 should be increased to increase the output current duration of the first photovoltaic module PV1. Therefore, it can be considered that the conduction time of the switching transistors of the bridge arms in the MPPT circuit is positively correlated with the difference between the first and second currents.

[0101] If the power converter's input is connected to only one photovoltaic module, i.e., only the first current or only the second current is detected, the upper arm of the primary circuit can be controlled to be off, or the lower arm of the primary circuit can be controlled to be off. The switch connected to the first negative input IN1- in the third arm of the MPPT circuit can be controlled to be off, and the switch connected to the second positive input IN2+ in the fourth arm can be controlled to be off. For example, referring to Figure 5c, the third switches S31a and S31b are off, or the fifth switches S33a and S33b are off. Furthermore, the other switches in the MPPT circuit can be in an active or conducting state, forming a full-bridge circuit with the active upper or lower arm of the primary circuit, and driven according to a complementary driving principle to achieve MPPT tracking of a single photovoltaic module.

[0102] For example, when the second positive input IN2+ and the second negative input IN2- are idle and no photovoltaic modules are installed, only the first photovoltaic module PV1 is connected, meaning only the first current is detected. In the primary circuit, the lower arms of the first bridge arm M1 and the second bridge arm M2 are in the off state, meaning the second switches S12a and S12b connected to the second negative input IN2- are in the off state, and the third switches S31a and S31b of the third bridge arm M3 and the fourth bridge arm M4 are in the off state. Furthermore, the second sub-bridge arm of the third bridge arm M3 replaces the lower arm of the second bridge arm M2 and is complementaryly connected to the upper arm of the first bridge arm M1, i.e., the first switch S11a; similarly, the second sub-bridge arm of the fourth bridge arm M4 replaces the lower arm of the first bridge arm M1 and is complementaryly connected to the upper arm of the second bridge arm M2, i.e., the first switch S11b. For example, the fifth switches S33a and S33b can be in the ON state, and the sixth switches S34a and S34b can be in the OFF state; or, the fifth switches S33a and S33b can be in the OFF state, and the sixth switches S34a and S34b can be in the ON state; or, both the fifth switches S33a and S33b and the sixth switches S34a and S34b can be in the OFF state. The fourth switches S32a and S32b can be in the ON state or the OFF state. For example, referring to Figure 5c, when the fifth switches S33a and S33b are in the on state, the first switch S11a and the fourth switch S32a in the first bridge arm M1 of the primary circuit operate in a similar state, and the first switch S11a and the fourth switch S32a are complementary to the sixth switch S34a in conducting; the first switch S11b and the fourth switch S32b in the second bridge arm M2 operate in a similar state, and the first switch S11b and the fourth switch S32b are complementary to the sixth switch S34b in conducting, and the first switch S11a and the sixth switch S34a can be phase-shifted to conduct.

[0103] Similarly, when the first positive input IN1+ and the first negative input IN1- are idle and no photovoltaic modules are installed, only the second photovoltaic module PV2 is connected, meaning only the second current is detected. In the primary circuit, the upper arms of the first bridge arm M1 and the second bridge arm M2 are in the off state, meaning the first switches S11a and S11b connected to the first positive input IN1+ are in the off state, and the fifth switches S33a and S33b of the third bridge arm M3 and the fourth bridge arm M4 are in the off state. Furthermore, the first sub-bridge arm of the third bridge arm M3 replaces the upper arm of the second bridge arm M2 and is complementaryly connected to the lower arm of the first bridge arm M1, i.e., the second switch S12a, and the first sub-bridge arm of the fourth bridge arm M4 replaces the upper arm of the first bridge arm M1 and is complementaryly connected to the lower arm of the second bridge arm M2, i.e., the second switch S12b.

[0104] Figures 5a, 5b, and 5c above are merely examples illustrating the driving timing of each switch in the MPPT circuit and primary-side circuit under different operating conditions. The actual driving timing of the switch is not limited to the above timing.

