A topology of a photovoltaic inverter with wide input and medium-high voltage ac output

Abstract

The application is a kind of topology structure of photovoltaic inverter with wide input and medium-high voltage AC output. The application relates to the technical field of power system, high-voltage power grid and photovoltaic power generation system, and the structure comprises a photovoltaic group string, a multi-path LLC resonant multi-level half-bridge circuit and a multi-cascade H-bridge half-bridge multi-level circuit. The photovoltaic group string is connected to the multi-path LLC resonant multi-level half-bridge circuit, the multi-path LLC resonant multi-level half-bridge circuit is connected to the multi-cascade H-bridge half-bridge multi-level circuit, and the multi-cascade H-bridge half-bridge multi-level circuit is connected to three phases of A, B and C respectively. The application can improve the voltage level of DC input and AC output of the photovoltaic inverter under the condition of the existing voltage level of power device, reduce the power loss on the circuit and cable line, improve the power generation efficiency of the whole photovoltaic system, reduce the number of power devices in the circuit by half, and reduce the investment cost of the power devices of the photovoltaic inverter.

Description

Technical Field

[0001] This invention relates to the fields of power systems, medium and high voltage power grids, and photovoltaic power generation systems, and is a topology of a photovoltaic inverter with wide input and medium and high voltage AC output. Background Technology

[0002] With my country's increasing emphasis on carbon emissions, the share of renewable energy generation in the country's annual new power generation is constantly rising. As a renewable energy source, solar energy boasts advantages such as abundant reserves, inexhaustible resources, and no geographical limitations, and is widely considered a new energy source capable of effectively replacing conventional fossil fuels in the future. Currently, reducing the initial investment cost of photovoltaic (PV) power generation systems and improving their operating efficiency are important research directions in the field of solar power generation. Most mainstream PV inverters now employ Maximum Power Point Tracking (MPPT) technology to control the DC / DC converter directly connected to the PV string, achieving full utilization of solar energy and enabling the PV string to convert solar energy into output electrical energy to the maximum extent possible.

[0003] Currently, the input voltage of photovoltaic (PV) inverters in solar photovoltaic (PV) power plants is generally below 820V, and the output voltage is mostly a low-voltage system of 270V or 315V. To increase the output power of a PV system, multiple inverters must be connected in parallel. However, due to limitations in the voltage rating of power devices, it's difficult to increase the output voltage of PV inverters. To increase the PV power generation capacity, the current must be increased by connecting inverters in parallel. This results in very high current flowing through the power components of the inverter when a large-capacity PV power generation system operates at full power or even under overload conditions. This leads to excessively high switching stress on the devices, high circuit losses, and strong electromagnetic interference, affecting system stability. Furthermore, the high current rating complicates the selection of switching equipment and cables for the PV power plant, increasing the investment cost in these components.

[0004] To improve the voltage level of photovoltaic inverters, given the limitations of existing power device voltage levels, photovoltaic inverter circuit topologies often employ cascaded single-phase H-type full-bridge circuits. However, while the single-phase H-type full-bridge circuit has a simple structure, it uses a large number of power devices, indirectly increasing the investment cost of photovoltaic power generation systems and hindering the application of cascaded circuit topologies in photovoltaic power generation systems.

[0005] Furthermore, while using a single-phase H-type full-bridge circuit cascade method to improve the inverter's output voltage level is simple in circuit structure and relatively easy to control, the power generation of each photovoltaic string is difficult to keep consistent, resulting in different power generation of each phase of the photovoltaic inverter. This can easily generate circulating current inside the photovoltaic inverter, affecting its operating efficiency and stability. Summary of the Invention

[0006] This invention aims to increase the DC input and AC output voltage levels of photovoltaic inverters under the limitations of existing power device voltage levels, thereby reducing power losses in circuits and cables and improving the overall power generation efficiency of the photovoltaic system. This invention provides a topology for a photovoltaic inverter with wide input voltage and medium-to-high voltage AC output. The invention offers the following technical solutions:

[0007] A topology for a photovoltaic inverter with wide input and medium-high voltage AC output is disclosed. The topology includes: a photovoltaic string, a multi-channel LLC resonant multi-level half-bridge circuit, and a multi-cascaded H-bridge half-bridge multi-level circuit. The photovoltaic string is connected to the multi-channel LLC resonant multi-level half-bridge circuit, and the multi-channel LLC resonant multi-level half-bridge circuit is connected to the multi-cascaded H-bridge half-bridge multi-level circuit. The multi-cascaded H-bridge half-bridge multi-level circuit is connected to phases A, B, and C respectively.

