Photovoltaic converter with novel series topology

Abstract

The utility model provides a novel series topology photovoltaic converter. The photovoltaic converter comprises a common mode inductor, a BOOST circuit and an inverter circuit which are connected in sequence on a direct current bus between a photovoltaic direct current power supply and a three-phase alternating current power supply, because the common mode inductor adopts a reverse winding method that two coils are wound on the same iron core, and the number of turns and the phase are the same, when normal current in a circuit flows through the common mode inductor, the current generates reverse magnetic fields in the inductance coils wound in the same phase so as to cancel out each other, so that the common mode inductor is formed. At the moment, the current is mainly influenced by coil resistance and a small amount of damping caused by leakage inductance; when a common-mode current flows through the coil, due to the homodirectivity of the common-mode current, a homodromous magnetic field can be generated in the coil to increase the inductive reactance of the coil, so that the coil shows high impedance and generates a relatively strong damping effect, the common-mode current is attenuated, the purpose of filtering is achieved, the filtering capability of a photovoltaic current can be greatly enhanced, and a leakage current can be greatly inhibited.

Description

Technical Field

[0001] The present application relates to the technical field of photovoltaic converters, and in particular to a novel series topology photovoltaic converter. Background Art

[0002] In recent years, due to the increasing shortage of non-renewable energy and the burning of large amounts of fossil fuels, serious environmental pollution has occurred. Therefore, it is urgent to seek new environmentally friendly and renewable resources. At present, new energy sources such as photovoltaics are rapidly developing from supplementary power sources to main power sources. When photovoltaics are connected to the grid, photovoltaic inverters are generally used.

[0003] The topology of existing photovoltaic converters is as follows: Figure 1 As shown, Figure 1 In the figure, PV is the photovoltaic DC power supply of the photovoltaic solar panel, C1 is a capacitor, L1 is an inductor, Q1 is an insulated gate bipolar transistor (hereinafter referred to as IGBT), and D1 is a diode, which constitutes a DC-DC BOOST boost circuit; when Q1 switches at a certain frequency, the L1 inductor stores energy and boosts the voltage, raising the PV voltage, which is unidirectionally conducted through the D1 diode to prevent current backflow. C2 and C3 are bus capacitors for filtering and energy storage. In the DC-AC circuit on the AC side, Q3, Q4, Q7, Q8, Q11, and Q12 are IGBTs of the inverter circuit. Figure 1 In the figure, there is a two-level inverter topology. Q3 and Q4 convert DC power into three-phase A-phase power, Q7 and Q8 convert DC power into three-phase B-phase power, and Q11 and Q12 convert DC power into three-phase C-phase power, so as to realize photovoltaic grid connection.

[0004] However, with the greatly increased number of applications of photovoltaic inverters, the harmonics and noise generated by existing photovoltaic inverters have become an increasingly serious burden on the power grid. The resulting grid harmonic disturbances and oscillation problems have caused the potential in some areas to rise above the prescribed level. In addition, the three-phase imbalance has also caused continuous turbulence in the power grid. Harmonic noise interference has seriously affected the clean energy of the power grid. If these phenomena are not standardized and serious, they may even cause the power grid to collapse, which in turn seriously endangers the safe and stable operation of the power system. Utility Model Content

[0005] The purpose of the present application is to solve at least one of the above-mentioned technical defects, especially the technical defect of photovoltaic converters in the prior art that affects the safe and stable operation of the power system.

[0006] The present application provides a novel series topology photovoltaic converter, which includes a common-mode inductor, a BOOST boost circuit and an inverter circuit connected in sequence on a DC bus between a photovoltaic DC power supply and a three-phase AC power supply;

[0007] The BOOST boost circuit includes two IGBTs connected in series and a first power inductor connected in series with the midpoints of the two IGBTs, and the first power inductor is connected to the neutral point of the inverter circuit;

[0008] The inverter circuit includes a T-type three-level topology structure.

