Bidirectional flyback converter-based grid-forming microinverter and method therefor

Abstract

The present invention relates to the technical field of photovoltaic power generation. Disclosed are a bidirectional flyback converter-based grid-forming microinverter and a method therefor. The method comprises: by means of an output voltage and an output current of the grid-forming microinverter, calculating an active power and a reactive power; on the basis of a power loop control principle, generating a reference signal of a voltage loop by means of using a preset power reference value; generating a reference signal of a peak current control loop according to an actual output voltage; and, according to primary side current signals of a first bidirectional flyback converter and a second bidirectional flyback converter, generating a drive signal for each switch transistor under the regulation of the peak current control loop. The present invention generates power grid voltage phases directly by means of the power loop without requiring a phase-locked loop stage, thus ensuring stable operation even in weak power grid environments; in addition, the present invention uses a bidirectional structure topology, involves a simple topological structure, low cost, high efficiency and low control complexity, and achieves bidirectional power flow, and furthermore, the present invention adjusts an output power factor, thus providing reactive power support for power grids.

Description

A grid-type micro-inverter based on a bidirectional flyback converter and a method thereof Technical Field

[0001] The present invention relates to the technical field of photovoltaic power generation, and in particular to a grid-type micro-inverter based on a bidirectional flyback converter and a method thereof. Background Art

[0002] Currently, the use of dedicated micro-PV grid-connected inverters to connect each PV module to the grid has become a popular trend in distributed photovoltaic power generation technology. These micro-inverters offer advantages such as small capacity, high efficiency, and ease of installation, making them particularly suitable for small, household distributed photovoltaic power generation scenarios. However, with the increasing proportion of renewable energy generation systems entering grid operation and the increasing proportion of power electronic equipment connected to the grid, modern power grids are gradually exhibiting weak grid characteristics, placing higher demands on micro-inverters.

[0003] Traditional microinverters typically use a unidirectional, two-stage flyback inverter, allowing power to flow in only one direction. However, in modern power grids, especially in weak grid environments, these two-stage inverters present several challenges. First, they typically employ a phase-locked loop (PLL) to synchronize the grid voltage phase, but in weak grid environments, the stability of the PLL can be compromised. Second, traditional microinverters operating in unity power factor output mode are unable to provide reactive power support for the grid, making them prone to off-grid or islanded operation in weak grid environments. Furthermore, the traditional two-stage topology imposes certain limitations on the conversion efficiency of the microinverter.

[0004] Therefore, to adapt to the weak grid characteristics of modern power grids, micro-PV grid-connected inverter technology urgently needs to be optimized and improved. Phase-locked loop stability issues need to be addressed, and micro-inverters need to be able to support bidirectional power flow to provide reactive power support to the grid. Furthermore, micro-inverter topology needs to be optimized to improve conversion efficiency. These improvements will better address the challenges posed by high penetration rates of renewable energy generation and a high proportion of power electronics connected to the grid.

[0005] Summary of the Invention

[0006] In view of the problems existing in the phase-locked loop stability and power flow capability of the existing micro inverter, the present invention is proposed.

[0007] Therefore, the problem to be solved by the present invention is how to improve the stability of the micro inverter and enable the inverter to have the ability of bidirectional power flow.

[0008] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0009] In a first aspect, an embodiment of the present invention provides a method for a grid-type micro-inverter based on a bidirectional flyback converter, which includes a bidirectional flyback converter and a grid-type micro-inverter; the grid-type micro-inverter includes a power loop, a voltage loop and a peak current control loop; active power and reactive power are calculated by the output voltage and output current of the grid-type micro-inverter; based on the control of the power loop, a preset power reference value is used to generate a reference signal of the voltage loop; according to the actual output voltage, a reference signal of the peak current control loop is generated under the control of the voltage loop; according to the primary current signals of the first bidirectional flyback converter and the second bidirectional flyback converter, a drive signal of each switch tube is generated under the regulation of the peak current control loop.

[0010] As a preferred solution of the method for forming a grid-type micro-inverter based on a bidirectional flyback converter according to the present invention, the method of using a preset power reference value to generate a reference signal of the voltage loop includes the following steps: the voltage loop obtains a voltage error signal by comparing the voltage reference value generated by the power loop with the actual output voltage; the obtained voltage error signal is processed by a PID controller to generate a primary current reference signal of a peak current control loop; the peak current control loop compares the primary current reference signal generated by the voltage loop with the primary current signals of the first bidirectional flyback converter and the second bidirectional flyback converter; when the primary current signals of the first bidirectional flyback converter and the second bidirectional flyback converter are greater than When the primary current signal of the first bidirectional flyback converter and the second bidirectional flyback converter is equal to the primary current reference signal of the first bidirectional flyback converter and the second bidirectional flyback converter, the primary switching tubes of the first bidirectional flyback converter and the second bidirectional flyback converter are turned off; when the primary current signal of the first bidirectional flyback converter and the second bidirectional flyback converter is less than the primary current reference signal of the first bidirectional flyback converter and the second bidirectional flyback converter, the primary switching tubes of the first bidirectional flyback converter and the second bidirectional flyback converter are turned on, thereby generating driving signals for the switching tubes of the first bidirectional flyback converter and the second bidirectional flyback converter; the grid-type micro-inverter generates the grid voltage phase through the power control loop, realizes the synchronization of the micro-inverter and the grid, and ensures stable operation of the system.

