An Expandable Topology for a Photovoltaic Inverter with Wide Input and High-Voltage AC Output

Abstract

An expandable topology structure of a photovoltaic inverter with wide input and high-voltage AC output, which relates to the power system, especially the photovoltaic power generation system. The present invention solves the problem that the voltage level of the existing photovoltaic system is difficult to be further improved, which is not conducive to the improvement of system efficiency and cost reduction. The present invention improves the voltage levels of the DC input and AC output of the photovoltaic inverter through the multi-level and cascaded methods, reduces the input and output currents under the same power, reduces the power loss on the circuit and cable, and improves the overall power generation efficiency of the whole photovoltaic system. In the expandable topology structure of the present invention, the An module, Bn module and Cn module form a delta connection of the three-phase power supply, the A0 module, B0 module and C0 module are respectively used as the three output terminals of the three-phase power supply, the Ai module is connected in series between the A0 module and the An module, the Bi module is connected in series between the B0 module and the Bn module, and the Ci module is connected in series between the C0 module and the Cn module. The present invention is applicable to the photovoltaic power generation system.

Description

Technical Field

[0001] The present invention relates to a power system, and more particularly to a photovoltaic power generation system. Background Art

[0002] In order to solve the current situation of energy shortage, achieve the development goal of green energy, reduce air pollution, and realize the sustainability of energy development. The photovoltaic system is one of the most mature technologies in the renewable energy power generation system, and has the advantages of power scalability, simple installation, less maintenance, and modularity. For existing photovoltaic inverter equipment, the DC input voltage level is within 1500V, and the AC output voltage level is within 800V. It is connected to the grid through a power frequency step-up transformer. Restricted by the withstand voltage level of the components, it is currently difficult to further increase the voltage level of the photovoltaic system, which is not conducive to improving the efficiency and reducing the cost of the system. Traditional photovoltaic inverters require a huge number of power electronic switching devices, and each switching device requires a related gate drive circuit and protection circuit, resulting in the entire system being very expensive and complex. For the adaptive control of the medium-voltage direct-connected photovoltaic converter device, due to manufacturing technology limitations, the higher the voltage level and power level requirements, the lower the switching frequency of the power electronic devices. To adapt to high-voltage and high-power occasions, the switching tubes are usually connected in series and parallel, but this will cause problems such as voltage sharing of the switching tubes. If a traditional two-level inverter is directly adopted, the inverters need to be connected in series and parallel, but how to achieve simultaneous triggering of the switching devices and ensure the balance of the current borne by each inverter becomes a thorny problem. Therefore, exploring an inverter structure more suitable for application in the high-voltage and high-power field has become the main research content in the field of medium-voltage and high-voltage photovoltaic grid-connected inverters. The modular multilevel converter realizes the expansion of voltage and power by connecting multiple sub-modules in series, and stands out among many high-voltage and high-power inverter topologies. However, due to the problems of voltage sharing, circulating current, and fault tolerance existing in the modular multilevel inverter itself, its control is complex and its application is not extensive. The existing patent document CN114189168A realizes the increase of the output voltage through the cascade of three half-bridge circuits. And because both the front-stage multilevel LLC circuit and the rear-stage cascade multilevel circuit adopt the half-bridge form, the number of power devices can be effectively reduced, saving the cost of the photovoltaic inverter. However, since the topology of the photovoltaic inverter is already determined, when the withstand voltage level of the power devices in the circuit remains unchanged, if you want to continue to increase the voltage, you can only rely on modifying the number of levels of the cascade circuit. Currently, the three-level form is adopted. If a higher AC voltage needs to be output, then a five-level or seven-level three-phase half-bridge circuit must be selected for cascade, which will make the operation and control complex. Summary of the Invention

[0003] The present invention solves the problem that it is difficult to further increase the voltage level of the existing photovoltaic system, which is not conducive to improving the efficiency and reducing the cost of the system.

[0004] Under the limitation of the existing power device voltage level, the present invention improves the voltage levels of the DC input and AC output of the photovoltaic inverter through the multi-level and cascaded methods, reduces the input and output currents under the same power, reduces the power losses on the circuit and cables, and improves the overall power generation efficiency of the entire photovoltaic system.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] An expandable topology structure of a photovoltaic inverter with wide input and high-voltage AC output includes A0 module, B0 module, C0 module, Ai module, An module, Bi module, Bn module, Ci module and Cn module, where i = 1, 2,..., n - 1; the An module, Bn module and Cn module form a delta connection of a three-phase power supply, and the A0 module, B0 module and C0 module are respectively used as the three output terminals of the three-phase power supply. Among them, n - 1 Ai modules are connected in series between the A0 module and the An module at the A-phase output terminal, the n - 1 Bi modules are connected in series between the B0 module and the Bn module at the B-phase output terminal, and the n - 1 Ci modules are connected in series between the C0 module and the Cn module at the C-phase output terminal.

[0007] Preferably, the above A0 module, B0 module and C0 module have the same structure. The A0 module includes 3 photovoltaic strings, 3 isolated DC / DC conversion circuits, a cascaded three-phase inverter half-bridge circuit and 3 filter circuits. Each isolated DC / DC conversion circuit is connected in series between a photovoltaic string and one phase signal input terminal of the cascaded three-phase inverter half-bridge circuit. A filter circuit is connected in series between each of the three output terminals of the cascaded three-phase inverter half-bridge circuit and the three output terminals of the A0 module.

