Topology and control method of T-type three-level single-stage DAB micro-inverter based on magnetic integration

Abstract

This invention discloses a T-type three-level single-stage DAB micro-inverter topology and control method based on magnetic integration, belonging to the field of inverter technology. The topology includes a photovoltaic input, grid output, symmetrical input capacitors, a primary-side bridge arm, a transformer, a secondary-side AC bridge arm, symmetrical output capacitors, and an output filter inductor. Magnetic integration technology integrates the transformer and output filter inductor together, reducing the number of independent components, thereby reducing size and cost. Simultaneously, this technology effectively reduces core losses, thereby increasing the system's power density. In terms of control, single-stage power conversion is achieved through three-level modulation of the primary-side bridge arm and grid synchronization control of the secondary-side bidirectional switching transistors. This topology combines the advantages of both single-stage and multi-stage structures, reducing device voltage stress and enabling a wide range of input voltages.

Description

Technical Field

[0001] This invention relates to the field of inverter technology, and in particular to a T-type three-level single-stage DAB micro inverter topology and control method based on magnetic integration. Background Technology

[0002] Inverters are a crucial component of photovoltaic (PV) power generation systems. Their primary function is to convert the direct current (DC) generated by PV panels into alternating current (AC) for grid transmission and residential use, while also providing maximum power point tracking (MPPT) for the PV panels. Traditional string inverters suffer from several key drawbacks: their efficiency is susceptible to performance mismatches among the components within the string (the "weakest link" effect), leading to overall power generation losses; fault location and maintenance are difficult, lacking component-level monitoring; they have high heat dissipation requirements, and poor installation environments can shorten their lifespan; parallel operation of multiple inverters may increase the risk of grid harmonic interference; a single unit failure can interrupt power generation across multiple strings; furthermore, overcoming mismatch issues often requires the addition of optimizers, potentially increasing system costs.

[0003] These drawbacks are particularly pronounced in complex installation environments or scenarios with high operation and maintenance requirements. Currently, microinverters have become a popular choice for photovoltaic inverters. By independently performing maximum power point tracking (MPPT) for individual or a small number of photovoltaic modules, microinverters effectively solve the power mismatch problem, significantly increasing system power generation and offering advantages such as module-level monitoring, high security, and flexible installation. However, microinverters require an independent inverter unit for each (or 1-2) module, leading to a significant increase in material, manufacturing, and installation costs per unit power. Furthermore, the limited space on the back of the module restricts heat dissipation. Under high power density designs, the temperature rise of internal components (such as electrolytic capacitors and MOSFETs) accelerates aging, affecting lifespan and reliability, and making it difficult to increase power ratings.

[0004] Existing microinverter topologies can be divided into single-stage and multi-stage types. Among multi-stage structures, the two-stage structure is common. In a two-stage structure, the front-stage DC-DC converter primarily boosts the voltage on the photovoltaic panel side to a level matching the grid voltage; this stage performs maximum power point tracking (MPPT). The rear-stage DC-AC converter is responsible for converting the direct current (DC) into alternating current (AC) that is in phase and frequency with the grid.

[0005] In contrast, a single-stage structure simultaneously performs DC-DC and DC-AC conversions within a single stage. Both single-stage and multi-stage structures have their drawbacks. Multi-stage structures experience increased cumulative losses due to multiple energy conversion stages, resulting in typically lower peak efficiency compared to single-stage structures. They require multiple power devices and control circuits, leading to a larger number of components, higher costs, and more complex heat dissipation designs. The space occupied by multiple circuits and transformers results in lower power density, limiting the power output of individual units. Single-stage structures, on the other hand, have a limited input voltage range, restricting their operating range. Furthermore, high switching stress limits the ZVS range and efficiency. Summary of the Invention

[0006] In view of this, the purpose of the present invention is to provide a T-type three-level single-stage DAB micro inverter topology and control method based on magnetic integration, which can reduce device voltage stress.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] The present invention provides a T-type three-level single-stage DAB micro inverter topology based on magnetic integration, including a photovoltaic input port, a grid output port, an input capacitor unit, a primary-side bridge arm circuit, a transformer, a secondary-side AC bridge arm, and an output filter unit;

[0009] The input capacitor unit is composed of a first input capacitor Cin1 and a second input capacitor Cin2 connected in series, with both ends connected to the photovoltaic input port;

[0010] The primary-side bridge arm circuit includes:

[0011] The first bridge arm is composed of switching transistors S1 and S2 connected in series, with its midpoint connected to one end of the primary winding NP of the transformer; the other end of the primary winding NP of the transformer is connected to the midpoint of the second bridge arm.

