Photovoltaic micro inverter

Abstract

The invention discloses a photovoltaic micro inverter. The photovoltaic micro inverter comprises at least two transformers, at least two pre-stage circuits and an alternating current side circuit. The transformer is used for boosting voltage and comprises a primary winding and a secondary winding; wherein the primary windings of the at least two transformers are connected in parallel; the secondary windings of the at least two transformers are connected in series, and the output port is defined as a boost output port. The pre-stage circuit is used for converting direct current of the direct current port into alternating current; dC input ports of the at least two pre-stage circuits are connected to two ends of the DC port; aC output ports of the at least two pre-stage circuits are correspondingly connected with primary windings of the at least two transformers. The AC side circuit is connected to two ends of the boost output port. The alternating current side circuit is used for converting the boosted alternating current into power frequency alternating current. According to the invention, the performance requirement on the transformer is reduced, so that the cost is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of photovoltaic power generation, and in particular to a photovoltaic micro inverter. Background Art

[0002] The continuous implementation of green development and environmental protection concepts has driven the continuous development of new energy power facilities. Photovoltaic power generation, as a green and pollution-free source of electricity, is becoming increasingly popular. As a key component of photovoltaic power generation, the performance of photovoltaic microinverters plays a vital role in the development of photovoltaic power generation.

[0003] In the prior art, in order to convert the output voltage of the photovoltaic panel into the industrial frequency voltage, the photovoltaic micro-inverter requires a transformer with a high transformation ratio, which places high requirements on the performance of the transformer and leads to a high cost of the photovoltaic micro-inverter. Summary of the Invention

[0004] The present invention provides a photovoltaic micro-inverter to reduce the performance requirements on the transformer and reduce the cost.

[0005] According to one aspect of the present invention, there is provided a photovoltaic micro-inverter, comprising:

[0006] At least two transformers, each transformer being used to boost voltage and comprising a primary winding and a secondary winding; wherein the primary windings of the at least two transformers are connected in parallel; and the secondary windings of the at least two transformers are connected in series, and their output ports are defined as boost output ports;

[0007] At least two front-stage circuits, each of which is configured to convert DC power from a DC port into AC power; DC input ports of the at least two front-stage circuits are connected to both ends of the DC port; and AC output ports of the at least two front-stage circuits are correspondingly connected to the primary windings of the at least two transformers;

[0008] An AC side circuit is connected to both ends of the boost output port; the AC side circuit is used to convert the boosted AC power into industrial frequency AC power.

[0009] Optionally, the front-stage circuit includes a full-bridge circuit, a DC input port of the full-bridge circuit serves as the DC input port of the front-stage circuit, and an AC output port of the full-bridge circuit serves as the AC output port of the front-stage circuit.

[0010] Optionally, the full-bridge circuit includes a first bridge arm and a second bridge arm connected in parallel;

[0011] The first bridge arm includes a first transistor and a second transistor connected in series; a connection point between the first transistor and the second transistor serves as a first output terminal of the full-bridge circuit;

[0012] The second bridge arm includes a third transistor and a fourth transistor connected in series; the connection point of the third transistor and the fourth transistor serves as the second output end of the full-bridge circuit, and the first output end and the second output end constitute the AC output port.

[0013] Optionally, at least part of the front-stage circuits share one first bridge arm; or at least part of the front-stage circuits share one second bridge arm.

[0014] Optionally, the front-stage circuit includes a half-bridge circuit, a DC input port of the half-bridge circuit serves as the DC input port of the front-stage circuit, and an AC output port of the half-bridge circuit serves as the AC output port of the front-stage circuit.

[0015] Optionally, the half-bridge circuit includes a first bridge arm and a second bridge arm connected in parallel;

[0016] The first bridge arm includes a first capacitor and a second capacitor connected in series; the connection point between the first capacitor and the second capacitor serves as the first output end of the half-bridge circuit;

[0017] The second bridge arm includes a third transistor and a fourth transistor connected in series; the connection point of the third transistor and the fourth transistor serves as the second output end of the half-bridge circuit, and the first output end and the second output end constitute the AC output port.

[0018] Optionally, at least part of the front-stage circuits share one first bridge arm.

[0019] Optionally, the AC side circuit includes a first resonant inductor, a third bridge arm and a fourth bridge arm connected in parallel;

[0020] The first resonant inductor is connected in series with at least two secondary windings of the transformer;

[0021] The third bridge arm includes a third upper bridge arm and a third lower bridge arm, and a connection point between the third upper bridge arm and the third lower bridge arm serves as a third output end of the AC side circuit;

[0022] The fourth bridge arm includes a fourth upper bridge arm and a fourth lower bridge arm, and the connection point of the fourth upper bridge arm and the fourth lower bridge arm serves as the fourth output end of the AC side circuit; the third output end and the fourth output end constitute the industrial frequency AC power output port of the AC side circuit.

