Photovoltaic system, micro inverter and control method thereof

Abstract

The invention relates to a photovoltaic system, a micro inverter and a control method thereof. The micro inverter comprises a primary side capacitor, wherein the input end of the primary side capacitor is used for being connected with a renewable energy source conversion device; a primary side H-bridge circuit; a transformer; a bidirectional switch bridge arm; the controller is used for acquiring an input signal of the primary side H-bridge circuit, a specified control signal and a grid-connected state of the micro inverter and determining a connection state of the micro inverter and the renewable energy source conversion device according to the input signal and the specified control signal of the primary side H-bridge circuit and the grid-connected state of the micro inverter; the specified control signal is a control signal loaded to the primary side H-bridge circuit and the bidirectional switch bridge arm. In the micro inverter, the controller determines the connection state of the micro inverter and the renewable energy source conversion device according to the input signal of the primary side H-bridge circuit, the specified control signal and the grid-connected state of the micro inverter, so that the risk of misjudgment of access detection is effectively reduced.

Description

Technical Field

[0001] This application relates to the field of power electronics technology, and in particular to a photovoltaic system, a micro-inverter and its control method. Background Technology

[0002] An inverter is a key device that converts direct current (DC) to alternating current (AC). In renewable energy systems such as solar photovoltaic and wind power generation, inverters are widely used as crucial core components. Inverters control the parameters of the output AC power, synchronizing it with the frequency and voltage of the power grid, thus enabling applications such as grid connection. With the continuous maturation of energy technologies and the miniaturization of energy systems, micro-inverters have emerged.

[0003] In related technologies, to prevent users from connecting or disconnecting components during grid-connected operation, inverters must be equipped with hot-swap detection functions to ensure that after a misoperation, the relay is immediately shut down, insulation monitoring is performed, and then grid connection is restored. Additionally, before grid connection, it is necessary to detect the presence of components and handle the situation using appropriate algorithms. This is because the floating voltage of unconnected circuits is affected by the transformer secondary side; appropriate circuit-loss control algorithms can maintain a constant floating voltage.

[0004] However, the above-mentioned connection detection method for micro-inverters has the following technical problems:

[0005] Existing connection detection methods based on open-circuit voltage magnitude and voltage loop output difference have many false positives, resulting in low efficiency and poor accuracy in connection detection. Summary of the Invention

[0006] Therefore, it is necessary to provide a photovoltaic system, micro-inverter, and control method that can improve the accuracy of connection detection of renewable energy conversion devices before and after grid connection, in order to address the above-mentioned technical problems.

[0007] In a first aspect, this application provides a micro inverter, comprising:

[0008] Primary-side capacitors, the input terminals of which are used to connect to renewable energy conversion devices;

[0009] The primary-side H-bridge circuit has its input terminal connected to the output terminal of the primary-side capacitor.

[0010] The transformer's primary winding is connected to the output terminal of the primary H-bridge circuit.

[0011] The bidirectional switch arm has its input end connected to the secondary winding of the transformer, and its output end is used to connect to the power grid.

[0012] The controller is used to acquire and determine the connection status between the microinverter and the renewable energy conversion device based on the input signal of the primary-side H-bridge circuit, the specified control signal, and the grid connection status of the microinverter.

[0013] The specified control signal is the control signal applied to the primary-side H-bridge circuit and the bidirectional switching bridge arm.

[0014] In one embodiment, the controller is used to obtain the voltage of the primary capacitor before the microinverter is connected to the grid, and when the voltage of the primary capacitor is greater than a first threshold voltage, it determines that the primary side is connected to a renewable energy conversion device.

[0015] The first threshold voltage is less than the minimum voltage for grid-connected operation of the primary H-bridge circuit, and greater than the preset reference voltage for out-of-circuit operation of the primary H-bridge circuit.

[0016] In one embodiment, the controller is used to obtain the voltage of the primary capacitor in the grid-connected state after the microinverter is connected to the grid, and determine that the renewable energy conversion device is hot-disconnected when the grid current peak reference value is greater than or equal to 0 and the voltage of the primary capacitor is less than a second threshold voltage.

[0017] The second threshold voltage is less than the preset reference voltage for the primary-side H-bridge circuit to operate in the off-circuit mode.

[0018] In one embodiment, the controller is used to acquire the primary current under grid-connected conditions after the microinverter is connected to the grid, and to determine that the renewable energy conversion device is hot-plugged when the peak reference value of the grid current is less than 0 and the primary current is continuously less than the preset disconnection detection threshold current within a preset time window.

[0019] In one embodiment, the controller is used to obtain a reference value of the grid current peak when the microinverter is in a circuit-out condition, and to determine the hot access of the renewable energy conversion device when the reference value of the grid current peak is greater than the preset reference current for the primary H-bridge circuit to operate in a circuit-out condition.

[0020] The preset reference current for the primary-side H-bridge circuit to operate in a circuit-free state is greater than 0.

[0021] In one embodiment, the controller is used to acquire the voltage of the primary capacitor in the off-circuit state when the microinverter is in an off-circuit condition, and to determine that the renewable energy conversion device is hot-connected when the voltage of the primary capacitor is greater than a preset access detection threshold voltage.

[0022] Among them, the access detection threshold voltage is greater than the minimum voltage for grid-connected operation of the primary H-bridge circuit.

[0023] In one embodiment, the controller is used to control the primary-side H-bridge circuit and the bidirectional switching arm to operate in corresponding operating modes according to the connection status of the micro-inverter to the renewable energy conversion device. The operating modes include grid-connected operating mode and circuit-free operating mode.

[0024] In one embodiment, the controller includes:

[0025] The maximum power point tracking unit is connected to the primary-side H-bridge circuit. The maximum power point tracking unit is used to track the maximum power point of the renewable energy conversion device and outputs a tracking reference voltage corresponding to the maximum power point.

[0026] The voltage loop regulation unit is connected to the maximum power point tracking unit and the primary capacitor respectively. The voltage loop regulation unit is used to output the peak reference value of the grid current based on the voltage of the primary capacitor and the tracking reference voltage.

[0027] The current loop control unit is connected to the voltage loop regulation unit. The current loop control unit is used to control the primary H-bridge circuit and the bidirectional switching bridge arm to work in the corresponding working mode according to the reference value of the grid current peak value. The working modes include grid-connected working mode and circuit-out working mode.

[0028] The access detection unit is used to connect to the primary capacitor and the voltage loop regulation unit respectively. The access detection unit is used to obtain and determine the connection status of the microinverter to the renewable energy conversion device based on the voltage of the primary capacitor, the primary current of the primary H-bridge circuit, the peak reference value of the grid current, and the grid connection status of the microinverter.

[0029] In one embodiment, the renewable energy conversion device is a photovoltaic module.

[0030] In one embodiment, there are multiple primary-side H-bridge circuits and transformers of the same quantity, and the multiple primary-side H-bridge circuits and multiple transformers are connected in a one-to-one correspondence.

