Bidirectional dc-dc circuit and photovoltaic energy storage inverter

Abstract

The application discloses a bidirectional DCDC circuit and a photovoltaic energy storage inverter. The photovoltaic energy storage inverter is used for connecting a photovoltaic module, a battery and an alternating current end. The bidirectional DCDC circuit comprises a first direct current end, a second direct current end, a transformer, a first full-bridge circuit connected between the first direct current end and a primary side of the transformer, a second full-bridge circuit connected between a secondary side of the transformer and the second direct current end and a first capacitor. The first full-bridge circuit is directly connected with the primary side of the transformer and / or the second full-bridge circuit is directly connected with the secondary side of the transformer. The first capacitor is located between the second full-bridge circuit and the second direct current end and is connected with positive and negative poles of the second direct current end. The bidirectional DCDC circuit provided in the application uses leakage inductance of the primary side of the transformer and the first capacitor to form an LC resonant circuit instead of an LC resonant circuit arranged at two ends of the transformer, so that the function of the resonant circuit is realized while the number and volume of electrical elements of a topological structure are reduced, thereby reducing the cost.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of photovoltaic power generation, and more particularly to a bidirectional DCDC circuit and a photovoltaic energy storage inverter. BACKGROUND

[0002] The photovoltaic energy storage inverter is connected with a photovoltaic module, a battery and an alternating current end, and includes a bidirectional DCDC circuit connected between the battery and the alternating current end. The primary side and the secondary side of a transformer in the bidirectional DCDC circuit are each connected with an LC resonant circuit, which is used to filter out frequency components that are not needed by the bidirectional DCDC circuit, retain the required signals, and improve the reliability and stability of the circuit. However, the bidirectional DCDC circuit has more electrical elements and is more expensive, which results in a higher cost of the photovoltaic energy storage inverter. In addition, in order to accommodate a large number of electrical elements and meet the safety distance and heat dissipation requirements of the large number of electrical elements, the bidirectional DCDC circuit needs to occupy a large space, which increases the volume of the photovoltaic energy storage inverter. SUMMARY

[0003] The present application provides a bidirectional DCDC circuit and a photovoltaic energy storage inverter to solve at least one of the above technical problems.

[0004] The bidirectional DCDC circuit of the present application is used in a photovoltaic energy storage inverter, and the photovoltaic energy storage inverter is used to connect a photovoltaic module, a battery and an alternating current end. The bidirectional DCDC circuit includes:

[0005] a first direct current end for connecting the battery;

[0006] a second direct current end;

[0007] a transformer;

[0008] a first full-bridge circuit connected between the first direct current end and the primary side of the transformer;

[0009] a second full-bridge circuit connected between the secondary side of the transformer and the second direct current end, the first full-bridge circuit being directly connected with the primary side of the transformer and / or the second full-bridge circuit being directly connected with the secondary side of the transformer;

[0010] a first capacitor located between the second full-bridge circuit and the second direct current end and connected with the positive and negative poles of the second direct current end.

[0011] Compared with the conventional technology, the bidirectional DCDC circuit provided in the application cancels the LC resonant circuit arranged at both ends of the transformer, utilizes the leakage inductance of the primary side of the transformer and a first capacitor to form an LC resonant circuit instead of the LC resonant circuit arranged at both ends of the transformer, realizes the function of the resonant circuit while reducing the number of electrical elements in the topology structure, thereby reducing the cost, and in addition, due to the reduction in the number of electrical elements, the space occupied by the bidirectional DCDC circuit is reduced, which is conducive to reducing the volume of the photovoltaic energy storage inverter.

[0012] In some embodiments, the bidirectional DCDC circuit further comprises a first inductor arranged between the primary side of the transformer and the first full-bridge circuit or between the secondary side of the transformer and the second full-bridge circuit.

[0013] In this way, the first inductor can form an LC resonant circuit with the first capacitor and the leakage inductance of the primary side of the transformer, so that the leakage inductance of the primary side of the transformer can be eliminated as needed, thereby improving the performance of the bidirectional DCDC circuit.

[0014] In some embodiments, the capacitance value of the first capacitor ranges from 1 to 1.2 μF.

[0015] In this way, the first capacitor and the leakage inductance of the primary side form an LC resonant circuit, and in the LC resonant circuit, the capacitance value and the inductance jointly determine the resonant frequency, the resonant frequency of the LC resonant circuit is inversely proportional to the square root of the capacitance value of the first capacitor, and the bidirectional DCDC circuit usually requires a higher resonant frequency, so the first capacitor only needs a lower capacitance value.