[0023] Optionally, the third upper bridge arm includes a fifth transistor and a sixth transistor connected in series, and the third lower bridge arm includes a third capacitor; the fourth upper bridge arm includes a seventh transistor and an eighth transistor connected in series, and the fourth lower bridge arm includes a fourth capacitor;

[0024] Alternatively, the third upper bridge arm includes a fifth transistor and a sixth transistor connected in series, and the third lower bridge arm includes a third capacitor; the fourth upper bridge arm includes a seventh transistor and an eighth transistor connected in series, and the fourth lower bridge arm includes a fourth capacitor and the third capacitor;

[0025] Alternatively, the third upper bridge arm includes a third capacitor, and the third lower bridge arm includes a fifth transistor and a sixth transistor connected in series; the fourth upper bridge arm includes a seventh transistor and an eighth transistor connected in series, and the fourth lower bridge arm includes a fourth capacitor.

[0026] Optionally, the industrial frequency AC power output port of the AC side circuit further includes a neutral point terminal, and a connection point between the third lower bridge arm and the fourth lower bridge arm serves as the neutral point terminal.

[0027] Optionally, the AC side circuit includes a first resonant circuit and a second resonant circuit, the first resonant circuit and the second resonant circuit have the same circuit structure, and are symmetrically connected between the boost output port and the industrial frequency AC power port, and the common point of the first resonant circuit and the second resonant circuit is connected to the connection point of at least two secondary windings of the transformer.

[0028] Optionally, the first resonant circuit includes a fifth capacitor, a ninth transistor, a tenth transistor, and a second resonant inductor connected in series across the secondary windings of a portion of the transformer, with the connection point between the fifth capacitor and the ninth transistor serving as a third output terminal of the AC side circuit; the second resonant circuit includes a sixth capacitor, an eleventh transistor, a twelfth transistor, and the second resonant inductor connected in series across the secondary windings of another portion of the transformer, with the connection point between the sixth capacitor and the eleventh transistor serving as a fourth output terminal of the AC side circuit; the third output terminal and the fourth output terminal constitute a power frequency AC power output port of the AC side circuit;

[0029] Alternatively, the first resonant circuit includes a third resonant inductor, a fifth capacitor, a ninth transistor, and a tenth transistor connected in series at both ends of a secondary winding of a portion of the transformer, and the connection point of the fifth capacitor and the ninth transistor serves as the third output end of the AC side circuit; the second resonant circuit includes a fourth resonant inductor, a sixth capacitor, an eleventh transistor, and a twelfth transistor connected in series at both ends of the secondary winding of another portion of the transformer, and the connection point of the sixth capacitor and the eleventh transistor serves as the fourth output end of the AC side circuit; the third output end and the fourth output end constitute the industrial frequency AC power output port of the AC side circuit.

[0030] The embodiment of the present invention provides at least two transformers, at least two front-stage circuits, and an AC-side circuit. Through the at least two front-stage circuits, the parallel connection of the inputs of at least two transformers and the series connection of the outputs can be realized. The superimposed voltage after the at least two transformers step up can be output at the boost output port, so that a single transformer can adopt a smaller transformation ratio. Therefore, the embodiment of the present invention reduces the power concentration of each transformer, which is beneficial to thermal design, thereby reducing the performance requirements for the transformer and reducing costs. Furthermore, the photovoltaic micro-inverter provided by the embodiment of the present invention supports phase modulation control, which greatly reduces the number of harmonics in the output voltage, reduces the performance requirements for the EMI filter of the back-stage circuit, and further reduces costs.

[0031] It should be understood that the content described in this section is not intended to identify the key or important features of the embodiments of the present invention, nor is it intended to limit the scope of the present invention. Other features of the present invention will become readily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0033] Figure 1 is a circuit diagram of a photovoltaic micro-inverter provided according to an embodiment of the present invention;

[0034] Figure 2 is a circuit diagram of another photovoltaic micro-inverter provided according to an embodiment of the present invention;

[0035] Figure 3 is a circuit diagram of another photovoltaic micro-inverter provided according to an embodiment of the present invention;

[0036] Figure 4is a circuit diagram of another photovoltaic micro-inverter provided according to an embodiment of the present invention;

