A three-level DC-AC inverter suitable for photovoltaic grid-connected hydrogen production

Abstract

The present invention discloses a three-level DC-AC inverter suitable for photovoltaic grid-connected hydrogen production, including: a first transformer and a second transformer, used to convert the direct current outputted by a photovoltaic direct current power supply into alternating current; a clamping circuit, connected to the primary coils of the first transformer and the second transformer, used to clamp the voltage of the primary coils of the first transformer and the second transformer, wherein the primary coils of the first transformer and the second transformer are connected in parallel and respectively connected to the photovoltaic direct current power supply; a three-level conversion circuit, connected to the secondary coils of the first transformer and the second transformer, used to boost and convert the alternating current outputted by the secondary coils of the first transformer and the second transformer into three-level alternating current, wherein the secondary coils of the first transformer and the second transformer are connected in series; and a grid-connected control circuit, used to connect the three-level alternating current outputted by the three-level conversion circuit to the hydrogen production grid. The present invention has high gain and can suppress the generation of leakage current.

Description

Technical Field

[0001] The invention relates to an inverter, and in particular to a three-level DC-AC inverter suitable for photovoltaic grid-connected hydrogen production. Background Art

[0002] As energy crisis and environmental pollution become increasingly serious, solar power generation technology has become a hot topic of concern and research in countries around the world. However, solar power has poor quality and strong randomness, and cannot be applied in most application scenarios. Solar hydrogen production has become an important means of absorbing solar energy. Solar hydrogen production usually requires raising the photovoltaic voltage to the high-voltage bus voltage required for grid connection, and then converting it into AC power by the grid-connected inverter, which is then transmitted to the hydrogen production plant through the transmission line. Grid-connected inverter matching becomes crucial.

[0003] At present, although many existing grid-connected inverters can reduce switching losses and improve efficiency under certain conditions, there are still some obvious shortcomings, namely, the voltage gain is relatively low, and it is necessary to increase the turns ratio and the duty cycle of the active switch to obtain a higher voltage gain. In addition, the inductive capacitance caused by the photovoltaic panel will cause leakage current in the DC two-level grid-connected inverter and the three-level inverter, which will cause equipment short circuit and cause personal danger. The leakage current will also return to the ground from the positive pole of the photovoltaic panel through the inverter, causing greater losses, and bringing voltage and current distortion, reducing the power quality of the power grid. Summary of the invention

[0004] In view of the problems existing in the prior art, an object of the present invention is to provide a three-level DC-AC inverter which has high voltage gain and can suppress leakage current and is suitable for photovoltaic grid-connected hydrogen production.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] A three-level DC-AC inverter suitable for photovoltaic grid-connected hydrogen production, comprising:

[0007] 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;

[0008] An interleaved parallel circuit is used to connect the photovoltaic power source to the primary coils of the first transformer and the second transformer in an interleaved parallel manner respectively;

[0009] A dual three-port three-level boost circuit, comprising a third capacitor C3, a fourth capacitor C4, a fifth capacitor C5, a sixth capacitor C6, a third diode D3 and a sixth diode D6, wherein the first end of the secondary coils of the first transformer and the second transformer connected in series are respectively connected to the first end of the fourth capacitor C4 and the first end of the sixth capacitor C6, the second end of the secondary coils of the first transformer and the second transformer connected in series are respectively connected to the first end of the third capacitor C3 and the second end of the fifth capacitor C5, the second end of the fourth capacitor C4 is connected to the positive electrode of the third diode D3, the negative electrode of the third diode D3 is connected to the first end of the fifth capacitor C5, the second end of the sixth capacitor C6 is connected to the negative electrode of the sixth diode D6, and the positive electrode of the sixth diode D6 is connected to the second end of the third capacitor C3;

[0010] The three-port inverter circuit is used to convert the direct current output by the dual three-port three-level boost circuit into alternating current and then output it to the hydrogen production grid.