[0009] Optionally, two bus capacitors connected in series are provided between the BOOST boost circuit and the inverter circuit.

[0010] Optionally, the BOOST boost circuit further includes a first capacitor, a second power inductor and two diodes;

[0011] Wherein, the first capacitor and the two IGBTs connected in series are sequentially arranged between the positive bus and the negative bus of the DC bus;

[0012] The second power inductor is arranged between the first capacitor and two IGBTs connected in series, and is located on the positive busbar of the DC busbar;

[0013] The two diodes are arranged between the two IGBTs connected in series and the two bus capacitors connected in series.

[0014] Optionally, the working process of the BOOST boost circuit is:

[0015] When the IGBT close to the photovoltaic DC power supply is turned on and the IGBT far from the photovoltaic DC power supply is turned off, the current flows from the positive electrode of the photovoltaic DC power supply through the common-mode inductor to the second power inductor, and flows to the neutral point of the inverter circuit through the IGBT close to the photovoltaic DC power supply and the first power inductor;

[0016] When the IGBT close to the photovoltaic DC power supply is turned off and the IGBT far from the photovoltaic DC power supply is turned on, the current flows from the neutral point of the inverter circuit to the first power inductor, and flows back to the negative electrode of the photovoltaic DC power supply through the IGBT far from the photovoltaic DC power supply and the common-mode inductor.

[0017] Optionally, one of the diodes is arranged on the positive busbar of the DC busbar to prevent the output current of the photovoltaic DC power supply from flowing back;

[0018] Another diode is arranged on the negative busbar of the DC busbar, and is used to prevent the two busbar capacitors connected in series from discharging to the negative electrode of the photovoltaic DC power supply.

[0019] Optionally, the T-type three-level topology structure has three groups, and each group is respectively connected to one phase of the three-phase AC power supply.

[0020] Optionally, each group of T-type three-level topology structures consists of a first IGBT, a second IGBT, a third IGBT and a fourth IGBT;

[0021] The first IGBT and the second IGBT are connected in series laterally, the third IGBT and the fourth IGBT are connected in series longitudinally, the second IGBT and the third IGBT are close to each other and complement each other, and the first IGBT and the fourth IGBT are far from each other and complement each other.

[0022] Optionally, the first IGBTs in each group of T-type three-level topology structures are respectively connected to the neutral point;

[0023] The second IGBT in each group of T-type three-level topological structures is connected to each phase of the AC power supply respectively.

[0024] Optionally, the third IGBT in each group of T-type three-level topology structures is connected to the positive bus of the DC bus;

[0025] The fourth IGBT in each group of T-type three-level topological structures is connected to the negative bus of the DC bus.

[0026] Optionally, the inverter circuit also includes an LCL filter capacitor.

[0027] It can be seen from the above technical solutions that the embodiments of the present application have the following advantages:

[0028] The present application provides a novel series topology photovoltaic converter, which includes a common-mode inductor, a BOOST boost circuit and an inverter circuit connected in sequence on a DC bus between a photovoltaic DC power supply and a three-phase AC power supply; since the common-mode inductor adopts a reverse winding method in which two coils are wound on the same iron core with the same number of turns and phase, when the normal current in the circuit flows through the common-mode inductor, the current generates a reverse magnetic field in the inductor coil wound in the same phase and cancels each other out, and the current is mainly affected by the coil resistance and a small amount of damping caused by leakage inductance; when a common-mode current flows through the coil, due to the isotropy of the common-mode current, a magnetic field in the same direction will be generated in the coil to increase the inductive reactance of the coil, so that the coil exhibits a high impedance and produces a strong damping effect, thereby attenuating the common-mode current to achieve the purpose of filtering, and can greatly enhance the filtering ability of the photovoltaic current and suppress leakage current; further, the BOOST boost circuit of the present application includes two series-connected IGBTs and a first power inductor connected in series with the midpoint of the two IGBTs, and the first power inductor is connected to the neutral point of the inverter circuit; this Thus, when two IGBTs in series are used alternately, the potential of the neutral line N can be kept unchanged; and, compared with a single IGBT, the series connection can not only maintain the same boost effect, but also reduce the original frequency of use by half, or increase the same frequency to twice the original frequency, thereby suppressing the ripple effect to half of the original or even lower; in addition, the midpoint of the two IGBTs in series and the neutral point of the inverter circuit are connected together. When the three-phase oscillation is unbalanced, current will flow between the two. For example, when the potential at point N is low, the duty cycle of one of the IGBTs can be appropriately adjusted to increase and the duty cycle of the other IGBT can be reduced for charging; when the potential at point N is high, the duty cycle of one of the IGBTs can be appropriately adjusted to reduce and the duty cycle of the other IGBT can be increased for discharge; the first power inductor in the middle series can use its property that the current cannot change suddenly to mitigate the current fluctuation, and feedback the imbalance by sampling the current size, thereby effectively adjusting the potential of the neutral line N. This method plays a great role in dealing with the three-phase imbalance effect.Furthermore, the inverter circuit of the present application includes a T-type three-level topology structure, and a neutral line N is introduced into the T-type three-level topology structure, so that the balance of the neutral line can be coordinated with the DC side to make the control more stable; and the T-type three-level topology structure adopted in the present application can not only improve the voltage level, but also obtain more orders of output voltage, which will make the output waveform closer to a sine wave, with less harmonic content, small voltage change rate, and large output capacity; in terms of loss, in each switching cycle, the two-level output is positive and negative levels, and the three-level output is positive, negative, and zero levels, so the two-level topology loss is higher; in terms of output harmonics, the more steps the three-level output level has, the closer the waveform is to a sine wave, and the fewer harmonics are brought out; in terms of switching frequency, the three-level can reduce the switching frequency and reduce switching losses; in terms of harmonic control, in conjunction with the control algorithm, the three-level topology can also absorb and control the harmonics of the power grid; in terms of operation, the three-level control is more stable and safer. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0030] Figure 1 It is a schematic diagram of the topological structure of an existing photovoltaic converter;

[0031] Figure 2 A schematic diagram of the overall structure of a novel series topology photovoltaic converter provided in an embodiment of the present application;

[0032] Figure 3 A schematic diagram of the topological structure of a photovoltaic converter with a novel series topology provided in an embodiment of the present application. DETAILED DESCRIPTION

[0033] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0034] In one embodiment, Figure 2 As shown, Figure 2A schematic diagram of the overall structure of a photovoltaic inverter with a new series topology provided in an embodiment of the present application; the present application provides a photovoltaic inverter with a new series topology, the photovoltaic inverter comprising a common-mode inductor, a BOOST boost circuit and an inverter circuit connected in sequence on a DC bus between a photovoltaic DC power supply and a three-phase AC power supply.

[0035] The BOOST boost circuit includes two IGBTs connected in series and a first power inductor connected in series with the midpoints of the two IGBTs, and the first power inductor is connected to the neutral point of the inverter circuit; the inverter circuit includes a T-type three-level topology structure.

[0036] In this embodiment, Figure 2 As shown, the present application provides a common-mode inductor, a BOOST boost circuit and an inverter circuit on the DC bus between the photovoltaic DC power supply and the three-phase AC power supply, wherein the common-mode inductor is arranged near the photovoltaic DC power supply, the inverter circuit is arranged near the three-phase AC power supply, and the BOOST boost circuit is arranged between the common-mode inductor and the inverter circuit. Since the common-mode inductor adopts a reverse winding method in which two coils are wound on the same iron core with the same number of turns and phase, when the normal current in the circuit flows through the common-mode inductor, the current generates reverse magnetic fields in the inductor coils wound in the same phase and cancel each other out. At this time, the current is mainly affected by the coil resistance and a small amount of damping caused by leakage inductance; when a common-mode current flows through the coil, due to the isotropic nature of the common-mode current, a magnetic field in the same direction will be generated in the coil, increasing the inductive reactance of the coil, making the coil exhibit high impedance and producing a strong damping effect, thereby attenuating the common-mode current and achieving the purpose of filtering, and can greatly enhance the filtering ability of the photovoltaic current and suppress leakage current; in addition, the present application can also achieve the purpose of boosting through a BOOST boost circuit, and convert the DC power output by the intermediate DC circuit into an AC power supply with arbitrarily adjustable frequency and voltage through an inverter circuit.