[0008] Preferably, the photovoltaic string includes a first photovoltaic string, a second photovoltaic string, and a third photovoltaic string; the multi-channel LLC resonant multilevel half-bridge circuit includes a first LLC resonant multilevel half-bridge circuit, a second LLC resonant multilevel half-bridge circuit, and a third LLC resonant multilevel half-bridge circuit.

[0009] The first LLC resonant multilevel half-bridge circuit includes diode D. 1a Capacitor C 1a Capacitor C 2a diode D 2a diode D 3a Capacitor C 3a Switching transistor Q 1a Switching transistor Q 2a Switching transistor Q 3a Switching transistor Q 4a diode D 4a diode D 5a diode D 6a diode D 7a Inductor L ra Capacitor C ra、 Inductor L ma and mutual inductance coil T a ;

[0010] One end of the first photovoltaic string is connected to diode D. 1a One end of the diode D 1a The other end is connected to capacitor C. 1a Switching transistor Q 1a and diode D 4a One end of the capacitor C 1a The other end is connected to capacitor C. 2a and capacitor C raOne end of the capacitor C 2a The other end is connected to the other end of the first photovoltaic string and the switch Q. 4a and diode D 7a One end;

[0011] The switching transistor Q 1a and diode D 4a The other end is connected to diode D 2a Capacitor C 3a Switching transistor Q 2a and diode D 5a One end, the switching transistor Q 2a and diode D 5a The other end is connected to inductor L ra Switching transistor Q 3a and diode D 6a One end, diode D 2a The other end is connected to diode D 3a One end of the diode D 3a The other end is connected to capacitor C. 3a Switching transistor Q 3a diode D 6a Switching transistor Q 4a and diode D 7a The other end; the inductor L ra The other end is connected to inductor L ma and mutual inductance coil T a One end of the primary coil, inductance L ma and mutual inductance coil T a The other end of the primary coil is connected to a capacitor C. ra The other end.

[0012] Preferably, the first LLC resonant multilevel half-bridge circuit, the second LLC resonant multilevel half-bridge circuit, and the third LLC resonant multilevel half-bridge circuit have the same structure, and the connection methods of the second photovoltaic string and the third photovoltaic string with the second LLC resonant multilevel half-bridge circuit and the third LLC resonant multilevel half-bridge circuit are the same as the connection methods of the first photovoltaic string with the first LLC resonant multilevel half-bridge circuit.

[0013] Preferably, the multi-cascaded H-bridge half-bridge multilevel circuit includes a first-cascaded H-bridge half-bridge multilevel circuit, a second-cascaded H-bridge half-bridge multilevel circuit, and a third-cascaded H-bridge half-bridge multilevel circuit.

[0014] The first cascaded H-bridge half-bridge multilevel circuit includes: diode D 8a diode D 9a Capacitor C 4a Switching transistor Q 5a Switching transistor Q6a Switching transistor Q 7a Switching transistor Q 8a Switching transistor Q 9a Switching transistor Q 10a Switching transistor Q 11a Switching transistor Q 12a Switching transistor Q 13a Switching transistor Q 14a Switching transistor Q 15a Switching transistor Q 16a Switching transistor Q 17a Switching transistor Q 18a Switching transistor Q 19a Switching transistor Q 20a diode D 10a diode D 11a diode D 12a diode D 13a diode D 14a diode D 15a diode D 16a diode D 17a diode D 18a diode D 19a diode D 20a diode D 21a diode D 22a diode D 23a diode D 24a diode D 25a diode D 26a diode D 27a diode D 28a diode D 29a diode D 30a diode D 31a Capacitor C 5a and capacitor C 6a ;

[0015] Mutual inductance coil T a One end of the secondary coil is connected to the switching transistor Q. 6a and switching transistor Q 7a One end, mutual inductance coil T a The other end of the secondary coil is connected to diode D. 8a diode D 9a Capacitor C 6a diode D 15a diode D 18a and diode D 24a One end;

[0016] Diode D 8a The other end is connected to capacitor C. 4a Switching transistor Q6a and switching transistor Q 5a One end of the capacitor C 4a The other end is connected to diode D 9a and switching transistor Q 7a At the other end, the switching transistor Q 7a The other end is connected to the switching transistor Q. 8a One end;