[0008] Preferably, the above filter circuit is implemented by an inductance filter circuit, an LC filter circuit, an LCL filter circuit or an LCCR filter circuit.

[0009] Preferably, the cascaded three-phase half-bridge inverter circuit includes three single-phase half-bridge circuits. The first single-phase half-bridge circuit includes transistors Q1a, Q2a, Q3a, Q4a, Q5a, and Q6a. The second single-phase half-bridge circuit includes transistors Q1b, Q2b, Q3b, Q4b, Q5b, and Q6b. The third single-phase half-bridge circuit includes transistors Q1c, Q2c, Q3c, Q4c, Q5c, and Q6c. Between the emitter of transistor Q1a and the collector of transistor Q2a of the first single-phase half-bridge circuit, it is connected to between the emitter of transistor Q1c and the collector of transistor Q2c of the third single-phase half-bridge circuit. Between the emitter of transistor Q3a and the collector of transistor Q4a of the first single-phase half-bridge circuit, it is connected to between the emitter of transistor Q1b and the collector of transistor Q2b of the second single-phase half-bridge circuit. Between the emitter of transistor Q5a and the collector of transistor Q6a of the first single-phase half-bridge circuit, it is connected to between the emitter of transistor Q1c and the collector of transistor Q2c of the third single-phase half-bridge circuit. Between the emitter of transistor Q5b and the collector of transistor Q6b of the second single-phase half-bridge circuit, it is connected to between the emitter of transistor Q3c and the collector of transistor Q4c of the third single-phase half-bridge circuit. The filter circuit includes La, Lb, and Lc. The filter circuit La is connected between the emitter of transistor Q5a and the collector of transistor Q6a and is connected to the output terminal of the A0 module. The filter circuit Lb is connected between the emitter of transistor Q5b and the collector of transistor Q6b and is connected to the output terminal of the A0 module. The filter circuit Lc is connected between the emitter of transistor Q5c and the collector of transistor Q6c and is connected to the output terminal of the A0 module. The second isolated DC / DC conversion circuit is connected to the third isolated DC / DC conversion circuit.

[0010] Preferably, the above-mentioned Ai module and An module have the same structure. The Ai module includes two photovoltaic strings, two isolated DC / DC conversion circuits, and a cascaded three-phase inverter half-bridge circuit. Each isolated DC / DC conversion circuit is connected in series between a photovoltaic string and the cascaded three-phase inverter half-bridge circuit. The cascaded three-phase half-bridge inverter circuit includes two single-phase half-bridge circuits. The emitter of transistor Q5b and the collector of transistor Q6b of the second single-phase half-bridge circuit are connected between the emitter of transistor Q3c and the collector of transistor Q4c of the third single-phase half-bridge circuit. The emitter of transistor Q1b and the collector of transistor Q2b of the second single-phase half-bridge circuit are connected to the output terminal of the Ai module. The emitter of transistor Q3b and the collector of transistor Q4b of the second single-phase half-bridge circuit are connected to the output terminal of the Ai module. The emitter of transistor Q1c and the collector of transistor Q2c of the third single-phase half-bridge circuit are connected to the output terminal of the Ai module. The emitter of transistor Q5c and the collector of transistor Q6c of the third single-phase half-bridge circuit are connected to the output terminal of the Ai module.

[0011] Preferably, the above-mentioned Bi module and Bn module have the same structure. The Bi module includes two photovoltaic strings, two isolated DC / DC conversion circuits, and a cascaded three-phase inverter half-bridge circuit. Each isolated DC / DC conversion circuit is connected in series between a photovoltaic string and the cascaded three-phase inverter half-bridge circuit. The cascaded three-phase half-bridge inverter circuit includes two single-phase half-bridge circuits. The emitter of transistor Q1a and the collector of transistor Q2a of the first single-phase half-bridge circuit are connected to the output terminal of the Bi module. The emitter of transistor Q3a and the collector of transistor Q4a of the first single-phase half-bridge circuit are connected to the output terminal of the Bi module. The emitter of transistor Q5c and the collector of transistor Q6c of the three-phase single half-bridge circuit are connected to the output terminal of the Bi module. The emitter of transistor Q3c and the collector of transistor Q4c of the three-phase single half-bridge circuit are connected to the output terminal of the Bi module. The emitter of transistor Q5a and the collector of transistor Q6a of the first single-phase half-bridge circuit are connected between the emitter of transistor Q1c and the collector of transistor Q2c of the third single-phase half-bridge circuit.

[0012] Preferably, the above-mentioned Ci module and Cn module have the same structure. The Ci module includes two photovoltaic strings, two isolated DC / DC conversion circuits, and a cascaded three-phase inverter half-bridge circuit. Each isolated DC / DC conversion circuit is connected in series between a photovoltaic string and the cascaded three-phase inverter half-bridge circuit. The cascaded three-phase half-bridge inverter circuit includes two single-phase half-bridge circuits. The output terminal of the Ci module is connected between the emitter of transistor Q1a and the collector of transistor Q2a of the first single-phase half-bridge circuit, and also between the emitter of transistor Q5a and the collector of transistor Q6a of the first single-phase half-bridge circuit. The output terminal of the Ci module is connected between the emitter of transistor Q3b and the collector of transistor Q4b of the second single-phase half-bridge circuit, and also between the emitter of transistor Q5b and the collector of transistor Q6b of the second single-phase half-bridge circuit. The emitter of transistor Q3a and the collector of transistor Q4a of the first single-phase half-bridge circuit are connected between the emitter of transistor Q1b and the collector of transistor Q2b of the third single-phase half-bridge circuit.