[0016] The photovoltaic energy storage inverter of another embodiment of the application is used in a photovoltaic energy storage system, and comprises an alternating current end, a battery end for connecting a direct current battery, and the bidirectional DCDC circuit of any one of the above-mentioned embodiments, wherein the battery end is connected to the first direct current end, and the alternating current end is connected to the second direct current end.

[0017] In some embodiments, the photovoltaic energy storage inverter further comprises a bidirectional DCAC circuit connected between the alternating current end and the bidirectional DCDC circuit.

[0018] In this way, the bidirectional DCAC circuit can realize efficient and stable electric energy conversion, which is conducive to reducing energy loss.

[0019] In some embodiments, the bidirectional DCAC circuit comprises a second capacitor and a third full-bridge circuit connected between the bidirectional DCDC circuit and the alternating current end, and the second capacitor is arranged between the second full-bridge circuit and the alternating current end and is connected in parallel across the alternating current end.

[0020] Therefore, the third full-bridge circuit has high output voltage and stable performance, and can ensure that the photovoltaic energy storage inverter can provide stable and reliable power output under various working conditions. The buffer capacitor can effectively suppress the overvoltage generated in the switching process, and improve the stability of the photovoltaic energy storage inverter.

[0021] In some embodiments, the bidirectional DCAC circuit further comprises a first power switch tube and a second power switch tube, a source of the first power switch tube is connected to one end of the AC end, a drain of the first power switch tube is connected to a drain of the second power switch tube, and a source of the second power switch tube is connected to the other end of the AC end.

[0022] Therefore, the first power switch tube and the second power switch tube form an aggregated loop, which will not generate a higher voltage spike, is conducive to reducing the stress in the circuit, reducing external radiation, and is conducive to improving the electromagnetic compatibility of the circuit.

[0023] In some embodiments, the photovoltaic energy storage inverter further comprises a single-stage bidirectional DCDC circuit, which is connected between the second full-bridge circuit and the bidirectional DCAC circuit.

[0024] Therefore, the single-stage bidirectional DCDC circuit can adjust the rising and falling amplitude of the voltage by adjusting the duty cycle of the switch tube in the circuit, which is simpler than directly adjusting the resonant frequency in the bidirectional DCDC circuit.

[0025] In some embodiments, the photovoltaic energy storage inverter further comprises a photovoltaic end for connecting a photovoltaic module and a BUCK-BOOST circuit, which is connected between the photovoltaic end and the bidirectional DCAC circuit.

[0026] Therefore, the BUCK-BOOST circuit can realize accurate adjustment of the output voltage of the photovoltaic module, so as to ensure that the photovoltaic module always works near the maximum power point, which is conducive to improving the power generation efficiency of the photovoltaic module and prolonging the service life of the photovoltaic cell.

[0027] In some embodiments, the AC end comprises a load and two power inductors, and the load is connected to the bidirectional DCAC circuit through the two power inductors respectively.

[0028] Therefore, the power inductor can filter the alternating current component in the current, so that the voltage is more stable.

[0029] Additional aspects and advantages of the embodiments disclosed herein will be set forth in part in the description that follows, and in part will become apparent to those skilled in the art upon examination of the following description and drawings. BRIEF DESCRIPTION OF DRAWINGS

[0030] The above and / or additional aspects and advantages of the present application will become apparent and more readily appreciated from the following description, taken in conjunction with the following drawings in which:

[0031] Figure 1 is a circuit schematic diagram of a bidirectional DCDC circuit of a photovoltaic energy storage inverter of embodiments of the present application;

[0032] Figure 2 is a circuit schematic diagram of a photovoltaic energy storage inverter of embodiments of the present application;

[0033] Figure 3 is a circuit schematic diagram of a bidirectional DCAC circuit of a photovoltaic energy storage inverter of embodiments of the present application;

[0034] Figure 4 is a circuit schematic diagram of a single-stage bidirectional DCDC circuit of a photovoltaic energy storage inverter of embodiments of the present application;

[0035] Figure 5 is a timing diagram of a bidirectional DCDC circuit and a single-stage bidirectional DCDC circuit of embodiments of the present application;

[0036] Figure 6 is a circuit schematic diagram of a BUCK-BOOST circuit of a photovoltaic energy storage inverter of embodiments of the present application.