[0017] The switching transistor Q 5a The other end is connected to the switching transistor Q. 9a Capacitor C 5a Switching transistor Q 13a and switching transistor Q 17a One end, capacitor C 5a The other end is connected to capacitor C 6a One end, the switching transistor Q 9a The other end is connected to the switching transistor Q. 10a and diode D 14a One end of the diode D 14a The other end is connected to diode D 15a One end, the switching transistor Q 10a The other end is connected to the switching transistor Q. 11a One end;

[0018] Switching transistor Q 13a The other end is connected to diode D 20a and switching transistor Q 14a One end, diode D 20a The other end is connected to diode D 21a One end, the switching transistor Q 14a The other end is connected to the switching transistor Q. 15a One end;

[0019] Switching transistor Q 17a The other end is connected to diode D 26a and switching transistor Q 18a One end, diode D 26a The other end is connected to diode D. 27a One end, the switching transistor Q 18a The other end is connected to the switching transistor Q. 19a One end;

[0020] The switching transistor Q 8a The other end is connected to the switching transistor Q. 12a Switching transistor Q 16a and switching transistor Q 20a One end; switching transistor Q 12a The other end is connected to diode D 15a and switching transistor Q 11a At the other end, the switching transistor Q 16aThe other end is connected to diode D 21a and switching transistor Q 15a At the other end, the switching transistor Q 20a The other end is connected to diode D 27a and switching transistor Q 19a The other end;

[0021] Switching transistor Q 10a The other end is connected to phase A inductor L a .

[0022] Preferably, diode D 10a diode D 11a diode D 12a diode D 13a diode D 16a diode D 17a diode D 18a diode D 19a diode D 22a diode D 23a diode D 24a diode D 25a diode D 28a diode D 29a diode D 30a and diode D 31a These are the switching transistors Q and Q. 5a Switching transistor Q 6a Switching transistor Q 7a Switching transistor Q 8a Switching transistor Q 9a Switching transistor Q 10a Switching transistor Q 11a Switching transistor Q 12a Switching transistor Q 13a Switching transistor Q 14a Switching transistor Q 15a Switching transistor Q 16a Switching transistor Q 17a Switching transistor Q 18a Switching transistor Q 19a and switching transistor Q 20a Transistors.

[0023] Preferably, the first cascaded H-bridge half-bridge multilevel circuit, the second cascaded H-bridge half-bridge multilevel circuit, and the third cascaded H-bridge half-bridge multilevel circuit have the same structural connection method.

[0024] Preferably, the switching transistor Q in the first cascaded H-bridge half-bridge multilevel circuit 14a The other end is connected to the switching transistor Q in the second cascaded H-bridge half-bridge multilevel circuit. 10b The other end; the switching transistor Q in the second cascaded H-bridge half-bridge multilevel circuit18b The other end is connected to the switching transistor Q in the second cascaded H-bridge half-bridge multilevel circuit. 14c The other end.

[0025] The present invention has the following beneficial effects:

[0026] This invention, under the limitations of existing power device voltage levels, increases the DC input and AC output voltage levels of photovoltaic inverters, reduces power losses in circuits and cables, and improves the overall power generation efficiency of the photovoltaic system. It also reduces the number of power devices in the circuit by half, lowering the initial investment cost of photovoltaic inverter power devices; and reduces DC transmission current, AC output current, and the cross-sectional area of ​​power station cables, thus reducing the cost of photovoltaic power station switching equipment and transmission cables. This effectively improves the operating efficiency of photovoltaic power stations and reduces initial investment costs. Furthermore, the use of a three-phase multi-level circuit cascade effectively achieves power balance among the three phases of the photovoltaic inverter, improving the stability and reliability of photovoltaic inverter operation.

[0027] This invention employs an LLC resonant multilevel half-bridge circuit to effectively improve the input voltage range of the photovoltaic string. When using conventional 1200V power devices in current photovoltaic power plants, it can withstand a maximum DC input voltage of 1600V, effectively increasing the input voltage range of the photovoltaic inverter. Furthermore, the LLC resonant multilevel half-bridge circuit transforms the unstable output voltage of the photovoltaic string into a stable DC bus voltage, supplying the subsequent multilevel three-phase half-bridge circuit. The subsequent cascaded H-bridge half-bridge multilevel circuit inverts the stable DC voltage converted by the LLC resonant multilevel half-bridge circuit into AC voltage. Through cascading, the subsequent multilevel three-phase half-bridge circuits increase the output voltage level of the photovoltaic inverter. When using conventional 1200V power devices in current photovoltaic power plants, a maximum AC output voltage of 3400V can be achieved.

