A Phase-Shifted Full-Bridge Micro-Inverter and Its Modulation Method

Abstract

The present invention provides a phase-shifted full-bridge micro-inverter, which includes a DC-side full-bridge module, a high-frequency transformer, and an AC-side rectification module. The topology of the AC rectification module is based on a common rectification circuit and can achieve bidirectional power flow. This micro-inverter can be applied to relatively large power levels. By reasonably designing the dead time of the switching tubes in the phase-shifted full-bridge circuit, zero-current or zero-voltage turn-on of all switching tubes can be achieved, which is beneficial to reducing switching losses. The present invention also provides a modulation method for the phase-shifted full-bridge micro-inverter. By sampling the DC-side voltage and the grid voltage and combining with the given value of the grid current, the trajectory of the internal phase-shift angle is planned; according to the positive or negative of the grid voltage, the turn-on logic of the power-frequency switching tubes is determined, and according to the positive or negative of the transformer current, the turn-on logic of the high-frequency switching tubes is determined, so that a sinusoidal AC current output can be achieved, thereby greatly improving the grid connection stability of the micro-inverter and improving the total harmonic distortion rate (THD) of the output current.

Description

Technical Field

[0001] The present invention relates to the technical field of photovoltaic micro-inverters, and specifically, to a phase-shifted full-bridge micro-inverter and its modulation method. Background Art

[0002] A micro-inverter generally refers to an inverter in a photovoltaic power generation system with a power less than or equal to 1000W and having the ability of component-level maximum power point tracking. Different from centralized and string-type photovoltaic inverter systems, a micro-inverter is directly connected to a single photovoltaic module. Its advantages are that it can perform independent MPPT control on each module, which can greatly improve the overall efficiency while avoiding problems such as high DC voltage, poor low-light effect, and the barrel effect existing in centralized inverters.

[0003] According to the position and structural characteristics of the DC bus, micro-inverters can be divided into three categories: DC bus structure, pseudo-DC bus structure, and non-DC bus structure. Among them, the micro-inverter with a DC bus structure is a two-stage structure. The front-stage DC-DC conversion circuit uses fixed-duty-cycle modulation, and the rear-stage DC-AC circuit uses SPWM modulation. The two-stage circuits are independently decoupled and controlled, but the loss of the rear-stage DC-AC conversion circuit is relatively high; the micro-inverter with a pseudo-DC bus structure is also a two-stage structure, in which the front-stage DC-DC conversion circuit uses SPWM modulation and the rear-stage DC-AC circuit uses power-frequency square-wave modulation. The disadvantage is that the control of the front-stage DC-DC circuit is relatively complex and prone to distortion of the AC output current; the micro-inverter without a DC bus is a single-stage circuit using matrix control, which uses fewer switching devices and has a high conversion efficiency, so it has more advantages.

[0004] Existing non-DC bus micro-inverters all adopt the phase-shift control of a DAB converter (dual active bridge converter), which can be specifically divided into two types. The first is to make the micro-inverter work in a single-phase-shift modulation state. Under this modulation strategy, the micro-inverter has only one control degree of freedom, and the effective value of the transformer secondary current is large, resulting in low efficiency; the second is to make the micro-inverter work in an extended phase-shift modulation state. Although this method improves the problem of large effective value of the current under single-phase-shift modulation, the relationship between the transmission power of the micro-inverter and the internal and external phase-shift angles is highly non-linear, so it brings great difficulty to the design of the controller. Based on the above problems, it is necessary to improve the architecture of the micro-inverter.

[0005] Currently, no description or report of similar technologies to the present invention has been found, and no similar materials at home and abroad have been collected. Summary of the Invention

[0006] In view of the above deficiencies in the prior art, the present invention provides a phase-shifted full-bridge micro-inverter and its modulation method.

[0007] According to one aspect of the present invention, a phase-shifted full-bridge micro-inverter is provided, comprising: a DC-side full-bridge module, a high-frequency transformer, and an AC-side rectification module; wherein:

[0008] The DC port of the DC-side full-bridge module is connected in parallel with the DC-side bus capacitor C bus ; wherein, the DC-side full-bridge module is mainly composed of switching tubes S1 to S4. The source of the switching tube S1 is connected to the drain of the switching tube S2, the source of the switching tube S3 is connected to the drain of the switching tube S4, the drain of the switching tube S1 is connected to the drain of the switching tube S3 and is connected to the positive electrode of the DC-side bus capacitor C bus ; the source of the switching tube S2 is connected to the source of the switching tube S4 and is connected to the negative electrode of the DC-side bus capacitor C bus ;

[0009] The positive pole of the primary side of the high-frequency transformer is connected to the midpoint between the switching tubes S1 and S2, and the negative pole of the primary side of the high-frequency transformer is connected to the midpoint between the switching tubes S3 and S4;

[0010] The AC-side rectification module is connected in series with the secondary side of the high-frequency transformer.