[0037] Figure 5 is a circuit diagram of another photovoltaic micro-inverter provided according to an embodiment of the present invention;

[0038] Figure 6 is a circuit diagram of another photovoltaic micro-inverter provided according to an embodiment of the present invention;

[0039] Figure 7 is a circuit diagram of another photovoltaic micro-inverter provided according to an embodiment of the present invention;

[0040] Figure 8 is a circuit diagram of another photovoltaic micro-inverter provided according to an embodiment of the present invention;

[0041] Figure 9 is a circuit diagram of another photovoltaic micro-inverter provided according to an embodiment of the present invention;

[0042] Figure 10 is a circuit diagram of another photovoltaic micro-inverter provided according to an embodiment of the present invention;

[0043] Figure 11 is a circuit diagram of another photovoltaic micro-inverter provided according to an embodiment of the present invention;

[0044] Figure 12 is a circuit diagram of another photovoltaic micro-inverter provided according to an embodiment of the present invention. DETAILED DESCRIPTION

[0045] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0046] It should be noted that the terms "first", "second", etc. in the description and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that the numbers used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0047] An embodiment of the present invention provides a photovoltaic micro-inverter. Figure 1 A circuit diagram of a photovoltaic micro-inverter provided by an embodiment of the present invention. Figure 1 The photovoltaic micro-inverter includes: at least two transformers 1, at least two pre-stage circuits 2, and an AC side circuit 3. The transformer 1 is used to boost voltage. Specifically, each transformer 1 includes a primary winding and a secondary winding. The primary windings of at least two transformers 1 are connected in parallel. The secondary windings of at least two transformers 1 are connected in series, and their output ports are defined as boost output ports 6. The pre-stage circuit 2 is used to convert the DC power from the DC port 4 into AC power. The DC input ports of at least two pre-stage circuits 2 are connected to both ends of the DC port 4, that is, at least two pre-stage circuits 2 are connected in parallel. The AC output ports 5 of at least two pre-stage circuits 2 are correspondingly connected to the primary windings of at least two transformers 1. This connection method enables the primary windings of at least two transformers 1 to be connected in parallel. The AC side circuit is connected to both ends of the boost output port 6. The AC side circuit is used to convert the boosted AC power into industrial frequency AC power.

[0048] Photovoltaic panels absorb solar energy to generate photovoltaic power and output a low DC voltage. To meet the grid's normal power demand, the panels must be connected to a photovoltaic micro-inverter to convert this DC power into AC power and then boost it to a commercial frequency voltage. For example, two transformers 1 are configured. The DC port 4 of the photovoltaic micro-inverter is directly connected to the photovoltaic panel. The DC input ports of the two pre-stage circuits 2 are connected to both ends of the DC port 4. The two pre-stage circuits 2 can invert the DC power input from the DC port 4, converting it into two identical or different AC voltages. Each pre-stage circuit 2 is equipped with a transformer 1. Through the AC output ports 5 of the two pre-stage circuits 2, the AC power inverted by the two pre-stage circuits 2 is input through the primary windings into the two transformers 1. The two transformers 1 then boost the input AC power. Because the secondary windings of the two transformers 1 are connected in series, the voltage output at the boosted output port 6 is the sum of the boosted voltages of the two transformers 1.

[0049] Compared to the prior art, which uses a single transformer, the embodiments of the present invention achieve transformer voltage division. If two transformers and two pre-stage circuits are used, the transformation ratio of each transformer is half that of the prior art transformer. If three transformers and three pre-stage circuits are used, the transformation ratio of each transformer is one-third that of the prior art transformer. Thus, the embodiments of the present invention can reduce the transformer transformation ratio and the power concentration of each transformer, which is beneficial for thermal design, thereby reducing the performance requirements for the transformer and reducing costs.

[0050] Furthermore, using the circuit topology of the embodiment of the present invention, the photovoltaic micro-inverter can be controlled using either frequency modulation or phase modulation. Using frequency modulation requires real-time adjustment of the duty cycle of each switching device in the front-stage circuit 2 to achieve different equivalent voltages outputted by the boost output port 6 at different times, thereby generating a power frequency voltage output. However, frequency modulation generates a large number of harmonics, placing high demands on the performance of the EMI (Electromagnetic Interference) Filter 8 in the back-stage circuit.