[0031] Secondly, this application also provides a photovoltaic system, comprising:

[0032] As described in any of the first aspects, a micro inverter;

[0033] One or more photovoltaic modules, with the output terminal of each photovoltaic module connected to the input terminal of a micro-inverter.

[0034] Thirdly, this application also provides a control method for a microinverter, the microinverter including a primary capacitor, a primary H-bridge circuit, a transformer, and a bidirectional switching arm; the input terminal of the primary capacitor is used to connect to a renewable energy conversion device, the input terminal of the primary H-bridge circuit is connected to the output terminal of the primary capacitor, the primary winding of the transformer is connected to the output terminal of the primary H-bridge circuit, the input terminal of the bidirectional switching arm is connected to the secondary winding of the transformer, and the output terminal of the bidirectional switching arm is used to connect to the power grid; the method includes:

[0035] Obtain the input signals and control signals of the primary-side H-bridge circuit, as well as the grid connection status of the micro-inverter;

[0036] Based on the input signal and control signal of the primary-side H-bridge circuit and the grid connection status of the micro-inverter, determine the connection status of the micro-inverter to the renewable energy conversion device;

[0037] The control signal is the control signal applied to the primary H-bridge circuit and the bidirectional switching bridge arm.

[0038] In one embodiment, the connection status of the microinverter to the renewable energy conversion device is determined based on the input signal of the primary-side H-bridge circuit, the control signal, and the grid connection status of the microinverter, including:

[0039] Obtain the voltage of the primary capacitor before the microinverter is connected to the grid;

[0040] When the voltage of the primary capacitor is greater than the first threshold voltage, it is determined that a renewable energy conversion device is connected to the primary side.

[0041] The first threshold voltage is less than the minimum voltage for grid-connected operation of the primary H-bridge circuit, and greater than the preset reference voltage for out-of-circuit operation of the primary H-bridge circuit.

[0042] In one embodiment, the connection status of the microinverter to the renewable energy conversion device is determined based on the input signal of the primary-side H-bridge circuit, the control signal, and the grid connection status of the microinverter, including:

[0043] After the microinverter is connected to the grid, the voltage of the primary capacitor in the grid-connected state is obtained;

[0044] When the peak reference value of the grid current is greater than or equal to 0 and the voltage of the primary capacitor is less than the second threshold voltage, the renewable energy conversion device is determined to be hot-plugged.

[0045] The second threshold voltage is less than the preset reference voltage for the primary-side H-bridge circuit to operate in the off-circuit mode.

[0046] In one embodiment, the connection status of the microinverter to the renewable energy conversion device is determined based on the input signal of the primary-side H-bridge circuit, the control signal, and the grid connection status of the microinverter, including:

[0047] After the microinverter is connected to the grid, the voltage of the primary capacitor in the grid-connected state is obtained;

[0048] When the peak reference value of the grid current is greater than or equal to 0 and the voltage of the primary capacitor is less than the second threshold voltage, the renewable energy conversion device is determined to be hot-plugged.

[0049] The second threshold voltage is less than the preset reference voltage for the primary-side H-bridge circuit to operate in the off-circuit mode.

[0050] In one embodiment, the connection status of the microinverter to the renewable energy conversion device is determined based on the input signal of the primary-side H-bridge circuit, the control signal, and the grid connection status of the microinverter, including:

[0051] After the microinverter is connected to the grid, the primary current under grid-connected conditions is obtained;

[0052] When the peak reference value of the grid current is less than 0 and the primary current remains below the preset disconnection detection threshold current within a preset time window, the renewable energy conversion device is determined to be hot-disconnected.

[0053] In one embodiment, the connection status of the microinverter to the renewable energy conversion device is determined based on the input signal of the primary-side H-bridge circuit, the control signal, and the grid connection status of the microinverter, including:

[0054] When the microinverter is in a circuit-free operating condition, obtain the reference value of the peak grid current;

[0055] When the peak reference value of the grid current is greater than the preset reference current for the primary H-bridge circuit to operate without a circuit, the renewable energy conversion device is hot-connected.

[0056] The preset reference current for the primary-side H-bridge circuit to operate in a circuit-free state is greater than 0.

[0057] In one embodiment, the connection status of the microinverter to the renewable energy conversion device is determined based on the input signal of the primary-side H-bridge circuit, the control signal, and the grid connection status of the microinverter, including:

[0058] When the microinverter is in a circuit-out condition, obtain the voltage of the primary capacitor in the circuit-out state;

[0059] When the voltage of the primary capacitor is greater than the preset access detection threshold voltage, the renewable energy conversion device is determined to be in hot connection.

[0060] Among them, the access detection threshold voltage is greater than the minimum voltage for grid-connected operation of the primary H-bridge circuit.

[0061] In one embodiment, the method further includes:

[0062] Depending on the connection of the microinverter to the renewable energy conversion device, control the primary-side H-bridge circuit and the bidirectional switching bridge arm to operate in the corresponding working mode.

[0063] The operating modes include grid-connected operating mode and circuit-deficient operating mode.

[0064] The aforementioned photovoltaic system, micro-inverter, and control method have at least the following beneficial effects:

[0065] In a microinverter, the controller not only acquires the input signal from the primary-side H-bridge circuit and the specified control signal, but also the grid connection status of the microinverter. It fully considers the fluctuations in the input signal of the primary-side H-bridge circuit under different grid connection states, thus combining these three data dimensions to comprehensively determine the connection status between the microinverter and the renewable energy conversion device, thereby improving the accuracy of connection detection. In determining the connection status, the judgment is based on the parameter relationships of the circuit under different states, reducing the possibility of misjudgments. Attached Figure Description

[0066] To more clearly illustrate the technical solutions in the embodiments or related technologies of this application, the accompanying drawings used in the description of the embodiments or related technologies will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0067] Figure 1 This is a schematic diagram of a micro inverter in one embodiment of this application;

[0068] Figure 2 This is a schematic diagram of the structure of a micro inverter in one embodiment of this application;

[0069] Figure 3 This is a schematic diagram of the control flow of the controller in one embodiment of this application;

[0070] Figure 4 This is a structural block diagram of a micro inverter and its control circuit in one embodiment of this application;

[0071] Figure 5 This is a first flowchart illustrating the control method of a micro-inverter in one embodiment of this application;

[0072] Figure 6 This is a second flowchart illustrating the control method of a micro-inverter in another embodiment of this application;

[0073] Figure 7 This is a third flowchart illustrating the control method for a micro-inverter in another embodiment of this application;

[0074] Figure 8 This is a fourth flowchart illustrating the control method for a micro-inverter in another embodiment of this application;

[0075] Figure 9 This is a fifth flowchart illustrating the control method for a micro-inverter in another embodiment of this application;

[0076] Figure 10 This is a sixth flowchart illustrating the control method for a micro-inverter in another embodiment of this application;

[0077] Figure 11 This is a seventh flowchart illustrating the control method for a micro-inverter in another embodiment of this application.

