A two-stage flyback micro-inverter circuit

Abstract

The utility model relates to a two-stage flyback micro inverter circuit belongs to photovoltaic technical field. The two-stage flyback micro inverter circuit includes at least one staggered flyback circuit as the first stage and single-phase or three-phase inverter circuit as the second stage, each staggered flyback circuit is connected with corresponding photovoltaic module, realizes the voltage-lift of photovoltaic module output and MPPT, and the inverter circuit realizes inversion, grid connection and high-precision controllable active power and reactive power output, and the high-voltage bus capacitor Cbus between the first stage and the second stage realizes the power decoupling between the first stage and the second stage. The two-stage flyback micro inverter circuit retains the advantages of single-stage staggered flyback micro inverter, such as easy to realize multiple component input, low cost and high reliability, also greatly reduces the transformer primary current stress, reduces the loss, and the EMC problem is also greatly improved.

Description

Technical Field

[0001] This utility model relates to the field of photovoltaic technology, and particularly to the field of micro-inverter technology, specifically a two-stage flyback micro-inverter circuit. Background Technology

[0002] In recent years, as the proportion of photovoltaic power generation in the power system has gradually increased, the stability of the power system and the power quality are facing severe challenges. As a result, countries have introduced new laws, regulations and grid connection standards, which have put forward higher requirements for the reactive power output capacity and output current harmonics of inverters.

[0003] With the development of technology, various electronic devices are widely used in real life. In order to enable these electronic devices to work together stably without interfering with each other, countries began in-depth research in the field of electromagnetic compatibility in the 1980s. Corresponding laws, regulations and EMC standards have been gradually improved and implemented. In recent years, as more and more inverter devices have been connected to the power grid, countries have become increasingly strict in their EMC requirements for inverters.

[0004] Micro inverters are popular in the home market for their safety, reliability, stability, and compact size. Micro inverters independently boost and perform maximum power point tracking on each component. Due to their low input voltage, a high-frequency transformer is used internally to electrically isolate the component input from the grid. Furthermore, compared to traditional string inverters, micro inverters are safer, more reliable, and operate more stably due to their fully enclosed design and internal potting treatment.

[0005] Among numerous microinverter solutions, the single-stage interleaved flyback microinverter, which is easy to implement with multiple component inputs, has gradually become the mainstream solution in the market due to its low cost and high reliability. However, because the single-stage interleaved flyback inverter lacks power decoupling, as the component input power increases, the primary current stress of the transformer increases significantly, and the losses also increase accordingly. At the same time, EMC issues are gradually becoming more prominent.

[0006] Therefore, how to provide a flyback micro-inverter circuit that can achieve power decoupling, reduce transformer primary current stress, and reduce losses has become an urgent problem to be solved in this field. Utility Model Content

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide a two-stage flyback micro inverter and its circuit that can achieve power decoupling, reduce transformer primary current stress, and reduce losses.

[0008] To achieve the above objectives, the two-stage flyback micro-inverter circuit of this invention has the following configuration:

[0009] At least one interleaved flyback circuit is provided as the first stage. The input of each interleaved flyback circuit is connected to the output of the corresponding photovoltaic module to achieve voltage boost and maximum power point tracking for each module. The output of each interleaved flyback circuit is connected to the high-voltage bus.

[0010] The inverter circuit, as the second stage, is connected to the high-voltage bus to realize inversion and grid connection;

[0011] A high-voltage bus capacitor Cbus is connected between the positive and negative cables of the high-voltage bus between the first and second stages to achieve power decoupling between the first and second stages.

[0012] In this two-stage flyback micro inverter circuit, the inverter circuit is a single-phase inverter circuit, including MOSFETs Q1~Q4 and inductors L1 and L2. MOSFETs Q1 and Q2 are connected in series between the positive and negative cables of the high-voltage bus, and the middle node of MOSFETs Q1 and Q2 is connected to one end of inductor L1. MOSFETs Q3 and Q4 are also connected in series between the positive and negative cables of the high-voltage bus, and the middle node of MOSFETs Q3 and Q4 is connected to one end of inductor L2. The gates of MOSFETs Q1~Q4 are all connected to external control signals. The other ends of inductors L1 and L2 are respectively connected to the negative cable of the high-voltage bus through capacitors C1 and C2, and a single-phase AC output voltage is provided between these two ends of inductors L1 and L2.