[0011] As a preferred solution of the grid-type micro-inverter method based on the bidirectional flyback converter of the present invention, the power loop includes an active-frequency droop link and a reactive-voltage droop link, and the relevant formulas are as follows:

[0012] Among them, n p is the active power droop coefficient, n q is the reactive droop coefficient, ω ref is the micro-inverter output voltage frequency reference value, ω is the micro-inverter output voltage frequency, P ref and Q ref are all pre-set power reference values, p eThe active power output of the micro inverter, u ref is the voltage loop reference voltage, U ref is the voltage loop reference voltage amplitude, U0 is the output voltage of the grid-type micro-inverter, q e is the reactive power output by the micro-inverter, and t is the time.

[0013] As a preferred solution of the method for constructing a grid-type micro-inverter based on a bidirectional flyback converter according to the present invention, the method includes the following steps based on the primary current signals of the first bidirectional flyback converter and the second bidirectional flyback converter: the first bidirectional flyback converter and the second bidirectional flyback converter both operate in an inductor current continuous mode; when the first bidirectional flyback converter is operating, the circuit is divided into mode one and mode two according to the third switch tube being turned off and the sixth switch tube being turned off; when the second bidirectional flyback converter is operating, the circuit is divided into mode three and mode four according to the sixth switch tube being turned off and the third switch tube being turned on.

[0014] As a preferred solution of the grid-type micro-inverter method based on the bidirectional flyback converter of the present invention, the relevant formula of the mode 1 is as follows:

[0015] Among them, L m1 is the inductance of the primary winding of the first flyback transformer, i 10 is the initial value of the primary current of the first flyback transformer, T1 is the on-time of the primary switch of the first bidirectional flyback transformer in one switching cycle, U DC is the DC input voltage, i 1m is the peak current of the primary side current of the first flyback transformer in one switching cycle.

[0016] The relevant formula of the second mode is as follows:

[0017] Among them, L m2 is the inductance of the secondary winding of the first flyback transformer, i 20 is the initial value of the primary current of the first flyback transformer, T2 is the off time of the primary switch of the first bidirectional flyback transformer in one switching cycle, u0 is the actual output voltage, i 2m is the peak current of the secondary side of the first flyback transformer in one switching cycle.

[0018] The beneficial effect of the present invention is that the inverter and the power grid are directly synchronized through the power loop, thereby saving the phase-locked loop link required by the traditional micro-inverter. This innovation not only reduces the complexity of control, but also solves the problem that the traditional micro-inverter cannot operate stably in a weak power grid environment, thereby improving the stability of the inverter; at the same time, a grid-forming control is adopted to adjust the active power, reactive power and power factor output by the grid-forming micro-inverter according to the grid dispatching instructions, providing active support and reactive support for the power grid, overcoming the deficiency that the traditional micro-inverter can only output active power but cannot provide reactive power support.

[0019] In the second aspect, an embodiment of the present invention provides a grid-type micro-inverter based on a bidirectional flyback converter, which includes: a photovoltaic DC input source, an input filter capacitor, a first bidirectional flyback transformer, a second bidirectional flyback transformer, a first switch tube, a second switch tube, a third switch tube, a fourth switch tube, a fifth switch tube, a sixth switch tube, a first output capacitor, a second output capacitor, a first output filter inductor, a second output filter inductor, a first output filter capacitor, a second output filter capacitor, a grid-side inductor, an equivalent power grid and a grid-type micro-inverter.

[0020] As a preferred embodiment of the grid-type micro-inverter based on the bidirectional flyback converter described in the present invention, the positive electrode of the input filter capacitor is electrically connected to the positive electrode of the photovoltaic DC input source, the primary side of the first bidirectional flyback transformer, and the primary side of the second bidirectional flyback transformer; the negative electrode of the input filter capacitor is electrically connected to the negative electrode of the DC input source, the source electrode of the first switching tube, and the source electrode of the fourth switching tube; the other end of the primary side of the first bidirectional flyback transformer is electrically connected to the drain electrode of the first switching tube; one end of the secondary side of the first bidirectional flyback transformer is electrically connected to the source electrode of the second switching tube; the other end of the secondary side of the first bidirectional flyback transformer is electrically connected to the source electrode of the third switching tube, the negative electrode of the first output capacitor, and the negative electrode of the first output filter capacitor; the source electrode of the second switching tube is electrically connected to the source electrode of the third switching tube, the positive electrode of the first output capacitor, and one end of the first output filter inductor; the other end of the first output filter inductor is electrically connected to the positive electrode of the first output filter capacitor and one end of the grid-side inductor; and the other end of the grid-side inductor is electrically connected to one end of the equivalent grid.