[0078] Explanation of reference numerals in the attached figures: 100, microinverter; 111, photovoltaic module; 112, primary-side switch; 113, primary-side capacitor; 114, primary-side H-bridge circuit; 120, transformer; 130, bidirectional switch arm; 140, secondary-side capacitor circuit; 200, controller; 210, access detection unit; 220, maximum power point tracking unit; 230, voltage loop regulation unit; 240, current loop control unit; 300, renewable energy conversion device. Detailed Implementation

[0079] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0080] This application provides a photovoltaic system, a micro-inverter, and a control method thereof.

[0081] The micro inverter and its control method provided in this application can be applied to, for example... Figure 1 The system shown includes a renewable energy conversion device 300 and a micro-inverter 100.

[0082] The renewable energy conversion device 300 is used to convert renewable energy into electrical energy. The output terminal of the renewable energy conversion device 300 is connected to the input terminal of the micro inverter 100. The output terminal of the micro inverter 100 is used to connect to the power grid and / or load.

[0083] For example, renewable energy includes, but is not limited to, solar, wind, hydro, biomass, geothermal, and ocean energy. The renewable energy conversion device 300 corresponds to, but is not limited to, photovoltaic modules 111, wind turbines, hydroelectric generators, biomass power generation equipment, geothermal power generation systems, and wave energy converters.

[0084] In one exemplary embodiment, please refer to Figure 2 A micro inverter 100 is provided, including a primary-side capacitor 113, a primary-side H-bridge circuit 114, a transformer 120, a bidirectional switching bridge arm 130, and a controller 200.

[0085] The input terminal of the primary capacitor 113 is used to connect to the renewable energy conversion device 300. The input terminal of the primary H-bridge circuit 114 is connected to the output terminal of the primary capacitor 113. The primary winding of the transformer 120 is connected to the output terminal of the primary H-bridge circuit 114. The input terminal of the bidirectional switch arm 130 is connected to the secondary winding of the transformer 120. The output terminal of the bidirectional switch arm 130 is used to connect to the power grid. The controller 200 is used to acquire and determine the connection status between the micro-inverter 100 and the renewable energy conversion device 300 based on the input signal of the primary H-bridge circuit 114, the specified control signal, and the grid connection status of the micro-inverter 100.

[0086] The specified control signal is the control signal applied to the primary-side H-bridge circuit 114 and the bidirectional switching bridge arm 130.

[0087] Specifically, it can be like Figure 2 As shown, the primary-side capacitor 113 is connected to the photovoltaic module 111, and the primary-side capacitor 113 and the photovoltaic module 111 are connected in parallel. Optionally, a primary-side switch 112 is also provided between the primary-side capacitor 113 and the photovoltaic module 111.

[0088] Specifically, the primary-side H-bridge circuit 114 can refer to a circuit structure used for converting electrical energy, and can also be used on the primary side of the isolation transformer 120. The primary-side H-bridge circuit 114 can include several switching elements, which are distributed to form a bridge-like circuit topology resembling the letter "H". By controlling the on and off states of the switches, the direction and magnitude of current flow can be adjusted. The switching elements in the primary-side H-bridge circuit 114 can be composed of transistors.

[0089] Specifically, transformer 120 can refer to a circuit element used to change the voltage and current in a circuit. Transformer 120 may include a primary winding and a secondary winding. The primary winding can be connected to the primary H-bridge circuit 114 to obtain the primary input signal. The secondary winding is connected to the secondary circuit to output the converted input signal through the secondary circuit.

[0090] Specifically, the bidirectional switching bridge arm 130 can refer to a circuit element used to achieve bidirectional control. The bidirectional switching bridge arm 130 can consist of multiple switching elements configured to form a bridge circuit topology connecting the positive and negative terminals of the power supply and the load. By controlling the conduction of the switching elements, the direction of current can be controlled. The switching elements in the bidirectional switching bridge arm 130 can be composed of transistors.

[0091] In implementation, to prevent users from connecting or disconnecting components during grid-connected operation, the inverter must be equipped with a hot-swap detection function to ensure that the relay is immediately shut down after a misoperation, and grid connection is only resumed after insulation monitoring. Additionally, before grid connection, it is necessary to detect the presence of components and handle the situation using appropriate algorithms. This is because the floating voltage of unconnected circuits is affected by the secondary side of the transformer (120V), and the corresponding circuit-shortage control algorithm can maintain a constant floating voltage.

[0092] However, the connection detection method of the micro inverter 100 mentioned above has the following problems: the existing connection detection method based on the open circuit voltage magnitude and voltage loop output difference has many false judgment results, resulting in low efficiency and poor accuracy of connection detection.

[0093] Given the aforementioned deficiencies in related technologies, based on the circuit architecture of the microinverter 100 described in this application, the controller 200 can acquire the input signal of the primary-side H-bridge circuit 114, the specified control signal, and the grid connection status of the microinverter 100. Furthermore, based on the input signal of the primary-side H-bridge circuit 114, the specified control signal, and the grid connection status of the microinverter 100, it determines the connection status between the microinverter 100 and the renewable energy conversion device 300. This fully considers the different impacts on the input signal of the primary-side H-bridge circuit 114 under different grid connection statuses, ensuring the accuracy of the microinverter 100 connection detection results. Consequently, it can promptly perform protective actions such as wave blocking control in case of malfunction, thereby improving the accuracy and reliability of the microinverter 100's operation control.

[0094] In this embodiment, the number of secondary-side circuits is not limited. This embodiment illustrates the structure of the micro-inverter 100 using an exemplary example. When the micro-inverter 100 includes multiple primary-side circuits and one secondary-side circuit, please refer to [reference needed]. Figure 2 The microinverter 100100 has an N-to-1 topology, enabling N-channel power decoupling. Other optional topologies for the microinverter 100 are implemented similarly to the example and will not be elaborated upon.

[0095] In one embodiment, such as Figure 2 As shown, the primary-side H-bridge circuit 114 may include a first switch S1, a second switch S2, a third switch S3, and a fourth switch S4. The first switch S1 and the second switch S2 are connected in series to form the first inverter bridge arm, and the third switch S3 and the fourth switch S4 are connected in series to form the second inverter bridge arm. The common terminal of the first switch S1 and the second switch S2 serves as the first output terminal of the primary-side H-bridge circuit 114, and the common terminal of the third switch S3 and the fourth switch S4 serves as the second output terminal of the primary-side H-bridge circuit 114.

[0096] In one embodiment, such as Figure 2 As shown, the microinverter 100 may further include a secondary capacitor circuit 140, which is connected to the secondary winding of the transformer 120. The secondary capacitor circuit 140 is used to filter the signal output from the secondary side of the microinverter 100 and also provides energy storage buffer protection during load surges. By including the secondary capacitor circuit 140, the stability of the secondary circuit and the overall output performance of the microinverter 100 can be improved.