[0037] Main component symbol explanation: photovoltaic energy storage inverter 100, AC end 10, load 11, power inductor 12, battery end 20, bidirectional DCDC circuit 30, first DC end 31, second DC end 32, transformer 33, first full-bridge circuit 34, first switch tube 341, first parasitic capacitor 3411, second switch tube 342, second parasitic capacitor 3421, third switch tube 343, third parasitic capacitor 3431, fourth switch tube 344, fourth parasitic capacitor 3441, second full-bridge circuit 35, fifth switch tube 351, fifth parasitic capacitor 3511, sixth switch tube 352, sixth parasitic capacitor 3521, seventh switch tube 353, seventh parasitic capacitor 3531, eighth switch tube 354, eighth parasitic capacitor 3541, first capacitor 36, first inductor 37, third capacitor 38, bidirectional DCAC circuit 40, second capacitor 41, third full-bridge circuit 42, first power switch tube 43, second power switch tube 44, single-stage bidirectional DCDC circuit 50, second inductor 51, third power switch tube 52, fourth power switch tube 53, fourth capacitor 54, photovoltaic end 60, BUCK-BOOST circuit 70, fifth power switch tube 71, sixth power switch tube 72, first power diode 73, second power diode 74, fifth capacitor 75, third inductor 76, sixth capacitor 77. DETAILED DESCRIPTION

[0038] The embodiments of the present application will be described in detail below with reference to the drawings, in which the same or similar components have the same or similar designations and functions throughout the drawings and a repeated description of the same or similar components will be omitted. The embodiments described below are examples in which the present application is applied to a refrigerator, and the present application is not limited to the refrigerator. The embodiments described below are exemplary and are for the purpose of explaining the present application only and should not be understood as limiting the present application. In the description of the present application, it should be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", and the like are based on the orientation or positional relationship shown in the drawings, and are used only to facilitate the description of the present application and simplify the description, and thus should not be construed as indicating or implying that the device or element pointed thereby must have a particular orientation, be constructed and operated in a particular orientation, and thus should not be construed as limiting the present application. In the description of the present application, the meaning of "a plurality of" is two or more, unless explicitly specified and limited otherwise.

[0039] In the description of the present application, it should be noted that, unless explicitly specified and limited otherwise, the terms "mount", "connected", "connection" should be understood broadly, for example, can be fixed connection, can be detachable connection, or integral connection. Can be mechanical connection, can be electrical connection. Can be directly connected, can be indirectly connected through an intermediate medium, can be the internal communication of two elements or the interaction relationship between two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0040] In the present application, unless explicitly specified and limited otherwise, "on" or "under" of a first feature to a second feature can include that the first and second features are in direct contact, or that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, "on", "above" and "on" of the first feature to the second feature includes that the first feature is directly above and obliquely above the second feature, or only indicates that the first feature is higher than the second feature in horizontal height. "Below", "under" and "under" of the first feature to the second feature includes that the first feature is directly below and obliquely below the second feature, or only indicates that the first feature is lower than the second feature in horizontal height.

[0041] The disclosure provides a number of different embodiments or examples for implementing different structures of the application. In order to simplify the disclosure of the application, the components and arrangements of specific examples are described herein. Of course, they are merely examples and are not intended to limit the application. In addition, the application can repeatedly refer to numbers and / or letters in different examples, and such repetition is for the purpose of simplification and clarity, which does not indicate the relationship between the various embodiments and / or arrangements discussed. In addition, the application provides examples of various specific processes and materials, but those skilled in the art can realize the application of other processes and / or the use of other materials.

[0042] Please refer to Figure 1 and Figure 2 , the application embodiment provides a photovoltaic energy storage inverter 100, the photovoltaic energy storage inverter 100 includes an alternating current end 10, a battery end 20 for connecting a direct current battery and a bidirectional DCDC circuit 30, the bidirectional DCDC circuit 30 includes a first direct current end 31 for connecting the battery, a second direct current end 32, a transformer 33, a first full bridge circuit 34 connected between the first direct current end 31 and the primary side of the transformer 33, a second full bridge circuit 35 connected between the secondary side of the transformer 33 and the second direct current end 32 and a first capacitor 36, the first full bridge circuit 34 is directly connected with the primary side of the transformer 33 and / or the second full bridge circuit 35 is directly connected with the secondary side of the transformer 33;The first capacitor 36 is located between the second full bridge circuit 35 and the second direct current end 32, and connects the positive and negative poles of the second direct current end 32, the battery end 20 is connected with the first direct current end 31, and the alternating current end 10 is connected with the second direct current end 32.

[0043] The bidirectional DCDC circuit 30 provided in the application cancels the LC resonant circuit arranged at both ends of the transformer 33 compared with the conventional technology, and forms an LC resonant circuit with the leakage inductance of the primary side of the transformer 33 and the first capacitor 36 instead of the LC resonant circuit arranged at both ends of the transformer 33, so as to realize the function of the resonant circuit while reducing the number and volume of electrical elements of the topology structure, thereby reducing the cost, in addition, due to the reduction of the number of electrical elements, the space occupied by the bidirectional DCDC circuit 30 is reduced, which is beneficial to reduce the volume of the photovoltaic energy storage inverter 100.