[0037] Specifically, the BOOST boost circuit of the present application includes two IGBTs connected in series and a first power inductor connected in series with the midpoint of the two IGBTs, and the first power inductor is connected to the neutral point of the inverter circuit; in this way, when the two IGBTs connected in series are used alternately, the potential of the neutral line N can be kept unchanged; and, compared with a single IGBT, the series connection can not only maintain the same boost effect, but also reduce the original frequency of use by half, or increase the same frequency to twice the original, thereby suppressing the ripple effect to half of the original or even lower; in addition, the midpoint of the two IGBTs connected in series is connected to the neutral point of the inverter circuit. When the three-phase oscillation is unbalanced, current will flow between the two. For example, when the potential at point N is low, the duty cycle of one of the IGBTs can be appropriately increased and the duty cycle of the other IGBT can be reduced for charging; when the potential at point N is high, the duty cycle of one of the IGBTs can be appropriately reduced and the duty cycle of the other IGBT can be increased for discharging; the first power inductor connected in series in the middle can use the property that its current cannot change suddenly to alleviate the current fluctuation, and feedback the imbalance condition by sampling the current size, thereby effectively adjusting the potential of the neutral line N. This method plays a great role in dealing with the three-phase imbalance effect.

[0038] Furthermore, the inverter circuit of the present application includes a T-type three-level topology structure, and a neutral line N is introduced into the T-type three-level topology structure, so that the balance of the neutral line can be coordinated with the DC side to make the control more stable; and the T-type three-level topology structure adopted in the present application can not only improve the voltage level, but also obtain more orders of output voltage, which will make the output waveform closer to a sine wave, with less harmonic content, small voltage change rate, and large output capacity; in terms of loss, in each switching cycle, the two-level output is positive and negative levels, and the three-level output is positive, negative, and zero levels, so the two-level topology loss is higher; in terms of output harmonics, the more steps the three-level output level has, the closer the waveform is to a sine wave, and the fewer harmonics are brought out; in terms of switching frequency, the three-level can reduce the switching frequency and reduce switching losses; in terms of harmonic control, in conjunction with the control algorithm, the three-level topology can also absorb and control the harmonics of the power grid; in terms of operation, the three-level control is more stable and safer.

[0039] In one embodiment, Figure 3 As shown, Figure 3 A schematic diagram of the topological structure of a photovoltaic converter with a novel series topology provided in an embodiment of the present application; two bus capacitors connected in series are arranged between the BOOST boost circuit and the inverter circuit.

[0040] In this embodiment, Figure 3As shown, two bus capacitors C2 and C3 are connected in series between the BOOST boost circuit and the inverter circuit, and the two bus capacitors C2 and C3 are set between the positive bus and the negative bus of the DC bus. It can be understood that in order for the active power filter to work properly and achieve the expected compensation effect, the DC side must have a sufficiently high capacitor voltage and maintain stability to ensure that the required compensation current can be output according to the control requirements at any moment of dynamic compensation.

[0041] In one embodiment, the BOOST voltage-boosting circuit further includes a first capacitor, a second power inductor and two diodes.

[0042] The first capacitor and the two IGBTs connected in series are sequentially arranged between the positive bus and the negative bus of the DC bus.

[0043] The second power inductor is arranged between the first capacitor and two IGBTs connected in series, and is located on the positive busbar of the DC busbar.

[0044] The two diodes are arranged between the two IGBTs connected in series and the two bus capacitors connected in series.