[0012] The second bridge arm is composed of switching transistors S3 and S4 connected in series, with its midpoint connected to one end of the primary-side bidirectional switching transistor S5, and the other end of the primary-side bidirectional switching transistor S5 connected to the midpoint of the input capacitor unit.

[0013] The bidirectional switch S5 includes a bidirectional switch S5a and a bidirectional switch S5b; the sources of the bidirectional switch S5a and the bidirectional switch S5b are connected to form a bidirectional switch.

[0014] The secondary AC bridge arm is composed of bidirectional switching transistor S6 and bidirectional switching transistor S7, which are connected in series and then in parallel with the output capacitor unit.

[0015] The output filtering unit includes an output capacitor unit and an output filtering inductor Lo;

[0016] The output capacitor unit is composed of a first output capacitor Co1 and a second output capacitor Co2 connected in series.

[0017] One end of the output filter inductor Lo is connected to the bidirectional switch S6, and the other end is connected to the power grid output port;

[0018] The midpoint of the first output capacitor Co1 and the second output capacitor Co2 connected in series is connected to the secondary side of the transformer, and the other end of the secondary side of the transformer is connected to the midpoint of the secondary side AC bridge arm.

[0019] The output filter inductor Lo and the transformer T are integrated on the same magnetic core through a magnetic integration structure;

[0020] The magnetic integrated structure includes:

[0021] A symmetrical magnetic circuit structure formed by interlocking two E-type magnetic cores and one I-type magnetic core;

[0022] The output filter inductor Lo has its winding No wound on the center post of the right-side E-type magnetic core;

[0023] The primary winding NP and secondary winding NS of the transformer are wound on the central column of the left-side E-type magnetic core, using a multi-layer wrapping winding method.

[0024] Furthermore, the leakage inductance of the transformer T is Llk, and the turns ratio is 1:n; where n represents the turns ratio of the transformer.

[0025] Furthermore, both the left and right E-shaped core columns of the magnetic core are provided with air gaps.

[0026] Furthermore, the winding No of the output filter inductor Lo is wound in a single-layer flat winding manner on the central column of the right-side E-type magnetic core.

[0027] Furthermore, the secondary AC bridge arm includes a bidirectional switch S6 and a bidirectional switch S7. The bidirectional switch S6 is composed of S6a and S6b; the bidirectional switch S7 is composed of S7a and S7b. During the positive half-cycle of the grid voltage, S6b and S7b remain normally open, while S6a and S7a are alternately turned on. During the negative half-cycle of the grid voltage, S6a and S7a remain normally closed, while S6b and S7b are alternately turned on.

[0028] Furthermore, the first input capacitor Cin1 and the second input capacitor Cin2 have equal capacitance values ​​and are symmetrically distributed in the circuit topology.

[0029] The control method for a magnetically integrated T-type three-level single-stage DAB micro inverter provided by this invention includes the following steps:

[0030] S10: Receives DC power through the photovoltaic input port, and divides the voltage through the first input capacitor Cin1 and the second input capacitor Cin2 connected in series;

[0031] S20: Controls the primary-side bridge arm circuit to operate in three-level mode.

[0032] The switching transistors S1 and S2 of the first bridge arm are turned on complementaryly to generate the first level path;

[0033] The switching transistors S3 and S4 of the second bridge arm are turned on complementaryly to generate a second level path;

[0034] Control the on / off state of the primary-side bidirectional switch S5 to inject the midpoint voltage of the input capacitor into the primary winding NP of the transformer;

[0035] S30: Grid synchronization control is performed via bidirectional switches S6 and S7 on the secondary AC bridge arm.

[0036] The bidirectional switching transistor S6 is composed of S6a and S6b; the bidirectional switching transistor S7 is composed of S7a and S7b.

[0037] During the positive half-cycle of the grid voltage: keep S6b and S7b constantly on, and alternately turn on S6a and S7a;

[0038] During the negative half-cycle of the grid voltage: keep S6a and S7a constantly open, and alternately open S6b and S7b;

[0039] S40: Energy transfer coupled using a magnetically integrated structure:

[0040] The primary winding NP of the transformer and the winding No of the output filter inductor Lo are integrated into the same magnetic core;

[0041] Single-stage power conversion is achieved through electromagnetic coupling between the primary winding NP and the secondary winding NS of the transformer, and the power is transmitted to the grid output port through the output filter inductor Lo.