[0105] In practical power converter scenarios, because the positive output terminal structures of the first photovoltaic module PV1 and the second photovoltaic module PV2 are identical, and their negative output terminal structures are also identical, installers may incorrectly connect the first photovoltaic module PV1 and the second photovoltaic module PV2 to the power converter during installation. In other words, in this incorrect connection case, a certain input of the power converter that should be connected to a certain terminal of the first photovoltaic module PV1 is incorrectly connected to a certain terminal of the second photovoltaic module PV2. Figure 6b is a schematic diagram of such an incorrect connection. It can be seen that, compared to the correct connection in Figure 6a, in this incorrect connection case, the negative output of the first photovoltaic module PV1 is incorrectly connected to the second negative input IN2- of the power converter, and the negative output of the second photovoltaic module PV2 is incorrectly connected to the first negative input IN1- of the power converter. After the incorrect connection occurs, the output of the first photovoltaic module PV1 is used as the total input of the power converter, and the entire power generation system of the power converter can still operate normally. However, the loop formed by the positive and negative outputs of the second photovoltaic module PV2 will cause a short circuit in the second photovoltaic module PV2, which may lead to risks such as fire.

[0106] To avoid short circuits in photovoltaic modules caused by incorrect terminal connections, referring to Figures 6a and 6b, in some embodiments of this application, a short-circuit protection circuit can be connected between the first negative input IN1- and the second positive input IN2+. This short-circuit protection circuit can include at least one switch. The freewheeling direction of this switch is from the first negative input IN1- to the second positive input IN2+, and it has the function of blocking current flow from the second positive input IN2+ to the first negative input IN1-. This effectively prevents the formation of short-circuit current between the positive and negative outputs of the second photovoltaic module PV2, effectively avoiding risks such as fires caused by short circuits. Specifically, the switch included in the short-circuit protection circuit can be implemented using a metal-oxide-semiconductor field-effect transistor (MOSFET). The anode of a diode connected in parallel with the MOSFET is connected to the first negative input IN1-, and the cathode of the diode is connected to the second positive input IN2+.

[0107] In this application, the short-circuit protection circuit also enhances safety when the power converter is powered off. Generally, the output voltage of a single photovoltaic module is relatively safe for users. However, when the output voltages of two photovoltaic modules are superimposed, the total output voltage is high, posing a safety threat to the user. Specifically, in the embodiment shown in Figure 2, when the power converter stops working, the user may encounter a high output voltage from a photovoltaic module, which is the sum of the output voltages of the first photovoltaic module PV1 and the second photovoltaic module PV2. This could pose a safety threat to the user. In the embodiment shown in Figure 6a, by actively turning off the switch in the short-circuit protection circuit, the user can only encounter the output voltage of one of the first photovoltaic modules PV1 or the second photovoltaic module PV2, greatly reducing the safety threat posed by excessively high voltage.

[0108] Referring to Figure 6a, in some embodiments of this application, the short-circuit protection circuit may specifically include a first switch S41, one end of which is connected to the first negative input IN1-, and the other end of which is connected to the second positive input IN2+. The connection methods between the third bridge arm M3 and the fourth bridge arm M4 and the first switch S41 can be varied. For example, referring to Figure 6a, one end of the third bridge arm M3 is connected to the first negative input IN1-, and one end of the fourth bridge arm M4 is connected to the second positive input IN2+. Alternatively, referring to Figure 7, one end of both the third bridge arm M3 and the fourth bridge arm M4 is connected to the first negative input IN1-. Alternatively, referring to Figure 8, one end of both the third bridge arm M3 and the fourth bridge arm M4 is connected to the second positive input IN2+.

[0109] Referring to FIG9, in some other embodiments of this application, the short-circuit protection circuit may also include multiple switches. For example, the short-circuit protection circuit may include a first switch S41 and a second switch S42 connected in series between the first negative input IN1- and the second positive input IN2+. The third bridge arm M3 and the fourth bridge arm M4 may both be connected to the connection point of the first switch S41 and the second switch S42.

