A high-gain bipolar grid-connected inverter applied to a photovoltaic hydrogen production system

Abstract

The present invention discloses a high-gain bipolar grid-connected inverter applied to a photovoltaic hydrogen production system, which includes a first transformer, a second transformer, a two-phase interleaved inverter unit, a three-level rectifier unit, and a half-bridge inverter. Among them, the primary coils of the first transformer and the second transformer are connected in parallel, and the secondary coils are connected in series in the opposite direction; the two-phase interleaved inverter unit is used to alternately connect the photovoltaic power supply in parallel with the primary coils of the first transformer and the second transformer respectively, and complement the current ripple of the direct current output by the photovoltaic; the three-level rectifier unit is used to increase the alternating current voltage output by the first transformer and the second transformer, and convert the alternating current after the voltage is increased into a direct current with bipolar characteristics for output; the half-bridge inverter is used to convert the direct current output by the three-level rectifier unit into alternating current and then output it to the hydrogen production power grid. The present invention can suppress leakage current, has low cost, small volume, and realizes three-level output.

Description

Technical Field

[0001] The present invention relates to a grid-connected inverter, and in particular to a high-gain bipolar grid-connected inverter applied to a photovoltaic hydrogen production system. Background Art

[0002] With the increasingly serious energy crisis and environmental pollution problems, solar power generation technology has become a hot topic of concern and research in various countries around the world. However, the power quality of solar energy is poor and has strong randomness, and it cannot be applied to most application scenarios. Therefore, using solar energy to produce hydrogen has become an important means to consume solar energy. When using solar energy to produce hydrogen, it is usually necessary to boost the photovoltaic voltage to the high-voltage bus voltage required for grid connection, and then convert it into alternating current by an inverter, and transmit it to the hydrogen production plant through the power transmission line of the hydrogen production power grid to reduce power transmission losses. Therefore, the matching of the grid-connected inverter becomes crucial.

[0003] Existing grid-connected inverters generally use a two-level DC converter with an interleaved Flyback (flyback) + full-bridge power-frequency inversion topology to realize the transfer of energy to the grid. The full-bridge inverter has a large number of switching tubes, high cost, large volume, and large bus capacitor voltage ripple in the DC two-level structure, which easily causes a short service life of the grid-connected inverter. Moreover, due to the large parasitic capacitance of the photovoltaic panel, it will cause a large leakage current. The leakage current will return from the positive pole of the photovoltaic panel to the ground through the grid-connected inverter, causing large losses, voltage and current distortion, and reducing the power quality of the power grid. In addition, the input current ripple of the existing two-level DC converter is large, and the photovoltaic panel is usually equivalent to a current source. The large current ripple reduces the overall output power of the photovoltaic panel.

[0004] At present, the traditional clamping structure cannot realize the output three-level function. In order to realize the three-level structure, the existing technology usually adopts the method of adding more than three coils. This method increases the cost and volume of the transformer, and brings a large voltage static error, causing uneven voltage of the three-level voltage and leakage current. Summary of the Invention

[0005] Aiming at the problems existing in the prior art, the purpose of the present invention is to provide a high-gain bipolar grid-connected inverter applied to a photovoltaic hydrogen production system, which can suppress leakage current, has low cost, small volume, and realizes three-level output.

[0006] In order to achieve the above invention purpose, the present invention provides the following technical solutions:

[0007] A high-gain bipolar grid-connected inverter applied to a photovoltaic hydrogen production system, comprising:

[0008] A first transformer and a second transformer, wherein the primary coils of the first transformer and the second transformer are connected in parallel, and the secondary coils are connected in series;

[0009] Two interleaved inverter units, which are used to alternately connect the photovoltaic power source in parallel with the primary coils of the first transformer and the second transformer respectively, and complement the current ripple of the direct current output by the photovoltaic system;