[0028] Since the LLC resonant multilevel half-bridge circuit proposed in this patent uses a half-bridge structure LLC resonant soft-switching multilevel circuit and a three-phase half-bridge multilevel circuit, it can save half the number of power devices compared with the traditional full-bridge circuit photovoltaic inverter topology, thus significantly reducing the cost of photovoltaic inverters.

[0029] Furthermore, since the three-phase half-bridge multilevel circuits of phases A, B, and C are connected together in a cascaded manner, the power output of each phase is provided by the photovoltaic strings of the three phases, thereby achieving power balance among the three phases of the photovoltaic inverter, eliminating the circulating current caused by the power imbalance of the photovoltaic strings among the three phase outputs of the inverter, and improving the reliability of the photovoltaic inverter.

[0030] This patent significantly improves the input and output voltage levels of photovoltaic (PV) power generation systems under the limitations of existing power device voltage ratings. It reduces the DC transmission current from the combiner box to the inverter and the AC output current of the PV inverter while maintaining the same PV power output, thus lowering the cost of PV power plant switching equipment. The reduced current transmission through cables within the power plant allows for a smaller cross-sectional area of ​​the cables, thereby reducing cable costs and losses. Therefore, adopting this patented solution can significantly reduce the initial investment cost of PV power plants and improve their power generation efficiency. Attached Figure Description

[0031] Figure 1 A topology block diagram of a low-cost photovoltaic inverter with wide input and medium-to-high voltage AC output. Detailed Implementation

[0032] The present invention will be described in detail below with reference to specific embodiments. Specific Implementation Example 1:

[0034] according to Figure 1 As shown, the present invention provides a topology for a photovoltaic inverter with wide input and medium-high voltage AC output. The structure includes: a photovoltaic string, a multi-channel LLC resonant multi-level half-bridge circuit, and a multi-cascaded H-bridge half-bridge multi-level circuit. The photovoltaic string is connected to the multi-channel LLC resonant multi-level half-bridge circuit, the multi-channel LLC resonant multi-level half-bridge circuit is connected to the multi-cascaded H-bridge half-bridge multi-level circuit, and the multi-cascaded H-bridge half-bridge multi-level circuit is connected to phases A, B, and C respectively.

[0035] The photovoltaic string includes a first photovoltaic string, a second photovoltaic string, and a third photovoltaic string; the multi-channel LLC resonant multilevel half-bridge circuit includes a first LLC resonant multilevel half-bridge circuit, a second LLC resonant multilevel half-bridge circuit, and a third LLC resonant multilevel half-bridge circuit.

[0036] The first LLC resonant multilevel half-bridge circuit includes diode D. 1a Capacitor C 1a Capacitor C 2a diode D 2a diode D 3a Capacitor C 3a Switching transistor Q 1a Switching transistor Q 2a Switching transistor Q 3a Switching transistor Q 4a diode D 4a diode D 5a diode D 6a diode D 7a Inductor L ra Capacitor Cra、 Inductor L ma and mutual inductance coil T a ;

[0037] One end of the first photovoltaic string is connected to diode D. 1a One end of the diode D 1a The other end is connected to capacitor C. 1a Switching transistor Q 1a and diode D 4a One end of the capacitor C 1a The other end is connected to capacitor C. 2a and capacitor C ra One end of the capacitor C 2a The other end is connected to the other end of the first photovoltaic string and the switch Q. 4a and diode D 7a One end;

[0038] The switching transistor Q 1a and diode D 4a The other end is connected to diode D 2a Capacitor C 3a Switching transistor Q 2a and diode D 5a One end, the switching transistor Q 2a and diode D 5a The other end is connected to inductor L ra Switching transistor Q 3a and diode D 6a One end, diode D 2a The other end is connected to diode D 3a One end of the diode D 3a The other end is connected to capacitor C. 3a Switching transistor Q 3a diode D 6a Switching transistor Q 4a and diode D 7a The other end; the inductor L ra The other end is connected to inductor L ma and mutual inductance coil T a One end of the primary coil, inductance L ma and mutual inductance coil T a The other end of the primary coil is connected to a capacitor C. ra The other end.