[0011] Preferably, the AC-side rectification module includes: a switching tube assembly mainly composed of multiple groups of bidirectional switching tubes and an AC-side inductor connected in series with the output end of the switching tube assembly.

[0012] Preferably, the AC-side rectification module adopts any one of the following topological structures:

[0013] - Adopting a high-frequency link matrix converter structure; the high-frequency link matrix converter structure includes: the switching tube assembly includes the first switching tube to the eighth switching tube; wherein, the drain of the first switching tube is connected to the drain of the fifth switching tube, the source of the first switching tube is connected to the source of the second switching tube, the drain of the second switching tube is connected to the drain of the third switching tube and is connected to the positive pole of the secondary side port of the high-frequency transformer, the source of the third switching tube is connected to the source of the fourth switching tube, the drain of the fourth switching tube is connected to the drain of the eighth switching tube, the source of the fifth switching tube is connected to the source of the sixth switching tube, the drain of the sixth switching tube is connected to the drain of the seventh switching tube and is connected to the negative pole of the secondary side port of the high-frequency transformer, and the source of the seventh switching tube is connected to the source of the eighth switching tube;

[0014] - Adopt a parallel structure of bidirectional switch groups; the parallel structure of bidirectional switch groups includes: the switch tube assembly includes: the first switch tube to the fourth switch tube; wherein, the drain of the first switch tube is connected to the positive pole of the secondary side port of the high-frequency transformer, the source of the first switch tube is connected to the source of the second switch tube, the drain of the second switch tube is connected to the drain of the fourth switch tube, the source of the fourth switch tube is connected to the source of the third switch tube, and the drain of the fourth switch tube is connected to the negative pole of the secondary side port of the high-frequency transformer;

[0015] - Adopt a series structure of bidirectional switch groups; the series structure of bidirectional switch groups includes: the switch tube assembly includes: the first switch tube to the fourth switch tube; wherein, the drain of the first switch tube is connected to the positive pole of the secondary side port of the high-frequency transformer, the source of the first switch tube is connected to the source of the second switch tube, the drain of the second switch tube is connected to the drain of the third switch tube, the source of the third switch tube is connected to the source of the fourth switch tube, and the drain of the fourth switch tube is connected to the negative pole of the secondary side port of the high-frequency transformer.

[0016] Preferably, the inductance value L of the AC side inductor out , includes:

[0017]

[0018] wherein, is the equivalent load resistance, U N is the effective value of the rated output voltage on the AC side, P load is the output power on the AC side. The greater the output power on the AC side, the smaller the value of the equivalent load resistance; δI is the corresponding output current ripple rate, f sw is the switching frequency.

[0019] Preferably, the high-frequency transformer adopts any one of the following structures:

[0020] - Adopt a high-frequency double-winding transformer with a primary-secondary turns ratio of 1:n;

[0021] - Adopt a high-frequency three-winding transformer with a primary-secondary turns ratio of 1:n:n.

[0022] Preferably, the number of secondary turns n of the high-frequency transformer includes:

[0023]

[0024] wherein, V in,min is the minimum input voltage, D max is the maximum duty cycle allowed by the phase-shifted full bridge, V out,max is the maximum output voltage, V f,rec is the forward conduction voltage drop of the rectifier diode;

[0025] The leakage inductance value L of the high-frequency transformer r , including:

[0026]

[0027] Wherein, C oss is the parallel resonance capacitor of the switching tubes S1 - S4, V in,max is the maximum input voltage, I p,max is the maximum primary current, I out,ripple is the output current ripple threshold.

[0028] Preferably, for the DC-side full-bridge module, its internal phase-shift angle is defined as: the ratio of the time that the driving signal of the switching tube S1 leads the driving signal of the switching tube S4 to the switching period.

[0029] According to another aspect of the present invention, there is provided a modulation method for the phase-shifted full-bridge micro-inverter described in any one of the above, by adjusting the internal phase-shift angle of the DC-side full-bridge module and controlling the switching tube logic of the AC-side rectification module, to achieve the sinusoidal AC current output of the phase-shifted full-bridge micro-inverter.

[0030] Preferably, the adjusting the internal phase-shift angle of the DC-side full-bridge module includes:

[0031] According to the sampled values of the grid voltage, the DC-side voltage, and the grid current given value, the variation trajectory of the internal phase-shift angle θ is obtained as:

[0032]

[0033] Wherein, n is the number of turns of the secondary side of the high-frequency transformer, L s is the leakage inductance of the low-voltage side, i g,ref is the grid current given value, v g is the grid voltage, V dc is the sampled value of the DC-side voltage, f sw is the switching frequency.