[0010] Three-level rectifier unit, which is used to boost the alternating current voltage output by the first transformer and the second transformer, and convert the boosted alternating current into a direct current with bipolar characteristics for output; specifically including the first diode D1, the second diode D2, the third diode D3, the fourth diode D4, the fifth diode D5, the sixth diode D6, the first capacitor C1, the second capacitor C2, the first bipolar capacitor C o1 、the second bipolar capacitor C o2 、the third bipolar capacitor C o3 、the fourth bipolar capacitor C o4 . The first ends of the secondary coils of the first transformer and the second transformer after being connected in series are respectively connected to the first end of the first capacitor C1, the first end of the second capacitor C2, the negative electrode of the first diode D1, and the positive electrode of the second diode D2. The positive electrode of the third diode D3 is connected to the negative electrode of the second diode D2. The positive electrode of the fourth diode D4 is respectively connected to the negative electrode of the third diode D3 and the second end of the first capacitor C1. The first end of the fourth bipolar capacitor C o4 is connected to the negative electrode of the second diode D2, and the second end is connected to the negative electrode of the fourth diode D4. The second ends of the secondary coils of the first transformer and the second transformer after being connected in series are respectively connected to the first end of the first bipolar capacitor C o1 and the first end of the second bipolar capacitor C o2 . The second end of the first bipolar capacitor C o1 is respectively connected to the positive electrode of the first diode D1, the negative electrode of the sixth diode D6, and the first end of the third bipolar capacitor C o3 . The second end of the second bipolar capacitor C o2 is connected to the first end of the fourth bipolar capacitor C o4 . The positive electrode of the sixth diode D6 is connected to the second end of the second capacitor C2. The second end of the third bipolar capacitor C o3 is connected to the second end of the second capacitor C2 through the forward fifth diode D5;

[0011] Half-bridge inverter, which is used to convert the direct current output by the three-level rectifier unit into alternating current and then output it to the hydrogen production power grid.

[0012] Further, the two interleaved inverter units include the first switch tube S C1 、the second switch tube S C2 、the third switch tube S1, the fourth switch tube S2, the first capacitor C C1 、the second capacitor CC2 , wherein the drain of the first switching transistor S C1 is connected to the first photovoltaic output terminal through a first capacitor C C1 , and the source is connected to the first photovoltaic output terminal through a primary coil of a first transformer. The drain of the third switching transistor S1 is connected to the source of the first switching transistor S C1 , and the source is connected to the second photovoltaic output terminal. The drain of the second switching transistor S C2 is connected to the first photovoltaic output terminal through a second capacitor C C2 , and the source is sequentially connected to the first photovoltaic output terminal through a primary coil of a second transformer. The drain of the fourth switching transistor S2 is connected to the source of the second switching transistor S C2 , and the source is connected to the second photovoltaic output terminal.

[0013] Furthermore, the half-bridge inverter includes the first bipolar capacitor C o1 , the second bipolar capacitor C o2 , the third bipolar capacitor C o3 , the fourth bipolar capacitor C o4 , as well as a fifth switching transistor Q1, a sixth switching transistor Q2, and a filter inductor L f . The drain of the fifth switching transistor Q1 is connected to the second end of the fourth bipolar capacitor C o4 , the source is connected to the drain of the sixth switching transistor Q2. The source of the sixth switching transistor Q2 is connected to the second end of the third bipolar capacitor C o3 , and the drain is connected to the first input terminal of the hydrogen production power grid. One end of the filter inductor L f is connected to the second input terminal of the hydrogen production power grid, and the other end is connected to the first end of the second bipolar capacitor C o2 .

[0014] Furthermore, the secondary coils of the first transformer and the second transformer are connected in series in the reverse direction. The turns ratios of the primary coils and the secondary coils of the first transformer and the second transformer are the same.