[0097] Optionally, the upper half-bridge arm of the secondary-side capacitor circuit 140 includes at least one capacitor, and the lower half-bridge arm of the secondary-side capacitor circuit 140 includes at least one capacitor.

[0098] In one implementation, it can be as follows Figure 2 As shown, the upper half-bridge arm of the secondary-side capacitor circuit 140 includes a secondary-side capacitor Ca, and the lower half-bridge arm includes a secondary-side capacitor Cb.

[0099] In one implementation, such as Figure 2 As shown, the upper half of the bidirectional switch bridge arm 130130 includes a fifth switch S5 and a sixth switch S6 connected in series, and the lower half of the bidirectional switch bridge arm 130130 includes a seventh switch S7 and an eighth switch S8 connected in series. The input terminal of the bidirectional switch bridge arm 130130 can be connected to the secondary winding of the transformer 120120, and the output terminal of the bidirectional switch bridge arm 130130 is used to connect to the power grid and / or a load.

[0100] For example, the controller 200 can acquire the input signals of the primary-side H-bridge circuit 114 and specified control signals. The controller 200 can also acquire the grid connection status of the micro-inverter 100 and determine the connection status between the micro-inverter 100 and the renewable energy conversion device 300 based on the grid connection status. The input signals of the primary-side H-bridge circuit 114 include electrical signals that can be directly measured in the primary-side H-bridge circuit 114, such as the voltage Ucap of the primary-side capacitor 113 and the primary-side current. The specified control signals include a first threshold voltage Ucon, a minimum voltage Umin for primary-side grid connection operation, a preset reference voltage U*ref for off-circuit operation of the primary-side H-bridge circuit 114, a second threshold voltage Uco, a peak grid current reference value Iref, an access detection threshold voltage Uci, a preset reference current I*ref for off-circuit operation, and an access detection threshold current Ipvmin. The specified control signals can be preset and input by technicians or obtained in real-time from the grid side through detection and calculation during the processing of the controller 200. The grid connection status of the microinverter 100 can include before and after grid connection.

[0101] For example, based on the input signal of the primary-side H-bridge circuit 114, the specified control signal, and the grid connection status of the micro-inverter 100 obtained by the controller 200, the connection status between the micro-inverter 100 and the renewable energy conversion device 300 can be determined in the following example scenarios.

[0102] In one embodiment, the controller 200 is used to obtain the voltage Ucap of the primary side capacitor 113 before the microinverter 100 is connected to the grid, and when the voltage Ucap of the primary side capacitor 113 is greater than the first threshold voltage Ucon, it determines that the primary side is connected to the renewable energy conversion device 300.

[0103] Wherein, the first threshold voltage Ucon is less than the minimum voltage Umin for grid-connected operation of the primary-side H-bridge circuit 114, and greater than the preset reference voltage U*ref for off-circuit operation of the primary-side H-bridge circuit 114, that is, it satisfies the following relationship:

[0104] U*ref <Ucon<Umin。

[0105] In this embodiment, if the microinverter 100 is connected to the renewable energy conversion device 300, then the connection voltage, i.e., the voltage Ucap of the primary capacitor 113, must be greater than or equal to the minimum voltage Umin for grid-connected operation of the primary H-bridge circuit 114. Therefore, it must be greater than the first threshold voltage Ucon. Thus, whether the connection is established can be determined by comparing the voltage Ucap of the primary capacitor 113 with the first threshold voltage Ucon. If the voltage Ucap of the primary capacitor 113 is less than or equal to the first threshold voltage Ucon, it can be determined that the connection is not established, and the circuit is switched to the off-circuit condition. At this time, the floating voltage is the preset reference voltage U*ref for the off-circuit operation of the primary H-bridge circuit 114. The preset reference voltage U*ref for the off-circuit operation of the primary H-bridge circuit 114 is also less than the minimum voltage Umin for grid-connected operation of the primary H-bridge circuit 114. At this time, the corresponding off-circuit control can be executed to switch the connection state between the microinverter 100 and the renewable energy conversion device from the off-circuit condition to the hot-connection condition.

[0106] In implementation, by setting the first threshold voltage between the minimum voltage for grid-connected operation of the primary circuit and the preset reference voltage for unconnected operation of the primary circuit, the risk of misjudgment in grid connection detection is effectively reduced. By directly monitoring the voltage of the primary capacitor 113 and comparing it with the first threshold voltage, the connection status of the photovoltaic string can be determined, which helps to improve the accuracy of grid connection detection results.

[0107] In one embodiment, the controller 200 is further configured to acquire the voltage Ucap of the primary capacitor 113 in the grid-connected state after the microinverter 100 is connected to the grid, and determine that the renewable energy conversion device 300 is hot-disconnected when the grid current peak reference value Iref is greater than or equal to 0 and the voltage Ucap of the primary capacitor 113 is less than the second threshold voltage Uco.

[0108] Wherein, the second threshold voltage Uco is less than the preset reference voltage U*ref for the primary-side H-bridge circuit 114 when it is out of circuit, that is, it satisfies the following relationship:

[0109] Uco <U*ref<Ucon<Umin。

[0110] Specifically, when the connection between the microinverter 100 and the renewable energy conversion device 300 changes from grid-connected operation to hot-disconnected operation, there are two possible operating states. The first is that the voltage drops to 0 instantaneously due to waveform generation, and the second is that it maintains stable operation at a certain voltage. These two phenomena depend on the magnitude of the grid current peak reference value Iref. When the grid current peak reference value Iref is greater than or equal to 0, positive power will be output after hot disconnection, and the floating voltage of the primary capacitor 113 will be released immediately, causing the voltage to drop to 0 instantaneously. When the grid current peak reference value Iref is less than 0, secondary power will be output after hot disconnection, and the floating voltage of the renewable energy conversion device 300 will rise to balance the losses, thereby maintaining stable operation at a certain voltage. In this embodiment, the detection and determination of hot disconnection is performed for the first phenomenon.

[0111] Specifically, a second threshold voltage Uco can be preset by technicians, and the second threshold voltage Uco is less than the preset reference voltage U*ref for the primary-side H-bridge circuit 114 when it is out of circuit. This helps to reduce the possibility of misjudgment caused by secondary ripple during low-voltage operation and improves the accuracy of hot-stripping detection under grid-connected conditions and when the renewable energy conversion device 300 is outputting positive power.

[0112] In this embodiment, one type of circuit phenomenon in a hot-pull-out scenario is analyzed, thereby enabling the detection and judgment of hot-pull-out under the operating conditions of this circuit phenomenon, which helps to improve the accuracy of hot-pull-out detection.

[0113] In one embodiment, the controller 200 is further configured to acquire the primary current under grid-connected conditions after the microinverter 100 is connected to the grid, and determine that the renewable energy conversion device 300 is hot-pulled out when the grid current peak reference value Iref is less than 0 and the primary current is continuously less than the preset pull-out detection threshold current Ipvmin within a preset time window T.