[0034] Preferably, the switching tube logic of the AC-side rectification module includes:

[0035] Determine the turn-on logic of the first switching tube according to the positive and negative of the grid voltage;

[0036] Determine the turn-on logic of the second switching tube according to the positive and negative of the current of the high-frequency transformer;

[0037] Wherein:

[0038] The turn-on logic of the first switching tube includes:

[0039] When the voltage of the power grid is positive, the switching transistor with a negative drain-source voltage in a group of bidirectional switching transistors serves as a power-frequency switching transistor to maintain constant conduction, and the other switching transistor corresponding to the power-frequency switching transistor serves as a high-frequency switching transistor for high-frequency operation;

[0040] When the voltage of the power grid is negative, the switch with a positive drain-source voltage in a group of bidirectional switching transistors serves as a power-frequency switching transistor to maintain constant conduction, and the other switching transistor corresponding to the power-frequency switching transistor serves as a high-frequency switching transistor for high-frequency operation;

[0041] The turn-on logic of the second switching transistor includes:

[0042] When the current of the high-frequency transformer is positive, the switching transistor with the current flowing from the source to the drain is turned on, and the switching transistor with the current flowing from the drain to the source is turned off;

[0043] When the current of the high-frequency transformer is negative, the switching transistor with the current flowing from the source to the drain is turned on, and the switching transistor with the current flowing from the drain to the source is turned off.

[0044] Due to the adoption of the above technical solution, compared with the prior art, the present invention has at least one of the following beneficial effects:

[0045] A phase-shifted full-bridge micro-inverter provided by the present invention can select the topology of the corresponding AC-side rectification module according to different voltage and current levels to be applicable to working conditions of different power levels, broadening the application scenarios of the micro-inverter.

[0046] A modulation method of a phase-shifted full-bridge micro-inverter provided by the present invention can sample the DC-side voltage, combine the power grid voltage and the given value of the power grid current, plan the inner phase-shift angle trajectory, and at the same time control the switching transistor logic of the AC-side rectification module, so as to achieve sinusoidal AC current output, thereby greatly improving the grid connection stability of the micro-inverter and improving the total harmonic distortion rate (THD) of the output current. Description of the Drawings

[0047] By reading the detailed description of the non-limiting embodiments with reference to the following drawings, other features, purposes and advantages of the present invention will become more obvious:

[0048] Figure 1 Schematic diagram of a micro-inverter circuit with a full-bridge rectification circuit as the AC rectification module in a preferred embodiment of the present invention;

[0049] Figure 2 Schematic diagram of a micro-inverter circuit with a full-wave rectification circuit as the AC rectification module in a preferred embodiment of the present invention;

[0050] Figure 3 Schematic diagram of a micro-inverter circuit with a half-wave rectification circuit as the AC rectification module in a preferred embodiment of the present invention;

[0051] Figure 4 Schematic diagram of a micro-inverter circuit where the AC rectification module is a double-flow rectification circuit in a preferred embodiment of the present invention;

[0052] Figure 5 Waveform schematic diagrams of the driving logic of the switching tubes, the primary voltage of the transformer, the secondary voltage of the transformer, and the secondary current of the transformer in a phase-shifted full-bridge micro-inverter when the AC rectification module is a full-bridge rectification circuit in a preferred embodiment of the present invention. Detailed implementation manners

[0053] The present invention will be described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, which all fall within the protection scope of the present invention. For the parts not described below, reference can be made to the content recorded in the invention content or the prior art.

[0054] An embodiment of the present invention provides a phase-shifted full-bridge micro-inverter.

[0055] In this embodiment, the phase-shifted full-bridge micro-inverter includes: a DC-side full-bridge module, a high-frequency transformer, and an AC-side rectification module. Among them, the DC-side full-bridge module is mainly composed of switching tubes S1 to S4, and its DC port is connected in parallel with the DC-side bus capacitor C bus and is directly connected to the photovoltaic module; among them, the source of switching tube S1 is connected to the drain of switching tube S2, the source of switching tube S3 is connected to the drain of switching tube S4, the drain of switching tube S1 is connected to the drain of switching tube S3, and is connected to the positive electrode of the DC-side bus capacitor C bus and the source of switching tube S2 is connected to the source of switching tube S4 and is connected to the negative electrode of the DC-side bus capacitor C bus ; the positive pole of the primary side of the high-frequency transformer is connected to the midpoint between switching tube S1 and switching tube S2, and the negative pole of the primary side of the high-frequency transformer is connected to the midpoint between switching tube S3 and switching tube S4; the DC-side full-bridge module is connected in series with the high-frequency transformer and then connected to the AC-side rectification module.