[0042] In step S40, the magnetic integrated structure is formed in the following manner:

[0043] The primary winding NP of the transformer is wound on the middle column of the left E-type magnetic core, and the winding No of the output filter inductor Lo is wound on the middle column of the right E-type magnetic core. The I-type magnetic core is placed between the left and right E-type magnetic cores to form a closed symmetrical magnetic circuit structure.

[0044] The beneficial effects of this invention are as follows:

[0045] This invention provides a T-type three-level single-stage DAB micro-inverter topology and control method based on magnetic integration. This topology combines the advantages of both single-stage and multi-stage topologies. It reduces device voltage stress, enables a wide voltage input range, reduces the number of components used, lowers costs, and achieves high efficiency. However, the T-type three-level single-stage DAB micro-inverter topology also has disadvantages. Compared to traditional single-stage topologies, it adds a bidirectional switching transistor. Furthermore, the control of this topology is more complex, requiring a high-performance controller.

[0046] This topology's magnetic integration technology combines the transformer and output filter inductor, reducing the number of independent components, thereby decreasing size and cost. Simultaneously, this technology effectively reduces core losses, thus increasing the system's power density.

[0047] This circuit structure can solve the problems of high voltage stress and limited input voltage range of single-stage structure devices, as well as the problems of large number of components, high cost and low efficiency of multi-stage structure devices; it also solves the problems of low power density and limited power.

[0048] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0049] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the following drawings are provided for illustration.

[0050] Figure 1 This is a T-type three-level single-stage DAB micro inverter topology.

[0051] Figure 2 This is a schematic diagram of working mode 1.

[0052] Figure 3 This is a schematic diagram of working mode 2.

[0053] Figure 4 This is a schematic diagram of working mode 3.

[0054] Figure 5 This is a schematic diagram of working mode 4.

[0055] Figure 6 This is a schematic diagram of working mode 5.

[0056] Figure 7 This is a schematic diagram of working mode 6.

[0057] Figure 8 This is a schematic diagram of working mode 7.

[0058] Figure 9 This is a schematic diagram of working mode 8.

[0059] Figure 10 This is a schematic diagram of different operating modes and circuit waveforms during the positive half-cycle of the power grid.

[0060] Figure 11 This refers to the core structure and magnetic flux distribution.

[0061] Figure 12 This is a detailed circuit connection diagram for the magnetic integrated structure. Detailed Implementation

[0062] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0063] Example 1

[0064] like Figure 1 As shown, Figure 1 This embodiment provides a T-type three-level single-stage DAB micro-inverter topology based on magnetic integration, including a photovoltaic input port, a grid output port, an input capacitor unit, a primary-side bridge arm circuit, a transformer, a secondary-side AC bridge arm, and an output filter unit.

[0065] The input capacitor unit is composed of a first input capacitor Cin1 and a second input capacitor Cin2 connected in series, with both ends connected to the photovoltaic input port;

[0066] The primary-side bridge arm circuit includes:

[0067] The first bridge arm is composed of switching transistors S1 and S2 connected in series, with its midpoint connected to one end of the primary winding NP of the transformer; the other end of the primary winding NP of the transformer is connected to the midpoint of the second bridge arm, which is the midpoint of the series connection of switching transistors S3 and S4.

[0068] The second bridge arm is composed of switching transistors S3 and S4 connected in series. The midpoint is connected to one end of the primary bidirectional switching transistor S5, and the other end of the primary bidirectional switching transistor S5 is connected to the midpoint of the input capacitor unit, that is, the midpoint of the series connection of the first input capacitor Cin1 and the second input capacitor Cin2.

[0069] In this embodiment, the bidirectional switch S5 includes bidirectional switch S5a and bidirectional switch S5b; the sources of bidirectional switch S5a and bidirectional switch S5b are connected (common source) to form a bidirectional switch. The series-connected S5 is connected between the midpoint of the second bridge arm (midpoint of S3 / S4) and the midpoint of the input capacitor (midpoint of Cin1 / Cin2).

[0070] The secondary AC bridge arm is composed of bidirectional switching transistor S6 and bidirectional switching transistor S7, which are connected in series and then in parallel with the output capacitor unit.