[0044] Specifically, in the embodiment of the application, as shown in Figure 1 , the first full bridge circuit 34 includes a first switch tube 341, a second switch tube 342, a third switch tube 343 and a fourth switch tube 344, wherein the first switch tube 341 and the second switch tube 342 are connected in series to form a first bridge arm, the third switch tube 343 and the fourth switch tube 344 are connected in series to form a second bridge arm, and the first bridge arm and the second bridge arm are connected in parallel.

[0045] The second full-bridge circuit 35 includes a fifth switch tube 351, a sixth switch tube 352, a seventh switch tube 353, and an eighth switch tube 354, wherein the fifth switch tube 351 and the sixth switch tube 352 are connected in series to form a third bridge arm, the seventh switch tube 353 and the eighth switch tube 354 are connected in series to form a fourth bridge arm, and the third bridge arm and the fourth bridge arm are connected in parallel.

[0046] In the embodiment of the present application, the bidirectional DCDC circuit 30 further includes a third capacitor 38, one end of which is connected to the positive pole of the first DC end 31, and the other end of which is connected to the negative pole of the first DC end 31.

[0047] In some embodiments, the bidirectional DCDC circuit 30 further includes a first inductor 37, which is arranged between the primary side of the transformer 33 and the first full-bridge circuit 34, or between the secondary side of the transformer 33 and the second full-bridge circuit 35.

[0048] In this way, the first inductor 37 can replace the leakage inductance of the primary side of the transformer 33 and form an LC resonance circuit with the first capacitor 36, so that the leakage inductance of the primary side of the transformer 33 can be eliminated as needed, thereby improving the performance of the bidirectional DCDC circuit 30.

[0049] Specifically, when the load 11 changes, the change of the leakage potential of the leakage inductance of the primary side of the transformer 33 may cause electromagnetic interference and harmonic disturbance to other devices in the network, thereby causing instability of the power system and affecting the stable operation of the entire power system. Therefore, in some embodiments, the first inductor 37 can be arranged between the primary side of the transformer 33 and the first full-bridge circuit 34, or between the secondary side of the transformer 33 and the second full-bridge circuit 35, to replace the leakage inductance of the primary side and form an LC resonance circuit with the first capacitor 36, thereby improving the performance of the bidirectional DCDC circuit 30.

[0050] In some embodiments, the capacitance value of the first capacitor 36 is in the range of 1-1.2 μF.

[0051] In this way, the first capacitor 36 and the leakage inductance of the primary side form an LC resonance circuit, in which the capacitance value and the inductance jointly determine the resonance frequency. The resonance frequency of the LC resonance circuit is inversely proportional to the square root of the capacitance value of the first capacitor 36, and the bidirectional DCDC circuit 30 usually requires a higher resonance frequency, so the first capacitor 36 only needs a lower capacitance value.

[0052] Specifically, the bidirectional DCDC circuit 30 usually requires a large-capacitance DC support capacitor, usually more than 50pF. In the embodiment of the present application, the first capacitor 36 interacts with the primary leakage inductance to form an LC resonant circuit. The capacitance and inductance of the LC resonant circuit jointly determine the resonant frequency, and the resonant frequency of the LC resonant circuit is inversely proportional to the square root of the capacitance of the first capacitor 36. Therefore, a smaller-capacitance first capacitor 36 can be used to replace the original support capacitor, because the bidirectional DCDC circuit 30 usually requires a high resonant frequency. The capacitance of the first capacitor 36 can be selected according to actual needs, which will not be described here.

[0053] Please refer to Figure 2 and Figure 3 In some embodiments, the photovoltaic energy storage inverter 100 further comprises a bidirectional DCAC circuit 40 connected between the AC end 10 and the bidirectional DCDC circuit 30.

[0054] In this way, the bidirectional DCAC circuit 40 can realize efficient and stable power conversion, which is conducive to reducing energy loss.

[0055] Specifically, in the embodiment of the present application, the bidirectional DCAC circuit 40 is responsible for converting the DC power of the photovoltaic end 60 or the battery end 20 into AC power for use by the AC end 10, or converting the AC power of the AC end 10 into DC power for charging the battery end 20.

