A micro-inverter, photovoltaic system and control method

Abstract

The application discloses a micro inverter, a photovoltaic system and a control method. The micro inverter comprises a secondary side bridge arm circuit, N primary side windings, N secondary side windings and N primary side H bridge circuits; N is an integer greater than or equal to 2; the N primary side windings and the N primary side H bridge circuits are connected one by one, the N secondary side windings are connected together in parallel to connect the secondary side bridge arm circuit; a controller is configured to obtain an ith grid-connected current according to grid-connected power of an ith primary side H bridge circuit, and control an inner phase-shifting angle of the ith primary side H bridge circuit and an outer phase-shifting angle between the ith primary side winding and the secondary side bridge arm circuit according to the ith grid-connected current and an ith current reference value; the ith primary side H bridge circuit is any one of the N primary side H bridge circuits. Since the grid-connected power of each channel is easy to obtain, the technical solution is easy to implement, independent scheduling of the power of each channel is realized, and the power control between the channels does not affect each other.

Description

Technical Field

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

[0002] As photovoltaic (PV) power generation continues to mature, it is increasingly being applied to homes, i.e., residential PV systems. With the development of residential PV systems, inverters are becoming smaller and smaller, leading to the emergence of micro-inverters.

[0003] Currently, microinverters can include at least one primary winding, each primary winding being used to connect to a corresponding photovoltaic panel. Each primary winding is connected to a corresponding primary H-bridge circuit.

[0004] Micro-inverters can achieve grid connection by controlling the inner and outer phase shift angles of the primary-side H-bridge circuit and the secondary-side bridge arm circuit. The inner phase shift angle refers to the phase shift angle of the internal switching transistors in the primary-side H-bridge circuit, while the outer phase shift angle refers to the phase shift angle between the switching transistors in the primary-side H-bridge circuit and the secondary-side bridge arm circuit.

[0005] A microinverter can include multiple inputs and one output. Since the secondary side shares a single output circuit, independent power control for each input cannot be achieved solely by relying on the grid-connected current. Summary of the Invention

[0006] In view of this, this application provides a micro inverter, a photovoltaic system and a control method that can realize independent control of each power source without affecting each other.

[0007] This application provides a micro inverter, comprising: a secondary bridge arm circuit, N primary windings, N secondary windings, and N primary H-bridge circuits; where N is an integer greater than or equal to 2.

[0008] N primary windings and N primary H-bridge circuits are connected one-to-one, and N secondary windings are connected in parallel to the secondary bridge arm circuit.

[0009] The controller is used to obtain the i-th grid-connected current based on the grid-connected power of the i-th primary H-bridge circuit, and to control the inner phase shift angle of the i-th primary H-bridge circuit and the outer phase shift angle between the i-th primary winding and the secondary bridge arm circuit based on the i-th grid-connected current and the i-th current reference value; the i-th primary H-bridge circuit is any one of the N primary H-bridge circuits.

[0010] Preferably, the controller is specifically used to obtain the grid-connected power of the i-th primary-side H-bridge circuit based on the input voltage and input current of the i-th primary-side H-bridge circuit.

[0011] Preferably, the controller is specifically configured to obtain the input power of the i-th primary-side H-bridge circuit based on the input voltage and input current of the i-th primary-side H-bridge circuit, and to obtain the grid-connected power of the i-th primary-side H-bridge circuit based on the input power and efficiency of the i-th primary-side H-bridge circuit.

[0012] Preferably, the controller is specifically used to obtain the grid-connected current of the i-th channel based on the grid voltage, grid phase angle, and grid-connected power of the i-th primary-side H-bridge circuit.

[0013] Preferably, the controller is specifically configured to obtain the instantaneous value of the i-th grid-connected current based on the grid voltage, the cosine value of the grid phase angle, and the grid-connected power of the i-th primary H-bridge circuit, obtain the comparison result between the instantaneous value of the i-th grid-connected current and the reference value of the i-th current, and control the inner phase shift angle of the i-th primary H-bridge circuit and the outer phase shift angle between the i-th primary winding and the secondary bridge arm circuit based on the comparison result.