[0045] In this embodiment, the BOOST boost circuit of the present application includes not only two IGBTs connected in series and a first power inductor connected in series with the midpoint of the two IGBTs, but also a first capacitor, a second power inductor and two diodes. The first capacitor and the two IGBTs connected in series are sequentially arranged between the positive bus and the negative bus of the DC bus, the second power inductor is arranged between the first capacitor and the two IGBTs connected in series, and is located on the positive bus of the DC bus, and the two diodes are arranged between the two IGBTs connected in series and the two bus capacitors connected in series.

[0046] Specifically, Figure 3As shown, the first capacitor of the present application is C1, the second power inductor is L2, the two IGBTs connected in series are Q1 and Q2, the two diodes are D1 and D2, and the first power inductor is L3. Since IGBT is a voltage-driven device, as long as a certain voltage is given to the G pole, a certain voltage difference exists between GS, and VGS>VGS(th) is used, the IGBT tube can be turned on. In addition, the present application can also give PWM a square wave of a certain frequency, so that Q1 and Q2 are turned on and controlled in turn. When the IGBT switches from the off state to the on state, the current flows from PV+ to L2, passes through Q1 and Q2, and then flows back to the negative electrode. Almost all the photovoltaic power supply is given to the inductor L2, the inductor stores energy, and C2 and C3 associated with the load discharge. The unidirectional conduction property of the diode D2 prevents C2 and C3 from discharging to PV-; when the IGBT switches from the on state to the off state, the current flows from PV+ to L2, passes through D1, and then flows back to the negative electrode after passing through the load. Since the inductor is an energy storage element, the current cannot change suddenly, so when the IGBT is disconnected, the inductor releases energy to the outside world. In this process, the voltage of the load must be greater than the input voltage, thereby achieving the purpose of boosting.

[0047] In one embodiment, the working process of the BOOST boost circuit is:

[0048] When the IGBT close to the photovoltaic DC power supply is turned on and the IGBT far from the photovoltaic DC power supply is turned off, the current flows from the positive electrode of the photovoltaic DC power supply through the common-mode inductor to the second power inductor, and flows to the neutral point of the inverter circuit through the IGBT close to the photovoltaic DC power supply and the first power inductor.

[0049] When the IGBT close to the photovoltaic DC power supply is turned off and the IGBT far from the photovoltaic DC power supply is turned on, the current flows from the neutral point of the inverter circuit to the first power inductor, and flows back to the negative electrode of the photovoltaic DC power supply through the IGBT far from the photovoltaic DC power supply and the common-mode inductor.

[0050] In this embodiment, the BOOST boost circuit is composed of a first capacitor C1, a second power inductor L2, two IGBTs Q1 and Q2 connected in series, two diodes D1 and D2, and a first power inductor L3, so that after a square wave of a certain frequency is given to PWM, Q1 and Q2 can be turned on and controlled in turn. For example, when Q1 is turned on, Q2 is turned off, and the current flows to the neutral line N. When Q1 is turned off, Q2 is turned on and the current flows back to PV- from the neutral line; when a certain frequency is reached, Q1 and Q2 are used alternately to keep the potential of the neutral line N unchanged. Compared with a single IGBT, the series connection can reduce the original frequency by half to maintain the same boost effect, or increase the same frequency to twice the original, suppressing the ripple effect to half of the original or even lower. In addition, the present application connects the midpoint of the series connection and the neutral point of the inverter circuit together. When the three-phase oscillation is unbalanced, current will flow between the two. Specifically, when the potential at point N is low, the duty cycle of Q1 can be appropriately adjusted to increase and the duty cycle of Q2 can be reduced for charging; when the potential at point N is high, the duty cycle of Q1 can be appropriately adjusted to reduce and the duty cycle of Q2 can be increased for discharging; the inductor connected in series in the middle can also use its property that the current cannot change suddenly to alleviate the current fluctuation, and the imbalance condition can be fed back by sampling the current size, thereby effectively adjusting the potential of the neutral line N, which plays a great role in dealing with the three-phase imbalance effect.