[0039] The first LLC resonant multilevel half-bridge circuit, the second LLC resonant multilevel half-bridge circuit, and the third LLC resonant multilevel half-bridge circuit have the same structure. The connection methods between the second photovoltaic string and the third photovoltaic string and the second LLC resonant multilevel half-bridge circuit and the third LLC resonant multilevel half-bridge circuit are the same as the connection methods between the first photovoltaic string and the first LLC resonant multilevel half-bridge circuit.

[0040] The multi-cascaded H-bridge half-bridge multilevel circuit includes a first-cascaded H-bridge half-bridge multilevel circuit, a second-cascaded H-bridge half-bridge multilevel circuit, and a third-cascaded H-bridge half-bridge multilevel circuit.

[0041] The first cascaded H-bridge half-bridge multilevel circuit includes: diode D 8a diode D 9a Capacitor C 4a Switching transistor Q 5a Switching transistor Q 6a Switching transistor Q 7a Switching transistor Q 8a Switching transistor Q 9a Switching transistor Q 10a Switching transistor Q 11a Switching transistor Q 12a Switching transistor Q 13a Switching transistor Q 14a Switching transistor Q 15a Switching transistor Q 16a Switching transistor Q 17a Switching transistor Q 18a Switching transistor Q 19a Switching transistor Q 20a diode D 10a diode D 11a diode D 12a diode D 13a diode D 14a diode D 15a diode D 16a diode D 17a diode D 18a diode D 19a diode D 20a diode D 21a diode D 22a diode D 23a diode D 24a diode D 25a diode D 26a diode D 27a diode D 28a diode D 29a diode D 30a diode D 31a Capacitor C5a and capacitor C 6a ;

[0042] Mutual inductance coil T a One end of the secondary coil is connected to the switching transistor Q. 6a and switching transistor Q 7a One end, mutual inductance coil T a The other end of the secondary coil is connected to diode D. 8a diode D 9a Capacitor C 6a diode D 15a diode D 18a and diode D 24a One end;

[0043] Diode D 8a The other end is connected to capacitor C. 4a Switching transistor Q 6a and switching transistor Q 5a One end of the capacitor C 4a The other end is connected to diode D 9a and switching transistor Q 7a At the other end, the switching transistor Q 7a The other end is connected to the switching transistor Q. 8a One end;

[0044] The switching transistor Q 5a The other end is connected to the switching transistor Q. 9a Capacitor C 5a Switching transistor Q 13a and switching transistor Q 17a One end of the capacitor C 5a The other end is connected to capacitor C 6a One end, the switching transistor Q 9a The other end is connected to the switching transistor Q. 10a and diode D 14a One end of the diode D 14a The other end is connected to diode D 15a One end, the switching transistor Q 10a The other end is connected to the switching transistor Q. 11a One end;

[0045] Switching transistor Q 13a The other end is connected to diode D 20a and switching transistor Q 14a One end, diode D 20a The other end is connected to diode D 21a One end, the switching transistor Q 14a The other end is connected to the switching transistor Q. 15a One end;

[0046] Switching transistor Q17a The other end is connected to diode D 26a and switching transistor Q 18a One end, diode D 26a The other end is connected to diode D. 27a One end, the switching transistor Q 18a The other end is connected to the switching transistor Q. 19a One end;

[0047] The switching transistor Q 8a The other end is connected to the switching transistor Q. 12a Switching transistor Q 16a and switching transistor Q 20a One end; switching transistor Q 12a The other end is connected to diode D 15a and switching transistor Q 11a At the other end, the switching transistor Q 16a The other end is connected to diode D 21a and switching transistor Q 15a At the other end, the switching transistor Q 20a The other end is connected to diode D 27a and switching transistor Q 19a The other end;

[0048] Switching transistor Q 10a The other end is connected to phase A inductor L a .

[0049] Diode D 10a diode D 11a diode D 12a diode D 13a diode D 16a diode D 17a diode D 18a diode D 19a diode D 22a diode D 23a diode D 24a diode D 25a diode D 28a diode D 29a diode D 30a and diode D 31a These are the switching transistors Q and Q. 5a Switching transistor Q 6a Switching transistor Q 7a Switching transistor Q 8a Switching transistor Q 9a Switching transistor Q 10a Switching transistor Q 11a Switching transistor Q 12a Switching transistor Q 13a Switching transistor Q 14aSwitching transistor Q 15a Switching transistor Q 16a Switching transistor Q 17a Switching transistor Q 18a Switching transistor Q 19a and switching transistor Q 20a Transistors.