[0011] Furthermore, the staggered parallel circuit includes a first switch tube S1, a second switch tube S2, a fourth diode D4, and a fifth diode D5, wherein the source of the first switch tube S1 is connected to the negative electrode of the photovoltaic power supply, and the drain is connected to the positive electrode of the photovoltaic power supply through the primary coil of the second transformer, the source of the second switch tube S2 is connected to the negative electrode of the photovoltaic power supply, and the drain is connected to the positive electrode of the photovoltaic power supply through the primary coil of the first transformer, the positive electrode of the fourth diode D4 is connected to the drain of the second switch tube S2, and the negative electrode is connected to the second end of the fourth capacitor C4, and the positive electrode of the fifth diode D5 is connected to the second end of the sixth capacitor C6, and the negative electrode is connected to the source of the second switch tube S2.

[0012] Furthermore, the staggered parallel circuit also includes a clamping circuit, which includes a first diode D1, a second diode D2, a first capacitor C1 and a second capacitor C2. The drain of the second switch tube S2 is connected to the positive electrode of the fourth diode D4 through the first capacitor C1, and the negative electrode of the fifth diode D5 is connected to the source of the second switch tube S2 through the second capacitor C2. The positive electrode of the first diode D1 is connected to the positive electrode of the fourth diode D4, and the negative electrode is connected to the drain of the first switch tube S1. The positive electrode of the second diode D2 is connected to the negative electrode of the fifth diode D5, and the negative electrode is respectively connected to the drain of the first switch tube S1 and the second end of the secondary coils of the first transformer and the second transformer connected in series.

[0013] Further, the three-port inverter circuit includes the third capacitor C3, the fourth capacitor C4, the fifth capacitor C5, the sixth capacitor C6, the third diode D3, the sixth diode D6, the third switch tube T1, the fourth switch tube T2 and the filter inductor L f, wherein the drain of the third switch tube T1 is connected to the cathode of the third diode D3, the source is connected to the drain of the fourth switch tube T2, and the filter inductor L f The source of the fourth switch tube T2 is connected to the second end of the third capacitor C3.

[0014] Further, the gate of the first switch tube S1 inputs the first PWM control wave signal, the gate of the second switch tube S2 inputs the second PWM control wave signal, the gate of the third switch tube T1 inputs the fourth PWM control wave signal, and the gate of the fourth switch tube T2 inputs the fourth PWM control wave signal. The duty ratios of the first switch tube S1 and the second switch tube S2 are both 0.55. The first switch tube S1 and the second switch tube S2 are both NMOS tubes. The third switch tube T1 and the fourth switch tube T2 are both NMOS tubes.

[0015] Furthermore, a turns ratio between the primary coil L1 and the secondary coil L3 of the first transformer is 1, and a turns ratio between the primary coil L2 and the secondary coil L4 of the second transformer is 1.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] The present invention adopts a dual three-port three-level boost, which has positive voltage, negative voltage or zero voltage characteristics, and the voltage stress of all components is also positive voltage, negative voltage or zero voltage, so as to achieve high voltage gain; when one boost unit is charged, the other boost unit will discharge at the same time, and the two cooperate with alternating control to control their respective boost units respectively, and cooperate with the staggered control mode to offset each other, so that the DC bus voltage ripple is low, so that the C3 and C5 withstand voltage values ​​of the DC bus capacitors are low, and the CBB capacitor can be used to extend the service life of the inverter. The staggered parallel dual-coupled inductor structure is used to reduce the input current ripple of the converter, and at the same time, the voltage stress of the semiconductor device can be reduced, the current of the single-channel transformer can be reduced, and the transformer volume can be reduced; the secondary coil is connected in series to achieve the purpose of greater voltage gain and lower voltage stress for the power device; the three-level structure can be used to effectively reduce the DC bus voltage ripple and device voltage stress, so as to improve the overall efficiency, and the three-port inverter circuit composed of the dual three-port three-level boost circuit and the bipolar half-bridge inverter can be designed by specific parameters of the dual three-port three-level boost circuit. The present invention reduces the voltage difference between the photovoltaic voltage to the ground and the voltage on the grid side of the inverter as much as possible, thereby ensuring that the voltage fluctuation of the inductive capacitor is small and suppressing the leakage current generated by it. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1An electrical schematic diagram of a three-level DC-AC inverter suitable for photovoltaic grid-connected hydrogen production provided by an embodiment of the present invention;