[0051] Phase modulation control is described in detail below: During phase modulation control, the system frequency remains constant. The waveforms output by the two preceding circuits 2 are continuously phase-adjusted to adjust the equivalent voltage at the boost output port 6. For example, when the two preceding circuits 2 are in phase, the output voltage of the boost output port 6 is equivalent to the sum of the output voltages of the two transformers 1, resulting in the highest output voltage. When the two preceding circuits 2 are in phase, the output voltage of the boost output port 6 is equivalent to the mutual cancellation of the output voltages of the two transformers 1, resulting in a zero output voltage. When the phases of the two preceding circuits 2 are staggered, the pulse width is reduced, and the output voltage of the boost output port 6 is between zero and the maximum voltage. Thus, by phase-modulating the two transformers 1, the output voltage of the boost output port 6 can be adjusted. Because phase modulation control does not change the duty cycle of the switching devices, the number of harmonics in the output voltage is significantly reduced, lowering the performance requirements for the EMI filter 8 in the subsequent circuit.

[0052] In other implementations, a hybrid control of frequency modulation and phase modulation may also be adopted, which may be set as needed in practical applications.

[0053] In summary, the embodiment of the present invention provides at least two transformers 1, at least two front-stage circuits 2, and an AC side circuit 3. Through the at least two front-stage circuits 2, the parallel connection of the inputs of at least two transformers 1 and the series connection of the outputs can be realized. The superimposed voltage after the boost of at least two transformers 1 can be output at the boost output port 6, so that a single transformer 1 can adopt a smaller transformation ratio. Therefore, the embodiment of the present invention reduces the power concentration of each transformer, which is beneficial to thermal design, thereby reducing the performance requirements for the transformer and reducing costs. Furthermore, the photovoltaic micro-inverter provided by the embodiment of the present invention supports phase modulation control, which greatly reduces the number of harmonics in the output voltage, reduces the performance requirements for the EMI Filter 8 of the post-stage circuit, and further reduces costs.

[0054] In the above embodiments, there are many ways to configure the front-stage circuit 2 and the AC-side circuit 3, which are described in detail below but are not intended to limit the present invention.

[0055] Figure 2 Another photovoltaic micro-inverter circuit diagram provided by the embodiment of the present invention is shown in FIG. Figure 2 In one embodiment of the present invention, optionally, the pre-stage circuit 2 includes a full-bridge circuit, the DC input port of the full-bridge circuit serves as the DC input port of the pre-stage circuit 2, and the AC output port 5 of the full-bridge circuit serves as the AC output port 5 of the pre-stage circuit 2.

[0056] The front-stage circuit 2 may be configured as a full-bridge circuit, and the voltage is adjusted by the full-bridge circuit. During the adjustment process, the full-bridge circuit has a large output power and high working efficiency.

[0057] Continue to refer Figure 2 Based on the above embodiments, optionally, the full-bridge circuit includes a first bridge arm 21 and a second bridge arm 22 connected in parallel. The first bridge arm 21 includes a first transistor 211 and a second transistor 212 connected in series; the connection point between the first transistor 211 and the second transistor 212 serves as the first output terminal of the full-bridge circuit. The second bridge arm 22 includes a third transistor 213 and a fourth transistor 214 connected in series; the connection point between the third transistor 213 and the fourth transistor 214 serves as the second output terminal of the full-bridge circuit. The first output terminal and the second output terminal constitute the AC output port 5.

[0058] The first bridge arm 21 and the second bridge arm 22 are connected in parallel to form a full-bridge circuit. The first transistor 211 and the second transistor 212 are connected in series to form the first bridge arm 21. The third transistor 213 and the fourth transistor 214 are connected in series to form the second bridge arm 22. The full-bridge circuit changes the output of the AC output port 5 by controlling the on and off switching of the transistors. For example, during the positive half-cycle, the first transistor 211 and the fourth transistor 214 are closed, and the second transistor 212 and the third transistor 213 are opened. The positive electrode of the DC port 4 enters the primary winding of the transformer 1 through the first transistor 211 and then returns to the negative electrode of the DC port 4 through the fourth transistor 214. During the negative half-cycle, the second transistor 212 and the third transistor 213 are closed, and the first transistor 211 and the fourth transistor 214 are opened. The negative electrode of the DC port 4 enters the primary winding of the transformer 1 through the third transistor 213 and then returns to the positive electrode of the DC port 4 through the second transistor 212. This achieves DC to AC conversion.

[0059] Optionally, each transistor is a MOS tube or an IGBT.

[0060] Figure 3 A circuit diagram of another photovoltaic micro-inverter provided by an embodiment of the present invention is shown in FIG. Figure 3 In another embodiment of the present invention, optionally, at least part of the front-stage circuit 2 shares a first bridge arm 21; or at least part of the front-stage circuit 2 shares a second bridge arm 22.