[0015] Furthermore, the high-gain bipolar grid-connected inverter satisfies the following conditions:

[0016] C s1 ≤4N 2 I in 2 L k1 / V o 2

[0017] C s2 ≤4N 2 I in 2 L k2 / Vo 2

[0018] In the formula, C s1 = C s2 , C s1 , C s2 respectively represent the parasitic capacitances of the third switching transistor S1 and the fourth switching transistor S2, N represents the turns ratio of the first transformer and the second transformer, I in represents the magnitude of the current output by the photovoltaic power source, L k1 , L k2 respectively represent the leakage inductances of the first transformer and the second transformer, V o represents the output voltage of the high-gain bipolar grid-connected inverter.

[0019] Furthermore, the first switching transistor S C1 receives a first PWM control wave signal at its gate, the second switching transistor S C2 receives a second PWM control wave signal at its gate, the third switching transistor S1 receives a third PWM control wave signal at its gate, the fourth switching transistor S2 receives a fourth PWM control wave signal at its gate, the first PWM control wave signal and the second PWM control wave signal are staggered by 180°, and the third PWM control wave signal and the fourth PWM control wave signal are staggered by 180°. The fifth switching transistor Q1 receives a fifth PWM control wave signal at its gate, and the sixth switching transistor Q2 receives a sixth PWM control wave signal at its gate.

[0020] Furthermore, the first switching transistor S C1 , the second switching transistor S C2 , the third switching transistor S1, and the fourth switching transistor S2 are all NMOS transistors. The fifth switching transistor Q1 and the sixth switching transistor Q2 are both NMOS transistors.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows: The two-phase interleaved inverter unit of the present invention realizes the complementarity of the input current ripple, reduces the function of the input current ripple, and at the same time reduces the single-channel power level and the requirement for the inductance; the three-level rectifier unit is controlled by the S1, S2 interleaved 180° control method to generate three levels of positive, negative, and zero, effectively reducing the voltage stress of the components of the three-level rectifier unit, and at the same time being positive and negative symmetric, effectively increasing the bus voltage composed of C o1 -C o4 in series. The output voltage of the three-level rectifier unit has a bipolar characteristic, which not only realizes the conversion from AC to DC, but also realizes high voltage gain and increases the bus voltage of the inverter; the half-bridge inverter uses C o1 -C o4In series, the voltages of the four capacitors are added to form the bus voltage. The four capacitors are alternately charged and discharged with each other in pairs, effectively reducing the ripple of the bus voltage and the requirement for the capacitance values of these four capacitors. CBB capacitors can be used to replace electrolytic capacitors, greatly increasing the service life of the inverter. The bus voltage of the half-bridge inverter has a bipolar characteristic, and Q1 and Q2 adopt a power-frequency complementary control method; the inverter also has two clamping structures (S C1 、S C2 、C C1 、C C2 ), which not only achieve voltage clamping but also resonate with L k1 、L k2 to achieve soft switching of S1 and S2; S C1 、S C2 、S1 and S2 adopt an interleaved 180° control method and are complementary to S C1 、S C2 . This control method is a characteristic of achieving three levels; the inverter has isolation performance and bipolar function, which can effectively reduce the leakage current caused by the parasitic capacitance of the input-side photovoltaic panel; the overall circuit has few components, low cost, and small volume. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is the electrical schematic diagram of the high-gain bipolar grid-connected inverter applied to the photovoltaic hydrogen production system provided by the embodiment of the present invention;

[0023] Figure 2 is the electrical schematic diagram of the embodiment of the present invention when working in Mode I;

[0024] Figure 3 is the electrical schematic diagram of the embodiment of the present invention when working in Mode II;

[0025] Figure 4 is the electrical schematic diagram of the embodiment of the present invention when working in Mode III;

[0026] Figure 5 is the electrical schematic diagram of the embodiment of the present invention when working in Mode IV;

[0027] Figure 6 is the electrical schematic diagram of the embodiment of the present invention when working in Mode V;

[0028] Figure 7 is the electrical schematic diagram of the embodiment of the present invention when working in Mode VI;

[0029] Figure 8 is the theoretical waveform of the embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0030] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention.