[0056] In a preferred embodiment, the AC-side rectification module includes multiple groups of bidirectional switch tubes and an AC-side inductor. The multiple groups of bidirectional switch tubes form a switch tube assembly, and its output terminal is connected in series with the AC-side inductor. According to different voltage stresses and current stresses, the AC-side rectification module can be divided into different topologies. In a specific application example, the AC-side rectification module can be a high-frequency link matrix converter, or a parallel connection of bidirectional switch groups, or a series connection of bidirectional switch groups; according to different topologies of the AC-side rectification module, the high-frequency transformer can be a high-frequency double-winding transformer with a primary-secondary turn ratio of 1:n, or a high-frequency three-winding transformer with a turn ratio of 1:n:n, and the magnetizing inductance referred to the primary side is L m .

[0057] In a preferred embodiment, a high-frequency link matrix converter structure is adopted; the high-frequency link matrix converter structure includes: the switch tube assembly includes the first switch tube to the eighth switch tube; wherein, the drain of the first switch tube is connected to the drain of the fifth switch tube, the source of the first switch tube is connected to the source of the second switch tube, the drain of the second switch tube is connected to the drain of the third switch tube and is connected to the positive pole of the secondary side port of the high-frequency transformer, the source of the third switch tube is connected to the source of the fourth switch tube, the drain of the fourth switch tube is connected to the drain of the eighth switch tube, the source of the fifth switch tube is connected to the source of the sixth switch tube, the drain of the sixth switch tube is connected to the drain of the seventh switch tube and is connected to the negative pole of the secondary side port of the high-frequency transformer, and the source of the seventh switch tube is connected to the source of the eighth switch tube.

[0058] In a preferred embodiment, a parallel connection structure of bidirectional switch groups is adopted; the parallel connection structure of bidirectional switch groups includes: the switch tube assembly includes: the first switch tube to the fourth switch tube; wherein, the drain of the first switch tube is connected to the positive pole of the secondary side port of the high-frequency transformer, the source of the first switch tube is connected to the source of the second switch tube, the drain of the second switch tube is connected to the drain of the fourth switch tube, the source of the fourth switch tube is connected to the source of the third switch tube, and the drain of the fourth switch tube is connected to the negative pole of the secondary side port of the high-frequency transformer.

[0059] In a preferred embodiment, a series connection structure of bidirectional switch groups is adopted; the series connection structure of bidirectional switch groups includes: the switch tube assembly includes: the first switch tube to the fourth switch tube; wherein, the drain of the first switch tube is connected to the positive pole of the secondary side port of the high-frequency transformer, the source of the first switch tube is connected to the source of the second switch tube, the drain of the second switch tube is connected to the drain of the third switch tube, the source of the third switch tube is connected to the source of the fourth switch tube, and the drain of the fourth switch tube is connected to the negative pole of the secondary side port of the high-frequency transformer.

[0060] In a preferred embodiment, the method for designing the turn ratio of the high-frequency transformer is where V in,min is the minimum input voltage, Dmax is the maximum duty cycle of the phase-shifted full-bridge, V out,max is the maximum output voltage, V f,rec is the forward conduction voltage drop of the rectifier diode; The design of the leakage inductance value of the high-frequency transformer needs to consider the implementation requirements of soft switching. For In the formula, C oss is the resonant capacitor, V in,max is the maximum input voltage, I p,max is the maximum primary current, I out,ripple is the output current ripple threshold.

[0061] In a preferred embodiment, the design of the inductance value of the AC side inductor needs to consider the output current ripple requirement. Therefore, the value of the AC side inductor should satisfy where is the equivalent load resistance. The larger the load power, the smaller this value. δI is the corresponding output current ripple rate, f sw is the switching frequency.

[0062] In a preferred embodiment, for the DC side full-bridge module, the internal phase-shift angle is defined as: the proportion of the time when the driving signal of switch tube S1 leads the driving signal of switch tube S4 in the switching period.

[0063] An embodiment of the present invention also provides a modulation method for a phase-shifted full-bridge micro-inverter, which realizes the output of sinusoidal alternating current by adjusting the internal phase-shift angle of the DC side full-bridge module and controlling the switch tube logic of the AC side rectification module.

[0064] In a preferred embodiment, adjusting the internal phase-shift angle of the DC side full-bridge module includes:

[0065] According to the sampled values of the grid voltage, the DC side voltage, and the grid current given value, the variation trajectory of the internal phase-shift angle θ is adjusted to be:

[0066]

[0067] In the formula, the transformer turns ratio is 1:n, the leakage inductance on the low-voltage side is Ls, the grid current given value is i g,ref , the grid voltage is v g , and the sampled value of the DC side voltage is v dc .

[0068] In a preferred embodiment, the method for determining the switch tube logic of the AC side rectification module includes: determining the turn-on logic of the first switch tube according to the positive and negative of the grid voltage, and determining the turn-on logic of the second switch tube according to the positive and negative of the transformer current.