[0021] As a preferred solution of the grid-type micro-inverter based on the bidirectional flyback converter described in the present invention, it further includes: the other end of the primary side of the second bidirectional flyback transformer is electrically connected to the drain of the fourth switch tube; one end of the secondary side of the second bidirectional flyback transformer is electrically connected to the source of the fifth switch tube; the other end of the secondary side of the second bidirectional flyback transformer is electrically connected to the source of the sixth switch tube, the negative electrode of the second output capacitor and the negative electrode of the second output filter capacitor; the source of the fifth switch tube is electrically connected to the source of the sixth switch tube, the positive electrode of the second output capacitor and one end of the second output filter inductor; the other end of the second output filter inductor is electrically connected to the positive electrode of the second output filter capacitor and the other end of the equivalent grid.

[0022] As a preferred solution of the grid-type micro-inverter based on the bidirectional flyback converter described in the present invention, the driving signals of the first switching tube and the second switching tube, the fourth switching tube, the fifth switching tube, the third switching tube and the sixth switching tube are complementary.

[0023] As a preferred solution of the grid-type micro-inverter based on the bidirectional flyback converter described in the present invention, the working states of the first bidirectional flyback converter and the second bidirectional flyback converter are completely symmetrical, wherein the first bidirectional flyback converter operates in the positive half cycle of the grid voltage, and the second bidirectional flyback converter operates in the negative half cycle of the grid voltage.

[0024] In a third aspect, an embodiment of the present invention provides a computer device comprising a memory and a processor, wherein the memory stores a computer program, wherein: when the computer program instructions are executed by the processor, the steps of constructing a grid-type micro-inverter based on a bidirectional flyback converter as described in the first aspect of the present invention are implemented.

[0025] In a fourth aspect, an embodiment of the present invention provides a computer-readable storage medium having a computer program stored thereon, wherein: when the computer program instructions are executed by a processor, the steps of constructing a grid-type micro-inverter based on a bidirectional flyback converter as described in the first aspect of the present invention are implemented.

[0026] The beneficial effects of the present invention are as follows: the present invention adopts a single-stage topology, simplifies the traditional two-stage micro-inverter into a single stage, saves costs and improves the transmission efficiency of the system; by adopting a bidirectional structure topology, it supports bidirectional power flow, overcomes the deficiency of unidirectional energy flow of traditional micro-inverters, and its topology is simple, low cost, high efficiency and low control complexity. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] To more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive effort. Among them:

[0028] FIG1 is a circuit structure diagram of a grid-type micro-inverter based on a bidirectional flyback converter according to Example 1.

[0029] FIG2 is a control block diagram of a grid-type micro-inverter based on a bidirectional flyback converter according to Example 1.

[0030] FIG3 is a primary current waveform of a grid-type micro-inverter based on a bidirectional flyback converter in Example 1. FIG.

[0031] FIG4 is a driving signal diagram of a grid-type micro-inverter based on a bidirectional flyback converter according to Example 1. ...

[0032] FIG5 shows embodiment 1 of a grid-type micro-inverter based on a bidirectional flyback converter.

[0033] FIG6 , embodiment 1, is a working mode diagram of mode 1 of a grid-type micro-inverter based on a bidirectional flyback converter.

[0034] FIG7 , embodiment 1, is a working mode diagram of mode 2 of a grid-type micro-inverter based on a bidirectional flyback converter.

[0035] FIG8 , embodiment 1, is a working mode diagram of mode 3 of a grid-type micro-inverter based on a bidirectional flyback converter.

[0036] FIG9 , embodiment 1, is a working mode diagram of mode 4 of a grid-type micro-inverter based on a bidirectional flyback converter.

[0037] FIG10 shows a second embodiment of the invention, which is a steady-state output waveform of a grid-type micro-inverter based on a bidirectional flyback converter when the output has a leading power factor.

[0038] FIG11 shows an example 2 of a droop characteristic curve of the output power of a grid-type micro-inverter based on a bidirectional flyback converter.

[0039] FIG12 shows embodiment 2, which is a simulation waveform of the output leading power factor of a grid-type micro-inverter based on a bidirectional flyback converter.

[0040] FIG13 shows the simulated waveforms of the output voltage and current of the grid-type micro-inverter based on the bidirectional flyback converter in Example 2 when the power factor is lagging.

[0041] FIG14 shows embodiment 2, which is a simulation waveform of active power and frequency phase of a grid-type micro-inverter based on a bidirectional flyback converter. DETAILED DESCRIPTION

[0042] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0043] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0044] Secondly, the term "one embodiment" or "embodiment" herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in various places throughout this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive of other embodiments.

[0045] Example 1

[0046] 1 to 9 , which are the first embodiment of the present invention, a method for a meshed micro-inverter based on a bidirectional flyback converter is provided, comprising a bidirectional flyback converter and a meshed micro-inverter; the meshed micro-inverter comprises a power loop, a voltage loop, and a peak current control loop;

[0047] S1: Calculate the active power and reactive power through the output voltage and output current of the grid-connected micro-inverter.