[0061] Among them, sharing the first bridge arm 21 or the second bridge arm 22 can achieve the same effect, and can be specifically set according to actual conditions. Figure 2 The diagram shows a situation where part of the front-stage circuit 2 shares a second bridge arm 22 . By sharing the second bridge arm 22 , the use of transistors can be reduced, thereby lowering the cost of the front-stage circuit 2 .

[0062] Figure 4 A circuit diagram of another photovoltaic micro-inverter provided by an embodiment of the present invention is shown in FIG. Figure 4 In another embodiment of the present invention, optionally, the front-stage circuit 2 includes a half-bridge circuit, the DC input port of the half-bridge circuit serves as the DC input port of the front-stage circuit 2, and the AC output port 5 of the half-bridge circuit serves as the AC output port 5 of the front-stage circuit.

[0063] Pre-stage circuit 2 can be configured as a half-bridge circuit, which regulates voltage. During regulation, the half-bridge circuit has a certain degree of immunity to imbalance and places low demands on circuit symmetry. Furthermore, the half-bridge circuit accommodates a wide power range, from tens of watts to kilowatts, and has lower circuit costs than a full-bridge circuit.

[0064] Continue to refer Figure 4 Based on the above embodiments, optionally, the half-bridge circuit includes a first bridge arm 21 and a second bridge arm 22 connected in parallel. The first bridge arm 21 includes a first capacitor C1 and a second capacitor C2 connected in series; the connection point between the first capacitor C1 and the second capacitor C2 serves as the first output terminal of the half-bridge circuit. The second bridge arm 22 includes a third transistor 213 and a fourth transistor 214 connected in series; the connection point between the third transistor 213 and the fourth transistor 214 serves as the second output terminal of the half-bridge circuit. The first output terminal and the second output terminal constitute the AC output port 5.

[0065] The first bridge arm 21 is composed of a first capacitor C1 and a second capacitor C2 connected in series, while the half-bridge circuit is composed of the first bridge arm 21 and the second bridge arm 22 connected in parallel. When the magnetic flux generated in the circuit is unbalanced, a DC bias current will appear in the line. When this DC bias current reaches a certain level, magnetic flux saturation will occur. By providing the first capacitor C1 and the second capacitor C2, the half-bridge circuit can prevent DC current from passing through, thereby enhancing the circuit's ability to resist imbalance. Compared to the full-bridge circuit, the use of transistors is reduced, reducing the cost of the front-stage circuit 2.

[0066] Figure 5 A circuit diagram of another photovoltaic micro-inverter provided by an embodiment of the present invention is shown in FIG. Figure 5 Based on the above embodiments, optionally, at least part of the front-stage circuit 2 shares a first bridge arm 21.

[0067] Among them, at least part of the front stage circuit 2 shares a first bridge arm 21, which can further simplify the circuit design and Figure 3 The half-bridge circuit shown has the same functionality.

[0068] Continue to refer Figure 5Based on the above embodiments, optionally, the AC side circuit 3 includes a first resonant inductor L1, a third bridge arm 23, and a fourth bridge arm 24 connected in parallel. The first resonant inductor L1 is connected in series with the secondary windings of at least two transformers 1. The third bridge arm 23 includes a third upper bridge arm 231 and a third lower bridge arm 232. The connection point between the third upper bridge arm 231 and the third lower bridge arm 232 serves as the third output terminal of the AC side circuit 3. The fourth bridge arm 24 includes a fourth upper bridge arm 241 and a fourth lower bridge arm 242. The connection point between the fourth upper bridge arm 241 and the fourth lower bridge arm 242 serves as the fourth output terminal of the AC side circuit 3. The third output terminal and the fourth output terminal constitute the industrial frequency AC power output port of the AC side circuit.

[0069] For example, when the voltage regulation of the front-stage circuit 2 is completed, the output voltage of the boost output port 6 of the AC side circuit 3 is not the industrial frequency AC voltage of 50Hz. In order to ensure the power demand of the back-end equipment, frequency regulation is required through the AC side circuit 3. The AC side circuit 3 can convert the AC voltage into the industrial frequency AC voltage of 50Hz by setting the first resonant inductor L1 and the third bridge arm 23 and the fourth bridge arm 24 connected in parallel, thereby realizing the supply of industrial frequency voltage.