[0069] Further, the turn-on logic of the first switch tube includes:

[0070] When the voltage of the power grid is positive, the switching transistor with a negative drain-source voltage in a group of bidirectional switching transistors is used as a power-frequency switching transistor to maintain continuous conduction, and the other switching transistor corresponding to the power-frequency switching transistor is used as a high-frequency switching transistor for high-frequency operation;

[0071] When the voltage of the power grid is negative, the switching transistor with a positive drain-source voltage in a group of bidirectional switching transistors is used as a power-frequency switching transistor to maintain continuous conduction, and the other switching transistor corresponding to the power-frequency switching transistor is used as a high-frequency switching transistor for high-frequency operation.

[0072] Furthermore, the turn-on logic of the second switching transistor includes:

[0073] When the current of the high-frequency transformer is positive, the switching transistor with the current flowing from the source to the drain conducts, and the switching transistor with the current flowing from the drain to the source is turned off;

[0074] When the current of the high-frequency transformer is negative, the switching transistor with the current flowing from the source to the drain conducts, and the switching transistor with the current flowing from the drain to the source is turned off.

[0075] In a specific application example:

[0076] When the AC rectification module is a full-bridge rectification circuit, as Figure 1 shown, for its power-frequency switching transistors, when the grid voltage is positive, the switching transistors S6, S8, S10, and S12 are always on. For its high-frequency switching transistors, when the transformer current is positive, the switching transistors S5 and S11 conduct, and the switching transistors S7 and S9 are turned off. When the transformer current is negative, the switching transistors S5 and S11 conduct, and the switching transistors S7 and S9 are turned off; when the grid voltage is negative, the switching transistors S5, S7, S9, and S11 are always on. For its high-frequency switching transistors, when the transformer current is positive, the switching transistors S6 and S12 conduct, and the switching transistors S8 and S10 are turned off. When the transformer current is negative, the switching transistors S8 and S10 conduct, and the switching transistors S6 and S12 are turned off.

[0077] When the AC rectification module is a full-wave rectification circuit, as Figure 2 shown, for its power-frequency switching transistors, when the grid voltage is positive, the switching transistors S5 and S7 are always on. For its high-frequency switching transistors, when the transformer current is positive, the switching transistor S6 conducts, and the switching transistor S8 is turned off. When the transformer current is negative, the switching transistor S8 conducts, and the switching transistor S6 is turned off; when the grid-side voltage is negative, the switching transistors S6 and S8 are always on. For its high-frequency switching transistors, when the transformer current is positive, the switching transistor S5 conducts, and the switching transistor S7 is turned off. When the transformer current is negative, the switching transistor S7 conducts, and the switching transistor S5 is turned off;

[0078] When the AC rectification module is a half-wave rectification circuit, as Figure 3As shown, for its power frequency switching tubes, when the grid voltage is positive, switching tubes S5 and S8 are always on. For its high-frequency switching tubes, when the transformer current is positive, switching tube S6 is turned on and switching tube S7 is turned off; when the transformer current is negative, switching tube S7 is turned on and switching tube S6 is turned off. When the grid-side voltage is negative, switching tubes S6 and S7 are always on. For its high-frequency switching tubes, when the transformer current is positive, switching tube S5 is turned on and switching tube S8 is turned off; when the transformer current is negative, switching tube S8 is turned on and switching tube S5 is turned off.

[0079] When the AC rectification module is a current-doubling rectification circuit, such as Figure 4 As shown, for its power frequency switching tubes, when the grid voltage is positive, switching tubes S5 and S7 are always on. For its high-frequency switching tubes, when the transformer current is positive, switching tube S6 is turned on and switching tube S8 is turned off; when the transformer current is negative, switching tube S8 is turned on and switching tube S6 is turned off. When the grid-side voltage is negative, switching tubes S6 and S8 are always on. For its high-frequency switching tubes, when the transformer current is positive, switching tube S5 is turned on and switching tube S7 is turned off; when the transformer current is negative, switching tube S7 is turned on and switching tube S5 is turned off.

[0080] The following further illustrates the technical solutions provided in the above embodiments of the present invention in conjunction with the accompanying drawings and a specific application example.