[0019] Figure 2 is an electrical schematic diagram of an interleaved parallel circuit in an embodiment of the present invention;

[0020] Figure 3 1 is an electrical schematic diagram of a dual three-port three-level boost circuit according to an embodiment of the present invention;

[0021] Figure 4 is an electrical schematic diagram of a three-port inverter circuit in an embodiment of the present invention;

[0022] Figure 5 This is an electrical schematic diagram of an embodiment of the present invention when working in mode 1;

[0023] Figure 6 This is an electrical schematic diagram of an embodiment of the present invention when working in mode 2;

[0024] Figure 7 This is an electrical schematic diagram of an embodiment of the present invention when working in mode 3;

[0025] Figure 8 This is an electrical schematic diagram of an embodiment of the present invention when working in mode 4;

[0026] Fig. 9 This is an electrical schematic diagram of an embodiment of the present invention when working in mode 5;

[0027] Fig.10 This is an electrical schematic diagram of an embodiment of the present invention when working in mode 6;

[0028] Fig.11 This is an electrical schematic diagram of an embodiment of the present invention when working in mode 7;

[0029] Fig.12 This is an electrical schematic diagram of an embodiment of the present invention when working in mode 8;

[0030] Fig.13 This is an electrical schematic diagram of an embodiment of the present invention when working in mode 9;

[0031] Fig.14 This is an electrical schematic diagram of an embodiment of the present invention when working in mode 10. DETAILED DESCRIPTION

[0032] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0033] An embodiment of the present invention provides a three-level DC-AC inverter suitable for photovoltaic grid-connected hydrogen production, including a first transformer, a second transformer, an interleaved parallel circuit, a dual three-port three-level boost circuit, and a three-port inverter circuit, wherein the primary coils of the first transformer and the second transformer are connected in parallel, and the secondary coils are connected in series; the interleaved parallel circuit is used to interleave the photovoltaic power source with the primary coils of the first transformer and the second transformer respectively in parallel; the dual three-port three-level boost circuit is used to increase the voltage and convert it into three-level direct current; the three-port inverter circuit is used to convert the direct current output by the dual three-port three-level boost circuit into alternating current and then output it to the hydrogen production grid.

[0034] like Figure 1 and Figure 2 As shown, the staggered parallel circuit includes a first switch tube S1, a second switch tube S2, a fourth diode D4, a fifth diode D5 and a clamping circuit (a first diode D1, a second diode D2, a first capacitor C1 and a second capacitor C2); wherein the source of the first switch tube S1 is connected to the negative electrode of the photovoltaic power supply, and the drain is connected to the positive electrode of the photovoltaic power supply through the primary coil of the second transformer, the source of the second switch tube S2 is connected to the negative electrode of the photovoltaic power supply, and the drain is connected to the positive electrode of the photovoltaic power supply through the primary coil of the first transformer, the positive electrode of the fourth diode D4 is connected to the drain of the second switch tube S2 through the first capacitor C1, and the negative electrode is connected to the second end of the fourth capacitor C4, the positive electrode of the fifth diode D5 is connected to the second end of the sixth capacitor C6, and the negative electrode is connected to the source of the second switch tube S2 through the second capacitor C2. The clamping circuit can be removed, but the inverter with the clamping circuit has better performance. The anode of the first diode D1 is connected to the anode of the fourth diode D4, and the cathode is connected to the drain of the first switch tube S1. The anode of the second diode D2 is connected to the cathode of the fifth diode D5, and the cathode is respectively connected to the drain of the first switch tube S1 and the second end of the secondary coils of the first transformer and the second transformer connected in series. The clamping circuit is used to achieve voltage clamping, and the clamping circuit can be removed, but the inverter with the clamping circuit has better performance.