[0071] The output filtering unit includes an output capacitor unit and an output filtering inductor Lo;

[0072] The output capacitor unit is composed of a first output capacitor Co1 and a second output capacitor Co2 connected in series.

[0073] One end of the output filter inductor Lo is connected to the bidirectional switch S6, and the other end is connected to the power grid output port;

[0074] The midpoint of the first output capacitor Co1 and the second output capacitor Co2 connected in series is connected to the secondary side of the transformer, and the other end of the secondary side of the transformer is connected to the midpoint of the secondary side AC bridge arm.

[0075] The output filter inductor Lo and the transformer T are integrated on the same magnetic core through a magnetic integration structure;

[0076] The magnetic integrated structure includes:

[0077] A symmetrical magnetic circuit structure formed by interlocking two E-type magnetic cores and one I-type magnetic core;

[0078] The output filter inductor Lo has its winding No wound on the center column of the right-side E-type magnetic core; the output filter inductor Lo is composed of the winding No wound on the center column of the right-side E-type magnetic core.

[0079] The primary winding NP and secondary winding NS of the transformer are wound on the central column of the left-side E-type magnetic core, using a multi-layer wrapping winding method.

[0080] The leakage inductance of the transformer T is Llk, and the turns ratio is 1:n; where n represents the turns ratio of the transformer.

[0081] In this embodiment, both the left and right E-type core columns of the magnetic core are provided with air gaps. The air gap in the right E-type core is used to adjust the output filter inductance value and prevent core saturation; the air gap in the left E-type core is used to adjust the magnetizing inductance and prevent transformer core saturation.

[0082] In this embodiment, the winding No of the output filter inductor Lo is wound in a single-layer flat winding method on the right-side E-type magnetic core. This winding method can optimize magnetic performance;

[0083] In this embodiment, the primary winding NP and secondary winding NS of the transformer are wound in a multi-layer wrapping method on the left-side E-type magnetic core column.

[0084] In this embodiment, during the positive half-cycle of the mains voltage, the bidirectional switches S6 and S7 of the secondary AC bridge arm are normally open (S6b and S7b) and alternately turned on (S6a and S7a); during the negative half-cycle of the mains voltage, S6a and S7a are normally on (S6b and S7b) and alternately turned on. This method can support single-stage energy conversion. S6a and S6b are two independent switches constituting the bidirectional switch S6; S7a and S7b are two independent switches constituting the bidirectional switch S7. They are connected either source-to-source (common source) or back-to-back in series. When one is on, current is allowed to flow in one direction; when the other is on, current is allowed to flow in the opposite direction.

[0085] In this embodiment, the first input capacitor Cin1 and the second input capacitor Cin2 have equal capacitance values ​​and are symmetrically distributed in the circuit topology. This symmetrical design of the input capacitors can improve stability.

[0086] The topology provided in this embodiment can be applied to photovoltaic microinverter systems.

[0087] The control method for the magnetically integrated T-type three-level single-stage DAB micro inverter in this embodiment includes the following steps:

[0088] S10: Receives DC power through the photovoltaic input port, and divides the voltage through the first input capacitor Cin1 and the second input capacitor Cin2 connected in series;

[0089] S20: Controls the primary-side bridge arm circuit to operate in three-level mode.

[0090] The switching transistors S1 and S2 of the first bridge arm are turned on complementaryly to generate the first level path;

[0091] The switching transistors S3 and S4 of the second bridge arm are turned on complementaryly to generate a second level path;

[0092] Control the on / off state of the primary-side bidirectional switch S5 to inject the midpoint voltage of the input capacitor into the primary winding NP of the transformer;

[0093] S30: Grid synchronization control is performed via bidirectional switches S6 and S7 on the secondary AC bridge arm.

[0094] During the positive half-cycle of the grid voltage: keep S6b and S7b constantly on, and alternately turn on S6a and S7a;

[0095] During the negative half-cycle of the grid voltage: keep S6a and S7a constantly open, and alternately open S6b and S7b;

[0096] S40: Energy transfer coupled using a magnetically integrated structure:

[0097] The primary winding NP of the transformer and the winding No of the output filter inductor Lo are integrated into the same magnetic core;

[0098] Single-stage power conversion is achieved through electromagnetic coupling between the primary winding NP and the secondary winding NS of the transformer, and the power is transmitted to the grid output port via the output filter inductor Lo.