[0081] Figure 1 It is a schematic diagram of a micro-inverter circuit with an AC rectification module being a full-bridge rectification circuit. Referring to Figure 1 As shown, this micro-inverter circuit consists of a photovoltaic panel assembly, a DC bus capacitor, a primary full-bridge circuit, a high-frequency transformer, a secondary rectification circuit, and a grid-side filter inductor. The primary full-bridge circuit includes switching tubes S1 to S4, and the secondary rectification circuit is a full-bridge rectification, including switching tubes S5 to S12. The turns ratio of the primary and secondary sides of the high-frequency transformer is 1:n, and the magnetizing inductance referred to the primary side is L m and the leakage inductance of the transformer referred to the primary side is L k . Among them, the photovoltaic panel and the DC-side bus capacitor C busAfter being connected in parallel, it is connected to the DC port at the input end of the primary full-bridge circuit. The AC-side output end of the primary full-bridge is connected to the primary side of the high-frequency transformer. The secondary side of the high-frequency transformer is connected to the AC port of the secondary rectifier circuit. The DC port of the secondary rectifier circuit is connected to the filter inductor, and the filter inductor is directly connected to the AC grid. In the primary full-bridge circuit, the source electrode of switch tube S1 and the drain electrode of switch tube S2 are connected and connected to the positive pole of the primary port of the high-frequency transformer. The source electrode of switch tube S3 and the drain electrode of switch tube S4 are connected and connected to the negative pole of the primary port of the high-frequency transformer. The drain electrode of switch tube S1 and the drain electrode of switch tube S3 are connected and connected to the positive pole of the DC-side bus capacitor. The source electrode of switch tube S2 and the source electrode of switch tube S4 are connected and connected to the negative pole of the DC-side bus capacitor. In the secondary full-bridge circuit, the drain electrode of switch tube S5 and the drain electrode of switch tube S9 are connected. The source electrode of switch tube S5 and the source electrode of switch tube S6 are connected. The drain electrode of switch tube S6 and the drain electrode of switch tube S7 are connected and connected to the positive pole of the secondary port of the transformer. The source electrode of switch tube S7 and the source electrode of switch tube S8 are connected. The drain electrode of switch tube S8 is connected to the drain electrode of switch tube S12. The source electrode of switch tube S9 and the source electrode of switch tube S10 are connected. The drain electrode of switch tube S10 and the drain electrode of switch tube S11 are connected and connected to the negative pole of the secondary port of the transformer. The source electrode of switch tube S11 and the source electrode of switch tube S12 are connected.

[0082] Figure 2 The schematic diagram of the micro-inverter circuit with the AC rectification module being a full-wave rectifier circuit. Refer to Figure 2 As shown, this micro-inverter circuit consists of a photovoltaic panel assembly, a DC bus capacitor, a primary full-bridge circuit, a high-frequency transformer, a secondary rectifier circuit, and a grid-side filter inductor. The high-frequency transformer is a three-winding transformer, and the turns ratio of the primary and secondary sides is 1:n:n. The magnetizing inductance referred to the primary side is L m , and the leakage inductance of the transformer referred to the primary side is L k ; The secondary rectifier circuit is a full-wave rectifier, including switch tubes S5 to S8. The drain electrode of switch tube S5 is connected to the positive pole of the secondary port of the transformer. The source electrode of switch tube S5 and the source electrode of switch tube S6 are connected. The drain electrode of switch tube S6 and the drain electrode of switch tube S8 are connected. The source electrode of switch tube S8 and the source electrode of switch tube S7 are connected. The drain electrode of switch tube S7 is connected to the negative pole of the secondary port of the transformer. The other components are the same as those of the micro-inverter circuit shown in Figure 1 and will not be elaborated here.

[0083] Figure 3 The schematic diagram of the micro-inverter circuit with the AC rectification module being a half-wave rectifier circuit. Refer to Figure 3As shown in the figure, the micro-inverter circuit consists of a photovoltaic panel assembly, a DC bus capacitor, a primary full-bridge circuit, a high-frequency transformer, a secondary rectifier circuit, and a grid-side filter inductor. The secondary rectifier circuit is a half-wave rectifier, including switching transistors S5 to S8. The drain of switching transistor S5 is connected to the positive pole of the secondary port of the transformer, the source of switching transistor S5 is connected to the source of switching transistor S6, the drain of switching transistor S6 is connected to the drain of switching transistor S7, the source of switching transistor S7 is connected to the source of switching transistor S8, the drain of switching transistor S8 is connected to the negative pole of the secondary port of the transformer, and the remaining components are the same as those of the Figure 1 micro-inverter circuit shown, so they will not be elaborated here.

[0084] Figure 4 The figure shows a schematic diagram of a micro-inverter circuit with a double-current rectifier circuit as the AC rectification module. Refer to Figure 4 As shown in the figure, the micro-inverter circuit consists of a photovoltaic panel assembly, a DC bus capacitor, a primary full-bridge circuit, a high-frequency transformer, a secondary rectifier circuit, and a grid-side filter inductor. The high-frequency transformer is a three-winding transformer, and the turns ratio of the primary to secondary is 1:n:n. The magnetizing inductance referred to the primary is L m , and the leakage inductance of the transformer referred to the primary is L k ; the secondary rectifier circuit is a double-current rectifier, including switching transistors S5 to S8. The drain of switching transistor S5 is connected to the positive pole of the secondary port of the transformer, the source of switching transistor S5 is connected to the source of switching transistor S6, the drain of switching transistor S6 is connected to the drain of switching transistor S8, the source of switching transistor S8 is connected to the source of switching transistor S7, and the drain of switching transistor S7 is connected to the negative pole of the secondary port of the transformer. The remaining components are the same as those of the Figure 1 micro-inverter circuit shown, so they will not be elaborated here.