[0110] Referring to FIG10, in some embodiments of this application, the primary circuit may further include a DC blocking capacitor, namely a first capacitor C10. The first capacitor C10 is connected between the midpoint of the first bridge arm M1 or the midpoint of the second bridge arm M2 and the transformer T. FIG10 illustrates the example of the first capacitor C10 being set between the midpoint of the second bridge arm M2 and the other end of the primary winding of the transformer T. The first capacitor C10 can reduce signal interference between the primary circuit and the transformer.

[0111] Referring to Figures 2, 4, 6a, and 7 to 10, in some embodiments of this application, the power converter generally also provides multiple DC blocking capacitors on the DC side, such as capacitor C11 between the first positive input IN1+ and the second negative input IN2-, capacitor C12 between the first positive input IN1+ and the first negative input IN1-, and second capacitor C13 between the second positive input IN2+ and the second negative input IN2-, etc.

[0112] Referring to Figures 2, 4, 6a, and 7 to 10, in some embodiments of this application, the power converter may further include a filter circuit disposed on the AC side. The filter circuit is used to suppress differential-mode and common-mode noise, and may specifically employ a single-stage EMI filter structure or a two-stage EMI filter structure, etc., which are not limited here.

[0113] In this application, the secondary circuit can be implemented using various circuit topologies.

[0114] Referring to Figures 2, 4, 6a, 7 to 10, in some embodiments of this application, the secondary circuit may include a fifth bridge arm M5. The fifth bridge arm M5 includes an upper bridge arm and a lower bridge arm. The upper bridge arm includes two switches with opposite freewheeling directions, such as the seventh switch S21 and the eighth switch S22. The lower bridge arm includes two switches with opposite freewheeling directions, such as the ninth switch S23 and the tenth secondary switch S24. The connection point of the upper and lower bridge arms is connected in series with an inductive device Lr and then connected to one end of the secondary winding of the transformer T.

[0115] Referring to Figures 2, 4, 6a, and 7 to 10, in some other embodiments of this application, the secondary circuit may further include a second capacitor C21 and a third capacitor C22. The second capacitor C21 and the third capacitor C22 can serve as resonant capacitors to form a resonant element with the inductive device Lr, or the second capacitor C21 and the third capacitor C22 can also serve as voltage divider capacitors. The second capacitor C21 and the third capacitor C22 are connected in series and then connected in parallel with the fifth bridge arm M5. The connection point of the second capacitor C21 and the third capacitor C22 is connected to the other end of the secondary winding of the transformer T.

[0116] Referring to FIG11, in some other embodiments of this application, the secondary circuit may further include a fourth capacitor C23, which is connected between the connection point of the seventh switch S21 and the eighth switch S22 and the connection point of the ninth switch S23 and the tenth switch S24.

[0117] Referring to FIG12, in some other embodiments of this application, the secondary circuit may further include a fifth capacitor C24, which is connected between the upper half-bridge arm or the lower half-bridge arm and the other end of the secondary winding of the transformer T. FIG12 illustrates the example of the fifth capacitor C24 being connected between the lower half-bridge arm and the other end of the secondary winding of the transformer T.

[0118] Referring to Figure 13, in some other embodiments of this application, the secondary circuit may further include a sixth bridge arm M6 connected in parallel with the fifth bridge arm M5. The upper half of the fifth bridge arm M5 includes a seventh switch S21a and an eighth switch S22a with opposite freewheeling directions, and the lower half of the fifth bridge arm M5 includes a ninth switch S23a and a tenth switch S24a with opposite freewheeling directions. The upper half of the sixth bridge arm M6 includes a seventh switch S21b and an eighth switch S22b with opposite freewheeling directions, and the lower half of the sixth bridge arm M6 includes a ninth switch S23b and a tenth switch S24b with opposite freewheeling directions. The connection point of the upper and lower half of the fifth bridge arm M5 is connected to one end of the secondary winding of the transformer T after being connected in series with an inductive device Lr, and the connection point of the upper and lower half of the sixth bridge arm M6 is connected to the other end of the secondary winding of the transformer T.