[0099] In this embodiment, the energy transfer of the magnetic integrated structure in step S40 includes:

[0100] The primary winding NP of the transformer is wound on the left side of the E-type magnetic core, and the winding No of the output filter inductor Lo is wound on the right side of the E-type magnetic core, forming a closed magnetic circuit through the I-type magnetic core.

[0101] This embodiment also includes an air gap adjustment step:

[0102] Air gaps are set in the left and right E-type magnetic core columns to adjust the core saturation characteristics.

[0103] In this embodiment, based on the design target values ​​of the transformer magnetizing inductance and the output filter inductance Lo, the required air gap length of the left and right E-type magnetic core columns is initially calculated and estimated using the air gap formula:

[0104]

[0105] Where lg is the required air gap length, Ae is the effective cross-sectional area of ​​the magnetic core, and N is the number of winding turns. Here, represents the vacuum permeability. After calculating the air gap length, its suitability must be verified. Therefore, it is necessary to check whether the magnetic flux density Bmax at the maximum operating current is lower than the saturation magnetic flux density of the core material. The formula for calculating Bmax is:

[0106]

[0107] in, This represents the peak current flowing through the winding;

[0108] If Bmax is too high, it means the magnetic core is too small. A larger magnetic core needs to be selected. At the same time, the number of turns N needs to be adjusted to maintain the inductance L. Then repeat the above calculation until the requirements are met.

[0109] After obtaining the required air gap length, this length is ground off the center column, and then non-magnetic material (such as insulating pads) is used to fill and fix the air gap to ensure air gap consistency. The air gap length is fine-tuned to achieve the design target by experimentally measuring the transformer primary inductance and output filter inductance. At the same time, the core saturation is tested under different load conditions to further optimize the air gap and ensure stable operation of the system across the full power range.

[0110] The magnetic integration in this embodiment improves power density and efficiency. By integrating the transformer and output filter inductor onto a composite magnetic core with a symmetrical magnetic circuit structure, the physical level significantly reduces the volume and number of traditional discrete magnetic components, directly increasing power density. Electromagnetically, it utilizes the different phases of the transformer and inductor currents to generate opposite magnetic fluxes in the shared Type I magnetic core, resulting in a partial flux cancellation effect. This significantly reduces the magnetic flux density and core loss in the shared magnetic circuit. Meanwhile, the independent air gap and winding design ensure their respective optimal performance. This structural optimization ultimately contributes to the improvement of system efficiency.

[0111] Meanwhile, by adopting a T-type three-level structure, the topology introduces a bidirectional switch S5 in the primary arm of the bridge, injecting the midpoint voltage of the input capacitor into the primary winding of the transformer, so that each switch only needs to bear half of the input voltage stress, thereby significantly reducing the voltage stress of the device.

[0112] Example 2

[0113] This embodiment details the specific structure and operation of a magnetically integrated T-type three-level single-stage DAB micro-inverter topology.

[0114] (1) T-type three-level single-stage DAB micro inverter:

[0115] This embodiment replaces the secondary-side switches of a traditional T-type three-level dual active bridge (DAB) converter with bidirectional switches and replaces one bridge arm with a capacitor to obtain a T-type three-level single-stage DAB micro inverter, the topology of which is as follows: Figure 1 As shown, the T-type three-level single-stage DAB micro-inverter topology possesses the advantages of a T-type three-level dual active full-bridge converter, exhibiting high performance advantages. The T-type three-level single-stage DAB micro-inverter topology mainly includes a photovoltaic panel (input photovoltaic voltage V...). PV The components include two input capacitors (first input capacitor Cin1 and second input capacitor Cin2), the first bridge arm (composed of switching transistors S1 / S2), the second bridge arm (composed of switching transistors S3 / S4), the primary side bidirectional switching transistor S5, the transformer T (with a turns ratio of 1:n), the transformer leakage inductance Llk, the secondary side AC bridge arm (composed of bidirectional switching transistors S6 / S7), the first output capacitor Co1 and the second output capacitor Co2, the output filter inductor Lo, and the mains voltage Vg.

[0116] The circuit structure of the T-type three-level single-stage DAB micro-inverter topology in this embodiment is symmetrical, and the circuit operation states during the positive and negative half-cycles of the grid voltage are similar. The difference lies in the following: During the positive half-cycle: the input voltage is positive at the top and negative at the bottom, and among the bidirectional switches S6 and S7, S6b and S7b are always conducting, while S6a and S7a conduct alternately. During the negative half-cycle: the input voltage is negative at the top and positive at the bottom, and among the bidirectional switches S6 and S7, S6a and S7a are always conducting, while S6b and S7b conduct alternately.