[0013] Preferably, the above-mentioned Ai module, An module, Bi module, Bn module, Ci module, and Cn module have the same structure. The Ai module includes two photovoltaic strings, two isolated DC / DC conversion circuits, and two single-phase full-bridge circuits. Each isolated DC / DC conversion circuit is connected in series between a photovoltaic string and a single-phase full-bridge circuit. The first single-phase full-bridge circuit includes transistors Q1a, Q2a, Q3a, and Q4a, and the second single-phase full-bridge circuit includes transistors Q1b, Q2b, Q3b, and Q4b. The output terminal of the Ai module is connected between the emitter of transistor Q1a and the collector of transistor Q2a of the first single-phase full-bridge circuit, and also between the emitter of transistor Q3a and the collector of transistor Q4a of the first single-phase full-bridge circuit. The output terminal of the Ai module is connected between the emitter of transistor Q1b and the collector of transistor Q2b of the second single-phase full-bridge circuit, and the output terminal of the general Ai is connected between the emitter of transistor Q3b and the collector of transistor Q4b of the second single-phase full-bridge circuit.

[0014] Technical effects

[0015] The object of the present invention is to provide an expandable topology structure of a photovoltaic inverter with wide input and high-voltage AC output, which can, under the limitation of the voltage rating of existing power devices, improve the voltage ratings of the DC input and AC output of the photovoltaic inverter through the multi-level and cascaded methods, reduce the input and output currents at the same power, reduce the power losses on the circuit and cables, and improve the overall power generation efficiency of the entire photovoltaic system. The cascaded module composed of the X-topology circuit has the ability of three-phase power adaptive balance. By adopting a suitable PWM modulation method, it can make the three-phase output power adaptively balanced under the condition of unbalanced power generation of the photovoltaic modules, eliminating the circulating current caused by the unbalanced power of the photovoltaic strings between the three-phase outputs of the inverter, and reducing the control difficulty of the three-phase photovoltaic inverter by adopting the Y-structure topology circuit type. And because the present solution works in a module-cascaded manner and the modules are interchangeable with each other, if a certain module (except the input-end module) fails, it can be cut off. Since the photovoltaic inverter of this patent has the ability of three-phase power self-balancing, the photovoltaic inverter composed of the remaining modules can still work normally, improving the reliability of the photovoltaic inverter.

[0016] Compared with the prior art, the present invention has the following several advantages:

[0017] 1. For the expandable topology structure of a photovoltaic inverter with wide input and high-voltage AC output described in the present invention, under the limitation of the voltage rating of existing power devices, it improves the AC output voltage rating of the photovoltaic inverter through the cascaded method, and improves the input voltage rating through the multi-level method, eliminating the limitation of the breakdown voltage rating of the power device on the output voltage of the photovoltaic inverter, effectively reducing the losses brought by the power frequency transformer in the traditional photovoltaic inverter grid-connected scheme, and improving the operation efficiency of the photovoltaic inverter system. By means of multi-level and cascaded methods, it improves the voltage ratings of the DC input and AC output of the photovoltaic inverter, reduces the input current and output current ratings of the photovoltaic inverter system, reduces the power losses on the circuit and cables, improves the operation efficiency of the photovoltaic inverter system, and finally improves the overall power generation efficiency of the entire photovoltaic system.

[0018] 2. The expandable topology structure of a photovoltaic inverter with wide input and high-voltage AC output according to the present invention can improve the AC output voltage level of the photovoltaic inverter in a cascaded manner and the input voltage level in a multi-level manner under the limitation of the existing power device voltage level, eliminating the limitation of the power device withstand voltage level on the output voltage of the photovoltaic inverter, effectively reducing the increased cost brought by the power frequency transformer in the traditional photovoltaic inverter grid connection scheme, and reducing the cost invested in the power frequency transformer. By means of multi-level and cascaded methods, the voltage levels of the DC input and AC output of the photovoltaic inverter are increased, and the input current and output current levels of the photovoltaic inverter system are reduced. The cross-sectional area requirement of the cables in the photovoltaic power station and the current level requirement of the switching equipment in the photovoltaic power station are reduced, thereby reducing the costs of the photovoltaic power station on the transmission cables and switching equipment. The cost of the topology structure of the photovoltaic inverter can be effectively reduced.

[0019] 3. The expandable topology structure of a photovoltaic inverter with wide input and high-voltage AC output according to the present invention adopts the X-structure topology circuit type. The cascaded module composed of the X-topology type circuit has the ability of three-phase power self-adaptive balance. By adopting a suitable PWM modulation method, it can make the three-phase output power self-adaptively balanced under the condition of unbalanced power generation power of the photovoltaic modules, eliminating the circulating current caused by the unbalanced power of the photovoltaic strings between the three-phase outputs of the inverter.

[0020] 4. The expandable topology structure of a photovoltaic inverter with wide input and high-voltage AC output according to the present invention uses the Y-structure topology circuit type to form the cascaded module of the circuit. The Y-structure topology circuit type is simpler than the X-structure topology circuit type, reducing the control difficulty of the entire topology structure of the photovoltaic inverter.

[0021] 5. The expandable topology structure of a photovoltaic inverter with wide input and high-voltage AC output according to the present invention operates in a module-cascaded manner, and the modules are interchangeable. If a certain module (except the input-end module) fails, the module can be removed. Since the photovoltaic inverter has the ability of three-phase power self-balance, the photovoltaic inverter composed of the remaining modules can still operate normally, improving the system fault tolerance rate and making the topology structure of the photovoltaic inverter more reliable.