[0050] The first cascaded H-bridge half-bridge multilevel circuit, the second cascaded H-bridge half-bridge multilevel circuit, and the third cascaded H-bridge half-bridge multilevel circuit have the same structural connection method.

[0051] The switching transistor Q in the first cascaded H-bridge half-bridge multilevel circuit 14a The other end is connected to the switching transistor Q in the second cascaded H-bridge half-bridge multilevel circuit. 10b The other end; the switching transistor Q in the second cascaded H-bridge half-bridge multilevel circuit 18b The other end is connected to the switching transistor Q in the second cascaded H-bridge half-bridge multilevel circuit. 14c The other end.

[0052] Using this circuit topology, under the current condition of conventionally using 1200V power devices in photovoltaic power plants, a maximum photovoltaic string voltage input of 1600V and a maximum AC voltage level output of 3000V can be achieved. This effectively improves the input voltage range and output voltage level of the photovoltaic inverter. The front-end of the photovoltaic inverter is directly connected to the photovoltaic string, and the photovoltaic array is connected in series and parallel to increase the output voltage and power level of the photovoltaic string. The output voltage of the photovoltaic string is directly connected to the photovoltaic inverter.

[0053] The three sets of photovoltaic modules are connected to the first arms of phases A, B, and C, respectively. The first arm of each of the three phases A, B, and C, and the inductor L ra L ma Capacitor C raThe LLC resonant multilevel half-bridge circuit converts the unstable photovoltaic voltage, which fluctuates with light intensity and angle, into a stable DC voltage. It can achieve a stable DC voltage of up to 1600V using 1200V power devices. The LLC resonant multilevel half-bridge circuits in phases A, B, and C are not unique; each phase can connect to multiple photovoltaic strings, and each photovoltaic string is connected to one LLC resonant multilevel half-bridge circuit. The DC outputs of multiple LLC resonant multilevel half-bridge circuits are connected in parallel to the DC side of the subsequent three-phase half-bridge multilevel circuit. The third, fourth, and fifth arms of each of the three phases (A, B, and C) form the three-phase half-bridge multilevel circuit. Each phase's three-phase half-bridge multilevel circuit converts the DC voltage from the LLC resonant multilevel half-bridge circuit into stable AC voltage. The three-phase half-bridge multilevel circuits (phases A, B, and C) are cascaded together to increase the output voltage level of the photovoltaic inverter. The power output of each phase is provided by the three-phase photovoltaic strings, thus achieving power balance among the three phases of the photovoltaic inverter. Specifically, the fourth arm of phase A is connected to the third arm of phase B; the fifth arm of phase A is connected to the third arm of phase C; and the fifth arm of phase B is connected to the fourth arm of phase C.

[0054] Under the condition of using 1200V power devices, the maximum AC voltage output can reach 3400V, which effectively improves the output voltage level of the photovoltaic inverter. Specific Implementation Example 2:

[0056] In a photovoltaic power station, each photovoltaic string has a maximum output voltage of 1500V and a maximum output power of 26kW. In the photovoltaic inverter proposed in this patent, each photovoltaic string is connected to an LLC resonant multilevel half-bridge circuit for voltage conversion and MPPT control, stabilizing the photovoltaic output voltage to 1500V DC. Every four photovoltaic strings and their corresponding LLC resonant multilevel half-bridge circuits are connected in parallel to a three-phase half-bridge multilevel circuit. The three three-phase half-bridge multilevel circuits are cascaded together to achieve an AC output of 3000V and 300kW.

[0057] In this scheme, the LLC resonant multilevel half-bridge circuit and the three-phase half-bridge multilevel circuit are both three-level circuits. In practice, to further improve the input and output voltage levels, five-level, seven-level or even more-level circuits can be used.

[0058] Furthermore, to increase the capacity of the photovoltaic inverter, multiple photovoltaic strings can be connected in parallel. In the example provided in this patent, each phase uses four photovoltaic strings and their corresponding half-bridge LLC resonant soft-switching multilevel converter connected in parallel. If necessary, the number of photovoltaic strings connected in parallel can be further increased.