[0035] like Figure 1 and Figure 3As shown, the dual three-port three-level boost circuit includes a third capacitor C3, a fourth capacitor C4, a fifth capacitor C5, a sixth capacitor C6, a third diode D3 and a sixth diode D6, wherein the first ends of the secondary coils of the first transformer and the second transformer connected in series are respectively connected to the first end of the fourth capacitor C4 and the first end of the sixth capacitor C6, the second ends of the secondary coils of the first transformer and the second transformer connected in series are respectively connected to the first end of the third capacitor C3 and the second end of the fifth capacitor C5, the second end of the fourth capacitor C4 is connected to the positive electrode of the third diode D3, the negative electrode of the third diode D3 is connected to the first end of the fifth capacitor C5, the second end of the sixth capacitor C6 is connected to the negative electrode of the sixth diode D6, and the positive electrode of the sixth diode D6 is connected to the second end of the third capacitor C3.

[0036] like Figure 1 and Figure 4 As shown, the three-port inverter circuit includes the third capacitor C3, the fourth capacitor C4, the fifth capacitor C5, the sixth capacitor C6, the third diode D3, the sixth diode D6, the third switch tube T1, the fourth switch tube T2 and the filter inductor L f , wherein the drain of the third switch tube T1 is connected to the cathode of the third diode D3, the source is connected to the drain of the fourth switch tube T2, and the filter inductor L f The source of the fourth switch tube T2 is connected to the second end of the third capacitor C3.

[0037] In the embodiment of the present invention, some devices are shared between the unit circuits, mainly because these devices play multiple roles at the same time, that is, they play roles in multiple unit circuits respectively.

[0038] The gate of the first switch tube S1 inputs the first PWM control wave signal, the gate of the second switch tube S2 inputs the second PWM control wave signal, the gate of the third switch tube T1 inputs the fourth PWM control wave signal, and the gate of the fourth switch tube T2 inputs the fourth PWM control wave signal. The PWM control wave signal is output by the external drive circuit to control the switching of the corresponding switch tube.

[0039] Among them, the diode D4, the capacitor C4, the secondary coil L3, the secondary coil L4 and the diode D3 constitute a boost unit; the diode D5, the capacitor C6, the secondary coil L3, the secondary coil L4 and the diode D6 constitute another boost unit; when one of the boost units is charged, the other boost unit will discharge at the same time. Voltage U P1P2 with U P2P3 The voltages between them are completely complementary, where U P1P2 is the voltage between the three ports P1 and P2, UP2P3 is the voltage between the three-port P2 and P3. When S1 is turned on, P2 is grounded with the power supply; when the switch tube S2 is turned on, P2 is not grounded with the power supply. Therefore, P2 is a floating ground, which can reduce electromagnetic influence and reduce the voltage stress of the switch tubes S1 and S2.

[0040] The duty ratio of the first PWM control wave signal and the second PWM control wave signal must be set to 0.55 according to the voltage difference between capacitors C3 and C5 being equal to zero. The turns ratio of the primary coil L1 and the secondary coil L3 of the first transformer, and the turns ratio of the primary coil L2 and the secondary coil L4 of the second transformer must be set to 1 according to the voltage difference between capacitors C3 and C5 being equal to zero. Under the condition that the voltage difference between capacitors C3 and C5 is equal to zero, the leakage current can be suppressed by setting the duty ratio to 0.55 and the turns ratio to 1.

[0041] In each figure, L m1 and L K1 Represent the magnetizing inductance and leakage inductance between the primary coil L1 and the secondary coil L3 respectively. m2 and L K2 They represent the magnetizing inductance and leakage inductance between the primary coil L2 and the secondary coil L4 respectively.