[0022] The present invention is applicable to the photovoltaic power generation system. Description of the Drawings

[0023] Figure 1 It is a schematic diagram of the expandable topology structure of the photovoltaic inverter with wide input and high-voltage AC output described in Embodiment 1.

[0024] Figure 2 It is a schematic diagram of the circuit structure topology of the A0 module described in Embodiment 4.

[0025] Figure 3 is Figure 2 a simplified schematic diagram of the circuit structure topology shown

[0026] Figure 4 is a schematic diagram of the X structure topology corresponding to the Ai module described in Embodiment 5

[0027] Figure 5 is Figure 4 a simplified schematic diagram of the X circuit structure topology shown

[0028] Figure 6 is a schematic diagram of the X structure topology corresponding to the Bi module shown in Embodiment 6

[0029] Figure 7 Figure 6 a simplified schematic diagram of the X circuit structure topology shown

[0030] Figure 8 is a schematic diagram of the X structure topology corresponding to the Ci module described in Embodiment 7

[0031] Figure 9 is Figure 8 a simplified schematic diagram of the X structure topology shown

[0032] Figure 10 is a schematic diagram of the Y structure topology corresponding to the Ai module described in Embodiment 8

[0033] Figure 11 is Figure 10 a simplified schematic diagram of the Y structure topology shown

[0034] Figure 12 is a schematic diagram of the topology structure of a photovoltaic inverter with a 35 kV output composed of 1200 V voltage class power devices Specific embodiments

[0035] The technical solutions of the present application will be described below with reference to the accompanying drawings

[0036] Embodiment 1. Refer to Figure 1To describe this embodiment, a scalable topology of a photovoltaic inverter with wide input and high-voltage AC output is provided. The topology includes Module A0, Module B0, Module C0, Module Ai, Module An, Module Bi, Module Bn, Module Ci, and Module Cn, where i = 1, 2,..., n - 1. Module An, Module Bn, and Module Cn form a delta connection of a three-phase power supply. Module A0, Module B0, and Module C0 serve as the three output terminals of the three-phase power supply respectively. Among them, n - 1 Module Ai are connected in series between Module A0 and Module An at the A-phase output terminal, n - 1 Module Bi are connected in series between Module B0 and Module Bn at the B-phase output terminal, and n - 1 Module Ci are connected in series between Module C0 and Module Cn at the C-phase output terminal. The scalable topology of the photovoltaic inverter with wide input and high-voltage AC output in this embodiment improves the AC output voltage level of the photovoltaic inverter in a cascaded manner and improves the input voltage level in a multi-level manner under the limitation of the existing voltage level of power devices, eliminating the limitation of the breakdown voltage level of power devices on the output voltage of the photovoltaic inverter, effectively reducing the losses brought by the power frequency transformer in the traditional photovoltaic inverter grid-connected scheme, and improving the operation efficiency of the photovoltaic inverter system. By means of multi-level and cascaded methods, the DC input and AC output voltage levels of the photovoltaic inverter are increased, the input current and output current levels of the photovoltaic inverter system are reduced, the power losses on the circuit and cable are reduced, the operation efficiency of the photovoltaic inverter system is improved, and finally the overall power generation efficiency of the entire photovoltaic system is improved. At the same time, the module-cascaded method is adopted for operation, and the modules are interchangeable. If a certain module (except the input terminal module) fails, the module can be removed. Since the photovoltaic inverter has the ability of three-phase power self-balancing, the photovoltaic inverter composed of the remaining modules can still work normally, improving the system fault tolerance rate and making the topology of the photovoltaic inverter more reliable.

[0037] Embodiment 2. Refer to Figure 2 To describe this embodiment, this embodiment is an example of the structures of Module A0, Module B0, and Module C0 in the scalable topology of the photovoltaic inverter with wide input and high-voltage AC output described in Embodiment 1. In this embodiment, Module A0, Module B0, and Module C0 have the same structure. Module A0 includes 3 photovoltaic strings, 3 isolated DC / DC conversion circuits, a cascaded three-phase inverter half-bridge circuit, and 3 filter circuits. Each isolated DC / DC conversion circuit is connected in series between a photovoltaic string and one-phase signal input terminal of the cascaded three-phase inverter half-bridge circuit. A filter circuit is connected in series between each of the three output terminals of the cascaded three-phase inverter half-bridge circuit and the three output terminals of Module A0 respectively.

[0038] This embodiment further defines the A0 module, B0 module, and C0 module in Embodiment 1. The three modules have the same structure and are respectively connected to the A, B, and C phase lines. The three modules serve as the input terminals of the expandable topology of the entire photovoltaic inverter. From Figure 2 it can be seen that the energy at each output terminal in the A0, B0, and C0 modules is jointly provided by 3 photovoltaic strings. Therefore, under the selection of an appropriate PWM modulation method, adaptive balance of the three-phase output energy can be achieved among the three output terminals of the A0, B0, and C0 modules, reducing the control difficulty of the photovoltaic inverter under the condition of unbalanced power generation energy of the photovoltaic strings and improving the reliability of the operation of the photovoltaic inverter.

[0039] Embodiment 3. The filter circuit in the expandable topology of the photovoltaic inverter with wide input and high-voltage AC output described in this embodiment is implemented by an inductor, an LC filter circuit, a CLC filter circuit, or an LCCR filter circuit.