[0117] Since the T-type three-level single-stage DAB micro inverter has different operating modes depending on the control method, this embodiment only uses the positive half-cycle of one mode as an example to analyze the operating state of the T-type three-level single-stage DAB micro inverter.

[0118] Figures 2 to 9 The eight operating modes of the circuit are given, and the corresponding circuit waveforms are shown below. Figure 10 , Figure 10This is a schematic diagram of different operating modes and circuit waveforms during the positive half-cycle of the power grid.

[0119] Where iLlk is the leakage inductance current, Vp is the primary input voltage of the transformer, Vs is the AC input voltage, and S6b and S7b of the bidirectional switching transistors S6 and S7 are always on.

[0120] The specific working mode is as follows:

[0121] Mode 1 (e.g.) Figure 2 As shown): In this state, the circuit waveform corresponds to Figure 10 During the t0~t1 stage, switches S1, S3, and S7a are turned on, and the photovoltaic input V... PV The first input capacitor Cin1 and the second input capacitor Cin2 are charged to store energy. At this time, Vp is 0, Vs is -Vg / 2, and the leakage inductance current iLlk changes at the rate of change of:

[0122]

[0123] Mode 2 (e.g.) Figure 3 As shown): In this state, the circuit waveform corresponds to Figure 10 During the t1~t2 phase, switches S1 and S7a remain on, switch S3 is off, and switch S4 is on, allowing energy to be transferred from the input side to the grid side. In this state, Vp is V PV Vs is -Vg / 2, and the rate of change of leakage inductance current iLlk is:

[0124]

[0125] Mode 3 (e.g.) Figure 4 As shown): In this state, the circuit waveform corresponds to Figure 10 During the t2~t3 phase, switches S1 and S4 remain on, switch S7a is off, and switch S6a is on, meaning energy is still transferred from the input side to the grid side. In this state, Vp is V PV Vs is Vg / 2, and the rate of change of leakage inductance current iLlk is:

[0126]

[0127] Mode 4 (e.g.) Figure 5 As shown): In this state, the circuit waveform corresponds to Figure 10 During the t3~t4 stage, switches S1 and S6a remain on, switch S4 is off, and bidirectional switch S5 is on. At this time, energy is released from the input capacitor and transferred to the AC side. In this state, Vp is V PV / 2, Vs is Vg / 2, and the rate of change of leakage inductance current iLlk is:

[0128]

[0129] Mode 5 (e.g.) Figure 6 As shown): In this state, the circuit waveform corresponds to Figure 10 During the t4~t5 stage, switch S6a remains on, switch S1 and bidirectional switch S5 are off, and switches S2 and S4 are on, resulting in photovoltaic input V. PV The first input capacitor Cin1 and the second input capacitor Cin2 are charged to store energy, and no energy is transferred to the AC side. In this state, Vp is 0, Vs is Vg / 2, and the leakage inductance current iLlk changes at the rate of change of:

[0130]

[0131] Mode 6 (e.g.) Figure 7 As shown): In this state, the circuit waveform corresponds to Figure 10 During the t5~t6 stage, switches S2 and S6a remain on, switch S4 is off, and switch S3 is on, allowing energy to be transferred from the input side to the grid side. In this state, Vp is -V. PV Vs is Vg / 2, and the rate of change of leakage inductance current iLlk is:

[0132]

[0133] Mode 7 (e.g.) Figure 8 As shown): In this state, the circuit waveform corresponds to Figure 10 During the t6~t7 stage, switches S2 and S3 remain on, switch S6a is off, and switch S7a is on, allowing energy to continue flowing from the input side to the grid side. In this state, Vp is -V. PV Vs is -Vg / 2, and the rate of change of leakage inductance current iLlk is:

[0134]

[0135] Mode 8 (e.g.) Figure 9 As shown): In this state, the circuit waveform corresponds to Figure 10 During the t7~t8 phase, switches S2 and S7a remain on, switch S3 is off, and bidirectional switch S5 is on, allowing energy to be released from the input capacitor and transferred to the AC side. In this state, Vp is -V. PV / 2, Vs is -Vg / 2, the rate of change of leakage inductance current iLlk is:

[0136]

[0137] (2) Magnetic integration:

[0138] To address the issues of large size, high cost, low power density, and power limitation caused by discrete components, this embodiment utilizes sampling magnetic integration technology to integrate the output filter inductor Lo and transformer T onto a single magnetic core. The core structure and flux distribution are as follows: Figure 11 As shown, Figure 11 The magnetic core structure and flux distribution are described. This magnetic core consists of two E-type magnetic cores and one I-type magnetic core. The two E-type magnetic cores are symmetrical from left to right, and the I-type magnetic core is in the middle, forming a physical connection, ultimately forming a composite magnetic core with a symmetrical magnetic circuit structure.