[0014] Preferably, the secondary bridge arm circuit includes a bidirectional switching bridge arm and a capacitor bridge arm;

[0015] The upper and lower arms of the bidirectional switch bridge arm both include bidirectional switches, and the upper and lower arms of the capacitor bridge arm each include a first secondary capacitor and a second secondary capacitor with equal capacitance values.

[0016] Preferably, it further includes: N decoupling inductors;

[0017] N decoupling inductors are connected in series with N primary windings in a one-to-one correspondence; or, N decoupling inductors are connected in series with N secondary windings in a one-to-one correspondence; or, the decoupling inductors are the leakage inductance of the corresponding transformer.

[0018] This application also provides a photovoltaic system, including the micro-inverter described above; and further including: N photovoltaic arrays;

[0019] In a micro-inverter, N primary-side H-bridge circuits are connected one-to-one with N photovoltaic arrays;

[0020] A micro inverter is used to convert the direct current (DC) from N photovoltaic arrays into alternating current (AC) output.

[0021] This application also provides a control method for a micro inverter, the micro inverter comprising: a secondary bridge arm circuit, N primary windings, N secondary windings and N primary H-bridge circuits; N is an integer greater than or equal to 2; the N primary windings and the N primary H-bridge circuits are connected one-to-one, and the N secondary windings are connected in parallel to the secondary bridge arm circuit.

[0022] The control method includes:

[0023] Obtain the grid-connected power of the i-th primary-side H-bridge circuit; the i-th primary-side H-bridge circuit is any one of the N primary-side H-bridge circuits;

[0024] The i-th grid-connected current is obtained based on the grid-connected power of the i-th primary H-bridge circuit. Based on the i-th grid-connected current and the i-th current reference value, the inner phase shift angle of the i-th primary H-bridge circuit and the outer phase shift angle between the i-th primary winding and the secondary bridge arm circuit are controlled.

[0025] Preferably, obtaining the grid-connected power of the i-th primary-side H-bridge circuit specifically includes:

[0026] The grid-connected power of the i-th primary-side H-bridge circuit is obtained from the input voltage and input current of the i-th primary-side H-bridge circuit.

[0027] Preferably, the grid-connected power of the i-th primary-side H-bridge circuit is obtained based on the input voltage and input current of the i-th primary-side H-bridge circuit, specifically including:

[0028] The input power of the i-th primary-side H-bridge circuit is obtained from the input voltage and input current of the i-th primary-side H-bridge circuit. The grid-connected power of the i-th primary-side H-bridge circuit is obtained from the input power and efficiency of the i-th primary-side H-bridge circuit.

[0029] Preferably, the grid-connected current of the i-th primary-side H-bridge circuit is obtained based on the grid-connected power of the i-th primary-side H-bridge circuit, specifically including:

[0030] The grid-connected current of the i-th path is obtained based on the grid voltage, grid phase angle, and grid-connected power of the i-th primary-side H-bridge circuit.

[0031] Preferably, the i-th grid-connected current is obtained based on the grid-connected power of the i-th primary-side H-bridge circuit, and the inner phase shift angle of the i-th primary-side H-bridge circuit and the outer phase shift angle between the i-th primary-side winding and the secondary-side bridge arm circuit are controlled based on the i-th grid-connected current and the i-th current reference value. Specifically, this includes:

[0032] The instantaneous value of the grid-connected current of the i-th path is obtained based on the grid voltage, the cosine value of the grid phase angle, and the grid-connected power of the i-th primary H-bridge circuit. The comparison result between the instantaneous value of the i-th grid-connected current and the reference value of the i-th current is obtained. Based on the comparison result, the inner phase shift angle of the i-th primary H-bridge circuit and the outer phase shift angle between the i-th primary winding and the secondary bridge arm circuit are controlled.