[0070] Continue to refer Figure 5 On the basis of the above embodiments, optionally, on the basis of the above embodiments, optionally, the third upper bridge arm 231 includes a fifth transistor 215 and a sixth transistor 216 connected in series, and the third lower bridge arm 232 includes a third capacitor C3; the fourth upper bridge arm 241 includes a seventh transistor 217 and an eighth transistor 218 connected in series, and the fourth lower bridge arm 242 includes a fourth capacitor C4. Figure 6 A circuit diagram of another photovoltaic micro-inverter provided by an embodiment of the present invention is shown in FIG. Figure 6 The third upper bridge arm 231 includes a fifth transistor 215 and a sixth transistor 216 connected in series, and the third lower bridge arm 232 includes a third capacitor C3; the fourth upper bridge arm 241 includes a seventh transistor and an eighth transistor connected in series, and the fourth lower bridge arm 242 includes a fourth capacitor C4 and a third capacitor C3. Figure 7 A circuit diagram of another photovoltaic micro-inverter provided by an embodiment of the present invention is shown in FIG. Figure 7 The third upper bridge arm 231 includes a third capacitor C3, and the third lower bridge arm 232 includes a fifth transistor 215 and a sixth transistor 216 connected in series; the fourth upper bridge arm 241 includes a seventh transistor 217 and an eighth transistor 218 connected in series, and the fourth lower bridge arm 242 includes a fourth capacitor C4.

[0071] The first resonant inductor L1, the leakage inductance of the two transformers 1, and the third and fourth capacitors C3 and C4 form a resonant circuit. At this point, the transistors in the AC-side circuit 3 act as soft switches. By introducing resonance before and after the switching process, the voltage drops to zero before the transistor turns on, and the current drops to zero before it turns off. This eliminates voltage and current overlap during the switching process, significantly reducing or even eliminating switching losses. Furthermore, the resonance process limits the rate of change of voltage and current during the switching process, reducing switching noise. Soft switching ensures that the third bridge arm 23 and the fourth bridge arm 24 are not disconnected and connected instantly, but rather gradually, from low to high, completing the connection process and from high to low, completing the disconnection process, resulting in a smoother adjustment process.

[0072] Figure 8 A circuit diagram of another photovoltaic micro-inverter provided by an embodiment of the present invention is shown in FIG. Figure 8 Based on the above embodiments, optionally, the industrial frequency AC power output port of the AC side circuit 3 further includes a neutral point terminal N, and the connection point of the third lower bridge arm 232 and the fourth lower bridge arm 242 serves as the neutral point terminal N.

[0073] Among them, this setting method increases the neutral point terminal N, expands the application range of the photovoltaic microinverter, and makes it applicable to the US standard power grid.

[0074] Figure 9 A circuit diagram of another photovoltaic micro-inverter provided by an embodiment of the present invention is shown in FIG. Figure 9 Based on the above embodiments, optionally, the AC side circuit 3 includes a first resonant circuit 71 and a second resonant circuit 72. The first resonant circuit 71 and the second resonant circuit 72 have the same circuit structure and are symmetrically connected between the boost output port 6 and the industrial frequency AC power port. The common point of the first resonant circuit 71 and the second resonant circuit 72 is connected to the connection point of the secondary windings of at least two transformers 1.

[0075] The independently provided first resonant circuit 71 and second resonant circuit 72 can make the circuit connection relationship of the AC side circuit 3 clearer, and facilitate wiring and maintenance.

[0076] Continue to refer Figure 9Based on the above embodiments, optionally, the first resonant circuit 71 includes a fifth capacitor C5, a ninth transistor 219, a tenth transistor 2110, and a second resonant inductor L2 connected in series across the secondary winding of a portion of the transformer, and the connection point between the fifth capacitor C5 and the ninth transistor 219 serves as the third output terminal of the AC side circuit 3. The second resonant circuit 72 includes a sixth capacitor C6, an eleventh transistor 2111, a twelfth transistor 2112, and the second resonant inductor L2 connected in series across the secondary winding of another portion of the transformer, and the connection point between the sixth capacitor C6 and the eleventh transistor 2111 serves as the fourth output terminal of the AC side circuit 3. The third output terminal and the fourth output terminal constitute the industrial frequency AC power output port of the AC side circuit 3.

[0077] The first resonant circuit 71 and the second resonant circuit 72 share the second resonant inductor L2 , which has a simple structure and simplifies the control method of the resonant circuit.