[0139] The output filter inductor winding (No) is wound on the center post of the right-side E-type magnetic core using a single-layer flat winding method; the primary winding (NP) and secondary winding (NS) of the transformer T are wound on the center post of the left-side E-type magnetic core (leakage inductance is Llk), using a multi-layer wrapping winding method (sandwich structure) to enhance coupling, and the leakage inductance can be adjusted by adjusting the interlayer distance.

[0140] Air gaps are opened in the center column of both E-type magnetic cores. The main function of the air gap in the center column of the right E-type magnetic core is to adjust the output filter inductance value and prevent the output filter inductor core from saturating and stabilize the inductance. The main function of the air gap in the center column of the left E-type magnetic core is to adjust the excitation inductance and prevent the transformer core from saturating.

[0141] When the magnetic flux of the output filter inductor and the transformer passes through the type I magnetic core, some of the magnetic flux cancels out, reducing the loss of the type I magnetic core. The specific connection method between the integrated magnetic core and the circuit is as follows: Figure 12 As shown, Figure 12 This is a detailed circuit connection diagram.

[0142] exist Figure 12In the specific circuit connection diagram, the input capacitor unit consists of a first input capacitor Cin1 and a second input capacitor Cin2 connected in series, with both ends connected to the photovoltaic input port; the first bridge arm consists of a switch S1 and a switch S2 connected in series, with the midpoint connected to one end of the primary winding NP of the transformer, and the other end of the primary winding NP of the transformer connected to the midpoint of the second bridge arm, i.e., the midpoint of the series connection of switches S3 and S4; the second bridge arm consists of a switch S3 and a switch S4 connected in series, with the midpoint connected to one end of the primary bidirectional switch S5, and the other end of the primary bidirectional switch S5 connected to the midpoint of the input capacitor unit, i.e., the first input capacitor Cin1. 1. The midpoint of the series connection between the first and second input capacitors Cin2; the secondary AC bridge arm consists of bidirectional switching transistors S6 and S7, which are connected in series and then in parallel with the output capacitor unit, which consists of the first output capacitor Co1 and the second output capacitor Co2 connected in series; one end of the output filter inductor Lo is connected to the bidirectional switching transistor S6, and the other end is connected to the mains output port; the midpoint of the series connection between the first output capacitor Co1 and the second output capacitor Co2 is connected to the secondary side of the transformer, and the other end of the secondary side of the transformer is connected to the midpoint of the secondary AC bridge arm; the output filter inductor Lo and the transformer T are integrated on the same magnetic core through a magnetic integration structure.

[0143] The above-described embodiments are merely preferred embodiments provided to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the claims.

Claims

1. A T-type three-level single-stage DAB micro-inverter topology based on magnetic integration, comprising a photovoltaic input port, a grid output port, an input capacitor unit, a primary-side bridge arm circuit, a transformer, a secondary-side AC bridge arm, and an output filter unit, characterized in that: The input capacitor unit is composed of a first input capacitor Cin1 and a second input capacitor Cin2 connected in series, with both ends connected to the photovoltaic input port; The primary-side bridge arm circuit includes a first bridge arm and a second bridge arm: The first bridge arm is composed of switching transistors S1 and S2 connected in series, and the midpoint of the first bridge arm is connected to one end of the primary winding NP of the transformer; the other end of the primary winding NP of the transformer is connected to the midpoint of the second bridge arm. The second bridge arm is composed of switching transistors S3 and S4 connected in series. The midpoint of the second bridge arm is connected to one end of the bidirectional switching transistor S5 on the primary side, and the other end of the bidirectional switching transistor S5 on the primary side is connected to the midpoint of the input capacitor unit. The bidirectional switch S5 includes a bidirectional switch S5a and a bidirectional switch S5b; the sources of the bidirectional switch S5a and the bidirectional switch S5b are connected to form a bidirectional switch. The secondary AC bridge arm is composed of bidirectional switching transistor S6 and bidirectional switching transistor S7, which are connected in series and then in parallel with the output capacitor unit. The output filtering unit includes an output capacitor unit and an output filtering inductor Lo; The output capacitor unit is composed of a first output capacitor Co1 and a second output capacitor Co2 connected in series. One end of the output filter inductor Lo is connected to the bidirectional switch S6, and the other end is connected to the power grid output port; The midpoint of the first output capacitor Co1 and the second output capacitor Co2 connected in series is connected to the secondary side of the transformer, and the other end of the secondary side of the transformer is connected to the midpoint of the secondary side AC bridge arm. The output filter inductor Lo and the transformer T are integrated on the same magnetic core through a magnetic integration structure; The magnetic integrated structure includes: A symmetrical magnetic circuit structure formed by interlocking two E-type magnetic cores and one I-type magnetic core; The output filter inductor Lo has its winding No wound on the center post of the right-side E-type magnetic core; The primary winding NP and secondary winding NS of the transformer are wound on the central column of the left-side E-type magnetic core, using a multi-layer wrapping winding method.