[0048] Specifically, the power loop includes the active power-frequency droop link and the reactive power-voltage droop link, and the relevant formulas are as follows:

[0049] Among them, n p is the active power droop coefficient, n q is the reactive droop coefficient, ω ref is the micro-inverter output voltage frequency reference value, ω is the micro-inverter output voltage frequency, P ref and Q ref are all pre-set power reference values, p e The active power output of the micro inverter, u ref is the voltage loop reference voltage, U ref is the voltage loop reference voltage amplitude, U0 is the output voltage of the grid-type micro-inverter, q e is the reactive power output by the micro-inverter, and t is the time.

[0050] Furthermore, the core of the controller is a power loop consisting of droop control, which controls the voltage and frequency of the microinverter by simulating the droop characteristics of the synchronous generator in the traditional power system by detecting the active and reactive components of the output power.

[0051] Furthermore, in a weak grid environment, since the grid impedance cannot be ignored, it is usually regarded as an inductor with a large inductance value. The specific formula for the power transmission characteristics of the microinverter is as follows:

[0052] Among them, p is the active power output of the micro inverter, U inv is the effective value of the micro-inverter output voltage, U g is the effective value of the grid voltage, δ is the phase difference between the micro-inverter output voltage and the grid voltage, X g is the grid impedance.

[0053] Specifically, the output active power of the microinverter is linearly related to the frequency, and the output reactive power is linearly related to the output voltage amplitude. Since the power angle is usually small, the specific formula for the approximate power transfer characteristics of the microinverter is as follows:

[0054] Among them, p is the active power output by the microinverter, q is the reactive power output by the microinverter, U inv is the effective value of the micro-inverter output voltage, U g is the effective value of the grid voltage, X g is the grid impedance, ω inv is the inverter output voltage angular frequency, and t is the time.

[0055] S2: Based on the control of the power loop, a preset power reference value is used to generate a reference signal for the voltage loop.

[0056] Specifically, the voltage loop obtains a voltage error signal by comparing the voltage reference value generated by the power loop with the actual output voltage; the obtained voltage error signal is processed by the PID controller to generate the primary current reference signal of the peak current control loop.

[0057] Furthermore, the peak current control loop compares the primary current reference signal generated by the voltage loop with the primary current signals of the first bidirectional flyback converter and the second bidirectional flyback converter; when the primary current signals of the first bidirectional flyback converter and the second bidirectional flyback converter are greater than or equal to the primary current reference signals of the first bidirectional flyback converter and the second bidirectional flyback converter, the primary switching tubes of the first bidirectional flyback converter and the second bidirectional flyback converter are turned off; when the primary current signals of the first bidirectional flyback converter and the second bidirectional flyback converter are less than the primary current reference signals of the first bidirectional flyback converter and the second bidirectional flyback converter, the primary switching tubes of the first bidirectional flyback converter and the second bidirectional flyback converter are turned on, thereby generating driving signals for the switching tubes of the first bidirectional flyback converter and the second bidirectional flyback converter.

[0058] Furthermore, the grid-connected micro-inverter generates the grid voltage phase through the power control loop, achieving synchronization between the micro-inverter and the grid, and ensuring stable operation of the system.

[0059] S3: Generate a reference signal for the peak current control loop under the control of the voltage loop according to the actual output voltage.

[0060] S4: Generate driving signals for each switch tube under the control of a peak current control loop according to the primary current signals of the first bidirectional flyback converter and the second bidirectional flyback converter.

[0061] Specifically, the first bidirectional flyback converter and the second bidirectional flyback converter both operate in the inductor current continuous mode; when the first bidirectional flyback converter operates, the circuit is divided into mode 1 and mode 2 according to whether the third switch tube and the sixth switch tube are turned off.

[0062] Furthermore, the photovoltaic DC input power source transmits energy to the primary side of the first flyback transformer, and the secondary side of the first flyback transformer does not work. At this time, the grid current is freewheeled by turning on the anti-parallel diodes of the third and sixth switching tubes. Assuming the turn-on time is T1, the relevant formulas for mode 1 are as follows:

[0063] Among them, L m1 is the inductance of the primary winding of the first flyback transformer, i 10 is the initial value of the primary current of the first flyback transformer, T1 is the on-time of the primary switch of the first bidirectional flyback transformer in one switching cycle, U DC is the DC input voltage, i 1m is the peak current of the primary side current of the first flyback transformer in one switching cycle.

[0064] Furthermore, the secondary side of the first flyback transformer transmits energy to the grid, and the primary side of the first flyback transformer does not work. Assuming the off time is T2, the relevant formula of mode 2 is as follows:

[0065] Among them, L m2 is the inductance of the secondary winding of the first flyback transformer, i 20 is the initial value of the primary current of the first flyback transformer, T2 is the off time of the primary switch of the first bidirectional flyback transformer in one switching cycle, u0 is the actual output voltage, i 2m is the peak current of the secondary side of the first flyback transformer in one switching cycle.