[0114] Specifically, when the micro inverter 100 is hot-disconnected under grid-connected conditions, if the peak reference value of the grid current Iref is less than 0, that is, when the output is negative power, in order to maintain the constant voltage of the primary capacitor 113, the primary current will drop below 0. Therefore, the primary current within the preset time window T can be detected. If the primary current is less than the preset disconnection detection threshold current Ipvmin, it can be determined that the micro inverter is hot-disconnected.

[0115] In this embodiment, another circuit phenomenon in the hot-pull-out scenario is analyzed, and hot-pull-out detection and judgment are performed under the operating conditions of this circuit phenomenon. This helps to improve the accuracy of hot-pull-out detection, so that different circuit scenarios can be covered in this solution, thereby reducing the possibility of misjudgment and missed judgment.

[0116] In one embodiment, the controller 200 is further configured to acquire a grid current peak reference value Iref when the microinverter 100 is in a circuit-out condition, and determine that the renewable energy conversion device 300 is hot-connected when the grid current peak reference value Iref is greater than the preset reference current I*ref for the primary-side H-bridge circuit 114 is in a circuit-out condition.

[0117] Among them, the preset reference current for the primary-side H-bridge circuit 114 to operate in the off-circuit mode is greater than 0.

[0118] Specifically, in the hot-connection detection scenario, in the unconnected state, the unconnected circuit is controlled in the circuit-out control loop under the circuit-out condition. At this time, the primary-side H-bridge circuit 114 operates at the preset reference voltage U*ref during circuit-out operation. Since no power is output to the secondary side (i.e., the grid side) during circuit-out operation, the voltage loop output is relatively small, usually negative. Due to the sudden connection, the reference voltage Uref for circuit-out control is generally less than the minimum maximum power point voltage within the specification. Therefore, the voltage reference value is significantly different from the open-circuit voltage of the connected component, causing a sudden increase in the voltage loop output. In this scenario, a judgment condition can be set for the circuit state change during hot connection. When the peak reference value of the grid current Iref is greater than the preset reference current I*ref for the primary-side H-bridge circuit 114 operating at circuit-out operation, the renewable energy conversion device 300 is determined to be hot-connected.

[0119] In one embodiment, the controller 200 is further configured to acquire the voltage Ucap of the primary capacitor 113 in the off-circuit state when the microinverter 100 is in an off-circuit state, and determine that the renewable energy conversion device 300 is hot-connected when the voltage Ucap of the primary capacitor 113 is greater than a preset access detection threshold voltage Uci.

[0120] Among them, the access detection threshold voltage Uci is greater than the minimum voltage Umin for grid-connected operation of the primary H-bridge circuit 114.

[0121] Specifically, in another embodiment of the hot-access scenario, since the floating voltage is much lower than the access voltage during hot access, a hot-access voltage threshold Uci can be set accordingly. The hot-access voltage threshold Uci is set as a condition that it is greater than the minimum voltage Umin for primary-side grid connection. When the voltage Ucap of the primary-side capacitor 113 is greater than the hot-access voltage threshold, it can be determined as hot access. Specifically, the hot-access voltage threshold satisfies the following relationship:

[0122] Uco <U*ref<Ucon<Umin<Uci。

[0123] In this way, we can obtain the following: Figure 3 The micro inverter 100 shown is used for connection status detection and judgment, as well as the corresponding control process.

[0124] In one embodiment, it can be as follows Figure 3 As shown, the controller 200 is also used to control the primary-side H-bridge circuit 114 and the bidirectional switching bridge arm 130 to operate in the corresponding operating modes according to the situation of the micro-inverter 100 being connected to the renewable energy conversion device 300. The operating modes include grid-connected operating mode and circuit-free operating mode.

[0125] Specifically, the controller 200 can control the operating mode switching of the micro-inverter 100 by controlling the switching transistors of the primary-side H-bridge circuit 114 and the bidirectional switching bridge arm 130. The connection status between the renewable energy conversion device 300 and the primary-side H-bridge circuit 114 includes connection and disconnection. When it is determined that the renewable energy conversion device 300 is connected to the primary-side H-bridge circuit 114, the controller 200 controls the primary-side H-bridge circuit 114 to operate in grid-connected mode; when it is determined that the renewable energy conversion device 300 is disconnected from the primary-side H-bridge circuit 114, the controller 200 controls the primary-side H-bridge circuit 114 to operate in off-circuit mode.

[0126] In one embodiment, it can be as follows Figure 4 As shown, the controller 200 includes: a maximum power point tracking unit 220, a voltage loop adjustment unit 230, a current loop control unit 240, and an access detection unit 210.

[0127] The maximum power point tracking unit 220 is connected to the primary-side H-bridge circuit 114. The maximum power point tracking unit 220 tracks the maximum power point of the renewable energy conversion device 300 and outputs a tracking reference voltage corresponding to the maximum power point. The tracking reference voltage includes a preset reference voltage U*ref for when the primary-side H-bridge circuit 114 is out of service.

[0128] Specifically, Maximum Power Point Tracking (MPPT) is a technology used to optimize renewable energy equipment such as photovoltaic systems (e.g., solar panels) and wind power systems. Its main purpose is to automatically adjust the system's operating point under different environmental conditions (e.g., temperature, light intensity, wind speed) to ensure that the output power reaches its maximum. In the specific processing of the MPPT unit 220, the output characteristics of the renewable energy conversion module are affected by various factors, typically exhibiting a non-linear current-voltage curve, with a point on the curve representing the maximum power point (MPP). The MPPT unit 220 monitors the voltage and current of the solar panels in real time and calculates the current output power. Commonly used MPPT algorithms include:

[0129] Perturb and Observe (P&O): This method involves making small perturbations to the voltage or current and then observing the changes in output power to determine the direction of adjustment.

[0130] Incremental Conductance (InCond): Based on derivative analysis of current and voltage, it finds the maximum power point by calculating the slope.

[0131] Fuzzy logic control: Using fuzzy logic algorithms to handle uncertainty and complexity.

[0132] The voltage loop adjustment unit 230 is connected to the maximum power point tracking unit 220 and the primary capacitor 113 respectively. The voltage loop adjustment unit 230 is used to output the peak reference value Iref of the grid current according to the voltage Ucap of the primary capacitor 113 and the tracking reference voltage.

[0133] Specifically, the voltage loop regulation unit 230 can be based on the proportional-integral processing unit, taking the voltage Ucap of the primary capacitor 113 and the primary voltage reference value Uref as inputs, and outputting the peak reference value Iref of the grid current.

[0134] The current loop control unit 240 is connected to the voltage loop regulation unit 230. The current loop control unit 240 is used to control the primary H-bridge circuit 114 and the bidirectional switch bridge arm 130 to work in the corresponding working mode according to the grid current peak reference value Iref. The working modes include grid-connected working mode and circuit-free working mode.

[0135] Specifically, the current loop control unit 240 may include a wave generator 200, which can convert the issued current reference value into a switching sequence for grid-connected control.