[0040] The filter circuit described in this embodiment implemented by an inductor has the advantages of good filtering effect and small DC loss, and at the same time can make the load current smooth and has a smoothing effect.

[0041] Embodiment 4. Refer to Figure 2 and 3This embodiment is an illustrative example of the specific structure of the cascaded three-phase half-bridge inverter circuit in the expandable topology of a photovoltaic inverter with wide input and high-voltage AC output described in Embodiment 2. In this embodiment, the cascaded three-phase half-bridge inverter circuit includes three single-phase half-bridge circuits. The first single-phase half-bridge circuit includes transistors Q1a, Q2a, Q3a, Q4a, Q5a, Q6a, diodes D1a, D2a, D3a, D4a, D5a, D6a, capacitor C1a, and capacitor C2a. The second single-phase half-bridge circuit includes transistors Q1b, Q2b, Q3b, Q4b, Q5b, Q6b, diodes D1b, D2b, D3b, D4b, D5b, D6b, capacitor C1b, and capacitor C2b. The third single-phase half-bridge circuit includes transistors Q1c, Q2c, Q3c, Q4c, Q5c, Q6c, diodes D1c, D2c, D3c, D4c, D5c, D6c, capacitor C1c, and capacitor C2c. The emitter of transistor Q1a of the first single-phase half-bridge circuit is connected between the emitter and the collector of transistor Q1c of the third single-phase half-bridge circuit. The emitter of transistor Q3a of the first single-phase half-bridge circuit is connected between the emitter and the collector of transistor Q1b of the second single-phase half-bridge circuit. The emitter of transistor Q5a of the first single-phase half-bridge circuit is connected between the emitter and the collector of transistor Q1c of the third single-phase half-bridge circuit. The emitter of transistor Q5b of the second single-phase half-bridge circuit is connected between the emitter and the collector of transistor Q3c of the third single-phase half-bridge circuit. The filter circuit includes La, Lb, and Lc. The filter circuit La is connected between the emitter and the collector of transistor Q5a and is connected to the output terminal of the A0 module. The filter circuit Lb is connected between the emitter and the collector of transistor Q5b and is connected to the output terminal of the A0 module. The filter circuit Lc is connected between the emitter and the collector of transistor Q5c and is connected to the output terminal of the A0 module. The second isolated DC / DC conversion circuit is connected to the third isolated DC / DC conversion circuit.

[0042] The cascaded three-phase half-bridge inverter circuit described in this embodiment is formed by cascading three single-phase half-bridge circuits, and its simplified schematic diagram is as Figure 3As shown, where Q1a to Q6c are fully controlled devices, such as BJT, GTO, IGBT or MOSFET, etc., D1a to D6c are freewheeling diodes, and La, Lb and Lc represent filter circuits, and the filter circuits are implemented by inductance filter circuits, LC filter circuits, LCL filter circuits or LCCR filter circuits. According to Figure 1 , 2 and 3, it can be obtained that for the A0 module, A01 corresponds to Figure 2 the output terminal 1 of the three-phase cascaded circuit shown in Figure 2 , A02 corresponds to Figure 2 the output terminal 2 of the three-phase cascaded circuit shown in Figure 2 , and A03 corresponds to Figure 2 the output terminal 3 of the three-phase cascaded circuit shown in Figure 2 ; for the B0 module, B01 corresponds to Figure 2 the output terminal 2 of the three-phase cascaded circuit shown in Figure 2 , B02 corresponds to Figure 2 the output terminal 3 of the three-phase cascaded circuit shown in Figure 2 , and B03 corresponds to Figure 2 the output terminal 1 of the three-phase cascaded circuit shown in Figure 2 ; C01 corresponds to Figure 2 the output terminal 3 of the three-phase cascaded circuit shown in Figure 2 , C02 corresponds to Figure 2 the output terminal 1 of the three-phase cascaded circuit shown in

[0043] Embodiment 5. Refer to Figure 4 and 5This embodiment is an illustrative example of the structures of the Ai module and the An module in the expandable topology of a photovoltaic inverter with wide input and high-voltage AC output described in Embodiment 1. In this embodiment, the Ai module and the An module have the same structure. The Ai module includes two photovoltaic strings, two isolated DC / DC conversion circuits, and a cascaded three-phase inverter half-bridge circuit. Each isolated DC / DC conversion circuit is connected in series between a photovoltaic string and the cascaded three-phase inverter half-bridge circuit. The cascaded three-phase half-bridge inverter circuit includes two single-phase half-bridge circuits. The second single-phase half-bridge circuit includes transistors Q1b, Q2b, Q3b, Q4b, Q5b, Q6b, diodes D1b, D2b, D3b, D4b, D5b, D6b, capacitor C1b, and capacitor C2b. The third single-phase half-bridge circuit includes transistors Q1c, Q2c, Q3c, Q4c, Q5c, Q6c, diodes D1c, D2c, D3c, D4c, D5c, D6c, capacitor C1c, and capacitor C2c. The emitter of transistor Q5b and the collector of transistor Q6b in the second single-phase half-bridge circuit are connected to the emitter of transistor Q3c and the collector of Q4c in the third single-phase half-bridge circuit. The emitter of transistor Q1b and the collector of transistor Q2b in the second single-phase half-bridge circuit are connected to the output terminal of the Ai module. The emitter of transistor Q3b and the collector of transistor Q4b in the second single-phase half-bridge circuit are connected to the output terminal of the Ai module. The emitter of transistor Q1c and the collector of Q2c in the third single-phase half-bridge circuit are connected to the output terminal of the Ai module. The emitter of transistor Q5c and the collector of Q6c in the third single-phase half-bridge circuit are connected to the output terminal of the Ai module.