[0056] In some embodiments, the bidirectional DCAC circuit 40 comprises a second capacitor 41 and a third full-bridge circuit 42. The third full-bridge circuit 42 is connected between the bidirectional DCDC circuit 30 and the AC end 10. The second capacitor 41 is connected in parallel between the second full-bridge circuit 35 and the AC end 10.

[0057] In this way, the third full-bridge circuit 42 has high output voltage and stable performance, which can ensure that the photovoltaic energy storage inverter 100 can provide stable and reliable power output under various working conditions. The buffer capacitor can effectively suppress the overvoltage generated in the switching process, thereby improving the stability of the photovoltaic energy storage inverter 100.

[0058] Specifically, in the embodiment of the present application, the full-bridge circuit has bidirectional conversion capability and can realize flexible conversion between AC and DC. The design of the full-bridge circuit with a buffer capacitor can also reduce energy loss and electromagnetic interference. The buffer capacitor can smooth the ripples in the current and reduce the harmonic components, thereby improving the power quality. At the same time, the buffer capacitor can effectively reduce the generation and propagation of electromagnetic interference, thereby protecting surrounding electronic devices and systems from interference.

[0059] Please refer to Figure 3In some embodiments, the bidirectional DCAC circuit 40 further comprises a first power switch 43 and a second power switch 44, the source of the first power switch 43 is connected to one end of the AC terminal 10, the drain of the first power switch 43 is connected to the drain of the second power switch 44, and the source of the second power switch 44 is connected to the other end of the AC terminal 10.

[0060] In this way, the first power switch 43 and the second power switch 44 form a closed loop, which will not generate a high voltage peak, thus reducing the stress in the circuit, reducing the radiation to the outside, and improving the electromagnetic compatibility of the circuit.

[0061] Specifically, in the embodiments of the present application, when the photovoltaic module and the battery charge the AC terminal 10, the first power switch 43 and the second power switch 44 act as freewheeling diodes, and the switches of the third full-bridge circuit 42 act as voltage reduction diodes. When the AC terminal 10 charges the battery, the first power switch 43 and the second power switch 44 act as voltage boost diodes, and the switches of the third full-bridge circuit 42 act as freewheeling diodes.

[0062] Please refer to Figure 2 and Figure 4 In some embodiments, the photovoltaic energy storage inverter 100 further comprises a single-stage bidirectional DCDC circuit 50 connected between the second full-bridge circuit 35 and the bidirectional DCAC circuit 40.

[0063] In this way, the single-stage bidirectional DCDC circuit 50 can adjust the voltage boost and drop range by adjusting the duty cycle of the switches in the circuit, which is simpler than directly adjusting the resonant frequency of the bidirectional DCDC circuit 30.

[0064] Specifically, the single-stage bidirectional DCDC circuit 50 comprises a second inductor 51, a third power switch 52, a fourth power switch 53, and a fourth capacitor 54. One end of the second inductor 51 is connected to the positive electrode of the second DC terminal 32, and the other end of the second inductor 51 is connected to the drain of the third power switch 52 and the source of the fourth power switch 53, respectively. The source of the third power switch 52 is connected to the negative electrode of the second DC terminal 32 and the negative electrode of the second capacitor 41, respectively. The positive electrode of the second capacitor 41 is connected to the drain of the fourth power switch 53, and one end of the fourth capacitor 54 is connected to the source of the third power switch 52, and the other end is connected to the drain of the fourth power switch 53.

[0065] Please refer to Figure 5 , the solid line and the dashed line respectively represent the timing diagrams of the bidirectional DCDC circuit 30 and the single-stage bidirectional DCDC circuit 50 in the forward and reverse working states. Vg1 is the driving signal of the bidirectional DCDC circuit 30, Vg2 is the driving signal of the single-stage bidirectional DCDC circuit 50, f DThe switching frequency of the bidirectional DC-DC circuit 30 is T, and the corresponding period is T. D D represents the duty cycle of the first switching transistor 341. The switching frequency f of the single-stage bidirectional DC-DC circuit 50 is... B The switching frequency f of the bidirectional DC-DC circuit is 30. D T times, corresponding to a period of T. B d is the duty cycle of the fourth power switch 53. Figure 6 [t0-t] b The fourth power switch 53, representing the single-stage bidirectional DC-DC circuit 50, is turned on. At this time, energy flows to capacitor C3, and the current flowing through the second inductor 51 decreases; b -t3] indicates that the third power switch 52 is turned on. At this time, energy flows from the first capacitor 36 to the second inductor 51, and the current flowing through the second inductor 51 increases.