[0136] The access detection unit 210 is used to connect the primary capacitor 113 and the voltage loop adjustment unit 230 respectively. The access detection unit 210 is used to obtain and determine the connection status of the micro inverter 100 to the renewable energy conversion device 300 based on the voltage Ucap of the primary capacitor 113, the primary current of the primary H-bridge circuit 114, the peak reference value of the grid current Iref, and the grid connection status of the micro inverter 100.

[0137] Specifically, the access detection unit 210 can detect the opening and closing status of the switching transistors in the primary H-bridge circuit 114 and the bidirectional switching bridge arm 130.

[0138] In one embodiment, the renewable energy conversion device 300 may be a photovoltaic module 111.

[0139] In one embodiment, there are multiple primary-side H-bridge circuits 114 and transformers 120, and the number of each type is the same. The multiple primary-side H-bridge circuits 114 and the multiple transformers 120 are connected in a one-to-one correspondence.

[0140] In the aforementioned micro-inverter 100, the controller 200 compares the voltage of the primary-side capacitor 113 with a first threshold voltage to determine whether the photovoltaic string is connected or disconnected from the primary circuit. By setting the first threshold voltage between the minimum voltage for grid-connected operation of the primary circuit and the preset reference voltage for unconnected operation, the risk of false detection during connection is effectively reduced. By directly monitoring the voltage of the primary-side capacitor 113 and comparing it with the first threshold voltage, the connection status of the photovoltaic string is determined, and subsequent branch discrimination and processing are performed based on the monitored connection status. In implementation, by leveraging the bidirectional power flow characteristic of the DAB topology and selecting an appropriate voltage detection threshold, the accuracy of hot disconnection detection is improved through directly measured and stable current and voltage parameters. By controlling the voltage loop reference value through unconnection control, zero false detection of hot connection is achieved through voltage loop output detection combined with directly measured voltage parameters. Ultimately, this enables access detection and hot-plug detection, which require testing, to form a certain detection logic, mutually verify and support each other, thereby improving the control stability of the inverter.

[0141] In one exemplary embodiment, a photovoltaic system is provided, including a photovoltaic module 111 and a microinverter 100.

[0142] The photovoltaic string 111 is connected to the micro-inverter 100. Regarding the specific composition, functional implementation process, and beneficial effects of the micro-inverter 100 in the photovoltaic system, please refer to the description in the above embodiments, which will not be repeated here. The photovoltaic system provided in this application, by incorporating the aforementioned micro-inverter 100, can accurately realize the access detection and hot-plug detection of the photovoltaic modules 111 during the operation of the photovoltaic system. Based on the accurate detection results, protective actions such as wave blocking control can be performed in a timely manner when needed, thereby improving the overall performance of the photovoltaic system.

[0143] Furthermore, there is no limit to the number of photovoltaic strings 111 and micro-inverters 100 included in the photovoltaic system; the specific number can be set according to the actual situation.

[0144] Based on the same inventive concept, this application also provides a control method for a micro inverter 100. The micro inverter 100 includes a primary capacitor 113, a primary H-bridge circuit 114, a transformer 120, a bidirectional switching arm 130, and a controller 200. The input terminal of the primary capacitor 113 is connected to a renewable energy conversion device 300. The input terminal of the primary H-bridge circuit 114 is connected to the output terminal of the primary capacitor 113. The primary winding of the transformer 120 is connected to the output terminal of the primary H-bridge circuit 114. The input terminal of the bidirectional switching arm 130 is connected to the secondary winding of the transformer 120. The output terminal of the bidirectional switching arm 130 is connected to the power grid.

[0145] In an exemplary embodiment, the method is described using the controller 200 as an example. Figure 5 As shown, the method includes:

[0146] Step 502: Obtain the input signal, control signal, and grid connection status of the micro-inverter from the primary-side H-bridge circuit.

[0147] The control signal is the control signal applied to the primary H-bridge circuit and the bidirectional switching bridge arm.

[0148] The input signals to the primary-side H-bridge circuit include electrical signals that can be directly measured within the circuit, such as the voltage Ucap of the primary-side capacitor and the primary-side current. The specified control signals include the first threshold voltage Ucon, the minimum voltage Umin for primary-side grid-connected operation, the preset reference voltage U*ref for primary-side H-bridge circuit out-of-circuit operation, the second threshold voltage Uco, the peak reference value Iref for grid current, the connection detection threshold voltage Uci, the preset reference current I*ref for out-of-circuit operation, and the disconnection detection threshold current Ipvmin. These specified control signals can be preset and input by technicians or calculated in real-time on the grid side during controller processing. The grid-connected status of the microinverter can include both before and after grid connection.

[0149] For example, the controller can acquire the input signals of the primary-side H-bridge circuit, the control signals, and the grid connection status of the microinverter.

[0150] Step 504: Determine the connection status of the microinverter to the renewable energy conversion device based on the input signal and control signal of the primary H-bridge circuit and the grid connection status of the microinverter.

[0151] For example, after acquiring the input signal, control signal, and grid connection status of the microinverter from the primary-side H-bridge circuit, the controller can determine the connection status of the microinverter to the renewable energy conversion device based on the relationship between different signals in the application scenario.

[0152] In one embodiment, before the microinverter is connected to the grid, the controller executes step 504 as follows: Figure 6 As shown, it includes:

[0153] Step 602: Obtain the voltage of the primary capacitor before the microinverter is connected to the grid.

[0154] Step 604: When the voltage of the primary capacitor is greater than the first threshold voltage, determine that the primary side is connected to the renewable energy conversion device.

[0155] Among them, the first threshold voltage Ucon is less than the minimum voltage Umin for grid-connected operation of the primary H-bridge circuit, and greater than the preset reference voltage U*ref for out-of-circuit operation of the primary H-bridge circuit.

[0156] In this embodiment, if the microinverter is connected to a renewable energy conversion device, the connection voltage, i.e., the voltage Ucap of the primary capacitor, must be greater than or equal to the minimum voltage Umin for grid-connected operation of the primary H-bridge circuit. Therefore, it must be greater than the first threshold voltage Ucon. Thus, the connection status can be determined by comparing the voltage Ucap of the primary capacitor with the first threshold voltage Ucon, which helps to reduce the false positive probability of connection detection and improve the accuracy of connection detection.

[0157] In one embodiment, after the microinverter is connected to the grid, when the connection between the microinverter and the renewable energy conversion device changes from grid-connected operation to hot-disconnected operation, there are two possible operating states. The first is that the voltage drops to 0 instantaneously due to waveform generation, and the second is that it maintains stable operation at a certain voltage. These two phenomena depend on the magnitude of the grid current peak reference value Iref. When the grid current peak reference value Iref is greater than or equal to 0, positive power will be output after hot disconnection, and the floating voltage of the primary capacitor will be released immediately, resulting in a voltage drop to 0 instantaneously. When the grid current peak reference value Iref is less than 0, secondary power will be output after hot disconnection, and the floating voltage of the renewable energy conversion device will rise, balancing the losses and thus maintaining stable operation at a certain voltage. In this embodiment, hot disconnection detection is performed for the first phenomenon. The controller executes step 404 as follows: Figure 7 As shown, it includes:

[0158] Step 702: After the microinverter is connected to the grid, obtain the voltage of the primary capacitor in the grid-connected state.