[0119] Referring to Figure 14, in some other embodiments of this application, the secondary circuit may also employ a three-phase output. Specifically, the secondary circuit may include a fifth bridge arm M5, a sixth bridge arm M6, and a seventh bridge arm M7 connected in parallel. One end of each of the fifth bridge arm M5, the sixth bridge arm M6, and the seventh bridge arm M7 is connected in series with an inductive device Lr and then connected to one end of the secondary winding of the transformer T. The other end of each of the fifth bridge arm M5, the sixth bridge arm M6, and the seventh bridge arm M7 is connected to the other end of the secondary winding of the transformer T. Specifically, the fifth bridge arm M5, the sixth bridge arm M6, and the seventh bridge arm M7 can each include an upper half-bridge arm and a lower half-bridge arm. The upper half-bridge arm of the fifth bridge arm M5 includes a seventh switch S21a and an eighth switch S22a with opposite freewheeling directions. The lower half-bridge arm of the fifth bridge arm M5 includes a second capacitor C21a. The connection point between the upper and lower half-bridge arms of the fifth bridge arm M5 is connected to the first output of the power converter. The upper half-bridge arm of the sixth bridge arm M6 includes a seventh switch S21a with opposite freewheeling directions. b and the eighth switch S22b, the lower half of the sixth bridge arm M6 includes the second capacitor C21b, the connection point of the upper half of the sixth bridge arm M6 and the lower half of the sixth bridge arm M6 is connected to the second output of the power converter; the upper half of the seventh bridge arm M7 includes the seventh switch S21c and the eighth switch S22c with opposite freewheeling directions, the lower half of the seventh bridge arm M7 includes the second capacitor C21c, the connection point of the upper half of the seventh bridge arm M7 and the lower half of the seventh bridge arm M7 is connected to the third output of the power converter.

[0120] It should be understood that the various embodiments provided in Figures 2, 4, 6a, 7 to 14 above can be combined or modified to form new circuits, and the new circuits should also be included within the scope of protection claimed in this application.

[0121] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A power converter, characterized in that, include: Transformer, primary circuit, secondary circuit, maximum power point voltage (MPPT) circuit and controller; The power converter has inputs including a first positive input, a second positive input, a first negative input, and a second negative input. The first negative input and the second positive input are connected. The first positive input and the first negative input are used to connect to a photovoltaic module, and the second positive input and the second negative input are used to connect to another photovoltaic module or energy storage battery. The primary-side circuit is connected between the input of the power converter and the transformer. The primary-side circuit includes a first bridge arm and a second bridge arm connected in parallel. The two ends of the first bridge arm and the second bridge arm are respectively connected to the first positive input and the second negative input. Both the first bridge arm and the second bridge arm include an upper bridge arm and a lower bridge arm. The connection point between the upper bridge arm and the lower bridge arm of the first bridge arm is the midpoint of the first bridge arm. The connection point between the upper bridge arm and the lower bridge arm of the second bridge arm is the midpoint of the second bridge arm. The secondary circuit is connected between the transformer and the output of the power converter. The output of the power converter is used to connect to the power grid or load. The power converter is used to convert the DC power output by the photovoltaic module or the energy storage battery into AC power and output it to the power grid or load. The MPPT circuit is connected between the input of the power converter and the primary circuit, and the controller is used to control the MPPT circuit to perform maximum power point tracking on the photovoltaic module.