[0044] The transistors Q1b to Q6b, diodes D1b to D6b, transistors Q1c to Q6c, and diodes D1c to D6c described in this embodiment respectively form two single-phase half-bridge circuits. The two single-phase half-bridge circuits are cascaded with each other and have four output terminals 1, 2, 3, and 4. Its simplified schematic diagram can be as Figure 5 shown. For the Ai module, Ai1 corresponds to Figure 5 the output terminal 1 of the three-phase cascaded circuit shown in Figure 5 , Ai2 corresponds to Figure 5 the output terminal 4 of the three-phase cascaded circuit shown in Figure 5The output terminal 3 of the three-phase cascaded circuit shown in [Figure]. Under the limitation of the existing power device voltage level, the AC output voltage level of the photovoltaic inverter can be increased by cascading. The X-structured topology circuit type is adopted. The cascaded module composed of the X-topology circuit type has the ability of three-phase power adaptive balance. By adopting a suitable PWM modulation method, the three-phase output power can be adaptively balanced under the condition of unbalanced power generation of the photovoltaic modules, and the circulating current caused by the unbalanced power of the photovoltaic strings between the three-phase outputs of the inverter is eliminated.

[0045] Embodiment 6. Refer to Figure 6 and 7 This embodiment will be described. This embodiment is an example of the specific structures of the Bi module and the Bn module in the expandable topology structure of a photovoltaic inverter with wide input and high-voltage AC output described in Embodiment 1. In this embodiment, the Bi module and the Bn module have the same structure. The Bi module includes 2 photovoltaic strings, 2 isolated DC / DC conversion circuits, and a cascaded three-phase inverter half-bridge circuit. Each isolated DC / DC conversion circuit is connected in series between a photovoltaic string and the cascaded three-phase inverter half-bridge circuit. The cascaded three-phase half-bridge inverter circuit includes 2 single-phase half-bridge circuits. The first single-phase half-bridge circuit includes transistors Q1a, Q2a, Q3a, Q4a, Q5a, Q6a, diodes D1a, D2a, D3a, D4a, D5a, D6a, capacitors C1a and C2a. The third single-phase half-bridge circuit includes transistors Q1c, Q2c, Q3c, Q4c, Q5c, Q6c, diodes D1c, D2c, D3c, D4c, D5c, D6c, capacitors C1c and C2c. The output terminal of the Bi module is connected between the emitter of transistor Q1a and the collector of transistor Q2a of the first single-phase half-bridge circuit. The output terminal of the Bi module is connected between the emitter of transistor Q3a and the collector of transistor Q4a of the first single-phase half-bridge circuit. The output terminal of the Bi module is connected between the emitter of transistor Q5c and the collector of transistor Q6c of the three-phase single-phase half-bridge circuit. The output terminal of the Bi module is connected between the emitter of transistor Q3c and the collector of transistor Q4c of the three-phase single-phase half-bridge circuit. The emitter of transistor Q5a of the first single-phase half-bridge circuit is connected to the collector of transistor Q6a, and the emitter of transistor Q1c and the collector of transistor Q2c of the three-phase single-phase half-bridge circuit are connected.

[0046] The transistors Q1a to Q6a, diodes D1a to D6b, transistors Q1c to Q6c, and diodes D1c to D6c described in this embodiment respectively form two single-phase half-bridge circuits. The two single-phase half-bridge circuits are cascaded with each other and have four output terminals 1, 2, 3, and 4. The simplified schematic diagram can be as Figure 7 shown. For the Bi module, Bi1 corresponds to Figure 7 the output terminal 4 of the three-phase cascaded circuit shown in Figure 7 Bi2 corresponds to Figure 7 the output terminal 2 of the three-phase cascaded circuit shown in Figure 7 Bi3 corresponds to the output terminal 3 of the three-phase cascaded circuit shown in

[0047] Embodiment 7. Refer to Figure 8 and 9To illustrate this embodiment, this embodiment is an example of the specific structures of the Ci module and the Cn module in the expandable topology of a photovoltaic inverter with wide input and high-voltage AC output described in Embodiment 1. In this embodiment, the Ci module and the Cn module have the same structure. The Ci module includes two photovoltaic strings, two isolated DC / DC conversion circuits, and a cascaded three-phase inverter half-bridge circuit. Each isolated DC / DC conversion circuit is connected in series between a photovoltaic string and the cascaded three-phase inverter half-bridge circuit. The cascaded three-phase half-bridge inverter circuit includes two single-phase half-bridge circuits. The first single-phase half-bridge circuit includes transistors Q1a, Q2a, Q3a, Q4a, Q5a, Q6a, diodes D1a, D2a, D3a, D4a, D5a, D6a, capacitor C1a, and capacitor C2a. The second single-phase half-bridge circuit includes transistors Q1b, Q2b, Q3b, Q4b, Q5b, Q6b, diodes D1b, D2b, D3b, D4b, D5b, D6b, capacitor C1b, and capacitor C2b. The output terminal of the Ci module is connected between the emitter of transistor Q1a and the collector of transistor Q2a of the first single-phase half-bridge circuit, and between the emitter of transistor Q5a and the collector of transistor Q6a of the first single-phase half-bridge circuit. The output terminal of the Ci module is connected between the emitter of transistor Q3b and the collector of transistor Q4b of the second single-phase half-bridge circuit, and between the emitter of transistor Q5b and the collector of transistor Q6b of the second single-phase half-bridge circuit. The emitter of transistor Q3a and the collector of transistor Q4a of the first single-phase half-bridge circuit are connected between the emitter of transistor Q1b and the collector of transistor Q2b of the third single-phase half-bridge circuit.