[0085] Figure 5 The figure shows the driving waveforms of the switching transistors and the voltage and current waveforms of the primary and secondary sides of the transformer in a phase-shifted full-bridge micro-inverter when the AC rectification module is a full-bridge rectifier circuit. Refer to Figure 5 As shown in the figure, the primary side of the transformer in the phase-shifted full-bridge micro-inverter can output three levels {v p , 0, -v p}, and the secondary side can output two levels {|v s | / 2, -|v s | / 2}. Where v p is the voltage at the photovoltaic module terminal, and |v s | is the absolute value of the grid-side voltage. Figure 5 In the figure, t1 is the turn-off time of switching transistor S3, t2 is the turn-off time of switching transistor S7, t3 is the turn-off time of switching transistor S4, t4 is the turn-off time of switching transistor S5, T s is the switching period, and i s is the secondary current.

[0086] Furthermore, the phase-shifted full-bridge micro-inverter realizes sinusoidal AC current output by adjusting the internal phase shift angle of the DC side full-bridge module and controlling the switch tube logic of the AC side rectifier module, wherein the internal phase shift angle θ is defined as the angle between the negative rising edge of the primary square wave voltage and the positive rising edge of the primary square wave voltage, that is, the angle between the drive pulse of the switch tube S4 and the drive pulse of the switch tube S1, and the value range of θ is 0≤θ≤π.

[0087] Of course, the specific circuits in the above embodiments are only preferred embodiments of the present invention and are not intended to limit the present invention. In other embodiments, other circuit forms may be used to achieve the same function.

[0088] The phase-shifted full-bridge micro-inverter and modulation method thereof provided by the above-mentioned embodiment of the present invention, compared with the micro-inverter based on the flyback converter, the topology based on the phase-shifted full-bridge can be applied to a larger power level, and can realize the zero current or zero voltage opening of all the switch tubes, thereby reducing the switching loss. By sampling the DC side voltage, combining the grid voltage and grid current given values, planning the internal phase shift angle trajectory, and controlling the switch tube logic of the AC side rectifier module at the same time, the micro-inverter can realize the sinusoidal AC current output, thereby greatly improving the grid-connected stability of the micro-inverter and improving the total harmonic distortion (THD) of the output current.

[0089] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art may make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A modulation method for a phase-shifted full-bridge micro-inverter, characterized in that: The phase-shifted full-bridge micro-inverter includes: a DC-side full-bridge module, a high-frequency transformer, and an AC-side rectification module; where: The DC ports of the full-bridge module on the DC side are connected in parallel with the DC-side bus capacitor C bus ; Among them, the full-bridge module on the DC side is composed of switching tubes S1 to S4. The source of the switching tube S1 is connected to the drain of the switching tube S2. The source of the switching tube S3 is connected to the drain of the switching tube S4. The drain of the switching tube S1 is connected to the drain of the switching tube S3 and is connected to the positive electrode of the DC-side bus capacitor C bus ; The source of the switching tube S2 is connected to the source of the switching tube S4 and is connected to the negative electrode of the DC-side bus capacitor C bus ; The positive pole of the primary side of the high-frequency transformer is connected to the midpoint between the switch tube S1 and the switch tube S2, and the negative pole of the primary side of the high-frequency transformer is connected to the midpoint between the switch tube S3 and the switch tube S4; The AC-side rectification module is connected in series with the secondary side of the high-frequency transformer; The modulation method realizes the sinusoidal AC current output of the phase-shifted full-bridge micro-inverter by adjusting the internal phase-shift angle of the DC-side full-bridge module and controlling the switch logic of the AC-side rectification module; The switch logic of the AC-side rectification module includes: Determine the turn-on logic of the first switch tube according to the positive and negative of the grid voltage; Determine the turn-on logic of the second switch tube according to the positive and negative of the current of the high-frequency transformer; Where: The turn-on logic of the first switch tube includes: When the grid voltage is positive, the switch tube with a negative drain-source voltage in a group of bidirectional switch tubes is used as the power-frequency switch tube to maintain constant conduction, and the other switch tube corresponding to the power-frequency switch tube is used as the high-frequency switch tube for high-frequency operation; When the grid voltage is negative, the switch with a positive drain-source voltage in a group of bidirectional switch tubes is used as the power-frequency switch tube to maintain constant conduction, and the other switch tube corresponding to the power-frequency switch tube is used as the high-frequency switch tube for high-frequency operation; The turn-on logic of the second switch tube includes: When the current of the high-frequency transformer is positive, the switch tube with the current flowing from the source to the drain is turned on, and the switch tube with the current flowing from the drain to the source is turned off; When the current of the high-frequency transformer is negative, the switch tube with the current flowing from the source to the drain is turned on, and the switch tube with the current flowing from the drain to the source is turned off.