[0031] An embodiment of the present invention provides a high-gain bipolar grid-connected inverter applied to a photovoltaic hydrogen production system, which includes a first transformer, a second transformer, a two-phase interleaved inverter unit, a three-level rectifier unit, and a half-bridge inverter. Among them, the primary coils of the first transformer and the second transformer are connected in parallel, and the secondary coils are connected in series in the opposite direction; the two-phase interleaved inverter unit is used to alternately connect the photovoltaic power supply to the primary coils of the first transformer and the second transformer, and complement the current ripple of the direct current output by the photovoltaic; the three-level rectifier unit is used to increase the voltage of the alternating current output by the first transformer and the second transformer, and convert the increased alternating current into direct current with bipolar characteristics for output; the half-bridge inverter is used to convert the direct current output by the three-level rectifier unit into alternating current and output it to the hydrogen production power grid.

[0032] As Figure 1 shown, the two-phase interleaved inverter unit includes a first switch tube S C1 , a second switch tube S C2 , a third switch tube S1, a fourth switch tube S2, a first capacitor C C1 , a second capacitor C C2 . Among them, the drain of the first switch tube S C1 is connected to the first photovoltaic output terminal through the first capacitor C C1 , and the source is connected to the first photovoltaic output terminal through the primary coil of the first transformer. The drain of the third switch tube S1 is connected to the source of the first switch tube S C1 , and the source is connected to the second photovoltaic output terminal. The drain of the second switch tube S C2 is connected to the first photovoltaic output terminal through the second capacitor C C2 , and the source is sequentially connected to the first photovoltaic output terminal through the primary coil of the second transformer. The drain of the fourth switch tube S2 is connected to the source of the second switch tube S C2 , and the source is connected to the second photovoltaic output terminal.

[0033] As Figure 1 shown, the three-level rectifier unit specifically includes a first diode D1, a second diode D2, a third diode D3, a fourth diode D4, a fifth diode D5, a sixth diode D6, a first capacitor C1, a second capacitor C2, a first bipolar capacitor C o1 , a second bipolar capacitor C o2 , a third bipolar capacitor C o3 , a fourth bipolar capacitor C o4, the first ends of the secondary coils of the first transformer and the second transformer after being connected in series are respectively connected to the first end of the first capacitor C1, the first end of the second capacitor C2, the negative electrode of the first diode D1, and the positive electrode of the second diode D2. The positive electrode of the third diode D3 is connected to the negative electrode of the second diode D2. The positive electrode of the fourth diode D4 is respectively connected to the negative electrode of the third diode D3 and the second end of the first capacitor C1. The first end of the fourth bipolar capacitor C o4 is connected to the negative electrode of the second diode D2, and the second end is connected to the negative electrode of the fourth diode D4. The second ends of the secondary coils of the first transformer and the second transformer after being connected in series are respectively connected to the first end of the first bipolar capacitor C o1 and the first end of the second bipolar capacitor C o2 . The second end of the first bipolar capacitor C o1 is respectively connected to the positive electrode of the first diode D1, the negative electrode of the sixth diode D6, and the first end of the third bipolar capacitor C o3 . The second end of the second bipolar capacitor C o2 is connected to the first end of the fourth bipolar capacitor C o4 . The positive electrode of the sixth diode D6 is connected to the second end of the second capacitor C2. The second end of the third bipolar capacitor C o3 is connected to the second end of the second capacitor C2 through the forward fifth diode D5.

[0034] As Figure 1 shown, the half-bridge inverter includes the first bipolar capacitor C o1 , the second bipolar capacitor C o2 , the third bipolar capacitor C o3 , the fourth bipolar capacitor C o4 , and the fifth switching transistor Q1, the sixth switching transistor Q2, and the filter inductor L f . The drain of the fifth switching transistor Q1 is connected to the second end of the fourth bipolar capacitor C o4 . The source is connected to the drain of the sixth switching transistor Q2. The source of the sixth switching transistor Q2 is connected to the second end of the third bipolar capacitor C o3 . The drain is connected to the first input end of the hydrogen production power grid. One end of the filter inductor L f is connected to the second input end of the hydrogen production power grid, and the other end is connected to the first end of the second bipolar capacitor C o2 . The first bipolar capacitor C o1 , the second bipolar capacitor C o2 , the third bipolar capacitor C o3 , the fourth bipolar capacitor C o4It is located in both the three-level rectifier unit and the half-bridge inverter. These devices play two roles and are therefore included in the two unit circuits.