[0042] The working principle of the present invention is: in the working mode, it is divided into 10 modes, as follows:

[0043] like Figure 5 As shown, mode 1 [t0~t1]: When t=t0, S1 is turned on and S2 is turned off. Diode D2 and diode D4 are turned on. Diode D1, diode D3, diode D5 and diode D6 are reversely cut off. Leakage inductance L K1 The energy in the secondary coil L3 is transferred to the capacitor C2. As the leakage inductance energy decreases, the current of the diode D2 gradually decreases. The energy stored in the secondary coil L3 and the secondary coil L4 is transferred to the capacitor C4 through the capacitor C1, charging the capacitor C4. The capacitor C5 and the capacitor C3 are V g Power supply. When diode D6 is turned on with zero current at time t1, the first mode ends. The frequency of switch tubes T1 and T2 is 50Hz, which is much lower than the frequency of S1 and S2, 50kHz. Therefore, in one switching cycle of S1 and S2, switch tube T1 will be turned on all the time while T2 will be turned off all the time, or T2 will be turned on all the time while T1 will be turned off all the time. That is, during this mode, the switch states of T1 and T2 remain unchanged. Therefore, for convenience, the switch states of T1 and T2 are not described.

[0044] like Figure 6As shown, mode 2 [t1-t2]: At t1, diode D6 is turned on with zero current, diode D2 and diode D4 remain on, and diode D1, diode D3, and diode D5 are reversely cut off. The current of the primary inductor L2 continues to increase linearly. At this time, the energy stored in the secondary coil L3 and the secondary coil L4 is transferred to V through capacitor C5. g During this period, capacitor C3 starts to charge. When the current of diode D2 drops to zero at time t2, the second mode ends. During this mode, the switch states of T1 and T2 remain unchanged.

[0045] like Figure 7 As shown, mode 3 [t2-t3]: At t2, when the current of diode D2 drops to zero, part of the inductor leakage energy is transferred to capacitor C2, and the current of diode D2 drops to zero, and it is naturally turned off. Diodes D4 and D6 remain on, and diodes D1, D3, and D5 are reversely cut off. Part of the energy stored in secondary coils L3 and L4 is transferred to V g , and part of it is used to charge capacitor C3. When the switch S2 is turned on at time t3, the third mode ends. During this mode, the switch states of T1 and T2 remain unchanged.

[0046] like Figure 8 As shown, mode 4 [t3~t4]: At t3, switch tube S2 is turned on, and switch tube S1 is still in the on state. Diode D6 remains in the on state, and the other diodes are reversed and cut off. Photovoltaic power supply input voltage V in The primary coil L1 is charged from zero through the switch tube S2, and the switch tube S2 is turned on with zero current. Since the two secondary coils are coupled in opposite directions, the voltages of the two secondary coils cancel each other out and are in the current freewheeling state, and the current begins to gradually decrease. In this mode, the capacitor C3 begins to discharge. The capacitor C5 continues to supply V g Provide energy. When the secondary current continues to flow at time t4, the fourth mode ends. During this mode, the switch states of T1 and T2 remain unchanged.

[0047] like Fig. 9 As shown, mode 5 [t4-t5]: At t4, the freewheeling of secondary coils L3 and L4 ends, and diode D6 is naturally turned off. Switch tube S1 and switch tube C2 remain turned on. In this mode, all diodes are cut off due to reverse voltage. In this mode, capacitors C3 and C5 continue to supply V g When the switch S1 turns off at t5, the fifth mode ends. During this mode, the switch states of T1 and T2 remain unchanged.

[0048] like Fig.10As shown, mode 6 [t5-t6]: At t5, switch tube S1 is turned off, and switch tube S2 remains on. Diode D2, diode D3, diode D4, and diode D6 are cut off due to reverse voltage. Diode D1 is turned on, and the energy of capacitor C1 increases. Secondary coil L3 and secondary coil L4 charge capacitor C6 through diode D5. In this mode, capacitor C3 and capacitor C5 provide V g When the diode D3 is turned on with zero current at time t6, the sixth mode ends. During this mode, the switch states of T1 and T2 remain unchanged.