2. The power converter as described in claim 1, characterized in that, The MPPT circuit includes a third bridge arm and a fourth bridge arm. The third bridge arm is connected between the first negative input and the midpoint of the first bridge arm, and the fourth bridge arm is connected between the second positive input and the midpoint of the second bridge arm. Both the third bridge arm and the fourth bridge arm include two switching transistors with opposite freewheeling directions. When the difference between the first current and the second current is greater than a set value, the controller is used to control the third bridge arm and the fourth bridge arm to be in a working state. The working state is a state in which at least one switch in the bridge arm continuously switches between the on and off states. The first current is the output current of a photovoltaic module connected to the first positive input and the first negative input, and the second current is the output current of another photovoltaic module connected to the second positive input and the second negative input.

3. The power converter as described in claim 2, characterized in that, When only the first current is detected, the controller is also used to control the third bridge arm and the fourth bridge arm to be in the working state, and to control the switching transistor of the lower bridge arm in the primary circuit to be in the off state. When only the second current is detected, the controller is also configured to control the third and fourth bridge arms to be in an operating state, and the switch of the upper bridge arm in the primary circuit is in an off state.

4. The power converter as described in claim 2 or 3, characterized in that, The midpoint of the first bridge arm is connected to one end of the primary winding of the transformer, and the midpoint of the second bridge arm is connected to the other end of the primary winding of the transformer. The third and fourth bridge arms each contain two switching transistors with opposite freewheeling directions connected in series.

5. The power converter as described in claim 2 or 3, characterized in that, The third bridge arm and the fourth bridge arm each include two sub-bridge arms connected in parallel. Each of the two sub-bridge arms connected in parallel includes two switching transistors with opposite current directions and connected in series. The connection point of the two switching transistors with opposite current directions and connected in series is the midpoint of the corresponding sub-bridge arm. The two sub-arms of the third bridge arm are connected in parallel between the first negative input and one end of the primary winding of the transformer. The midpoint of one sub-arm of the third bridge arm is connected to the upper bridge arm of the first bridge arm, and the midpoint of the other sub-arm of the third bridge arm is connected to the lower bridge arm of the first bridge arm. The two sub-arms of the fourth bridge arm are connected in parallel between the second positive input and the other end of the primary winding of the transformer. The midpoint of one sub-arm of the fourth bridge arm is connected to the upper bridge arm of the second bridge arm, and the midpoint of the other sub-arm of the fourth bridge arm is connected to the lower bridge arm of the second bridge arm.

6. The power converter according to any one of claims 1-5, characterized in that, The power converter further includes a first switching transistor connected between the first negative input and the second positive input, wherein the freewheeling direction of the first switching transistor is from the first negative input to the second positive input.

7. The power converter as described in claim 6, characterized in that, One end of the third bridge arm is connected to the first negative input, and one end of the fourth bridge arm is connected to the second positive input; or... One end of the third bridge arm and one end of the fourth bridge arm are both connected to the first negative input; or... One end of the third bridge arm and one end of the fourth bridge arm are both connected to the second positive input.

8. The power converter as described in claim 6, characterized in that, The power converter further includes a second switch, and the first switch and the second switch are connected in series between the first negative input and the second positive input; One end of the third bridge arm and one end of the fourth bridge arm are both connected to the connection point of the first switch and the second switch.

9. The power converter according to any one of claims 1-8, characterized in that, The secondary circuit includes a fifth bridge arm, which includes an upper bridge arm and a lower bridge arm. The upper bridge arm includes two switching transistors with opposite freewheeling directions, and the lower bridge arm includes two switching transistors with opposite freewheeling directions. The connection point of the upper and lower bridge arms of the fifth bridge arm is connected to one end of the secondary winding of the transformer. The secondary circuit also includes two capacitors, which are connected in series and then in parallel with the fifth bridge arm. The connection point of the two capacitors is connected to the other end of the secondary winding of the transformer.