[0066] Furthermore, the specific formula for the equivalent inductance value on the second winding of the transformer is as follows:

[0067] L m2 =(L m1 N2 2 ) / N1 2

[0068] Wherein, N1 is the number of turns of the primary winding of the first bidirectional flyback transformer, and N2 is the number of turns of the secondary winding of the first bidirectional flyback transformer.

[0069] Specifically, when the second bidirectional flyback converter is operating, the circuit is divided into mode three and mode four according to the sixth switch being turned off and the third switch being turned on.

[0070] Furthermore, in mode three, the photovoltaic DC input power source transmits energy to the primary side of the second bidirectional flyback transformer, while the secondary side of the second bidirectional flyback transformer is inoperative. At this point, the grid current freewheels through the anti-parallel diodes connecting the third and sixth switches. Assuming the on-time of the primary switch of the second bidirectional flyback transformer is T3, the relevant formula for mode three is as follows:

[0071] Among them, L m3 is the inductance of the primary winding of the second bidirectional flyback transformer, i 30 is the initial value of the primary current of the second bidirectional flyback transformer, T3 is the on-time of the primary switch of the second bidirectional flyback transformer in one switching cycle, U DC is the DC input voltage, i 3m is the peak current of the primary side current of the second bidirectional flyback transformer in one switching cycle.

[0072] Furthermore, in mode 4, the fourth switch is turned off and the fifth switch is turned on, the secondary side of the second bidirectional flyback transformer transmits energy to the grid, and the primary side of the second bidirectional flyback transformer does not work. The relevant formulas for mode 4 are as follows:

[0073] Among them, L m4 is the inductance of the secondary winding of the second bidirectional flyback transformer, i 40is the initial value of the primary current of the second bidirectional flyback transformer, T4 is the off time of the primary switch of the second bidirectional flyback transformer in one switching cycle, u0 is the actual output voltage, i 4m is the peak current of the secondary side of the second flyback transformer in one switching cycle.

[0074] Furthermore, this embodiment also provides a grid-type micro-inverter based on a bidirectional flyback converter, including: a photovoltaic DC input source, an input filter capacitor, a first bidirectional flyback transformer, a second bidirectional flyback transformer, a first switch tube, a second switch tube, a third switch tube, a fourth switch tube, a fifth switch tube, a sixth switch tube, a first output capacitor, a second output capacitor, a first output filter inductor, a second output filter inductor, a first output filter capacitor, a second output filter capacitor, a grid-side inductor, an equivalent power grid, and a grid-type micro-inverter.

[0075] Specifically, the positive electrode of the input filter capacitor is electrically connected to the positive electrode of the photovoltaic DC input source, the primary side of the first bidirectional flyback transformer and the primary side of the second bidirectional flyback transformer; the negative electrode of the input filter capacitor is electrically connected to the negative electrode of the DC input source, the source of the first switch tube and the source of the fourth switch tube; the other end of the primary side of the first bidirectional flyback transformer is electrically connected to the drain of the first switch tube; one end of the secondary side of the first bidirectional flyback transformer is electrically connected to the source of the second switch tube; the other end of the secondary side of the first bidirectional flyback transformer is electrically connected to the source level of the third switch tube, the negative electrode of the first output capacitor and the negative electrode of the first output filter capacitor; the source level of the second switch tube is electrically connected to the source level of the third switch tube, the positive electrode of the first output capacitor and one end of the first output filter inductor; the other end of the first output filter inductor is electrically connected to the positive electrode of the first output filter capacitor and one end of the grid-side inductor; the other end of the grid-side inductor is electrically connected to one end of the equivalent power grid.

[0076] Furthermore, the other end of the primary side of the second flyback transformer is electrically connected to the drain of the fourth switching tube; one end of the secondary side of the second flyback transformer is electrically connected to the source of the fifth switching tube; the other end of the secondary side of the second flyback transformer is electrically connected to the source of the sixth switching tube, the negative electrode of the second output capacitor, and the negative electrode of the second output filter capacitor; the source of the fifth switching tube is electrically connected to the source of the sixth switching tube, the positive electrode of the second output capacitor, and one end of the second output filter inductor; the other end of the second output filter inductor is electrically connected to the positive electrode of the second output filter capacitor and the other end of the equivalent grid; The other end of the primary side of the second bidirectional flyback transformer is electrically connected to the drain of the fourth switching tube; one end of the secondary side of the second bidirectional flyback transformer is electrically connected to the source of the fifth switching tube; the other end of the secondary side of the second bidirectional flyback transformer is electrically connected to the source of the sixth switching tube, the negative electrode of the second output capacitor and the negative electrode of the second output filter capacitor; the source of the fifth switching tube is electrically connected to the source of the sixth switching tube, the positive electrode of the second output capacitor and one end of the second output filter inductor; the other end of the second output filter inductor is electrically connected to the positive electrode of the second output filter capacitor and the other end of the equivalent power grid.