[0049] like Fig.11 As shown, mode 7 [t6-t7]: at t6, diode D3 is turned on with zero current, diode D1 and diode D5 remain on, and diode D2, diode D4 and diode D6 are reversely cut off. In this stage, secondary coil L3 and secondary coil L4 begin to charge capacitor C5 through capacitor C4. At t7, when the current of diode D1 drops to zero, the seventh mode ends. During this mode, the switch states of T1 and T2 remain unchanged.

[0050] like Fig.12 As shown, mode 8 [t7-t8]: at t7, part of the energy of the primary leakage inductance is transferred to capacitor C1, and the current of diode D1 drops to zero and turns off naturally. Diode D3 and diode D5 remain in the on state, and diode D2, diode D4 and diode D6 are reversely cut off. The energy stored in secondary coil L3 and secondary coil L4 is still transferred to capacitor C5 through capacitor C4 at this time, and capacitor C5 continues to be charged. At t3, when the turn-on signal of switch tube S1 comes, the eighth mode ends. During this mode, the switch states of T1 and T2 remain unchanged.

[0051] like Fig.13 As shown, mode 9 [t8-t9]: At t3, switch tube S1 is turned on, and switch tube S2 is still in the on state. The primary coil L1 and the primary coil L2 are connected in parallel and the input power supply V in Charging, the currents of the two primary coils rise together. Similar to the switch tube S2 in mode 4, the switch tube S1 in this mode achieves zero current opening. Since the two secondary coils are coupled in opposite directions, the voltages of the two secondary coils cancel each other out at this time, and are in the current continuous flow state, and the current begins to gradually decrease. And the capacitor C5 begins to discharge in this mode. At t9, when the secondary coil current continuous flow ends, the ninth mode ends. During this mode, the switch states of T1 and T2 remain unchanged.

[0052] like Fig.14 As shown, mode 10[t9~t 10]: At t9, the freewheeling of the secondary coils L3 and L4 ends, and the diode D3 is naturally turned off. The switch tubes S1 and S2 remain turned on. In this mode, all diodes are cut off due to the reverse voltage. In this mode, the capacitors C3 and C5 provide V g Power supply. When t 10 At this moment, when the switch tube S2 turns off signal, the tenth mode ends. 10 The moment is the moment t0 of the next working cycle. During this mode, the switching states of T1 and T2 remain unchanged.

[0053] In the topology of a conventional converter, the duty cycle D of the switch control signal of the switch tube S1 and the switch tube S2 has an operating range of 0.5-1, and the voltage gain is low when the duty cycle D is slightly greater than 0.5. However, due to the optimization of the topology, the operating range of the duty cycle D of the switch control signal of the switch tube S1 and the switch tube S2 is 0-1, and has high gain in the whole range. Compared with the conventional topology, the operating range of the duty cycle D is broadened, and the voltage gain can be effectively improved. When the duty cycle of the switch tube S1 and the switch tube S2 is 0.55, and the two pulses maintain a certain phase difference, at least one switch tube in the circuit can always be maintained in the on state. During this period, the states of the switch tubes T1 and T2 remain unchanged.

[0054] Based on the modal analysis, the expression of the voltage gain of the DC part of the inverter is further derived.

[0055] The voltage of capacitor C1 and the voltage across capacitor C2 Equal to the photovoltaic power supply output voltage V in Therefore, the voltage across capacitors C1 and C2 is:

[0056]

[0057] Wherein, D is the duty cycle, that is, the proportion of the duration of the conduction of the switches S1 and S2 in the duration of the entire working cycle.

[0058] During mode 1 to mode 3, the switch tube S1 is in the on state, and the switch tube S2 is in the off state.

[0059]

[0060] In the formula, Respectively represent the voltages of the primary coil L1, primary coil L2, secondary coil L3, and secondary coil L4 during mode 1 to mode 3, N A 、N BThey represent the turns ratio of the first and second transformers respectively, and K represents the coupling coefficient between the primary coil and the secondary coil. In this embodiment, the coupling coefficients of the two sets of transformers are the same, both K.