[0033] Therefore, this application has the following beneficial effects:

[0034] The micro-inverter provided in this application does not directly obtain the grid-connected current. Instead, it obtains the grid-connected power of each circuit, and then obtains the grid-connected current of each circuit from the grid-connected voltage and the grid-connected power of each circuit. Finally, it compares the grid-connected current with a reference current value to achieve closed-loop control of the power of each circuit. Since the grid-connected power of each circuit is readily available, this technical solution is easy to implement and can achieve independent scheduling of the power of each circuit, with the power control between circuits not affecting each other. Attached Figure Description

[0035] Figure 1 A schematic diagram of a single-stage microinverter provided in an embodiment of this application;

[0036] Figure 2 A schematic diagram of a single-stage dual-input microinverter provided in an embodiment of this application;

[0037] Figure 3 A schematic diagram of a micro inverter provided in an embodiment of this application;

[0038] Figure 4 The control principle diagram of the micro inverter provided in the embodiments of this application;

[0039] Figure 5 A schematic diagram of a photovoltaic system provided in an embodiment of this application;

[0040] Figure 6 A flowchart illustrating a control method for a microinverter provided in this application embodiment;

[0041] Figure 7 A flowchart of another control method for a micro inverter provided in an embodiment of this application. Detailed Implementation

[0042] To enable those skilled in the art to better understand and implement the technical solutions provided in the embodiments of this application, the application scenarios will be described below in conjunction with the accompanying drawings.

[0043] Taking the application of microinverters in photovoltaic power generation as an example, the input terminal of the microinverter is connected to a photovoltaic array. This application does not specifically limit the number of photovoltaic modules included in the photovoltaic array; it can be multiple or a single module.

[0044] See Figure 1 The figure is a schematic diagram of a single-stage micro-inverter provided in an embodiment of this application.

[0045] A microinverter typically includes a primary-side H-bridge circuit, a transformer, and a secondary-side bridge arm circuit. The transformer consists of primary and secondary windings. The input of a microinverter will be described using a photovoltaic array (PV array) as an example.

[0046] The secondary-side bridge arm circuit includes a bidirectional switching bridge arm and a capacitor bridge arm. The transformer is a high-frequency transformer, which enables voltage boosting and electrical isolation between the primary and secondary sides.

[0047] The micro-inverter can achieve grid connection function of a single-stage micro-inverter by controlling the inner phase shift angle of the primary H-bridge circuit and the outer phase shift angle between the primary H-bridge circuit and the secondary bridge arm circuit.

[0048] For example, the first arm of the primary-side H-bridge circuit includes switches S1 and S2 connected in series, and the second arm includes switches S3 and S4 connected in series. The input capacitance of the primary-side H-bridge circuit is Cbus, and the turns ratio of the primary winding to the secondary winding of the transformer is 1:n.

[0049] The bidirectional switching bridge arm includes bidirectional switches, with the upper half consisting of S5 and S6, and the lower half consisting of S7 and S8. The upper and lower arms of the capacitor bridge arm each include a first secondary capacitor C1 and a second secondary capacitor C2 with equal capacitance values. Additionally, the microinverter includes a decoupling inductor Lk, which can be connected in series with either the primary or secondary winding. It should be noted that Lk can be a physical inductor or the leakage inductance of the transformer. Figure 1 uses the example of Lk being connected in series with the secondary winding. Furthermore, Lm represents the magnetizing inductance of the transformer.

[0050] When the grid voltage is greater than zero, the secondary switching transistors operate in mode one: S5 and S7 act as high-frequency transistors for high-frequency chopping, while S6 and S8 are directly connected. When the grid voltage is less than zero, the secondary switching transistors operate in mode two: S6 and S8 act as high-frequency transistors for high-frequency chopping, while S5 and S7 are directly connected.

[0051] The microinverter has two degrees of freedom: the inner phase shift angle D1 and the outer phase shift angle D2. Energy transfer in the microinverter can be achieved by controlling D1 and D2. D1 is defined as the angle by which the drive signal of transistor S4 lags behind the drive signal of transistor S1, and D2 is defined as the angle by which the drive signal of transistor S5 (S8) lags behind the drive signal of transistor S1.