2. The modulation method of the phase-shifted full-bridge micro-inverter according to claim 1, wherein The AC-side rectification module includes: a switch tube assembly composed of multiple groups of bidirectional switch tubes and an AC-side inductor connected in series with the output end of the switch tube assembly.

3. The modulation method of the phase-shifted full-bridge micro-inverter according to claim 2, wherein The AC-side rectification module adopts any one of the following topological structures: - Adopt a high-frequency link matrix converter structure; the high-frequency link matrix converter structure includes: the switch tube assembly includes the first switch tube to the eighth switch tube; where, the drain of the first switch tube is connected to the drain of the fifth switch tube, the source of the first switch tube is connected to the source of the second switch tube, the drain of the second switch tube is connected to the drain of the third switch tube and is connected to the positive pole of the secondary side port of the high-frequency transformer, the source of the third switch tube is connected to the source of the fourth switch tube, the drain of the fourth switch tube is connected to the drain of the eighth switch tube, the source of the fifth switch tube is connected to the source of the sixth switch tube, the drain of the sixth switch tube is connected to the drain of the seventh switch tube and is connected to the negative pole of the secondary side port of the high-frequency transformer, and the source of the seventh switch tube is connected to the source of the eighth switch tube; - Adopt a parallel structure of a bidirectional switch group; the parallel structure of the bidirectional switch group includes: the switch tube assembly includes: the first switch tube to the fourth switch tube; wherein, the drain of the first switch tube is connected to the positive pole of the secondary side port of the high-frequency transformer, the source of the first switch tube is connected to the source of the second switch tube, the drain of the second switch tube is connected to the drain of the fourth switch tube, the source of the fourth switch tube is connected to the source of the third switch tube, and the drain of the fourth switch tube is connected to the negative pole of the secondary side port of the high-frequency transformer; - Adopt a series structure of a bidirectional switch group; the series structure of the bidirectional switch group includes: the switch tube assembly includes: the first switch tube to the fourth switch tube; wherein, the drain of the first switch tube is connected to the positive pole of the secondary side port of the high-frequency transformer, the source of the first switch tube is connected to the source of the second switch tube, the drain of the second switch tube is connected to the drain of the third switch tube, the source of the third switch tube is connected to the source of the fourth switch tube, and the drain of the fourth switch tube is connected to the negative pole of the secondary side port of the high-frequency transformer.

4. The modulation method of the phase-shifted full-bridge micro-inverter according to claim 2 or 3, characterized in that, The inductance value L of the AC-side inductor out , includes: Among them, is the equivalent load resistance, U N is the effective value of the rated output voltage on the AC side, P load is the output power on the AC side. The larger the output power on the AC side, the smaller the value of the equivalent load resistance; δI is the corresponding output current ripple rate, f sw is the switching frequency.

5. The modulation method of the phase-shifted full-bridge micro-inverter according to claim 1, wherein, The high-frequency transformer adopts any one of the following structures: - Adopt a high-frequency double-winding transformer with a primary-secondary turn ratio of 1:n; - Adopt a high-frequency three-winding transformer with a primary-secondary turn ratio of 1:n:n.

6. The modulation method of the phase-shifted full-bridge micro-inverter according to claim 5, characterized in that, The secondary turns n of the high-frequency transformer include: Among them, V in,min is the minimum input voltage, D max is the maximum duty cycle allowed by the phase-shifted full bridge, V out,max is the maximum output voltage, V f,rec is the forward conduction voltage drop of the rectifier diode; The leakage inductance value L of the high-frequency transformer r , includes: Among them, C oss is the parallel resonance capacitor of switching transistors S1 - S4, V in,max is the maximum input voltage, I p,max is the maximum primary current, I out,ripple is the output current ripple threshold value.

7. The modulation method of the phase-shifted full-bridge micro-inverter according to claim 1, characterized in that For the full-bridge module on the DC side, its phase-shift angle is defined as: the proportion of the time when the driving signal of the switch tube S1 leads the driving signal of the switch tube S4 in the switching period.

8. The modulation method of the phase-shifted full-bridge micro-inverter according to claim 1, characterized in that Adjusting the internal phase-shift angle of the full-bridge module on the DC side includes: According to the sampling values of the grid voltage, the DC side voltage, and the grid current given value, the change trajectory of the internal phase-shift angle θ is obtained as: Among them, n is the number of turns of the secondary side of the high-frequency transformer, L s is the leakage inductance of the low-voltage side, i g,ref is the given value of the grid current, v g is the grid voltage, V dc is the sampled value of the DC-side voltage, f sw is the switching frequency.

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