2. The T-type three-level single-stage DAB micro-inverter topology based on magnetic integration as described in claim 1, characterized in that: The leakage inductance of the transformer T is Llk, and the turns ratio is 1:n; where n represents the turns ratio of the transformer.

3. The T-type three-level single-stage DAB micro inverter topology based on magnetic integration as described in claim 1, characterized in that: Both the left and right E-shaped core columns of the magnetic core have air gaps.

4. The T-type three-level single-stage DAB micro-inverter topology based on magnetic integration as described in claim 1, characterized in that: The output filter inductor Lo has a winding No that is wound in a single-layer flat winding manner on the right-side E-type magnetic core column.

5. The T-type three-level single-stage DAB micro inverter topology based on magnetic integration as described in claim 1, characterized in that: The secondary AC bridge arm includes bidirectional switching transistors S6 and S7. Bidirectional switching transistor S6 is composed of S6a and S6b; bidirectional switching transistor S7 is composed of S7a and S7b. During the positive half-cycle of the grid voltage, S6b and S7b remain normally open, while S6a and S7a conduct alternately. During the negative half-cycle of the grid voltage, S6a and S7a remain normally closed, while S6b and S7b conduct alternately.

6. The T-type three-level single-stage DAB micro inverter topology based on magnetic integration as described in claim 1, characterized in that: The first input capacitor Cin1 and the second input capacitor Cin2 have equal capacitance values ​​and are symmetrically distributed in the circuit topology.

7. A control method for a magnetically integrated T-type three-level single-stage DAB microinverter as described in claim 1, characterized in that, Includes the following steps: S10: Receives DC power through the photovoltaic input port, and divides the voltage through the first input capacitor Cin1 and the second input capacitor Cin2 connected in series; S20: Controls the primary-side bridge arm circuit to operate in three-level mode. The switching transistors S1 and S2 of the first bridge arm are turned on complementaryly to generate the first level path; The switching transistors S3 and S4 of the second bridge arm are turned on complementaryly to generate a second level path; Control the on / off state of the primary-side bidirectional switch S5 to inject the midpoint voltage of the input capacitor into the primary winding NP of the transformer; S30: Grid synchronization control is performed via bidirectional switches S6 and S7 on the secondary AC bridge arm. The bidirectional switching transistor S6 is composed of S6a and S6b; the bidirectional switching transistor S7 is composed of S7a and S7b. During the positive half-cycle of the grid voltage: keep S6b and S7b constantly on, and alternately turn on S6a and S7a; During the negative half-cycle of the grid voltage: keep S6a and S7a constantly open, and alternately open S6b and S7b; S40: Energy transfer coupled using a magnetically integrated structure: The primary winding NP of the transformer and the winding No of the output filter inductor Lo are integrated into the same magnetic core; Single-stage power conversion is achieved through the electromagnetic coupling of the primary winding NP and the secondary winding NS of the transformer, and the power is transmitted to the grid output port through the output filter inductor Lo. In step S40, the magnetic integrated structure is formed in the following manner: The primary winding NP of the transformer is wound on the middle column of the left E-type magnetic core, and the winding No of the output filter inductor Lo is wound on the middle column of the right E-type magnetic core. The I-type magnetic core is placed between the left and right E-type magnetic cores to form a closed symmetrical magnetic circuit structure.

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