[0159] Step 704: When the peak reference value of the grid current is greater than or equal to 0 and the voltage of the primary capacitor is less than the second threshold voltage, determine that the renewable energy conversion device is hot-plugged.

[0160] The second threshold voltage is less than the preset reference voltage for the primary-side H-bridge circuit to operate in the off-circuit mode.

[0161] In this embodiment, a second threshold voltage Uco is preset by a technician, and the second threshold voltage Uco is less than the preset reference voltage U*ref for the primary H-bridge circuit to operate in the off-circuit state. This helps to reduce the possibility of misjudgment caused by secondary ripple during low-voltage operation and improves the accuracy of hot-stripping detection under grid-connected conditions and when the renewable energy conversion device outputs positive power.

[0162] In one embodiment, for the detection and determination of the second phenomenon of hot-pull-out, the process of the controller executing step 504 can be as follows: Figure 8 As shown, it includes:

[0163] Step 802: After the microinverter is connected to the grid, obtain the primary current under grid-connected conditions.

[0164] Step 804: When the peak reference value of the grid current is less than 0 and the primary current is continuously less than the preset pull-out detection threshold current within the preset time window, the renewable energy conversion device is determined to be hot-pulled out.

[0165] In one embodiment, when the microinverter is in a circuit-off condition, it can be as follows: Figure 9 As shown, step 504 includes:

[0166] Step 902: When the microinverter is in a circuit-free condition, obtain the reference value of the peak grid current.

[0167] Step 904: When the peak reference value of the grid current is greater than the preset reference current for the primary H-bridge circuit to operate without a circuit, determine the hot connection of the renewable energy conversion device.

[0168] The preset reference current for the primary-side H-bridge circuit to operate in a circuit-free state is greater than 0.

[0169] For example, in a hot-connection detection scenario, in the unconnected state, the unconnected circuit is controlled in the circuit-out control loop under the circuit-out condition. At this time, the primary-side H-bridge circuit operates at the preset reference voltage U*ref. Since no power is output to the secondary side (i.e., the grid side) during a circuit outage, the voltage loop output is small, typically negative. Due to the sudden connection, the reference voltage Uref for circuit outage control is generally less than the minimum maximum power point voltage within the specification. Therefore, the voltage reference value differs significantly from the open-circuit voltage of the connected component, causing a sudden increase in the voltage loop output. In this scenario, a judgment condition can be set for the circuit state change during hot connection. When the peak reference value of the grid current Iref is greater than the preset reference current I*ref for the primary-side H-bridge circuit operating at a circuit outage, the renewable energy conversion device is determined to be hot-connected.

[0170] In one embodiment, when the microinverter is in a circuit-free condition, the controller can, as follows: Figure 10 As shown, step 504 includes:

[0171] Step 1002: When the microinverter is in a circuit-out condition, obtain the voltage of the primary capacitor in the circuit-out state.

[0172] Step 1004: When the voltage of the primary capacitor is greater than the preset access detection threshold voltage, the renewable energy conversion device is confirmed to be in hot connection.

[0173] Among them, the access detection threshold voltage is greater than the minimum voltage for grid-connected operation of the primary H-bridge circuit.

[0174] For example, in another embodiment of the hot access scenario, since the floating voltage will be much smaller than the access voltage during hot access, a hot access voltage threshold Uci can be set accordingly. The hot access voltage threshold Uci is greater than the minimum voltage Umin for primary side grid connection as the setting condition. When the voltage Ucap of the primary side capacitor is greater than the hot access voltage threshold, it can be determined as hot access.

[0175] In one embodiment, it can be as follows Figure 11 As shown, the above method also includes:

[0176] Step 1102: Based on the connection status of the microinverter to the renewable energy conversion device, control the primary-side H-bridge circuit and the bidirectional switching bridge arm to operate in the corresponding working mode.

[0177] The operating modes include grid-connected operating mode and circuit-deficient operating mode.

[0178] For example, the controller can output a signal sequence for controlling the switching transistors of the primary-side H-bridge circuit and the bidirectional switching arm, depending on whether the microinverter is connected to the renewable energy conversion device, thereby controlling the primary-side H-bridge circuit and the bidirectional switching arm to operate in the corresponding operating mode.

[0179] It should be understood that although the steps in the flowcharts of the embodiments described above are shown sequentially according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless explicitly stated herein, there is no strict order restriction on the execution of these steps, and they can be executed in other orders. Moreover, at least some steps in the flowcharts of the embodiments described above may include multiple steps or multiple stages. These steps or stages are not necessarily completed at the same time, but can be executed at different times. The execution order of these steps or stages is not necessarily sequential, but can be performed alternately or in turn with other steps or at least some of the steps or stages of other steps.

[0180] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0181] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. A micro-inverter, characterized by, The micro-inverter comprises: a primary side capacitor, an input end of the primary side capacitor being used for connecting a renewable energy conversion device; a primary side H-bridge circuit, an input end of the primary side H-bridge circuit being connected to an output end of the primary side capacitor; a transformer, a primary side winding of the transformer being connected to an output end of the primary side H-bridge circuit; a bidirectional switch bridge arm, an input end of the bidirectional switch bridge arm being connected to a secondary side winding of the transformer, and an output end of the bidirectional switch bridge arm being used for connecting a power grid; a controller, the controller being used for acquiring and determining a connection state of the micro-inverter and the renewable energy conversion device according to an input signal of the primary side H-bridge circuit, a specified control signal, and a grid-connected state of the micro-inverter; the specified control signal being a control signal loaded to the primary side H-bridge circuit and the bidirectional switch bridge arm.

2. The micro-inverter of claim 1, wherein, The controller is used for acquiring a voltage of the primary side capacitor before the micro-inverter is connected to the power grid, and determining that the renewable energy conversion device is connected to the primary side when the voltage of the primary side capacitor is greater than a first threshold voltage. The first threshold voltage is less than a minimum voltage of the primary side H-bridge circuit in a grid-connected working state, and greater than a preset reference voltage of the primary side H-bridge circuit in an off-grid working state.

3. The micro-inverter of claim 1, wherein, The controller is used for acquiring the voltage of the primary side capacitor in the grid-connected state after the micro-inverter is connected to the power grid, and determining that the renewable energy conversion device is hot pulled out when the voltage of the primary side capacitor is less than a second threshold voltage and a grid current peak reference value is greater than or equal to 0. The second threshold voltage is less than the preset reference voltage of the primary side H-bridge circuit in the off-grid working state.