[0013] In this two-stage flyback micro inverter circuit, the inverter circuit is a three-phase inverter circuit, which also includes MOSFETs Q5 and Q6 and inductor L3. MOSFETs Q5 and Q6 are connected in series between the positive and negative cables of the high-voltage bus, and the middle node of MOSFETs Q5 and Q6 is connected to one end of inductor L3. The gates of MOSFETs Q5 and Q6 are both connected to external control signals. The other end of inductor L3 is connected to the negative cable of the high-voltage bus through capacitor C3, and this end of inductors L1, L2, and L3 provides a three-phase AC output voltage.

[0014] This utility model discloses a two-stage flyback microinverter circuit, comprising at least one interleaved flyback circuit as the first stage and a single-phase or three-phase inverter circuit as the second stage. Each interleaved flyback circuit is connected to a corresponding photovoltaic module, enabling boosting of the photovoltaic module output and maximum power point tracking. The output terminals of each interleaved flyback circuit are connected to a high-voltage bus. The inverter circuit is connected to the high-voltage bus, realizing inversion, grid connection, and high-precision controllable active and reactive power output. A high-voltage bus capacitor Cbus is also connected between the positive and negative cables of the high-voltage bus between the first and second stages, achieving power decoupling between the first and second stages. This two-stage flyback microinverter circuit retains the advantages of the single-stage interleaved flyback microinverter scheme, such as easy implementation of multiple component inputs, low cost, and high reliability, while significantly reducing transformer primary current stress, reducing losses, and greatly improving EMC issues. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the structure of a two-stage flyback micro inverter circuit according to the present invention.

[0016] Figure 2 This is a schematic diagram of the circuit structure of the interleaved flyback circuit used in this utility model;

[0017] Figure 3 This is a schematic diagram of the circuit structure of a single-phase inverter circuit that can be used in this utility model;

[0018] Figure 4 This is a schematic diagram of the circuit structure of a three-phase inverter circuit that can be used in this utility model. Detailed Implementation

[0019] In order to better understand the technical content of this utility model, the following embodiments are provided for detailed description.

[0020] Please see Figure 1 The diagram shown is a schematic diagram of a two-stage flyback micro-inverter circuit according to this utility model.

[0021] In one implementation, the two-stage flyback micro-inverter circuit, such as Figure 1 As shown, it includes:

[0022] At least one interleaved flyback circuit is provided as the first stage. The input of each interleaved flyback circuit is connected to the output of the corresponding photovoltaic module to achieve voltage boost and maximum power point tracking for each module. The output of each interleaved flyback circuit is connected to the high-voltage bus.

[0023] The inverter circuit, as the second stage, is connected to the high-voltage bus to realize inversion and grid connection;

[0024] A high-voltage bus capacitor Cbus is connected between the positive and negative cables of the high-voltage bus between the first and second stages to achieve power decoupling between the first and second stages.

[0025] The circuit structure of the interleaved flyback circuit is as follows: Figure 2 As shown, this includes two parallel flyback circuits, controlled by MOSFETs to operate at different phases. One flyback circuit consists of a MOSFET, a flyback transformer, a rectifier diode, and an output capacitor. The primary winding is connected to the PV voltage of the photovoltaic module. When the MOSFET is on, electrical energy is stored in the primary winding of the transformer, and the secondary diode is off. When the MOSFET is off, the induced electromotive force in the primary winding of the transformer reverses, the secondary diode conducts, and the energy stored in the magnetic field is released through the secondary winding. The MOSFETs of the two flyback circuits alternately turn on and off.

[0026] In a preferred embodiment, the inverter circuit can be as follows: Figure 3 The diagram shows a single-phase inverter circuit. This single-phase inverter circuit includes MOSFETs Q1-Q4 and inductors L1 and L2. MOSFETs Q1 and Q2 are connected in series between the positive and negative cables of the high-voltage bus. In the diagram, MOSFETs Q1, Q2, Q3, and Q4 are all NMOS transistors. The source of the upper transistor Q1 is connected to the drain of the lower transistor Q2. The drain of the upper transistor Q1 is connected to the positive cable of the high-voltage bus, and the source of the lower transistor Q2 is connected to the negative cable of the high-voltage bus. The series connection method of the MOSFETs in this application is the same. The intermediate nodes of MOSFETs Q1 and Q2 are connected to one end of inductor L1; MOSFETs Q3 and Q4 are connected in series between the positive and negative cables of the high-voltage bus, and the intermediate nodes of MOSFETs Q3 and Q4 are connected to one end of inductor L2; the gates of MOSFETs Q1 to Q4 are all connected to control signals provided by an external control module; the other ends of inductors L1 and L2 are respectively connected to the negative cable of the high-voltage bus through capacitors C1 and C2, and a single-phase AC output voltage Vg is provided between these two ends of inductors L1 and L2.