[0061] During mode 1 to mode 3, the Kirchhoff voltage law expression is written for capacitor C1, capacitor C4, capacitor C6, capacitor C3, secondary coil L3 and secondary coil L4, and the voltage of capacitor C4 can be obtained. And capacitor C3 voltage The expression is as follows:

[0062]

[0063] During mode 6 to mode 8, the switch tube S2 is in the on state, and the switch tube S1 is in the off state.

[0064]

[0065] In the formula, They respectively represent the voltages of the primary coil L1, the primary coil L2, the secondary coil L3, and the secondary coil L4 during mode 6 to mode 8.

[0066] During mode 6 to mode 8, the Kirchhoff voltage law expression is written for capacitor C6, capacitor C2, secondary coil L3, and secondary coil L4, and the voltage of capacitor C6 can be obtained as follows:

[0067]

[0068] Based on the voltage expression of mode 3 capacitor C3 and the expression of capacitor C4, Kirchhoff's voltage law expression is written for capacitor C4, capacitor C5, secondary coil C3, and secondary coil C4, and the voltage of capacitor C5 can be obtained as follows:

[0069]

[0070] During mode 5, the capacitors C3, C5 and the grid V g The expression of Kirchhoff's voltage law is listed to obtain the inverter output voltage V o for:

[0071]

[0072] The inverter voltage gain M expression is obtained:

[0073]

[0074] When the turns ratio of the two primary coils and secondary coils is the same, N A =N B =N, and K=1, M can be further expressed as:

[0075]

[0076] It can be seen from the above formula that the inverter of the present invention can achieve high voltage gain under non-limit duty cycle conditions. As the transformer turns ratio increases, the voltage gain of the converter will be greatly improved.

[0077] When analyzing the voltage stress between semiconductor devices in the interleaved parallel converter, it is assumed that N A =N B =N, and K = 1. According to the formula, the voltage stress of switch tube S1 and switch tube S2 is equal to that of capacitor C1 and capacitor C2:

[0078]

[0079] When the turns ratio is greater than 1, the absolute value of the voltage stress of the switch tube device is less than 1 / 5 of the output voltage. Therefore, the inverter can choose a switch device with a lower rated voltage, which usually has a lower on-state resistance R DS(ON) .

[0080] When diode D1 and diode D2 are in the off state, the voltage stress on diode D1 and the voltage stress of diode D2 Equal, the expression is:

[0081]

[0082] When diode D3 and diode D6 are in the off state, the voltage stress of diode D3 and diode D6 voltage stress Equal, the expression is:

[0083]

[0084] When diode D4 and diode D5 are in the off state, the voltage stress of diode D4 and diode D5 voltage stress Equal, the expression is:

[0085]

[0086] From the voltage stress analysis of semiconductor devices, it can be seen that the voltage stress of diodes D4 and D5 is the highest among the semiconductor devices in the inverter. The highest voltage stress of semiconductor devices in the inverter is still much lower than the output voltage. The inverter has the advantage of low voltage stress of semiconductor devices.

[0087] It should be noted that, in this document, relational terms such as first and second, etc. are merely used to distinguish one entity or operation from another entity or operation, but do not necessarily require or imply any actual relationship or order between these entities or operations.

[0088] It should be understood that the above embodiments and descriptions only describe the principles, main features and advantages of the present invention. Without departing from the spirit and scope of the present invention, the present invention may be subject to various changes and improvements, and these changes and improvements all fall within the scope of protection of the present invention.