[0052] The following is combined Figure 2 This section introduces microinverters with multiple inputs, but for ease of explanation, we will use a two-input example.

[0053] See Figure 2 The figure is a schematic diagram of a single-stage dual-input micro inverter provided in an embodiment of this application.

[0054] The input terminal of the first primary-side H-bridge circuit is connected to the first photovoltaic array PV1, and the input terminal of the second primary-side H-bridge circuit is connected to the second photovoltaic array PV2.

[0055] Figure 2It includes two primary-side H-bridge circuits, corresponding to two primary windings and two secondary windings. The specific connection relationship is as follows: Figure 1 Similarly, the structures of the primary-side H-bridge circuit and the secondary-side bridge arm circuit are both similar to... Figure 1 The same applies, so I won't repeat it here.

[0056] It should be understood that when multiple transformers are involved, i.e., multiple primary windings and multiple secondary windings, the turns ratio of the multiple transformers is the same, which is 1:n.

[0057] Since the secondary bridge arm circuits share a single circuit and only have one grid-connected current sample, the current method used is to perform closed-loop control using a single grid-connected current. However, during power dispatching, power control is required for each input path, and relying solely on grid-side grid-connected current control cannot achieve independent power control for each path.

[0058] When a microinverter performs power control on each input path under multi-input conditions, in order to achieve independent power control for each path, it is necessary to obtain the active and reactive power of each path. Based on the power of each path, independent control of each path can be achieved through power closed-loop or current closed-loop.

[0059] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the embodiments of this application will be further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0060] See Figure 3 The figure is a schematic diagram of a micro inverter provided in an embodiment of this application.

[0061] The micro inverter provided in this application includes: a secondary bridge arm circuit, N primary windings, N secondary windings, N decoupling inductors, and N primary H-bridge circuits; N is an integer greater than or equal to 2;

[0062] For ease of understanding and description, this application uses a micro-inverter with two inputs as an example. It should be understood that a micro-inverter may include more inputs, such as three, four or more. However, in actual applications, some input terminals may not be connected to the photovoltaic array, that is, some primary-side H-bridge circuits may not be connected to the photovoltaic array, while the input terminals of other primary-side H-bridge circuits may be connected without affecting the normal operation of the micro-inverter.

[0063] The two paths correspond to the first primary-side H-bridge circuit 100 and the second primary-side H-bridge circuit 200, respectively. The input terminal of the first primary-side H-bridge circuit 100 is connected to the first photovoltaic array PV1, and the input terminal of the second primary-side H-bridge circuit 200 is connected to the second photovoltaic array PV2.

[0064] N primary windings and N primary H-bridge circuits are connected one-to-one; N secondary windings are connected in parallel to the secondary bridge arm circuit 300; N decoupling inductors are connected in series with N primary windings one-to-one, or N decoupling inductors are connected in series with N secondary windings one-to-one. Figure 3 This example uses the decoupling inductor Lk connected in series with the secondary winding. For ease of calculation and control, the inductance values ​​of each decoupling inductor can be the same.

[0065] The decoupling inductor is used to decouple the power between the circuits, meaning that each circuit can be controlled independently without affecting each other.

[0066] Since the control of each channel does not affect each other, the following introduction will take the control of any one channel as an example, and the control of other channels is similar.

[0067] The controller is used to obtain the i-th grid-connected current based on the grid-connected power of the i-th primary H-bridge circuit, and to control the inner phase shift angle of the i-th primary H-bridge circuit and the outer phase shift angle between the i-th primary winding and the secondary bridge arm circuit based on the i-th grid-connected current and the i-th current reference value; the i-th primary H-bridge circuit is any one of the N primary H-bridge circuits.

[0068] When a microinverter has multiple inputs, the grid-connected power of each input can be obtained from the input power of each DC-side input. The input power of each DC-side input can be obtained from the input current and input voltage of that input. It should be understood that the input voltage and input current of each DC-side input can be obtained in real time. The input voltage can be obtained using a voltage sensor, and the input current can be obtained using a current sensor. Alternatively, the input voltage and input current can also be obtained through other methods. Here, the input voltage and input current represent the voltage and current of the photovoltaic array connected to the input terminals, respectively.