4. The micro-inverter of claim 1, wherein, The controller is used for acquiring a primary side current in the grid-connected state after the micro-inverter is connected to the power grid, and determining that the renewable energy conversion device is hot pulled out when the primary side current is less than a preset pull-out detection threshold current in a preset time window and the grid current peak reference value is less than 0.

5. The micro-inverter of claim 1, wherein, The controller is used for acquiring the grid current peak reference value when the micro-inverter is in the off-grid working state, and determining that the renewable energy conversion device is hot connected when the grid current peak reference value is greater than a preset reference current of the primary side H-bridge circuit in the off-grid working state. The preset reference current of the primary side H-bridge circuit in the off-grid working state is greater than 0.

6. The micro-inverter of claim 1, wherein, The controller is used for acquiring a voltage of the primary side capacitor in the off-grid state when the micro-inverter is in the off-grid working state, and determining that the renewable energy conversion device is hot connected when the voltage of the primary side capacitor is greater than a preset connection detection threshold voltage. The connection detection threshold voltage is greater than a minimum voltage of the primary side H-bridge circuit in the grid-connected working state.

7. The micro-inverter according to any of claims 1-6, wherein, The controller is used for controlling the primary side H-bridge circuit and the bidirectional switch bridge arm to work in corresponding working modes according to a connection state of the micro-inverter and the renewable energy conversion device, the working modes including a grid-connected working mode and an off-grid working mode.

8. The micro-inverter according to any one of claims 1-6, wherein, The controller comprises: a maximum power point tracking unit, the maximum power point tracking unit being connected to the primary side H-bridge circuit, and the maximum power point tracking unit being used for tracking a maximum power point of the renewable energy conversion device and outputting a tracking reference voltage corresponding to the maximum power point; a voltage loop regulating unit, connected with the maximum power point tracking unit and the primary capacitor respectively, configured to output a grid current peak reference value according to the voltage of the primary capacitor and the tracking reference voltage; a current loop control unit, connected with the voltage loop regulating unit, configured to control the primary H-bridge circuit and the bidirectional switch bridge arm to work in corresponding working modes according to the grid current peak reference value, the working modes including a grid-connected working mode and an off-grid working mode; an access detection unit, connected with the primary capacitor and the voltage loop regulating unit respectively, configured to determine the access of the micro-inverter to the renewable energy conversion device according to the voltage of the primary capacitor, the primary current of the primary H-bridge circuit, the grid current peak reference value and the grid-connected state of the micro-inverter.

9. The micro-inverter according to any one of claims 1-6, wherein, The renewable energy conversion device is a photovoltaic module.

10. The micro-inverter according to any one of claims 1-6, wherein, The primary H-bridge circuit and the transformer are multiple and have the same number, and the multiple primary H-bridge circuits and the multiple transformers are connected one by one.

11. A photovoltaic system characterized by, The micro-inverter comprises: The micro-inverter of any one of claims 1-10; one or more photovoltaic modules, and the output end of each photovoltaic module is connected with the input end of the micro-inverter.

12. A control method of a micro inverter, characterized by, The micro-inverter comprises a primary capacitor, a primary H-bridge circuit, a transformer and a bidirectional switch bridge arm; the input end of the primary capacitor is configured to connect with a renewable energy conversion device; the input end of the primary H-bridge circuit is connected with the output end of the primary capacitor; the primary winding of the transformer is connected with the output end of the primary H-bridge circuit; the input end of the bidirectional switch bridge arm is connected with the secondary winding of the transformer; and the output end of the bidirectional switch bridge arm is configured to connect with a grid; and the method comprises: obtaining an input signal of the primary H-bridge circuit, a control signal and a grid-connected state of the micro-inverter; determining the access of the micro-inverter to the renewable energy conversion device according to the input signal of the primary H-bridge circuit, the control signal and the grid-connected state of the micro-inverter; The control signal is a control signal loaded to the primary H-bridge circuit and the bidirectional switch bridge arm.

13. The method of claim 12, wherein, The determination of the access of the micro-inverter to the renewable energy conversion device according to the input signal of the primary H-bridge circuit, the control signal and the grid-connected state of the micro-inverter comprises: obtaining the voltage of the primary capacitor before the micro-inverter is connected with the grid; when the voltage of the primary capacitor is greater than a first threshold voltage, determining that the primary is connected with the renewable energy conversion device; The first threshold voltage is less than the minimum voltage of the grid-connected working mode of the primary H-bridge circuit and greater than a preset reference voltage of the off-grid working mode of the primary H-bridge circuit.

14. The control method of a micro-inverter according to claim 12, wherein The determination of the access of the micro-inverter to the renewable energy conversion device according to the input signal of the primary H-bridge circuit, the control signal and the grid-connected state of the micro-inverter comprises: after the micro-inverter is connected with the grid, obtaining the voltage of the primary capacitor under the grid-connected state; determining that the renewable energy conversion device is hot-plugged when the grid current peak reference value is greater than or equal to 0 and the voltage of the primary side capacitor is less than a second threshold voltage. The second threshold voltage is less than a preset reference voltage of the primary side H-bridge circuit in the open-circuit working condition.

15. The control method of a micro-inverter according to claim 12, wherein The determining the condition of the micro-inverter accessing the renewable energy conversion device according to the input signal of the primary side H-bridge circuit, the control signal and the grid-connected state of the micro-inverter comprises: acquiring the primary side current in the grid-connected state after the micro-inverter is grid-connected; determining that the renewable energy conversion device is hot-plugged when the grid current peak reference value is less than 0 and the primary side current is less than a preset plugging detection threshold current in a preset time window.

16. The control method of a micro-inverter according to claim 12, wherein The determining the condition of the micro-inverter accessing the renewable energy conversion device according to the input signal of the primary side H-bridge circuit, the control signal and the grid-connected state of the micro-inverter comprises: acquiring the grid current peak reference value when the micro-inverter is in the open-circuit working condition; determining that the renewable energy conversion device is hot-plugged when the grid current peak reference value is greater than a preset reference current of the primary side H-bridge circuit in the open-circuit working condition. The preset reference current of the primary side H-bridge circuit in the open-circuit working condition is greater than 0.

17. The control method of a micro-inverter according to claim 12, wherein The determining the condition of the micro-inverter accessing the renewable energy conversion device according to the input signal of the primary side H-bridge circuit, the control signal and the grid-connected state of the micro-inverter comprises: acquiring the voltage of the primary side capacitor in the open-circuit state when the micro-inverter is in the open-circuit working condition; determining that the renewable energy conversion device is hot-plugged when the voltage of the primary side capacitor is greater than a preset plugging detection threshold voltage. The plugging detection threshold voltage is greater than a minimum voltage of the primary side H-bridge circuit in the grid-connected working condition.

18. The method according to any one of claims 12-17, characterized by, The method further comprises: controlling the primary side H-bridge circuit and the bidirectional switch bridge arm to work in a corresponding working mode according to the condition of the micro-inverter accessing the renewable energy conversion device; The working mode comprises a grid-connected working mode and an open-circuit working mode.

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