[0059] The above description is merely a preferred embodiment of a photovoltaic inverter topology with wide input and medium-high voltage AC output. The protection scope of this photovoltaic inverter topology is not limited to the above embodiments; all technical solutions falling within this conceptual framework are within the protection scope of this invention. It should be noted that for those skilled in the art, any improvements and variations made without departing from the principles of this invention should also be considered within the protection scope of this invention.

Claims

1. A topology for a photovoltaic inverter with wide input and medium-to-high voltage AC output, characterized by: The structure includes: a photovoltaic string, a multi-channel LLC resonant multi-level half-bridge circuit, and a multi-cascaded H-bridge half-bridge multi-level circuit. The photovoltaic string is connected to the multi-channel LLC resonant multi-level half-bridge circuit, and the multi-channel LLC resonant multi-level half-bridge circuit is connected to the multi-cascaded H-bridge half-bridge multi-level circuit. The multi-cascaded H-bridge half-bridge multi-level circuit is connected to phases A, B, and C respectively. The photovoltaic string includes a first photovoltaic string, a second photovoltaic string, and a third photovoltaic string; the multi-channel LLC resonant multilevel half-bridge circuit includes a first LLC resonant multilevel half-bridge circuit, a second LLC resonant multilevel half-bridge circuit, and a third LLC resonant multilevel half-bridge circuit. The first LLC resonant multilevel half-bridge circuit includes diode D. 1a Capacitor C 1a Capacitor C 2a diode D 2a diode D 3a Capacitor C 3a Switching transistor Q 1a Switching transistor Q 2a Switching transistor Q 3a Switching transistor Q 4a diode D 4a diode D 5a diode D 6a diode D 7a Inductor L ra Capacitor C ra、 Inductor L ma and mutual inductance coil T a ; One end of the first photovoltaic string is connected to diode D. 1a One end of the diode D 1a The other end is connected to capacitor C. 1a Switching transistor Q 1a and diode D 4a One end of the capacitor C 1a The other end is connected to capacitor C. 2a and capacitor C ra One end of the capacitor C 2a The other end is connected to the other end of the first photovoltaic string and the switch Q. 4a and diode D 7a One end; The switching transistor Q 1a and diode D 4a The other end is connected to diode D 2a Capacitor C 3a Switching transistor Q 2a and diode D 5a One end, the switching transistor Q 2a and diode D 5a The other end is connected to inductor L ra Switching transistor Q 3a and diode D 6a One end, diode D 2a The other end is connected to diode D 3a One end of the diode D 3a The other end is connected to capacitor C. 3a Switching transistor Q 3a diode D 6a Switching transistor Q 4a and diode D 7a The other end; the inductor L ra The other end is connected to inductor L ma and mutual inductance coil T a One end of the primary coil, inductance L ma and mutual inductance coil T a The other end of the primary coil is connected to a capacitor C. ra The other end.

2. The topology of a photovoltaic inverter with wide input and medium-high voltage AC output according to claim 1, characterized in that: The first LLC resonant multilevel half-bridge circuit, the second LLC resonant multilevel half-bridge circuit, and the third LLC resonant multilevel half-bridge circuit have the same structure. The connection methods between the second photovoltaic string and the third photovoltaic string and the second LLC resonant multilevel half-bridge circuit and the third LLC resonant multilevel half-bridge circuit are the same as the connection methods between the first photovoltaic string and the first LLC resonant multilevel half-bridge circuit.