[0069] Considering the power loss and other losses during the energy conversion process of a microinverter, a conversion efficiency exists. This efficiency can be obtained from the efficiency curves of each circuit, and the corresponding output power can be derived from the efficiency and input power. The output power of each circuit is then its grid-connected power.

[0070] When the grid-connected power of each circuit is known, the grid-connected voltage is also known, i.e., it is the grid voltage, which can be sampled. Therefore, the grid-connected current of each circuit can be obtained based on the grid-connected voltage and grid-connected power, and then the power closed-loop control of each circuit can be performed based on the grid-connected current and the reference current value.

[0071] The micro-inverter provided in this application does not directly obtain the grid-connected current. Instead, it obtains the grid-connected power of each circuit, and then obtains the grid-connected current of each circuit from the grid-connected voltage and the grid-connected power of each circuit. Finally, it compares the grid-connected current with a reference current value to achieve closed-loop control of the power of each circuit. Since the grid-connected power of each circuit is readily available, this technical solution is easy to implement and can achieve independent scheduling of the power of each circuit, with the power control between circuits not affecting each other.

[0072] The following is combined Figure 4 A general overview will be provided.

[0073] See Figure 4 The figure is a control principle diagram of the micro inverter provided in the embodiment of this application.

[0074] This application continues to use two-channel input as an example for illustration. There can be more channels, and the control principle is similar, so it will not be described again here.

[0075] The input terminal of the first primary-side H-bridge circuit is used to connect PV1, and the input terminal of the second primary-side H-bridge circuit is used to connect PV2.

[0076] The controller obtains the input currents I1 and I2 from each DC side and the input voltages U1 and U2 from each DC side, and thus obtains the input power of the two channels as follows:

[0077] Pin1 = I1 * U1;

[0078] Pin2 = I2 * U2.

[0079] Pin1 and Pin2 represent the input power of the first primary-side H-bridge circuit and the input power of the second primary-side H-bridge circuit, respectively.

[0080] The controller determines the efficiency of each channel by analyzing its efficiency curves, and thus obtains the output power of each channel:

[0081] Pout1 = η1 * Pin1;

[0082] Pout2 = η2 * Pin2.

[0083] Pout1 and Pout2 are the output powers of the first and second primary-side H-bridge circuits, respectively. η1 and η2 are the efficiencies of the first and second primary-side H-bridge circuits, respectively. It should be understood that different input powers may correspond to different efficiencies. The corresponding efficiency can be obtained based on the current input power, for example, by looking up a table.

[0084] The controller 400 can obtain the grid-connected current based on the output power of each channel, the grid-side voltage, and the grid phase angle θ. That is, by sampling the grid voltage as Ug, the grid phase angle θ can be obtained using a phase-locked loop, and then the grid-connected current of each channel can be obtained as follows:

[0085] ig1 = Pout1 / Ug * sin(θ);

[0086] ig2 = Pout2 / Ug*sin(θ).

[0087] ig1 and ig2 are the grid-connected currents of the first primary-side H-bridge circuit and the second primary-side H-bridge circuit, respectively.

[0088] The controller 400 is used to obtain a first input power Pin1 based on the input current i1 and input voltage U1 of the first primary-side H-bridge circuit, obtain a first output power Pout1 based on the first input power and a first efficiency, obtain a first grid-connected current ig1 based on the first output power Pout1, grid voltage Ug and grid phase angle θ, compare ig1 with the corresponding first current reference value iref1, and obtain the inner phase shift angle D11 of the first primary-side H-bridge circuit and the outer phase shift angle D12 between the first primary-side H-bridge circuit and the secondary-side bridge arm circuit.

[0089] The controller 400 is used to obtain the second input power Pin2 based on the input current i2 and input voltage U2 of the second primary H-bridge circuit, obtain the second output power Pout2 based on the second input power and the second efficiency, obtain the second grid-connected current ig2 based on the second output power Pout2, the grid voltage Ug and the grid phase angle θ, compare ig2 with the corresponding second current reference value iref2, and obtain the inner phase shift angle D21 of the second primary H-bridge circuit and the outer phase shift angle D22 between the second primary H-bridge circuit and the secondary bridge arm circuit.