[0066] In the first working mode, i.e., the time interval [t0-t1], such as Figure 1 and Figure 5 As shown, at time t0, the parasitic capacitances of the first switch transistor 341 and the fourth switch transistor 344 finish charging the parasitic capacitances of the second switch transistor 342 and the third switch transistor 343, and the voltage across the first switch transistor 341 and the fourth switch transistor 344 drops to 0. At this time, the first switch transistor 341 and the fourth switch transistor 344 are turned on, achieving zero-voltage turn-on. Similarly, the parasitic capacitances of the fifth switch transistor 351 and the eighth switch transistor 354 finish charging the parasitic capacitances of the sixth switch transistor 352 and the seventh switch transistor 353, and the voltage across the fifth switch transistor 351 and the eighth switch transistor 354 drops to 0, achieving zero-voltage turn-on of the fifth switch transistor 351 and the eighth switch transistor 354. During the t0-t1 stage, the leakage inductance of the source side of the transformer 33 resonates with the first capacitor 36, and the leakage inductance current i LK The resonance increases from 0 at time t0. The mathematical model for this mode can be expressed by the following equation:

[0067]

[0068] Among them, R s V is the sum of the internal resistance of the power supply and the on-resistance of the switching transistor. c L is the voltage across the first capacitor 36. k V1 is the primary leakage inductance, V1 is the voltage across the third capacitor (38), and C... r The capacitance value of the first capacitor is 36, C s6 The capacitance of the sixth parasitic capacitance 3521 is given, where N is a constant and i LB The current is for the second inductor 51.

[0069] In the second working mode, i.e. the period of [t1-t2], at the moment of t1, the resonant current oscillates to the lowest point, at which the first switch tube 341 and the fourth switch tube 344 are turned off, and the zero current turn-off is approximately realized. Similarly, the current of the secondary side switch tube is the difference between the resonant current and the excitation current, the turn-off current is close to 0, and the fifth switch tube 351 and the eighth switch tube 354 also realize the zero current turn-off. After the first switch tube 341 and the fourth switch tube 344 are turned off in the t1-t2 stage, the parasitic capacitances of the second switch tube 342 and the third switch tube 343 are first charged to the parasitic capacitances of the first switch tube 341 and the fourth switch tube 344, and after the charging is completed, the reverse parallel diodes of the second switch tube 342 and the third switch tube 343 continue to flow, and the inductance current satisfies the following equation:

[0070]

[0071] wherein V c is the voltage of the first capacitor 36, L k is the leakage inductance of the primary side, V1 is the voltage of the third capacitor 38, and N is a constant.

[0072] In the third working mode, i.e. the period of [t2-t3], at the moment of t2, the inductance current drops to 0, the reverse parallel diodes of the second switch tube 342 and the third switch tube 343 are turned off, and the parasitic capacitances of the transformer 33 on both sides are repeatedly charged and discharged until the voltage of the primary side of the transformer 33 is 0. In this mode, the leakage inductance current of the transformer 33 is in the oscillation decay state. Since the first capacitor 36 is much larger than the parasitic capacitance, it can be assumed that the voltage V c remains unchanged during the process. Initially, the first parasitic capacitor 3411 and the fourth parasitic capacitor 3441 charge the second parasitic capacitor 3421 and the third parasitic capacitor 3431; the sixth parasitic capacitor 3521 and the seventh parasitic capacitor 3531 charge the fifth parasitic capacitor 3511 and the eighth parasitic capacitor 3541, and the inductance current reversely increases, satisfying the following equation:

[0073]

[0074] wherein V c is the voltage of the first capacitor 36, L k is the leakage inductance of the primary side, V1 is the voltage of the third capacitor 38, C r is the capacitance value of the first capacitor 36, C s6 is the capacitance value of the sixth parasitic capacitor 3521, N is a constant, u Cs4 is the potential difference between the fourth parasitic capacitor 3441, u Cs6 is the potential difference between the sixth parasitic capacitor 3521, C s6 is the capacitance value of the fourth parasitic capacitor 3441, and C s6The capacitance value of the sixth parasitic capacitance 3521.