[0077] Furthermore, the driving signals of the first switching tube and the second switching tube, the fourth switching tube, the fifth switching tube, the third switching tube and the sixth switching tube are complementary respectively; the working states of the first bidirectional flyback converter and the second bidirectional flyback converter are completely symmetrical, wherein the first bidirectional flyback converter operates in the positive half cycle of the grid voltage, and the second bidirectional flyback converter operates in the negative half cycle of the grid voltage.

[0078] This embodiment also provides a computer device suitable for a grid-type micro-inverter based on a bidirectional flyback converter, comprising a memory and a processor; the memory is used to store computer-executable instructions, and the processor is used to execute the computer-executable instructions to implement the grid-type micro-inverter based on a bidirectional flyback converter as proposed in the above embodiment.

[0079] The computer device may be a terminal, comprising a processor, a memory, a communication interface, a display screen and an input device connected via a system bus. The processor of the computer device is used to provide computing and control capabilities. The memory of the computer device comprises a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system and a computer program. The internal memory provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. The communication interface of the computer device is used to communicate with an external terminal in a wired or wireless manner, and the wireless manner may be achieved through WIFI, an operator network, NFC (near field communication) or other technologies. The display screen of the computer device may be a liquid crystal display or an electronic ink display screen, and the input device of the computer device may be a touch layer covering the display screen, or a button, trackball or touchpad provided on the housing of the computer device, or an external keyboard, touchpad or mouse.

[0080] This embodiment also provides a storage medium having a computer program stored thereon, which, when executed by a processor, implements the following steps: a bidirectional flyback converter and a grid-type micro-inverter, wherein the controller includes a power loop, a voltage loop, and a peak current control loop; active power and reactive power are calculated through the output voltage and output current of the grid-type micro-inverter; a reference signal for the voltage loop is generated based on the control of the power loop using a preset power reference value; a reference signal for the peak current control loop is generated under the control of the voltage loop according to the actual output voltage; and a drive signal for each switch tube is generated under the regulation of the peak current control loop according to the primary current signals of the first bidirectional flyback converter and the second bidirectional flyback converter.

[0081] In summary, the present invention directly generates the grid voltage phase through the power loop, without the need for a phase-locked loop link, so that it can maintain stable operation even in a weak grid environment; at the same time, it adopts a bidirectional structure topology, which has a simple topology, low cost, high efficiency and low control complexity, realizing bidirectional power flow, and can adjust the output power factor to provide reactive support for the grid.

[0082] Example 2

[0083] 10 to 14 , a second embodiment of the present invention is shown. This embodiment provides a grid-type micro-inverter based on a bidirectional flyback converter. To verify the beneficial effects of the present invention, economic benefit calculations and simulation experiments are used for scientific demonstration.

[0084] Specifically, the grid-type micro-inverter based on the bidirectional flyback converter includes a photovoltaic DC input source U PV , input filter capacitor C i , first bidirectional flyback transformer T1, second bidirectional flyback transformer T2, first switch tube S 11, the second switch tube S 12 , the third switch tube S 13 , the fourth switch tube S 21 , the fifth switch tube S 22 , the sixth switch tube S 23 , the first output capacitor C o1 , the second output capacitor C o2 , the first output filter inductor L f1 , the second output filter inductor L f2 , the first output filter capacitor C f1 , the second output filter capacitor C f2 , grid-side inductance L g , equivalent power grid u g and controller.

[0085] Furthermore, as shown in FIG10 , during the time period t0-t1, the first bidirectional flyback converter operates in the inductor current continuous mode, the second bidirectional flyback converter is inoperative, the sixth switch is on, and the third switch is off. Based on the on-state of the first switch and the on-off state of the second switch, the circuit can be divided into two modes.

[0086] Furthermore, during the period t1-t2, the grid voltage and current reverse, and power flows from the grid to the first bidirectional flyback converter. At this time, the first bidirectional flyback converter still operates in the inductor current continuous mode, the second bidirectional flyback converter is inoperative, the sixth switch is on, and the third switch is off. The operating modes during this period remain the same as Mode 1 and Mode 2 during the period t0-t1, with only the power flow direction changed.

[0087] Specifically, during the t2-t3 period, the grid voltage and grid current are in the same direction, both in the negative half-cycle. At this time, the second bidirectional flyback converter operates in the inductor current continuous mode, the first bidirectional flyback converter is inoperative, the third switch is on, and the sixth switch is off. The circuit can be divided into two modes based on the on / off behavior of the fourth and fifth switches. It should be noted that the modal analysis of the circuit during this period is completely symmetrical with that during the t0-t1 period, except that the first bidirectional flyback converter is replaced by the second bidirectional flyback converter.