[0090] It should be understood that both ifef1 and ifef2 are known instruction values.

[0091] It should be noted that the micro-inverter provided in the above embodiments does not specifically limit the type of each switch in the primary-side H-bridge circuit and the secondary-side bridge arm circuit. For example, it can be an Insulated Gate Bipolar Transistor (IGBT), a Metal Oxide Semiconductor Field Effect Transistor (MOSFET), or a SiC MOSFET (Silicon Carbide Metal Oxide Semiconductor Field Effect Transistor). When the switching transistor is a MOSFET, it can specifically be a PMOS transistor or an NMOS transistor; this application embodiment does not specifically limit this.

[0092] Based on the micro inverter provided in the above embodiments, this application also provides a photovoltaic system, which will be described in detail below with reference to the accompanying drawings.

[0093] See Figure 5 The figure is a schematic diagram of a photovoltaic system provided in an embodiment of this application.

[0094] The photovoltaic system provided in this application includes the micro-inverter 1000 described in the above embodiments; it also includes N photovoltaic arrays; N is an integer greater than or equal to 2.

[0095] In the micro inverter 1000, the N primary-side H-bridge circuits are connected one-to-one with the N photovoltaic arrays; that is, the N photovoltaic arrays are PV1-PVN.

[0096] The micro inverter 1000 is used to convert the DC power from N photovoltaic arrays into AC power output.

[0097] The embodiments of this application do not specifically limit the scenario of the photovoltaic system. For example, it can be a residential photovoltaic system, and the load can be home appliances, etc. At the same time, the photovoltaic system can achieve grid-connected power generation.

[0098] This photovoltaic system does not detect the final grid-side current, but obtains the grid-connected power of each line by detecting the input power of each line in the micro-inverter, and then obtains the grid-connected current of each line based on the grid-connected power of each line, so as to achieve independent control of the power of each line. This control method is simple and the lines do not affect each other.

[0099] Based on the micro inverter and photovoltaic system provided in the above embodiments, this application also provides a control method for the micro inverter, which will be described in detail below with reference to the accompanying drawings.

[0100] See Figure 6The figure is a flowchart of a control method for a micro inverter provided in an embodiment of this application.

[0101] The control method for a micro-inverter provided in this application includes:

[0102] S601: Obtain the grid-connected power of the i-th primary-side H-bridge circuit; the i-th primary-side H-bridge circuit is any one of the N primary-side H-bridge circuits.

[0103] For ease of understanding and description, this application uses a micro-inverter with two inputs as an example. It should be understood that a micro-inverter may include more inputs, such as three, four or more. However, in actual applications, some input terminals may not be connected to the photovoltaic array, that is, some primary-side H-bridge circuits may not be connected to the photovoltaic array, while the input terminals of other primary-side H-bridge circuits may be connected without affecting the normal operation of the micro-inverter.

[0104] S602: Obtain the i-th grid-connected current based on the grid-connected power of the i-th primary H-bridge circuit, and control the inner phase shift angle of the i-th primary H-bridge circuit and the outer phase shift angle between the i-th primary winding and the secondary bridge arm circuit based on the i-th grid-connected current and the i-th current reference value.

[0105] When a microinverter has multiple inputs, the grid-connected power of each input can be obtained from the input power of each DC-side input. The input power of each DC-side input can be obtained from the input current and input voltage of that input. It should be understood that the input voltage and input current of each DC-side input can be obtained in real time. The input voltage can be obtained using a voltage sensor, and the input current can be obtained using a current sensor. Alternatively, the input voltage and input current can also be obtained through other methods. Here, the input voltage and input current represent the voltage and current of the photovoltaic array connected to the input terminals, respectively.