[0075] At time t3, the inductor current oscillation decays to 0, and the second switch tube 342 and the third switch tube 343 realize zero-voltage turn-on, and the converter enters the second half of the switching cycle. The working mode is symmetrical with the first half of the cycle. In the reverse working mode, energy is transmitted from the right side to the left side. Similarly, a complete switching cycle can be divided into six working modes, and the timing waveform is symmetrical with that in the forward working mode, and thus will not be described one by one. In addition, for the magnetic reset problem of the high-frequency transformer 33, it can be known from the foregoing analysis that, in the steady-state operation of the converter, due to the symmetry of the working modes of the first half and the second half of the cycle in a period, the voltage of the first capacitor 36 applied to the excitation inductance of the transformer 33 is equal in size and opposite in direction in the first half and the second half of the cycle. In the first half, the first capacitor 36 provides positive volt-second to the excitation inductance; in the second half, the first capacitor 36 provides negative volt-second to the excitation inductance, and the two are equal, realizing the magnetic reset of the transformer 33 and ensuring the long-time stable operation of the converter. c In the first half and the second half of the cycle, the waveforms are equal, the voltage of the first capacitor 36 applied to the excitation inductance of the transformer 33 is equal in size and opposite in direction. In the first half, the first capacitor 36 provides positive volt-second to the excitation inductance; in the second half, the first capacitor 36 provides negative volt-second to the excitation inductance, and the two are equal, realizing the magnetic reset of the transformer 33 and ensuring the long-time stable operation of the converter.

[0076] Please refer to Figure 2 and Figure 6 In some embodiments, the photovoltaic energy storage inverter 100 further comprises a photovoltaic end 60 for connecting a photovoltaic module and a BUCK-BOOST circuit 70, and the BUCK-BOOST circuit 70 is connected between the photovoltaic end 60 and the bidirectional DCAC circuit 40.

[0077] In this way, the BUCK-BOOST circuit 70 can realize accurate regulation of the output voltage of the photovoltaic module, so as to ensure that the photovoltaic module always works near the maximum power point, which is beneficial to improve the power generation efficiency of the photovoltaic module and prolong the service life of the photovoltaic cell.

[0078] Specifically, in the embodiments of the present application, the BUCK-BOOST circuit 70 comprises a fifth power switch tube 71, a sixth power switch tube 72, a first power diode 73, a second power diode 74, a fifth capacitor 75 and a third inductor 76; the drain of the fifth power switch tube 71 is connected to the positive end of the photovoltaic end 60, the source of the fifth power switch tube 71 is connected to the cathode of the first power diode 73, and the anode of the first power diode 73 is connected to the negative end of the photovoltaic end 60; one end of the first energy storage inductor is connected to the cathode of the first power diode 73, and the other end is respectively connected to the drain of the sixth power switch tube 72 and the anode of the second power diode 74, and the source of the sixth power switch tube 72 is connected to the anode of the first power diode 73; the cathode of the second power diode 74 is connected to the drain of the second power switch tube 44 through the fifth capacitor 75, so that the two ends of the fifth capacitor 75 are respectively connected to the positive and negative electrodes of the photovoltaic end 60.

[0079] Further, the BUCK-BOOST circuit 70 further comprises a sixth capacitor 77 connected in parallel to the photovoltaic side 60.

[0080] When the photovoltaic side input voltage U C5 is greater than the bus voltage hysteresis upper limit, i.e. U C5 > U C2 + V th , the fifth power switch 71 is high-frequency switched, the sixth power switch 72 is always off, and the duty cycle of the fifth power switch 71 is D = U C2 / U C5 , where U C2 is the voltage of the second capacitor 41, and V th is the bus voltage hysteresis range, usually 10-15V. In this state, the photovoltaic side is in BUCK mode, and the bus voltage U C2 is less than the photovoltaic input voltage U C5 , the bus voltage is reduced, and the power tube safety margin is improved.

[0081] When the photovoltaic side input voltage is greater than the bus voltage hysteresis lower limit and less than the bus voltage hysteresis upper limit, i.e. U C2 -V th <U C5 <U C2 + V th , the fifth power switch 71 and the sixth power switch 72 are synchronously high-frequency switched, and the duty cycle is D = 1 + U C2 / U C5 . In this state, the photovoltaic side is in BUCK-BOOST mode, and the bus voltage is adjusted to be close to the photovoltaic input voltage by adjusting the duty cycle.

[0082] When the photovoltaic side input voltage is less than the bus voltage hysteresis lower limit, i.e. U C5 <U C2 -V th , the sixth power switch 72 is high-frequency switched, the duty cycle is D = 1-U C5 / U C2 , and the fifth power switch 71 is always on. In this state, the photovoltaic side is in BOOST mode, and the bus voltage is adjusted to be greater than the photovoltaic input voltage by adjusting the duty cycle.

[0083] In some embodiments, the AC side 10 comprises a load 11 and two power inductors 12, and the load 11 is connected to the bidirectional DCAC circuit 40 through the two power inductors 12 respectively.

[0084] In this way, the power inductor 12 can filter the AC component in the current, making the voltage more stable.