[0088] Furthermore, during the t3-t4 period, the grid voltage and grid current are in opposite directions, and power flows from the grid to the second bidirectional flyback converter. At this time, the second bidirectional flyback converter still operates in the inductor current continuous mode, the first bidirectional flyback converter is not operating, the third switch is on, and the sixth switch is off. The operating modes during this period remain the same as Mode 3 and Mode 4 during the t2-t3 period, except that the power flow direction has changed. Here, t0 is the zero-crossing point when the grid voltage changes from the negative half-cycle to the positive half-cycle; t1 is the zero-crossing point when the grid current changes from the positive half-cycle to the negative half-cycle; t2 is the zero-crossing point when the grid voltage changes from the positive half-cycle to the negative half-cycle; t3 is the zero-crossing point when the grid current changes from the negative half-cycle to the positive half-cycle; and t4 is the zero-crossing point when the grid voltage changes from the negative half-cycle to the positive half-cycle at the beginning of the next cycle.

[0089] Furthermore, as shown in Figure 11, when the microinverter outputs active power P0 and reactive power Q0, the frequency of the microinverter's output voltage is f0 and the amplitude is V0, meaning it operates at the rated operating point A of the droop characteristic curve. When the microinverter outputs active power P1 and reactive power Q1, the frequency of the microinverter's output voltage is f1 and the amplitude is V1, meaning it operates at point B of the droop characteristic curve. In summary, droop control can adjust the phase and amplitude of the microinverter's output voltage through the control principle of the power loop, thereby adjusting its output active power and reactive power.

[0090] Specifically, a simulation model of a grid-connected microinverter based on a bidirectional flyback converter was constructed using PLECS software for verification. Figure 12 shows the output voltage and current waveforms at a leading power factor, with a 48V PV DC input voltage and a 100kHz switching frequency for the bidirectional flyback converter. To simulate a weak grid environment, the grid-side inductor was set to 30mH. As shown in Figure 13, the microinverter's output current exceeds the output voltage, outputting active power and capacitive reactive power to the grid.

[0091] Furthermore, grid-connected micro-inverters based on bidirectional flyback converters can operate at any output power factor, providing reactive power support for weak grids. Furthermore, because grid-connected micro-inverters based on bidirectional flyback converters have a single-stage topology, they do not require DC bus electrolytic capacitors, improving cost, size, and reliability.

[0092] Furthermore, as shown in FIG14 , it can be seen that when the active power reference value changes from 200 W to 300 W, the active power output by the microinverter can track the active power reference value well, and can generate the microinverter output voltage phase θ without the need for a phase-locked loop, thereby achieving synchronization with the grid voltage.

[0093] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for constructing a grid-type micro-inverter based on a bidirectional flyback converter, characterized in that: Including bidirectional flyback converter and grid-type micro inverter; The grid-type micro-inverter includes a power loop, a voltage loop and a peak current control loop; Calculate active power and reactive power through the output voltage and output current of the grid-connected micro-inverter; Based on the power loop control principle, a preset power reference value is used to generate a reference signal for the voltage loop; generating a reference signal for the peak current control loop under the control of the voltage loop according to the actual output voltage; According to the primary current signals of the first bidirectional flyback converter and the second bidirectional flyback converter, a driving signal of each switch tube is generated under the regulation of a peak current control loop.

2. The method for constructing a grid-type micro-inverter based on a bidirectional flyback converter according to claim 1, wherein: The step of generating a reference signal for the voltage loop using a preset power reference value comprises the following steps: The voltage loop obtains a voltage error signal by comparing the voltage reference value generated by the power loop with the actual output voltage; The obtained voltage error signal is processed by a PID controller to generate the primary current reference signal of the peak current control loop; The peak current control loop compares the primary current reference signal generated by the voltage loop with the primary current signals of the first bidirectional flyback converter and the second bidirectional flyback converter; When the primary current signals of the first bidirectional flyback converter and the second bidirectional flyback converter are greater than or equal to the primary current reference signals of the first bidirectional flyback converter and the second bidirectional flyback converter, the primary switching tubes of the first bidirectional flyback converter and the second bidirectional flyback converter are turned off; When the primary current signals of the first bidirectional flyback converter and the second bidirectional flyback converter are less than the primary current reference signals of the first bidirectional flyback converter and the second bidirectional flyback converter, the primary switching tubes of the first bidirectional flyback converter and the second bidirectional flyback converter are turned on, thereby generating driving signals for the switching tubes of the first bidirectional flyback converter and the second bidirectional flyback converter; The grid-connected micro-inverter generates the grid voltage phase through the power control loop, realizes the synchronization between the micro-inverter and the grid, and ensures the stable operation of the system.

3. The method for constructing a grid-type micro-inverter based on a bidirectional flyback converter according to claim 1 or 2, characterized in that: The power loop includes an active-frequency droop link and a reactive-voltage droop link, and the related formulas are as follows: Among them, n p is the active power droop coefficient, n q is the reactive droop coefficient, ω ref is the micro-inverter output voltage frequency reference value, ω is the micro-inverter output voltage frequency, P ref and Q ref are all pre-set power reference values, p e The active power output of the micro inverter, u ref is the voltage loop reference voltage, U ref is the voltage loop reference voltage amplitude, U0 is the output voltage of the micro inverter, q e is the reactive power output by the micro-inverter, and t is the time.