10. The power converter according to any one of claims 1-8, characterized in that, The secondary circuit includes a fifth bridge arm and a sixth bridge arm connected in parallel. Each of the fifth bridge arm and the sixth bridge arm includes an upper bridge arm and a lower bridge arm. Each of the upper bridge arms of the fifth bridge arm and the sixth bridge arm includes two switching transistors with opposite freewheeling directions. Each of the lower bridge arms of the fifth bridge arm and the sixth bridge arm includes two switching transistors with opposite freewheeling directions. The connection point of the upper and lower half of the fifth bridge arm is connected to one end of the secondary winding of the transformer; the connection point of the upper and lower half of the sixth bridge arm is connected to the other end of the secondary winding of the transformer.

11. The power converter as described in claim 4, characterized in that, When the first current is greater than the second current and the difference is greater than the set value, the controller controls the upper bridge arm of the first bridge arm and the upper bridge arm of the second bridge arm to conduct complementaryly; when the switch of the upper bridge arm of the first bridge arm is in the conducting state, the controller controls the lower bridge arm of the fourth bridge arm and the lower bridge arm of the second bridge arm to conduct complementaryly; when the switch of the upper bridge arm of the second bridge arm is in the conducting state, the controller controls the lower bridge arm of the third bridge arm and the lower bridge arm of the first bridge arm to conduct complementaryly. Wherein, the complementary conduction means that when the switch of one bridge arm is in the conducting state, the switch of the other bridge arm is in the off state.

12. The power converter as described in claim 4, characterized in that, When only the first current is detected, the controller is used to control the switching transistors of the lower bridge arm in the first bridge arm and the lower bridge arm in the second bridge arm to be in the off state, control the third bridge arm to be complementaryly connected with the upper bridge arm of the first bridge arm, and control the fourth bridge arm to be complementaryly connected with the upper bridge arm of the second bridge arm. When only the second current is detected, the controller is used to control the switching transistors of the upper bridge arm in the first bridge arm and the upper bridge arm in the second bridge arm to be in the off state, control the third bridge arm to be complementaryly connected with the lower bridge arm of the first bridge arm, and control the fourth bridge arm to be complementaryly connected with the lower bridge arm of the second bridge arm. Wherein, the complementary conduction means that when the switch of one bridge arm is in the conducting state, the switch of the other bridge arm is in the off state.

13. The power converter as described in claim 5, characterized in that, When the difference between the first current and the second current is less than a set value, the controller is also used to control the switching transistors connected to the input of the power converter in the sub-bridge arm of the MPPT circuit to be in the off state. When the difference between the first current and the second current is greater than the set value, the controller is also used to control a switch in the third bridge arm connected to the input of the power converter to be in a turned-off state, and to control a switch in the fourth bridge arm connected to the input of the power converter to be in a turned-off state.

14. The power converter as described in claim 5, characterized in that, When only the first current or only the second current is detected, the controller is also configured to control a switch in the third bridge arm connected to the input of the power converter to be in a turned-off state, and to control a switch in the fourth bridge arm connected to the input of the power converter to be in a turned-off state.

15. The power converter as described in claim 13, characterized in that, When the difference between the first current and the second current is less than a set value, the controller is used to control the switch in the third bridge arm connected between the upper bridge arm of the first bridge arm and the primary winding to be complementaryly connected with the lower bridge arm of the second bridge arm; control the switch in the third bridge arm connected between the lower bridge arm of the first bridge arm and the primary winding to be complementaryly connected with the upper bridge arm of the second bridge arm; control the switch in the fourth bridge arm connected between the upper bridge arm of the second bridge arm and the primary winding to be complementaryly connected with the lower bridge arm of the first bridge arm; and control the switch in the fourth bridge arm connected between the lower bridge arm of the second bridge arm and the primary winding to be complementaryly connected with the upper bridge arm of the first bridge arm. Wherein, the complementary conduction means that when the switch of one bridge arm is in the conducting state, the switch of the other bridge arm is in the off state.

16. The power converter as described in claim 11 or 13, characterized in that, In the MPPT circuit, the on-time of the bridge arm switch is positively correlated with the difference between the first current and the second current.

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