[0106] Considering the power loss and other losses during the energy conversion process of a microinverter, a conversion efficiency exists. This efficiency can be obtained from the efficiency curves of each circuit, and the corresponding output power can be derived from the efficiency and input power. The output power of each circuit is then its grid-connected power.

[0107] When the grid-connected power of each circuit is known, the grid-connected voltage is also known, i.e., it is the grid voltage, which can be sampled. Therefore, the grid-connected current of each circuit can be obtained based on the grid-connected voltage and grid-connected power, and then the power closed-loop control of each circuit can be performed based on the grid-connected current and the reference current value.

[0108] The micro-inverter provided in this application does not directly obtain the grid-connected current. Instead, it obtains the grid-connected power of each circuit, and then obtains the grid-connected current of each circuit from the grid-connected voltage and the grid-connected power of each circuit. Finally, it compares the grid-connected current with a reference current value to achieve closed-loop control of the power of each circuit. Since the grid-connected power of each circuit is readily available, this technical solution is easy to implement and can achieve independent scheduling of the power of each circuit, with the power control between circuits not affecting each other.

[0109] Obtaining the grid-connected power of the i-th primary-side H-bridge circuit specifically includes: obtaining the grid-connected power of the i-th primary-side H-bridge circuit based on the input voltage and input current of the i-th primary-side H-bridge circuit.

[0110] The grid-connected power of the i-th primary-side H-bridge circuit is obtained based on the input voltage and input current of the i-th primary-side H-bridge circuit. Specifically, this includes: obtaining the input power of the i-th primary-side H-bridge circuit based on the input voltage and input current of the i-th primary-side H-bridge circuit, and obtaining the grid-connected power of the i-th primary-side H-bridge circuit based on the input power and efficiency of the i-th primary-side H-bridge circuit.

[0111] The i-th grid-connected current is obtained based on the grid-connected power of the i-th primary H-bridge circuit, specifically including: obtaining the i-th grid-connected current based on the grid voltage, grid phase angle and the grid-connected power of the i-th primary H-bridge circuit.

[0112] The i-th grid-connected current is obtained based on the grid-connected power of the i-th primary H-bridge circuit. Based on the i-th grid-connected current and the i-th current reference value, the inner phase shift angle of the i-th primary H-bridge circuit and the outer phase shift angle between the i-th primary winding and the secondary bridge arm circuit are controlled. Specifically, this includes: obtaining the instantaneous value of the i-th grid-connected current based on the grid voltage, the cosine value of the grid phase angle, and the grid-connected power of the i-th primary H-bridge circuit; obtaining the comparison result between the instantaneous value of the i-th grid-connected current and the i-th current reference value; and controlling the inner phase shift angle of the i-th primary H-bridge circuit and the outer phase shift angle between the i-th primary winding and the secondary bridge arm circuit based on the comparison result.

[0113] See Figure 7 The figure is a flowchart of another control method for a micro inverter provided in an embodiment of this application.

[0114] This embodiment will continue to use two-channel input as an example for further explanation.

[0115] S901: Samples the input voltages U11 and U2, and the input currents I1 and I2.

[0116] S902: Calculate the input power Pin1 and Pin2.

[0117] S903: Obtain the efficiencies η1 and η2 corresponding to the input power.

[0118] S904: Obtain the grid voltage Ug on the grid side.

[0119] S905: Obtain the grid-connected currents Ig1 and Ig2 for each circuit.

[0120] S906: Obtain the grid phase θ through a phase-locked loop.

[0121] S907: Obtain grid-connected currents ig1 and ig2.

[0122] S908: Obtains the inner and outer phase shift angles of each path through a closed loop.

[0123] This control method does not detect the final grid-side current, but obtains the grid-connected current of each line by detecting the input power of each line in the micro-inverter, thereby realizing independent control of the power of each line. This control method is simple and the lines do not affect each other.

[0124] It should be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the systems or apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the descriptions are relatively simple, and relevant parts can be referred to the method section.