Claims

1. A three-level DC-AC inverter suitable for photovoltaic grid-connected hydrogen production, characterized in that: include: 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; An interleaved parallel circuit, used to connect the photovoltaic power source to the primary coils of the first transformer and the second transformer in an interleaved parallel manner respectively; Dual three-port three-level boost circuit including a third capacitor , the fourth capacitor , the fifth capacitor 、The sixth capacitor , the third diode and the sixth diode , wherein the first ends of the secondary coils of the first transformer and the second transformer connected in series are respectively connected to the fourth capacitor The first terminal and the sixth capacitor The first end of the first transformer and the second transformer secondary coil are connected in series, and the second end of the second transformer secondary coil is connected to the third capacitor The first terminal and the fifth capacitor The second end of the fourth capacitor The second end of the third diode is connected The anode of the third diode The negative terminal of the fifth capacitor is connected to The first end of the sixth capacitor The second end of the sixth diode is connected to The cathode of the sixth diode The positive terminal of the third capacitor is connected to The second end of A three-port inverter circuit is used to convert the direct current output by the dual three-port three-level boost circuit into alternating current and then output it to the hydrogen production grid; The staggered parallel circuit includes a first switch tube , the second switch tube , the fourth diode , the fifth diode , wherein the first switch tube The source electrode is connected to the negative electrode of the photovoltaic power source, and the drain electrode is connected to the positive electrode of the photovoltaic power source through the primary coil of the second transformer. The source electrode is connected to the negative electrode of the photovoltaic power source, the drain electrode is connected to the positive electrode of the photovoltaic power source through the primary coil of the first transformer, and the fourth diode The positive electrode is connected to the second switch tube The drain terminal of the fourth capacitor is connected to the negative terminal of The second end of the fifth diode The positive terminal of the sixth capacitor is connected to The second end of the negative electrode is connected to the second switch tube The source of The staggered parallel circuit also includes a clamping circuit, which includes a first diode , the second diode , the first capacitor and the second capacitor , the second switch tube The drain of the Connect to the fourth diode The positive electrode of the fifth diode The negative electrode passes through the second capacitor Connect to the second switch The source of the first diode The anode of the fourth diode is connected to The positive electrode and the negative electrode are connected to the first switch tube The drain of the second diode The anode of the fifth diode is connected to The negative electrode is connected to the first switch tube The drain of the first transformer and the second end of the secondary coils of the second transformer are connected in series.

2. The three-level DC-AC inverter suitable for photovoltaic grid-connected hydrogen production according to claim 1, characterized in that: The three-port inverter circuit includes the third capacitor , the fourth capacitor , the fifth capacitor , the sixth capacitor , the third diode , the sixth diode The third switch tube T1, the fourth switch tube T2 and the filter inductor L f , wherein the drain of the third switch tube T1 is connected to the third diode The negative electrode and the source electrode are connected to the drain electrode of the fourth switch tube T2, and the filter inductor L f connected to one end of the hydrogen production grid, and the other end of the hydrogen production grid is connected to the fifth capacitor The source of the fourth switch tube T2 is connected to the third capacitor The second end.

3. The three-level DC-AC inverter suitable for photovoltaic grid-connected hydrogen production according to claim 1, characterized in that: The first switch tube The gate inputs the first PWM control wave signal, and the second switch tube The gate inputs the second PWM control wave signal.

4. The three-level DC-AC inverter suitable for photovoltaic grid-connected hydrogen production according to claim 2, characterized in that: The gate of the third switch tube T1 inputs the fourth PWM control wave signal, and the gate of the fourth switch tube T2 inputs the fourth PWM control wave signal.

5. The three-level DC-AC inverter suitable for photovoltaic grid-connected hydrogen production according to claim 3, characterized in that: The duty ratios of the first PWM control wave signal and the second PWM control wave signal are both 0.

55.

6. The three-level DC-AC inverter suitable for photovoltaic grid-connected hydrogen production according to claim 1, characterized in that: The primary coil of the first transformer and the secondary coil The turns ratio is 1, the primary coil of the second transformer and the secondary coil The turns ratio is 1.

7. The three-level DC-AC inverter suitable for photovoltaic grid-connected hydrogen production according to claim 1, characterized in that: The first switch tube , the second switch tube Both are NMOS tubes.

8. The three-level DC-AC inverter suitable for photovoltaic grid-connected hydrogen production according to claim 2, characterized in that: The third switch tube T1 and the fourth switch tube T2 are both NMOS tubes.

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