[0027] In another preferred embodiment, the inverter circuit can also be Figure 4 The three-phase inverter circuit shown is compared to... Figure 3 The single-phase inverter circuit includes MOSFETs Q5 and Q6 and inductor L3. MOSFETs Q5 and Q6 are connected in series between the positive and negative cables of the high-voltage bus. The middle node of MOSFETs Q5 and Q6 is connected to one end of inductor L3. The gates of MOSFETs Q5 and Q6 are connected to control signals provided by an external control module. The other end of inductor L3 is connected to the negative cable of the high-voltage bus via capacitor C3. A three-phase AC output voltage Vg is provided between this end of inductors L1, L2, and L3.

[0028] This utility model discloses a two-stage flyback microinverter circuit, comprising at least one interleaved flyback circuit as the first stage and a single-phase or three-phase inverter circuit as the second stage. Each interleaved flyback circuit is connected to a corresponding photovoltaic module, enabling boosting of the photovoltaic module output and maximum power point tracking. The output terminals of each interleaved flyback circuit are connected to a high-voltage bus. The inverter circuit is connected to the high-voltage bus, realizing inversion, grid connection, and high-precision controllable active and reactive power output. A high-voltage bus capacitor Cbus is also connected between the positive and negative cables of the high-voltage bus between the first and second stages, achieving power decoupling between the first and second stages. This two-stage flyback microinverter circuit retains the advantages of the single-stage interleaved flyback microinverter scheme, such as easy implementation of multiple component inputs, low cost, and high reliability, while significantly reducing transformer primary current stress, reducing losses, and greatly improving EMC issues.

[0029] In this specification, the present invention has been described with reference to specific embodiments thereof. However, it will be apparent that various modifications and variations can be made without departing from the spirit and scope of the present invention. Therefore, the specification and drawings should be considered illustrative rather than restrictive.

Claims

1. A two-stage flyback micro-inverter circuit, characterized in that, include: At least one interleaved flyback circuit is provided as the first stage. The input of each interleaved flyback circuit is connected to the output of the corresponding photovoltaic module to achieve voltage boost and maximum power point tracking for each module. The output of each interleaved flyback circuit is connected to the high-voltage bus. The inverter circuit, as the second stage, is connected to the high-voltage bus to realize inversion and grid connection; A high-voltage bus capacitor Cbus is connected between the positive and negative cables of the high-voltage bus between the first and second stages to achieve power decoupling between the first and second stages.

2. The two-stage flyback micro-inverter circuit according to claim 1, characterized in that, The inverter circuit is a single-phase inverter circuit, including MOSFETs Q1-Q4 and inductors L1 and L2. MOSFETs Q1 and Q2 are connected in series between the positive and negative cables of the high-voltage bus, and the middle node of MOSFETs Q1 and Q2 is connected to one end of inductor L1. MOSFETs Q3 and Q4 are also connected in series between the positive and negative cables of the high-voltage bus, and the middle node of MOSFETs Q3 and Q4 is connected to one end of inductor L2. The gates of MOSFETs Q1-Q4 are all connected to external control signals. The other ends of inductors L1 and L2 are respectively connected to the negative cable of the high-voltage bus through capacitors C1 and C2, and this end of inductors L1 and L2 provides a single-phase AC output voltage.

3. The two-stage flyback micro-inverter circuit according to claim 2, characterized in that, The inverter circuit is a three-phase inverter circuit, which also includes MOSFETs Q5 and Q6 and inductor L3. MOSFETs Q5 and Q6 are connected in series between the positive and negative cables of the high-voltage bus, and the middle node of MOSFETs Q5 and Q6 is connected to one end of inductor L3. The gates of MOSFETs Q5 and Q6 are both connected to external control signals. The other end of inductor L3 is connected to the negative cable of the high-voltage bus through capacitor C3, and this end of inductors L1, L2, and L3 provides a three-phase AC output voltage.

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