[0035] Among them, the first switching tube S C1 , the second switching tube S C2 , the third switching tube S1, and the fourth switching tube S2 are all NMOS transistors. The fifth switching tube Q1 and the sixth switching tube Q2 are both NMOS transistors. The gate of the first switching tube S C1 inputs the first PWM control wave signal, the gate of the second switching tube S C2 inputs the second PWM control wave signal, the gate of the third switching tube S1 inputs the third PWM control wave signal, the gate of the fourth switching tube S2 inputs the fourth PWM control wave signal, the first PWM control wave signal and the second PWM control wave signal are staggered by 180°, and the third PWM control wave signal and the fourth PWM control wave signal are staggered by 180°. The gate of the fifth switching tube Q1 inputs the fifth PWM control wave signal, and the gate of the sixth switching tube Q2 inputs the sixth PWM control wave signal. Each PWM control wave signal can control the on and off of the switching tube, which is specifically output by an external drive circuit.

[0036] The high-gain bipolar grid-connected inverter of the present invention satisfies the following conditions:

[0037] C s1 ≤ 4N 2 I in 2 L k1 / V o 2

[0038] C s2 ≤ 4N 2 I in 2 L k2 / V o 2

[0039] In the formula, C s1 = C s2 C s1 C s2 respectively represent the parasitic capacitances of the third switching tube S1 and the fourth switching tube S2, N represents the turns ratio of the first transformer and the second transformer, and the turns ratios of the two are the same. I in represents the magnitude of the current output by the photovoltaic power source, L k1 L k2 respectively represent the leakage inductances of the first transformer and the second transformer, and V o represents the output voltage of the high-gain bipolar grid-connected inverter. The finally achieved bus voltage gain is: M CCM= 4N / (1 - D), where D is the duty cycle of the PWM control signals of S1 and S2.

[0040] The working principle of the present invention will be described below. In the figure, Lk1 and Lk2 are the leakage inductances of the first transformer and the second transformer, and Lm 11 , Lm 21 are the exciting inductances of the primary coils of the first transformer and the second transformer.

[0041] As Figure 2 shown, in Mode I, S1 and S2 are turned on simultaneously, and L k1 , L k2 , L m11 , L m21 are connected in interleaved parallel and charged by the photovoltaic power supply. The three-level rectifier unit does not work. Since Q1 and Q2 adopt the power-frequency complementary control method, when Q1 is turned on and Q2 is turned off, C o2 and C o4 are connected in series to supply energy to the power grid. When Q2 is turned on and Q1 is turned off, C o1 and C o3 are connected in series to supply energy to the hydrogen-making power grid.

[0042] As Figure 3 shown, in Mode II, S1 is turned on and S2 is turned off. L k1 , L m11 are charged by the photovoltaic power supply. L k2 , L m21 release energy and resonate with C C2 . Due to the special design of the resonant working mode, the current of L k2 reverses, which can achieve the soft switching of S2 in Mode III. The three-level rectifier unit works at this time. The port voltages of L2 and L4 are positive at point A and negative at point B. L2 and L4 are connected in series to charge C o2 through D2, L2, L4, and C1 are connected in series to charge C o4 through D4, L2, L4, and C o1 are connected in series to charge C2 through D6, and C o1 discharges. In addition, C o3 also discharges. Since Q1 and Q2 adopt the power-frequency complementary control method, when Q1 is turned on and Q2 is turned off, C o2 and C o4 are connected in series to supply energy to the hydrogen-making power grid. When Q2 is turned on and Q1 is turned off, C o1 and C o3 are connected in series to supply energy to the hydrogen-making power grid.