[0078] Figure 10 A circuit diagram of another photovoltaic micro-inverter provided by an embodiment of the present invention is shown in FIG. Figure 10 The first resonant circuit 71 includes a third resonant inductor L3, a fifth capacitor C5, a ninth transistor 219, and a tenth transistor 2110 connected in series across the secondary winding of a portion of the transformer. The connection point between the fifth capacitor C5 and the ninth transistor 219 serves as the third output terminal of the AC side circuit 3. The second resonant circuit 72 includes a fourth resonant inductor L4, a sixth capacitor C6, an eleventh transistor 2111, and a twelfth transistor 2112 connected in series across the secondary winding of another portion of the transformer. The connection point between the sixth capacitor C6 and the eleventh transistor 2111 serves as the fourth output terminal of the AC side circuit 3. The third output terminal and the fourth output terminal constitute the industrial frequency AC power output port of the AC side circuit 3.

[0079] The first resonant circuit 71 resonates through the fifth capacitor C5, the third resonant inductor L3, and the leakage inductance of the transformer 1. The second resonant circuit 72 resonates through the sixth capacitor C6, the fourth resonant inductor L4, and the leakage inductance of the transformer 1. This configuration makes the first resonant circuit 71 and the second resonant circuit 72 independent of each other, making it easier to implement the resonant circuits.

[0080] Figure 11 A circuit diagram of another photovoltaic micro-inverter provided by an embodiment of the present invention is shown in FIG. Figure 11 ,exist Figure 10On the basis of the above, a seventh capacitor C7 and an eighth capacitor C8 are added. The seventh capacitor C7 is connected in parallel with the series circuit consisting of the third resonant inductor L3, the fourth resonant inductor L4, the sixth capacitor C6, and the two sets of transformers 1. The eighth capacitor C8 is connected in parallel with the series circuit consisting of the third resonant inductor L3, the fourth resonant inductor L4, the fifth capacitor C5, and the two sets of transformers 1. The addition of the seventh capacitor C7 and the eighth capacitor C8 allows for more capacitor options during operation of the resonant circuit, thereby increasing the number of ways to achieve resonance.

[0081] The technical solutions provided by the embodiments of the present invention are not limited to providing two transformers 1 and two pre-stage circuits 2. Multiple transformers 1 and multiple pre-stage circuits 2 can also be provided. For example, the number of transformers 1 can be three, four, or five, and the number of pre-stage circuits 2 can also be three, four, or five, depending on the number of transformers 1. In actual use, the specific design can be based on the actual output voltage of the circuit and the design cost. Figure 12 A circuit diagram of another photovoltaic micro-inverter provided by an embodiment of the present invention is shown in FIG. Figure 12 , showing a configuration of three transformers 1 .

[0082] It should be understood that the various forms of the processes shown above can be used to reorder, add, or delete steps. For example, the steps described in the present invention can be performed in parallel, sequentially, or in a different order, as long as the desired results of the technical solution of the present invention can be achieved. This is not limited herein.

[0083] The above specific embodiments do not limit the scope of protection of the present invention. Those skilled in the art will appreciate that various modifications, combinations, sub-combinations, and substitutions may be made based on design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention are intended to be included within the scope of protection of the present invention.

Claims

1. A photovoltaic micro-inverter, characterized in that: include: At least two transformers, each transformer being used to boost voltage and comprising a primary winding and a secondary winding; wherein the primary windings of the at least two transformers are connected in parallel; and the secondary windings of the at least two transformers are connected in series, and their output ports are defined as boost output ports; At least two front-stage circuits, each of which is configured to convert DC power from a DC port into AC power; DC input ports of the at least two front-stage circuits are connected to both ends of the DC port; and AC output ports of the at least two front-stage circuits are correspondingly connected to the primary windings of the at least two transformers; An AC side circuit is connected to both ends of the boost output port; the AC side circuit is used to convert the boosted AC power into industrial frequency AC power.

2. The photovoltaic micro-inverter according to claim 1, characterized in that: The front-stage circuit includes a full-bridge circuit, a DC input port of the full-bridge circuit serves as the DC input port of the front-stage circuit, and an AC output port of the full-bridge circuit serves as the AC output port of the front-stage circuit.

3. The photovoltaic micro-inverter according to claim 2, characterized in that: The full-bridge circuit comprises a first bridge arm and a second bridge arm connected in parallel; The first bridge arm includes a first transistor and a second transistor connected in series; a connection point between the first transistor and the second transistor serves as a first output terminal of the full-bridge circuit; The second bridge arm includes a third transistor and a fourth transistor connected in series; the connection point of the third transistor and the fourth transistor serves as the second output end of the full-bridge circuit, and the first output end and the second output end constitute the AC output port.

4. The photovoltaic micro-inverter according to claim 3, characterized in that: At least part of the front-stage circuits share one first bridge arm; or at least part of the front-stage circuits share one second bridge arm.