3. The topology of a photovoltaic inverter with wide input and medium-high voltage AC output according to claim 2, characterized in that: The multi-cascaded H-bridge half-bridge multilevel circuit includes a first-cascaded H-bridge half-bridge multilevel circuit, a second-cascaded H-bridge half-bridge multilevel circuit, and a third-cascaded H-bridge half-bridge multilevel circuit. The first cascaded H-bridge half-bridge multilevel circuit includes: diode D 8a diode D 9a Capacitor C 4a Switching transistor Q 5a Switching transistor Q 6a Switching transistor Q 7a Switching transistor Q 8a Switching transistor Q 9a Switching transistor Q 10a Switching transistor Q 11a Switching transistor Q 12a Switching transistor Q 13a Switching transistor Q 14a Switching transistor Q 15a Switching transistor Q 16a Switching transistor Q 17a Switching transistor Q 18a Switching transistor Q 19a Switching transistor Q 20a diode D 10a diode D 11a diode D 12a diode D 13a diode D 14a diode D 15a diode D 16a diode D 17a diode D 18a diode D 19a diode D 20a diode D 21a diode D 22a diode D 23a diode D 24a diode D 25a diode D 26a diode D 27a diode D 28a diode D 29a diode D 30a diode D 31a Capacitor C 5a and capacitor C 6a ; Mutual inductance coil T a One end of the secondary coil is connected to the switching transistor Q. 6a and switching transistor Q 7a One end, mutual inductance coil T a The other end of the secondary coil is connected to diode D. 8a diode D 9a Capacitor C 6a diode D 15a diode D 18a and diode D 24a One end; Diode D 8a The other end is connected to capacitor C. 4a Switching transistor Q 6a and switching transistor Q 5a One end of the capacitor C 4a The other end is connected to diode D 9a and switching transistor Q 7a At the other end, the switching transistor Q 7a The other end is connected to the switching transistor Q. 8a One end; The switching transistor Q 5a The other end is connected to the switching transistor Q. 9a Capacitor C 5a Switching transistor Q 13a and switching transistor Q 17a One end of the capacitor C 5a The other end is connected to capacitor C 6a One end, the switching transistor Q 9a The other end is connected to the switching transistor Q. 10a and diode D 14a One end of the diode D 14a The other end is connected to diode D 15a One end, the switching transistor Q 10a The other end is connected to the switching transistor Q. 11a One end; Switching transistor Q 13a The other end is connected to diode D 20a and switching transistor Q 14a One end, diode D 20a The other end is connected to diode D 21a One end, the switching transistor Q 14a The other end is connected to the switching transistor Q. 15a One end; Switching transistor Q 17a The other end is connected to diode D 26a and switching transistor Q 18a One end, diode D 26a The other end is connected to diode D. 27a One end, the switching transistor Q 18a The other end is connected to the switching transistor Q. 19a One end; The switching transistor Q 8a The other end is connected to the switching transistor Q. 12a Switching transistor Q 16a and switching transistor Q 20a One end; switching transistor Q 12a The other end is connected to diode D 15a and switching transistor Q 11a At the other end, the switching transistor Q 16a The other end is connected to diode D 21a and switching transistor Q 15a At the other end, the switching transistor Q 20a The other end is connected to diode D 27a and switching transistor Q 19a The other end; Switching transistor Q 10a The other end is connected to phase A inductor L a .

4. The topology of a photovoltaic inverter with wide input and medium-high voltage AC output according to claim 3, characterized in that: Diode D 10a diode D 11a diode D 12a diode D 13a diode D 16a diode D 17a diode D 18a diode D 19a diode D 22a diode D 23a diode D 24a diode D 25a diode D 28a diode D 29a diode D 30a and diode D 31a These are the switching transistors Q and Q. 5a Switching transistor Q 6a Switching transistor Q 7a Switching transistor Q 8a Switching transistor Q 9a Switching transistor Q 10a Switching transistor Q 11a Switching transistor Q 12a Switching transistor Q 13a Switching transistor Q 14a Switching transistor Q 15a Switching transistor Q 16a Switching transistor Q 17a Switching transistor Q 18a Switching transistor Q 19a and switching transistor Q 20a Transistors.

5. The topology of a photovoltaic inverter with wide input and medium-high voltage AC output according to claim 3 or 4, characterized in that: The first, second, and third cascaded H-bridge half-bridge multilevel circuits have the same structural connection method.

6. The topology of a photovoltaic inverter with wide input and medium-high voltage AC output according to claim 5, characterized in that: The switching transistor Q in the first cascaded H-bridge half-bridge multilevel circuit 14a The other end is connected to the switching transistor Q in the second cascaded H-bridge half-bridge multilevel circuit. 10b The other end; the switching transistor Q in the second cascaded H-bridge half-bridge multilevel circuit 18b The other end is connected to the switching transistor Q in the second cascaded H-bridge half-bridge multilevel circuit. 14c The other end.

7. The topology of a photovoltaic inverter with wide input and medium-high voltage AC output according to claim 6, characterized in that: The number of LLC resonant multilevel half-bridge circuits in phases A, B, and C is not unique. Each phase is connected to multiple photovoltaic strings, and each photovoltaic string is connected to one LLC resonant multilevel half-bridge circuit.

Images