[0043] As Figure 4 shown, in Mode III, S1 and S2 are turned on simultaneously, and L k1 , L m11 are charged by the photovoltaic power supply, Lk2 , L m21 releases energy and resonates with C C2 . Due to the special design of the resonant working mode, the current of L k2 reverses, enabling the soft switching of S2 for Mode III. The three-level rectifier unit operates at this time. The port voltages of L2 and L4 are positive at point A and negative at point B. L2 and L4 are connected in series to charge C o2 through D2. L2 L4 and C1 in series charge C o4 through D4. L2 and L4 in series with C o1 charge C2 through D6. C o1 discharges. In addition, C o3 also discharges. Since Q1 and Q2 adopt a power-frequency complementary control method, when Q1 is on and Q2 is off, C o2 and C o4 in series supply energy to the hydrogen production power grid. When Q2 is on and Q1 is off, C o1 and C o3 in series supply energy to the hydrogen production power grid.

[0044] As Figure 5 shown, in Mode IV, S1 and S2 are turned on simultaneously. L k1 , L k2 , L m11 , L m21 are connected in interleaved parallel and charged by the photovoltaic power source. The three-level rectifier unit does not operate. Since Q1 and Q2 adopt a power-frequency complementary control method, when Q1 is on and Q2 is off, C o2 and C o4 in series supply energy to the hydrogen production power grid. When Q2 is on and Q1 is off, C o1 and C o3 in series supply energy to the hydrogen production power grid.

[0045] As Figure 6 shown, in Mode V, S2 is turned on and S1 is turned off. L k2 , L m21 are charged by the photovoltaic power source. L k1 , L m11 release energy and resonate with C C1 . Due to the special design of the resonant working mode, the current of L k1 reverses, enabling the soft switching of S1 for Mode VI. The three-level rectifier unit operates at this time. The port voltages of L2 and L4 are positive at point B and negative at point A. L2 and L4 in series with C o2 charge C1 through D3. L2 and L4 in series with C2 charge C o3 through D5. L2 and L4 charge C o1 through D1. C o1 and Co3 Charging. In addition, C o2 and C o4 Discharging. Since Q1 and Q2 adopt the power frequency complementary control method, when Q1 is turned on and Q2 is turned off, C o2 and C o4 are in series to provide energy for the hydrogen production power grid. When Q2 is turned on and Q1 is turned off, C o1 and C o3 are in series to provide energy for the hydrogen production power grid.

[0046] As Figure 7 shown, in Mode VI, S1 and S2 are turned on simultaneously, and L k1 , L k2 , L m11 , L m21 are interleaved in parallel and charged by the photovoltaic power supply. The three-level rectifier unit works at this time. The port voltage at point B of L2 and L4 is positive and point A is negative. L2 and L4 in series with C o2 charge C1 through D3. L2 and L4 in series with C2 charge C o3 through D5. L2 and L4 charge C o1 through D1. C o1 and C o3 are charged. In addition, C o2 and C o4 discharge. Since Q1 and Q2 adopt the power frequency complementary control method, when Q1 is turned on and Q2 is turned off, C o2 and C o4 are in series to provide energy for the hydrogen production power grid. When Q2 is turned on and Q1 is turned off, C o1 and C o3 are in series to provide energy for the hydrogen production power grid.

[0047] The main theoretical waveforms of the high-gain bipolar grid-connected inverter are as Figure 8 shown.