5. The photovoltaic micro-inverter according to claim 1, characterized in that: The front-stage circuit includes a half-bridge circuit, a DC input port of the half-bridge circuit serves as the DC input port of the front-stage circuit, and an AC output port of the half-bridge circuit serves as the AC output port of the front-stage circuit.

6. The photovoltaic micro-inverter according to claim 5, characterized in that: The half-bridge circuit comprises a first bridge arm and a second bridge arm connected in parallel; The first bridge arm includes a first capacitor and a second capacitor connected in series; the connection point between the first capacitor and the second capacitor serves as the first output end of the half-bridge circuit; The second bridge arm includes a third transistor and a fourth transistor connected in series; the connection point of the third transistor and the fourth transistor serves as the second output end of the half-bridge circuit, and the first output end and the second output end constitute the AC output port.

7. The photovoltaic micro-inverter according to claim 6, characterized in that: At least part of the front-stage circuits share one first bridge arm.

8. The photovoltaic micro-inverter according to claim 1, characterized in that: The AC side circuit includes a first resonant inductor, a third bridge arm and a fourth bridge arm connected in parallel; The first resonant inductor is connected in series with at least two secondary windings of the transformer; The third bridge arm includes a third upper bridge arm and a third lower bridge arm, and a connection point between the third upper bridge arm and the third lower bridge arm serves as a third output end of the AC side circuit; The fourth bridge arm includes a fourth upper bridge arm and a fourth lower bridge arm, and the connection point of the fourth upper bridge arm and the fourth lower bridge arm serves as the fourth output end of the AC side circuit; the third output end and the fourth output end constitute the industrial frequency AC power output port of the AC side circuit.

9. The photovoltaic micro-inverter according to claim 8, characterized in that: The third upper bridge arm includes a fifth transistor and a sixth transistor connected in series, and the third lower bridge arm includes a third capacitor; the fourth upper bridge arm includes a seventh transistor and an eighth transistor connected in series, and the fourth lower bridge arm includes a fourth capacitor; Alternatively, the third upper bridge arm includes a fifth transistor and a sixth transistor connected in series, and the third lower bridge arm includes a third capacitor; the fourth upper bridge arm includes a seventh transistor and an eighth transistor connected in series, and the fourth lower bridge arm includes a fourth capacitor and the third capacitor; Alternatively, the third upper bridge arm includes a third capacitor, and the third lower bridge arm includes a fifth transistor and a sixth transistor connected in series; the fourth upper bridge arm includes a seventh transistor and an eighth transistor connected in series, and the fourth lower bridge arm includes a fourth capacitor.

10. The photovoltaic micro-inverter according to claim 8 or 9, characterized in that: The industrial frequency AC power output port of the AC side circuit further includes a neutral point end, and a connection point between the third lower bridge arm and the fourth lower bridge arm serves as the neutral point end.

11. The photovoltaic micro-inverter according to claim 1, characterized in that: The AC side circuit includes a first resonant circuit and a second resonant circuit. The first resonant circuit and the second resonant circuit have the same circuit structure and are symmetrically connected between the boost output port and the industrial frequency AC power port. The common point of the first resonant circuit and the second resonant circuit is connected to the connection point of at least two secondary windings of the transformer.

12. The photovoltaic micro-inverter according to claim 11, characterized in that: The first resonant circuit includes a fifth capacitor, a ninth transistor, a tenth transistor, and a second resonant inductor connected in series across a portion of the secondary winding of the transformer, wherein the connection point between the fifth capacitor and the ninth transistor serves as a third output terminal of the AC side circuit; the second resonant circuit includes a sixth capacitor, an eleventh transistor, a twelfth transistor, and the second resonant inductor connected in series across another portion of the secondary winding of the transformer, wherein the connection point between the sixth capacitor and the eleventh transistor serves as a fourth output terminal of the AC side circuit; the third output terminal and the fourth output terminal constitute a power frequency AC power output port of the AC side circuit; Alternatively, the first resonant circuit includes a third resonant inductor, a fifth capacitor, a ninth transistor, and a tenth transistor connected in series at both ends of a secondary winding of a portion of the transformer, and the connection point of the fifth capacitor and the ninth transistor serves as the third output end of the AC side circuit; the second resonant circuit includes a fourth resonant inductor, a sixth capacitor, an eleventh transistor, and a twelfth transistor connected in series at both ends of the secondary winding of another portion of the transformer, and the connection point of the sixth capacitor and the eleventh transistor serves as the fourth output end of the AC side circuit; the third output end and the fourth output end constitute the industrial frequency AC power output port of the AC side circuit.

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