[0085] Specifically, in the embodiments of the present application, the power inductor 12 is connected in series across the load 11. When the current changes, the inductor coil generates an induced electromotive force, thereby offsetting the change component in the current, achieving the purpose of filtering. This filtering effect helps to reduce the ripple in the power supply, improve the purity of the power supply, and provide stable DC voltage for electronic devices. Because the inductor coil has impedance characteristics, when current passes through the inductor coil, it will generate a certain impedance, thereby suppressing the propagation of electromagnetic interference signals.

[0086] In addition, the power inductor 12 can also limit the current to prevent damage to the circuit caused by excessive current. When the current exceeds the set value, the inductor coil will generate a larger impedance, thereby limiting the increase of the current.

[0087] In the description of the present specification, the description of the terms "some embodiments", "one embodiment", "some embodiments", "illustrative embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in connection with the described embodiments or examples are included in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily mean the same embodiment or example. Moreover, the described specific features, structures, materials or characteristics can be combined in any one or more embodiments or examples in a suitable manner.

[0088] In addition, the terms "first", "second" are only for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. Therefore, the features defined with "first", "second" can explicitly or implicitly include at least one of the features. In the description of the present application, the meaning of "multiple" is at least two, for example, two, three, unless otherwise specifically limited.

[0089] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limiting the present application. Those skilled in the art can make changes, modifications, replacements and variations to the above embodiments within the scope of the present application, and the scope of the present application is defined by the claims and their equivalents.

Claims

1. A bidirectional DC-DC circuit for a photovoltaic energy storage inverter, wherein the photovoltaic energy storage inverter is used to connect photovoltaic modules, batteries, and an AC terminal, characterized in that, The bidirectional DC-DC circuit includes: For connecting the first DC terminal of the battery; Second DC terminal; transformer; A first full-bridge circuit connected between the first DC terminal and the primary side of the transformer; A second full-bridge circuit is connected between the secondary side of the transformer and the second DC terminal, wherein the first full-bridge circuit is directly connected to the primary side of the transformer and / or the second full-bridge circuit is directly connected to the secondary side of the transformer; The first capacitor is located between the second full-bridge circuit and the second DC terminal, and is connected to the positive and negative terminals of the second DC terminal.

2. The bidirectional DC-DC circuit according to claim 1, characterized in that, The bidirectional DC-DC circuit further includes a first inductor, which is disposed between the primary side of the transformer and the first full-bridge circuit, or between the secondary side of the transformer and the second full-bridge circuit.

3. The bidirectional DC-DC circuit according to claim 1, characterized in that, The capacitance value of the first capacitor ranges from 1 to 1.2 μF.

4. A photovoltaic energy storage inverter for use in a photovoltaic energy storage system, characterized in that, The photovoltaic energy storage inverter includes an AC terminal, a battery terminal for connecting a DC battery, and a bidirectional DC-DC circuit as described in any one of claims 1-3, wherein the battery terminal is connected to the first DC terminal, and the AC terminal is connected to the second DC terminal.

5. The photovoltaic energy storage inverter according to claim 4, characterized in that, The photovoltaic energy storage inverter also includes a bidirectional DCAC circuit, which is connected between the AC terminal and the bidirectional DC-DC circuit.

6. The photovoltaic energy storage inverter according to claim 5, characterized in that, The bidirectional DC-AC circuit includes a second capacitor and a third full-bridge circuit. The third full-bridge circuit is connected between the bidirectional DC-DC circuit and the AC terminal. The second capacitor is located between the second full-bridge circuit and the AC terminal and is connected in parallel across the two ends of the AC terminal.

7. The photovoltaic energy storage inverter according to claim 6, characterized in that, The bidirectional DCAC circuit further includes a first power switch and a second power switch. The source of the first power switch is connected to one end of the AC terminal, the drain of the first power switch is connected to the drain of the second power switch, and the source of the second power switch is connected to the other end of the AC terminal.

8. The photovoltaic energy storage inverter according to claim 5, characterized in that, The photovoltaic energy storage inverter also includes a single-stage bidirectional DC-DC circuit, which is connected between the second full-bridge circuit and the bidirectional DC-AC circuit.

9. The photovoltaic energy storage inverter according to claim 5, characterized in that, The photovoltaic energy storage inverter also includes a photovoltaic terminal for connecting the photovoltaic module and a BUCK-BOOST circuit, wherein the BUCK-BOOST circuit is connected between the photovoltaic terminal and the bidirectional DCAC circuit.

10. The photovoltaic energy storage inverter according to claim 5, characterized in that, The AC terminal includes a load and two power inductors, and the two ends of the load are respectively connected to the bidirectional DCAC circuit through the two power inductors.

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