4. The method for constructing a grid-type micro-inverter based on a bidirectional flyback converter according to claim 2, wherein: The method comprises the following steps based on the primary current signals of the first bidirectional flyback converter and the second bidirectional flyback converter: The first bidirectional flyback converter and the second bidirectional flyback converter both operate in an inductor current continuous mode; When the first bidirectional flyback converter is operating, the circuit is divided into mode 1 and mode 2 according to whether the third switch tube is turned off and whether the sixth switch tube is turned off; When the second bidirectional flyback converter is operating, the circuit is divided into mode three and mode four according to the sixth switch being turned off and the third switch being turned on.

5. The method for constructing a grid-type micro-inverter based on a bidirectional flyback converter according to claim 4, wherein: The relevant formula of the mode 1 is as follows: Among them, L m1 is the inductance of the primary winding of the first flyback transformer, i 10 is the initial value of the primary current of the first flyback transformer, T1 is the on-time of the primary switch of the first bidirectional flyback transformer in one switching cycle, U DC is the DC input voltage, i 1m is the peak current of the primary side current of the first flyback transformer in one switching cycle; The relevant formula of the second mode is as follows: Among them, L m2 is the inductance of the secondary winding of the first flyback transformer, i 20 is the initial value of the primary current of the first flyback transformer, T2 is the off time of the primary switch of the first bidirectional flyback transformer in one switching cycle, u0 is the actual output voltage, i 2m is the secondary current of the first flyback transformer in one switching cycle Peak.

6. A grid-type micro-inverter based on a bidirectional flyback converter, based on the method for grid-type micro-inverter based on a bidirectional flyback converter according to any one of claims 1 to 5, characterized in that: It includes a photovoltaic DC input source, an input filter capacitor, a first bidirectional flyback transformer, a second bidirectional flyback transformer, a first switch tube, a second switch tube, a third switch tube, a fourth switch tube, a fifth switch tube, a sixth switch tube, a first output capacitor, a second output capacitor, a first output filter inductor, a second output filter inductor, a first output filter capacitor, a second output filter capacitor, a grid-side inductor, an equivalent grid, and a grid-type micro-inverter.

7. The grid-connected micro-inverter based on a bidirectional flyback converter according to claim 6, characterized in that: The positive electrode of the input filter capacitor is electrically connected to the positive electrode of the photovoltaic DC input source, the primary side of the first bidirectional flyback transformer and the primary side of the second bidirectional flyback transformer; the negative electrode of the input filter capacitor is electrically connected to the negative electrode of the DC input source, the source electrode of the first switching tube and the source electrode of the fourth switching tube; the other end of the primary side of the first bidirectional flyback transformer is electrically connected to the drain electrode of the first switching tube; one end of the secondary side of the first bidirectional flyback transformer is electrically connected to the source electrode of the second switching tube; the other end of the secondary side of the first bidirectional flyback transformer is electrically connected to the source stage of the third switching tube, the negative electrode of the first output capacitor and the negative electrode of the first output filter capacitor; the source stage of the second switching tube is electrically connected to the source stage of the third switching tube, the positive electrode of the first output capacitor and one end of the first output filter inductor; the other end of the first output filter inductor is electrically connected to the positive electrode of the first output filter capacitor and one end of the grid-side inductor; and the other end of the grid-side inductor is electrically connected to one end of the equivalent power grid.

8. The grid-connected micro-inverter based on a bidirectional flyback converter according to claim 7, characterized in that: It also includes the other end of the primary side of the second bidirectional flyback transformer electrically connected to the drain of the fourth switch tube; one end of the secondary side of the second bidirectional flyback transformer electrically connected to the source of the fifth switch tube; the other end of the secondary side of the second bidirectional flyback transformer electrically connected to the source of the sixth switch tube, the negative electrode of the second output capacitor and the negative electrode of the second output filter capacitor; the source of the fifth switch tube electrically connected to the source of the sixth switch tube, the positive electrode of the second output capacitor and one end of the second output filter inductor; the other end of the second output filter inductor electrically connected to the positive electrode of the second output filter capacitor and the other end of the equivalent power grid.

9. The grid-type micro-inverter based on a bidirectional flyback converter according to claim 6, characterized in that: The driving signals of the first switching tube are complementary to those of the second switching tube, the fourth switching tube, the fifth switching tube, the third switching tube and the sixth switching tube.

10. The grid-connected micro-inverter based on a bidirectional flyback converter according to claim 6, characterized in that: The working states of the first bidirectional flyback converter and the second bidirectional flyback converter are completely symmetrical, wherein the first bidirectional flyback converter works in the positive half cycle of the grid voltage, and the second bidirectional flyback converter works in the negative half cycle of the grid voltage.

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