[0048] The transistors Q1a to Q6a, diodes D1a to D6b, transistors Q1c to Q6c, and diodes D1c to D6c described in this embodiment respectively form two single-phase half-bridge circuits. The two single-phase half-bridge circuits are cascaded with each other and have four output terminals 1, 2, 3, and 4. Its simplified schematic diagram can be as Figure 9 shown. For the Ci module, Ci1 corresponds to Figure 9 the output terminal 3 of the three-phase cascaded circuit shown in Figure 9 Ci2 corresponds to Figure 9 the output terminal 4 of the three-phase cascaded circuit shown in Figure 9Output terminal 2 of the three-phase cascaded circuit shown. Under the limitation of the existing power device voltage level, the AC output voltage level of the photovoltaic inverter can be increased by cascading. The X-structured topology circuit type is adopted. The cascaded module composed of the X-topology circuit type has the ability of three-phase power adaptive balance. By adopting a suitable PWM modulation method, the three-phase output power can be adaptively balanced under the condition of unbalanced power generation of the photovoltaic modules, eliminating the circulating current caused by the unbalanced power of the photovoltaic strings between the three-phase outputs of the inverter.

[0049] Embodiment VIII. Refer to Figure 10 and 11 to describe this embodiment. This embodiment is an example of the specific structures of the Ai module, An module, Bi module, Bn module, Ci module, and Cn module in the expandable topology structure of a photovoltaic inverter with wide input and high-voltage AC output described in Embodiment I. In this embodiment, the Ai module, An module, Bi module, Bn module, Ci module, and Cn module have the same structure; the Ai module includes 2 photovoltaic strings, 2 isolated DC / DC conversion circuits, and 2 single-phase full-bridge circuits. Each isolated DC / DC conversion circuit is connected in series between 1 photovoltaic string and 1 single-phase full-bridge circuit; the first single-phase full-bridge circuit includes transistors Q1a, Q2a, Q3a, Q4a, capacitor C1a, and capacitor C2a, and the second single-phase full-bridge circuit includes transistors Q1b, Q2b, Q3b, and Q4b, capacitor C1a, and capacitor C2a; the output terminal of the Ai module is connected between the emitter of transistor Q1a and the collector of transistor Q2a of the first single-phase full-bridge circuit, the output terminal of the Ai module is connected between the emitter of transistor Q3a and the collector of transistor Q4a of the first single-phase full-bridge circuit, the output terminal of the Ai module is connected between the emitter of transistor Q1b and the collector of transistor Q2b of the second single-phase full-bridge circuit, and the output terminal of the common Ai is connected between the emitter of transistor Q3b and the collector of transistor Q4b.

[0050] The transistors Q1a~Q4a, diodes D1a~D4b, transistors Q1b~Q4b, and diodes D1b~D4b described in this embodiment respectively form two single-phase full-bridge circuits. The two single-phase full-bridge circuits are independent of each other and have four output terminals 1, 2, 3, and 4. Its simplified schematic diagram can be as Figure 11 shown. For the Ai, Bi, and Ci modules, Ai1, Bi1, and Ci1 correspond to Figure 10 output terminal 1 of the three-phase cascaded circuit shown in Figure 10 Ai2, Bi2, and Ci2 correspond to Figure 10The output terminals 3, Ai4, Bi4, and Ci4 of the three-phase cascaded circuit shown in Figure 10 correspond to the output terminals 4 of the three-phase cascaded circuit shown in. The Y-structured topology circuit type is adopted in this embodiment. The cascaded modules of the circuit are formed by using the Y-structured topology circuit type. The Y-structured topology circuit type is simpler than the X-structured topology circuit type, reducing the control difficulty of the entire photovoltaic inverter topology structure.

[0051] Embodiment Nine. Refer to Figure 12 To illustrate this embodiment, this embodiment is an example of the specific structure of an expandable topology structure of a photovoltaic inverter with wide input and high-voltage AC output described in Embodiment One. In this embodiment, with power devices of the 1200V voltage class, through the cascading of 62 modules, that is: n = 62, the output voltage of the photovoltaic inverter can reach 35kV, the power frequency transformer at the output terminal can be eliminated, and the direct grid connection of the photovoltaic inverter to the 35kV power grid can be realized.

[0052] The output voltage of the photovoltaic module is adjusted to a DC bus voltage of about 800V through a DC / DC converter, and then the DC voltage is inverted into a 50Hz power frequency AC voltage through a three-phase half-bridge inverter circuit. In the A1 - A62, B1 - B62, C1 - C62 modules, the output voltage of the photovoltaic string is also adjusted to a DC bus voltage of about 800V through a DC / DC converter. In this implementation example, the A1 - A62, B1 - B62, C1 - 62 modules adopt a Y-type topology structure. During the implementation process, the circuit structure of any one or several groups of modules can be changed to an X-type topology structure. In the inverter topology structure, the more X-type topology structures are adopted, the stronger the power adaptive balance ability of the three-phase output terminals of the photovoltaic inverter. In this application example, since a two-level circuit topology is adopted, the DC / DC converter converts the output voltage of the photovoltaic string to a DC bus voltage of about 800V. If a three-level, five-level or even more-level circuit topology structure is adopted, the voltage level of the DC bus in the photovoltaic inverter can be further increased.