[0051] In one embodiment, one of the diodes is disposed on the positive busbar of the DC busbar to prevent the output current of the photovoltaic DC power source from flowing back.

[0052] Another diode is arranged on the negative busbar of the DC busbar, and is used to prevent the two busbar capacitors connected in series from discharging to the negative electrode of the photovoltaic DC power supply.

[0053] In this embodiment, Figure 3 As shown, the BOOST boost circuit of the present application includes two diodes, one of which is arranged on the positive bus of the DC bus to prevent the output current of the photovoltaic DC power supply from flowing back, and the other diode is arranged on the negative bus of the DC bus to prevent the two bus capacitors connected in series from discharging the negative electrode of the photovoltaic DC power supply, thereby protecting the circuit.

[0054] In one embodiment, the T-type three-level topology structure has three groups, and each group is respectively connected to one phase of the three-phase AC power supply.

[0055] In this embodiment, the inverter circuit can adopt a T-type three-level topology structure. In order to correspond to the three-phase AC power supply, the present application can set three groups of T-type three-level topology structures, each group is connected to one phase of the three-phase AC power supply.

[0056] It can be understood that the two-level inverter circuit controls the alternating conduction state of the IGBTs of the upper bridge and the lower bridge, so that three-phase AC with a phase difference of 120° is obtained on the output terminals A, B, and C. The present application adopts a T-type three-level topology structure, which can not only improve the voltage level, but also obtain more orders of output voltage, which will make the output waveform closer to a sine wave, with less harmonic content, small voltage change rate, and large output capacity.

[0057] In one embodiment, each group of T-type three-level topology structures consists of a first IGBT, a second IGBT, a third IGBT and a fourth IGBT.

[0058] The first IGBT and the second IGBT are connected in series laterally, the third IGBT and the fourth IGBT are connected in series longitudinally, the second IGBT and the third IGBT are close to each other and complement each other, and the first IGBT and the fourth IGBT are far from each other and complement each other.

[0059] In this embodiment, Figure 3 As shown, each group of T-type three-level topology consists of a first IGBT, a second IGBT, a third IGBT and a fourth IGBT. That is, the first group of T-type three-level topology consists of Q3-Q6, the second group of T-type three-level topology consists of Q7-Q10, and the third group of T-type three-level topology consists of Q11-Q14. Among them, Q5 and Q6 are connected in series horizontally, Q3 and Q4 are connected in series vertically, and Q3 and Q5 are complementary, and Q4 and Q6 are complementary; Q9 and Q10 are connected in series horizontally, Q7 and Q8 are connected in series vertically, and Q7 and Q9 are complementary, and Q8 and Q10 are complementary; Q14 and Q15 are connected in series horizontally, Q11 and Q12 are connected in series vertically, and Q11 and Q13 are complementary, and Q12 and Q14 are complementary.

[0060] In one embodiment, the first IGBTs in each group of T-type three-level topology structures are respectively connected to the neutral point; and the second IGBTs in each group of T-type three-level topology structures are respectively connected to each phase of the AC power supply.

[0061] In this embodiment, Figure 3 As shown, the first IGBT in each group of T-type three-level topology structures is connected to the neutral point, so that when the three-phase oscillation is unbalanced, current will flow between the two series-connected IGBTs in the BOOST boost circuit and the neutral point in the inverter circuit. The second IGBT in each group of T-type three-level topology structures is connected to each phase of the AC power supply to convert the DC power output by the intermediate DC circuit into a three-phase AC power supply with arbitrarily adjustable frequency and voltage.

[0062] In one embodiment, the third IGBT in each group of T-type three-level topology structures is connected to the positive busbar of the DC busbar; and the fourth IGBT in each group of T-type three-level topology structures is connected to the negative busbar of the DC busbar.