[0048] The two-phase interleaved inverter unit in the embodiment of the present invention realizes the complementary input current ripple and reduces the input current ripple function. At the same time, it reduces the single-channel power level and the demand for inductance. The three-level rectifier unit is controlled by the S1 and S2 interleaved 180° control method, generating three levels of positive, negative, and zero, effectively reducing the voltage stress of the components of the three-level rectifier unit. At the same time, the positive and negative are symmetrical, effectively improving the bus voltage composed of C o1 -C o4 in series. The output voltage of the three-level rectifier unit has a bipolar characteristic, not only realizing the conversion from AC to DC, but also realizing high voltage gain and improving the bus voltage of the inverter. The half-bridge inverter adopts C o1 -C o4In series, the voltages of four capacitors are added to form the bus voltage. The four capacitors are alternately charged and discharged with each other in pairs, effectively reducing the pulsation of the bus voltage and the requirement for the capacitance values of these four capacitors. CBB capacitors can be used to replace electrolytic capacitors, greatly improving the service life of this inverter. The bus voltage of the half-bridge inverter has bipolar characteristics, and Q1 and Q2 adopt a power-frequency complementary control method; this inverter also has two clamping structures (S C1 、S C2 、C C1 、C C2 ), which not only realizes voltage clamping but also resonates with L k1 、L k2 to realize the soft switching of S1 and S2; S C1 、S C2 、S1 and S2 adopt an interleaved 180° control method and are complementary to S C1 、S C2 . This control method is the characteristic of realizing three levels; this inverter has isolation performance and bipolar functions, which can effectively reduce the leakage current caused by the parasitic capacitance of the photovoltaic panel on the input side; the overall circuit has few components, low cost and small volume.

[0049] It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations.

[0050] It should be understood that the above embodiments and the description in the specification are only the principles, main features and advantages of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements fall within the protection scope of the present invention.

Claims

1. A high-gain bipolar grid-connected inverter applied to a photovoltaic hydrogen production system, characterized in that including a first transformer and a second transformer, wherein the primary coils of the first transformer and the second transformer are connected in parallel, and the secondary coils are connected in series; two interleaved inverter units, configured to respectively and interleavedly connect a photovoltaic power source in parallel with the primary coils of the first transformer and the second transformer, and complement the current ripple of the direct current output by the photovoltaic; Three-level rectifier unit, which is used to increase the AC voltage output by the first transformer and the second transformer, and convert the increased AC voltage into a DC voltage with bipolar characteristics for output; specifically includes the first diode D1, the second diode D2, the third diode D3, the fourth diode D4, the fifth diode D5, the sixth diode D6, the first capacitor C1, the second capacitor C2, the first bipolar capacitor C o1 , the second bipolar capacitor C o2 , the third bipolar capacitor C o3 , the fourth bipolar capacitor C o4 . The first ends of the secondary coils of the first transformer and the second transformer after being connected in series are respectively connected to the first end of the first capacitor C1, the first end of the second capacitor C2, the negative electrode of the first diode D1, and the positive electrode of the second diode D2. The positive electrode of the third diode D3 is connected to the negative electrode of the second diode D2. The positive electrode of the fourth diode D4 is respectively connected to the negative electrode of the third diode D3 and the second end of the first capacitor C1. The first end of the fourth bipolar capacitor C o4 is connected to the negative electrode of the second diode D2, and the second end is connected to the negative electrode of the fourth diode D4. The second ends of the secondary coils of the first transformer and the second transformer after being connected in series are respectively connected to the first end of the first bipolar capacitor C o1 and the first end of the second bipolar capacitor C o2 . The second end of the first bipolar capacitor C o1 is respectively connected to the positive electrode of the first diode D1, the negative electrode of the sixth diode D6, and the first end of the third bipolar capacitor C o3 . The second end of the second bipolar capacitor C o2 is connected to the first end of the fourth bipolar capacitor C o4 . The positive electrode of the sixth diode D6 is connected to the second end of the second capacitor C2. The second end of the third bipolar capacitor C o3 is connected to the second end of the second capacitor C2 through the forward fifth diode D5; a half-bridge inverter, configured to convert the direct current output by the three-level rectifier unit into alternating current and then output it to the hydrogen production power grid.