[0053] The above are only the embodiments of the present invention and do not limit the present invention. The value of n is greater than or equal to 1 and is set according to on-site requirements. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the scope of the claims of the present invention.

Claims

1. An expandable topology structure of a photovoltaic inverter with wide input and high-voltage AC output, characterized in that, the topology structure includes A0 module, B0 module, C0 module, Ai module, An module, Bi module, Bn module, Ci module and Cn module, where i = 1, 2,..., n - 1; The An module, Bn module and Cn module form a delta connection of a three-phase power supply. The A0 module, B0 module and C0 module are respectively used as the three output terminals of the three-phase power supply. Among them, n - 1 Ai modules are connected in series between the A0 module and the An module at the A-phase output terminal, the n - 1 Bi modules are connected in series between the B0 module and the Bn module at the B-phase output terminal, and the n - 1 Ci modules are connected in series between the C0 module and the Cn module at the C-phase output terminal; The A0 module, B0 module and C0 module have the same structure. The A0 module includes 3 photovoltaic strings, 3 isolated DC / DC conversion circuits, a cascaded three-phase inverter half-bridge circuit and 3 filter circuits. Each isolated DC / DC conversion circuit is connected in series between a photovoltaic string and one phase signal input terminal of the cascaded three-phase inverter half-bridge circuit. A filter circuit is connected in series between each of the three output terminals of the cascaded three-phase inverter half-bridge circuit and the three output terminals of the A0 module; The cascaded three-phase half-bridge inverter circuit includes three single-phase half-bridge circuits. The first single-phase half-bridge circuit includes transistors Q1a, Q2a, Q3a, Q4a, Q5a and Q6a. The second single-phase half-bridge circuit includes transistors Q1b, Q2b, Q3b, Q4b, Q5b and Q6b. The third single-phase half-bridge circuit includes transistors Q1c, Q2c, Q3c, Q4c, Q5c and Q6c; The emitter of transistor Q1a of the first single-phase half-bridge circuit is connected to the emitter of transistor Q1c of the third single-phase half-bridge circuit between the collector of transistor Q2a, and the emitter of transistor Q3a of the first single-phase half-bridge circuit is connected to the emitter of transistor Q1b of the second single-phase half-bridge circuit between the collector of transistor Q4a. The emitter of transistor Q5a of the first single-phase half-bridge circuit is connected to the emitter of transistor Q1c of the third single-phase half-bridge circuit between the collector of transistor Q6a. The emitter of transistor Q5b of the second single-phase half-bridge circuit is connected to the emitter of transistor Q3c of the third single-phase half-bridge circuit between the collector of transistor Q6b. The filter circuit includes La, Lb, and Lc. The filter circuit La is connected between the emitter of transistor Q5a and the collector of transistor Q6a, and the filter circuit La is connected to the output terminal of the A0 module. The filter circuit Lb is connected between the emitter of transistor Q5b and the collector of transistor Q6b, and the filter circuit Lb is connected to the output terminal of the A0 module. The filter circuit Lc is connected between the emitter of transistor Q5c and the collector of transistor Q6c, and the filter circuit Lc is connected to the output terminal of the A0 module. The second isolated DC / DC conversion circuit is connected to the third isolated DC / DC conversion circuit.

2. The expandable topology structure of a photovoltaic inverter with wide input and high-voltage AC output according to claim 1, characterized in that, the filter circuit is implemented by an inductance filter circuit, an LC filter circuit, an LCL filter circuit or an LCCR filter circuit.

3. The expandable topology structure of a photovoltaic inverter with wide input and high-voltage AC output according to claim 1, characterized in that, the Ai module and the An module have the same structure. The Ai module includes 2 photovoltaic strings, 2 isolated DC / DC conversion circuits and a cascaded three-phase inverter half-bridge circuit. Each isolated DC / DC conversion circuit is connected in series between a photovoltaic string and the cascaded three-phase inverter half-bridge circuit.

4. The expandable topology structure of a photovoltaic inverter with wide input and high-voltage AC output according to claim 1, characterized in that, the Bi module and the Bn module have the same structure. The Bi module includes 2 photovoltaic strings, 2 isolated DC / DC conversion circuits and a cascaded three-phase inverter half-bridge circuit. Each isolated DC / DC conversion circuit is connected in series between a photovoltaic string and the cascaded three-phase inverter half-bridge circuit.

5. The expandable topology structure of a photovoltaic inverter with wide input and high-voltage AC output according to claim 1, characterized in that, the Ci module and the Cn module have the same structure. The Ci module includes 2 photovoltaic strings, 2 isolated DC / DC conversion circuits and a cascaded three-phase inverter half-bridge circuit. Each isolated DC / DC conversion circuit is connected in series between a photovoltaic string and the cascaded three-phase inverter half-bridge circuit.

6. The expandable topology of a photovoltaic inverter with wide input and high-voltage AC output according to claim 1, characterized in that, the Ai module, An module, Bi module, Bn module, Ci module and Cn module have the same structure; the Ai module includes 2 photovoltaic strings, 2 isolated DC / DC conversion circuits, and 2 single-phase full-bridge circuits, and each isolated DC / DC conversion circuit is connected in series between 1 photovoltaic string and 1 single-phase full-bridge circuit.

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