[0063] In one embodiment, the inverter circuit further includes an LCL filter capacitor. Compared with the L filter, the LCL filter capacitor increases the filter inductance and filter capacitance, which effectively reduces the high-frequency content of the grid current. In addition, the connection method of the LCL filter capacitor in the present application can refer to the method of setting the LCL filter capacitor in the inverter circuit in the prior art, and is not limited here.

[0064] Finally, it should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0065] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The various embodiments can be combined as needed, and the same or similar parts can refer to each other.

[0066] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A novel series topology photovoltaic converter, characterized in that: The photovoltaic converter includes a common mode inductor, a BOOST boost circuit and an inverter circuit connected in sequence on a DC bus between a photovoltaic DC power supply and a three-phase AC power supply; The BOOST boost circuit includes two IGBTs connected in series and a first power inductor connected in series with the midpoints of the two IGBTs, and the first power inductor is connected to the neutral point of the inverter circuit; The inverter circuit includes a T-type three-level topology structure.

2. The novel series topology photovoltaic converter according to claim 1 is characterized in that: Two bus capacitors connected in series are arranged between the BOOST voltage-boosting circuit and the inverter circuit.

3. The novel series topology photovoltaic converter according to claim 2 is characterized in that: The BOOST boost circuit also includes a first capacitor, a second power inductor and two diodes; Wherein, the first capacitor and the two IGBTs connected in series are sequentially arranged between the positive bus and the negative bus of the DC bus; The second power inductor is arranged between the first capacitor and two IGBTs connected in series, and is located on the positive busbar of the DC busbar; The two diodes are arranged between the two IGBTs connected in series and the two bus capacitors connected in series.

4. The novel series topology photovoltaic converter according to claim 3 is characterized in that: When the IGBT close to the photovoltaic DC power source is turned on and the IGBT far from the photovoltaic DC power source is turned off, the current flow direction of the photovoltaic converter is: The current flows from the positive electrode of the photovoltaic DC power supply to the second power inductor through the common mode inductor, and flows to the neutral point of the inverter circuit through the IGBT close to the photovoltaic DC power supply and the first power inductor; When the IGBT close to the photovoltaic DC power source is turned off and the IGBT far from the photovoltaic DC power source is turned on, the current flow direction of the photovoltaic converter is: The current flows from the neutral point of the inverter circuit to the first power inductor, and flows back to the negative electrode of the photovoltaic DC power supply through the IGBT far away from the photovoltaic DC power supply and the common mode inductor.

5. The novel series topology photovoltaic converter according to claim 3 is characterized in that: One of the diodes is arranged on the positive busbar of the DC busbar, and is used to prevent the output current of the photovoltaic DC power supply from flowing back; Another diode is arranged on the negative busbar of the DC busbar, and is used to prevent the two busbar capacitors connected in series from discharging to the negative electrode of the photovoltaic DC power supply.

6. The novel series topology photovoltaic converter according to any one of claims 1 to 5, characterized in that: The T-type three-level topology structure has three groups, and each group is connected to one phase of the three-phase AC power supply.

7. The novel series topology photovoltaic converter according to claim 6, characterized in that: Each group of T-type three-level topology structures consists of a first IGBT, a second IGBT, a third IGBT and a fourth IGBT; The first IGBT and the second IGBT are connected in series laterally, the third IGBT and the fourth IGBT are connected in series longitudinally, the second IGBT and the third IGBT are close to each other and complement each other, and the first IGBT and the fourth IGBT are far from each other and complement each other.

8. The novel series topology photovoltaic converter according to claim 7, characterized in that: The first IGBT in each group of T-type three-level topology structures is connected to the neutral point respectively; The second IGBT in each group of T-type three-level topological structures is connected to each phase of the AC power supply respectively.

9. The novel series topology photovoltaic converter according to claim 7, characterized in that: The third IGBT in each group of T-type three-level topological structures is connected to the positive bus of the DC bus; The fourth IGBT in each group of T-type three-level topological structures is connected to the negative bus of the DC bus.

10. The novel series topology photovoltaic converter according to claim 1, characterized in that: The inverter circuit also includes an LCL filter capacitor.

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