2. The high-gain bipolar grid-connected inverter applied to the photovoltaic hydrogen production system according to claim 1, wherein, The two interleaved inverter units include a first switch S C1 , a second switch S C2 , a third switch S1, a fourth switch S2, a first capacitor C C1 , a second capacitor C C2 . Among them, the drain of the first switch S C1 is connected to the first photovoltaic output terminal through the first capacitor C C1 , and the source is connected to the first photovoltaic output terminal through the primary coil of the first transformer. The drain of the third switch S1 is connected to the source of the first switch S C1 , and the source is connected to the second photovoltaic output terminal. The drain of the second switch S C2 is connected to the first photovoltaic output terminal through the second capacitor C C2 , and the source is sequentially connected to the first photovoltaic output terminal through the primary coil of the second transformer. The drain of the fourth switch S2 is connected to the source of the second switch S C2 , and the source is connected to the second photovoltaic output terminal.

3. The high-gain bipolar grid-connected inverter applied to the photovoltaic hydrogen production system according to claim 2, wherein The half-bridge inverter includes the first bipolar capacitor C o1 , the second bipolar capacitor C o2 , the third bipolar capacitor C o3 , the fourth bipolar capacitor C o4 , and the fifth switch Q1, the sixth switch Q2, and the filter inductor L f . The drain of the fifth switch Q1 is connected to the second terminal of the fourth bipolar capacitor C o4 . The source is connected to the drain of the sixth switch Q2. The source of the sixth switch Q2 is connected to the second terminal of the third bipolar capacitor C o3 . The drain is connected to the first input terminal of the hydrogen production power grid. One end of the filter inductor L f is connected to the second input terminal of the hydrogen production power grid, and the other end is connected to the first terminal of the second bipolar capacitor C o2 .

4. The high-gain bipolar grid-connected inverter applied to the photovoltaic hydrogen production system according to claim 3, wherein, The secondary coils of the first transformer and the second transformer are connected in series in opposite directions.

5. The high-gain bipolar grid-connected inverter applied to the photovoltaic hydrogen production system according to claim 4, wherein, The turns ratio of the primary coils and the secondary coils of the first transformer and the second transformer is the same.

6. The high-gain bipolar grid-connected inverter applied to the photovoltaic hydrogen production system according to claim 5, characterized in that, The high-gain bipolar grid-connected inverter satisfies the following conditions: C s1 ≤4N 2 I in 2 L k1 / V o 2 C s2 ≤4N 2 I in 2 L k2 / V o 2 Wherein, C s1 = C s2 , C s1 , C s2 respectively represent the parasitic capacitances of the third switching transistor S1 and the fourth switching transistor S2, N represents the turns ratio of the first transformer and the second transformer, I in represents the magnitude of the current output by the photovoltaic power supply, L k1 , L k2 respectively represent the leakage inductances of the first transformer and the second transformer, V o represents the output voltage of the high-gain bipolar grid-connected inverter.

7. The high-gain bipolar grid-connected inverter applied to the photovoltaic hydrogen production system according to claim 2, wherein, The first switching transistor S C1 has its gate receiving a first PWM control wave signal, the second switching transistor S C2 has its gate receiving a second PWM control wave signal, the third switching transistor S1 has its gate receiving a third PWM control wave signal, and the fourth switching transistor S2 has its gate receiving a fourth PWM control wave signal. The first PWM control wave signal and the second PWM control wave signal are staggered by 180°, and the third PWM control wave signal and the fourth PWM control wave signal are staggered by 180°.

8. The high-gain bipolar grid-connected inverter applied to the photovoltaic hydrogen production system according to claim 3, characterized in that, A fifth PWM control wave signal is input to the gate of the fifth switch tube Q1, and a sixth PWM control wave signal is input to the gate of the sixth switch tube Q2.

9. The high-gain bipolar grid-connected inverter applied to the photovoltaic hydrogen production system according to claim 2, wherein The first switching transistor S C1 , the second switching transistor S C2 , the third switching transistor S1, and the fourth switching transistor S2 are all NMOS transistors.

10. The high-gain bipolar grid-connected inverter applied to the photovoltaic hydrogen production system according to claim 3, characterized in that, Both the fifth switch tube Q1 and the sixth switch tube Q2 are NMOS tubes.

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