[0125] The above description of the disclosed embodiments enables those skilled in the art to make or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A micro inverter, characterized in that, include: The system comprises a controller, a secondary bridge arm circuit, N primary windings, N secondary windings, and N primary H-bridge circuits; where N is an integer greater than or equal to 2. The N primary windings and the N primary H-bridge circuits are connected in a one-to-one correspondence, and the N secondary windings are connected in parallel to the secondary bridge arm circuit. The controller is used to obtain the instantaneous value of the i-th grid-connected current based on the grid voltage, the cosine value of the grid phase angle, and the grid-connected power of the i-th primary H-bridge circuit, and to control the inner phase shift angle of the i-th primary H-bridge circuit and the outer phase shift angle between the i-th primary winding and the secondary bridge arm circuit based on the instantaneous value of the i-th grid-connected current and the reference value of the i-th current. The i-th primary-side H-bridge circuit is any one of the N primary-side H-bridge circuits.

2. The micro inverter according to claim 1, characterized in that, The controller is specifically used to obtain the grid-connected power of the i-th primary-side H-bridge circuit based on the input voltage and input current of the i-th primary-side H-bridge circuit.

3. The micro inverter according to claim 2, characterized in that, The controller is specifically configured to obtain the input power of the i-th primary-side H-bridge circuit based on the input voltage and input current of the i-th primary-side H-bridge circuit, and to obtain the grid-connected power of the i-th primary-side H-bridge circuit based on the input power and efficiency of the i-th primary-side H-bridge circuit.

4. The micro inverter according to any one of claims 1-3, characterized in that, The secondary bridge arm circuit includes a bidirectional switching bridge arm and a capacitor bridge arm; The upper and lower arms of the bidirectional switch bridge arm both include bidirectional switches, and the upper and lower arms of the capacitor bridge arm each include a first secondary capacitor and a second secondary capacitor with equal capacitance values.

5. The micro inverter according to claim 1, characterized in that, Also includes: N decoupling inductors; The N decoupling inductors are connected in series with the N primary windings in a one-to-one correspondence, or the N decoupling inductors are connected in series with the N secondary windings in a one-to-one correspondence; or the decoupling inductors are the leakage inductance of the corresponding transformer.

6. A photovoltaic system, characterized in that, It includes the microinverter as described in any one of claims 1-5; and further includes: N photovoltaic arrays; The N primary-side H-bridge circuits in the micro inverter are connected one-to-one with the N photovoltaic arrays; The micro inverter is used to convert the direct current from the N photovoltaic arrays into alternating current output.

7. A control method for a micro inverter, characterized in that, The micro inverter includes: a secondary bridge arm circuit, N primary windings, N secondary windings, and N primary H-bridge circuits; where N is an integer greater than or equal to 2; the N primary windings and the N primary H-bridge circuits are connected in a one-to-one correspondence, and the N secondary windings are connected in parallel to the secondary bridge arm circuit. The control method includes: Obtain the grid-connected power of the i-th primary-side H-bridge circuit; the i-th primary-side H-bridge circuit is any one of the N primary-side H-bridge circuits; The instantaneous value of the i-th grid-connected current is obtained based on the grid voltage, the cosine value of the grid phase angle, and the grid-connected power of the i-th primary H-bridge circuit. Based on the instantaneous value of the i-th grid-connected current and the reference value of the i-th current, the inner phase shift angle of the i-th primary H-bridge circuit and the outer phase shift angle between the i-th primary winding and the secondary bridge arm circuit are controlled.

8. The control method according to claim 7, characterized in that, Obtaining the grid-connected power of the i-th primary-side H-bridge circuit specifically includes: The grid-connected power of the i-th primary-side H-bridge circuit is obtained based on the input voltage and input current of the i-th primary-side H-bridge circuit.

9. The control method according to claim 8, characterized in that, The step of obtaining the grid-connected power of the i-th primary-side H-bridge circuit based on its input voltage and input current specifically includes: The input power of the i-th primary-side H-bridge circuit is obtained based on the input voltage and input current of the i-th primary-side H-bridge circuit, and the grid-connected power of the i-th primary-side H-bridge circuit is obtained based on the input power and efficiency of the i-th primary-side H-bridge circuit.

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